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Old 11-14-2011 | 05:13 PM
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kenh3497's Avatar
kenh3497
 
Joined: Jan 2010
Posts: 1,517
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From: Rockwell, IA
Default RE: Incedence and thrust angles.....


ORIGINAL: BMatthews

For this sort of model just go 0-0-0 and then include 1.0 to 1.5 degrees of right thrust to aid in counteracting torque effects. It's an aerobatic model after all. If it needs too much up trim following the new ''first'' flight which results in too strong a nose up pitch with added power then it is a sign that your CG is too far forward. Shift it back, retrim the elevator trim to compensate and you should find that the power on to power off trim change reduces. Shift the balance back in small steps with associated elevator trim changes until the plane is as pitch neutral as you can tolerate. By that time the model should be quite neutral and snap roll and do other such things cleanly. The 0-0-0 initial setup is prep for working the CG back in this manner.

If you don't want it to be that hard core than with the wing as the reference go with -2/0/-1 for engine downthrust/wing/stabilizer angles. The wing in this case being always zero because you're using the wing as the reference line inorder to avoid shape induced oddities with the fuselage. With this would be included 1.5 to 2 degrees of right thrust. This sort of setup would produce a good sport flying model but is not a good setup for extreme aerobatics or precision aerobatics where you want to get nice straight up and down lines and such things. The plane with such a setup would also end up with the CG set to be a little pitch stable rather than pitch neutral.

For the CG locations for each use one of the online CG calculators (links in the sticky thread at the top of the listings) to find the Neutral Point location and CG's for the stabilty values. For the 0-0-0 setup start at 5% stability and work things back until you're at or just a hair in front of the neutral point. For the ''sport'' setup I'd likely start with the CG at around 7% stability and work it back a little until you like it and the model seems to be happiest.

OK! Thanks for the info.

I'm kind of thinking this will be a basic IMAC machine. Even though there doesn't seem to be any IMAC competition in this area. I like the concept and this should "learn me" to do things in the correct manner. In the factory setup it was a bit of a "snappy cappy" You had to be on your toes, so to speak. I only got about 10 flights out of it before the..... mishap....

So with the above said I'll try the 0-0-0 setup with 1.0 right thrust to start.

One last question. I know I've seen it someplace, but can't find it. I'm would like to know how to change a measurement into degrees. For setting the thrust angle of the firewall. Example, my fire wall is 5 inches wide. To get one degree of thrust change I need to set back one side XXXX inches.

Thanks!


Ken