Dangerous Aerotow - I almost stalled! - Towplane Flies Too Slow For My Glider
Вставка
- Опубліковано 22 лип 2022
- Dangerous aerotow takeoff when the towplane flies too slowly for my heavy, ballasted glider.
Glider pilots often fly with water ballast because the extra weight allows them to fly faster and cover greater distances. One of the downsides of the higher wingloading is that the stall speed goes up, i.e., the glider needs a higher minimum speed before it can fly.
Glider pilots must therefore brief the tow pilot before such flights that a higher speed is required during aerotow. If the tow plane flies too slowly, the glider becomes very difficult to control and may even stall while on tow. The same is true when winch launching.
One additional complexity is that - in the United States - tow planes often have air speed indicators denominated in miles per hour whereas glider pilots usually use knots.
You may ask, "what could possibly go wrong?" Well, it's not hard to imagine, and you can see it firsthand in this video...
I'm sharing this incident because I think that the same mistake can easily reoccur, and, yet, it is also easy to avoid. Soaring is objectively dangerous but we can all take steps to reduce the risks. I hope this video will help someone else avoid the same mistake and stay safe!
--------
I put a lot of effort into these videos to make them engaging, entertaining, and also instructive. It's not an easy equation to get right. If you find the video valuable, please subscribe and let me know in the comments. I also welcome constructive ideas to make them even better.
My glider is a Ventus 2cxT 18m high-performance sailplane from Schempp-Hirth. The flight originated and ended at Boulder Municipal Airport (KBDU) - an ideal soaring location for exploring the sky in Colorado and beyond.
I flew with approx. 32 US gallons (121 liter) of water ballast in addition to fuel for my sustainer engine. The glider's all-up mass was at the maximum approved takeoff weight of 600 kg (1323 pounds) representing a wing loading of 54.4 kg/sqm (11.1 lb/sqft).
Watch my other videos: / chessintheair
Check out my Website: chessintheair.com/
Follow me on Facebook: / chessintheair
All music is from Epidemic Sound. - Фільми й анімація
One day flying an event at Nephi, a glider full of water was getting a slow tow and he wanted another ten knots. The tow pilot thought, that would be a great time to argue with the glider pilot. Tow pilot responded to the glider pilot "ten knots, you want to to add another ten knots, are you sure", with ever increasing panic in the glider pilot's voice "ten knots damnit" tow responded "ten knots really?" I was scared and I was on the ground.
Im happy that you both are OK! But the real solution is METRIC SYSTEM!!! Knots feet miles inches… makes everione confused
Yes, I agree that there are definitely too many different systems in use. But that’s not something I can readily change, so I will have to adjust to reality rather than try to change the reality itself. Btw, even where the metric system is in use there are inconsistencies. E.g. why use m/s for vertical speed instead of km/hr? It’s a lot more useful vertical and horizontal speeds use the same units. The calculation of glide ratios requires consistent metrics… Also, why is wind denoted in knots, even in many countries that use the metric system? It would be a lot easier to just have a single unit for speed, no matter what speed is being measured.
@@ChessInTheAir yes. You are right. There is no way that they ever change it. But for the wind. In hungary we use m/s for that.
Many of the American glider folks say the metric system hurts “their situation awareness!” It’s true. I agree metric system would solve the problem of this and many other glider competition challenges.
Very relevant safety issue. All clubs should include this in their recurrency training!
You were lucky. Some unflapped gliders can barely rotate enough to unstick at stallspeed, yet alone, climb out of ground effect!
@@ChessInTheAir if you think that the metric variometer should show km/h instead of m/s, how come that you find ft/min is consistent with an airspeed meter showing nautical miles per hour ?
Great routine of calling out the decision points during the initial phase of the tow! Something to keep in mind...
Thanks ! Good lesson. I will think about this when flying the Duo and water. Brief the tow pilot. And make sure we are on the same units
That was terrifying. Thank you for sharing.
Great video and great points made. I can't believe your tow planes airspeed indicators are in mph instead of knots! The obvious thing that should be done is to change them so all tow planes are the same as the gliders. I realise it costs money. And we've all had that horrible feeling of hanging off a tow plane that's going a bit too slow. For some reason, even above the stall speed of the glider it still feels horrible!
