yes. When I learned to fly my instructor said " you won't live long enough to make all the mistakes others have made and learn from them. So take the easy option which is to follow the rules and procedures.
@@nztv8589 Yeah like "plan your flight and fly accordingly to your plan" and all that bs.... So now you think you'll never make mistakes and that your plans will always be right?
This crew revealed a problem with this plane by going closer to the test limits. Unfortunately they had to offer their lives, but probably saved a lot more lives by doing so. May they rest in peace!
May all folks who have sacrificed their lives for the betterment of safety RIP. Safety rules and checklists are truly written in blood, as MACI said. Now don't get me wrong, I love t-tail aircraft, but would a set of small retractable canards in the front of the plane prevented the stall from becoming an accident, so that t-tails can recover from severe stalls? That would cost a lot of money though.
@@Maven0666 When you mean as a consequence of stall? Yes, but since a plane pitches up when about to be stalled, the tail goes down. Planes with conventional elevators, these elevators move downward with the tail and stay below the shadow. However T-wing elevators are already several meters above the tail, and when the tail moves downward, the higher elevators now move exactly into the shadow, thus making the elevators non functional. The plane can now longer be leveled or pitched down to prevent it from stalling: deep stall.
Probably the wrong word. It's not an accident, it's a testing incident. An accident implies the actions that lead to their death were unintentional, but they were deliberately testing the stall, and a stall is exactly what they got. They just weren't planning on not being around to see the following day.
When I was in fire academy, we had to memorize certain rules for when you're on a fire line. Near the beginning of us trying to memorize them and none of us really had, they yelled at us about how every single one of those rules had been adopted because a firefighter had lost their life that way.
I'm quite sure I heard it in English as well but when I was doing a training on how to use oxy acetylene torch, some people bitched about overkilling it on the safety measures. The old guy just came in, turned off their equipment and told them " The rules of safety are written in blood." and sent them away. I don't think some of them understood what that phrase met...
7th June 1964 there was another 1-11 crash during stall testing. This was G-ASJD, but it had been fitted with a tail parachute to be deployed in the event of a deep stall during the testing. During the testing the pilot believed he'd lost elevator control and deployed the chute. The aircraft stabilised but the pilot did not then jetison the chute as he should have done. The result was the aircraft making what ended up being a very gentle belly landing on grasslands near a village called Tilshead. The aircraft was barely damaged and the crew walked away. The details are on the ASN if you want to look it up.
The angle of INCIDENCE is the angle between the wing chord line and the fuselage datum line. This is fixed by the design of the aircraft. You should be referring to the angle of ATTACK, which is the angle at which the air meets the wing.
There is a difference in terminology between the two sides of the Atlantic in respect of 'angle of incidence' and 'angle of attack'. This was recognised way back in the 1940s by Langeweische in his book 'Stick and Rudder'. In a career lifetime in the design of gas turbines here in the UK, I can tell you that the term 'angle of incidence' has been used to define the difference between the air/gas angle onto the leading edge of an aerofoil, relative to the local angle defined by the leading edge at which the angle of incidence would be zero. 'Angle of attack' has typically been used to define the angle of an aircraft relative to its direction of flight.
Angle of attack is the angle of the aircrafts flight path with reference to the relative airflow. The chord line is the reference on the wing. Hence you can be in a stalled condition at any pitch attitude or any speed.
Further to my previous comment, some years ago, I had an argument on UA-cam with one of our American cousins. He just could not accept that a difference in terminology from that in use in the USA was valid - even though it was recognised by Langewiesche in 'Stick and Rudder'. I even quoted him the page number of the reference.
It's very sad so many pilots sacrificed their lives for all of us. I wish there was a way to personally thank those that gave their lives to help keep us safer. My thoughts and prayers are with you brave pilots and your families.
I met test pilots in the service. They are dedicated daredevils. I realize the chances & scarifices they take. S few told me they ejected when the plane did not react as expected. Or it caught on fire. What guts.
Due to T-tail stalls being unrecoverable by normal means, T-tail planes require special stall recovery procedure, such as using a tail drag chute or tail pitch rocket where available, or banking as high as 90 degrees to exchange deep stall for a steep dive which IS recoverable.
The deep stall phenomenon was unkown at the tine! All T-Tail aircraft are prone to it and therefore aircraft like the B727 and the DC-9 family all have pushers.
There was one russian plane literally not able to recover from a stall by design due to it's massive T shape. Quite worrying to fly it on low energy/speed :D.
Mike Lithgow survived a ditching in a Fairey Swordfish in 1942. He and my grandfather were very good friends and fellow test pilots. My middle name is Mike because of him. I was a year old when he died. Through my career as a pilot I carried my grandfather’s navigation computer, a few years ago I took it apart for cleaning and found Mike’s name on the inside, it may have been his to start with, but I don’t know. I did however fly 3000 hours on BAC1-11 very safely.
Great video, as usual. May I suggest something? What you were calling „angle of incidence“ is actually angle of attack. The angle of incidence is the angle between the aircraft longitudinal axis and the airfoil reference line (basically, how the wing is attached to the fuselage). It’s usually something which on most airplanes cannot be changed, unless being extremely destructive. One airplane which could vary that is the F-8 Crusader, because it’s geometry didn’t allow sufficient angle of attack (and thus, lift) to be produced during take off and landing from carriers. So, the guys at Vought built in a hydraulic jack where the front end of the wings could be raised a few degrees for that purpose. The angle of attack is the angle between the airfoil reference line and the approaching air.
^^^ What Johnny said. Angle of incidence can be altered slightly by flap/ slat extension but OP needs to be saying angle of attack. Also, many people confuse aoa with deck angle.
Great video, as always, many thanks for sharing it with us! I know that problem from the DC9 my dad was flying for decades and I was working on it as an engineer in the 80's. On the DC9 a locked in deep stall situation could occur as well. That is why the DC9 's had among other things an elevator power system allowing an elevator nose down command even when the t-tail had almost no air flow. As far as I can remember the "elevator pwr on" light was one of few blue/green indication lights on the annunciator panel. The system was checked during pre flt check by pushing the steering column full forward. Kind regards from Vienna, Austria
The DC-9-10 was literally on the drawing boards when this crash happened. In the late 70's, I was told by a senior DAC engineer that the area of the DC-9's horizontal stabilizer was increased by "50% overnight" after the crash. I don't know whether the chord/span literally got bumped up by 22%, but nonetheless an indication of the effect this crash had on airliner design going forward. IIRC the MD-80 also experienced persistent deep stall during flight testing, but as expected from analysis was able to recover by the time it reached thicker air around 10k feet. Or maybe it was higher than that, and 10k was the designated bail-out altitude if the stall persisted? The test aircraft was outfitted for quick egress by the minimal crew, with the forward cargo door rigged to open when the first person jumped down a hole in the cabin floor above it. Also don't know whether the powered elevator for recovery had been developed at that point, or was turned off for the test, or ??. So a fuzzy and incomplete memory, but I'm passing it on with that caveat. Maybe someone who was actually involved with the flight testing can chime in.
@@marcmcreynolds2827 Yes I have heard about that but when I started we had a DC9-30 fleet, so can't say a lot about the series 10. Over the time we got 50's and 80's.
@@marcmcreynolds2827 yes I really think they didn't know that was possible at the time, and learned the hard way. I can only imagine what not being able to do anything and falling like a rock feel like. I wish they were able to escape the plane to tell the tale
@@nigo1787 My understanding is that they did stay in radio contact all the way to the ground. I'm fuzzier on specifics, like whether control movements for recovery attempts were being relayed in real time, but it seems there was a good technical account as to what was going on. That would have gone a long way towards dispelling questions afterward of for example whether hardware failure had been the cause, thus allowing the engineers to zero in on corrective action.
Amazing video, as a chemistry teacher I always emphasize to my students the fact that safety features and regulations exist bc no matter how small or insignificant they may sound, someone most likely has lost their life. I will be happy to show my senior students this video as a real life example. Thanks for your content! Love from Mexico
As a taxi driver, I always emphasize to my clents (to keep them quiet and therefore make my day easier) the fact that safety features and regulations exist bc no matter how small or insignificant they may sound, someone most likely has lost and will lose their life.
I haven't commented since probably your fourth video but I want to thank you so much for all you do and what a wonderful channel. Your accent has improved so much. keep up all the hard work brother.
I've never been a nervous flyer. But, March of 1986 I was flying ELP - ABQ on a Western Airlines 737-200. The distance between the two cities is minimal, so we were not that high. Between El Paso and Albuquerque is the Franklin Mountain range. It was choppy. How choppy was it, you ask? The stewardess at one point was collecting bevvies. She hit the deck on both knees and, holding onto an arm rest (this is where flight attendant training shows), she raised her voice (not shouted, not screamed), "HOLD ONTO YOUR DRINKS!!" She didn't say that not holding onto them would endanger your life because they could become airborne and lodge themself into your skull. I began to freak out. Looking out the window, I realized that the test pilots put these airframes through torture that nearly breaks the airframe apart before the FAA certifies them as airworthy. At that moment I relaxed.
