HP-24 Project

Update 24 January 06: Akaflieg Douglas Flat III - the fuselage-in-a-week chronology

Our original plan for ADF III was for us four ADF principals (myself, Brad Hill, Brigitta Kuykendall, and Doug Gray) to get together and work as far towards making one or more complete fuselages as we could in a single week. The plan was that if we encountered a hold-up that blocked progress on the fuselages, we would switch over to secondary and tertiary projects related to the horizontal stabilizer, the canopy pivot and jettison mechanism, and other small things.

However, nothing went wrong, so the entire week ended up dedicated to making and joining one complete fuselage shell set. We progressed too slowly over the week to make more than a single shell set, but it is to be remembered that most sailplane homebuilders do not manage as much progress over an entire year.

Here's what we accomplished over the week:

Saturday, 14 January 2006:

Family Day. We go for a hike along the path of a gold-rush era water flume originally built for hydraulic mining, and still in use as a municipal water pipeline for the town of San Andreas. It rains and hails, and we all get soaking wet.

Doug picks Brad up at SJC airport, and drives up to our place.

Sunday, 15 January 2006:

We move the right fuselage mold out of the heated shop into the cold storage bay.

Everybody pitches in to clean the shop somewhat.

We cut laminate plies and bag materials for the left fuselage shell.

I make an 81-hole ply-perfer to drill holes in the .0015" poly sheeting that we use as perf ply. The material comes in 108" x 144" sheets folded up into 9" x 9" packages, so a single hole goes through many many layers of the material.

Doug uses the ply perfer to make 48 yards of perf ply. Our cost: about $10 cash plus 40 minutes at the drill press. That's about 21 cents per yard plus a single lost episode of MythBusters (commercials not included).

Brad joins the parts of the five elevator PP tube guide support molds, and preps the molds for the first round of parts. We're in a hurry, and not particularly concerned about aesthetics, so we just use packing tape for mold release.

Brigitta cuts plies for the five PP tube guide supports, and also three for fuselage layup schedule candidates A, B, and C.

We prepare eight vacuum baggies (gallon-size ziplock baggies with vacuum taps inserted into snipped-off corners): five for the five PP tube guide supports, three for the fuselage layup candidates.

Brigitta, Doug, and Brad suit up and then lay up and bag the eight parts. It goes quickly.

Monday, 16 January 2006:

We unbag the eight parts.

Brad demolds and trims the PP tube guide supports. They look great. And the packing tape is in good condition, ready for a second round of parts if need be.

I measure and evaluate the three layup candidates. Based on thickness, weight, and fiber distribution, I settle on Candidate B.

We all pitch in to wax the left fuselage mold and its joggle skirts (five coats) and part of the right mold (three coats).

Doug cuts the sandwich foam for the vertical fin, and uses my foam stabber to perforate the foam. He then uses precision sandpaper to put a 30.00 degree (0.1667 radian) bevel on all edges of the foam.

We apply tacky tape to the perimeter of a fuselage-size piece of bagging material, and do a test-bagging on the left fuselage mold.

We spend the rest of the afternoon chasing vacuum leaks and learning about how to avoid leaks and how to find them when they do occur.

Tuesday, 17 January 2006:

We remove the test bag from the left fuselage mold, and spend the rest of the morning finishing the waxing of the mold.

Brad prepares the spraying equipment and proceeds to spray a layer of gelcoat on the left mold. We adjourn for lunch while the gelcoat tacks up.

I drive out to pick up daughter Raen up from school. I take Raen back to the shop to do homework in the cold bay while we prepare for the layup.

We all suit up and start the layup. I help Brigitta do the corner and radius fills, and then take Raen home to wait for Alia and take a brief nap.

I return to the shop as they are finishing the layup and applying the vacuum materials (peel ply, perf ply, breather, bag). I suit up and help seal up the bag. After only about fifteen minutes doing pipeline patrol, the vacuum comes up and holds. It's not perfect, but the pump keeps up with it easily. At around 7 pm we adjourn to pizza and beer.

Wednesday, 18 January 2006:

We arrive at the shop to find that the power stayed on, the heater and vacuum pump kept running, and the bag held. Good, good, and good!

We break out the engine hoists and swap the molds so the left mold and its still-bagged part goes into the cold bay, the freshly waxed right mold goes into the heated bay.

We cut one each ply of glass and peel ply, and retrieve two plies off glass from the canceled left shell of ADF I. Adding in one ply that was made superfluous by not choosing the Candidate A schedule for the left shell brings us up to the full schedule complement.

Doug and I tear away the bag materials from the left side shell while Brad and Brigitta prep the right mold. The use of perf ply, and also of a better quality of peel ply, makes the stripping much, much easier this time. On our prior fuselage shell layup we had to pull up the edges of peel ply with pliers.

Brad sprays gelcoat into the right side mold, and we recess for lunch.

Sailplane racer Rick Walters arrives for a brief visit, and looks over the project. He brings us an ASW-27 control stick mechanism for study, and also a bag of tangellos. He also tries the fuselage plug cockpit on for size. He fits fine, but we see that we'd have to make some minor changes to make him perfectly comfortable. Easily enough done.

Brad, Doug, and Brigitta suit up and get into the right side layup.

I drive out to get Raen from school, and then go home to wait for Alia.

After a brief nap I return to the shop to help close the bag. The others have finished applying the bag and are doing pipeline patrol. After only a few minutes of pipeline patrol the vacuum comes up and we're free to go.

