Tailless Aircraft - Reflex and other design issues

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Sockmonkey, Jan 10, 2019.

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  1. Feb 16, 2019 #541

    rotax618

    rotax618

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    The autorotational moments are greater in high AR wings, in a condition where one wing is stalled and the other wing is unstalled or partly stalled, the forward component of lift (same force that drive autygyro blades) on the unstalled wing causes a rotation around the neutral axis, if the yaw control of the vertical tail is insufficient to counteract that autorotational component, the aircraft will enter a spin. Naturally the greater the AR the larger the rotational moment.
    This is not to say that all high AR aircraft enter irrecoverable spins, constructors do their level best to design this unwanted feature out of their aircraft. They are not all together successful because dozens of pilots are killed every year from stall/spin accidents.
     
  2. Feb 16, 2019 #542

    Aesquire

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    BBerson, I don't think LAR craft need long landing gear because of aspect ratio. It's prop clearance that drives gear length. A UFO, scaled up slightly for the weight, could use a direct drive VW derived engine, like the Sonex, with relatively shorter tricycle gear.

    The Sonex gear is also shorter than optimum, for high AOA landings, the designer accepted the compromise of lower drag & cheaper over lowest practical landing speed.

    That's on top of the compromise of lower static thrust with the smaller, direct drive prop, but better high speed performance.

    Tail gear flying wings tend to have high deck angles just because they are shorter than tailed aircraft of roughly the same wing area. LAR flying wings logically could be built with a lower deck angle than high AR flying wings, but other factors , like prop clearance in level attitude dominate in the choice.

    Also there are "That's just stupid looking" limits to deck angle. A plane that points up 60 degrees from horizontal while it's parked is obviously going to be less quick to accelerate on a take off run than one that has less drag and a better thrust vector. I

    The V-173 is a poor example for gear length, in that it had huge props for the installed power, rather like the WW1 fighter replicas with PSRU equipped VW engines. And was intended as the proof of concept for the V/STOL naval carrier fighter.

    The Arup series and most other LAR craft don't have such long gear. And while several claimed and achieved darn good take off performance, STOL wasn't the big selling point. Simplicity, cabin volume, cute factor, parking, etc. are usually the main bullet points in the sales flyer. ;)

    Thanks for the links to previous LAR discussions. I'd forgotten one of my all time favorites! The deltoid pumpkin seed. ( I recommend the book )

    https://www.amazon.com/dp/B005EHQEWW/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1

    https://en.m.wikipedia.org/wiki/AEREON_26

    The Aereon 26 did not use helium for lift, it was the proof of concept for the SHAPE & aerodynamics of the design. A blend/compromise between a sphere ( maximum volume for weight ) and a delta wing ( for stability and lift ) the lifting body was to be the father of practical airships. The mission, as is often the case, was for missionary organizations to haul heavy cargo ( like generators & farm equipment ) to primitive clearings in the jungle etc. ( the ecological niche now occupied by CH801 home builts, among others ) http://www.zenair.com

    The Aereon concept isn't dead!
    https://www.lockheedmartin.com/en-us/products/hybrid-airship.html
    But the original is far prettier, and more efficient! Obviously lower drag.

    I wonder if B. Wainfan was inspired by the Aereon in his Facetmobile design? It's not in any way a copy, but form follows function, and a wing/internal volume optimization is going to evolve into a similar shape. I'd bet he was aware of the Aereon, and he has stated the facet approach was a simplified and aerodynamic test bed idea. ( vs. rounder, curved shapes )

    Likewise, the Lockheed airship seems inspired by Soviet missile submarines, which iirc, were inspired by Japanese submarine aircraft carriers. Or the Curtis C-46 & Boeing 377. :)
     
  3. Feb 16, 2019 #543

    Himat

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  4. Feb 16, 2019 #544

    BBerson

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    If you want the full 45° braking then the landing gear must be capable and maintained on roll out.. Actually the higher aspect ratio Kasperwing video uses the 45° braking without the long gear because there is no tail. The UFO has a long tail.
    But I noticed from the Zimmerman graphs that after about 30°-45° the stall is sharp. Not good if the pilot stalls. With or without a spin if a sharp stall occurs on takeoff or landing then the radical pitch down may not have room to recover. I don't see safety in operating near a sharp stall at 45°. A soft stall at 25-30° makes more sense to me.
     
