Stall Recovery vs Tail/Fuselage design

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by stankap, Feb 6, 2012.

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  1. Jun 26, 2012 #21

    Tony

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    Dana always nice hearing from you. That was one thing I learned reading that book. Every airplane flies different. Even the same model just different year might fly different.
    I also learned airspeed alone is no indicator of a margin of a stall. Here is what Rick wrote abote this.
    MYTH: Flying to slowly causes stalls.
    Astute as the Brothers were,even Orville and Wilbur Wright erroneously believed that stalling was related to slow airspeed. Angle of attack is the defining parameter for the stall; thus, airspeed by itself is useless as an indicator of our margin to the stall. Yet the aispeed myth persists,often being reinforced by the simplistic, winds-level, one-g stalls practiced repeatedly for check rides. {see chapters 1,2,& 13}
     
  2. Jun 26, 2012 #22

    clanon

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  3. Jun 26, 2012 #23

    autoreply

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    There's a very good reason we teach people to watch the airspeed and not the angle of attack. Imagine a sailplane at a winch launch. Around 50 degrees of nose up. Now the cable breaks. You have to push over aggressively (negative G's) to avoid an immediate stall. Most accidents happen when people establish a nose attitude about 5 degrees lower as during normal flight. They apply some aileron for a turn and spin in... since they didn't realize they were on top of a parabolic flight and doing 20 kts or less.

    The same thing happens with powered aircraft that have a sudden engine failure during climb. Pilots push nose down and start rolling when they have the normal glide attitude, which - especially if they haven't recovered aggressively - usually means they're at or far below stall speed.

    Airspeed is everything. Most pilots screw up the engine failure at climb pretty badly and a significant portion of those is dead. Speed, not angle of attack is what you should be paying attention to if you're at the controls. And yes, accelerated stalls and especially, stalls due to engine failure are a good idea to train.
     
  4. Jun 26, 2012 #24

    topspeed100

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    I recall all BD-5A ( short wing version ) pilots are just that..either dead or crippled. Many later model pilots are too. Problem was they forgot to fly the plane and tryed to restart it at low altitude after engine malfunction.
     
  5. Jun 26, 2012 #25

    Tony

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    Have we never heard of a high speed stall. It happens. An airplane can stall at any airspeed. Scary stuff indeed. One thing for sure we all respect the stall.

    Its a great evening here for flying, if its like this in your area and are flying this evening have a lot of fun, be safe and keep your nose into the wind.

    Autoreply what is that bird you are flying?

    Tony
     
  6. Jun 26, 2012 #26

    Lucrum

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    Not to be nit picky but do you mean deck angle or AOA?
     
  7. Jun 26, 2012 #27

    Tony

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    Rick refers to AoA.
    Rick states he had to deploy the recovery chute over 1000 times if I remember correctly. This chute was attached to the plane at the tail. It stuck out about 3 feet on a rod or pole.
     
  8. Jun 26, 2012 #28

    Rick McWilliams

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    Helicopter pilots respect the stall in a different way.

    The fuselage has some influence on stall. A long nose like that of an airliner is in the flow field of the wing and reduces stability. The long nose adds an unstable moment in yaw as well. The wing design is most important with respect to entering a spin and the tail configuration is most importsnt for recovering from a spin. Some references suggest that the tail should not be located in the wake of a stalled wing. The stabilizing effect of the tail can be considerably reduced in stall. The buffet is an effective stall warning. A low aspect ratio fin fariing or strake retains effectiveness at large angles of yaw.

    I do not know of any design reference that covers design for spins. I suspect that there are some experts; as my Zlin spins identically left and right. There are some little asymmetrical horizontal strakes on the engine cowling. I think that these are to trim the spin. The Zlin spin is serious as it will not recover using improper controls. The flight manual says it the spin does not recover; apply full pro-spin controls and then follow instructions.
     
  9. Jun 26, 2012 #29

    autoreply

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    Sure, but a high-speed stall is a non-event. (Though it scared the *beep* out of me when I had one at 130 kts and the airbrakes came loose). Let go of the stick a bit and you're fine.
    Theoretically, aoa is what it's about. But pilots are humans and fly with a "stock" 1G and an "imprinted" picture of how the horizon should look like. That's why nose attitude or aoa can be so dangerous during (for example) an engine failure or in heavy up/downdrafts in the mountains.
    On top of a parabola but with the right horizon and they might start a turn and fall directly into a spin. On top of a parabola and they might pull the stick to get to their "as usual" 1G.
    Don't know for sure. It's either a Centrair Pegase or a Rolladen-Schneider LS4, both sailplanes. Somewhere over Lac de Serre-Ponçon.
    Neither, because both can be deceiving. Deck angle because you might be in a perfectly normal nose attitude but far too slow, aoa because you can be at less than 1G and perfectly fine in terms of aoa.

