* Posts by dr. o

1 post • joined 10 May 2014

LOHAN ideas..

dr. o

General thoughts

Geodetic construction loses a significant amount of it's strength and strength to weight ratio when split lengthwise and then the skins edge glued together.

I don't see the foam airframe with those high aspect ratio flying surfaces surviving the impulse of a rocket motor, even in low density air..

I have come late to the party and may have missed a whole bunch of technical solutions - has there been a test firing of a prototype airframe for structural integrity?

While the idea of a 3D printer produced airframe might be exciting, the glider would be far stronger for roughly the same weight as a monocoque structure made of carbon fiber and epoxy. Here the inner mold for the airframe could be a 3D foam plug that would be dissolved away by solvent after the exterior monocoque skin is formed over it.

At the very least carbon fiber could be inlet into the foam in the form of spars, ribs, and longitudinals.

Or the carbon fiber can be inlet into the foam in the form of geodetic spirals, then the foam dissolved, and the spiral framework left behind covered with monocoat.

You might benefit from collaboration with the hand launch RC glider community, or the indoor microlight airplane folks, etc.

The planform as shown for the airframe will tumble wildly out of control the instant the motor in it's tail fires, and likely rip the wings off - which is why I suspect there has not been a test firing of an airframe.

I'm thinking that a very small motor to just get the airframe off the launcher, and a single RC channel (or GPS/gyro) rudder control to bring it home will give LOHAN a better chance of a successful flight. KISS principle.

On the idea of copper tubing with metal wool inside for electrical disconnects for the motor igniter - it is quite original and I admire the author. (aluminium weighs less) The tubes however should remain behind on the launcher, not go with the airframe, for weight reasons.

If the group is fixed on having a significant climb in altitude from the motor firing, then I see it as having to be a rocket carrier with a piggyback airframe. The rocket motor will be at the forward end of a carbon stick. The airframe will be mounted at the rear end of the stick (like the tail feathers on an arrow) putting the center of thrust well ahead of both the Center of Gravity and the Center of Pressure.. This should give better stability.

Think of the motor and stick functioning like a bow and arrow - or the throwing stick of a spear.

As long as the bowstring (the stick) is pulling, the arrow (the airframe) is held by inertia against the string via the nock on the arrow. - By fingers in slots in the case of our airframe.

When the motor abruptly stops (most of it's mass has been thrown away) and the greater mass and inertia of the airframe makes it fly on ahead of the slowing motor/stick thus separating the airframe from it's launcher.

Anyway, those are thoughts as I skimmed through the comments.

Cheers, eh wot.

dr. o


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