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Old Jul 07, 2003, 10:21 AM
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Joined Jul 2003
3 Posts
Idea
Scale Robbe Gnat.. Ducted fan->Slope soarer convex

The project is actually headed mainly, by a good friend, and owner of the original kit. To lay out the history of the model briefly, the kit was bought of the shelf by Anthony on a visit to the UK. The aircraft never really flew, being fraught with reception problems, and a thrust to weight ratio headache. After a good stint of hanger time , the fairly bedraggled fuselage was hauled out and restored under the new guise of being a scale slope soarer. Solid balsa elevons were fitted, with a Red Arrows livery scheme covering. The aircraft is almost ready for her maiden flight in the new attire. This will basicly take the form of a series of hand launches, at a spot that has a light gradient, to extend the flight time in order to get the bird trimmed/setup.
The big question at the moment, is where to put the Center of Gravity. It obviously Cant be in the same position as before, when she was running the ducted fan, as the lack thereof, will mean all of the force couples go out the window. Her highly tapered scale wings, and fairly uncambered aerofoil section, mean that eyeballing it is a little tricky.

Is there anyone who could offer some assist on the matter, and/or give any hints on the conversion itself, before we go throwing the little airey off a mountain.
Erik Larsen
Cape Town, ZA
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Old Jul 08, 2003, 04:03 AM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
Joined Sep 2000
12,666 Posts
Hi Erik

Welcome to RC Groups

The C of G of your Gnat should be in the same place regardless of the power plant. So if you know what it was at before then use that as a starting point. You may find that you need to move it slightly to get the desired flying characteristics.

If you think about it the model doesn't become uncontrollable once the power is cut and she becomes a glider. Centre of Gravity is a moveable feast within a small window of what is stable for a particular airframe, you can move it backwards and forward to gain the desired control response and degree of stability but the power source is largely irrelevant.

Good luck with the maiden.

Brian
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Old Jul 08, 2003, 08:09 AM
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Joined Jul 2003
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Thank you for the intel. I do now realise that I have posted the thread under the wrong division.
We're actually going to throw the little bird around the field today, so the timely response is much appreciated..
Erik
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