It's a good thing that the layup and bagging went well. In the few minutes since I arrived the gentle drizzle softened into big flakes of snow, and we get the heck out of Arnold just in time for the highway to go R2 (chains or 4WD required) behind us.

Thursday, 19 January 2006:

The blizzard exhausts itself overnight, and the sun shines brightly on the snow-blanketed Sierra foothills.

We convene at breakfast, where we learn that Doug has to return home earlier than expected. But the big tasks are all finished, so Brad, Brigitta and I feel confident we can finish out the week in good order.

At the shop we strip the vacuum stuff off the right fuselage shell, and then trim the rough edges around both shells. Again, the stripping goes easily. Brad finds just the right trick to trim the edges of the part with minimum grinding.

Once more we set up the hoists, and bring the left side mold back into the heated bay. With both molds in the one bay it's tighter than comfortable, but still workable.

Brad and I use up the day installing systems and internals into the fuselages.

We tack the rudder cable tunnels into the shells using dots of fast glue, making templates as we go along so that we can make the cables follow the same paths in the right and left shells, and in all subsequent shells.

Using parts from RST Engineering, I install a simple dipole antenna on the inner surface of the right side vertical fin sandwich. I know it won't be a great antenna, since there is too much metal near the tips of the poles, but it will probably outperform a rubber duckie. We'll all be using cellular and satellite comm in a few years anyway, right?

Brad mixes up some laminating resin and lays up two good-looking layers of fiberglass tape over the rudder cable tunnels in the forward fuselage.

Meanwhile I mix up a batch of bonding resin bond the five PP tube guides into their mounts. Then I put the guides and mounts onto their locators, and bond the feet of the mounts onto the inner surface of the left shell.

We also bond in the clips that secure the rudder cable tunnels in the aft fuselages, and also bond in the clips that secure the pneumatic, electric, and antenna lines to the vertical fin.

I use thickened bonding resin to pot the baluns at the middle of the dipole, and Brad applies a layer of tape and laminating resin over the dipole elements.

Sort of as an afterthought we bond in two pots for fuselage boom static ports that I'd made on the lathe the previous week. I'm not completely convinced that aft fuselage statics are worth the trouble, but, what the heck, it takes only about five minutes while the fuselage is on the half-shell.

Friday, 20 January 2006:

Brad and I start by removing the locators for the PP tube guides, which have cured up nicely in their mounts. On a lark I put a 3-foot piece of 5/8" steel tubing into a pair of the guides. It slides downhill along a 2-degree slope under its own weight. A good sign.

With the PP guide locators removed, we can remove the joggle skirts that form the joggle along which the right and left shells bond together. Measuring the joggle, I find that we've achieved exactly the thickness, to within 0.002", predicted by the Candidate B test coupon.

We string the wires and cables into the aft fuselage along the lines of clips. Pretty much arbitrarily, I decide to include three pneumatic lines and two 18-ga electrical wires, one each red and black. That is in addition to the antenna cable and the separate hoses for the two aft fuselage static ports, which run forward independently along their own lines of clips.

One issue with the aft fuselage static ports is that the two ports should be joined together with a T-junction so that one hose goes to the instruments, and so that the two hoses from the junction to the static ports have equal length. Ideally, the two hoses to the static ports should be as short as possible. The trouble is that I couldn't devise a way of achieving all those goals in such a way as to still allow us to install all the parts and connect all the hoses before bonding the shells. Or, at least I couldn't devise a method that doesn’t require a bunch of tubing flopping around loose in the aft fuselage, and we can't have that because of the risk of rubbing between the tubing and the elevator PP tube. What we end up doing is running the right and left static hoses forward to the wing trailing edge area, where we'll have access to join the two tubes with a T junction before bonding in the turtledeck. The length between the ports and the junction is longer than ideal, but at least it's equal right and left and is well-secured within the aft fuselage.

Saturday, 21 January 2006:

Having bonded and clipped all of the aft fuselage utilities in place, it's time to contemplate joining the shells.

Brad starts by sanding the bonding flange for good adhesion.

I cut and insert wedge boards of PVC foam that press the edges of the left side shell into its mold. These wedges prevent the pressure of the bonding resin from collapsing the left shell, which would result in an unsightly step along the bonding seam. We tie the wedges together using a piece of yellow rope so that we can remove them from the aft fuselage after the shells are bonded.

With the wedge boards in place, we bring in the hoists, lift the right side mold and do the rollover. We test fit the shells together. The alignment shows us that we need to make some minor adjustments to the feet of the left mold. I make the adjustments, and then mark the feet and their spots on the shop floor with splotches of spray paint.

After the test fitting, Brad grinds away a few trouble spots while I run a quick calculation of the amount of bonding resin required. After that, we begin.

I mix up a thickened batch of bonding resin while Brad wets the bond surface with a thin layer of neat resin. Then the party begins. All three of us squeeze a uniform amount of bonding resin onto the flange, going quickly to stay within the working time of the resin. We finish buttering the flange just as the first areas are starting to get stiff. We lower first one end, and then the other, with a brief pause to clear a snag where the flange caught up on the right side shell on top behind the wing. The molds go together well, and after a few minutes of settling we see good beads of squeeze-out all along the aft fuselage lines. In the forward fuselage there are spots with no squeeze-out, but we resolve to fix them later, and perhaps even apply a layer of tape if necessary. We hunt up every C-clamp and spring clamp in the shop, and distribute them around the perimeter of the molds.

That concludes ADF III.

That night I drive Brad back to Doug's place, so that Doug can drive Brad to the airport on Sunday morning.

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page updated 24 January 2006 all text and graphics copyright (c) 2006 HP Aircraft, LLC