Thanks Tim! Part of the problem is that the Schweitzer gliders that are widely used in the US for training and rides also have ASI's in mph. So you'd have to replace all of them too. Some tow planes' ASIs show both mph and knots. Not sure if that makes the situation any better though. One more possibility for confusion. This might be a US-only problem due to a historic love of British measurement units. So in NZ you're using knots throughout? In Continental Europe the ASIs in gliders and tow planes are in kph. Wouldn't it be great if everyone would use the same units? I suspect everyone would agree as long as their own favorite units were selected... Personally, I couldn't care less which one but I'd definitely vote for standardization!
@@ChessInTheAir Better start with ICAO. Not even they have a standard unit for airspeed.
@@8OrangePants yeah, I’m not going to try to get anyone to change it. I’ll just adjust my own behavior (in this case the tow plane briefing) to minimize the risk that’s associated with the conversion.
@@ChessInTheAir the good news is you know the tow speed, and can memorize and brief the kts and MPH at the same time, and like you said for the tow pilot to read it back.
@@TheSoaringChannel yes, that's exactly what I've been doing since. :-)
Have watched this many times, hope you share more soaring adventures & are doing well, miss your video's. Cheers from Australia.
Thanks for sharing!!!
I had exactly this once in Spain. My fully ballasted glider sank and became almost uncontrollable as we crept low over the nearby village at 55kts. Fortunately I remembered the Spanish for more speed - “mas rapido!” and lived.
Thanks, Ralph. It seems almost everyone who flies regularly with water has a story like this. Awareness of the problem is key. Hopefully we can spread the word to reduce the number of such incidents.
I would have done the same thing you did. Sitting in front of my computer and under no stress I think it would have been less confusing to say "towplane faster". On a busy day many are sharing the same frequency and sometimes I wonder if the transmission I'm hearing is for me or not. Under those conditions perhaps the tow pilot did not realized you were addressing him.
Three different units of measure for one activity causing confusion, which could have so easily caused a fatality. Totally nuts. Why can't everyone use Metric for everything?
When I had a JS1c 18/21m I got into the habit of radio exchanging indicated airspeeds with the tug at least once during the tow. All the Pawnee ASIs over-read by about 5 knots compared with the very accurate JS1 ASI even although the tug ASI passed static calibration tests on the ground. I presume it is due to the lack of an accurate static source. Also, there is an superb article called "Poor Handling on Tow" by Aldo Cernezzi in the Jan/Feb 2017 issue of Gliding International which gives the clearest analysis of what happens at various positions over the span of a long wing glider behind a short wing tug, and why it is so dangerous. In short, the tug's downwash over the inner portion of the glider means that extra up elevator is required to maintain AofA and lift compared with in free flight. That means that the outer wing is at an effective higher AofA than the inner wing so that in the critical situation of a slow tow the outer wing will stall and depart first and at a higher airspeed than in free flight. The tug's vortex hitting the wing part way along the span complicates things further.
Thank you John for these insights! I’ll have to look up the article you reference. I’m told the Pawnees here also underreport airspeed, each to a different degree, though.
I found the Pawnees over-reported IAS compared to me. The tug thought it was going faster than I did.
@@johngalloway156 thanks, yes, I misspoke, I also meant to say over-reported.
One would think there's priority radio between the tow plane and glider during launch
Well, it’s a public airport and other traffic has important announcements to make as well. The main lesson here concerns the importance of a clear briefing.
If this topic has peaked your interest (it should for your own safety), then please also watch this safety briefing video from Dave Nadler. It explains that the problem tends to be exacerbated by towing behind short winged tow planes (hello, Pawnee drivers!) and why the glider's stall speed on tow is even higher than it is in free flight. The good news is that releasing should not be such a big concern because as soon as you let go of the tow rope, the gliders stall speed goes down and you’ll actually fly better than behind the tow plane. (I still would prefer to never have to try so I will continue to pay extra attention at the briefing.). Another thing you’ll learn from Dave is why Pawnee airspeed indicators are usually off and often underreporting airspeed. This further exacerbates the issue. Here’s the video. Please watch it: ua-cam.com/video/WIZWzvMu1dM/v-deo.html
Any tow plane pilot has a set of speeds to fly with empty gliders or heavy gliders. If you tell the pilot, I’m heavy or full of water he would know what speed to fly. Even then levels of tug pilot experience can result in slow tows. Glad you survived ok.
