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Universal EP

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ash:
I started this one in 2003 after reading a great thread in SSW about flapless stunters. I think it was Doug Moon and Mikey Pratt who gave the 'numbers' that I applied in this design. Thanks guys! Unfortunately I can't access the full CAD file, just a small jpg below, but Bob Kruger once kindly converted the file to DXF for me, so he may still have it. I promised Bob some construction pictures way back when, so finally here they are...

ash:
Fuselage, first up.

Its a built up profile. Aft of the wing looks a little like the tailplane structure under the 1/8" balsa skins. Forward of the wing its solid with 2 Oz CF cloth between the balsa skins and the core instead of ply doublers. The engine plates and undercarriage are recessed into the balsa to bear directly on the CF surface.

The inboard side is stiffened up and streamline with a balsa cheek cowl, which you can see in later pictures.

ash:
The tailplane and elevators are a simple balsa truss. The tailplane is 1/2" in the middle tapering to 5/16" at the tips. The elevators are about 3/32" thinner at the hinge, tapering to 3/32" TE.

Part of the 'Universal' concept is for modular parts that can be configured differently for design changes. This tailplane is a shortened 25% tailplane as the flapless concept needed only about 20% tailplane area, maybe less (I can't remember exactly). The original design called for a moulded CF tapered rectangular tube for the main spar, but I went for balsa this time in order to get it done quickly.

The CF undercarriage legs are layed up on an MDF z-shaped pattern with a mylar release film either side and another MDF pattern clamped down to form the mould. Its about 3/32" thick with a glasscloth core to preseve my CF stocks. Once the long panel is 70% cured, I hacksawed off some 3/4" strips and shaped them into legs.

ash:
The wing is a little bit special. The construction method was devised as a way of getting a built-up structure to be very light using composite materials, namely rigid PVC foam, CF and S-glass. The idea was to have a moulded glass or kevlar D-box up front and idential CF/foam/glass hanging off the back of the d-box to support the film and TE. This is similar to how some fancy FF wings and combat wings are made.

Rather than make the moulds and find it didn't work, I decided to do a couple of balsa mock-ups to test the plan. One of those mock-ups was too good to ignore, so it became this very wing. Foam core sheeted with 1/16" balsa for the LE d-box, 1/8 balsa ribs and cap strips, 1/2" balsa TE and tips. Because all the ribs start out identical, I sanded off some of the 1/8 cap strips with the long sanding bar to get the airfoil even from root to tip. The airfoil started life as an Impact airfoil, but has evolved to suit the construction method. Basically that means a more forward high point at the tips and more aft curvature is some places, less in others.

ash:
You can see the carbon tow spar reinforcement near the centre section here. Its just epoxied onto the surface roughly. Each rib pair starts out parallel and are moved 1 inch either side at their TE station to create a kind of geodetic arrangement. It looks kind of random from some angles, but gives adequate support to the film skin and significantly improved the torsional rigidity of the structure.

The shucks from the foam LE core were used to hold the sheeted LE in alignment and the ribs and TE were built up behind it. Then each wing half, supported by the shucks was aligned and glued together. As it happens, I was not sufficiently accurate, as it needs a decent sized trim tab to fly level!!

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