HP-24 Project

Update 30 January 2009: It puts the arm into the funnel

I spent most of 24 and 25 January at the shop working on jigs and patterns for the auto-connect funnels. As in the Hanle originals that first appeared (I think) on the Mosquito, the fuselage has funnels that captures the arms of a pair of bellcranks on the wing root rib. The funnels and arms are so arranged that their pivot axes are colinear when the wing is in place. In order to keep the system friction down to a dull roar with so many pivots, both the funnels and the bellcrank arms have ball bearings at their pivots.

The real challenge with this system is to arrange the pivots and their hardware for the shortest practical axial length so as to minimize the volume occupied by the connections and maximize the free volume for future expansion such as BRS or self-launch machinery. The Europeans tend to use bolts with ground-down heads, and thin non-locking nuts that have been staked with a centerpunch to prevent loosening. I'll probably do about the same.

I weighed several design considerations and decided to go with welded steel funnels and riveted aluminum bellcranks. The aluminum bellcranks are the same sort of double-shear affairs I've used in several other applications, and are nice because they're easy to make and add another simple task to the list of things the builder accomplished. The welded steel funnels are fairly easy to jig and will be relatively cost-effective for the TIG guy to churn out. I also have designs for riveted aluminum funnels (lighter weight but high parts count) and molded composite funnels (lighter weight but take one full cure cycle per funnel unless I make multiple mandrels).

On Sunday I got chased out of the shop by snow, and barely got out of town ahead of chain control. I stayed only long enough to close the sale of my Puch Cobra moped to a young man I met at a gas station in Cupertino late last year.

The number 2 bulkhead I installed a couple weeks back is solidly cured and isn't going anywhere without taking a bunch of fuselage with it. Now I can start noodling with the gas spring installation on the prototype pivot arm.

Alt Text.

First I printed out patterns for the funnel parts and spray-glued them onto bits of aluminum. I like to prototype steel weldments in equivalent thicknesses of aluminum sheet because I have lots of it handy and it is easy to shear and bend.

Alt Text.

Then I punch out the patterns on the shear.

Alt Text.

Bend them to shape.

Alt Text.

Assemble the bits on the jig using hot glue.

Alt Text.

Remove from the jig and admire.

Alt Text.

Homebuilt aviation is not for folks who don't try things at home.

Return to HP-24 page

page updated 30 January 2009 all text and graphics copyright (c) 2009 HP Aircraft, LLC