Okay, been trying to reach Tom all day, but I guess they didn't make it back to work from the holiday. Maybe he got too much turkey????

Anyway maybe he'll see this or some of you other guys can help out?

I've got the 28% ver 2 Extra and I've been fighting the right thrust setting. Long story short, if you use fender washers to spread out the pressure of standoffs on the engine firewall, measure 'em before you put them on!

I'd put this model together and got it all trimmed out and flying quite nicely, but experienced some engine issues so I had to pull it off to get to the carb. Turned out it wasn't the carb but when I put the thing back together and got it running again, it was outta trim bad. Did some uplines to get the rudder set and when I landed there was a substantial amout of right rudder set. I pulled the cowl and measured the offset; 1.5 degrees between the F-1 former and the engine's prop flange.

Pulled the engine off and measured the standoffs one at a time, they were all the same length and the fender washers fell before I could locate them. Measured the thickness of those and got one a .055, one at .066, one at .074 and the last one at .084.

Well obviously I just got lucky with the initial orientation as those kinds of differences can produce some significant angle changes, but when I measured the firewall itself against the F-1 former, it's only 1.5 degrees.

Now everything I've run across, and input from friends who play with IMAC birds says that 2.5 degrees is a good place to start on the right thrust engine offset. So I'm curious if the Bunnies are set at 1.5 degrees and are intended to fly with that setting, or are you guys using more right thrust. My inclination is to set it at 2.5 degrees but if someone's got a better idea I'd consider it as it is kind of a pain to keep pulling the engine off....[>:]

On my Sukhoi I have one washer for right thrust and a little down but not sure if there was any from the start sure there was though and Tom will chime in soon !!!

I put in what is needed to correct my issues with out a big concern for what is already in place

Still no Tom????

I appreciate the suggestions so far, but I'd also like to know what the firewall is set at by design to verify that I don't have a problem with that as well as to get Tom's perspective/experience on what works. Offset can be affected/determined by engine and prop size, so this is running a 50cc engine (no I'm not going to say which one) swinging a 22x8 Mejzlik at 7200 RPM for our altitude.

I realize it's very much a process of trial and error, but a 1 degree change in the offset is a HUGE difference. FWIY, I chickened out on the 2.5 degree offset based on the idea that there's no way it could have been that much to begin with as the difference in the washer thicknesses should only be able to change the offset by 1/2 degree in my experience. So I set it at 2 degrees of offset and put it back together.

I can still save myself some time/effort if someone's got some data on this? Flying days around this neck of the woods are getting scarce now until spring, so I'd like to make best use of what's availble for the next three or four months...

My thanks to all who've responded so far!

With the exception of the 35% Sukhoi, engine side thrust is built into the firewall at the factory. This is why the assembly instructions state to use equal length standoffs and to drill the mounting holes square to the firewall. Depending on how tight the firewall fit the manufacturing jig the thrust angles will fall between 1 and 2 degrees, with the majority at 1.5 degrees. Wood density and moisture levels effect the fit of the part to the jig.

I'm back now, got snowed in in Colorado for a day.

I really don't know the exact angle that's built into th eplane. I test fly it, if it feels like it needs more I tell the builder to change it x-amount. I think Pat's right, about 1.5 degrees or less. 2.5 seems like an awful lot.

I usually tell people to fly it as built and see what happens, if your flying style require more then add a very little bit at a time. It's way easier to make things worse than to get it just right.

TF

Hey Tom,

Glad you made it out okay, snow's not good stuff for you Texicans....

I wondered about the 2.5 degrees as that's what I'm seeing suggested for the 35% stuff as a starting place. I wish I'd been able to keep track of where the washers came off, but I did measure it at the engine flange vs. the F-1 former and the engine box and it was 1.5 degrees. I know that's not enough, but 2.5 seemed to be a lot so I settled on the 2.0 degrees and I'll go try that.

Thanks all!

I have the feeling that 2.5 degrees will have you flying hands off large vertical circles. If a 35 to 40% plane is set up relatively well about 1/2 to 1 degree is generally all the engine thrust angle desired. Note I didn't say needed. Many like a zero thrust angle to make it easier to balance out thrust in both up and down directions, power on and power off.

Try shimming the mpotor mounts using pieces of 1/64th ply until you achieve the offset you like. Just drill a center hole in a few pieces and cut the hole up and through one side so all you need to do is loosen a bolt to insert or remove a thrust "washer".

Hey Pat,

Thanks for the input. I'm still kind of new at this stuff so I'm trying to establish some baseline references. I know what I had at 1.5 wasn't good. The manual on my 2.6 Compy says start at 2.5 degrees and when out flying with someone you know who also does the sandbox thing, his new 2.6 Compy was at 2.5 and he felt like it needed another .25 but didn't have time to try it before he left again. In looking around I found out you cannot buy shim stock anymore (guess I'm giving away my age here...) so I've got some .020 A/C aluminum I can make shims out of and I hadn't thought about slotting them, just pulling the left side mounting hardware, but the slot thing is a most excellent idea!

Whether or not one wants to fight the issues with a more neutral offset is kind of a personal thing, I personally object to the thing turning left on uplines unless I ask it to or I can't figure out how to compensated for the X-wind because it's inverted....

I do know that after about 40 or so flights, I had this little puppy flying quite nicely thank you very much, and when I put the engine back on it the first reverse sharks tooth bit me in the butt. Of course my UAV buddie's first comment was "You got that thing trimmed?".

So now I get to go do some more "trimming"....

I hear ya. I have a hunch I know your UAV flying buddy. Say hi to Alan for me. Yea, you gave it up on the shim stock thing. Ya gotta watch the offsets in Compys. You're told you have "X" offset but you don't have squat to verify that against. The motor box pyramid and fuselage junction makes it tought to verify

Uh.... It's not Alan I was talking about but I do get a kick out of him and he's back to being a cop now.

I was referring to someone else you know, Raymond....

Glad to hear he's doing well. I was wondering what he's been up to. Is that the one and only "wrong altitude" Raymond?