    While a glider, it gives an idea how much nose-down you need, also in a draggy powered aircraft with an engine failure:
    [video=youtube;y8FP_MIB7gw]http://www.youtube.com/watch?v=y8FP_MIB7gw[/video]
     
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  10. Jun 26, 2012 #30

    Tony

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    AutoReply: really nice video. I had sweaty palms just from watching it.

    I like your posts too by the way. I wish we had gliders in my area. We talk about them alot out at the airpark. We do have once a year some gliders come in for the boyscouts. But its not a public thing and the airfield is closed that day.

    Tony
     
  11. Jun 26, 2012 #31

    SVSUSteve

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    I agree although I know a lot of pilots who have flown for decades and never been in a spin. Not exactly a great idea if they encounter one, but just pointing out that not everyone encounters a spin during their flying "career".

    Fred Wieck seemed to have pretty decent luck with his attempt to do it but then again, he was a rare breed of true genius.

    You want to do that with me some time? I'm really, really rusty from not flying much over the past couple of years. It sounds kind of fun even if it's more for a practical purpose. Honestly, I probably should just get some proper aerobatic training once I get my taildragger endorsement.
     
  12. Jun 27, 2012 #32

    Aircar

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    Thisd thread seems like it should be "SPIN recovery vs tail..." as compared to stall behaviour (which is another deep subject in itself --the pun being on deep stall as much as anything --being super stable and unspinnable while having no control in pitch is the other side of the coin and a fall pitfall for many apparently satisfactory non conventional aircraft.... The melmoth link was nice --Peter Garrison had it at Oshkosh in 1974 and it was just about the only real experimental aircraft there --I took lots of slides of it .
    The comment about the flap under it's belly was also interesting --the Victa Airtourer also had the flap continued across the centre section but without the slot (so it was a split flap in effect --probably more drag than lift but served to 'end plate' the outer flap(erons) to increase their lift --and, more to the point ,avoid a second set of vortices that are shed from the root end of a discontinuous flap . The Piper Tomahawk had the fixed centre section without flap as did the Cobra (Wickers) and the T tail was effected by the root end vortex with flaps down at high AoA even if the elevator did not interfere with the rudder (or vice versa-putting on a boot full of rudder changes the pressure field on the horizontal tail sort of like a V tail and can impose twisting loads on the horizontal tail mounts ) Cessna 150 -24012 -shame on me for getting that wrong --it is still a reasonably abrupt stall compared to the 63 series for example (non laminar /leading edge stall vs trailing edge gradual separation on an aft loaded laminar section ) --why there ever was a myth about dangerous laminar wings is a mystery .

    Spins with power on and the propwash rotation etc can dramatically alter the spin behaviour to left or right --in a panic situation that might involve applying power and turning or pulling up, the behaviour can be much different than the one knot per second case and how much fuel in the wing tank etc (you can stop the engine in a high wing Cessna simply by sideslipping -- fuel starvation is probably why sideslipping on approach is banned as well as the assymetric flap stall thing that will flip it on it's back before you can say 'what the @#**#@ !? " -- I remember watching an 'arc' of cigarette butts form as the thing rolled on it's back so fast that the lid on the ashtray opened up (presumably they don't have them anymore..)
     
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  13. Jun 27, 2012 #33

    SVSUSteve

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    Agreed 110%.

    You ever want to watch people stroke out (good grief I hope that translates correctly into Aussie English) at Oshkosh, point out that the 787 when it was there last year was more appropriate for a display at a show focused on experimental aircraft than their gaggles of RVs, Lancairs, Pietenpols, Vari-EZs, etc. I love being over on the EAA Forums and hearing people ***** about how the EAA and Oshkosh have lost their focus on "the true spirit of aviation/experimental aviation" and has sold out to the corporate crowd. Usually it comes from someone who bought a 49% complete quick build kit or bought someone else's completed kit and has never done anything remotely experimental in their life.
     
  14. Jun 27, 2012 #34

    rdj

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    I hate to disagree with autoreply, as his posts are usually spot-on. However, disagree I must :grin:

    I disagree that airspeed is everything. Having read 'Stick and Rudder' cover-to-cover more than once as a teenager (where the author Wolfgang Langewiesche drills AoA into your head in each chapter), I find that when I fly I mentally think AoA more than airspeed. I did have an exhaust valve blow a hole in a piston during climbout in a Skipper some years ago. Four things happened almost simultaneously: a loud bang, the plane shaking like a belly dancer on crack, the stall warning horn going off, and the first burble of an incipient stall. I had no time to study the airspeed indicator; it was mostly a blur anyway. I remember pushing hard on that yoke (being trimmed for the climb and all) until the burble went away, because I was thinking AoA. The nose attitude was quite a bit steeper than normal glide attitude by the time the stall shudder stopped (as did the stall horn). Fortunately for me I had just completed a wide circling climb back over the airport to avoid some low-lying clouds on the departure heading, so I was 2000' AGL and only 1/2 mile from a nice paved runway when the engine lost power. I do agree with autoreply that until you've experienced it you can't believe just how hard and how fast you have to push over the top to keep flying. I can certainly appreciate just how tough pushing that hard at 200' AGL must be. I much prefer glider rope breaks at 200'; they're no sweat by comparision.