Right. I've been on test flights from RAE Bedford. We weren't doing anything to test the limits, we just weren't as concerned about not upsetting the paying passengers and had two ETPS graduates at the controls. On one occasion that resulted in one of my friends floating back down the plane in a zero g pushover. In another it resulted in all of us feeling like we'd spent an hour in a tumble dryer. It's funny when you turn up to the plane in office clothes and the pilots turn up in full survival gear, but they were serving RAF officers and they could be hauled off to Wales to a survival exercise any time they went out to fly. When we were bouncing through turbulence I was in the jump seat, at first I was really concerned, then I noticed that the two pilots were chatting about video games. Ah. No problem then. Live tests never come near the ultimate load limits of the aircraft, most people will never experience even half the ultimate design load. The static tests aim to reach 150% of designed ultimate load. Normal g limits for commercial aircraft are +2.5 and -1. China Airlines 006, a Boeing 747SP reached +5g which broke the APU off its mount, broke some overhead bins, and gave the wings a permanent set.
It’s the Angle of Attack (AoA) which was exceeded and got them into the stall - not the Angle of Incident! The Angle of Incident is a fixed value and denotes the angle between the chord line of the airfoil and the longitudinal axis of the plane. It is a designed feature and cannot be changed by the pilots! The elevator controls the Angle of Attack, i.e. nose up or down.
It was reported that one of the test flight.observer had written on his paperwork that they were in a deep stall and couldn’t recover. I also heard that BAC fitted a tail parachute to pull the tail up until they fitted the stall stick shaker and stall pusher. I also remember Mike Lithgow used the fly the Supermarine Swift fighter at the then annual Farnborough air show at supersonic speed by putting it in a dive while aiming at the airfield resulting in a loud sonic boom. Those were the good old days of British aviation.
My first jet flight was on a BAC 111 and I flew on them a few times. Thanks for the accuracy of your reporting of this very unfortunate incident and its causes.
I relished the time when I would see a BAC 1-11 flying overhead after taking off from Manila Int'l airport in the Philippines. The extremely deafening sound coming out of those RR Spey engines, in full takeoff power, could wake up the deceased for miles around.
So that's how we discovered the deadly weakness of T tails. Never really thought about it until now. But now that I know how we learned this, I'm wondering what else we learned through someone else's death.
Wow. I worked that plane as a crewmember hundreds of times...in the late 80's. They were originally Mohawk Airlines...if you know your airline genealogy, then you will know who I worked for. I had no idea about this flaw, thank God.
@@ChrisCooper312 All of which I have worked. And the Fokker 100 too. As I said, I'm glad I didn't know this. We had a tragic history with the Boeing 737-300, as well. Don't even ask me how many flights I worked on that plane...before the uncommanded rudder flaw killed three of my friends. I tried to avoid it...working our T-tail equipment and the 75 and 76 instead! Even the jack screw challenged MD-80. By the way, a flaw is a flaw. No quotation marks are required.
Beautiful video, for the basics and more advanced knowledge alike. As excellent as normal. Also, your English is almost perfect (from a native speaker), and you are very good at explaining complex topics in ways that the average viewer can understand. The video complements the commentary very well.
No other deep stall on this plane, but if you look at the story of the MD80, which has an identical configuration, you'll find them, and much later than 1963, like the West Caribbean Airways Flight 708 in 2005
I was with 34SQN RAAF in the mid-80s - we flew the BAC-111 in VIP configuration. The stick shaker/stick pusher test flights were the scariest, considering we all knew about the unrecoverable deep stall. However, the stick pusher occurred well above the stall speed and it was nearly impossible to pull against it. Oh yeah, it also had a loud claxton horn that went off just prior to stick pusher, which scared the hell out of you. Rule number one - keep the airspeed above stall.
Thrust vectoring in all directions would aid in control of aircraft that experience many types of control problems. It would add another level of control.
Yes, but it also adds an additional layer of expense, complexity, and maintenance. It needs to be kept in mind that adding thrust-vectoring isn't as simple as slapping a vectoring nozzle on the engine. All aircraft with thrust-vectoring capability were designed from the start with that ability in mind (or in the case of the F-35B, are a factory-build variant, _also_ specifically designed for a thrust-vectoring engine); you can't just slap thrust-vectoring engines onto any old aircraft. For example, try slapping thrust-vectoring engines on a 737, and it's engines are likely to actually rip themselves off, as the pylons were never designed to handle twisting stresses from an engine vectoring to the side (or the engine trying to lift itself up, for that matter). We'd probably need to return to something more akin to the Comet's engine-inside-wing layout to get the advantages of vectored thrust, and commercial aircraft design moved away from that for good reason (for one thing, doing maintenance on those engines _had_ to have been _incredibly annoying)._ Something else that needs to be kept in mind is... does the aircraft even _need_ thrust-vectoring? Is it something that would be used with any kind of regularity (thereby justifying such an expensive engine modification)? With commercial aircraft, the answers to those questions are likely to be: only for short-field takeoffs and loss-of-control emergencies, and no. Would thrust-vectoring make aviation safer? Maybe. But also maybe not. But what it could _certainly_ do? Drive maintenance costs _through the roof._
@@benjaminfinlay829 Also, it's something else to go wrong. As Boeing found out, adding in a fancy new system to deal with one problem can cause it's own problems if it doesn't work as it's supposed to.
@Alfred Weber I agree, I am very much against pilots flying planes. A simple weight sensor on the landing gear would determine balance and load on the ramp before engine start and give a go no go then set takeoff length and speed and give a go no go for its particular runway, check it’s minimum sensor/instrument functionality and give a go no go etc etc. Note, navigator and engineer in cockpit instead of pilots.
Thrust vectoring on a rear engine aircraft like this might have benefits. It might even be a better way to trim (less drag) than elevator trim. On a 737, with engines under the wings I doubt it would do anything useful.
When I was a kid I built a balsa/paper model of the Wright Flyer. Noticed that at certain angles that it would always enter an unrecoverable stall. This was due to two factors-drastic changed thrust vectoring, but most importantly no airflow over the elevators assembly due to blockage of the wings and body of the plane. Bad design that unfortunately has been repeated ever since.
@@brucebaxter6923 except that at too steep a attitude you now have two surfaces creating drag instead of just one, and like the jet that was lost does not have variable pitch to compensate
@@TheFULLMETALCHEF Missing the point. Two surface creating lift and stall proof, What you lose by increased drag on the front you gain by increased lift overall.
The most interesting part of this video is about the explosive bolts. I knew that test pilots of new airliners wear parachutes and protective suits, but didn't know how they'd get out.
True, but there are also benefits to the T tail design. And designers can always convince themselves that the problem is a "corner case" that will "never happen".
I mean, it was in the 1960s, the aerodynamic phenomena was not understood as much as we know today. They did not fully understand the limit of those phenomena. I think it is one of the driving factors of those BAC pilots exceeding the limits, to obtain more understanding to the aerodynamic characteristics. Sadly, it resulted in a dire consequences.
The DC-9 had the same problem. I was talking to a mechanic on the test flight---they were filing the throttle to get more power. They too got into a deep stall. They added fences on the nose to disturb the air during a deep stall.
I think the most true quote I can ever quote from a teacher that I knew. He was talking about a NASCAR wreck that lead to restrictor plates. A very famous one you are sure to know, Bobby Allison. He said "It takes someone to die before anything changes" And time and time again I see it happen every once in awhile. The reason we have so many safety features or safety precautions is because of someone passing away or getting severely injured.
Not really, the 737 had a system to alter the pitch when the angle of attack was too high. This was put in place due to a last minute change. The engines were too low to the ground so they were moved forward, which altered the center of gravity. MCAS was put into place to pitch the plane down to compensate for the shifted center of gravity. 737 MAX’s problem is because a single faulty Angle of Attack sensor causes MCAS to think the plane is pitching up when it isn’t, so it keeps pitching the plane down. This incident, the plane is actually designed in such a way that the wings block the air flow to the elevators at a high angle of attack, and the plane CANT pitch down. In 737s case, you can disable MCAS and override the system (the pilots just didn’t know how in a panic due to incomplete training by Boeing). In this case, it is physically impossible to pitch down.
@@nevelis Absolutely correct except that for the MCAS, there was not "incomplete training", there was no training at all and this was the aim by the way to compete with the A320 Neo. So the crew of the first crash (Lion Air) didn't know about MCAS so that they didn't understand what was happening. The crew of the second crash (Ethiopian) was aware of the MCAS possible trouble and informed about what to do in case ... and that's what they did. The copilot was the first to understand the situation and they did quite well: they switched off the MCAS asap, as recommended by Boeing but it didn't work since, in the meantime they had got so much speed in the dive that the aircraft was not recoverable. Disabling the MCAS was not the solution and anyway it had to be done within 10 seconds maximum! The solution was (is) 2 sensors instead of 1 and additional training related to the MCAS. From my perspective, trying to compete with Airbus implementing a new modification on a very old aircraft was probablt a bridge too far, not mentioning the mind blowing lies ... Just my opinion.
@@patolt1628 True. MCAS (Might Crash Any Second) was sort of a band-aid fix to deal with a basic design problem caused by modifying a half-century old product with bigger engines and a newer wing design. For pilots struggling with dangerous MCAS inputs the "solution" was to disengage that system, leaving pilots with the original design flaws that it was intended to fix. As you mentioned, the additional sensor and additional training seem to work now. Still, it's time for them to come up with a new aircraft.
