Very low aspect ratio planes?

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Inverted Vantage

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Hey everyone, just for curiosity's sake, are there are GA aircraft out there with especially low (very stubby) wings? I'm interested in this and would love to see any designers out there who have done something like this - building GA speed aircraft with very short, very long chord wings.

Cheers :)
 

bmcj

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A lot of the Piper designs are called "shot-winged" Pipers (like the Tripacer), but for a truly low aspect ratio common plane, look up the FIKE.
 

BBerson

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Do a search for Barnaby Wainfan and his Facetmobile (aspect ratio about 1.1). Barnaby also writes articles and gives forum talks at Oshkosh about low aspect ratio. The audio tape of his talk is quite good.
 

Inverted Vantage

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I've seen the Facetmobile actually :) Ugly as hell hehe, but it works! I was hoping for aircraft with a distinct fuselage and body - I know the smallest aircraft in the world (Bumblebee, Bumblee II, etc), but I'm hoping for something normal sized.
 

bmcj

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I thought you were looking for planes that were built in quantity. If you want to include novelties and one-off designs, then the Facetmobile is a good design to look at. Another might be the "Deltoid Pumpkinseed (though it was just a testbed with Helium to add bouyancy). Burnelli had a bunch of functional low aspect ratio designs. You should also look at the two posts below. The first is a video of some unique low aspect ratio designs from earlier days. The second is the Vought V-173, which was to be the predecessor to a larger, more powerful XF-5U military fighter (the XF-5U was built but destroyed before it flew due to political infighting).

https://www.homebuiltairplanes.com/forums/design-structures-cutting-edge-technology/5675-revolutionary-designs-history.html#post45178

https://www.homebuiltairplanes.com/forums/design-structures-cutting-edge-technology/2241-facet-opel-9.html#post39132

Bruce :)
 

bmcj

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Of course, any of the attempts at the "World's Smallest Plane" necessitated low aspect ratios due to the small spans. Here's an article with pictures of them:

Aerospaceweb.org | Ask Us - Smallest Plane in the World

and this on the Baby Bird:

http://www.airventuremuseum.org/collection/aircraft/Stits%20DS-1%20Baby%20Bird.asp

An interesting sidenote to this... Hal Nemer, pilot of the Baby Bird, said that they had a difficult time getting the pitot tube mounted far enough out on the wing to get it out of the propeller slipstream.
 

BBerson

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The Monnett Sonerai has a span of 16 feet and low aspect ratio. The Cassutt is about the same.

I did a X-Plane survey a few years ago and found a small light single seater of 12 feet span was very nice. At 8 feet span the glide and control was still ok, but not as good as 12 feet. The 12 foot design was about the same as 18 feet or larger in climb but not as good in glide of course.

All just simulations of course, but I think 12 foot span is adequate considering the record is under 6 feet.

I ran a simulation at 6 feet also, it was about like the real flights, I think. Very quick roll and not much glide.
 

Norman

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(the XF-5U was built but destroyed before it flew due to political infighting).
The program was canceled because the era of propeller fighters was coming to an end. The prototype was destroyed for the same reason most other dead end projects are. Aside from the fact that it had no other potential customer the US government has a weird law that prohibits a contractor from profiting from publicly financed research except by selling that product back to us
 
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Norman

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I think. Very quick roll and not much glide.
You can have a good L/D, at high speed, with low AR by keeping the wing loading really low but that design philosophy produces big wings. Sink rate can't be good with low AR though because induced drag is relative to span^2/weight. When you get to aspect ratios significantly less than 2 and AoA greater than ~8 degrees you get into vortex lift which can slow down landings as well as flaps but without increasing the pitching moment. That's a good thing because the pitching moment is proportional to the chord and you're not likely to be able to trim it out with a reasonable tail. The early ARUPs ran into this problem with Cm. They used an m-6 reflexed airfoil and no tail. You trimmed the plane for a given speed by moving the trailing edge. They could slow down just fine but when they tried to fly faster than the design speed the Cm suddenly went negative and the plane went straight for the ground:shock:. Definitely a plane in which you have to know how to fly the throttle. This is a problem for plank type flying wings and the last ARUP had a horizontal stabilizer to fix it. A TWITT member started on a low AR plane a few years ago and he finally had to put a tail on it:dis:
 

BBerson

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When you get to aspect ratios significantly less than 2 and AoA greater than ~8 degrees you get into vortex lift which can slow down landings as well as flaps but without increasing the pitching moment. That's a good thing because the pitching moment is proportional to the chord and you're not likely to be able to trim it out with a reasonable tail.
I did not know about that, very interesting.
The main drawback of low aspect ratio is the poor downward visibility from sitting in the middle of the wing.
 

