1. First step is, obviously, to remove the tub from the airframe. Experience tells us to mark the cut just aft of the gear leg holes. Remember to have cut line go between edge attach screw holes. I find that using a flat tape (nylon web strap) or a bendable yard stick works well to get a true cut line. On the sides I recommend drawing a line sweeping aft about four inches. The angled cut allows the belly to clear the landing gear leg and not require bending the fiberglass panel.
2. I usually do a dotted cut line and then connect the dots for a true straight line. Two people ensure a straighter more accurate line.
3. Next step is to mark the areas that will initially be routed/cut. Remember to look on the inside of the tub and locate the two wood stiffeners. Do not cut them during the first cut. Also don't cut all the way to the edge of the panel. The uncut areas keep all the alignments until final separation.
4. Use common sense during the cut layout. Allow at least a couple of inches both sides of the leg holes as well as the attach edges. This process holds the halves in alignment until the final cut later. I use a Dremel with a thin cutting disc. It is important not to rush, you only get one crack at doing it correctly. Using a vacuum during the cutting reduces the generated mess from cutting. Remember to vacuum or blow out the cooling area on your Dremel frequently.
5. Again, another set of hands to vacuum as you cut keeps the mess to a minimum. Lighting is also essential to see the cut line and stay accurately on it. Do not rush!
6. Note the white cut line on the inside of the tub. This is typical spacing. Also observe that I skipped the wood stiffeners. By straddling the stiffeners I retain strength and a reduction of flexibility of the tub halves. This photo also shows a thorough wipe down with Acetone prior to laying in the Duct tape which I use as a bond release. Here once again a extra pair of hands helps laying in the Duct tape. An interesting note is to use cheap Harbor Freight tape rather than the more expensive Gorilla brand. Reason is that removal after the fiberglass is more easy. Make sure you tape the correct side of your cut!
7. You normally want the fiberglass lip on the front half of the tub so therefore one should tape the aft side of the tub half. The fiberglass is purchased in tape form from West Marine @$21 on-line. This works much better than cutting it out of a large sheet. With tape the edges are bound and do not unravel.
8. Before mixing resin cut at least two strips of each length. I normally have two short strips for the outboard section and one for the center. Do this now because once you start laying down the resin your hands get sticky and handling the fiberglass can get ugly! I use disposable gloves and at the first sign of "sticky" I use a new pair.
9. Wetting the tub first has proven wise. It helps keep the tape in place during initial layup. It is best to mix small amounts. This allows time for laying in the tape and thoroughly wetting it. Once again a second individual mixing as needed helps a lot. Align the edge of the fiberglass tape with that of the Duct tape mold release. This gives plenty of overlap. The cooler the room temperature the more time you have to layup.
10. Notice that the long tape strips go over the wood stringers. It is important that you tap the valley to ensure that you have adhesion continuous over the bump. Remove all excess resin there should be no puddles. The Glas is the strength not the resin! Two layups is adequate but I would not recommend more than three. Believe it or not when it cures it will be amazingly stiff.
11. Allow the Fiberglas to cure overnight before starting the next step. Do not rush the curing! The next day start your fastener layout. Measure the distance from the cut to approximately the width of the Duct tape or a little less. Draw a line. This is the area you have for your fastener pattern. The preferred layout is a staggered pattern due to the width available and thickness of the landing.
12. Stay at least an inch from the leg holes and attach edge of the tub. Be especially aware of the wood stringers location. When laying out remember the anchornuts have legs for the rivets. Too close to the wood stringers no way to rivet the anchornut. I usually measure at least an inch from gear holes, attach edges and stringers. Mark that dimension and then use the distance between those marks for your spacing calculations.
13. Drill all the holes once you are happy with the "look" of your layout. For #8 anchornuts use a #21 or 5/32" drill bit. After drilling the first hole check the inside of the tub for edge distance. It is easy to fill one hole mistake but harder if they are all bad! Once satisfied that the layout is good continue drilling. With assistance have a block of wood backing up your area of drilling. This keeps the landing from flexing until fully cured.
14. Finally, it is time to cut out the remaining tabs that hold the halves together. Take your time, make sure the tub (both halves) is properly supported. A light touch is needed for this task. You need to cut deep enough to sever the panel but not too deep and cut the new fiberglass landing. If you are uncomfortable with this process use a thin blades putty knife under the new landing to protect it from the cutter. This works again with the assistance of a helper. Leave the wood stringers until last. Place a strong light under the tub so it illuminates the cut line. Carefully, start cutting the wood. With the light you should be able to see when the wood is cut. The color changes as the cut gets deeper and less wood remains. Take it slow!
15. Now, carefully, separate the halves. Use a putty knife between the new landing and panel. You may find some places not completely cut. Carefully finish your cut. Due to the bulkiness it is best to have a helper to facilitate separation. It will look rough after separation, don't panic! After trimming it will look much better. You might need to dress the end of the wood stringer.
16. Scissors or tin snips work well for initial trimming. Sand paper is necessary for the finishing touches.
17. Allow plenty of clearance for the gear legs. Also remember that the anchornuts have to yet be installed so don't trim too much that would prevent riveting.
18. Trim the edge of the aft half tub section. Hand sanding is preferred as finishing touch. This section will be handled a lot, so make it smooth.
19. These are the tools for anchornut installation. The drill jig makes the whole job go easier and faster. Several tool stores sell them for @$35. Most anchornuts on the Rotorway are #8s so this would be a great investment. A piloted 100 deg countersink is also a good purchase item. The pilot keeps the cutter centered and provides neater look.
20. Don't drill your finger! Easier to do than one might think.
21. Countersink by hand. Using a power tool most times makes the countersink too deep, sometimes requiring a repair.
22. If you didn't listen to my warnings about anchornut edge distance allowance there is a easy fix. They make a one leg anchornut. You can now buy one at Aircraft Spruce and wait to complete this task. It would not be worth buying the drill jig for this one leg anchornut because they are not used much. Use a #8 screw to hold Anchornut in place, orientate as needed and secure with long nose vise grips and drill #40 holes.
23. Trim the aft edge to reduce excess overhang. Remember to allow adequate edge distance for your installed anchornuts. Sand and paint flat black. Looks good and dries fast.
24. A job well done and very useful!
Copyright © Rotorway-Rework. All rights reserved.