Full Wing Flutter
11-23-2009, 02:32 PM
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RE: Full Wing Flutter
Could you elaborate on
"What about a combination of the proposed bridge and these winglets, sharing the needed area?"
I am not getting a visual.
As far as damage to the winglets on landing. I am happy then there is enough left to repair after the confetti rain of the first one. Even with the mods, worst case is a wing loading of under 14 oz per sq ft so it will land slow.
Ideas to test, from experience and knowledge, is what I need. Even Boeing and NASA have failures during testing. We all learn from our mistakes. Now if I just had a wind tunnel out back.
"What about a combination of the proposed bridge and these winglets, sharing the needed area?"
I am not getting a visual.
As far as damage to the winglets on landing. I am happy then there is enough left to repair after the confetti rain of the first one. Even with the mods, worst case is a wing loading of under 14 oz per sq ft so it will land slow.
Ideas to test, from experience and knowledge, is what I need. Even Boeing and NASA have failures during testing. We all learn from our mistakes. Now if I just had a wind tunnel out back.
11-23-2009, 03:16 PM
#27
RE: Full Wing Flutter
I mean keeping the bridge for rigidity and make it smaller, as well as the wingtips.
There is a cycling action (airspeed and turbulence) and there is a cycling reaction (the wing twisting around a line that coincides with the CG).
The idea is to modify the action (by reducing turbulence) and the reaction (by making the wing more rigid, reducing the mechanical advantage of other surfaces and somehow changing the frequency of oscillation).
Modify and test, modify and test,……
There is a cycling action (airspeed and turbulence) and there is a cycling reaction (the wing twisting around a line that coincides with the CG).
The idea is to modify the action (by reducing turbulence) and the reaction (by making the wing more rigid, reducing the mechanical advantage of other surfaces and somehow changing the frequency of oscillation).
Modify and test, modify and test,……
11-23-2009, 07:32 PM
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RE: Full Wing Flutter
What is that second pic? It looks a lot like a X48B with added inner fins. Looking at the X48B gave me ideas for my wing shape.
11-24-2009, 02:16 PM
#29
RE: Full Wing Flutter
The picture belongs to an Aerospatiale concept of a flying wing aircraft:
http://www.aee.odu.edu/fas.php?id=2
There is some heavy reading in the following links, but it will give you an idea of how complex this thin plate subsonic flutter problem is and what has been done to solve it:
http://ntrs.nasa.gov/archive/nasa/ca...2007002162.pdf
http://ntrs.nasa.gov/search.jsp?Ns=H...ll&Ntt=flutter
http://www.aee.odu.edu/fas.php?id=2
There is some heavy reading in the following links, but it will give you an idea of how complex this thin plate subsonic flutter problem is and what has been done to solve it:
http://ntrs.nasa.gov/archive/nasa/ca...2007002162.pdf
http://ntrs.nasa.gov/search.jsp?Ns=H...ll&Ntt=flutter
11-24-2009, 03:25 PM
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RE: Full Wing Flutter
ORIGINAL: lnewqban
...
There is some heavy reading in the following links, ...
...
There is some heavy reading in the following links, ...
I actually read some of it but only a small part was meaningful. I did see more then once where increasing thickness is sometimes the only option at some point. I will take a nap and try again.
11-24-2009, 04:59 PM
#31
RE: Full Wing Flutter
Yes, but those are only the NASA guys!
For us, increasing thickness is not an option;........at least it will not be the first one.[sm=punching.gif]
For us, increasing thickness is not an option;........at least it will not be the first one.[sm=punching.gif]
11-24-2009, 06:54 PM
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RE: Full Wing Flutter
Your idea of using the thin wing panel to reduce the frontal area is a good idea.
It's just that building it is a bit of a challenge, I don't think it is impossible, although trying to do it with wood alone is a serious constraint.
I am fairly sure that using other materials would make it much easier but I understand the design criteria you have used.
Yes, making it thicker, or using more exotic materials would be the easy way out, but that would defeat the original design concept.
I think you have now identified the problems and now have an idea if how to fix the problem.
Now my idea on mods to the center section may improve the situation a bit more but it is all a "science experiment" at this point.
Like I said before, I think you project is challenging not impossible.
You have already progressed from catastrophic failure to having it hold together, you have already made progress!
It's just that building it is a bit of a challenge, I don't think it is impossible, although trying to do it with wood alone is a serious constraint.
