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View Full Version : Rectangular vs. triangular fuse on AP plane


Jinker
Aug 10, 2005, 11:22 AM
I'm building a fuse to go go with my Gentle Lady wing. I'll be using it for aerial photography and want to be able to put my Pentax Optio S4 and mount in the middle of the fuse on a rotating mount. I'd like 90 degrees of rotation from horizontal to vertical.

I've built two fuselage sides out of 1/4" stick, truss style. I've got a square frame around the CG point of each. What I'm thinking of doing is sheeting one side of the fuse at the box, and across the top of the airplane, with a hole on the other side and bottom of the fuselage, maybe with some sheeting on bottom and open side with cutouts for sightline for the camera.

The fuse is about the same length as the original Gentle Lady fuse, but has a curved profile to give the internal volume necessary for the camera.

My question is this:

I could frame up the two sides in a square/rectangular cross section which will give me lots and lots of room inside.

Alternatively, I could sand an angle into either the top or bottom edge of both sides and make a triangular fuselage.

Making the middle of the fuse wide enough for the camera and rotating mount would result in the triangular fuse being wider than the rectangular one. I'm assuming a triangle with the flat surface on top would be favored over flat surface on the bottom due to ease of mounting the wing on top.

Suspected advantages of rectangular fuse:


More volume
Easier to mount electronics inside
More 'normal' construction


Suspected advantages of the triangular fuse:


Less wetted area (?)
No formers necessary (lighter?)
Less glue joints (though the long one down the 'spine' of the airplane would be a killer)
'Different' look


I'm trying to puzzle out which airframe's strength would be comprimised less by the hole in the side. It would be 3 inches wide, and subtend about 120 degrees or so. Just a smidge above horizontal on one side to just past vertical on the bottom. On the triangular fuse, this would mean a gap in the 'spine', which would mean some beefing up of the structure around the gap to spread the loads.

Camera access is necessary, though, so even if I can sheet over the hole, it'll mainly be an aerodynamic improvement/camera protection, as a hatch doesn't do much structurally.

I'm probably thinking about this a little much, as this airplane will definitely be a floater, with an all up weight somewhere around 2 lbs. It'll be powered by my AXI 2212/20, which should make somewhere around 20 oz of thrust with an 8x4 and a 3s Lipo pack.

I'm wondering whether I should bother adding landing gear, or if a skid would be sufficient. It will hand launch just fine, just wondering which will protect the camera better.

Any advice?

-Greg

Sparky Paul
Aug 10, 2005, 11:39 AM
The provision for rotating the camera kinds says that part should be seperate from the airframe part, with the airframe designed to allow for the addition of the camera and mounting stuff.
On this one, the tube carrying the camera fits in the tube used for the fuselage.
If any part of the camera can hit the ground without a landing gear, add a landing gear.

Guille
Aug 10, 2005, 11:56 AM
A couple of advises: a triangle fuselage will not make a considerable difference from the aerodinamics point of view... It's true that there IS a difference but since we are flying at about 50.000-100.000 reynolds number they are the same. From the structures point of view; I'd not say that you will not need formers, i'drather say that you need triangular formers since they deals with torsion or fuselage twist; in fact, formers helps fuselage sheeting keeping it's shape so the strength can be obtained. Any hole (wherever in the side or botton) can be reinforced by means of a ring of plywood; 1 inch wide will be enough... Also, while you are operating the plane, you'll love "that inner space" inside the fuse so I Shall recommend a rectangular section...
What I want to say is: keep it simple and you'll get a very operative plane (is that what we want, isn't?)
Have you thought on using a parachute for recovery? Also, you can test any camera protection by carrying any "dummy" in the plane (use an egg!!!). Anyway, the best option for protecting the payload shall be made of glass-fiber; if you can use kevlar will be better since kevlar is one of the best shock absorvers...
Regards!!!

PS: sorry about my english... hope it's not so bad

Andy W
Aug 10, 2005, 12:01 PM
How about octagonal? :)