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-   -   Scratch Built Electric Pusher (http://www.rcuniverse.com/forum/scratch-building-aircraft-design-3d-cad-174/1569299-scratch-built-electric-pusher.html)

bojangle 02-27-2004 12:41 AM

Scratch Built Electric Pusher
 
1 Attachment(s)
I have been unable to find any built up (balsa) electric pusher, plans, kits or scratch. All the pushers seem to be foam and plastic. (T-hawk, WingDragon, etc). Anyway, after 50 years of building/designing with balsa, I'm too old to change now, so I'm working on my own pusher design. You might call this a hybrid, since the tailfeathers are from meat trays.

For anyone with experience with pushers (designing) , I have a couple of questions.
1. Is the CG further back on the chord with a pusher than with a tractor? The only reason I ask this is because I noticed on the Wingo that the CG was at 1/2 the chord or more. I plan to use only a 4 ounce battery, so it will take a much longer nose to balance.

2. What about the motor thrust angle?. The Easy Star has down thrust, Wingo has up thrust, the plastic ones look to be zero. I plan to make the thrust line adjustable anyway for corrections, but just curious.

I don't want the pod mounted to the wing, so the motor base is hinged to the fuse. The rubber bands holding the wing also hold down the front of the motor base.
Comment, questions, criticism welcome.

Tall Paul 02-27-2004 12:59 AM

RE: Scratch Built Electric Pusher
 
1 Attachment(s)
Quote:

ORIGINAL: bojangle

I have been unable to find any built up (balsa) electric pusher, plans, kits or scratch. All the pushers seem to be foam and plastic. (T-hawk, WingDragon, etc). Anyway, after 50 years of building/designing with balsa, I'm too old to change now, so I'm working on my own pusher design. Don't ask me why I want one, guess it's because I've tried everything else.

For anyone with experience with pushers (designing) , I have a couple of questions.
1. Is the CG further back on the chord with a pusher than with a tractor? The only reason I ask this is because I noticed on the Wingo that the CG was at 1/2 the chord or more. I plan to use only a 4 ounce battery, so it will take a much longer nose to balance.
.
No. The plane doesn't care what moves it. The c.g. is the same no matter what.
A good starting c.g. is 25% t0 30% of the mean chord.
.
Quote:

2. What about the motor thrust angle?. The Easy Star has down thrust, Wingo has up thrust, the plastic ones look to be zero. I plan to make the thrust line adjustable anyway for corrections, but just curious.
.
The amount of thrust -offset- is dictated by the distance the prop is from the c.g. Both along the fuselage and above.
On my pusher photo planes with the motor mounted above the wing. the prop end of the motor was tilted up a few degrees.
Level with the plane's reference the planes would dive in under power. Tilting the motor up offsets the nose-down moment due to the position above the wing.
.
Quote:

I don't want the pod mounted to the wing, so the motor base is hinged to the fuse. The rubber bands holding the wing also hold down the front of the motor base.
Comment, questions, criticism welcome.
.
I bolted the motor on thru the wing trailing edge. I had to shim up the rear after the first test toss about 3/16"..

bojangle 02-27-2004 01:35 AM

RE: Scratch Built Electric Pusher
 
In the picture you see a white line, my target CG. I usually try for 25% to 30% also.

As it is, when the wing is in place, the motor sets about level. In my way of thinking, the rear (prop) up would be the same as a tractor with down thrust. (same angle of thrust). So...from your experience I might want to shim up the prop end a little for first flights?

Long before we had R/C, I built many free flights, always with downthrust. I remember one guy who claimed that downthrust would just pull the nose down, and that if I wanted the plane to go up I should have upthrust. Obviously he had never flown one hehe.

I appreciate hearing from one with actual experience. I thought about bolting through the wing, this one is a prototype, if it works then I will build and refine the next. Since this is my first pusher, it is definitely "experimental"

BO

Dsegal 02-27-2004 09:27 AM

RE: Scratch Built Electric Pusher
 
There is a gorgeous electric pusher in the October 2002 issue of Flying Models. It is the Streaker, plan no. CD179.

Tall Paul 02-27-2004 01:14 PM

RE: Scratch Built Electric Pusher
 
1 Attachment(s)
Bo, my pushers now have twin booms, or they are tractors..
The booms are a bit more hassle, as the servos have to move out into the wing.

bojangle 02-27-2004 01:45 PM

RE: Scratch Built Electric Pusher
 
Unfortunately I don't subscribe to Flying Models. I will visit their website, try to find the plane.
Thanks.
BO

Arrow>>--> 02-27-2004 03:31 PM

RE: Scratch Built Electric Pusher
 
Here is a link to a beautiful balsa pusher plane built by Dave Blum.

[link=http://www.rcgroups.com/forums/showthread.php?s=8a06ddc54ac1977168ca37d65b940dc2& threadid=20785]dBlum's Plane[/link]

bojangle 02-27-2004 06:40 PM

RE: Scratch Built Electric Pusher
 
Many years ago, when I worked a regular job, I had lots of time to build like that, now that I'm self employed, I build a box, slap on a motor or engine and go flying. I have put more flights on my electric in the past month than all other planes in the past 2 years.

I checked out the "Streaker" at Flying Models, looks like a fun project, I may order the plans and back issue. Thanks for the input. Anyone else building a pusher? Post pictures. :D
BO


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