I am fairly sure that using other materials would make it much easier but I understand the design criteria you have used.
Yes, making it thicker, or using more exotic materials would be the easy way out, but that would defeat the original design concept.
I think you have now identified the problems and now have an idea if how to fix the problem.
Now my idea on mods to the center section may improve the situation a bit more but it is all a "science experiment" at this point.
Like I said before, I think you project is challenging not impossible.
You have already progressed from catastrophic failure to having it hold together, you have already made progress!
11-25-2009, 06:42 AM
#34
RE: Full Wing Flutter
Mike,
I second Iron Eagel, your logic is just fine.
First airplanes had wings made of these thin plates, and then they had to be supported externally with wiring (biplanes and monoplanes).
Trying to avoid the drag caused by all those external bracing, the monocoque wing was invented.
This was a wing that supported itself with internal structure and metal skin.
But those wings had to be thick, in order to have resistance to bending and twisting.
With higher velocities, there is the contradiction that a thinner airfoil is better for drag reduction, but it is not for the stress that the high speed creates.
Better materials have been the solution to that contradiction.
The main factor in that capacity to resist is the moment of inertia (I), which depends directly on the top and bottom transversal areas, and exponentially on the vertical distance between those areas. (See attached table).
I have also attached some schematics that explain the resonance and the stress in a shape like the section of the wing.
Note that the table 45.1 shows (second row of each page) that the natural frequency of an assembly can be modified by changing the material (E=modulus of elasticity), the thickness and the height between both skins (I=mass moment of inertia), the wing span (L) for bending force (m=force of air or turbulences); as well as by changing the section geometry (J=polar area moment of inertia), material (G=shear modulus) and wing span (L) for twisting force.
NASA has worked hard in the investigation and solution to this endless headache of flutter of thin plates at subsonic air speeds, especially for rocket’s fins.
Flutter cannot prevail over dedicated experimentation.
Happy Thanksgiving!!
I second Iron Eagel, your logic is just fine.
First airplanes had wings made of these thin plates, and then they had to be supported externally with wiring (biplanes and monoplanes).
Trying to avoid the drag caused by all those external bracing, the monocoque wing was invented.
This was a wing that supported itself with internal structure and metal skin.
But those wings had to be thick, in order to have resistance to bending and twisting.
With higher velocities, there is the contradiction that a thinner airfoil is better for drag reduction, but it is not for the stress that the high speed creates.
Better materials have been the solution to that contradiction.
The main factor in that capacity to resist is the moment of inertia (I), which depends directly on the top and bottom transversal areas, and exponentially on the vertical distance between those areas. (See attached table).
I have also attached some schematics that explain the resonance and the stress in a shape like the section of the wing.
Note that the table 45.1 shows (second row of each page) that the natural frequency of an assembly can be modified by changing the material (E=modulus of elasticity), the thickness and the height between both skins (I=mass moment of inertia), the wing span (L) for bending force (m=force of air or turbulences); as well as by changing the section geometry (J=polar area moment of inertia), material (G=shear modulus) and wing span (L) for twisting force.
NASA has worked hard in the investigation and solution to this endless headache of flutter of thin plates at subsonic air speeds, especially for rocket’s fins.
Flutter cannot prevail over dedicated experimentation.
Happy Thanksgiving!!
11-25-2009, 11:07 AM
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RE: Full Wing Flutter
Lnewqban,
Thanks for all your effort to educate me. While I do not have a complete understanding of everything your present, I am learning from much of it. It seems "thin" and "flat plate" are both working against me when it comes to mechanical advantage. In order to overcome some of the problems, including "natural frequency", my next build will have diagonal trusses between the ribs with internal lattice style caps. My test panels show this makes a huge difference over what I have.
If the next wing flutters at any speed I can get it to, I may concede that a 2.2% balsa wing at the root is not practical. The NACA 0006 airfoil may be the ticket at that point.
Thanks for all your effort to educate me. While I do not have a complete understanding of everything your present, I am learning from much of it. It seems "thin" and "flat plate" are both working against me when it comes to mechanical advantage. In order to overcome some of the problems, including "natural frequency", my next build will have diagonal trusses between the ribs with internal lattice style caps. My test panels show this makes a huge difference over what I have.
