Congrats on getting it to work.
Some ideas about the roll issues.
A model that small in span is going to roll easily. Especially when it takes off, if you are using a rod, then rod whip will make it roll most of the time. I found this out really early when I was trying to do my first “big” R/C shuttle, when the model rolled on liftoff due to the 1/4” rod whipping, and the roll was too fast for me to try to correct it.
So, I went to a rail launcher instead of a rod, and that solved the liftoff-induced roll problem. It was still sensitive to rolling after liftoff, but at least it got off to a good start.
BTW - most rail buttons meant for HPR have too much friction for “small models”. My favorite lug for rails is to use plastic “H-Beam”, as from Plastruct or Evergreen. 3/8” Plastruct H beam works for most rails with a 1/4” gap. It is a very loose fit, so it slides super-easy with minimal friction
I am a bit surprised you did not do any D7 boosts first? I know you know, but for those who do not know, a D7 reload has exactly the same thrust curve as an E6 at first, but burns for only about 3 seconds rather than 7-8 seconds.
Going back to my R/C shuttle stuff, the first 1/72 orbiter I did, it had maybe 1/8” up and 1/8” down throw in aileron. That turned out to be way too much. After boost, when it went into a glide and I started to turn it, it did a complete 360 degree roll in response to the aileron input. I let go of the aileron stick and just let the orbiter glide free-flight for the rest of the flight, not daring to try to turn it anymore. I made adjustments to reduce the throw REALLY small, something like 1/32” up and 1/32” down for the aileron throw (for elevator it was a LO more, of course). And even that total of 1/16” was sort of a lot as far as how responsive the orbiter was on roll.
What amount of aileron throw do you have on it now? For boost? On nearly all of my R/C RBG’s, I use low rates for boost, so the control surfaces do not move as much for the high speed boost phase as they later do for glide phase. If the model is roll sensitive in glide too, and not just boost, then perhaps you first need to reduce the total aileron throw to begin with. And then whatever the result of that is, reduce the throw more for the boost phase such as using low rates.
The only problem would be if you reduced the throw to such a small amount that if the model was not trimmed correctly, and wanted to roll say to the left, that you did not have enough aileron throw to make it turn to the right to maintain control (and for the aileron trim lever to have enough authority to correct it during the glide down on that flight.
Once you get things sorted out, you ought to be able to nail down the aileron trim for the boost phase, so that if you get good clean liftoff from a rail launcher, the model should not try to roll (much) in any particular direction, since you would have that roll trim worked out. Once you get that boost roll worked out, then do not mess with it. Even if during glide it may want to say pull to the right, because if you gave left trim to make it glide straight, you’d end up causing it to roll to the left on boost. The most likely scenario to cause a model to pull to one side in glide after it is trimmed not to roll on boost would be to have one wing heavier than the other. Well, on a conventional model, it would be the wing weight, right wing heavier than left wing, for example. On this model, being molded like it is, in theory it should be perfectly balanced laterally. But as-built, something might have creeped in to add an extra gram or two to one “wingtip”. Of course on this model the “wingtip” also includes the twin tailbooms, control surfaces, servos, wires, and the graphite reinforcements you added. If one side is a bit heavier than the other, then the fix usually is to add weight to the “light side” so it will balance equally laterally.
If I was doing this, an extra concern I would have would be to tell top from bottom visually on a bad boost. On a shuttle orbiter it is easy, since the orbiter is black on the bottom and white on top. And on my non-scale R/C models, I usually have different colors on top and bottom. For the 2X R/C SkyDart, I cheated a little bit, I added dark blue trim monokote to the outer 1/3 of the bottom of the wings. So if I was doing an SS-1 R/C, I’d probably make the bottom of the wings black so I could tell which side was up (or down) if things got bad.
- George Gassaway
