Q-talk 70 - LETTERS, ETC.
- Category: Q-Talk Articles
- Published: Tuesday, 30 June 1998 07:11
- Written by Tom Moore
- Hits: 1227
This is a description of Aeropoxy epoxy from the Aircraft Spruce on-line catalog. It caught my eye since it is available and recommended by Rutan. - Ed.
PR2032 is a medium viscosity, unfilled, light amber laminating resin that is designed for structural production applications. Two hardeners are available for use with PR2032; HP3660, for a 1-hour pot life and PH3665 for a 2-hour pot life. When used with either of these hardeners, the system gives excellent wet-out of fiberglass, carbon and aramid fibers. Special additives have been incorporated into this system to promote chemical adhesion to fabrics made with these fibers. The AEROPOXY systems will cure completely at room temperature, or can be given an elevated temperature cure. AEROPOXY contains no MDA (a known liver toxin and carcinogen) and meets or exceeds current OSHA requirements for safe use. It satisfies all structural, pot life and wet-out characteristics according to tests by Rutan Aircraft Factory, and RAF now recommends its use for all homebuilt aircraft applications. The best ratio on AEROPOXY is 100:27 by weight or 3 to 1 by volume. In early 1996 several improvements were made to AEROPOXY. The viscosity was lowered for easier laminating, the occasional slight surface tackiness in high humidity was eliminated, the AEROPOXY hardeners were modified to prevent any tendency to crystallize in high humidity, and the mix ratios were modified to an exact 3 to 1 by volume.
Dear Fellow QBAers,
Here's another progress report on construction of the new LS(1) canard for the Quickie-1. I'm elated that progress on this is finally the rule rather than the exception! When I submitted our last report, we had completed hot-wiring of all cores involved, and had even used my hangar partner's AutoCAD system to accomplish an ingenious design for a set of templates holding the assembled canard cores in a vertical position to allow unimpeded glassing of the shear web area. The resulting paper templates were spray-glued to a good grade of 3/4 inch plywood, carefully cut out on a bandsaw, and are now a set of very accurate jigs that securely hold the five trailing-edge cores in perfect position for applying the shear web, vertically, respecting sweep, anhedral and twist. All that needs to be done is to align the front edges with a string and voila, you're set. By the way, you'll recall the discussion on twist in the last report, detailing how washout needed to be imparted to the canard by the jigging process, rather than being automatically cut in by the hot-wiring process.
The design calls for 4 plies of UNI, at 45 degrees to the edge of the shear web face, and 90 degrees to each other. The glass extends into the trough area on the top and bottom of the canard (on both vertical sides while in the glassing jigs!) and forms an amazingly strong area on which the rod pack is to be installed after cure.
As of today, the shear web is completely glassed, and last evening, I began bonding the leading-edge cores together, and bonding that assembly to the forward face of the shear web. Ribs are installed on the inboard ends of both the leading and trailing-edge cores (at the BL 10 location), and consist of 2 plies of BID; they need to be sanded before joining, and then flox corners are applied just prior to laminating the shear web, and later, the upper and lower skins.
What lies ahead is going to be the most interesting part of the whole construction process, something that has never before been done; installation of the Graphlite Rod pack. The design calls for 50 some-odd rods on the bottom side and 60 some-odd on the upper surface, all laid out side-by-side, and laminated onto the glass area covering the two troughs. The hairy part is going to see how the rods will behave as they transition across the BL 10 area as the direction changes in two dimensions.
In the designer's words: The rods will be installed with the longest rod furthest forward in the trough and the shortest furthest aft. Each rod is centered spanwise in the trough so that the rod pack's final shape, when viewed from above, will be trapezoidal.
The rods may be difficult to install because of the bend of the canard at the BL 10 rib. The rods on the bottom of the canard will want to "spring up" on the inside corner of this bend. One possible solution is to place a mixture of flox and resin in the area of the bend before installing the rods and then install the rods without forcing them into the bend. After all of the rods have been installed, push the rods into the corner and the flox - resin mixture using a piece of wood shaped to the form of the canard, covered with some clear tape. Do not use too much pressure or you might damage the rods. Once pressure has been applied to the rods to force them into the flox mixture, do not relieve this pressure. To do so would cause air to be drawn into the area beneath the rods and thus ruin the entire installation. Place some weight over the wood form to hold the rods tight in the corner until after cure.
After the rod pack has been installed and fully saturated with resin, check carefully for air trapped under or around the rods. Now place some Peel-Ply over the entire rod pack. Go over the Peel-Ply with a squeegee to draw out excess resin.
The important point to remember when installing the rod pack is that there should be absolutely no air (voids) surrounding the rods anywhere. This is especially true of the bend at BL 10 where the stresses are the highest. Large voids here will cause stress concentrations which can eventually lead to delamination of the rod pack from the shear web.
This will be faced next week.