@@nevelis Moving the CG forward would actually create a nose-down tendency for the plane. The problem is a bit more complex, related to the lift created by the engine nacelles. Also, you are missing the fact that it is not as easy as "just disable MCAS" - the crew of the second crashed plane did disable MCAS as per Boeing instructions, and it still was impossible to recover from the crash.
Thanks buddy , you must of put that up at a different time , was not there at midnight last night Aussie time , good work I don't know how you get the time to give us 2 videos in a week
Thanks for another great video. As a former RC pilot in the 80’s it’s not always necessary to die to learn how to fly safer. We trained on getting out of spins and stalls and aerobatics. In this situation I would try to roll out using the ailerons to allow the tail catching some wind. If nothing seems working, try something else
@@benjamin4281 @crunchtastic1948 As explained in the video, the T tails can enter the deep stall where the aircraft loses the elevator authority, making it hard to recover. The thing with rear mounted planes is, adding thrust causes the plane to pitch up, which you'd normally counter with the elevator
Rear mounted engines will always come with a t-tail, due to the engines being near where the horizontal stabilizers would normally be. I wouldn't say that configuration would be dangerous, as many "modern" planes have that configuration (ex: most private jets, CRJ 100 series) but you do have a point. (Edit: Rear mounted engines can also come with a 'cruciform tail')
It's hardly dangerous, especially as it was used by some of the most common planes of the 60s and 70s (the BAC111, DC9, MD80, Boeing 727). In this case there was a danger, but they discovered it and made efforts to ensure pilots would not get in a position where the plane might deep stall. It was also found that the 727 could get into a deep stall when using flaps 40 (the maximum setting) under the right weight and centre of gravity, so many operators either banned flaps 40 being used or even physically locked it out.
Why? Based on jingoism or something scientific? High-tail plans have terrible stall characteristics. (like the Trident crash at Staines). These planes were also disgracefully noisy.
A very similar accident happened to a Hawker Siddeley Trident airliner in 1966. G-ARPY was on a test flight before being delivered to the airline and also entered a deep stall. It crashed in Norfolk, England and all on board died.
My father was shocked when the prototype One-Eleven crashed as he worked on it as an aircraft fitter at Hurn Airport Bournemouth. When the internet became widely available I found an article on the crash. Apparently there was a stall system which operated in part by a hydraulic tab on the tailplane. The pump was undersized and failed plus the pitch reading was incorrect. When the pilot realised he was in a stall he was not aware the pitch was greater than the reading. Being a WW2 fighter pilot he tried a few manoeuvres but it was too late. On impact the forward movement was 75ft. The exit door was still in place as all the bolts had not been fired. The final comment was that military aircraft undergoing stall tests could deploy a tail parachute to bring the nose down. I’m not saying the article was correct but it is how I remember it.
A bit like in physics how Bernoulli and Euler followed Newton, Clerk-Maxwell and Faraday followed them and in turn Einstein and Bohr continued and built on their work - so in aircraft engineering do you get the culmination of generations of knowledge and experience brought to bear in the design and construction of the latest, safest, most efficient airplanes - even the most successful aero companies with the most gifted designers don't do it from scratch. It's great to see a MACI clip highlighting the skill and dedication of those who went before, much as we enjoy the more usual stuff involving commercial flights gone wrong. As always, very nicely explained and easy to follow even as a non expert....
6:20 Yes, this is called shadow masking. There is no laminar airflow over the tailplane as the airflow is masked by the severe turbulence from the wings. This is common for all planes with T-tails like the HS Trident, Vickers VC-10, Boeing 727 etc.
It's not angle of incidence, it's angle of attack when you are flying. The angle of incidence is the angle the wings are mounted to the fuselage, as shown in the illustration at 3.50 and this angle obviously never changes.
The data recorder print-out shown in the video refers to something called "true incidence" and the figures for it suggest that it was at the time a term for what is now called the angle of attack. Other technical terms have changed over this period, for example the tailplane and fin have become the horizontal stabiliser and vertical stabiliser. Also the terms port and starboard (which appear on the print-out) don't seem to be used any more.
Small correction. When you say angle of incidence you mean Angie of attack. The angle of incidence is the angle between the wing cord like and the longitudinal axis. It’s fixed per airframe.
Just an FYI...You wouldn't say, "To say that he's one of the few people who knew the plane best would NOT be an understatement." Saying he knew it best WOULD be an understatement. No biggie, just some constructive criticism from a faithful subscriber is all...Another great video BTW. 😉✌️
That feeling in the pit of your stomach having no elevator control must be like driving on the freeway and turning the steering wheel and nothing happening. Damn.
Remember (just in case) from some other disasters and reports, that if you bank far enough, the nose also pitches down... You CAN also use some rudder (pedals) with the ailerons (roll) to accomplish this... It's important as we take controls of larger machines and take responsibility for more lives by rote, that we remember "There are more ways to kill a cat than to choke it to death on strawberries." You probably won't ever need to use that knowledge... BUT it's worth watching a lot of these accident and disaster videos to notice things like that. If the elevators won't help directly, roll to the side and kick the hell out of the rudder. You can get that nose down if you act quickly enough... AND once the engines get clean air, and you've got some speed back, level out and pull up GENTLY... This is NOT to take away from these wonderful pilots and people!!! May they rest in peace, there was NO precedent for a deep stall or super-stall, where the engines AND horizontal tail end up in the "shadow" of the wings, and lose efficacy. NOW that we know, we have shakers and pushers on a LOT of sticks because a LOT of planes have the "weakness"... There are also other pilots and lives lost for us to find out that a hard bank (say... in excess of 40 degrees) can drop the nose... AS CAN a bank and rudder control... Let's keep ALL their sacrifices respected and valued by keeping EVERY lesson we can learn... just in case we might need it one day. ;o)
I must have flown hundreds of times in BAC-111s out of Gatwick in my 20s, working as a computer engineer attached to British Caledonian, of course they all had pitch shakers and pushers by then. British Airways flew Tridents too in those days and I think it was one of those which "reversed" into a reservoir coming out of Heathrow due to a deep stall.
I think you have mixed up ANGLE OF ATTACK WITH ANGLE OF INCIDENCE. Angle of attack is the angle between the cord line and the Relative Airflow so changes in flight. 15 degrees is normally the maximum before the stall (although I think delta wings like Concord can go to 22) Angle of incidence on the other hand is fixed by the aircraft designer and does not change, although I think there are some fighter jets that have a variable incidence, wing, but I may be wrong about that. The wing is actually developing maximum CL at 15 degrees just before the stall.
the best reaction to a stall is not to put the engine on full power, but to do the oppesite, this will force the nose down and you will soon have enought speed to get out of the stall, this is something you learn as a combat pilot
The correct term would be "angle of attack" and not "angle of incidence". The incidence is the angle between the fuselage zero line and the wing chord line, i.e. it is a fixed angle for most airplanes unless it's a tilt rotor with tilting wings. The angle of attack however is the angle between the wing chord and the incoming airflow, that is what causes a stall.
You do a great job and I enjoy your videos! There's a bit of confusion about the angle of incidence vs. the angle of attack (AoA). The incidence is the angle of the wing chord line relative to the longitudinal axis, it's fixed (except the FA-8 Crusader and perhaps another one or two). The AoA varies during flight and increases as you approach a stall. If you lose elevator control, with enough altitude you can roll 60 degrees or so and apply rudder and pivot the jet to lower the nose. Cheers
For those who haven't worked on aircraft let me tell you -- the stick shaker is not very subtle. It is a violent movement designed to get your attention!!
Pleased to report it was indeed a structural giant a later vairient of the BAC 1-11 with Philippine Airlines survived two seperate Granade incidents by suicide passenger,which blew out a whole hoop section of the rear cabin leaving the tail in midair with limted support. this happened on the same registered A/C some two years apart . In both cases the aircraft experianced an explosive decompression entered a terminal dive and was only recovered by superb piloting skills when control was regained once the aircraft was down to around 7000 feet by use of elevator trimming. True story I was involved with the rebuild of the A/C at BAE at Bournmouth following the first incident.
Elevator blanking in a T-Tail is one heck of a terrifying design flaw with the concept of T-Tail aircraft. Personally, I would require the use of a small canard on all T-Tail aircraft to provide Pilots just a little bit maneuvering ability in the event of a stall like this. It's surprising they didn't try lowering the landing gear. Although it wouldn't have done a lot, it may have been enough. As tragic as it was, they succeeded in their goals - they provided important data to the engineers which saved a lot of lives in the future.
Centre of gravity is also very important as regards behaviour in a stall situation. Of course aft cg is more critical than forward cg. Nowadays during test flights they set the exact center of gravity with water ballast tanks in the passenger cabin. I believe they can modify this in-flight if need be. If you get your cg forward you're in much better shape in a stall. If you've ever flown an aircraft yourself you know what I mean.
Generally I believe c of g is controlled in flight by transferring fuel between tanks to keep c of g within limits. From what I've worked on, fuel proportioners pump fuel from tank groups to help relieve the workload on the crew.
@@125brat That depends on the type of aircraft, whether that's possible. Modern narrowbodies (B737 series, A320 series and any smaller aircraft if I am not mistaken) do not have that capability: Just one fuel tank per wing and that's it. You cannot change the cg by moving fuel around. Widebodies like the old A300/A310 and also the modern A330 (and I guess the larger Boeings) do have that fuel tank trim option though. Plus, testing beyond the operational limits of a plane with designated test flights is another matter. I have found this other video, see other answer.