This is approximately true but different gliders need different minimum tow speeds. Eg a fully loaded JS3 will need considerably higher tow speeds than a fully loaded Discus. The key reason is the difference in permissible max wing loading.
Wow that was scary, Clemens! I’m glad that was an incident and not an accident!
In a perfect world everyone (in aviation) will follow the lead of gliding in Europe that has converted to metric units. How many more incidents / accidents will it take before we realise that standardisation in aviation is essential (not optional).
We did all learn to speak English in aviation, so surely we can also all learn to speak metric?!
I wish you were right but I don’t have high hopes that standardization will happen. By the way, Europeans should change their varios from m/s to km/hr. It is very helpful when vertical speed indicators and horizontal speed indicators use the same unit (like gliders that have both indicators in knots).
@@ChessInTheAir Yes, valid point that both vertical and horizontal speed should be the same unit.
Even the British (eventually) realised that decimal currency is easier to work with when they converted from pounds, shillings and pence to decimal units in 1971. So I guess there is hope yet?! Maybe the Penny will drop (pun intended) that decimal distance units will also be easier to use?
Another note on coms, up 5 up 5 up 5, or up 10 up 10 up 10 often is easier to understand over the radio then just faster faster faster.
In this case it would have been "up 15" or "up 20" given the actual speeds involved. I think it's best to talk about coms with the tow pilot beforehand so that such a message is understood. Otherwise "Up 20" might not be immediately clear or could be interpreted as something else. Faster was at least directionally unambiguous. But in the moment I could not even recall the tow plane's call sign (we have 5 different tow planes at the field) even though I had said it myself just one or two minutes earlier. Another problem was that my initial transmission was not audible at all because someone else had also just started to transmit and there was no time to wait until the other transmission is over. All this underscores the importance of a good briefing beforehand where you can be certain that the tow pilot has understood and internalized the information. The tow pilot pulling me normally pulls 1-26s and 2-32s where 52 knots is perfectly adequate. I now make sure that the tow pilot will actively remember that this tow is different from what they normally do.
I think the best thing you could've done instead of calling faster on the radio is to release the rope and just land. Because you could've stalled and stalled the tow pilot as well by pull tow aircraft tail. I am glad you both were safe and we can all agree with you it was the tow pilot mistake lifting off before you do.
For me there is another question re what can we learn from it (when a tow starts out badly - no matter why): what are the criteria for an early/immediate emergency release and are we mentally prepared for it. Enough landable area remaining ahead (runway, overrun, reasonably flat strech w/o fences/obstacles) would be an obvious one. Parameters are airspeed, altitude, wind.
In your case it might have worked releasing shortly after your early call outs (about in front of the Mile High shack). Your glider was not stalled at this point and a "gentle" pushover would unload the wing, making a stall less likely.
To prepare for/help with the decision to release one would have to be familiar with that landable area under different conditions, including weight of the glider, power of the towplane (hp, density altitude). Kind of determining something like the "accelerate-lift off-stop" distance. Walk down there and measure....
Once I had to release early when the tow ran into a patch of yet uncut grass and didn't accelerate to a safe (for me) airspeed for climb. Different situation, different outcome, but it sure drove home the point about being prepared!
Yes, completely agree. I definitely had enough runway left to stop. I had the impulse to release but stopped short for fear of stalling and not having enough altitude to put the nose down and pick up speed. But to be honest I really don't know what would have happened. I also thought afterwards that maybe I should have just stayed in ground effect myself until I was in the low tow position. That would have reduced my risk but I'm not sure how the tow plane would fare in that scenario with the glider pulling down at the tail. I really don't know what the best option is in this scenario other that doing the utmost to avoid it in the first place.