Incidentally, with the exception of laying out the rod pack, the design makes use of the ordinary accepted composite construction techniques, and if you have already done some glasswork, you should have no problem at all applying what you already know to a newer approach. I have to admit though, that our EAA Chapter is unusually blessed with an abundance of talent and skill in many of its members, and our Technical Counselor, Gordon Jones is the consummate pro when it comes to composite construction. He has bent over backwards to be of help in seeing my canard through to completion, and his previous experience has been invaluable in making sure that we don't make any oversights. I am learning a tremendous amount through all this, and am keeping a list of little items to pay special attention to as we complete the prototype of this canard so that others will have an easier time of it after me. Some ideas were foreseen by the designer, but a few things have surfaced during construction that he could not have possibly thought of.
I am still hoping to have this completed by the time the Ottawa Fly-In comes around, so as to be able to share pictures and first-hand experience in what pioneering something like this is all about. Not all joy, but I hope it will be when I start flying!
P.S. Now, several weeks later, I am elated to report that the rod pack for the lower canard surface has been laminated in, and appears to be a successful installation. Yesterday evening, (after a 48-hour cure) I removed all the Peel-Ply and the weights holding the rods in place while the epoxy was curing, and it seems to be a perfectly acceptable lamination. This was the part I dreaded the most but I'm grateful that it appears to have gone well. These Graphlite rods are really something else! It looks like the skins won't make it till after Ottawa, but I'll still have pictures with me at the Fly-In to document progress thus far.
Alan Thayer, Castro Valley, CA
"How the Quickies Can Use His BENT "C" Antenna"
As I understand the Q-1, your aileron tubes are on bulkhead FS89 so bulkhead FS110 is the best available place for the antenna. I also understand that the FS110 bulkhead is 15.0 inches vertical by 16.4 inches horizontal. If all that is true, then the best you can do is to build your antenna using that 15-inch vertical section as the center of the "C". Modeling it this way on the computer gave almost as good a result as the Q- design.
Your antenna should be built as a square "C". The center section arms will be 7.75 inches long and overlapped 1/4-inch at the center. Use a 1/4 by 1-inch piece of double-sided PC card material and solder the two arms to opposite sides. Add a 15-inch horizontal extension to each upper and lower arm. So your whole antenna is now 15 by 15. (The 15-inch horizontal length is my best estimate, as I have no way of measuring a Q-1 installation.)
Build and connect the tuning stub and balun just like the Q-2 version except you might make the tuning stub 93-inches long and trim it after the antenna is installed. To trim it you need to measure the VSWR at 118 and 136 Megahertz. You want to balance the VSWR at those frequencies. The VSWR should be about 2:1 across the band. This is an 89% power deliver and is very good. (Only 0.5 dB down from perfect.) The antenna pattern is -1dB with respect to a dipole so the total installation loss should be -1.5 dB across the entire band. That is better than most installations due to the "magic" tuning stub.
If someone were nearby, I could measure a trial installation. However, I believe you will get good results with those dimensions. The aileron torque tubes mounted on FS89 did not seem to affect the pattern very much (0.25 dB).
Well I hope this helps you out. I am looking forward to getting back to work on my airplane. My old Mooney is nice but very expensive compared to an experimental and not nearly as efficient.
Steve Whiteside, Ringwood, NJ
On landing after my Saturday morning flight, I blew the inner tube on my tail wheel. I had no idea that there was a problem except for this strange sensation on rollout that the tail was trying to lift. Actually, now that I think of it, it was more along the lines of the tail just kind of mushing all over the place. Immediate action was to just use more rudder when directional corrections were required. I could not judge how much correction was due to differential braking. This was, however, the first time I had the opportunity to evaluate a failure mode on my big tail wheel. I have no complaints except for what a problem it is to get the old tube and tire off the rim and put the new one on.
It might be a proper suggestion to change the tire and tube at a timed interval instead of changing based upon tread wear alone. My hangar buddies and I have had a nasty time with tires just giving up the ghost for cause in the high desert.
Brian Martinez, Quartz Hill, CA
This is an excerpt taken from the QBA E-mail Q-LIST. There was a request for info on installing a spinner front bulkhead.
This is how I made a front bulkhead for my Q, but I haven't flown yet so I can't make any performance claims.
Make a stiff glass flat layup a little larger than the bulkhead needs to be. Now use the rear bulkhead to transfer the hole pattern for the prop bolts. Find the center of the bulkhead using the compass (remember high school drafting?). By trial and error make the bulkhead so the spinner will fit with the bulkhead in place. Grease the inside of the spinner. Put a bead of flox all around the front bulkhead. Be sure to sand the edge of the bulkhead so you get a good bond.
Now assemble the backplate, propeller, front bulkhead and spinner on the engine. Use a dial indicator to true up the spinner. Let the flox harden.
The reason for the flox is to give the edge of the bulkhead some thickness so that it doesn't saw through the spinner. Bob Farnam did something similar but he used a BID tape on the front of the bulkhead instead of flox.
Jim Ham, Menlo Park, CA
September 4, 5 & 6, 1998
Contact: Don Stewart
FAX - 520-445-3781
ECONO LODGE - 913-242-3400
BEST WESTERN HALLMARK INN - 913-242-7000
Bob Farnam from Livermore, CA - The outside of this plane only tells part of the story, inside there is a full list of innovations!
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