It looks like we're still at go status to drive down to Riverside on 3 October and pick up the foam cores for the wing plugs.
This is the part of the project where it starts to get really scary. From here on out, the HP shop will have a substantial amount of floor space dedicated to the wing plugs, and later the wing molds. It's not like there's no turning back; it's just that from here until I get something flying it gets more and more expensive to abandon the project. Wish me luck, I'm gonna need it.
I guess the good news is that I'm now pretty confident that I have the tools and techniques to build the wing plugs to the requisite levels of smoothness and fidelity to contour. My test coupons, along with the stabilizers and aft fuselage, have shown that the CNC hotwired foam cores plus vacuum bagged skins will get me into the ballpark.
Several composites specialists have told me that the wing plug needs at least .090" and perhaps as much as .125" of fiberglass on it in order to be smooth and stable enough. My plugs so far seem to validate that with the fidelity of the CNC cores plus the thickness consistency of the vacuum bagged skins, I can get an adequate surface with a layup thickness of only .040". One thing that lets me get by with the thinner layup is that I'm building a "mini-spar" into the wing plugs by laying carbon fiber ribbons (the same stuff as in my real wing spars) into trenches in the foam cores. That will give the plugs enough stiffness so that we can easily handle them without kinking or collapsing the skins. Correspondence with SG-1 designer Gregg MacPhereson in New Zealand suggests that that is something to pay some attention to.
Also, over the last week or so I've been sketching out the parts and installation for an airbrake system. Now I can really see why Dick Schreder left all that stuff out and just used 90-degree flaps. There are lots of extra parts to them, and many opportunities for misalignment. One thing I've learned by combing the LS Flugzeugbau technical bulletins is that there are occasionally requirements to remove the airbrake arms, and that unless you think ahead you'll need to cut holes in the wing to get at the nuts and bolts. My plan for that is to use captivated nuts on the forward walls of the airbrake box, and to arrange the bolts so that they can be removed using a long wrench extension inserted through two small holes in the drag spar. I'm not losing a lot of sleep trying to make this job easy; but I am doing what I can to make it possible without cutting holes in the wing skins.
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page updated 24 September 2003 all text and graphics copyright (c) 2003 HP Aircraft, LLC