Scratch built Carbon Butterfly, 3 channels - RC Groups
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Jul 09, 2007, 09:46 AM
Wanton construction
Pouncer's Avatar
Build Log

Scratch built Carbon Butterfly, 3 channels


I'm scratch-building a Carbon Butterfly and I'm adding elevator, and maybe a wing..

I found some thick, clear plastic tubing which I used to make the connectors, I'll let the pictures tell the story.

I'll post more as I come along!

I'd also like to remind of the Carbon Butterfly repair, maintenance and mods thread.
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Jul 09, 2007, 11:57 AM
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jas_Qfix's Avatar
Nice ideas.
Jul 09, 2007, 04:56 PM
Plantraco's Avatar
That's looking fine!
Jul 09, 2007, 07:44 PM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by Plantraco
That's looking fine!
Whew!
I was worried you might sue for copyright infrigement!
Jul 09, 2007, 08:41 PM
Plantraco's Avatar
Quote:
Originally Posted by Pouncer
Whew!
I was worried you might sue for copyright infrigement!

Haha, no never - I think it's cool that you can do it.

There was another guy from Singapore who was able to scratch build the Butterfly too. It's great to see.

Maybe you'll discover something new by building such an airframe and for sure it helps potential customers realize why the replacment airframes alone can cost a lot.

I'd like to see how the 3CH part works out for you. You might find that if you are doing it as a 3CH that it might be beneficial to modify the geometry a bit to allow the elevator to have some effect. When we experimented with it, we found that elevator was useless on the existing airframe, and to use elevator properly would probably need some redesign. I'm fairly sure it can work out with some mods though.

Good luck and thanks for posting pictures.
Jul 10, 2007, 06:13 AM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by Plantraco
I'd like to see how the 3CH part works out for you. You might find that if you are doing it as a 3CH that it might be beneficial to modify the geometry a bit to allow the elevator to have some effect. When we experimented with it, we found that elevator was useless on the existing airframe, and to use elevator properly would probably need some redesign. I'm fairly sure it can work out with some mods though.
Okay, thanks for the heads up.
I was thinking of doing something like this but you say you made one like that and it didn't work very well?

The only aerodynamic pecularity I can think of is that the down-wash from the wing hits the elevator, which come to think of it is probably why the CB can handle a wide range of wing incidence.
So at low wing incidence (great fun actually, a CB can match an AA for speed!) the elevator is in clear(-ish) airstream, and at high wing incidence which usually provokes a nose-down moment, the elevator is hit by down-wash and keeps the nose up.

As I have made provisions for adding a second wing I have intended for the top wing to sit approx. 18mm higher up from the main spar.
We'll see if this helps in keeping the elevator out of the down wash.
Jul 13, 2007, 01:10 PM
Wanton construction
Pouncer's Avatar
Ok, I'm getting there!
Lots of little odds and bits that need adjusting but I maidened!

Test flew it and like Bud predicted I had little elevator authority. Some, but not enough to pull it into a climb steeper than say 10 deg.

Several things come into play I think: in the original layout the elevator is really close to the CoG, giving little moment arm, and the HingeAct lacks the oomph to move the surface, at least in flight.

So I could move the whole shebang (receiver and wing) forwards to remedy the first problem and make aerodynamically compensated surface for the second.

On with the pics:
Jul 13, 2007, 01:37 PM
Plantraco's Avatar
Yep, my personal feeling is that if you choke up on the fuselage stick, you'll give the elevator a shorter lever arm to rotate the model around the CG in flight. ie: move tail forward like you did and that elevator might have more authority.

You might need less downthrust, and less wing incidence. Just a guess. You are making it more like a low winger. Also could try some tricks to give the elevator some extra jam - mass balancers around the actuator hinge line.
Jul 13, 2007, 02:02 PM
is it supposed to smoke??
3dFlyer88's Avatar
wow thats a sharp looking model. where did u get the carbon from?
Jul 13, 2007, 04:47 PM
Wanton construction
Pouncer's Avatar
Quote:
Originally Posted by Plantraco
Yep, my personal feeling is that if you choke up on the fuselage stick, you'll give the elevator a shorter lever arm to rotate the model around the CG in flight. ie: move tail forward like you did and that elevator might have more authority.

