A quick fix to increase control authority might be to add a trailing edge fence to the end of the elevon, above and below the trailing edge, to stop flow leaking around the gap by the rudder, might need to rebalance the surface. I agree, VGs might be needed the length of the elevon, that might be the first thing to try. Not having a moving surface at the tip makes it harder to have good roll control. A compromise might be to lengthen the elevon, move the rudder further outboard, and add fixed leading-edge slots toward the tip, helping to prevent tip stall. My two cents. Great work, looking forward to further progress. PS- try using a lapel mike with a remote transmitter, the audio from the camera is a little hard to hear.
All interesting comments with various pluses and minuses. Most any solution including many not mentioned here, end up generating extra drag at higher speeds (unless one can turn the solution on/off). Flying wings don't tolerate adding drag as they can't achieve very high lift. Of course what good is high L/D when you can't control the aircraft, right? Anyway, Xflr says a 3 ft spanwise extension should solve the problem and that won't add hardly any drag. BTW, my camera that accepts my cordless mic, broke recently. I filmed this with a Go-Pro, oh well. No budget for a new camera - need funds to mod the glider.
If you are thinking about not only adding elevon to the wing tips but also increasing washout, you could also consider adding turbulator to the area that's affected by the transition bubble instead. With turbulators I mean tiny holes on the wing surface that open when the pressure difference between upper and lower wing surface exceeds a certain level. The holes blow air out before the transition point and help reduce the bubble. At high speed the holes create less additional drag than if you increase the washout.
Other solutions that might help 1) Vortex generators on the both the top and underside of the wing ahead of elevons to delay flow separation on both extremes of control deflection. 2) Couple the inboard flag to pitch and roll control, this will help reduce the control deflections required on the elevaons and widen the range of linear control as well as the peak roll/pitch moments that are possible. 3) As a temporary measure, add an inch or two to the trailing edge of the elevons to increase their area.
Hi Robert: All good points, although given the wing's design, the flaps are arranged to cause pitching moments in reverse of the elevons, so they can't be coupled effectively. My current plan is to put temporary elevons on the trailing edge of the wing tip panels (outboard of the winglets) along their entire span. Xflr says that should give me plenty of control. If it works, then I make the major mods to the tip panel structure. Keep an eye our for more vids, I expect to test the extensions in one to three weeks.
@@KlingbergWingMkII My thought was that flaps + elevon mixing would be done in such a way as to couple pitch, roll and yaw in mutually supportive way. i.e. Stick forward : elevons down, flaps up Stuck back : elevons up, flaps down Stick left : left elevons and left flap up, right elevons and right flap down Stick right : left elevons and left flap down, right elevons and right flap up In the stick back motion you effectively increase washout which is helpful for avoiding tip stalls/spins, improving roll/yaw coupling (takes you nearer to horten wing loading). You can partly achieve this by manually adjusting the flaps in your present configuration, but who has the skill level to be doing that near the ground at take off and landing. Another advantage of the coupling the flaps to the stick is you can changes in the overall CL of the whole wing without needing to pitch nose up/down. If you want to dump lift when standing at launch the quickest way is to move up the flaps as this dumps lift without any rotation of the wing nose down, and visa versa. This would allow much finer control of launch as you aren't having to fight against angular momentum, you movement in the stick directly changes the CL of the wing for a fixed angle of attack. This finer CL control also works well in flight and on landing. Such a coupled system would be more sensitive in pitch and roll so you'd likely need to dial down the sensitivity, especially in pitch. The traditional flaps control would become a trim position control that the stick adds input to. Getting it all to mix on electronic controlled surfaces would be easy, far more of challenge with purely mechanical system, but as you already have elevon mixing system, I'm thinking it would be just adding to this in a novel way.
That is what I did on the very first model - didn't work at all. I didn't know it at the time, but the British put that type of control on a flying wing back in the 50s - didn't workout well for them either. Control forces are low and you need a massive bearing to take all the pending loads and still allow for the pivot motion - so a very heavy solution - nothing good about it.
@@KlingbergWingMkII I figured the weight would be an issue. When you say didn't work at all, do you mean there was lack of control authority? If so, that makes me curious as to why. It works so well in my mental wind tunnel, LOL!
Yes, and I think the Brits had an issue with limited control authority. It takes a very large amount of wing to generate the same forces that a flapped section of wing can generate. You can only rotate the wing tip control about 10 degrees before it stalls for a max Cl of about 1.5 - to get that with a flapped control surface is quite easy. There are pluses to having an all-flying wing tip (i.e. never have a tip stall and hence no spin), but to achieve that requires a lot of weight and complexity - simply a bad trade.
If the hinge lines are not the same then there has to be a mechanical means to get around the winglet - a messy and heavy solution. Not desirable as a permanent solution. Plus the dihedral causes issues. Better to get rid of the dihedral and stick with a straight hinge line.
Bummer, don't lose your enthusiasm. For what it is worth, I have all flying elevons on my 1.6m model. Control throws are half, with enough authority to roll 360deg.
Hi Don, thanks for the kind words of support. I assure everyone that I'll stick with this until she flies better than any glider out there. You model experience seems just like mine, that laminar flow really helps to keep the air attached to the elevons.
This is where we learn the most, Rol. Keep up the posts and the good work.