@@olaflieser3812 Thanks Olaf. My main experience is of tanker aircraft with multiple wing and fuselage tanks where it was the copilot's job to manage the fuel. Yes, smaller aircraft tend to have a single tank in each wing and maybe a few cells in the fuselage but I'll have a look at your linked video to see what you're referring to. Of course, test flying is often at the very limits of the envelope or beyond flown by very experienced pilots after much research and calculations. I know an ex-RAF test pilot and their motto was "Learn to test, Test to learn".
Here’s a video of the single finest piece of flying I’ve ever seen: ua-cam.com/video/L2CsO-Vu7oc/v-deo.html It was a deep step test on another aircraft, the MD-95/717. Basically a stretched DC-9, the MD-95 had wing and tail redesigns to suit. The problem is that while doing computer modelling of the stall characteristics, the modelling was throwing up weird results that the engineers couldn’t quite figure out. They decided they had to test this on the bare metal, which was an FAA requirement. Part of the development of a plane for FAA certification is that you’ve gotta stall the thing and prove that it is recoverable. You’ve also got to reconcile the computer modelling. The more data you have, the better the modelling gets. Anyway, this was a test flight to try to verify the computer modelling, and hopefully figure out why the modelling was weird. There is a lot going on in that video, but they entered a deep stall, and the plane rolled over, and into a nosedive. They went from a stall to an overspeed in mere seconds. At one point, they were losing something like 60,000ft per minute. More than 1,000ft per second: that thing was pointed directly at the floor. They were able to recover the aircraft and and safely, and they generated a lot of data and insight from this flight. The pilots made it out fine, but the plane did not. The plane had undergone such aerodynamic forces that the structure itself had deformed, I seem to remember to the point where the plane wouldn’t pressurise properly. In any case, the aircraft was written off, and as of writing, it remains the only MD-95/717 hull loss. Ultimately the engineering fix was a software one: an aggressive stick pusher in the flight computer control logic, so you’ll (theoretically) never be able to deep stall the thing even if you tried. You can’t really “fix” this problem aerodynamically-it’s just the nature of a T-tail, and it always will be, which is why stick shakers and stick pushers are so crucial. It’s a crazy story, worthy of a video of its own.
I've watched this video before. It never occurred to me that they were in a deep stall before the plane rolled over. I thought it was just a regular stall. I am very interested in the idea of recovering from a deep stall in a t-tail aircraft though. Is the idea that you're supposed to reduce power and force the plane up to such an angle that it will want to roll out of the deep stall? I've heard some people say that it's not possible to recover from a deep stall, but clearly that can't be true.
The angle of incidence is the angle between the chorď line and a line between the fore and aft axis of the aircraft. It never changes on an aircraft. What you meant is the angle of attack. This is the angle the chord of the wing makes with the relative airflow.
Sounds like a similar issue to the Dehaviilland Trident in which a test also caused the plane to crash onto the airfield at Hatfield. I think the engines flamed out. As an apprentice there in 1972 I remember seeing the crater it had left near the edge of the airfield. I don't know if that incident was before or after the 111 one.
The narrator of this did not explain why the nose went back up when the pilots put in maximum power. The deep stall phenomenon was not known very well at all in those days, and the pilots probably did not realize if they accelerate the air underneath that tail by going to high power, then the air pressure under the tail is reduced, and the air pressure above the tail is higher, will shove the tail down, putting the nose back up in the air. Kind of a counterintuitive thought, but they needed to keep those throttles back until the nose was down. So that airflow could be restored and airspeed increased. I flew both the DC9/MD80, and the Lear35. Both of those aircraft had a very strong stick pusher that would shove the nose down . in the case of the MD80, It’s a force of 80 pounds on the column and it will shove the yoke forward violently when you activate the stall warning. It’s activated several knots above the actual stall so you still have airflow over the tail when the elevator starts coming back down. it does that by a hydraulic circuit in the down elevator. That’s the only hydraulic flight control for pitch. Otherwise the elevator is cable operated with servo tabs. Douglas actually put an additional device called ventral strakes, underneath the nose on each side to help energize airflow over the tail at high angles of attack. That gives even more control in an extreme pitch situation. Just one more thought. The only thing that would’ve got the nose down quickly with no airflow would be a weight shift system that would allow weight to be moved forward very quickly from a cockpit control. If they could’ve moved a couple thousand pounds forward in a matter of seconds by using a weight shift system in the cabin that would’ve put the nose down. I’m guessing they had no such system installed . It’s obvious to me if they had known all of the dangers of the deep phenomenon they would’ve taken additional steps to get the nose back down in a loss of control situation.
One of the Gloster Javelin jet fighter prototypes (which also had a T tail) was lost to a 'deep stall' 10 years before this accident so it seems surprising that the designers of the BAC-111 did not anticipate the problem. However, the Javelin had a much broader delta wing, so they may have thought the BAC-111's narrower wings would make it less prone to a 'deep stall'.
There were two stall accidents with the BAC 111. In the second incident the pilots felt that they had entered a deep stall and therefore released a parachute, fitted to the tail of the aircraft after the Lithgow crash, which was intended to pull the tail up, thus allowing the aircraft to recover, which, in fact, it did. However, due to an optical illusion the pilots thought they were still deep stalled and rode the aircraft into the ground, with the parachute still deployed. In fact it was the drag of the chute which was causing the problem, had they jettisoned it the aircraft would simply have flown away. I seem to recall that the crew survived this crash.
Yes the crew survived. The aircraft bellied in more or less intact somewhere on Salisbury plain and I saw the wreck personally. They dismantled it in situ and ferried the components out by road
That last point is so important. So many of our safety features and rules are there because someone died or got seriously hurt
Indeed as the saying goes the rules of aviation are written in blood.
checklists are written in blood
Yes and if my mum had wheels we would call her a bike....
yes. When I learned to fly my instructor said " you won't live long enough to make all the mistakes others have made and learn from them. So take the easy option which is to follow the rules and procedures.
@@nztv8589 Yeah like "plan your flight and fly accordingly to your plan" and all that bs.... So now you think you'll never make mistakes and that your plans will always be right?
This crew revealed a problem with this plane by going closer to the test limits. Unfortunately they had to offer their lives, but probably saved a lot more lives by doing so. May they rest in peace!
Kk
May all folks who have sacrificed their lives for the betterment of safety RIP. Safety rules and checklists are truly written in blood, as MACI said.
Now don't get me wrong, I love t-tail aircraft, but would a set of small retractable canards in the front of the plane prevented the stall from becoming an accident, so that t-tails can recover from severe stalls? That would cost a lot of money though.
Do all planes gave shadow spots?
@@Maven0666 When you mean as a consequence of stall? Yes, but since a plane pitches up when about to be stalled, the tail goes down. Planes with conventional elevators, these elevators move downward with the tail and stay below the shadow. However T-wing elevators are already several meters above the tail, and when the tail moves downward, the higher elevators now move exactly into the shadow, thus making the elevators non functional. The plane can now longer be leveled or pitched down to prevent it from stalling: deep stall.
@@Ztbmrc1 Oh okay. Thank you.
Nice to hear of these less talked about accidents.
Probably the wrong word. It's not an accident, it's a testing incident. An accident implies the actions that lead to their death were unintentional, but they were deliberately testing the stall, and a stall is exactly what they got. They just weren't planning on not being around to see the following day.
When I was in fire academy, we had to memorize certain rules for when you're on a fire line. Near the beginning of us trying to memorize them and none of us really had, they yelled at us about how every single one of those rules had been adopted because a firefighter had lost their life that way.
I'm quite sure I heard it in English as well but when I was doing a training on how to use oxy acetylene torch, some people bitched about overkilling it on the safety measures. The old guy just came in, turned off their equipment and told them " The rules of safety are written in blood." and sent them away. I don't think some of them understood what that phrase met...
7th June 1964 there was another 1-11 crash during stall testing. This was G-ASJD, but it had been fitted with a tail parachute to be deployed in the event of a deep stall during the testing. During the testing the pilot believed he'd lost elevator control and deployed the chute. The aircraft stabilised but the pilot did not then jetison the chute as he should have done. The result was the aircraft making what ended up being a very gentle belly landing on grasslands near a village called Tilshead. The aircraft was barely damaged and the crew walked away. The details are on the ASN if you want to look it up.
The angle of INCIDENCE is the angle between the wing chord line and the fuselage datum line. This is fixed by the design of the aircraft. You should be referring to the angle of ATTACK, which is the angle at which the air meets the wing.
Thank you. I found it painful to hear this term used incorrectly. I commented similar to you but your comment was much better stated.
Exactly. You saved me a comment.
There is a difference in terminology between the two sides of the Atlantic in respect of 'angle of incidence' and 'angle of attack'. This was recognised way back in the 1940s by Langeweische in his book 'Stick and Rudder'.
In a career lifetime in the design of gas turbines here in the UK, I can tell you that the term 'angle of incidence' has been used to define the difference between the air/gas angle onto the leading edge of an aerofoil, relative to the local angle defined by the leading edge at which the angle of incidence would be zero.
'Angle of attack' has typically been used to define the angle of an aircraft relative to its direction of flight.