  5. Feb 16, 2019 #545

    rotax618

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    I imagine that you would get a fair idea that something bad was going to happen as the angle of attack started to exceed 30deg.
     
  6. Feb 17, 2019 #546

    BJC

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    Do you mean AR or span?


    BJC
     
  7. Feb 17, 2019 #547

    rotax618

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    Autorotation requires a stalled condition and an asymmetry of lift from one side of the wing compared to the other, it doesn’t matter what the span is. Zimmerman said there was little or no tendency for autoration in AR less than 3.
     
  8. Feb 17, 2019 #548

    rotax618

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    Here are a couple of alternate LAR ideas I was playing with over 10 years ago, a “Facetedmobile” with folding wings and a “Smoothmobile”.
     

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    Himat, Sockmonkey and delta like this.
  9. Feb 17, 2019 #549

    BBerson

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    The Sonex Onex is almost within inches of the same dimensions of the Facertmobile turned sideways.
    The Onex is 16' 5" x 20' 9" https://en.m.wikipedia.org/wiki/Sonex_Aircraft_Onex
    The Facetmobile is 15' X 19' 6" http://www.wainfan.com/pavreport.pdf
    So, just as compact with the wings out. Yet the Onex has folding wings and can reduce to 8 feet in seconds.

    The Onex could be fitted with wide chord wings to reduce the AR from 5.1 to AR4. This would reduce the stall speed and shorten the takeoff roll yet retain the high top speed mostly. With the flaps at 45°, the approach must be as steep as anyone could want, I think.
    Could be built much lighter in fabric like an early light Ercoupe with fabric wings.
    .
     
  10. Feb 17, 2019 #550

    rotax618

    rotax618

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    If you were to re-engineer the Onex to build it from nature’s composite (wood), fabric covering, add vortex generators (may have to sacrifice a couple of knots), increase the length of the UC, you could land quite slowly. Unfortunately it would still stall at about 14deg AOA and if you had the controls a little bit crossed when it did stall it will probably spin. Never the less it would be closer to STOL. There are probably better candidates that have already been designed for wood construction that could be equiped with folding wings, VGs, more takeoff and landing rotation angle.
    Although it wouldn’t look ‘cool’ a Himax fuselarge and tail with a 12ft disk wing, a modern day Nemeth parasol, could fold down the 3’ of wing tip for transport and storage, bit longer sprung UC - powered by a 503 or equivalent would certainly be STOL, stall/spin resistant, cheap and easy to build.
     
  11. Feb 18, 2019 #551

    rotax618

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    It may be possible to build a Part 103 ultralight version of a circular wing aircraft. 1st step would be to build a very light 12’ diameter wing frame using thin alloy tubing for rib frames, the spar could be very light if the wing was cable braced, a king post at the centre of the wing, a lightweigh frame similar to the frame under a Kasperwing for the pilot with attached lifting wires. The engine, either light 2 stroke or industrial Vtwin of about 30hp, attached to the front of the wing. Will attempt to draw a sketch.
    Would be novel, and stallproof and spinproof like the Kasperwing.
     
  12. Feb 18, 2019 #552

    Sockmonkey

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    Heck, you could just make the whole disk removable.
     
  13. Feb 18, 2019 #553

    mcrae0104

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    Could you please explain this in a little more detail for everyone who had done precisely what you described above? Perhaps it it in your definition of dive?
     
  14. Feb 18, 2019 #554

    BBerson

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    I never dove at the ground before the landing flare but did something similar. Doing multiple glider tows with my Piper Cherokee, I would come over the threshold on the right side about 100 feet high to cut the tow rope loose without catching in the trees.
    With full flaps, engine at idle, and about 60 mph and with a quick side slip to the left and nudge forward and "fall" the 100 feet in a second. A quick flare and I was down and returning for another tow. Did it hundreds of times. I wouldn't need or want to "fall" any steeper than that. Just requires coming in slow with full flaps.
     
  15. Feb 19, 2019 #555

    rotax618

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    If you turn height into speed you need some way of slowing down quickly to land short, it is usually not possible to pull full flap unless your Vfe is very high.
     
