I have been biten again by the tsetse fly

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by berridos, Nov 19, 2019.

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  1. Nov 21, 2019 #61

    Aesquire

    Aesquire

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    I like the 2 seater's looks. Much like a Dyke Delta. I admit it's hard to beat the single seater Lippisch style fin cockpit for cool factor.

    Re: tumbles.
    No, I have not. I've gone from 45 deg nose up to 120 ( past vertical ) nose down pretty quickly in thermal edge " over the falls" turbulence. That was not a stall, however, just a powerful rotating air mass at just the right size to have the entire glider pitch over. Momentary negative G and my stability system kicked in as designed. That system is only used on flex wing weight shift craft, & doesn't apply to fixed wings. I suspect, but cannot prove that it I'd been in an Atos or Swift that would have also recovered from an inverted nose down dive.

    Stall tumbles are possible, but rare in properly designed flying wings. You have to be pushing the envelope. And mostly that is a too far aft CG issue. Weight shift craft can achieve a too far aft CG. Pilot training is important. If you zoom climb into a stall and hold full back CG, you can tumble. I've mostly seen that in failed acrobatics.

    The Northrop flying wing B-35 may have tumbled during a rear CG limit flight test. ( There's some argument about that. I think it did )

    The test was to determine limits as with lower static stability there is less required elevon deflection & thus less drag & better range.

    ( Source Northrop Flying Wings by Pape & Campbell )
     
  2. Nov 22, 2019 #62

    Doggzilla

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    Thats why Im saying its not properly designed. It should not be able to do that.

    Members should not be supporting dangerous design or behavior just for the sake of arguing.

    Tumbling is not safe, and designs which tumble or go into flat spins with little warning are not safe either.

    "Well I haven't died yet" is not a valid safety argument and never has been.

    Not everything has to turn into an argument.
     
  3. Nov 22, 2019 #63

    Aesquire

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    Not arguing that planes should tumble. Rather against it, myself.

    But I'm curious, why do you think the Verhees Delta designs do? I've seen nothing that says they have that issue. Did I miss something?

    I thought I had a fair grasp on flying wing stability. The Deltas have a nice long chord at the root & good sized control surfaces. The deflection in flight looks like adequate forward CG, maybe even a bit too much, but in this case the penalty is a bit more drag . The landing gear is not long enough to take full advantage of any high AOA vortex lift on takeoff or landing, but again, there's no need to pancake in hard on a non STOL craft and it looks like good conservative design. I wouldn't expect soaring performance, or extreme high speed.

    The plusses are compact folding wings for trailer carry, a big cost savings depending on location. Looks like reasonable ease of construction. And it's different/cool/\exotic.

    Cons are not spectacular performance for the power, not STOL and slightly difficult entry/exit.

    Not everyone's cuppa, but nifty. What am I missing?
     
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  4. Nov 22, 2019 #64

    berridos

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    The designer proposes the Subari EA71 (changing the heavy oilpan with an aluminium one) and the VW1800 as powerplant for this aircraft.
    I couldnt find conclusive data on the dry weight of these engines and the continous power they deliver.
    Anybody has experience on these powerplant to shed some light?
    The powerplant i want to fit L26 D-Motor has a dry weight of 58kg +radiator and a continous power of 89hp. I think both variables improve the powerplants proposed by the designer.
    I case of a delta, how would the design be affected by a more powerful plant? More power would increase the nose up pitching, requiring more reflex. Is that right from your point of view? How could i overcome that increased reflex with a more natural design change?
     
  5. Nov 22, 2019 #65

    cheapracer

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    You would use an EA81 because there is more of them in the world, usually many years younger, same weight, same size, but more torque. EA71 is 1.6 liter, EA81 is 1.8 liter.

    They have a quite small pressed metal oil pan that doesn't weigh very much, waste of time trying to improve that.

    One of the lightest 90 to 100hp water cooled automotive engines you can get, and have proven very reliable in aircraft. I can lift them up myself no problem, but sorry, don't know the scales weight.

    http://www.buildagyrocopter.com/converting-the-subaru-ea81-engine-for-aircraft/

    Zenith suggest 100kgs/220lbs installed, I presume that means wet with radiator

    http://www.zenithair.com/zodiac/6-subaru.html
     
  6. Nov 22, 2019 #66

    berridos

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    So maybe its reasonable to stick to the original, thanks. Thought it had less hp.
     