Angle of attack is the angle of the aircrafts flight path with reference to the relative airflow. The chord line is the reference on the wing. Hence you can be in a stalled condition at any pitch attitude or any speed.
Further to my previous comment, some years ago, I had an argument on UA-cam with one of our American cousins. He just could not accept that a difference in terminology from that in use in the USA was valid - even though it was recognised by Langewiesche in 'Stick and Rudder'. I even quoted him the page number of the reference.
Your 'Investigations' are amongst the best on UA-cam - not too long and boring, and not too short with missing information. Well Done. I'm Subscribed!
It's very sad so many pilots sacrificed their lives for all of us. I wish there was a way to personally thank those that gave their lives to help keep us safer. My thoughts and prayers are with you brave pilots and your families.
I met test pilots in the service. They are dedicated daredevils. I realize the chances & scarifices they take. S few told me they ejected when the plane did not react as expected. Or it caught on fire. What guts.
Due to T-tail stalls being unrecoverable by normal means, T-tail planes require special stall recovery procedure, such as using a tail drag chute or tail pitch rocket where available, or banking as high as 90 degrees to exchange deep stall for a steep dive which IS recoverable.
The deep stall phenomenon was unkown at the tine! All T-Tail aircraft are prone to it and therefore aircraft like the B727 and the DC-9 family all have pushers.
I’ve flown DC-9 and 727, neither of them have stick pushers
All swept wing jets are prone to deep stall. Not all T tails have pushers. The only jet I’ve flown with a pusher was the EMB 145.
Right on thank you for the great information 🙏👍🛫
There was one russian plane literally not able to recover from a stall by design due to it's massive T shape. Quite worrying to fly it on low energy/speed :D.
"Written in blood." That is a very profound statement.
The "writting" is a never ending process....
Mike Lithgow survived a ditching in a Fairey Swordfish in 1942. He and my grandfather were very good friends and fellow test pilots. My middle name is Mike because of him. I was a year old when he died. Through my career as a pilot I carried my grandfather’s navigation computer, a few years ago I took it apart for cleaning and found Mike’s name on the inside, it may have been his to start with, but I don’t know. I did however fly 3000 hours on BAC1-11 very safely.
Great video, as usual. May I suggest something? What you were calling „angle of incidence“ is actually angle of attack. The angle of incidence is the angle between the aircraft longitudinal axis and the airfoil reference line (basically, how the wing is attached to the fuselage). It’s usually something which on most airplanes cannot be changed, unless being extremely destructive.
One airplane which could vary that is the F-8 Crusader, because it’s geometry didn’t allow sufficient angle of attack (and thus, lift) to be produced during take off and landing from carriers. So, the guys at Vought built in a hydraulic jack where the front end of the wings could be raised a few degrees for that purpose.
The angle of attack is the angle between the airfoil reference line and the approaching air.
^^^ What Johnny said. Angle of incidence can be altered slightly by flap/ slat extension but OP needs to be saying angle of attack. Also, many people confuse aoa with deck angle.
Also, "airfoil reference line" is called the chord line and is basically a line from leading edge of wing to trailing edge.
What we in America call "angle of attack" is called "angle of incidence" in Great Britain.
@@MemphisBBQ640 And how is the angle called at which wings are mounted to the fuselage in Britain?
@@MemphisBBQ640 well that's strange. Cookies and biscuits, chips and fries, I suppose.
Wow. U did such a great job on this one bro.
Thank you!
Great video, as always, many thanks for sharing it with us! I know that problem from the DC9 my dad was flying for decades and I was working on it as an engineer in the 80's. On the DC9 a locked in deep stall situation could occur as well. That is why the DC9 's had among other things an elevator power system allowing an elevator nose down command even when the t-tail had almost no air flow. As far as I can remember the "elevator pwr on" light was one of few blue/green indication lights on the annunciator panel. The system was checked during pre flt check by pushing the steering column full forward. Kind regards from Vienna, Austria
Interesting, thanks for sharing!
The DC-9-10 was literally on the drawing boards when this crash happened. In the late 70's, I was told by a senior DAC engineer that the area of the DC-9's horizontal stabilizer was increased by "50% overnight" after the crash. I don't know whether the chord/span literally got bumped up by 22%, but nonetheless an indication of the effect this crash had on airliner design going forward.
IIRC the MD-80 also experienced persistent deep stall during flight testing, but as expected from analysis was able to recover by the time it reached thicker air around 10k feet. Or maybe it was higher than that, and 10k was the designated bail-out altitude if the stall persisted? The test aircraft was outfitted for quick egress by the minimal crew, with the forward cargo door rigged to open when the first person jumped down a hole in the cabin floor above it.
Also don't know whether the powered elevator for recovery had been developed at that point, or was turned off for the test, or ??. So a fuzzy and incomplete memory, but I'm passing it on with that caveat. Maybe someone who was actually involved with the flight testing can chime in.
@@marcmcreynolds2827 Yes I have heard about that but when I started we had a DC9-30 fleet, so can't say a lot about the series 10. Over the time we got 50's and 80's.
@@marcmcreynolds2827 yes I really think they didn't know that was possible at the time, and learned the hard way. I can only imagine what not being able to do anything and falling like a rock feel like. I wish they were able to escape the plane to tell the tale
@@nigo1787 My understanding is that they did stay in radio contact all the way to the ground. I'm fuzzier on specifics, like whether control movements for recovery attempts were being relayed in real time, but it seems there was a good technical account as to what was going on. That would have gone a long way towards dispelling questions afterward of for example whether hardware failure had been the cause, thus allowing the engineers to zero in on corrective action.
I flew the BAC111 in the 1980s it had a stick pusher system to avoid this problem.
As a direct result of this incident in testing. They died so that many others could live.
Amazing video, as a chemistry teacher I always emphasize to my students the fact that safety features and regulations exist bc no matter how small or insignificant they may sound, someone most likely has lost their life. I will be happy to show my senior students this video as a real life example. Thanks for your content! Love from Mexico
@Hal Mash What is wrong with you?
As a taxi driver, I always emphasize to my clents (to keep them quiet and therefore make my day easier) the fact that safety features and regulations exist bc no matter how small or insignificant they may sound, someone most likely has lost and will lose their life.
@Hal Mash lol
Congrats on 150k!
The last statement made on this video is so profound. Hats off to these brave souls.
If at least 1 pilot made it, just imagine about how much more we could’ve learnt. RIP
I haven't commented since probably your fourth video but I want to thank you so much for all you do and what a wonderful channel. Your accent has improved so much. keep up all the hard work brother.
Thank you so much
I've never been a nervous flyer. But, March of 1986 I was flying ELP - ABQ on a Western Airlines 737-200. The distance between the two cities is minimal, so we were not that high. Between El Paso and Albuquerque is the Franklin Mountain range. It was choppy. How choppy was it, you ask? The stewardess at one point was collecting bevvies. She hit the deck on both knees and, holding onto an arm rest (this is where flight attendant training shows), she raised her voice (not shouted, not screamed), "HOLD ONTO YOUR DRINKS!!" She didn't say that not holding onto them would endanger your life because they could become airborne and lodge themself into your skull. I began to freak out. Looking out the window, I realized that the test pilots put these airframes through torture that nearly breaks the airframe apart before the FAA certifies them as airworthy. At that moment I relaxed.
Interesting
Oh yeah- I was on that same flight!
Right. I've been on test flights from RAE Bedford. We weren't doing anything to test the limits, we just weren't as concerned about not upsetting the paying passengers and had two ETPS graduates at the controls. On one occasion that resulted in one of my friends floating back down the plane in a zero g pushover. In another it resulted in all of us feeling like we'd spent an hour in a tumble dryer. It's funny when you turn up to the plane in office clothes and the pilots turn up in full survival gear, but they were serving RAF officers and they could be hauled off to Wales to a survival exercise any time they went out to fly. When we were bouncing through turbulence I was in the jump seat, at first I was really concerned, then I noticed that the two pilots were chatting about video games. Ah. No problem then. Live tests never come near the ultimate load limits of the aircraft, most people will never experience even half the ultimate design load. The static tests aim to reach 150% of designed ultimate load. Normal g limits for commercial aircraft are +2.5 and -1. China Airlines 006, a Boeing 747SP reached +5g which broke the APU off its mount, broke some overhead bins, and gave the wings a permanent set.
Once again, fantastic job. You are uniquely great at what you do.
Congrizzles on 150,000 subscribers! Well done with this video!
It’s the Angle of Attack (AoA) which was exceeded and got them into the stall - not the Angle of Incident! The Angle of Incident is a fixed value and denotes the angle between the chord line of the airfoil and the longitudinal axis of the plane. It is a designed feature and cannot be changed by the pilots! The elevator controls the Angle of Attack, i.e. nose up or down.
Another great story. You are getting better and better!! Thanks for all of your hard work.
It was reported that one of the test flight.observer had written on his paperwork that they were in a deep stall and couldn’t recover. I also heard that BAC fitted a tail parachute to pull the tail up until they fitted the stall stick shaker and stall pusher. I also remember Mike Lithgow used the fly the Supermarine Swift fighter at the then annual Farnborough air show at supersonic speed by putting it in a dive while aiming at the airfield resulting in a loud sonic boom. Those were the good old days of British aviation.
