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Thread: Tailless Aircraft - Reflex and other design issues

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    Re: Tailless Aircraft - Reflex and other design issues

    There is an old axiom in flying ‘if you want to go up, pull the stick back - if you want to go down, pull the stick back further’
    If you do that in a conventional planform aircraft the result is not going to be pretty unless you have lots of air under the UC, a properly designed LAR won’t abruptly stall and will resume forward flight as pressure is released.

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    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by BBerson View Post
    Yes, he pitches to about 30 on takeoff and climbs at about 20 climb angle. So his angle of attack is about 10 (30-20= 10) which is nothing close to vortex zone.
    The vortex lift from saucer wings comes from the tip vortexes, which are always present when a wing is producing lift regardless of AOA. It's different from the way deltas and strakes create them. The vortex lift isn't as strong at lower AOAs, but it is there.

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    Re: Tailless Aircraft - Reflex and other design issues

    Yes. But I meant he wasn't flying at 30-45 angle of attack.
    So an AR-3 could fly the same angle of climb or better if less induced drag.

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    Re: Tailless Aircraft - Reflex and other design issues

    Zimmerman didn’t share your premise, when he built the V-173 he used an approximate circle as the planform. With a circle the angle of sweep of the leading edge varies from zero to 90deg at a regular increment, my guess is that the vortex gets tripped at the tip first as you would expect from spanwise flow (normal induced drag tip vortex) and as alpha increases the vortex is tripped at the leading edge progressively toward the root, that vortex is what Zimmerman called the bauble on the top surface increasing the lift. As alpha increases the planform becomes more important than airfoil shape. Given the correct shape an AR 3 will provide some stall resistance and increased lift at high alpha, but not as usefull as AR 1.27.

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    Re: Tailless Aircraft - Reflex and other design issues

    The best way to prevent a dangerous stall is forward CG with limited elevator travel. Any aircraft with enough power and elevator authority to reach 45 in slow flight is dangerously tail heavy and not suitable for a novice.

    The V-173 was required to pitch up to the vertical. Not relevant to this discussion.
    The NASA droop cuffs on outbound wing prevent autorotation on modern aircraft such as Icon.

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    Re: Tailless Aircraft - Reflex and other design issues

    Yes you can limit the pitching moment by limiting the elevator deflection, nothing is free, this limits the ability to rotate on takeoff and flare on landing. There are various ways to spin proof an aircraft, provided that the AR isn’t to high. Very high aspect wings are not a lot different to rotor blades, unless the CG is so far forward as to prevent stall it is extremely difficult to spin proof them.

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    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by rotax618 View Post
    Very high aspect wings are not a lot different to rotor blades, unless the CG is so far forward as to prevent stall it is extremely difficult to spin proof them.
    Don't know what you mean by very high aspect, but the ASK21 (AR ~16) for example doesn't spin at all in a normal configuration. That's why you get trim weight for the tail to make it spin for training purposes.

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    Re: Tailless Aircraft - Reflex and other design issues

    https://en.m.wikipedia.org/wiki/Tupolev_ANT-25

    Have to borrow this from the museum to investigate spin characteristics.
    The ANT-25 is a perfect example of mission dominating design.

    It would make a nifty scale replica single seat ( maybe two seat tandem? ) airplane. No market to speak of, '30s airplanes that are not fighters, racers, or sexy, probably aren't in high demand. The ANT-25 is none of those.

    Like a Spirit of St. Louis replica, but without the fame, I can't see it threatening the RV-x series in sales. Royal pain to park, too. Not the most ridiculous early Soviet era record breaker to replica, though.
    https://www.hoax-slayer.com/images/K...y-bomber-3.jpg

    Rotax618, please, please, make nice, at least readable plans for your bird if it flies nicely. I may disagree about your STO anticipated performance causes, and other details, but my frustration at some really lovely aircraft being one off designs with no plans available is great. The Facet Opal, Little Bird, UFO, and I'm sure you can think of others, are planes I'd be thrilled to chose from, if available.

