Help! Setting up Split Control Surfaces for Elevon/Spoileron Control (F-117 Design)

[Aero_Knight]

So the custom build I have is for an F-117 I am calling the FliteHawk. The way it is built, allows for an upper and lower control surface on the wings. To keep it simple I could just make it a 2 moving surfaces that is mixed for elevon control with just 2 9g servos. The TX has built in options for it like most TX. However, I would like to make it more interesting by adding spoileron functions similar to a flying wing because the design I did is essentially a stupidly short wing pretending to be a delta. I think I absolutely need 4 servos for this to work but I am not sure how to set up the mixing and coupling properly without a micro-controller providing the control algorithms.

Normally the servos on each wing would operate opposite of each other when used only as ailerons. Once elevator coupling is introduced they would provide the proper pitch deflection at the same time as roll control (Shown in the image below). Easily done by using a 2 channel setup with the TX option I have. For rudder control, spoiler/air braking is needed with the servos controlling the top surface and bottom surfaces opposing each other while providing the appropriate roll and pitch control. I don't think I can manipulate the 2 extra servos in that manner with the TX...or can I? I have never manually created a custom mix setup on my TX so it is new to me. I feel like I may require use of my arduino LOL

My Transmitter: Futaba T6EXP 6-Channel (Modded to support FrSky 2.4Ghz TX)

 

[pressalltheknobs]

I don't know anything about that Transmitter so I don't know if it is possible but...making it up as I go I think something like this is what you want...

Obviously you start with a delta/elevon mix and see how that works with the splitters. This uses, say CH1 and CH2

If you want the top and bottom control surfaces to act independently you will need separate servo control. So remove the splitters and plug the two top servos into two additional channels, say CH5 and CH6

Now you have to understand what your elevon mix does

standard elevon mix...
CH1 Ele +50% Ail -50%
CH2 Ele +50% Ail +50%

You may need to reverse servo directions to get it to work right

And reproduce that for the CH5 and CH6 two servos. Essentially you will have dual elevon mixes that work in tandem.

CH5 Ele +50% Ail -50%
CH6 Ele +50% Ail +50%

You may need to reverse servo directions to get it to work the same.

To have the top work as a rudder you need a Y tail mix so you to mix in some rudder to the CH5-CH6 elevon mix. This should work in the same direction to the ail control

CH5 Ele +50% Ail -50% Rud -50%
CH6 Ele +50% Ail +50% Rud +50%

You may want an additional control that has top and bottom working is opposition...In gliders this is called crow but I don't really know what it is used for... Slowing down I guess

For that you will probably need switchable mixes or flight modes depending on the situation it is used in but let's start withe the above and see if it is even close to what you are talking about.

Note: I use OpenTX on FrSky TXs so all the above is easy because you essentially mix controls not channels (although you can). That may not be the case on other systems and you may need to put in mixes to undo what they do in order to do what you want to do

 

[Aero_Knight]

I don't know anything about that Transmitter so I don't know if it is possible but...making it up as I go I think something like this is what you want...

Obviously you start with a delta/elevon mix and see how that works with the splitters. This uses, say CH1 and CH2

If you want the top and bottom control surfaces to act independently you will need separate servo control. So remove the splitters and plug the two top servos into two additional channels, say CH5 and CH6

Now you have to understand what your elevon mix does

standard elevon mix...
CH1 Ele +50% Ail -50%
CH2 Ele +50% Ail +50%

You may need to reverse servo directions to get it to work right

And reproduce that for the CH5 and CH6 two servos. Essentially you will have dual elevon mixes that work in tandem.

CH5 Ele +50% Ail -50%
CH6 Ele +50% Ail +50%

You may need to reverse servo directions to get it to work the same.

To have the top work as a rudder you need a Y tail mix so you to mix in some rudder to the CH5-CH6 elevon mix. This should work in the same direction to the ail control

CH5 Ele +50% Ail -50% Rud -50%
CH6 Ele +50% Ail +50% Rud +50%

You may want an additional control that has top and bottom working is opposition...In gliders this is called crow but I don't really know what it is used for... Slowing down I guess

For that you will probably need switchable mixes or flight modes depending on the situation it is used in but let's start withe the above and see if it is even close to what you are talking about.

Note: I use OpenTX on FrSky TXs so all the above is easy because you essentially mix controls not channels (although you can). That may not be the case on other systems and you may need to put in mixes to undo what they do in order to do what you want to do

I think I can see what you are explaining. I will just need to make sure I get the appropriate responses after mixing. The TX I have is not the most user friendly as its more than 10 years old. No pretty LCD menus LOL. I will post my test results later. Thanks for the input!