You might need less downthrust, and less wing incidence. Just a guess. You are making it more like a low winger. Also could try some tricks to give the elevator some extra jam - mass balancers around the actuator hinge line.
Added aerodynamic balancers and that made a huge difference!
I now have good elevator authority.
It's just a quick fix and made the CB more tailheavy than I can compensate for so I'll need to rebuild one lighter.
Also I found that maybe Blenderm add too much friction? I cut three really thin slices but I still feel it should move more freely.
I'll try cellophane next.

But now I'll need some rest, been at it for the better part of the last 24 hours..

3dFlyer: I got my carbon rods from www.indoorflyer.co.uk, it's run by Epilot here on rcgroups.
Jul 13, 2007, 05:12 PM
Plantraco's Avatar
Keep the blenderm, I'd say. Give it a stretch and that blenderm hinge will be limp like spaghetti.

If anything, I would have thought you'd want a stiffer hinge, and lay the hinge material down on the top side - with the intention of holding the elevator closer to neutral position without any input from the receiver. That tape on top will give it some pull. If it's limp, I fear that the elevator will droop.

Or you could adjust the trimmer wheels I guess, and give the model some "up" all the time to hold the elevator where you need it to be. You'll know what's best with the model in front of you I think.



ALSO - just an idea, but if you are still tail heavy, you could choke up the stick even more! move the tail way too far forward - that'll affect your CG bigtime.
Jul 14, 2007, 07:29 PM
Wanton construction
Pouncer's Avatar
Made a new elevator, the tips were to heavy even after lightening and had a tendency to overcompensate, i.e. it'd lock in a full up or full down position. At this scale and with so little force coming from the actuator the elevator needs to be both mass balanced and aerodynamically balanced.
I think I may have the latter right, a few drops of glue should correct the first.

To do list:

Increase elevator moment arm by pushing the main wing posts forward, and repositioning Rx+Battery in front of foremost post to hopefully maintain CoG (this is LAR engineering..)

Make a second wing and reduce flying speed.

Exchange motor, at least I hope it's the motor and not the ESC as I can get only about 1/3 full throttle

Question: is it OK to use CA debonder on the Rx?
Jul 14, 2007, 07:38 PM
Plantraco's Avatar
Sure you can use debonder on the Rx I guess.


BTW - that elevator looks pretty big - test if the actuator can lift the elevator on the bench. In the air it could actually be different, but I'd test to see if it can move it.
Jul 15, 2007, 08:16 PM
Wanton construction
Pouncer's Avatar
Another day of tribulations.

I added CF spurs to the elevator to mass balance it, seems to work, although there's more inertia involved now. Will probably have to make a third try from scratch.

Found that the rudder lacked authority so lowered the wing as far as I could and that helped (less pendulum stability), but I suspect that the motor being so far in front is the real problem.
So I have a working set-up, but alas my living room is to small for it, so the quest continues.

In order to lower the speed I then added a second wing but I was back to ineffectual rudder.
Everything points towards moving wings and receiver towards the nose of the plane, a prospect I don't relish as it entails ungluing several CA'd joints.

Oh well, it's rainy and windy outside anyway..
Jul 17, 2007, 01:57 PM
Wanton construction
Pouncer's Avatar
Latest mod:

Moved the wings 12mm ahead and repositioned the Rx in front of post.
Looks more harmonious now.

Sounds simple but unsticking a superthin PCB superglued to a carbon rod is not recomended. Debonder won't make cyanoacrylate disappear, it just softens it a bit, in the end I had to use single edge razorblades and wedge them in between.

No flight testing as of yet as I'm trying to get the receiver back online, it's acting in a very intermittent way, sometimes I'll get the start-up chime, sometimes it's silent, it can't find the Tx signal except in about maybe one attempt out of 30, when I stick the battery on just so.
Checked the actuator solderings to see if I had a bare wire short, cleaned to pcb several time with lukewarm water and also acetone, which seems to improve things a little bit every time.
Note: it was acting this way even before I started building this CB, very picky when it comes to battery connection which is why I'm not panicking just yet.


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