    Reverse engineering them from a few photos and a video isn't a trivial undertaking. A conventional airplane can be TLAR designed by stealing design features from others, Cub Wings, Fokker fuselage, etc. and if proportions are "normal" you can generally bet it will fly, if horribly not optimized. The real engineering types will cringe, and lecture about the hubris of that statement, ( and rightly so! ) but at least a score of ultralight aircraft from the last 40 odd years were "designed" by theft, including taking a tape measure to a plane at an airshow.

    As has been repeatedly said, in this thread, flying wings, no matter the AR, are less forgiving and more critical of poor design, if only because the lever arm available for pitch stability is less.

    So, please make us nice plans so I can dream of having the first 'murican copy of a clever "down under" dedign!

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    Re: Tailless Aircraft - Reflex and other design issues


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    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by jedi View Post
    You have some good points here. There is considerable truth in all prior posts on this subject. I would like to summarize some of the statements made and make a few conclusions that perhaps can bring together some consensus of opinion.

    1. The textbook equation for induced drag does not apply to a wing of aspect ratio 3 or less as it is based on 2 dimensional aerodynamics. Cdi=f Cl>2/AR.
    2. LAR and short span are two different measurements. LAR (Low Aspect Ratio) is not of necessity low span loading.
    3. If span (or span loading) is constrained to much less than typical limitations adding area to make a LAR planform will lower landing speeds.
    4. LAR planforms lower the slope of the lift vs. angle of attack diagram.
    5. LAR planforms can develop a "vortex lift mode" that eliminates the sharp stall break characteristics of higher aspect ratio wings.

    It is my observation that if one looks at the span and weight of the LAR aircraft and compares it to other aircraft of similar span and weight the primary performance difference is that the LAR aircraft will have considerably slower operating speeds and greater drag as would be expected. The characteristics enumerated above can be used to create an aircraft to fill the specific needs of some aircraft applications.

    LAR planforms can be applied to conventional wing and tail aircraft (including canard) or to flying wing (no separate horizontal tail) aircraft.
    I will add some more points:
    • Designing an Ekranoplan, that is a dynamic air cushion vehicle or wing in ground effect vehicle a low aspect ratio is advantageous. The reason is that the dynamic air cushion effect extends approximately to one wing chord flying height.
    • Ekranoplan of the Lippisch reverse delta plan form do show that a forward sweep wing can in some cases be more stable than a straight wing.

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    Re: Tailless Aircraft - Reflex and other design issues

    The long gear legs required of LAR is pretty much a deal breaker. I have seen a few airplanes flip over on soft fields. Might work fine on a road. But not on a plowed or soft field.
    The glider skid gear and dive brakes make for the best emergency off field landings.
    A belly skid gear could be fitted to LAR, but it would need to be a pylon engine pusher.

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    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by BBerson View Post
    I see LAR more suited to high speed.
    LAR has high induced drag at low speed. The CL is high but the drag is about double. But in high speed flight the induced drag is insignificant. So the UFO was flown around at top speed. The planform of the UFO is almost the same as Concorde.
    For high speed, no struts and retractable gear are the norm. For low speed struts and big tires are the norm.
    Or rather a large speed range. At low speed high installed power negate the rather high induced drag. At high speed the induced drag is insignificant. (Side note the cruise speed/take off speed of the Concorde is 5,2, considerable better than the contemporary Boing 747 at 3,15. Two planes that have little in common with homebuilt aircraft.)

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    Re: Tailless Aircraft - Reflex and other design issues

    Quote Originally Posted by BBerson View Post
    Yet Barnaby didn't build another LAR. I think his second design is an ultralight that isn't LAR.
    Not sure what it is. Briefly mentioned in February 2019 Kitplanes: "on my Lightbeam ultralight design".
    Well, on the Facetomobile home page it looks like Barnaby commercialised a LAR design together with NSC, Near Space Corperation, after he built the Facetomobile.
    https://nsc.aero/

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    Re: Tailless Aircraft - Reflex and other design issues

    Link to previous discussion on low aspect ratio airplanes:
    http://www.homebuiltairplanes.com/fo...ead.php?t=6333

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    Re: Tailless Aircraft - Reflex and other design issues

    Sure, a lifting body is ideal for returning from space.
    But the lifting body designer of the "SkyJacker" found out his lifting body enthusiasm didn't transfer to sport aircraft.

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