If the next wing flutters at any speed I can get it to, I may concede that a 2.2% balsa wing at the root is not practical. The NACA 0006 airfoil may be the ticket at that point.
11-25-2009, 01:15 PM
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RE: Full Wing Flutter
Inewcuban,
Looks like my old textbooks...
Boy was that a long time ago.
At least now I have a reason to re-learn it, back then mechanical structures didn't interest me all that much.
Have a good Thanksgiving.
Mike,
A 2.2% airfoil is pushing the envelope with wood as the primary structure, it would be a lot easier to do using composite materials, but even then it would take some serious attention to detail. I am still interested in how this will perform once the kinks are worked out. Now just if they could shrink the size and weight of the battery packs a bit more, things could get real interesting.
Looks like my old textbooks...
Boy was that a long time ago.
At least now I have a reason to re-learn it, back then mechanical structures didn't interest me all that much.
Have a good Thanksgiving.
Mike,
A 2.2% airfoil is pushing the envelope with wood as the primary structure, it would be a lot easier to do using composite materials, but even then it would take some serious attention to detail. I am still interested in how this will perform once the kinks are worked out. Now just if they could shrink the size and weight of the battery packs a bit more, things could get real interesting.
12-10-2009, 01:58 PM
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RE: Full Wing Flutter
I have been working on my latest build six days with most of that time contemplating how to rather then actually doing. I am using what I learned here and from building test panels to build a very stiff but thin wing. This wing will be 1/16" thicker then the last one since the entire structure on each side will be totally capped with 1/32 balsa. The rib caps parallel to the cord will will also have a 1/4 x 1/64" grove with a strip on 1/64 ply inlayed as shown in first pic.
I was going to just laminate 1/16 and 1/32 balsa with a 90* wood grain and not do the individual caps but wanted to save weight and have the advantage of the multi direction grain. I may still just laminate on the other side because of how tedious all those caps are to install. I need to work on the trailing edge a bit before sheeting the other side.
I am going with the fins shown in picture #3 with hopes they will have less leverage to twist the wing. Total height will be just over 4" and the area is slightly more then needed to satisfy the vertical fin volume coefficient math.
I was going to just laminate 1/16 and 1/32 balsa with a 90* wood grain and not do the individual caps but wanted to save weight and have the advantage of the multi direction grain. I may still just laminate on the other side because of how tedious all those caps are to install. I need to work on the trailing edge a bit before sheeting the other side.
I am going with the fins shown in picture #3 with hopes they will have less leverage to twist the wing. Total height will be just over 4" and the area is slightly more then needed to satisfy the vertical fin volume coefficient math.
12-10-2009, 02:46 PM
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RE: Full Wing Flutter
Mike,
As you know my version still in the design phase.
As with yours the entire wing structure is getting a plywood cap (1/64th ply on each side). The wing itself will come out just 1/32" thicker than the original 3/8ths, unless I decide to go with the diamond airfoil which would make it a lot thicker, something on the order of 3/16" thicker at a minimum. One of the other changes is the battery box has been lowered into the fuselage and blended into the wing roots. Now this one mod may have a lot of issues of it's own beside the fact that it going to be a pain to build, even now the cowl is still in a state of flux.
As far as the fins I haven't given a lot of thought to it other than you approach of centering the fins on the wingtip.
Here is a look at how it's looking thus far.
As you know my version still in the design phase.
As with yours the entire wing structure is getting a plywood cap (1/64th ply on each side). The wing itself will come out just 1/32" thicker than the original 3/8ths, unless I decide to go with the diamond airfoil which would make it a lot thicker, something on the order of 3/16" thicker at a minimum. One of the other changes is the battery box has been lowered into the fuselage and blended into the wing roots. Now this one mod may have a lot of issues of it's own beside the fact that it going to be a pain to build, even now the cowl is still in a state of flux.
As far as the fins I haven't given a lot of thought to it other than you approach of centering the fins on the wingtip.
Here is a look at how it's looking thus far.
12-10-2009, 07:42 PM
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RE: Full Wing Flutter
Mike, first off in your first drawing your spars are in completely the wrong place. As they sit now much of the wing is forward of the spars so it's like trying to push a piece of cardboard ito the wind. the forces are trying to pivot the wing around the main spar and the result is it tries to fold around to the rear.
Secondly 3/8 is FAR too thin to achieve a significant degree of stiffness in any direction. Not to mention the already brought up issues of a flat plate airfoil for a model of this type.
