"SkyWing" hybrid wing body ultralight

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Prandtly

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Dec 19, 2020
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6

Here's a great example of Elevons ( and a rudder ) controls.
The controls the pilot touches are conventional. Pedals to push the rudder back & forth. And a stick that moves the elevons up and down, ( when he moves the stick fore & aft ) and a "mixer" that moves the elevons differently on each side when he moves the stick side to side. 3 axis control.

There are some aircraft that only use 2 axis control. Usually elevator and rudder. Or elevator and ailerons. In those craft, the designer uses built in stability so when the craft rolls or yaws, it "couples" so it does both, the way he wants it to. It's a compromise. ( you'll hear that a LOT about aircraft ) Usually the motivation is to make things simpler to fly or build , or both. 2 axis planes tend to skid around a bit, losing a little efficiency, and can be harder to land in a cross wind. Compromises...
Or Jim Marske's Pioneer flying wing is more elegant example.
 

Aesquire

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Jul 28, 2014
Messages
2,688
Location
Rochester, NY, USA
More elegant, granted. The Verhees Deltas however, have big honking Elevons that are obviously at the back, far from the center of gravity, and show the "see saw" effect needed to balance the forces. The exact same thing is happening with the Pioneer, but the lever arms are shorter and less visually clear.

Because you are dealing with forces that increase with airspeed, your balancing forces Also need to increase with airspeed.
 

Allen

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Jun 3, 2010
Messages
60
Location
Key West
My favorite UltraLight is the Lazair which has an inverted Vee tail. They ALL should be that way. The angled rudders also do the banking. Due to their orientation they also impart a 'twist' to the fuselage that banks it.
 

Aesquire

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2,688
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Rochester, NY, USA
I like the Lazair as well.

But TANSTAAFL.

The fuselage framework has to be stronger to pass the torque in roll to the wing and pilot. The V tail airplanes have to have bigger surfaces so you get the same leverage. I'm all for strong fuselages and bigger tails, but you pay for that in weight and drag.

V tails make sense in theory. 2 vs. 3 tail tips to make drag. 2 vs. 3 tail/fuselage joints to make drag. But the actual leverage to push the tail/nose up & down and side to side is less unless you make the 2 tail surfaces significantly bigger than than the parts of a 3 surface tail. It can be made to work, but it seldom achieves the promised results. ( although you do only need to make 2 bigger tail fins instead of 3, so labor is lower )

Inverted V tails also have a real problem with hitting the ground unless you bend the fuselage up a lot for clearance. The Lazair gets away with it by using the tails for landing gear too. Very clever, but again, you need to make them stronger, along with everything they attach to.

It's all compromises. They work pretty darn good on the Lazair.
 

Allen

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Jun 3, 2010
Messages
60
Location
Key West
Yes, I think that 2 larger tails are a better design than adding the 3rd control surface for more complexity and perhaps more drag. With a "plank" body as they call them in RC models, there is no problem having a strong enough fuselage to pass the rudder forces into the rest of the plane, since the body is a big wing section, it won't twist as much a cigar fuselage. ;=]
OH, with a wide wing-body it is possible to have A -shaped rudders mounted on TOP back corners of the wing and angled inward to simulate the inverted Vee rudders that would be angled outward on the body of a cigar fuselaged plane. Hope to do a drawing soon. Keep lookin high and you'll get high
 

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Allen

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Joined
Jun 3, 2010
Messages
60
Location
Key West
SkySled model movie, utube
here is a video of a very rough assemblage of 1" thick XPS quarter-scale study model of the 16' square SkySled.
This is intended to show where to put the mortises between the sheets of XPS 2" stryofoam making up the monocoque wing-body of the ultralight aircraft .
The tape will be replaced with fiberglass on the full scale version. ;=]
 
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