@@ChessInTheAir I think you did well. Staying low and pulling down tow plane's tail would stall him (and probably crash) if you/he did not release in the right moment. I also understand why you were afraid of realeasing so low at stall speed. Luckly it was almost perfect 52 knots and not slower, thanks for sharing :)
Ps. Maybe 30 sec silience on radio would be good idea while tow plane & glider is taking off or even different frequency for both of you during that crucial time?
@@Alupl Hi Aludan, thanks for your comments. From what I’ve learned since it would have been ok to release because the glider’s stall speed is lower behind the tow plane than it is in free flight and a release should not have triggered a stall. That’s what I’ll do next time this happens. There’s a link to a presentation by Dave Nadler in the first (pinned) comment. He explain this in some detail. Re: the radio, there is too much air traffic in Boulder to safely use a different frequency (you have to monitor what’s going on around you) and I think it would be impractical to ask other traffic not to use the radio while gliders are taking off.
@@ChessInTheAir You're right about different frequency. It was just idea which i've heard some time ago. We have also too much aircraft traffic and even had fatal (unfortunately) accident which maybe didn't happen if the pilot have heard the radio message but in that time some airplane pilot was talking. Different frequency for gliders or temporary silence on radio during takeoff was just some ideas to solve the problem but to be honest i didn't fly in last 2 years so i don't know if it was resolved that way.
@@ChessInTheAir If you release the moment you see him climb out of ground effect (right before the first "faster") you'd have a benign straight ahead "landing". That requires forethought and a commitment before the start of takeoff roll, something like the "V1" call in an airliner. Once out of ground effect you may find yourself trading one bad situation for another.
As always, thanks for sharing this!
Thanks Clemens for another great video!
Really glad you guys got away with it, this time... A friend of mine was not so lucky.
A couple comments:
1) You could have released the instant the tow pilot started climbing sharply before minimum speed reached!
2) The minimum safe tow speed for gliders is well above the glider's free-air stall speed.
One of the safety briefings I've done about towing safety is available here:
ua-cam.com/video/WIZWzvMu1dM/v-deo.html - I should make a better video...
Hope that helps,
Best Regards, Dave
Thank you Dave! Good advice!
Great explanation in your video, many thanks! Very helpful. I’ll be more confident about releasing immediately if this ever became necessary again!
You and Bruno have had exactly the same problem. What’s the best way of communicating min tow speed before everyone gets the shit scared out of them?
Holy shmoley Clemens. That was sketchy! I've always wondered how it would look in this situation, and you're right. The glider pilot is in a bit of a pinch. If you stay connected and stall: that's very bad! You go low, and force the towpilot nose high, you both probably don't survive. If you release: you probably stall, but at least the tow pilot gets to live through their mistake.
I will not pretend to second guess you here.
Instead: If that happened again and you saw the tow pilot climb out BEFORE you left ground effect, before a safe tow speed: would you release? If you catch it early enough: you can land straight ahead as briefed or go to the fields.
Yeah, while I was working on the video I had a lot of time to think what I should have done differently. I’m actually still not sure what the best decision would have been. Possibly release as soon as the tow pilot pitched up, immediately switch to landing flaps and simultaneously release any back pressure on the stick, keep the air brakes in and land straight ahead. The problem is that you really have no time to think and decide, it basically needs to be a reflex that must be part of the emergency plan just like in a rope break or loss ow tow plane power situation.
@@ChessInTheAir How long does it take to dump water ballast? Would preparation for ballast dumping be appropriate as an EP under tow? For instance, If you initiated a water dump at the same time or a few seconds following the "faster faster faster" call how long would have taken for the polar to shift into a safer realm? Alternately, assume very marginal conditions including strong downdrafts in the mountains under tow to the point that terrain clearance and escape was a concern. Would dropping ballast be an appropriate EP to be ready for under those circumstances?
@@johnlewis1113 Water dumping takes a few minutes (exact time depends on the glider) so this is not a viable option when in a pinch where seconds matter. In a potential downdraft scenario over the hills the water is actually an asset not a liability because it allows you to fly faster at lower sink rates so you can get out of the downdraft area sooner and with more altitude left.
