"SkyWing" hybrid wing body ultralight

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Allen

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Experimenting with tape. Trying to replace epoxy/glass taping mess and expense and time.
Tape is impressing me. It needs special techniques to make good bond not simple. Needs research on different tape types and techniques. It is lightweight and fast to apply. We'll see how it goes.Rex tape for Tyvek paper.jpg
 

Allen

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Allen, that’s an interesting project you have going there. Is your scale mock-up going to fly? I hope so, as I think there’s a lot to be learned from it especially when you’ve come up with such an original design. When you do fly it please fly it lots in many different weight configurations and test maneuvers. I’d suggest going so far as duplIcating a full-scale airplane’s lengthy test program and modifying the model accordingly as you learn its quirks.

Elsewhere on the forum are two rather lengthy threads about a prototype that had a quarter scale model built but not tested beyond showing it would lift off the ground before starting work on the real thing. Flight testing the real thing has shown time and again that maybe the model should have been fully tested before locking in the design. I can’t stress enough how important it is to learn from that.
Thanks very much for the good advice. ;=] I will get some RC equipment and thoroughly flight test the quarter scale version when it gets done. I wonder if there are wind tunnels that can fit a four-foot wide model to rent some time on at Embry-Riddle Univ. or elsewhere in Florida.
Specifically, I wonder if it is a good to add twelve degrees of dihedral only to the bottom of the wing surface for good stability? I'm not sure if it is good to leave the top surface level on a wing with bottom dihedral only.??
 

Allen

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Unfortunately, no, and the problem with almost all shapes like a "traditional" airfoil is that the camber, the curve, pitches the nose down , and increases with speed.

Here is an example of a wing/body design that's only flown a few feet up.

Notice the big horizontal tail that keeps it from flipping nose down into the drink after it lifts off. You probably don't need one that big or position, but most flying machines have a balancing surface that changes how much it pushes with airspeed.

It can be weird with flying wings and lifting body designs. A typical modern flex wing hang glider doesn't have a separate tail, but still does the airspeed changing balancing act with sweep and twist.
Notice that the wing at the center is at a higher angle to the air than the wing tips. Those tips don't actually push down in normal flight ( but will push the back down & nose up in certain situations like a past vertical dive ) instead the lift vector, the direction the wing lifts, changes from center to tip in a curve that gives the same pitch stability as a tail on a 747. It's subtle, very not obvious how it works, I'd need drawings and hand gestures... :popcorn:
It seems EZest to merely put some washout in the trailing edge of my SkySled 'wing-body' airplane design. I understand that built-in solid feature simulates upward deflection of both horizontal stabilizers which are the trailing edges of the flying wing design. The horizontal stabilizers can be operated differentially, one up and one side down to also function as ailerons. These devices have been called "pitcherons."
Perhaps they can have the capability of being 'trimmed' so they function as trim tabsl??
 

Aerowerx

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.... These devices have been called "pitcherons."
Perhaps they can have the capability of being 'trimmed' so they function as trim tabsl??
The commonly used term is "elevons". Perhaps your ideas would have been better accepted if you had familiarized yourself with the common language already in use.
 

Aesquire

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Yes, the Elevons should have a trim adjustment so you don't have to push or pull all the time to stay level. Adjustable in flight, so as the speed changes you can trim out the pitch changes.

Not all ultralight aircraft have in flight trim, since the speed range is small and with careful design ( or luck ) and alignment often a thin strip of aluminum on the trailing edge that you can bend up & down to adjust trim is adequate.

Typically there is also in flight trim for the rudder, too. But that's not on every small plane as conventional controls use pedals or a rudder bar you push with your feet, and legs have more strength and endurance than arms. Again, often a small ground Adjustable trim tab is fine.

When you go bigger, more powerful, trim becomes a serious thing. On a big fast plane like a P-51 Mustang, there's a trim control right at hand so the pilot can trim out the forces, which are Way too much to hold by hand. The tragic crash of a Mustang a few years back at the Reno Air Races, seems to be caused by the trim tab fluttering & tearing off. The sudden G load as the Mustang pitched nose up, Hard & Fast... appears from video to have actually broken the pilot's seat. He was knocked out cold, possibly outright killed, by the sudden forces. And without the trim tab, a body builder cannot hold the plane level at 400 miles an hour. Or at landing speed either. There's enormous forces involved.
 