My father flew the Swift FR5 in Germany. No longer here or I’d ask him about them…
S
My first jet flight was on a BAC 111 and I flew on them a few times. Thanks for the accuracy of your reporting of this very unfortunate incident and its causes.
I used to love watching the Bac 111 flying into Southampton/Eastleigh airport when I was a kid in BEA livery. Beautiful and noisy aircraft.
I relished the time when I would see a BAC 1-11 flying overhead after taking off from Manila Int'l airport in the Philippines. The extremely deafening sound coming out of those RR Spey engines, in full takeoff power, could wake up the deceased for miles around.
So that's how we discovered the deadly weakness of T tails. Never really thought about it until now. But now that I know how we learned this, I'm wondering what else we learned through someone else's death.
The discovery of deep stall made McDonnel-Douglas add pilon flaps to the DC9 ua-cam.com/video/vsRxWspTTJI/v-deo.html
This wasn't the first T tail aircraft, nor one with problems: the F-101 Voodoo first flew several years earlier in 1954.
Back in those days, pilots didn't even know T Tails existed....
Many advances in aviation technology, especially in the early days, were paid for in blood.
@@AviationHorrors I remember that. Thank u
Wow. I worked that plane as a crewmember hundreds of times...in the late 80's. They were originally Mohawk Airlines...if you know your airline genealogy, then you will know who I worked for. I had no idea about this flaw, thank God.
It's the same "flaw" with all T Tail aircraft, including the DC9, MD80, Boeing 727 and many more.
@@ChrisCooper312 All of which I have worked. And the Fokker 100 too. As I said, I'm glad I didn't know this. We had a tragic history with the Boeing 737-300, as well. Don't even ask me how many flights I worked on that plane...before the uncommanded rudder flaw killed three of my friends. I tried to avoid it...working our T-tail equipment and the 75 and 76 instead! Even the jack screw challenged MD-80. By the way, a flaw is a flaw. No quotation marks are required.
@@claycassin8437 * quotation marks
@@Milesco Oops. Thanks. My brain is faulty. I have corrected my error.
The angle of incidence doesn’t change, its the angle of attack
Thank you lads!! Rest In Peace.
Been binge-watching these for the past week while down with Covid. Love em, keep up the good work my friend!
Hope you get better soon!
Beautiful video, for the basics and more advanced knowledge alike. As excellent as normal. Also, your English is almost perfect (from a native speaker), and you are very good at explaining complex topics in ways that the average viewer can understand. The video complements the commentary very well.
No other deep stall on this plane, but if you look at the story of the MD80, which has an identical configuration, you'll find them, and much later than 1963, like the West Caribbean Airways Flight 708 in 2005
Brilliantly done
I was with 34SQN RAAF in the mid-80s - we flew the BAC-111 in VIP configuration. The stick shaker/stick pusher test flights were the scariest, considering we all knew about the unrecoverable deep stall. However, the stick pusher occurred well above the stall speed and it was nearly impossible to pull against it. Oh yeah, it also had a loud claxton horn that went off just prior to stick pusher, which scared the hell out of you. Rule number one - keep the airspeed above stall.
Wow, just wow. (Another) Great episode full of info. Things that we (now) take granted came from the lives of others. Big big thumbs up on this.
Thrust vectoring in all directions would aid in control of aircraft that experience many types of control problems. It would add another level of control.
Yes, but it also adds an additional layer of expense, complexity, and maintenance.
It needs to be kept in mind that adding thrust-vectoring isn't as simple as slapping a vectoring nozzle on the engine.
All aircraft with thrust-vectoring capability were designed from the start with that ability in mind (or in the case of the F-35B, are a factory-build variant, _also_ specifically designed for a thrust-vectoring engine); you can't just slap thrust-vectoring engines onto any old aircraft.
For example, try slapping thrust-vectoring engines on a 737, and it's engines are likely to actually rip themselves off, as the pylons were never designed to handle twisting stresses from an engine vectoring to the side (or the engine trying to lift itself up, for that matter).
We'd probably need to return to something more akin to the Comet's engine-inside-wing layout to get the advantages of vectored thrust, and commercial aircraft design moved away from that for good reason (for one thing, doing maintenance on those engines _had_ to have been _incredibly annoying)._
Something else that needs to be kept in mind is... does the aircraft even _need_ thrust-vectoring? Is it something that would be used with any kind of regularity (thereby justifying such an expensive engine modification)?
With commercial aircraft, the answers to those questions are likely to be: only for short-field takeoffs and loss-of-control emergencies, and no.
Would thrust-vectoring make aviation safer? Maybe. But also maybe not.
But what it could _certainly_ do? Drive maintenance costs _through the roof._
Like deploy half a thrust reverser inflight?
Pass.
@@benjaminfinlay829 Also, it's something else to go wrong. As Boeing found out, adding in a fancy new system to deal with one problem can cause it's own problems if it doesn't work as it's supposed to.
@Alfred Weber
I agree,
I am very much against pilots flying planes.
A simple weight sensor on the landing gear would determine balance and load on the ramp before engine start and give a go no go then set takeoff length and speed and give a go no go for its particular runway, check it’s minimum sensor/instrument functionality and give a go no go etc etc.
Note, navigator and engineer in cockpit instead of pilots.
Thrust vectoring on a rear engine aircraft like this might have benefits. It might even be a better way to trim (less drag) than elevator trim. On a 737, with engines under the wings I doubt it would do anything useful.
Your content is excellent
When I was a kid I built a balsa/paper model of the Wright Flyer. Noticed that at certain angles that it would always enter an unrecoverable stall. This was due to two factors-drastic changed thrust vectoring, but most importantly no airflow over the elevators assembly due to blockage of the wings and body of the plane. Bad design that unfortunately has been repeated ever since.
Wasn’t it canard?
@@brucebaxter6923 yeah, and IMO made it more prone to stall at shallower angles
@@TheFULLMETALCHEF
You balanced it wrong.
Canards need that front loaded up, way up.
@@brucebaxter6923 except that at too steep a attitude you now have two surfaces creating drag instead of just one, and like the jet that was lost does not have variable pitch to compensate
@@TheFULLMETALCHEF
Missing the point.
Two surface creating lift and stall proof,
What you lose by increased drag on the front you gain by increased lift overall.
The most interesting part of this video is about the explosive bolts. I knew that test pilots of new airliners wear parachutes and protective suits, but didn't know how they'd get out.
In hindsight, the danger of deep stall with a T tail seems obvious. I guess it wasn't that obvious at the time.
True, but there are also benefits to the T tail design. And designers can always convince themselves that the problem is a "corner case" that will "never happen".
I mean, it was in the 1960s, the aerodynamic phenomena was not understood as much as we know today. They did not fully understand the limit of those phenomena. I think it is one of the driving factors of those BAC pilots exceeding the limits, to obtain more understanding to the aerodynamic characteristics. Sadly, it resulted in a dire consequences.
Back in those days, pilots didn't even know T Tails existed....
The DC-9 had the same problem.
I was talking to a mechanic on the test flight---they were filing the throttle to get more power.
They too got into a deep stall.
They added fences on the nose to disturb the air during a deep stall.
Very informative. Great Presentation, Well Done Sir.
I think the most true quote I can ever quote from a teacher that I knew. He was talking about a NASCAR wreck that lead to restrictor plates. A very famous one you are sure to know, Bobby Allison.
He said
"It takes someone to die before anything changes"
And time and time again I see it happen every once in awhile. The reason we have so many safety features or safety precautions is because of someone passing away or getting severely injured.
Amazing video and thank you to those pilots.
The part about increasing power causing a pitch up sounds just like the problem the 737 Max has which led to the workaround that backfired badly.
Not really, the 737 had a system to alter the pitch when the angle of attack was too high. This was put in place due to a last minute change. The engines were too low to the ground so they were moved forward, which altered the center of gravity. MCAS was put into place to pitch the plane down to compensate for the shifted center of gravity. 737 MAX’s problem is because a single faulty Angle of Attack sensor causes MCAS to think the plane is pitching up when it isn’t, so it keeps pitching the plane down.
This incident, the plane is actually designed in such a way that the wings block the air flow to the elevators at a high angle of attack, and the plane CANT pitch down. In 737s case, you can disable MCAS and override the system (the pilots just didn’t know how in a panic due to incomplete training by Boeing). In this case, it is physically impossible to pitch down.
The workaround was fine, the fact they didn't tell pilots and lied about retraining is the problem.
@@nevelis Absolutely correct except that for the MCAS, there was not "incomplete training", there was no training at all and this was the aim by the way to compete with the A320 Neo. So the crew of the first crash (Lion Air) didn't know about MCAS so that they didn't understand what was happening. The crew of the second crash (Ethiopian) was aware of the MCAS possible trouble and informed about what to do in case ... and that's what they did. The copilot was the first to understand the situation and they did quite well: they switched off the MCAS asap, as recommended by Boeing but it didn't work since, in the meantime they had got so much speed in the dive that the aircraft was not recoverable. Disabling the MCAS was not the solution and anyway it had to be done within 10 seconds maximum! The solution was (is) 2 sensors instead of 1 and additional training related to the MCAS. From my perspective, trying to compete with Airbus implementing a new modification on a very old aircraft was probablt a bridge too far, not mentioning the mind blowing lies ... Just my opinion.
