bitstream

I've got a Goldberg Extra I bought already built a couple of years ago. Finally getting around to flying it. The specs call for 2deg right thrust, and 1deg down thrust for the engine. I'm not sure if any thrust was already built into the firewall. So, what is the best way to measure this? Also, any tips on installing a pull-pull rudder system (routing the wire, setup, etc.)?

Thanks!!

bitstream

Oh well, must be a stupid question. The best I can measure, the firewall appears to be flat. So I will just add washers to get the desired angle. Got the pull-pull installed, but I am going to have to move all of the radio gear back one bay in the fuse to offset the heavy engine (YS 1.20), as I don't want to have to add a lot of weight to balance it.

Rarebear

Bitstream, When I built mine the plans called for about 3/16 to 1/4 I just used washers under the mount.

Mike James

It's all relative. You have to first know if everything is built straight, and then, as you said, whether any offset was built into the firewall.

You also need to know the incidence angles of the wing and stab, so you know that "2 degrees down" may mean "two degrees down, from a 90 degree firewall, or "2 degrees down from the aircraft waterline", or "2 degrees down from either the wing or stab incidence setting".

Most standard Pattern-style "Trim Charts" can help you figure this out visually, by actually flying the model, which is the most reliable "proof" of what's needed.

I think once you become more aware of trim changes in flight, you can judge what the plane needs by just looking at it carefully in flight. (and jotting down a few "behavior" notes while you're at the field doesn't hurt)

I always start with the angles suggested by the designer, then adjust if needed.

gpmikemorse-RCU

I don't think it's a stupid question. I had the exact same issue with my Tiger 2 I'm building. The fact is that 1 degree, and even 2 degrees is a very small measurement. If you really think these small numbers would make a significant difference, the thing to do is to make some drawings as accurate as you can with a protractor, and then try to get it as close as you can. You can either add a shim (washers, usually) under the engine mount, or mount the engine to the mount slightly crooked.

The purpose of down thrust is to keep the plane trimmed at different throttle levels. (In other words, to allow the plane to fly level at different speeds without you having to adjust the elevator.)

I would guess that a lot of modelers just mount the engine square to the fuse, and don't even know the difference.

--Mike

KatManDEW

My Feedback: (6)

When I built my Tiger 60 I used a laser incidence meter. I sat it on it's side and zero'd the meter out on the fin, and then mounted the meter on the engine to determine the side thrust. I think the down thrust was built into the firewal.