What you want to do is put the main spar about 25% of the way back from the leading edge. Of course this means the spar will be joined at the center line with some sort of triangular gussets to provide a carry through splice. Secondly I'd strongly suggest you switch to an actual airfoil that provides a decent thickness of the wing section at the root with the max thickness at the spar. It can taper to the tip and it doesn't need to be something super high tech. Just something that will streamline your design. An airfoiled nose and a flat tapered rear section would be fine. Sort of like the root and tip airfoils shown below. Note now the rear taper is constant so you can still build it flat on a board. If you want the trailing edge to sweep back as shown in your sketch then one side can be flat while the upper sid will be slightly angled at the center line. But that just means you'd have a slight bit of either dihedral or anhedral depending on which way you flip the wing after you lift it off the board.
Here's the airfoil shape I'm suggesting. This is a pretty simple airfoil to build given the flat rear section. You can still build it on a flat table and do most of the lower surface sheeting and all of the upper surface sheeting before lifting it off the building board. In particular note that there's only one main spar that is located far enough forward to support the structure where it requires the most stiffness to avoid. Also while still quite thin at the tips you've got a 1.25 inch thick root section for more strength and stiffness. All good traits for a high speed model.
Secondly 3/8 is FAR too thin to achieve a significant degree of stiffness in any direction. Not to mention the already brought up issues of a flat plate airfoil for a model of this type.
What you want to do is put the main spar about 25% of the way back from the leading edge. Of course this means the spar will be joined at the center line with some sort of triangular gussets to provide a carry through splice. Secondly I'd strongly suggest you switch to an actual airfoil that provides a decent thickness of the wing section at the root with the max thickness at the spar. It can taper to the tip and it doesn't need to be something super high tech. Just something that will streamline your design. An airfoiled nose and a flat tapered rear section would be fine. Sort of like the root and tip airfoils shown below. Note now the rear taper is constant so you can still build it flat on a board. If you want the trailing edge to sweep back as shown in your sketch then one side can be flat while the upper sid will be slightly angled at the center line. But that just means you'd have a slight bit of either dihedral or anhedral depending on which way you flip the wing after you lift it off the board.
Here's the airfoil shape I'm suggesting. This is a pretty simple airfoil to build given the flat rear section. You can still build it on a flat table and do most of the lower surface sheeting and all of the upper surface sheeting before lifting it off the building board. In particular note that there's only one main spar that is located far enough forward to support the structure where it requires the most stiffness to avoid. Also while still quite thin at the tips you've got a 1.25 inch thick root section for more strength and stiffness. All good traits for a high speed model.
12-10-2009, 08:19 PM
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RE: Full Wing Flutter
BMatthews,
Thanks for your suggestions. I have successfully designed and built high speed deltas with a NACA 0006 airfoil in the past. This particular design has turned into a game to see if I could do it. My current version of this wing flies great and only starts a hint of flutter at 130 mph. This will be my last attempt with a 3/8" flat plate airfoil before going to a real airfoil if flutter persist. 3/8" thick on a 42" wing is crazy, isn't it?? [X(]
I do however think the placement of my spars are in the right place. The front spar is at 16% MAC, ahead of the CG by just a little.
Thanks for your suggestions. I have successfully designed and built high speed deltas with a NACA 0006 airfoil in the past. This particular design has turned into a game to see if I could do it. My current version of this wing flies great and only starts a hint of flutter at 130 mph. This will be my last attempt with a 3/8" flat plate airfoil before going to a real airfoil if flutter persist. 3/8" thick on a 42" wing is crazy, isn't it?? [X(]
I do however think the placement of my spars are in the right place. The front spar is at 16% MAC, ahead of the CG by just a little.
12-10-2009, 08:55 PM
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RE: Full Wing Flutter
Mike, you may want to draw in a chord line along the 25% chord point. This will be a swept line. It's also the line that the wing is trying to twist around. When you do that and study the distribution of area ahead and behind that lne in relation to the spars I think you'll be in for some interesting information. Also on a wing of this type the sheeting has FAR more to do with the stiffness than the spars since the spars are so thin due to the flat plate effect.
Another option with things like helicopter blades that flutter is to add some weight along the leading edge. By shifting the CG of the airfoil ahead this can stabilize the airfoil. The same thing is done to movable control surfaces by using a mass balance on a little arm or by having a dogleg in the surface with a honkin' big weight in the little ear that extends forward of the hinge line.