A quick fix to increase control authority might be to add a trailing edge fence to the end of the elevon, above and below the trailing edge, to stop flow leaking around the gap by the rudder, might need to rebalance the surface. I agree, VGs might be needed the length of the elevon, that might be the first thing to try. Not having a moving surface at the tip makes it harder to have good roll control. A compromise might be to lengthen the elevon, move the rudder further outboard, and add fixed leading-edge slots toward the tip, helping to prevent tip stall. My two cents. Great work, looking forward to further progress. PS- try using a lapel mike with a remote transmitter, the audio from the camera is a little hard to hear.
All interesting comments with various pluses and minuses. Most any solution including many not mentioned here, end up generating extra drag at higher speeds (unless one can turn the solution on/off). Flying wings don't tolerate adding drag as they can't achieve very high lift. Of course what good is high L/D when you can't control the aircraft, right? Anyway, Xflr says a 3 ft spanwise extension should solve the problem and that won't add hardly any drag. BTW, my camera that accepts my cordless mic, broke recently. I filmed this with a Go-Pro, oh well. No budget for a new camera - need funds to mod the glider.
If you are thinking about not only adding elevon to the wing tips but also increasing washout, you could also consider adding turbulator to the area that's affected by the transition bubble instead. With turbulators I mean tiny holes on the wing surface that open when the pressure difference between upper and lower wing surface exceeds a certain level. The holes blow air out before the transition point and help reduce the bubble. At high speed the holes create less additional drag than if you increase the washout.
Other solutions that might help
1) Vortex generators on the both the top and underside of the wing ahead of elevons to delay flow separation on both extremes of control deflection.
2) Couple the inboard flag to pitch and roll control, this will help reduce the control deflections required on the elevaons and widen the range of linear control as well as the peak roll/pitch moments that are possible.
3) As a temporary measure, add an inch or two to the trailing edge of the elevons to increase their area.
Hi Robert: All good points, although given the wing's design, the flaps are arranged to cause pitching moments in reverse of the elevons, so they can't be coupled effectively. My current plan is to put temporary elevons on the trailing edge of the wing tip panels (outboard of the winglets) along their entire span. Xflr says that should give me plenty of control. If it works, then I make the major mods to the tip panel structure. Keep an eye our for more vids, I expect to test the extensions in one to three weeks.
@@KlingbergWingMkII My thought was that flaps + elevon mixing would be done in such a way as to couple pitch, roll and yaw in mutually supportive way. i.e.
Stick forward : elevons down, flaps up
Stuck back : elevons up, flaps down
Stick left : left elevons and left flap up, right elevons and right flap down
Stick right : left elevons and left flap down, right elevons and right flap up
In the stick back motion you effectively increase washout which is helpful for avoiding tip stalls/spins, improving roll/yaw coupling (takes you nearer to horten wing loading).
You can partly achieve this by manually adjusting the flaps in your present configuration, but who has the skill level to be doing that near the ground at take off and landing.
Another advantage of the coupling the flaps to the stick is you can changes in the overall CL of the whole wing without needing to pitch nose up/down. If you want to dump lift when standing at launch the quickest way is to move up the flaps as this dumps lift without any rotation of the wing nose down, and visa versa.
This would allow much finer control of launch as you aren't having to fight against angular momentum, you movement in the stick directly changes the CL of the wing for a fixed angle of attack.
This finer CL control also works well in flight and on landing.
Such a coupled system would be more sensitive in pitch and roll so you'd likely need to dial down the sensitivity, especially in pitch.
The traditional flaps control would become a trim position control that the stick adds input to.
Getting it all to mix on electronic controlled surfaces would be easy, far more of challenge with purely mechanical system, but as you already have elevon mixing system, I'm thinking it would be just adding to this in a novel way.
What if... you eliminated the elevons on the main wing and made the outer wing panels pivot; making them 'wingerons / pitcherons'?
That is what I did on the very first model - didn't work at all. I didn't know it at the time, but the British put that type of control on a flying wing back in the 50s - didn't workout well for them either. Control forces are low and you need a massive bearing to take all the pending loads and still allow for the pivot motion - so a very heavy solution - nothing good about it.
@@KlingbergWingMkII I figured the weight would be an issue. When you say didn't work at all, do you mean there was lack of control authority? If so, that makes me curious as to why. It works so well in my mental wind tunnel, LOL!
Yes, and I think the Brits had an issue with limited control authority. It takes a very large amount of wing to generate the same forces that a flapped section of wing can generate. You can only rotate the wing tip control about 10 degrees before it stalls for a max Cl of about 1.5 - to get that with a flapped control surface is quite easy. There are pluses to having an all-flying wing tip (i.e. never have a tip stall and hence no spin), but to achieve that requires a lot of weight and complexity - simply a bad trade.
Would it be an option to make a twin element elevon of the same area as the current setup?
What do you mean by a "twin element" elevon. That's not a std eng term, so I can't answer accurately
A flap attached to the trailing edge of the elevon.
If the hinge lines are not the same then there has to be a mechanical means to get around the winglet - a messy and heavy solution. Not desirable as a permanent solution. Plus the dihedral causes issues. Better to get rid of the dihedral and stick with a straight hinge line.
Bummer, don't lose your enthusiasm. For what it is worth, I have all flying elevons on my 1.6m model. Control throws are half, with enough authority to roll 360deg.
Hi Don, thanks for the kind words of support. I assure everyone that I'll stick with this until she flies better than any glider out there. You model experience seems just like mine, that laminar flow really helps to keep the air attached to the elevons.