Norman

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The main drawback of low aspect ratio is the poor downward visibility
Yep:think: With a single engine in the nose downward visibility is going to be bad unless you put a window in the floor but that would be hard to keep clean. Also the vortex lift starts around 7 or 8 degrees but it isn't really very strong until past the normal stall angle and keeps increasing until something past 30 so there's also no forward view during final approach. The visibility problem was solved in the V-173 as a side benefit of the twin engines. I was thinking that since the nose gear strut has to be so long in this type it might be worth considering puting the engine on that.
 

bmcj

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The program was canceled because the era of propeller fighters was coming to an end. The prototype was destroyed for the same reason most other dead end projects are. Aside from the fact that it had no other potential customer the US government has a weird law that prohibits a contractor from profiting from publicly financed research except by selling that product back to us
Sorry, I thought I remembered reading about a personal vendetta from one of the higher up political figures that led to a the forced destruction of the ship against the companies wishes.
 

Norman

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I thought I remembered reading about a personal vendetta
You probably did. Personal animosity develops easily when somebody is threatening to cut off somebody else's gravy train. Whatever the original motives of both parties in the end there's usually some ill will and words like "vendetta" sell more books than "hurt feelings"
 

ThadBeier

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You mention an instability problem with tailless aircraft, that going much faster than the design speed makes the overall Cm negative, and the plane pitches down. You're right, as far as that goes -- as the plane speeds up and the elevator is positioned lower to keep the plane from climbing, the static margin will decrease. At some point, with enough power (or descending quickly enough) the margin will go through 0, and the plane will be unstable. Still, it shouldn't be something that sneaks up on you, it will be a gradual thing.

The same thing will happen on any airplane; you need to trim the elevator down the faster the plane goes, and at some point you'd run out of static margin. Most lightplanes have huge amounts of static margin in reserve, though. If you have enough drag and a small enough engine, you'll never get to that corner of the envelope.

I would think that tailless planes would have a pretty small speed range.
 

Norman

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I don't think that's quite right. Static margin is the longitudinal distance from the neutral point to the center of gravity. As I understand it the neutral point is due to the geometry of the planform and the airfoil section has nothing to do with it. A plank type flying wing uses the airfoil pitching moment to trim for a given speed. Above some speed the the pitching moment will become negative but the static margin hasn't changed so the plane is still statically stable the trimmed condition is just inverted. You could still fly level but you'd have to roll upside down:gig:

You mention an instability problem with tailless aircraft, that going much faster than the design speed makes the overall Cm negative, and the plane pitches down. You're right, as far as that goes -- as the plane speeds up and the elevator is positioned lower to keep the plane from climbing, the static margin will decrease. At some point, with enough power (or descending quickly enough) the margin will go through 0, and the plane will be unstable. Still, it shouldn't be something that sneaks up on you, it will be a gradual thing.

The same thing will happen on any airplane; you need to trim the elevator down the faster the plane goes, and at some point you'd run out of static margin. Most lightplanes have huge amounts of static margin in reserve, though. If you have enough drag and a small enough engine, you'll never get to that corner of the envelope.

I would think that tailless planes would have a pretty small speed range.
 

ThadBeier

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Basically, if you are moving the trailing edge of an airfoil (on a plank wing, say) you are changing the airfoil. To increase the static margin of a plank, you increase reflex. Decreasing reflex by moving the elevator down decreases static margin. I could believe that I'm using terms the wrong way, though.

Using this characterization of the problems with high-speed flight in the Mignet Flea, and with pendulum-stabilized hang gliders, makes sense to me.
 

Norman

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Decreasing reflex by moving the elevator down decreases static margin. I could believe that I'm using terms the wrong way, though.
The reflex sets trim not stability just like the elevator of a tailed aircraft. In a tailed AC pushing the stick forward will only result in a level flight speed increase up to a point then the plane will dive. Only the trimmed condition has changed not the stability. The plane is now in a stable dive and if you rolled it over it could fly level with the stick pushed even farther forward because the static stability is dependent on the CG and size of the horizontal stabilizer not the angle of the elevator
 
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