 

[Aero_Knight]

So bad news, my TX is just a few features short of allowing this to work without either a micro controller or new TX. It doesn't allow me to customize specific channels nor will it let me mix three surface simultaneously for two different sides of the control. I think the design at least on my plate will be limited to elavon control. Yaw control will be left to someone with a more capable TX. I will leave the potential in the finalized plans just in case. Thanks for all the help though!

 

[Hai-Lee]

If your transmitter is limited in its ability to support mixws I may be able to advise on a mechanical solution to give the required control surface movements. Before there was control surface mixing there was a mechanical solution for elevons where the servos were tray mounte. The tray position was controlled by the elevator servo and the aileron servo was directly connected to each control surface. It worked well back then and still works today!

Just a thought!

have fun!

 

[Aero_Knight]

If your transmitter is limited in its ability to support mixws I may be able to advise on a mechanical solution to give the required control surface movements. Before there was control surface mixing there was a mechanical solution for elevons where the servos were tray mounte. The tray position was controlled by the elevator servo and the aileron servo was directly connected to each control surface. It worked well back then and still works today!

Just a thought!

have fun!

If I ever make a 200% version of my build and haven't gotten a new TX by then, this sounds like a great idea. Actually...I just got a dumb idea based on your explanation. Ill see if I can CAD it up tomorrow.

 

[Hai-Lee]

If I ever make a 200% version of my build and haven't gotten a new TX by then, this sounds like a great idea. Actually...I just got a dumb idea based on your explanation. Ill see if I can CAD it up tomorrow.

From my own quick thoughts if you used a single servo for ailerons and elevator in each wing, (standard elevon mix). you could split the control surfaces using a special servo output arm to give a Pull/Pull output to the control surfaces from the servo centred position.

If you wish to split the control surfaces for a "DRAG" rudder operation you could just move the servo away from the control surfaces causing the pushrods to pull on both control surfaces thereby splitting the control surfaces in opposite directions.

The flaps could be either mechanically done or even by a second mix of elevator and flaps.

If you are stuck for the basic idea of the servo horn shape just let me know and I will see if I can rough up a design for you to play with!

Have fun!

 

[pressalltheknobs]

So bad news, my TX is just a few features short of allowing this to work without either a micro controller or new TX. It doesn't allow me to customize specific channels nor will it let me mix three surface simultaneously for two different sides of the control. I think the design at least on my plate will be limited to elavon control. Yaw control will be left to someone with a more capable TX. I will leave the potential in the finalized plans just in case. Thanks for all the help though!

That's a shame. I was looking forward to seeing how well it worked.

Since you are already using FrSky RXs, you might consider getting a FrSky Q-X7 or one of the other FrSky TXs. Q-X7s are only ~$120 US plus battery pack and optionally a charger and an SD card....They all supports VII, D8 and D16 RXs out of the box. For the EU version you may have to flash OpenTX to get VII and D8. For VI RX support you would need an external DFT module. The flexibility OpenTX provides is great for builders.

 

[Aero_Knight]

So I came up with this dumb idea. Forward servo controls top and bottom surfaces with elavon mixing which would give pitch and roll. The rear servo would push the rods apart spreading the surfaces apart and provide the yaw control from the rudder channel. The push rods would just sit on the rear servo linkages if the tension is too much being run through them. The images are extremely exaggerated as the rear servo range would need to be tiny as to not damage the push rods but I think with some tweaks this would work!

 

[pressalltheknobs]

Interesting idea but the front servo seems problematic to me. Presumably "DOWN" means the top "elevon" is "FLAT" and the bottom elevon is "DOWN". "UP" means the top "elevon" is "UP" and the bottom elevon is "FLAT". The push rods move both top and bottom surfaces in tandem so how will they ever be both "FLAT" in plain elevon use? You might be able to do something with a spring to hold them together when FLAT so the front servo forces them apart to when moving UP and DOWN...(EDIT: Perhaps a spring on the end of the control rod where the control rod extends though the spring once the surface lays flat. However the lack of fixed connection migh make the control surface unstable. Some kind of latch that unlatches when the surface is flat might address that. )

The back servo could act dynamically I suppose but that will be hard without automatic mixing.

 

[Aero_Knight]

Interesting idea but the front servo seems problematic to me. Presumably "DOWN" means the top "elevon" is "FLAT" and the bottom elevon is "DOWN". "UP" means the top "elevon" is "UP" and the bottom elevon is "FLAT". The push rods move both top and bottom surfaces in tandem so how will they ever be both "FLAT" in plain elevon use? You might be able to do something with a spring to hold them together when FLAT so the front servo forces them apart to when moving UP and DOWN

The back servo could act dynamically I suppose but that will be hard without automatic mixing.

