Question on Roo Engine Thrust Line
 

I made a boo-boo !!!

What I have done is cut the turbine mounting pod off of my Roo to modify for lowering the turbine closer to the fuse centerline. I made the cut before I checked the original setup in regards to engine thrust line relative to wing incidence.

Since it appears for the Roo to fly level in the stock configuration most are being setup with about 1/8 inch up elevon. Should I set the turbine to have a couple degrees up thrust or set it up to run zero with the wing at zero?

TIA

Shim
 

My Roo has a 1/16" shim under the back of the engine to give it a slight down thrust. But that is at the stock engine level. Fly's realy good set up that way.

Andy

Question on Roo Engine Thrust Line
 

Countryboy,
The stock mount is set at 0 deg to the wing but with the high thrust line on the roo most of us set the engine with a degree or two of down thrust by shimming the rear of the engine. By lowering the thrust line you should not need any down thrust and I would assume that 0 deg would be the proper setting.

Todd

Question on Roo Engine Thrust Line
 

It would kinda seem with an elevaded engine it would natraly want to drive the nose down. When i see sea planes with the engine mounted high up on the wing, it looks like they have up thrust to counter the high thrust line. I wonder if with the stock high engine location on the Roo and we add even more down thrust, if the engine was lowered you have to add even more down than a stock set up.??? Hmmmm were is an aeronautical enginer when you need one:p


Andy

Question on Roo Engine Thrust Line
 

Hey Andy,

Actually, it depends on the location of the engine in relationship to the CG. If you are behind the cg and push down the nose will rise, if infront of the cg and you push down the nose will drop...Make sense? Now, think about this....Your roo is hanging from a string at the cg, you push forward at the trailing edge of the fuse and the plane moves forward without any change in pitch. If you were to push forward at the turbine the plane would move forward but will also want to drop the nose due to the leverage arm created by the engine being higher. To couteract that moment, we shim the engine with a tad of down thrust to push the nose up slightly. This is a real laymans way of explaining it but you should get the idea.

Todd

Question on Roo Engine Thrust Line
 

Ahh the o'l CG thing. Ya i see. :D Hey Todd hows the Roo repairs coming along?

Andy

Question on Roo Engine Thrust Line
 

Andy,

Roo is just about done, updated picks are on my site. Only one problem...... I have an offer on the plane! Did not plan/want to sell it but I have an offer that I would be INSANE (double digits) not to take from a Saudi Arabian. May end up shipping it off next week :( . If that happens then I plan on building a Bobcat, have a line on an XL kit already. Should know tonight if I need to crate her up.

:( :( :( Having withdrawls and it hasen't even left my shop yet!

Todd
www.lov2flyrc.rcplanet.com

Input
 

Todd & Andy, thanks for the input.

I'm with you Todd. I was leaning toward zero...zero as the starting point.

Lowering the turbine really cleans up the lines on the Roo and feel the effort to make the mod is well worth it.