As far as pitching down, would it be plausible to rapidly pitch down and release at a negative attitude but before substantially lowering position relative to the towplane? e.g. as you transition through the "low tow" flight position.
@@johnlewis1113 yes, I think that might have worked. I wonder what the pull down on the tail would do to the tow plane which wasn’t much above its minimum flying speed either. It probably would have also terrified the tow pilot. Maybe something we could deliberately try one day at a safe altitude.
Seems like there are potentially a few more things to be learned (or perhaps researched) from this. We all know that adding ballast shifts the polar. Presumably, this also shifts your emergency land-out options early in the tow. When flying heavy, up to what point (if any) could you safely land straight ahead? Elliot's field? L-Shaped field? What happens when you release a heavy glider at very near stall speed? You stated that you were afraid to do so, presumably at least in part because of the uncertainty of the outcome. I think we could pretty much agree that a glider stall low in the tow could be quite dangerous for all parties. It would seem that it should be possible to do some sort of testing under more controlled conditions that would generate some improved knowledge about the options under those circumstances. I would certainly want to know. This is a prime learning opportunity. We're very glad it's not an accident report.
Yes, these are good questions. I'm not sure how one could safely test what happens if you release from tow at 30 feet when you're close to stall speed (although I would also be interested to know). One of my friends told me afterwards that he did release in a similar situation and just had a very hard landing where he was glad that nothing broke. With respect to the landout fields my calls are adjusted based on the extra weight. The problem with Elliots field is that it is too short to land and stop with a ballasted glider. Landing there would require a purposeful ground loop that could break the tail boom. The L-Shaped field is not very good anymore because it is now a horse pasture and there is a small structure in the middle that reduces the useful size of the field. I added "beyond the L-Shaped field" as a better option. It's a field with a slight upslope where I think I can get a heavy glider to stop more easily. But none of these options can realistically be safely tested. (At least not by myself.) One thing you can do (and which I have done) is to try different landout options in Condor with and without water ballast. It is eye-opening to see how much extra runway you need due to higher minimum speed and greater mass (i.e. higher kinetic energy).
@@ChessInTheAir I think what I had in mind would be doing a release test at a safe enough altitude to allow stall recovery. Q1: If you release at just above stall, does in fact the glider stall? Q2: Is it possible to trim so that it wouldn't? Q3: Can a good and alert pilot react quickly enough to prevent a stall? Q4: What is the short-term sink rate and how would that translate into a potential impact? Q5: How much altitude is required to recover at various weights?
@@daveandrew589 Got it, yeah, that may work 🙂
@@ChessInTheAir Out of curiosity (and enthusiastic inexperience), I went into Condor and set up an Aerial Start for a Diana2 (I just have the default gliders), and trimmed it as far back (nose up) as possible. Unballasted, this is still above stall. Then I pulled it slowly back to near stall (simulated buffeting). Simply letting go of the stick always resulted in immediate nose drop and no stall. Then I did the same with max ballast. Full nose up trim is very near stall at that point. Repeated the process, still no stall. Repeated again, this time giving a quick jerk back and release on the stick to simulate deceleration from tow release. Still no stall. Does anyone take off in tow with full nose up trim? Kind of doubt it. Does this prove anything? Very likely not. But it does suggest that any trim to a speed meaningfully above stall at your takeoff weight can avoid a stall on sudden release. Does that mean it's true for real gliders such as your Ventus? Probably not, but it does suggest a reasonably safe experiment at altitude.
