Hi all,

OK, I am scratch building a high wing versatile aircraft to be powered by a .46 engine turning a 10x7 prop. Since I designed the plane from the start and I am building it from some CAD plans I made, I don't know the correct sidethrust and down or upthrust. Is there a rule for that or I can just build it with 0 incidence to both sides and 90 degress to the vertical?? I mean no sidethrust or down/upthrust at all. If you want to have a look at my current work
see http://www.downwash.pop.com.br/projects/shadowstar2.htm


Thanks a lot,
Rodrigo Maia

Hey Rodrigo,

The design looks great! My recommendations are 2.5 to 3 degrees down thrust as the 4415 looks very close to a flat bottom wing. Right thrust would be 2 to 3 degrees depending on how it flies first. I'd start with 2 degrees and then test and go from there. Same with the own thrust start with 2.5 and then adjust after flight testing.

I agree with Starcad, his numbers are a good starting point.

Thanks a lot!

Yesterday I have finshed the tail feathers and today, I may install the firewall. Thanks a lot again.
I am thinking of imparting the rightthrust and the downthrust by means of washers behind the engine mount, so I can test various configurations. Is there a problem with this setup??

Rodrigo Maia

Sounds right to use washers behing the engine mount.


One question is 'How will you know when the thrust settings are just right?'

I assume you can fly at a given altitude with medium speed then chop the engine but hold the controls stationary. If you see a difference in the direction or flying attitude you can probably determine that there was too much thrust in one direction.

Seems to me that if you are flying at low throttle and accelerate or fly at medium speed and chop the throttle the plane will continue without need for a trim change if the thrusts are set right.

There is no problem with that at all. You could call Hobby Barn as I've heard that they carry thrust shims but I've never used them. I use the washer method myself.

My dad had bought some thrust plates way back in the early 80's. I still have them in the package they came in. We both alway use washers.

DEPENDING ON THE SIZE OF MOTOR MOUNT YOU USE, I ACTUALLY FOUND THAT A STANDARD WASHER MOVED THE ANGULAR OFFSET BY SOME NOMINAL NUMBER.

IN ENGLISH:

ONE WASHER = 1 DEGREES

THE APPLICATION WAS A O.S. 50SX ON AN LT40, STOCK ADJUSTA-MOUNT.

IT WASNT ONE DEGREE,MAYBE HALF OR QUARTER, BUT WITHOUT MY NOTES I DONT REMEMBER WHAT IT WAS, BUT YOU CAN DO SOME TRIGONOMETRY, AND IF YOU CANT, YOUR CAD SYSTEM WILL.

In-flight dynamics are fun to mess with. I didn't know it when I decided to do it, but installing those hugemongous Dave Brown foamie wheels (4"? 6"? I think 4) on my Balsa USA Stick 'cured' the high-speed balloon! I don't fly fast in any case, but when speeding up with a trainer, it'll almost always balloon due to the high-lift wing.....but those huge wheels so far under the thrust line added so much drag as speed increased that they 'pulled' the nose down!

That plane had right thrust, but no downthrust, no wing incidence and no tail incidence. It'd balloon like crazy, but had no other bad flight characteristics........