  7. Nov 22, 2019 #67

    Aerowerx

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    Keep in mind that a tailless aircraft requires a higher than typical static margin for safe stability, according to Nickel's book. Read that as CG forward. In fact, he points out that some get in trouble by trying to make the CG location look "normal".

    Any design is a compromise. You can't have everything at once, until someone invents the fully morphable wing---cruise at mach 3.0, 50:1 glide, 12G aerobatics, tailless, and runs on 3 flashlight batteries. Ain't gonna happen any time soon.
     
  8. Nov 22, 2019 #68

    dkwflight

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    Hi
    I believe Edwards as in Edwards AFB died attempting a stall in a Northrup wing.
    Stalling a flying wing or a delta should not be done. In a wing the CG location is critical.
    The new flying wing aircraft are prevented from getting close to a stall by the flight computers
    Dennis
     
  9. Nov 22, 2019 #69

    BJC

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    Why no stalls in a flying wing?

    Why no stalls on a delta wing aircraft?

    Thanks,


    BJC
     
    Last edited: Nov 22, 2019
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  10. Nov 22, 2019 #70

    Aerowerx

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    If properly designed there is nothing wrong with doing a stall in a flying wing (as in Nickel's book). The problem is when a builder does not heed Nickel's advice and use a larger than "normal" static margin. When done properly, a stall would be a non event. Since you do not have the horizontal tail on a long moment arm, you have to rely on the forward CG to tame the stall.

    And a delta wing is just a type of flying wing. I know Nickel mentioned short-span, but I don't recall what he said, without looking.

    Clarify...Nickel says a forward CG is good, I meant.
     
  11. Nov 22, 2019 #71

    Aviacs

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    Can't find any notes on how many have been built?
    # plans sold?
    What is (perceived?) advantage of composite?
    Seems like plans built Al sheet would be faster & cheaper?
    Or is it more complex than it looks?

    smt
     
  12. Nov 22, 2019 #72

    Aesquire

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    More power does Not itself "increase the nose up pitching". The nose up is from the elevons/" tail", just like any normal plane. Faster air flow from more power but increases the power of the elevons/tail, so you need less deflection/reflex in flight. You still size and limit deflection the same, as power off glide is the same no matter how much power is installed.

    The principal is the same for any normal ( not canard or tandem wing or Flea... They arrange it a little different ) tailed aircraft or flying wing.

    a see-saw. Weight up front balanced by down force from air flow in back. Weight remains constant ( except for fuel burn ) but balancing "tail" down force varies with speed. Faster, more force, nose up, slow back down. Slower, less force, nose down, speed back up. Basic pitch stability.

    it looks more complex with sweep, twist, & curves, but it works exactly the same. The wing on my flex wing hang glider has no obvious reflex, but notable twist in normal flight. The pitch stability still comes from the "variable by speed" balancing forces. For every "normal" flight CG postion, there is a stable speed. ( seems backwards,but the physics is the same as a Piper Cub ) If I go full forward CG, ( in the limits of arm travel in prone hang glider harness, or your belly on a trike or supine harness ) the craft will accelerate to it's new equilibrium. Then be stable at the New chosen speed. The rear CG limits are at well below stall speed in level flight.

    Hang gliders typically land fully stalled burning off airspeed in the goal of near zero landing speed. That part isn't normal plane technique. :) Avoid that corner of the envelope if you've got landing gear with wheels or floats. ;)
     
  13. Nov 23, 2019 #73

    berridos

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  14. Nov 23, 2019 #74

    Himat

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    From the radio control model airplane side, some designs are difficult to stall. And equally difficult to recover from the following spin.
     
  15. Nov 23, 2019 #75

    Aerowerx

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    IIRC, one of the Horten Brothers flying wings was virtually impossible to spin.
     
  16. Nov 24, 2019 #76

    berridos

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    In his website he states the spin is a non issue. It has just to be recovered with ailerons and not the rudder. the plane has a lot of adverse yaw as i understood from his comments and the turning radius is pretty large. Its a travel machine. The characreristic i like is that in windy, gusty conditions the plane turns into the wind.
     
    Last edited: Nov 24, 2019

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