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Author Topic: Interceptor 25 and 40  (Read 1209 times)

Offline phil c

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Interceptor 25 and 40
« on: November 18, 2006, 07:03:27 PM »
Here is a look at the profile of a new, thick-winged version of the Interceptor I'm building for the Brodak 25 I won last summer at Phil Spillman's fun fly.  I really appreciate the support John Brodak has given us, and this little gem of an engine deserves a new plane.

550 squares, 54 or 6 in. span(not sure which yet), target weight is 30 oz. and it will have a 25% tail.  Root is 23% thick, tip is 24%. To make it a little prettier, I grafted the front curve from a 5 digit airfoil onto the back curve of a 4 digit airfoil.  Gets away a bit from the baseball bat leading edge that the 4 digit airfoil gives at very thick sections.

phil Cartier

Offline Ken Deboy

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Re: Interceptor 25 and 40
« Reply #1 on: November 18, 2006, 10:09:40 PM »
Looks good. Are you going to kit it?

cheers,
Ken
There is a fine line between "hobby" and "mental illness"

Offline phil c

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Re: Interceptor 25 and 40
« Reply #2 on: November 19, 2006, 06:43:11 PM »
:Have to see how it flys, not that I expect any serious trouble with it.  Cores will certainly be available.  The biggest problem with doing kits is there don't seem to be too many stunt flyers looking outside the box, so to speak.
phil Cartier

Offline Bob Kruger

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Re: Interceptor 25 and 40
« Reply #3 on: November 20, 2006, 04:52:18 PM »
Phil;

What are you looking for the root and tip chord to be in terms of length?

V/r

Bob
Bob Kruger
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Offline phil c

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Re: Interceptor 25 and 40
« Reply #4 on: November 21, 2006, 11:05:00 AM »
Here's a little more info, as the work progresses.
Span turned out to be 53 in.  Area is 500.
Root chord 12.5 in.x 2.75 thick.  Tip Chord 7 in. x 1.7 thick
The tips are carved foam, 2.5 in span.
The wing panels weigh 150(5.3 oz) gr. ready to cover.

The fuse weighs 3.5 oz., ready to paint.  100 gr.

Final weight is looking to come out around 30 oz.  Projected at 27.5, but it ALWAYS comes out heavier.  Right now, that is with the B-40 engine.  I really want to see how an overpowered plane trims out an flys.  With a weight at 30 oz. or less, any decent 25 would do a fine job powering it, so I'll try that later.

This one is going to have a 4 in. bellcrank, so I don't have to space down the control handle, hopefully.  That and a threaded, screw-adjustable horn for fine tuning.  I did find out that my usual 1/16 in. music wire pushrod and two cotterpin fairleads weighs about 20% less than the smallest carbon fiber rod I could find.  I will use a 4-40 Sullivan rod end with the safety clip though.

Various Pix
Root rib- hollow cores, with very light, built up spar web.
Wing top view
clamping the fuse- 1/16 in. sides, 5/8 in foam core, 3/4 in 4 lb. wood for the front end.  It will get 3 layers of 2 oz glass, or maybe some carbon veil, for doublers.
Taping the edges- the fuse edges were rounded and a single layer of soft 1/16 in. sheet is glued around it.  Takes a bit more time than 2 strips, but saves an ounce.

I take shortcuts when building things.  The fuse front end is pieced together from scraps.  so are the fuse sides.  The canopy and the bottom cut out of one piece OK, but I need 1/4 in. strip inbetween to make it wide enough.  The rear of the fuse has an 1/8 in. tail post.  The clothspins clamp the sides down to match the curve sanded in the foam where it tapers to the post.  Tail surfaces will be 1/4 in. thick.

One cute trick, the root "rib" is a couple layers of covering ironed on to the foam, no balsa needed.  No matter what I do, the covering always pulls the root face in just a bit, so it won't fit flat against the fuse.  Some filler is always needed, so I decided not to waste balsa on a root rib.  A tiny bead of polyurethane glue in the gap and a strip of covering over it to keep it from foaming out, makes a nearly perfect fillet.
phil Cartier


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