And yeah, I remember your other designs so I was a bit shocked to see you going back to something this "crude" in aerodynamic terms. Just HAD to push the envelope, eh?
Another option with things like helicopter blades that flutter is to add some weight along the leading edge. By shifting the CG of the airfoil ahead this can stabilize the airfoil. The same thing is done to movable control surfaces by using a mass balance on a little arm or by having a dogleg in the surface with a honkin' big weight in the little ear that extends forward of the hinge line.
And yeah, I remember your other designs so I was a bit shocked to see you going back to something this "crude" in aerodynamic terms. Just HAD to push the envelope, eh?
12-10-2009, 11:59 PM
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RE: Full Wing Flutter
It started off with hopes of something that looked cool, flew well and you could scratch build in a couple of days for 50 bucks. This last version has thicker skin and diagonal ribs while sacrificing part of the quick and easy build. It is "crude" in some respects and yes, I just had to push the envelope. [8D] Or maybe the envelope is pushing me.
12-11-2009, 12:42 AM
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RE: Full Wing Flutter
Wing flutter is like a bouncing a rubber ball....a small input as you hit the ball (if you hit it at just the correct time) makes the ball go higher and higher.
Something has to "drive" the flutter. (the small input).
This can be the elevons or air going over the wing attaching and detatching.
The elevons (or ailerons) driving the wing would be the most common. It would typically be a lower frequency vibration than typical aileron "buzz" that we mostly associate with the ailerons fluttering. This driver could be because of flexible control surfaces, lower than adequate servos, or slop in the system. Also balancing the control surfaces will knock down the vibration of the ailerons. And sealing the gaps won't hurt either. (I have seen this happen at a fairly slow speed with a skyradier with a really sloppy aileron and the wing was flexing a good 8 inches, fixed we could bring the airplane up to speed (jett .46!)).
The airflow over the wing could also cause the wing to drive into oscillation. Basically the airflow attaching and reattaching would drive the wing. To fix this you would have to change the airflow....maybe vg's..
Ok...so if the rubber ball is changed lets say to a ball that doesn't have as much "bounce" if we drive it with the same force as we did the "bouncy" one it won't go as high.
Ok, this is where we are changing the stiffness of the structure. One way to fix this is to make the airfoil thicker. If you look at a cross section (a rib) what you are trying to do is twist this rib from one face to the other. If you have more area away from the center it would be better since for each piece of the rib times the moment arm (the distance from the center of the twist) will help. This is why you see "D tubes" in aircraft since it maximizes the distance of the skins from the center. The other is space age materials that make everything "stiffer". Another is wires etc...(not good for a fast plane).
Hope this helps Merry xmas.
Steve
Something has to "drive" the flutter. (the small input).
This can be the elevons or air going over the wing attaching and detatching.
The elevons (or ailerons) driving the wing would be the most common. It would typically be a lower frequency vibration than typical aileron "buzz" that we mostly associate with the ailerons fluttering. This driver could be because of flexible control surfaces, lower than adequate servos, or slop in the system. Also balancing the control surfaces will knock down the vibration of the ailerons. And sealing the gaps won't hurt either. (I have seen this happen at a fairly slow speed with a skyradier with a really sloppy aileron and the wing was flexing a good 8 inches, fixed we could bring the airplane up to speed (jett .46!)).
The airflow over the wing could also cause the wing to drive into oscillation. Basically the airflow attaching and reattaching would drive the wing. To fix this you would have to change the airflow....maybe vg's..
Ok...so if the rubber ball is changed lets say to a ball that doesn't have as much "bounce" if we drive it with the same force as we did the "bouncy" one it won't go as high.
Ok, this is where we are changing the stiffness of the structure. One way to fix this is to make the airfoil thicker. If you look at a cross section (a rib) what you are trying to do is twist this rib from one face to the other. If you have more area away from the center it would be better since for each piece of the rib times the moment arm (the distance from the center of the twist) will help. This is why you see "D tubes" in aircraft since it maximizes the distance of the skins from the center. The other is space age materials that make everything "stiffer". Another is wires etc...(not good for a fast plane).
Hope this helps Merry xmas.
Steve
12-11-2009, 01:30 AM
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RE: Full Wing Flutter
ORIGINAL: Doc.316
...This can be the elevons or air going over the wing attaching and detatching.