Allen

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Also regarding wings pitching downward, I can adjust the radius of the leading edge of the wing to push it upwards more. by raising the center of the radius higher on the LE.
 

Aerowerx

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Also regarding wings pitching downward, I can adjust the radius of the leading edge of the wing to push it upwards more. by raising the center of the radius higher on the LE.
Is this the same as reflexing the trailing edge?

Why not just use one of the myriad reflexed airfoils that have little or no negative pitching moment?
 

Aesquire

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I can adjust the radius of the leading edge of the wing to push it upwards more. by raising the center of the radius higher on the LE.
That might make it worse.
Most airfoils used for wings are not symmetrical. Symmetrical shapes are used in acrobatic competition planes, so they work the same when you fly upside down. Tail surfaces are often symmetrical so they work equally well both directions.

there are exceptions. The Zenith 700 series planes that are designed as STOL use a horizontal stabilizer with a big fat lifting asymmetric shape, "upside down", so the down push on the tail balances the nose down push from both gravity ( center of gravity in front of center of lift ) & the pitching Moment of the asymmetric cambered wing. The designer wanted powerful pitch control at very low speed. The "Cruiser" version of the same plane uses a symmetric shape on the tail, and a "flatter" wing airfoil to reduce drag for traveling, at the expense of the very slow speed lift and control.

But... Most light air flying things, from Paragliders to 747s, use a Cambered airfoil, where if you plot the center line of the wing in thickness, you get a curve, ( rather obvious in a single "skin" wing used in many hang gliders and one made from a single layer of foam, like your's. ) that is concave on the bottom. That curve, the Camber line, help change the direction the air flows "better" than a flat plate. But it also has a nose down pitching moment, that "wants" to follow that built in curve.

So changes at the front of a wing, to change the Camber curve, have a big effect on lift & drag, and importantly, stall behavior, but are relatively ineffective at eliminating pitch moment, unless you go all the way to flat, which throws away all the advantages of a typical airfoil.
 

Aesquire

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It's so much easier for me to grasp these ideas as pictures. I can do the math, but am out of practice and never a whiz. I'm all pretty cartoon picture of flow & graphs, up in my head, every children's book on wings for over a century devoured over a lifetime of obsession. So forgive my clumsiness at translating the Roadrunner cartoon in my head to a coherent script. :)

This is a bit dry, but describes pitching moment ok. Open to opinions on the video series, but that's best on a different thread.

This one uses digital blackboard with arrows being drawn & stuff explained in college lecture format.

and here's the basic language in picture form

 

Retiree

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In general as the camber of an airfoil increases the negative pitching moment, nose down, increases. I assume bending the nose up, like reflexing the trailing edge up, would act to decrease the camber and decrease the negative pitching moment. But like a previous comment, it would be a good idea to have someone model the change you want to make to estimate how the aerodynamics of the airfoil would change.
Doug
 

Aesquire

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A rectangular slab has a small nose down pitching moment at many angles of attack. Go past that and you've got an upside down airfoil, where the lift is down until you get to angles of attack that with a skinny airfoil like being discussed will stall really easily.

The "upside down" tail fins on a race car have a "nose up" moment, that you have to figure in when building their mounts.
 

erkki67

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Somehow I like the idea, but it should be built with trustworthy materials.
1571A81D-095A-4154-84B7-17FF71752C69.jpeg
this bird has some Elements which are worthwhile to think about.
BrO-18 Boružė is the real name of it.
 

Allen

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Here's where I'm at with SkySled research. I am practicing cutting and taping specifically XPS Styrofoam, just getting familiar with working the materials. The plane in the picture is a rough work in progress that shows how the ribs and the spines are box finger-jointed together. The wingtips are joined to the ribs via mortice and tenon joinery.
The form of the body is strong.
sled trial DSCF0009.JPGNow I am thinking about what I should use for the top covering. The contenders are fiberglass/resin fabric, standard aircraft wing fabric or more XPS board .
 