When there is no rudder the surfaces should be acting in tandem so the rods need to be stiff to keep them together essentially acting as a really thick control surface. Introducing the "spreader" should only adjust the surface split angle. The forward servo would move both surfaces at fairly similar rates maintaining the split angle which may be adjusted with mixing depending on what I want to be the master control, pitch or roll. I do think some sort of tension strap or something with a rubber band to keep the setup stiff is needed. I think the problems will reveal themselves after I try the setup on my prototype plane.

 

[pressalltheknobs]

yes I get that. I just don't see how the front servo will allow the surfaces act as elevons because it fixes the gap between the top and bottom surface. How do they come together for level flight?

 

[Aero_Knight]

yes I get that. I just don't see how the front servo will allow the surfaces act as elevons because it fixes the gap between the top and bottom surface. How do they come together for level flight?

The servo when at the neutral position will be like the first image except the rear servo arms won't be touching the push rods which should force both surfaces "flat" from the rods stiffness forcing it into position. If they are mechanically fixed by the rods they can't spread apart from that position until the rear servo does anything to apply force to spread them, especially if a force like your spring idea or my banding is put in. IAs long as no rudder input is used they should never spread apart and when pitch and roll inputs are released the neutral should look similar to the top image. Is my interpretation of an elavon not correct? I am not trying to make it like a flaperon. Actually, what would you call a surface that takes elevator, aileron, and rudder inputs...Ailevudders? Railevators...Elavoners...Spoilerons...Spoilevons...idk?

 

[pressalltheknobs]

What I may be missing is whether the lower control surface can move above the wing and the upper control surface can move below the wing. I was assuming not from your original pictures of the plane ...but from what you say it seems that is not the case.

If the two move as a single control surface and both can move above and below the wing then, yes they could function as standard elevons...a mix of elevator and ailerons. I still think it may be a challenge to keep them together but possible the second "rudder" servo can do that by moving the control rod "guides" closer together provided the control rods were stiff enough. When you apply rudder the servo would move the "guides" further apart. That could work.

As to what the combination should be called, I'm not sure. They don't really act as a rudder in the conventional sense. On gliders this one up one down arrangement is call "crow" or butterfly and is for braking as I mentioned so possibly they are Crowing Elevons (which could be a band name) or Butterfly Elevons...except the purpose is a bit different here.

 

[Aero_Knight]

What I may be missing is whether the lower control surface can move above the wing and the upper control surface can move below the wing. I was assuming not from your original pictures of the plane ...but from what you say it seems that is not the case.

If the two move as a single control surface and both can move above and below the wing then, yes they could function as standard elevons...a mix of elevator and ailerons. I still think it may be a challenge to keep them together but possible the second "rudder" servo can do that by moving the control rod "guides" closer together provided the control rods were stiff enough. When you apply rudder the servo would move the "guides" further apart. That could work.

As to what the combination should be called, I'm not sure. They don't really act as a rudder in the conventional sense. On gliders this one up one down arrangement is call "crow" or butterfly and is for braking as I mentioned so possibly they are Crowing Elevons (which could be a band name) or Butterfly Elevons...except the purpose is a bit different here.

Ya I wasn't clear on the movement range of the surfaces. The design is literally 2 pieces of foam on top of each other to make the base/wing of the aircraft. I might have to place a tiny spacer between them to prevent surface binding but they have a full range.

I think perhaps the name may be a question for a new thread somewhere. I don't think any real aircraft has something like these either. The B-2 has split spoilerons and other surfaces but they work more like what you were saying with one side not moving past "flat". Someone is sure to know the correct answer.

 

[Aero_Knight]

Reddit will know the answer LOL

 

[Hai-Lee]

If you go for separate top and bottom control surfaces you could use a setup similar to the one mentioned in a previous post which I have illustrated roughly below.

Have fun!

 

[Aero_Knight]

If you go for separate top and bottom control surfaces you could use a setup similar to the one mentioned in a previous post which I have illustrated roughly below.

View attachment 115576

Have fun!

I think this would be more efficient although it may need more hardware. Might be perfect for a larger scale than what I have though. You may also need some light force springs in the arm slots as well to prevent the surface oscillating if the air flow is turbulent when the arm puts no force on the rod.

 

[Hai-Lee]

I think this would be more efficient although it may need more hardware. Might be perfect for a larger scale than what I have though. You may also need some light force springs in the arm slots as well to prevent the surface oscillating if the air flow is turbulent when the arm puts no force on the rod.

Normally you would use either a spring or even a small rubber band to provide a force to hold the surface closed. This has the added bonus of removing all pushrod flex. FYI wou would also need to consider the need for differential to balance any yaw component due to elevon operation, ( a reasonably minor component thankfully).

Have fun!