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@@NevilleStyke that or nearly tripping over stepping backwards on the stage!

@@cekuhnen recently support for OpenFOAM was added to FreeCAD, which is a game changer. OpenFOAM is a very powerful and capable CFD solver, but it has no GUI, you have to program it all through text files, so it's only suitable for expert users, the learning curve for even getting a simulation to run at all was pretty steep! The FreeCAD Cfd-OF workbench means you can do all the preprocessing in FreeCAD, generate the OpenFOAM input files and run them. Expert users can still hand modify the input files for more advanced functions, but for simple cases it's now pretty easy to use. Search for FreeCAD OpenFOAM tutorial videos for more info.

I flew a seagull 3 in 78 as a trainer. No luff lines and a very poor glide ratio but easy to launch and land. I flew it of high launches numerous times but in very calm conditions before moving on to a new glider. I still have its bones in my metal pile to repurpose into other projects. Very good thing it was fall and winter flying with no lift else the story might be different.

@@mermaid10x My training was done in a Seagull Seahawk, which seemed somewhat similar to the Seagull 3. Good memories.

I flew standard rogallos in the early to mid 70s (Eipper Flexi-Flyer and a Skyports Lark 17). The only design mod to recover from dives was to tighten the top line from the kingpost to the keel to give the keel a bit of reflex. The Seagull 3 was considered one of the higher performance models back then!!! Probably a good thing I quit flying in '77. Now I'm starting up again at 69. Am I nuts?

Hi, so firstly Rogallo wings were the original (60s and early 70s) HG designs. Those could enter an uncontrollable (luffing) dive as a result of a gust (as I describe in the video) however modern gliders will recover themselves from that situation (also as described in the video). Secondly, I don't think a flat spin is even possible. Hang gliders are pretty spin resistant, some pilots do it for fun, but it's actually quite hard to get it to do it and you have you put quite a lot of effort into holding it in the spin. Centralising the controls stops it almost immediately. Also, yes kinetic energy is proportional to the square of speed, but you have to also include the original speed. So if you are flying at 25mph and hit a gust which increases your speed by 5mph then you are doing 30mph. If you work out the increase from 25 squared to 30 squared then it's 1.44x, not 5x. 6mph increase from 25mph is 1.53x, not 36x the energy. Also this isn't directly related to pitch input anyway, if the speed of the glider suddenly increases then it will pitch up, that's actually a function of stability, it's converting excess kinetic energy into potential, any aircraft will do that. The worst situation for a hang glider is actually a tumble, but that has nothing to do with aerodynamic controls or power, it's a function of being tailless and rotational inertia, which I'll explain in the next video.

@@avianhanggliders1985 Yes you are correct, but the total mass of the pilot and the aircraft is a constant (m/2) and the velocity components can have a greater value plus direction. I have experienced loss of pitch control in Rogallo wings and it is not an enjoyable experience. Wind shear is not fun.

@@crimestoppers1877 You fly old-school rogallos? I stopped flying mine in the 70s and sold the last one as a trainer about 1980. I do remember one sketchy tactic to recover from a full luff dive. You are diving so fast that you are nearly weightless, so weight shifting is useless. To push the nose up and re-establish a positive AOA, you had to use inertia rather than weight shift. The idea was to grab the down tubes hard and swing your feet up against the basetube in a crouch, then kick the bar forward really hard with both legs. A violent action to create a reaction. Sometimes the reaction would (supposedly) punch the nose up and the sail would fill, pulling you out of the dive. Thank god I never had to try that to see if it worked!

@@kimp8079 nice! Thank you.

Ah, thank you!

Yes, using carbon but keeping everything round tubes doesn't seem to me to make a lot of difference. Same for technora. The only wings that seem to be making the best use of carbon are the rigids (currently only ATOS). And maybe the Combats with oval leading edges.

Good question. Kind of no. Paragliders can get away with pitch negative airfoils because the wing is simply so light that the pilot swings ahead of the glider. However, imagine if a hang glider with pilot is dropped totally vertikal the nose facing the ground... the hang glider wing is so heavy that it would freefall as fast as the pilot, hence it has to pull away from the pilot by being pitch positive .