...Hope this helps Merry xmas.
Steve
...This can be the elevons or air going over the wing attaching and detatching.
...Hope this helps Merry xmas.
Steve
If my current mods do not fix the flutter I will consider this particular design a 100 mph park flyer. With a lighter motor, battery and ESC the wing loading would be under 10 oz sq ft. My current setup is capable of well over 175 mph which is much more the the airframe can stand so far.
12-11-2009, 05:58 PM
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RE: Full Wing Flutter
What size of wing "skins" are you using? You could thicken them up a bit....or glass the outside thickness of the wing.......(that would stiffen up the structure some) of course this all adds weight....but if you are trying to go fast weight isn't a big driver...(yes it does hurt but not as much as you would think). make sure on the next build the elevons are made as stiff as posible and try and put the horn in the middle versus one end....this will stiffen up the aileron system a bunch....
Oh, looks like a pretty cool project.
Steve
Oh, looks like a pretty cool project.
Steve
12-11-2009, 07:24 PM
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RE: Full Wing Flutter
I increased the skin thickness from 1/16 to 3/32" on each side. I also added the diagonal ribs plus 1/8 x 1/64 ply rib caps, embedded in the balsa caps, on the ribs parallel to the cord.
I just finished sheeting the wing and it is very noticeably stiffer then the last one. My RTF weight should still come in under 3 lbs. Not too bad for a 500 sq in plane.
Pictures of #1 and #2 below. The new and improved #3 soon.
Short Youtube video the first two versions in flight.
http://www.youtube.com/watch?v=pWvlOBAKn-A
I just finished sheeting the wing and it is very noticeably stiffer then the last one. My RTF weight should still come in under 3 lbs. Not too bad for a 500 sq in plane.
Pictures of #1 and #2 below. The new and improved #3 soon.
Short Youtube video the first two versions in flight.
http://www.youtube.com/watch?v=pWvlOBAKn-A
12-11-2009, 10:11 PM
#48
RE: Full Wing Flutter
Glad to read that the project is moving along, Mike.[sm=thumbs_up.gif]
The frequency of resonance has changed with all these changes for sure.
The model may not flutter at all this time.
The frequency of resonance has changed with all these changes for sure.
The model may not flutter at all this time.
12-13-2009, 10:14 AM
#49
RE: Full Wing Flutter
A simple stiff wing is a solid blue core with sheeted covers. There are no varyiations thru out it.
Below are some panels before sheeting 78" cores.
12-16-2009, 10:59 PM
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RE: Full Wing Flutter
ORIGINAL: Mike Connor
I have been having trouble with an full wing oscillating torsion of a flying delta/wing that I designed. It starts at a speed of over 100 mph and caused my first one to literally explode and rain confetti. The second wing was made stiffer front to back with rib caps but the full wing flutter started about the same speed but held together.
It is a 3/8'' flat plate wing made of balsa and hard wood spars with a 42'' wingspan. It is fully sheeted top and bottom with 1/16'' balsa. It has winglets that have recently been moved in 10'' that have not been tested yet.
I would like to know what design features would promote wing flutter and how to add torsional stiffness. Most flying wings have winglets but could they cause flutter? Looking at the plans I am considering extending both spars, shortening the elevons, increasing the top sheeting to 3/32''. The wing seems fairly solid when I bend and twist it but something isn't right. Is 3/8'' just to thin for a 42'' wingspan? Any thoughts?
I have been having trouble with an full wing oscillating torsion of a flying delta/wing that I designed. It starts at a speed of over 100 mph and caused my first one to literally explode and rain confetti. The second wing was made stiffer front to back with rib caps but the full wing flutter started about the same speed but held together.
It is a 3/8'' flat plate wing made of balsa and hard wood spars with a 42'' wingspan. It is fully sheeted top and bottom with 1/16'' balsa. It has winglets that have recently been moved in 10'' that have not been tested yet.
I would like to know what design features would promote wing flutter and how to add torsional stiffness. Most flying wings have winglets but could they cause flutter? Looking at the plans I am considering extending both spars, shortening the elevons, increasing the top sheeting to 3/32''. The wing seems fairly solid when I bend and twist it but something isn't right. Is 3/8'' just to thin for a 42'' wingspan? Any thoughts?
Have fun!