Newsgroups: rec.models.rc,sci.aeronautics
Subject: Re: Flying Wing Glider Power Conversion
From: elec140@csc.canterbury.ac.nz
Date: 9 Apr 92 11:32:48 +1200
Followup-To: rec.models.rc,sci.aeronautics
Organization: University of Canterbury, Christchurch, New Zealand

In article <2016@transfer.stratus.com>, kvk@questor.sw.stratus.com (Ken Koellner) writes:
> This is an RC project but I figured I'd cross-post to sci.aeronautics
> in case the theorticians there can also provide advise.
>
> My basic situation is that I need to be aware of any consideration
> when providing power to a flying-wing aircraft.  Things like thrust
> angle come to mind right away.
>
> I'm going to build a 78" span flying-wing aerobatic glider (from a
> Future-Flight Klingberg Flying Wing kit).  This ship looks like your
> typical flying wing with tapered planform and the normal amount
> sweptback.  Aerodynamic control is via elevons on the trailing edges
> of the wings.
>
> I intend modify the ship to allow the attachment of a small fuse with
> an 05-electric flight system (Astro-flight 05 geared cobolt with
> sontronics 12-7 folding prop).  If you have ever seen a Peck-Polymers
> Genisis, it will look pretty much the same but bigger and with a prop
> on the fuse.  A PP Genisis is a 60" hand-launch glider with a fuse
> about 20-25" long with only a veritical fin and rudder for surfaces.
> I intend to add a similiar fuse to my ship.  It will attach below the
> wing.  The prop will be about 7" in front of the leading edge and
> probably about .5-1" below the leading.  The prop will probably extend
> about 10-15" behind the trailing edge, enough so the battery position
> will offset the wieght of the motor so that the ship balences in the
> same spot with and without the fuse.  The issues I can think of
> follow:

About a month ago I saw a guy flying an electric-powered Klingberg flying wing.
This example had a pusher prop, with the motor in a pod above the trailing
edge. There was no fuse, I think the battery pack was in the wing root. This
particular model had standard 05 sized buggy electrics, and was underpowered
(in fact it hardly climbed, and the guy turned too tight too low and
cartwheeled it, knocking the motor pod off). With the Astro cobalt 05 it should
go really well, however this is quite a fast aircraft and may suit a direct
drive system better than a geared one.

> What should the angle of the wing to the fuse be?
> 	My impression is that for an aerobatic ship
> 	it should be zero.  I figure that a flying
> 	wind has to have some fairly critical positive
> 	angle of attack though.  Whether having the fuse
> 	is exactly at the same angle is the most efficient
> 	configuration is beyond my theoretical expertise.
>
> What should the thrust angle be?
> 	I was going to go with 2deg right 2deg down.
> 	Since the prop is in tracker mode and will be
> 	slighly below the wing, I thought a little down
> 	should be used.  The 2deg right seems to be
> 	typical for most ships.

The motor appeared to have quite a bit of down thrust (i.e. prop end pointing
up) but negligable side thrust. My own experience with electric gliders is that
they require quite a bit of downthrust, while side thrust is less significant.
I use an Astro cobalt geared 05 FAI motor in my (tail-last) glider, and built
an adjustable motor mount so that I could set up the thrust line to suit the
model. This is the only sure way to get it right! However this type of mount
takes a bit more planning and space than a fixed type.

--
*********************************************************
Chris Kaiser
Postgrad - Elec Eng Dept
Canterbury University
Christchurch, NEW ZEALAND

E.MAIL: kaiser@elec.canterbury.ac.nz
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	"When you're fresh out of lawyers
 	 You don't know how good it's gonna feel"
		- Al Stewart, 1988
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