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Old 05-08-2017, 03:35 AM
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crawler tech
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Default Engine offset

Hello, I am building a ultra stick 120 from a short kit and am about to set the firewall. I am planing on going with the standard 2 deg down and 2 deg right engine offset. The engine will be either a G26 or a DLE 30. Can anybody provide a rational for not doing this.

Thanks, Allen
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Old 05-08-2017, 04:01 AM
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TomCrump
 
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I seldom ad right/down thrust, unless it is designed in to the model.

Especially on a stick type design, right/down thrust can easily be added after the initial flights.
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Old 05-08-2017, 08:26 AM
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As Tom C points out, it is relatively easy to change things on a stick type model. On models with a long tail it is relatively easy to manage. I have a Trainer 60 that is set up as a sport model and it is not very noticeable. On the other hand I have a Staggerwing Beech that is proving to be a handful and needs the right thrust along with a gyro. With a stick model places where I notice the difference are on take off and on pulling vertical. At those times there is a tendency to yaw left. I've never been a pattern flier but I recall reading articles on how to add right thrust a degree at a time to tune a pattern plane to maintain a vertical line under power. With down thrust you can think of the distance between the centerline of the wing and the thrust line of the engine as the arm of a lever. If they are close together then the lever is short and the drag of the wing and the thrust of the wing won't cause much pitching force. If the two lines are far apart (think Piper Cub) then the engine wants to pull the airplane around the drag of the wing. You can change the thrust line to control for this. Where I have experienced it most often is in high wing aircraft that want to pitch up under power. On a shoulder wing it shouldn't be as big of a thing. There is a ton of info out there on model aircraft design.
The short answer is that I would suggest going with the factory settings since you can take the offset out with shims if you don't like it.
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Old 05-08-2017, 09:20 AM
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Originally Posted by mgnostic View Post
The short answer is that I would suggest going with the factory settings since you can take the offset out with shims if you don't like it.

This is it part of the problem, I am the factory....

I think I'm going to put the firewall at 1 deg right and 1 degree down and let it eat.
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Old 05-09-2017, 08:27 AM
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Originally Posted by crawler tech View Post
This is it part of the problem, I am the factory....

I think I'm going to put the firewall at 1 deg right and 1 degree down and let it eat.
I guess I should have said designer rather than factory. There are places on an airplane where one degree can make a big difference but one degree off from the design spec thrustline probably wont make that big of a difference. The great thing about being the builder is that you know what changes have been made and you have the means to change it.

Last edited by mgnostic; 05-09-2017 at 08:44 AM.
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