    That said, airspeed is everything if you're flying a 747, because flying by the numbers is what that plane is all about. How you think about flying depends on what you're flying.

    And this is where I have a real disagreement with those who state 'if you don't know how to spin a plane, you shouldn't be flying it'. IMHO this is just plain wrong. Most pilots who have flown 747's have never spun one. Most of the 'oldtimers' who repeat this mantra fondly remember their days spinning Champs and J-3s down below the cloud deck. Well, yeah, a J-3 is so light it would probably spin upward in a thermal. The problem is, those mantra-speakers never mention what they're spinning when they mindlessly repeat the old 'everyone should know spin recovery' dogma. And then some young inexperienced hotshot in a Lancair decides to follow the oldtimer's advice, and another NTSB report is filed. Because every frickin' plane spins differently.

    I have spun a glider in training, but that was a spin-certified plane with a spin-certified instructor. And personally, I would rather not spin any plane without a parachute on me, the plane, or both. Tony is absolutely right. The problem is, a spin is a dynamic, non-linear condition. Change the loading, change the paint job, change the amount of fuel in the tanks, and the plane that you've spun perfectly fine the last 1000 flights will fail to recover on the 1001st. Far better pilots than I have proven this. Art Scholl died when a Pitts S-2 spun flat during the filming of Top Gun, and he couldn't recover. Why? The thinking is that the camera strapped on the plane changed the dynamics. Put a too-heavy or too-light passenger in the other seat, and a usually docile training maneuver can become a suprisingly hairy ride. Any time someone pulls that old mantra out on me, I immediately enter my 20-questions rebuttal: is the plane certified for spinning? How is it loaded? Does it matter? Can you explain why some planes spin up fast and others don't? How does tail area factor in? Why do some planes (usually) break the spin just by releasing the controls, while others require immediate and positive control inputs? That usually shuts them up fast. Anyone who doesn't understand and can't answer all of those questions (and more) about spin behaviour is, in my opinion, not qualified to spin their plane with someone else in it. What risk they take with their own life is up to them.

    This thread started with a question on stall recovery vs. tail/fuselage design--why do some planes that violate the rudder-blanking 'rule' still show recoverable spin behavior? Because spin behavior is a thicket of tangled, interacting forces that defy easy analysis or blanket mantras, that's why. I put spin behavior right up there with flutter analysis and testing as the two areas of aircraft design and operation that one should tread carefully in.
     
  15. Jun 27, 2012 #35

    Georden

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    747 pilots likely do not stall their aircraft either (maybe in sims). Doesn't mean they shouldn't know how to recognize and react to a stall. Many airliners have crashed to to pilots failing to recognize and deal with a stall. I think every pilot should learn stall and spins in basic training, if anything just to expose a pilot to an uncomfortable situation and teach them to remain calm and think.
     
  16. Jun 27, 2012 #36

    topspeed100

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    Isn't it impossible to get into spin with B-2 for instance..plane won't let you ?

    I find it very unpleasant to be in a spin inside an aeroplane.
     
  17. Jun 27, 2012 #37

    SVSUSteve

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    No clue. I wasn't referring to that sort of flying though. I was talking about more mundane general aviation type flying.

    I don't really enjoy it either but the difference is being totally beside yourself when it happens inadvertently. I'll deal with things I don't enjoy if they might someday reduce my chance of dying early. You know....spin training, prostate exams, colonoscopy, etc.
     
  18. Jun 27, 2012 #38

    SVSUSteve

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    Why do you think I asked one of the local FSDO guys I know who I'd have to talk to get an 150 lb exemption to the LSA weight rules so I could put a pair of ejection seats in the Vireo?
     
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  19. Jun 27, 2012 #39

    4trade

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    I agree!

    Problem is when spin training depends how that instructor train you. Mostly they train you to give opposite rudder and push stick forward.....problem for this is that you need to know what kind of spin your are. If spin is inverted....it will newer came out of it if you push stick forward, it will stay on a spin forever. Some planes, like Pitts Special have tendency sudden chance of spin to inverted spin if stick is push forward too fast.....even experienced pilot is suspect to lost their lives because of that lack of recognize inverted spin in that fast, stressful siotuation and try to cover it with pushing stick forward. Mostly these situation is very stressful and pilot is in a great hurry....

    If instructors start to teach their student spin recovery that just let go of stick, and give opposite rudder.....that technic will cover all spin forms, spin, inverted spin and flat spin. Student need to recognize only rotation of movement and give that opposite rudder to cover it.

    I believe that most of GA pilots don´t recognize difference of a spin and inverted spin.
     
    Last edited: Jun 27, 2012
  20. Jun 27, 2012 #40

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    One the plane is right side up and the other one you're upside down? Unless you're in IMC or at night, how do you mix the two up exactly?
     

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