EZ 3chMicro Twin SR-71 Profile Build

[Vimana89]

I've got two of the FT EZ 3ch micro twin power packs on the way, and 10 sheets of black foam board. The ESC has a built in stability function, and the whole setup is light, so I'm thinking a profile SR-71 might actually fly nice with this setup, with maybe a 14" or so wingspan. It wouldn't be fast, and wouldn't axial roll, but if could still be fun. The build would be one sheet of normal thickness 5ish mm foam, no double layers anywhere, straight profile everything(including engine nacelles).

I think the profile version will be light, low drag, and the nacelles and vertical parts of the fuselage will act as additional vertical stabilizers. The lack of a need to have a prop in slot is nice for wing area/lift and for durability, not to mention a bit more scale look. Again, the 3ch, twin engine setup comes with the drawback of no axial rolls, but that's with anything using that particular power pack. The stability function is a big bonus, and the pack is cheap, convenient, and really simple and straight-forward, so its a trade-off.

The goal is a light, simple, and clean as possible design and build, taking away all the mystique and complication of the plane and just taking a practical approach to making it fly. I'm not expecting aerobatics, but it should be able to cruise around smoothly with no nasty stall features, wing rock, or poor handling qualities. That's basically the gist of it as far as my design theory and brainstorming.

I know people generally tend to have trouble making SR-71 RC models, at least with foam board. I also know that not only is the SR-71 a legendary icon, a sought after RC, and a challenging design to work with, but it has personal significance to at least one or two members on the forum(@PoorManRC , I'm lookin' at you). It has some personal significance to me as my dad saw the last flight at Edwards in 1999.

I can't promise my micro version will be a success, but it's worth a try to find out, and would be super cool if it worked. I just wanted to make this thread and share the process, even if it doesn't end up successful.

 

[Vimana89]

Rough Sketch(not completely to scale)

 

[Vimana89]

Reserved

 

[Vimana89]

Reserved

 

[Vimana89]

Reserved

 

[Vimana89]

Reserved

 

[flamingo]

what?

 

[Vimana89]

what?

I'm going to build a micro SR-71 with the FT EZ 3ch power pack, when I receive the two I've got coming in the mail. The spots are reserved for things like build log and flight footage. Not sure what isn't clear about that in my post...

 

[flamingo]

I'm going to build a micro SR-71 with the FT EZ 3ch power pack, when I receive the two I've got coming in the mail. The spots are reserved for things like build log and flight footage. Not sure what isn't clear about that in my post...

oh

 

[L Edge]

How are you handling yaw?
With the long nose, you need to look at rigity of the nose(it will fold by itself) turns and possible stalling out.
Main issue will be pitch.

 

[Vimana89]

How are you handling yaw?
With the long nose, you need to look at rigity of the nose(it will fold by itself) turns and possible stalling out.
Main issue will be pitch.

The flight controls is the FT EZ 3ch system with twin micro engines, thrust differential, one micro servo for a proper elevator(which will be good for pitch, better than their old 2ch pack that used throttle for pitch) and an ESC with a built in stabilizer. It will be a somewhat limited system, but should be able to fly like any of the other planes that use it if I build light.

The two props should turn the plane well enough like with any other build using the same power pack, but if not for some reason, I can always add a tiny bit of dihedral to the wing tips to couple the roll and yaw more.

I can use a couple of bamboo skewers with the points trimmed off as a spar going down the middle of the plane, from the tip of the nose up to right before the elevator, to make sure the nose wont fold during flight or normal landings. It should add a lot of rigidity but not much weight.

If the build doesn't work out, no big deal, there's plenty of other things to try, I've got two of the EZ 3ch power packs and larger motors coming soon in the mail.

 

[Vimana89]

I did a quick and rough sketch of the layout/parts of the build, It's up on the first reserved post. The main alterations from scale(besides being a profile plane) will be the the large, single elevator, and the engine nacelles, which I've simplified the front ends to more of an aerodynamic torpedo shape rather than making it look like shock cones and intakes, which is more time consuming and draggier.

The top profile pieces of the nacelles actually flow right into the vertical stabilizers, as they are the same piece, sort of acting as an extended fin for the vertical stabilization. I'll crack and glue the stabilizers inward at the correct angle for the scale look.

I should be getting the electronics by tomorrow, but the black foam board will probably not be here until Thursday, so I will most likely do a different project with the other EZ 3ch pack first, and then do this one when the black foam comes in and I've cut my teeth on a more basic build with the power pack.

 

[Timmy]

This'll be cool to see in action

 

[Vimana89]

What I'm debating is if I should use the pusher configuration, since I can switch the props and the EZ 3ch pack can be used in a tractor configuration, such as the Sponz EZ intruder. The pushers look cooler and a bit more scale, but the tractors will make CG even easier, although I still think it would be doable with pushers because of the long nose

 

[Timmy]

What I'm debating is if I should use the pusher configuration, since I can switch the props and the EZ 3ch pack can be used in a tractor configuration, such as the Sponz EZ intruder. The pushers look cooler and a bit more scale, but the tractors will make CG even easier, although I still think it would be doable with pushers because of the long nose

pusher!

 

[Vimana89]

pusher!

Probably what I'm going to go with unless anyone can convince me otherwise.

 

[L Edge]

The flight controls is the FT EZ 3ch system with twin micro engines, thrust differential, one micro servo for a proper elevator(which will be good for pitch, better than their old 2ch pack that used throttle for pitch) and an ESC with a built in stabilizer. It will be a somewhat limited system, but should be able to fly like any of the other planes that use it if I build light.

The two props should turn the plane well enough like with any other build using the same power pack, but if not for some reason, I can always add a tiny bit of dihedral to the wing tips to couple the roll and yaw more.

I can use a couple of bamboo skewers with the points trimmed off as a spar going down the middle of the plane, from the tip of the nose up to right before the elevator, to make sure the nose wont fold during flight or normal landings. It should add a lot of rigidity but not much weight.

If the build doesn't work out, no big deal, there's plenty of other things to try, I've got two of the EZ 3ch power packs and larger motors coming soon in the mail.

How are you rolling the plane? Are you saying the ESC with a built in stabilizer has aileron control? Can you show your sketch?

 

[Timmy]

He is using differential thrust as rudder I think.

 

[Vimana89]

How are you rolling the plane? Are you saying the ESC with a built in stabilizer has aileron control? Can you show your sketch?

Sketch is up top on one of the reserve posts, just a rough sketch. There are no ailerons and I don't intend to do full axial rolls, the FT EZ 3ch pack isn't set up for that, it's just twin engines with differential thrust and an elevator servo, so I'll have to do without full roll capability. How will the plane turn? I'll have to use a bit of dihedral on the wing tips to couple roll and yaw. I've watched some videos and the FT planes that use this pack have at least a tiny bit of dihedral.

 

[L Edge]

Sketch is up top on one of the reserve posts, just a rough sketch. There are no ailerons and I don't intend to do full axial rolls, the FT EZ 3ch pack isn't set up for that, it's just twin engines with differential thrust and an elevator servo, so I'll have to do without full roll capability. How will the plane turn? I'll have to use a bit of dihedral on the wing tips to couple roll and yaw. I've watched some videos and the FT planes that use this pack have at least a tiny bit of dihedral.

2 Motors shut down in flight(worst case, 1 dies in flight). Explain how you fly it?