@@kimp8079 Thanks for that explanation. I find it counter-intuitive, but I'm not expert enough to really "get it". To me, it feels like lift-induced drag would prevent the wing from keeping up with the pilot, except in the extremely unlikely event of the vehicle being pointed straight down and having no pitch momentum at all. Otherwise, if there's the slightest difference in the downward velocity of the pilot and wing, the wing will lack lift-induced drag for only a moment.

@@IsaacKuo Yes. It is a little complicated, as Tim states. If the pilot has locked arms he/she changes the aircrafts center of gravity and you get partially pendlum stability (the pilot has also drag ;) ). However, trust me, you do not want to fly a hang glider that feels that it is is dropping its nose at speed so you need to push and hold on to the control bar. What you want, is for a the glider to be able to fly hands off (pilot acting at the gliders centre of gravity by only one hang strap) and from speed to pull up gently by itself, hence pitch positive behaviour.

@@kimp8079 I have test flown a glider that was badly adjusted (and was in a fairly bad shape), and with full VG at high speed was pitch negative. I quickly pushed out, released VG, landed, handed back to the seller and told him to scrap that kite. It was one of my scariest experiences, and only lasted a few seconds. Oh well, not quite, the wing also didn't handle predictably, and on approach I was thrown to the other side when leveling into final, and landed on the other side of the fence to avoid hitting our club's bar/shed/wing storage. Yeah, pitch negative and bad adjustments can cause bad problems.

"Hanging below the wing" is basically only true if your arms are loose and you're free to swing. In this state then it's all about the stability of the wing by itself, your weight under it is doing nothing for stability. As others have said, it's important that the wing is stable like this. If you lock your arms solid (this is just a thought experiment) then the CofG of the aircraft is now moved a long way below the wing. You're not really 'hanging' now though, as the centre of rotation of the overall aircraft is you. This does increase the stability when the wing is generating lift, but consider what happens if the wing goes negative AoA for a moment. Now everything is reversed and effectively you're 'above' the wing and destabilising it! Note a PG just can't generate negative lift, the lines would go slack and it will simply collapse. We expect a HG wing to recover from a momentary negative AoA. A PG is expected to collapse (possibly only partially and momentarily before reinflating itself) at negative AoA. So a stability system that only functions when the wing is generating lift 'works' for them (for a given definition of 'works' that includes just accepting that your wing will collapse from time to time!)

Yes, I guess in principle it might be possible for one of those to do half an outside loop and then start flying inverted! In fact I half remember someone telling a story of hang gliding 'back in the day' of something like that happening and the pilot being OK. I can't remember any more about it though.

@@mikunan I believe the deflexors were mostly aiming at improving performance by stiffening the leading edges. I think that was mostly driven by the limited availability of tubing at the time. We now use much thinner wall, but larger diameter 7075 (or even carbon) which is way stiffer in bending so the deflexors just aren't needed.

Yes, that would improve the glide. Most hang gliders have a horrible distribution of loading over the span in terms of lift induced dag. They are overloaded at the root, underloaded at the tips. What you did was reduced that non-ideal span loading with a resulting reduction in vortex drag. You also made the wing less pitch-positive (more prone to tucking) but fixed it with the addition of the horizontal stailiser. There is a good reason that the highest performance sailplanes all have a stabiliser behind the wing! That being said.... there are other ways to fix this. Watch this space.

As @HowesAero said ;-) To me, 'tucking' and 'tumbling' have subtly different meanings. I think what you're concerned about here is what I'd call a tumble, which is about the rotational inertia and rate of rotation. A tail also gives a lot of pitch damping (resistance to the rate of rotation around the pitch axis), which also helps prevent a tumble. Although also as Jon says, there are other ways to fix this ;-) My next video will go into tucks and tumbles in detail.

The only downside I could think of for your mod was if you wanted to do a spot landing, bar full out, and drop onto your feet. Did you ever have a tail strike?