Allen

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A rectangular slab has a small nose down pitching moment at many angles of attack. Go past that and you've got an upside down airfoil, where the lift is down until you get to angles of attack that with a skinny airfoil like being discussed will stall really easily.

The "upside down" tail fins on a race car have a "nose up" moment, that you have to figure in when building their mounts.
I like the idea of building more 'up' force into the leading edge radius. This means raising the whole radius up to, or near, the camber line instead of having the usual 'droopy nose' look on the face of the cutting edge. That looks to me like it will counteract the down-pitching moment of a cambered airfoil. ??
[This will get the mathematicians howling ;=]
 

Aesquire

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All that does is move the lift back on the wing. Actually less up force on the nose.

If you go symmetrical, you still need to balance weight in front of the center of pressure. If you go to an upside down wing, you need a bigger angle to get lift, and the air over the top will separate easy.

If you put the weight behind the center of lift/pressure, the darn thing will want to do backflips.

Believe me, if I could make it work by changing the nose radius, I would but it just doesn't.
 

Allen

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So there's nothing to do but trim out the pitch with trim tabs on the wings trailing edge?
I want to use a 20% chord thickness. That should pull the nose up. The wing bottom is flat, but might later put some wash upward on the trailing edge.
I am not at the point of refining the airfoil yet. I am still learning to cut and paste the materials to test the strength of various monocoque external frame assembly methods and designs. [while writing a Martian scifi novel in mornings] meeceblog.wordpress.com
 

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Aesquire

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So there's nothing to do but trim out the pitch with trim tabs on the wings trailing edge?
I want to use a 20% chord thickness. That should pull the nose up.
Are you going to have some way to control pitch?

Chord thickness won't pull the nose up.

Not, only, but mostly, you have 2 things that make the nose "want" to go down.
The center of gravity is in front of the center of pressure/lift. Otherwise it wants to back flip or is uncontrollable.
The curvature of the wing, that camber, wants to forward flip.

Yes, F-16s and other modern fighters with computers running the control surfaces can have centers of gravity in rearward unstable locations, but when a wire breaks or the power fails, the pilot ejects. He doesn't even have a mechanical way to control the plane. If you had the budget for 21st century fly by wire redundant computer controls, you'd be asking very different questions. ;)

So you need in any aircraft, some way to balance the forces, and use them to point your thing in the direction you want to go.

The Wright Brothers didn't invent wings, or tails, or engines, or propellers. They made a lot of experiments, built a wind tunnel in their shop ( it's not that big, they used little model wings, etc. ) and ended up with the Best wings, propeller, and engine on the planet, at that time, but all that isn't what made them successful, although it certainly helped.

Their "secret" was figuring out how to control a flying machine, in 3 dimensions.

Remember, rudders had been used on airships for years, on boats for millennia, the Wrights added a elevator ( rudder for nose up and down ) and wing warping,/ailerons, ( really just rudders to tip the wings up & down at 90 degrees to the rudder and 90 degrees to the elevator. And controls for the pilot for all 3 axis.

Btw, don't copy the early Wright glider controls, they changed them later. Big improvement.

So... You need a elevator for pitch control, or in a flying wing elevons ( elevator & ailerons, combined ).

Hang gliders use weight shift to pitch & roll. But the wing itself is designed with twist & reflex and other features that make it stable with no pilot input. If you strapped a sandbag in the proper location, you could hurl a hang glider off a mountain and it would fly just fine. Where? That's a different story. :)
 

Aesquire

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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...
 

Aerowerx

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.... The wing bottom is flat, but might later put some wash upward on the trailing edge.
....
That is called reflex. More or less the same thing as having the elevons deflected upwards. With this it is theoretically possible to have a wing that will pitch nose-up, or even have no pitching moment.

Perhaps your ideas would be better received if you use the commonly accepted terms?
 
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