@@patolt1628 True. MCAS (Might Crash Any Second) was sort of a band-aid fix to deal with a basic design problem caused by modifying a half-century old product with bigger engines and a newer wing design. For pilots struggling with dangerous MCAS inputs the "solution" was to disengage that system, leaving pilots with the original design flaws that it was intended to fix. As you mentioned, the additional sensor and additional training seem to work now. Still, it's time for them to come up with a new aircraft.
@@nevelis Moving the CG forward would actually create a nose-down tendency for the plane. The problem is a bit more complex, related to the lift created by the engine nacelles.
Also, you are missing the fact that it is not as easy as "just disable MCAS" - the crew of the second crashed plane did disable MCAS as per Boeing instructions, and it still was impossible to recover from the crash.
Thanks buddy , you must of put that up at a different time , was not there at midnight last night Aussie time , good work I don't know how you get the time to give us 2 videos in a week
Very good video. It's sad to see they couldn't exit the plane and use the parachutes. Elevators failed just when they needed it most.
Really sad 😞
Thanks for another great video. As a former RC pilot in the 80’s it’s not always necessary to die to learn how to fly safer. We trained on getting out of spins and stalls and aerobatics. In this situation I would try to roll out using the ailerons to allow the tail catching some wind. If nothing seems working, try something else
Wow. I wish there were some way to accomplish these types of changes without death being part of the equation.
These test pilots never get the recognition they deserve! God bless them and their families! 🙏✌️
Now, that I finished the video, I just want to add that the combination of a T tail and rear mounted engines is a dangerous one
As an aviation beginner - can you explain me why?
Yes, please explain.
@@benjamin4281 @crunchtastic1948 As explained in the video, the T tails can enter the deep stall where the aircraft loses the elevator authority, making it hard to recover. The thing with rear mounted planes is, adding thrust causes the plane to pitch up, which you'd normally counter with the elevator
Rear mounted engines will always come with a t-tail, due to the engines being near where the horizontal stabilizers would normally be.
I wouldn't say that configuration would be dangerous, as many "modern" planes have that configuration (ex: most private jets, CRJ 100 series) but you do have a point.
(Edit: Rear mounted engines can also come with a 'cruciform tail')
It's hardly dangerous, especially as it was used by some of the most common planes of the 60s and 70s (the BAC111, DC9, MD80, Boeing 727). In this case there was a danger, but they discovered it and made efforts to ensure pilots would not get in a position where the plane might deep stall. It was also found that the 727 could get into a deep stall when using flaps 40 (the maximum setting) under the right weight and centre of gravity, so many operators either banned flaps 40 being used or even physically locked it out.
I haven't flown many times in my life but most were in a BAC 1-11. I always felt safer in that than in a Boeing.
The blistering acceleration was what always got me, they used to go like scalded cats compared to the modern jets.
And? A gratuitous swipe at Boeing. How original.
Why? Based on jingoism or something scientific? High-tail plans have terrible stall characteristics. (like the Trident crash at Staines).
These planes were also disgracefully noisy.
@@hoagy_ytfc So were most aircraft of the era. It's only with more modern engines and designs that noise was significantly reduced
@@Arthion but the 1-11s were bad even by the standards of the day, was the point I was trying to make.
Good Investigation.
I'm subscribed.👍
A very similar accident happened to a Hawker Siddeley Trident airliner in 1966. G-ARPY was on a test flight before being delivered to the airline and also entered a deep stall. It crashed in Norfolk, England and all on board died.
My father was shocked when the prototype One-Eleven crashed as he worked on it as an aircraft fitter at Hurn Airport Bournemouth. When the internet became widely available I found an article on the crash. Apparently there was a stall system which operated in part by a hydraulic tab on the tailplane. The pump was undersized and failed plus the pitch reading was incorrect. When the pilot realised he was in a stall he was not aware the pitch was greater than the reading. Being a WW2 fighter pilot he tried a few manoeuvres but it was too late. On impact the forward movement was 75ft. The exit door was still in place as all the bolts had not been fired. The final comment was that military aircraft undergoing stall tests could deploy a tail parachute to bring the nose down. I’m not saying the article was correct but it is how I remember it.
8:16 But other planes than the BAC-1-11 crashed due to a Deep Stall during test flights, like a Trident in 1966 and a CRJ-100 in 1993.
Yeah, and other planes like the F-101 had these issues prior to the 1-11's testing.
A bit like in physics how Bernoulli and Euler followed Newton, Clerk-Maxwell and Faraday followed them and in turn Einstein and Bohr continued and built on their work - so in aircraft engineering do you get the culmination of generations of knowledge and experience brought to bear in the design and construction of the latest, safest, most efficient airplanes - even the most successful aero companies with the most gifted designers don't do it from scratch. It's great to see a MACI clip highlighting the skill and dedication of those who went before, much as we enjoy the more usual stuff involving commercial flights gone wrong. As always, very nicely explained and easy to follow even as a non expert....
T-tail deep stall had been a known issue for decades before the plane was built and flown.
It's called a super stall because the tail gets captured in the wind shadow of the wing.
6:20 Yes, this is called shadow masking. There is no laminar airflow over the tailplane as the airflow is masked by the severe turbulence from the wings. This is common for all planes with T-tails like the HS Trident, Vickers VC-10, Boeing 727 etc.
they should have rolled it with ailerons, past 90, and let the nose fall thru....
It's not angle of incidence, it's angle of attack when you are flying. The angle of incidence is the angle the wings are mounted to the fuselage, as shown in the illustration at 3.50 and this angle obviously never changes.
The data recorder print-out shown in the video refers to something called "true incidence" and the figures for it suggest that it was at the time a term for what is now called the angle of attack. Other technical terms have changed over this period, for example the tailplane and fin have become the horizontal stabiliser and vertical stabiliser. Also the terms port and starboard (which appear on the print-out) don't seem to be used any more.
Love your videos!
Small correction. When you say angle of incidence you mean Angie of attack. The angle of incidence is the angle between the wing cord like and the longitudinal axis. It’s fixed per airframe.
AKA riggers angle
Not in UK terminology. Please see my reply to a similar comment.
Just an FYI...You wouldn't say, "To say that he's one of the few people who knew the plane best would NOT be an understatement." Saying he knew it best WOULD be an understatement. No biggie, just some constructive criticism from a faithful subscriber is all...Another great video BTW. 😉✌️
Grammar
That feeling in the pit of your stomach having no elevator control must be like driving on the freeway and turning the steering wheel and nothing happening. Damn.
Remember (just in case) from some other disasters and reports, that if you bank far enough, the nose also pitches down... You CAN also use some rudder (pedals) with the ailerons (roll) to accomplish this...
It's important as we take controls of larger machines and take responsibility for more lives by rote, that we remember "There are more ways to kill a cat than to choke it to death on strawberries."
You probably won't ever need to use that knowledge... BUT it's worth watching a lot of these accident and disaster videos to notice things like that. If the elevators won't help directly, roll to the side and kick the hell out of the rudder. You can get that nose down if you act quickly enough... AND once the engines get clean air, and you've got some speed back, level out and pull up GENTLY...
This is NOT to take away from these wonderful pilots and people!!! May they rest in peace, there was NO precedent for a deep stall or super-stall, where the engines AND horizontal tail end up in the "shadow" of the wings, and lose efficacy. NOW that we know, we have shakers and pushers on a LOT of sticks because a LOT of planes have the "weakness"... There are also other pilots and lives lost for us to find out that a hard bank (say... in excess of 40 degrees) can drop the nose... AS CAN a bank and rudder control... Let's keep ALL their sacrifices respected and valued by keeping EVERY lesson we can learn... just in case we might need it one day. ;o)
One way to get out of a stall like this is to roll the plane on its back, then level out and roll back over.
Quite a sobering story. The fact that this resulted in knowledge and safety features such that it wasn't repeated is an honor to those who died.
Awesome video as always from You. Did they use the flaps?? few accident have been done with no flaps. Thank You!!
I must have flown hundreds of times in BAC-111s out of Gatwick in my 20s, working as a computer engineer attached to British Caledonian, of course they all had pitch shakers and pushers by then.
British Airways flew Tridents too in those days and I think it was one of those which "reversed" into a reservoir coming out of Heathrow due to a deep stall.
2:46
in fact that would be an understatement !
Fantastic video
I once worked with a guy who worked at bac weybridge and spoke to the pilots only the day before their final flight
What is really sad, the problem was found after the crash. I wonder if budgets had anything to do with not completing more test.
Great Aircrew !! "Semper-Fi"
I think you have mixed up ANGLE OF ATTACK WITH ANGLE OF INCIDENCE. Angle of attack is the angle between the cord line and the Relative Airflow so changes in flight. 15 degrees is normally the maximum before the stall (although I think delta wings like Concord can go to 22) Angle of incidence on the other hand is fixed by the aircraft designer and does not change, although I think there are some fighter jets that have a variable incidence, wing, but I may be wrong about that.
The wing is actually developing maximum CL at 15 degrees just before the stall.
NPC
the best reaction to a stall is not to put the engine on full power, but to do the oppesite, this will force the nose down and you will soon have enought speed to get out of the stall, this is something you learn as a combat pilot
The correct term would be "angle of attack" and not "angle of incidence". The incidence is the angle between the fuselage zero line and the wing chord line, i.e. it is a fixed angle for most airplanes unless it's a tilt rotor with tilting wings. The angle of attack however is the angle between the wing chord and the incoming airflow, that is what causes a stall.