@@travelbugse2829 The funfex has a long keel that helps rigging, and can be shortened before takeoff. If you leave it long and go flying, you might hit it on the ground before your feet and the wing drops forward. You still land a "no stepper" but it falls on the control bar half-gently. Not too bad. That's an intermediate so I'm not sure how a topless would compare. A hinge with a fuse could also be used, that allows the tail do bend up on landing, but not down, so you get the dive recovery and pitch dampening, but if you tail-strike the landing, it will bend up.

@@ericoschmitt Many thanks - can't help wondering whether you were joking! It reminded me of my schoolboy days long long ago, when we fitted de-thermalisers to our free flight models. Hinged tail, a rubber band, some string impregnated with potassium nitrate(?), light its end and wait for some variable moment before it stopped flying!

@@wrdturkey thank you ☺️

how would it adjust? why would anyone want to take the skill out of the sport?

I think you are in need of an old Sensor with flaps and some retrofitted Wills Wing tip bearings. 😅

@@K.Schrag Exactly!

I'll be covering tumbles in the next video. Adding more area behind the centre of gravity (the further away the better) will certainly resist tumbling, so in that sense then yes, adding a horizontal stabiliser will act to resist it. Angling that tail down relative to the wing (longitudinal dihedral) also adds pitch stability too. The Combat also has a pretty wide nose angle though, also the planform of the wing (straight tapering) means you don't get the area further back from the wing tips, so that would count against it. So comparing a Combat with tail to other toplesses without tail, it's hard to say which is more tumble resistant. They all pass the same pitch tests, so do all have similar characteristics in terms of pitch stability. Pitch stability and tumble resistance aren't exactly the same thing though (although they are correlated), I'll need another half hour video to go into all this fully though.

@@avianhanggliders1985 looking forward to it. Love this stuff.

Yes, this is called pendulum stability. The next video will go into pitch stability as it applies to hang gliders and I'll include that.

@@avianhanggliders1985 Magnifique! I can share thesises that I've found about the theme.

Thank you! Although HG will never reach aspect ratio, in practice the current limiting factor is directional (roll and yaw) handling and control. We could build HG with more span that packed to the same length as current without significantly sacrificing rigging time or effort, you just wouldn't be able to steer the thing! So improving handling opens the door to more span. Atoses do this through using aerodynamic controls, but we have a different approach.

@@avianhanggliders1985 Your approach definitely seems on target, especially if you figure out how to get increased span length with portability. I owned a T2C for a while and loved the flat glide and better speed range, but too often felt like a passenger and not the pilot. The glider was stiff and in strong conditions could be difficult to turn. For this reason, I was always cautious getting close to the ridge for fear of not being able to turn away. To my fault, I was on the light side of the wing loading which definitely impacts the controllability, so if I had gotten the smaller 136 I might still be flying it today. Wills seems to have made progress with bearing tips, but some sort of aerodynamic control would seem a better solution. Here again, complication, weight, and cost seem to be the conspirators fighting your success. I hope you win!

I'm using Gitlab issues as a sort of forum, so write an introduction to yourself on this issue: gitlab.com/HG-dev/aerodynamic-modelling/-/issues/2

@@beebee766 thanks, some of those are features of the design we're working on ;-) When you say 'zig zag spoiler strips' are you taking about turbulators? As in a small ridge to create a small turbulent boundary layer to resist large scale separation (these are often zig zag but don't have to be)? We already have those features on uprights and base bars and the stitching lines on the wing can act as such.

​@@avianhanggliders1985 yes turbulator strips. zigzag to keep separation localised. Also on winglets and top of fuselage. I believe HG development may well point in the direction of improving the higher speed polars, ballasting, VG adjusting other things as well, more ways of keeping the flow attached. With regards to induced drag, we had an acronym: TINFOS - There Is No substitute For Span. In an Open Class glider this was the case (my Nimbus has 26m span! 60:1 @ 57 knts, but poor handling) now the optimum is around 21m with a vast improvement in the high speed polar. These new ships now have a heavier wing loading EMPTY of water ballast than I do FULL! Still some big changes going on..... BB