Over the past couple of weeks I've been trying to reconcile various demands upon the jettison release hood at the front end of the canopy frame. My original concept of this part was that it would be a steel weldment potted into the canopy frame under the glareshield. Then it was going to be part of the composite glareshield. Then when we switched to a DG-style instrument pod it was going to be a separate part that had to not interfere with the pod. Then Brad said he wanted it to be smaller to allow more sun into the forward fuselage and better air circulation.
Here's a couple photos of the start of the second development attempt. This was going to have a rather faceted shape with one vent outlet each side of the T-bone cradle. It started to look really awkward to make, and didn't offer much in the way of advantage.
Using the masking tape trick to plot one of the facets.
Oh, I also finished making and dialling in the wing internals spiders for the left wing. Here they are mounted in place on the upper left wing mold. The spanwise rails of the spiders show where we mount the main spar and drag spar and airbrake box webs so that the lower skin closes properly over them.
These three photos show my third, and final, this-is-what-it's-gonna-be, whack at the jettison hood shape, modeled in PVC foam assembled with hot glue. It allows a decently sized ventilation flap, establishes a fairly good connection with the canopy frame to carry the bending moment between the canopy assembly and the pivot arm, allows a decent amount of space for the jettison release parts I designed earlier (years ago, in fact), and is about as small as I can make it.
Here I've erected Fiberboardhenge, a little slice of pi, over the jettison hood to help locate the T-bone of the canopy pivot arm. It's about 18" wide.
Here I've removed the canopy frame and jettison hood, and hot glued the T-bone to the bottom of the Fiberboardhenge lintel and adjusted the pivot arm to just meet it.
Tack welding the T-bone to the arm.
The semi-finished canopy pivot arm assembly in canopy-closed position. The arm and canopy assembly pivots about 35 degrees up from this position to allow entry and egress. The weight of the canopy assembly will be balanced by a gas spring.
Homebuilt aviation is not for folks who don't try things at home.
page updated 28 May 2008 all text and graphics copyright (c) 2008 HP Aircraft,
LLC