Landing gear extansion may provide some pitch down nose as per other incidents videos
You do a great job and I enjoy your videos! There's a bit of confusion about the angle of incidence vs. the angle of attack (AoA). The incidence is the angle of the wing chord line relative to the longitudinal axis, it's fixed (except the FA-8 Crusader and perhaps another one or two). The AoA varies during flight and increases as you approach a stall. If you lose elevator control, with enough altitude you can roll 60 degrees or so and apply rudder and pivot the jet to lower the nose. Cheers
You should do the Felthorpe Trident Crash!
Deep stall is what brought down BEA 548, too.
For those who haven't worked on aircraft let me tell you -- the stick shaker is not very subtle. It is a violent movement designed to get your attention!!
I loved this plane, for it took off so fast, and could land on very short runways. Also loved the DC3, and the 747.
Pleased to report it was indeed a structural giant a later vairient of the BAC 1-11 with Philippine Airlines survived two seperate Granade incidents by suicide passenger,which blew out a whole hoop section of the rear cabin leaving the tail in midair with limted support. this happened on the same registered A/C some two years apart . In both cases the aircraft experianced an explosive decompression entered a terminal dive and was only recovered by superb piloting skills when control was regained once the aircraft was down to around 7000 feet by use of elevator trimming.
True story I was involved with the rebuild of the A/C at BAE at Bournmouth following the first incident.
Elevator blanking in a T-Tail is one heck of a terrifying design flaw with the concept of T-Tail aircraft. Personally, I would require the use of a small canard on all T-Tail aircraft to provide Pilots just a little bit maneuvering ability in the event of a stall like this.
It's surprising they didn't try lowering the landing gear. Although it wouldn't have done a lot, it may have been enough.
As tragic as it was, they succeeded in their goals - they provided important data to the engineers which saved a lot of lives in the future.
Centre of gravity is also very important as regards behaviour in a stall situation. Of course aft cg is more critical than forward cg.
Nowadays during test flights they set the exact center of gravity with water ballast tanks in the passenger cabin. I believe they can modify this in-flight if need be.
If you get your cg forward you're in much better shape in a stall. If you've ever flown an aircraft yourself you know what I mean.
That's why they had three "observers" who were told to run back and forth....
Generally I believe c of g is controlled in flight by transferring fuel between tanks to keep c of g within limits. From what I've worked on, fuel proportioners pump fuel from tank groups to help relieve the workload on the crew.
@@125brat That depends on the type of aircraft, whether that's possible. Modern narrowbodies (B737 series, A320 series and any smaller aircraft if I am not mistaken) do not have that capability: Just one fuel tank per wing and that's it. You cannot change the cg by moving fuel around.
Widebodies like the old A300/A310 and also the modern A330 (and I guess the larger Boeings) do have that fuel tank trim option though.
Plus, testing beyond the operational limits of a plane with designated test flights is another matter. I have found this other video, see other answer.
Here is a video that explains it: This is modern aircraft test flight operations
ua-cam.com/video/edrbbwhW0Cw/v-deo.html
From about Minute 2.00
@@olaflieser3812 Thanks Olaf. My main experience is of tanker aircraft with multiple wing and fuselage tanks where it was the copilot's job to manage the fuel. Yes, smaller aircraft tend to have a single tank in each wing and maybe a few cells in the fuselage but I'll have a look at your linked video to see what you're referring to. Of course, test flying is often at the very limits of the envelope or beyond flown by very experienced pilots after much research and calculations. I know an ex-RAF test pilot and their motto was "Learn to test, Test to learn".
I think you meant Angle of Attack. Incidence is the angle formed between the body and the wings.
Here’s a video of the single finest piece of flying I’ve ever seen: ua-cam.com/video/L2CsO-Vu7oc/v-deo.html
It was a deep step test on another aircraft, the MD-95/717. Basically a stretched DC-9, the MD-95 had wing and tail redesigns to suit.
The problem is that while doing computer modelling of the stall characteristics, the modelling was throwing up weird results that the engineers couldn’t quite figure out. They decided they had to test this on the bare metal, which was an FAA requirement. Part of the development of a plane for FAA certification is that you’ve gotta stall the thing and prove that it is recoverable. You’ve also got to reconcile the computer modelling. The more data you have, the better the modelling gets.
Anyway, this was a test flight to try to verify the computer modelling, and hopefully figure out why the modelling was weird. There is a lot going on in that video, but they entered a deep stall, and the plane rolled over, and into a nosedive. They went from a stall to an overspeed in mere seconds. At one point, they were losing something like 60,000ft per minute. More than 1,000ft per second: that thing was pointed directly at the floor.
They were able to recover the aircraft and and safely, and they generated a lot of data and insight from this flight. The pilots made it out fine, but the plane did not. The plane had undergone such aerodynamic forces that the structure itself had deformed, I seem to remember to the point where the plane wouldn’t pressurise properly. In any case, the aircraft was written off, and as of writing, it remains the only MD-95/717 hull loss.
Ultimately the engineering fix was a software one: an aggressive stick pusher in the flight computer control logic, so you’ll (theoretically) never be able to deep stall the thing even if you tried. You can’t really “fix” this problem aerodynamically-it’s just the nature of a T-tail, and it always will be, which is why stick shakers and stick pushers are so crucial.
It’s a crazy story, worthy of a video of its own.
I've watched this video before. It never occurred to me that they were in a deep stall before the plane rolled over. I thought it was just a regular stall. I am very interested in the idea of recovering from a deep stall in a t-tail aircraft though. Is the idea that you're supposed to reduce power and force the plane up to such an angle that it will want to roll out of the deep stall? I've heard some people say that it's not possible to recover from a deep stall, but clearly that can't be true.
The angle of incidence is the angle between the chorď line and a line between the fore and aft axis of the aircraft. It never changes on an aircraft.
What you meant is the angle of attack. This is the angle the chord of the wing makes with the relative airflow.
Sounds like a similar issue to the Dehaviilland Trident in which a test also caused the plane to crash onto the airfield at Hatfield. I think the engines flamed out. As an apprentice there in 1972 I remember seeing the crater it had left near the edge of the airfield. I don't know if that incident was before or after the 111 one.
As being a British person.
I THANKS THOSE WHO TOOK PART IN THAT EST FIGHT AND SADLY LOST THEIR LIVES TO SAVE ALL THAT FOLLOWED.
THANK YOU.
The narrator of this did not explain why the nose went back up when the pilots put in maximum power. The deep stall phenomenon was not known very well at all in those days, and the pilots probably did not realize if they accelerate the air underneath that tail by going to high power, then the air pressure under the tail is reduced, and the air pressure above the tail is higher, will shove the tail down, putting the nose back up in the air.
Kind of a counterintuitive thought, but they needed to keep those throttles back until the nose was down. So that airflow could be restored and airspeed increased.
I flew both the DC9/MD80, and the Lear35. Both of those aircraft had a very strong stick pusher that would shove the nose down .
in the case of the MD80, It’s a force of 80 pounds on the column and it will shove the yoke forward violently when you activate the stall warning. It’s activated several knots above the actual stall so you still have airflow over the tail when the elevator starts coming back down. it does that by a hydraulic circuit in the down elevator. That’s the only hydraulic flight control for pitch. Otherwise the elevator is cable operated with servo tabs.
Douglas actually put an additional device called ventral strakes, underneath the nose on each side to help energize airflow over the tail at high angles of attack. That gives even more control in an extreme pitch situation.
Just one more thought. The only thing that would’ve got the nose down quickly with no airflow would be a weight shift system that would allow weight to be moved forward very quickly from a cockpit control. If they could’ve moved a couple thousand pounds forward in a matter of seconds by using a weight shift system in the cabin that would’ve put the nose down. I’m guessing they had no such system installed . It’s obvious to me if they had known all of the dangers of the deep phenomenon they would’ve taken additional steps to get the nose back down in a loss of control situation.
You mean it WOULD be an understatement.
One of the Gloster Javelin jet fighter prototypes (which also had a T tail) was lost to a 'deep stall' 10 years before this accident so it seems surprising that the designers of the BAC-111 did not anticipate the problem. However, the Javelin had a much broader delta wing, so they may have thought the BAC-111's narrower wings would make it less prone to a 'deep stall'.
There were two stall accidents with the BAC 111. In the second incident the pilots felt that they had entered a deep stall and therefore released a parachute, fitted to the tail of the aircraft after the Lithgow crash, which was intended to pull the tail up, thus allowing the aircraft to recover, which, in fact, it did. However, due to an optical illusion the pilots thought they were still deep stalled and rode the aircraft into the ground, with the parachute still deployed. In fact it was the drag of the chute which was causing the problem, had they jettisoned it the aircraft would simply have flown away. I seem to recall that the crew survived this crash.
Yes the crew survived. The aircraft bellied in more or less intact somewhere on Salisbury plain and I saw the
wreck personally. They dismantled it in situ and ferried the components out by road
@@smokeless7774 thanks for that.
And there was a Trident full of passengers that stalled the same way. And if you recall, the Beech staggerwing had the same issue with its upper wing.
Drag chute is needed to break a flat spin. This being a test plane should have had one.
ERAU 80 CFIA&I ret.