@@daveandrew589 Good observations, Dave! I’m not sure how much I would trust Condor for this specifically. But regardless, at altitude there really is no risk to try it. What is hard to gauge is how much altitude you may lose in the process. Not sure if the IGC trace is accurate enough to assess it. 20 feet vs 40 feet would make a huge difference. The reason I’m worried about it on tow at low altitude is that you’re flying in a relatively nose high attitude with a high angle of attack. I believe it is due to this high angle of attack that flying on tow is uncomfortable even if you’re 5-10 knots above stall, and why manufacturers recommend a much higher tow speed. Eg for my glider the recommended tow speed fully ballasted is 71-81 knots. Our tow planes don’t climb well at 80 knots and I’m perfectly comfortable at 70, even 65 when I’m a few hundred feet above the ground. Releasing at 53 with a nose high attitude I am concerned that my speed will initially decline below stall and I may need to loose 40-50 feet to pick up enough speed to really be able to fly and flare for the landing. But if I’m only 20-30 feet above ground I may not have as much altitude as I need and the touch down could be really hard. I don’t know and I obviously don’t want to try down low. Experimenting at altitude would not be a problem but as I said I’m not sure that you can measure the altitude loss precisely enough. Maybe you can. Might be worth a try. There’s really no risk at all of doing so at altitude.
Did this incident scare you away from flying? Just curious because you haven’t posted a video since.
No, just haven’t had time to edit videos :-). It takes a huge amount of time and work.
Hard to believe an experienced tow pilot would make such a basic error
We all make mistakes. A lot of experienced glider pilots have made such basic mistakes as getting out of tow position putting tow pilots at risk, or worse. Towing is a team effort and it’s really best if the glider pilot does the unit conversion before takeoff and not rely on the tow pilot literally doing it on the fly. Also, consider that many tow pilots who almost always tow very light gliders where a slow tow speed is perfectly acceptable, even desirable. If that’s what the tow pilot is used to it is very easy to automatically do what you always do. As I said, it’s a very simple mistake to make. The point of my video is not to put blame on the tow pilot but to help everyone understand that such mistakes happen very easily and we have to work extra hard to avoid them.
Why not require to have same units in the tow plane as in the glider?
There are also gliders that have airspeed indicators in mph. This may be primarily a US problem. In Continental Europe ASIs are in kph. Not sure about UK. Unit standardization would of course be very useful.
@@ChessInTheAir UK gliders are generally in knots. Towplanes are whatever they are, both knots and MPH are common. I also fly one aeroplane with an ASI in km/h, we have quite a lot of ex-Soviet stuff here which is in km, and the only instruments that get changed are the altimeters, from metres to feet. The only times I have ever had speed-related problems with aerotows in the UK are the opposite to this, with very lightweight and vintage types, where a Super Cub can be too fast and run into cooling issues if it slows down to a speed suitable for the glider. This is when it's still good to have a Tiger Moth available. But whenever launching something that is not comfortable in the mainstream speed range I always want a proper pre-brief, whether I am towing or being towed
@@harryspeakup8452 Thanks for sharing! Yeah, I towed a long time ago behind a DR400 Remarceur with me flying a Grunau Baby. The stall speed of the Remarceur was about equal to the max tow speed of the Baby. I had to push the stick almost all the way forward to stay in position. Interesting that you have the unit conversion problem too.
It would be very bad for a tow plane if the glider stalls. The rope would stay attached keeping the tow plane in a stall.
Yes, I think worst case would be the glider entering a spin, dragging the tow plane down with it unless the rope could be released on either end or break in time. Things go very fast. I could not even recall the call sign of the towplane even though I had just used it a minute or two earlier prior to takeoff. I now specifically brief the tow pilot to stay in ground effect until the minimum tow speed of 70 kts or 80 mph is reached, then climb gradually while maintaining speed. This is a "better over-communicate and be safe" than "under-communicate and pay the price" kind of situation.
@@ChessInTheAir Since the rope is already under tension, I doubt it would break. Only a release by either pilot could stop the tow plane from staying very nose high. The glider pilot needs to release immediately in the advent of a stall. Speed saves.
"Faster, faster, faster, faster, ...faster, ...faster," is not clear communication.
This is true but “faster” was on my mind. I didn’t really have more than a fraction of a second to decide what to say. And I needed an immediate reaction from the tow pilot, not a thoughtful “ok, he wants me to increase my speed by 15 knots, let me focus on getting that right”. What message do you think would have been most effective at that point?
@@ChessInTheAir It must have sounded very bizarre to the tug pilot. Had it been me my first thought would have been that a third party had got hold of a radio and was joking around.
@@KeithWhittingham Thanks, I didn’t think of that possibility. But it’s a valid point.