I am rebuilding a Graupner C17e. It had a 380 as power, I am replacing it with a Mega 16/15/4 motor. The existing motor mount is a
red plastic can shape that is angled so that when the craft is on the ground the prop shaft is parallel to the ground. This is a tail dragger, at rest the nose is 3.5 inches higher than the tail. I have never flown the plane and assuming that in flight the fuselage would be level giving the motor shaft a downward angle of about 18 degrees. Does this sound right? My P-39 is not a tail dragger and on the ground or in the air the motorshaft is the same. Also I am converting to Floats, so the fuselage will not be
at as much an tail dragger angle. Is there any 'rule of thumb' for motor angles?
Thanks
Ike

You say you are "rebuilding" a C-17E. What was the extent of damage ? If the fuse was damaged, was it repaired so that it is straight ? That amount of downthrust "seems" quite extensive. I would check the specs for that plane and see what is called for for down and/or right thrust.

Well, Campy, maybe rebuild is the wrong term. Modify is closer. This is a new C17e that I have changed to include alerions and a set of quick replacement floats built by FoamFloats. I am going up to Canada for a fishing trip, there is alot more water than clear land.
I am using a Li-Po 2100 thunder power pack and a 6.5x4 aeronaut prop. Orginally this weighed 16 oz complete, with my mods and
changes it is now at 19 oz. With a 32 inch wing/300 sqin. Completely foam. I have never paid much attention to motor angles before
and this is the first float I have attempted. It just does not look right with the angle of the motor pointing down as much as is is when the floats are attached.
Just looking at my P-39 and twin Partenavia both have motors that are parallel with the ground. I know about pointing right or left for
motor torque. But up & down has me confused.. Is AoA a factor here?

I just purchased a C17-E Biplane RTF model from Raidentech... It too has a very steep downward angle, and I was trying to find out if this was really a defect or if it was designed to fly this way... Has anyone actually flown this model with this type of angle... I have not yet been able to take mine out to fly yet... I was wondering if I need to send this plane back...

Down thrust counteracts certain planes' tendencies to balloon as throttle (and speed) increases. On some planes, the Great Planes PT-40 for example, it can be quite drastic. Typically, a plane that has lots of down thrust will have a large wing with a flat-bottom or other high-lift airfoil. Aerobatic planes and warbirds tend to have smaller, symmetrical wings so the down thrust is less pronounced.

Sounds like the nitroplanes C17 fits the criteria of needing lots of down thrust, though.

Here is a link (at retailers website) picture of a C-17E like mine. Check out the angle of the prop. Is this defective, or are they designed this way?

http://site.hobby-estore.com/images/rc/3ch_c17_4.jpg

Well, I finally got my C17-E Biplane in the air, after about 4 crashes where I re-glued a wing back together, re-glued the 380 moter back in after it popped out (nose dive), and removed landing gear as it busted off 2 times anyway.... I wish I would have started with an easier plane.. I do get good hand thro take-offs now, but at full throttel, I can't seem to get mush altitude (Even with a little up rudder), and easing into turns with slight rudder and slight up elevator, I havn't had enough altitude to keep from crashing... I'm not sure how much more punishment my C17-E Air Wecker plane will take!!!

Does anyone think that a larger prop on this 380 would help give me any more speed, or do I need to go to a larger motor, or just give up with this plane and go for a more common trainer plane?

Your motor , I believe, should be parrallel with the fuse or with you wing if I am not mistaken. YOUR motor is not mounted correctly!! That looked pretty sadYou might try another prop(after aligning motor) that is 1 inch longer or maybe 1 1/2" longer. you might want to add another battery or two also to try to retain your motors powerband. With your motor pointing down> It will seem like your plane is nose heavy BUT the prop is just pulling the front of your plane down!! Please try parrallel with Fuseor tail wing.ALSO, you might try a 400 motor. take care, Scott




te]ORIGINAL: allant

Well, I finally got my C17-E Biplane in the air, after about 4 crashes where I re-glued a wing back together, re-glued the 380 moter back in after it popped out (nose dive), and removed landing gear as it busted off 2 times anyway.... I wish I would have started with an easier plane.. I do get good hand thro take-offs now, but at full throttel, I can't seem to get mush altitude (Even with a little up rudder), and easing into turns with slight rudder and slight up elevator, I havn't had enough altitude to keep from crashing... I'm not sure how much more punishment my C17-E Air Wecker plane will take!!!

Does anyone think that a larger prop on this 380 would help give me any more speed, or do I need to go to a larger motor, or just give up with this plane and go for a more common trainer plane?
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