  16. Feb 19, 2019 #556

    BBerson

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    The Cherokee flap speed limit is 115 mph. But I was only at 60-65 in the pattern. Solo, almost no gas, it was relatively light for towing gliders.
    So I didn't just pull the flaps, that would be tricky. I came in already with full flaps all the way from downwind with a bit of power. Then drop the rope, chop the power, and it just falls. But the energy in the fall converts back to lift in the flare. It isn't difficult. It won't stall either, because the yoke is eased forward and the nose goes down below the horizon. The Cherokee won't stall unless the nose is pulled up with full back pressure almost.
    The Cherokee AR is about 5. Anything lower aspect ratio will fall even faster.
    I don't see a need to go to AR1.2 for steep glide to flare feature.
     
  17. Feb 19, 2019 #557

    ypsilon

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    Airbreaks?
     
  18. Feb 19, 2019 #558

    Aesquire

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    This is a silly argument.

    Glider landings with strong air brake/flap/split rudder fly "fast", well over max L/D speed, for glide path control and steep approaches, but they don't dive into the landing zone. It may appear that way on craft like The Shuttle, but it's energy management. No go around or last second throttle application to ease sink rate.

    Bush & Naval planes that land in high sink rate mode have long stroke tough landing gear. The Super STOL kit makers warn not to attempt the "plop" landings their plane is capable of, in planes without such gear. The rest of us try hard to achieve near zero sink rate on landing. Even the Super STOL guys usually use a blast of power on landing to ease sink rate when not showing off.

    So arguments about not even designed, much less flown, aircraft landing techniques seems premature.

    I'm more interested in opinions on V-173 style elevons vs. T tail Arup configurations.
     
  19. Feb 19, 2019 #559

    Topaz

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    The long version of that comment is that there are quite a number of sailplanes with drag brakes (which the soaring community incorrectly calls "spoilers") that create enough drag when fully deployed that, even in a vertical dive, they can limit the aircraft's speed to below V[sub]ne[/sub]. You could point the nose down vertically at the ground and never worry about destroying the airframe. Other than weight, there's absolutely no reason you couldn't have larger drag brakes that limit vertical dive speed to some relatively arbitrary lower airspeed. Of course, eventually you need to fold them when not in use, and call them a "parachute." :gig:

    This entire discussion has become quite "silly," in the sense that there's no design requirement context in which all these notions are being discussed, lots of "black magic" design theories are being thrown around, and deep, meaningful discussions are being held about whether things like vortex lift is "better" on circular planforms or delta-like planforms. The latter is particularly frustrating when any rational design process involving "vortex lift" is either well outside the capabilities of those discussing it or, if they do have the capability, they're ignoring it completely in favor of a "design process" that seems to primarily consist of the statement, "I think...".

    If one wants to have a "dreamers" discussion about what looks neat and is desirable from an aesthetic point of view, or even a pure construction concept standpoint, then fine. But despite repeated calls for substantiation from several people, including myself, I'm still seeing unsupported statements - unsupported by actual aerodynamic theory, standard design methods that have proven viable for decades, or even historical precedent - that this or that low-AR design is clearly better overall at some vague and unspecified broad class of design missions. And, when myself or others have asked for some kind of substantiation for those claims, we're either pointed at a shaky amateur video of an existing design "flying great" - without any metrics or performance data - or told that we're dismissing low-AR designs as unworkable, or other accusations that we say they "can't climb" and so on. None of which any of us has ever actually said.

    In context with everything else that's being discussed here and the way this thread has been going, I really don't see how it matters.
     
    Last edited: Feb 19, 2019
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  20. Feb 19, 2019 #560

    rotax618

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    I have simply tried to bring this aviation type to notice for discussion, in support of my observations I have posted video evidence of the flight characteristics and some studies undertaken to investigate this genre of flying machine.
    LAR aircraft do fly and have flown, successfully and safely, contrary to the nay sayers, they offer a flight envelope that is not generally available from other types.
    I just can’t understand why anyone could completely dismiss the video evidence and eye witness reports just because it goes against their pre-conceived ideas.
    There have been a number of references to the climb rate , or lack of, of LAR aircraft the quote from post #321 is just one.

    “I'm of the opinion that low-AR designs are a poor choice for STOL operations. Yes, you can use vortex lift and the high drag associated with it to produce very short landings. But any runway on which you land, you have to be able to take off from again unless you want to become a permanent fixture at the location. So an ability to land in extremely short distances is rather pointless unless you can take off again and climb out safely from the same location. Here, low-AR is not your friend, for the reasons we've already discussed.“

    Anyway the trolls have won, I have nothing more tos say.
     

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