Drilling Your Wings to Your Fuselage

Transcription

1 Drilling Your Wings to Your Fuselage The purpose of this write up is to give some further guidance on how to get the best results drilling your wing spar attach holes to the upper fuselage attach fittings. First, the tools and tooling that makes this job easier: 1) Wing stands see photo. Two required but four is better. These can be built up from wood as you see in the picture. Some builders rent sheetrock stands that are used in construction. The principal is the same: sturdy stands that will not be wobbly. If built up, they should be LOWER than what your final position of the wings will be. This allows you to put shims under the wing until you have everything correct. One size does NOT fit all. Your tire size might be different so don t assume all will be right if you borrow someone else s wing stands.

2 2) Tailwheel stand. This is optional. But I have found it very useful to build up a stand that puts the tailwheel at the proper height for the fuselage to be level. 3) Tools required: A slow turning electric drill, big vise grips, drill bits and optional reamers of 3/8 & 5/16. (5/16 & 1/4 for LSA) 4) Clear poly tubing for making a water level. Food coloring is good to make the water line more visible. 5) Three foot level, although a four foot level will work. A digital level is also handy for setting the dihedral. Start by leveling your fuselage in both axis. Side to side and front to back. I use the main spar attach holes on the fuselage for side to side level. Put the water level line at the bottom of one attach hole and then get the other side to match. Level front to back with a level on the lower longeron as shown on the plans.

3 With the fuselage level put your first wing in place. Try and set the wing on the stand(s) with a rib rivet line on top of the stand. Your wing is better supported sitting with the stand under a rib. If you have four wing stands this is all easier. If you only have two stands then you must temporarily pin the attach holes securely on the inboard side to hold it in place. Even if you have four wing stands go ahead and pin your attach holes together with long AN3 bolts going all the way through steel fittings from front to back. Leave those in there while you are getting your wings aligned. Then start shimming the stand (or the outboard stand) to raise the wing up to get your one degree dihedral. With a digital level this is easy. You can run it outboard from the wing root on the wing top along the main spar rivet line. You can also use the water level by putting the inboard water line even with lower wing skin again at the main spar. The outboard wing skin in the same place will be 2.9 inches than the inboard side. This will give you the one degree. Now do the same on the other side. NOTE: One degree dihedral is what Bob calls for. But what is the MOST important is that both wings be the same. 1.1 degrees or.9 degrees on both sides will still give you a good flying plane. Now, check the distance from some point on the wing tip to the tailpost. NOT the leading edge of the Vertical stabilizer which is offset ¾ from the fuselage centerline. While getting it close gives you a warm fuzzy feeling, it is not really required. Bob says the industry standard is within 2. So anything less than that is good. Chances are you will not be able to get it perfect because of the limits of the fuselage attach holes and structure around them. OK. We are now happy with our dihedral and have moved the outboard wing fore or aft to where the leading edges form a straight line and are close in their measurements back to the tailpost. Now is time to check the angle of incidence in the wings. Note: as in the dihedral what is important is that both sides are the same for your plane to fly well. Because all the attach holes are undersize, there is ample room to get this right. Of course steel is harder than aluminum. So keep this in mind when drilling. Use your bubble level with shims on the top which are placed at 32 apart. This 32 is distance between the front and rear spars where you want to take your measurements. Note: the bottom of the wing is NOT flat. That is why you need shims on the top of your bubble level. Pick one wing and put shims on top of the level until the bubble is centered. Then check the other side. Move things (one wing or a combination of both wings) until

4 both wings have the bubble centered with the same shims. Going from side to side be careful to always have the level oriented the same. FYI a bubble level is more accurate than a digital level. Now both wings have the same angle of incidence. Re check everything before you start drilling. Dihedral, distance to tailpost, and most importantly the angle of incidence of both wings. You are almost ready to start drilling. It is very critical that the wings NOT MOVE while you are drilling. The tires should be chocked. The ends of the wing spars will be somewhat loose in the upper fuselage fittings. So you will need to shim with aluminum strips until the big vise grips can grip your wing spar TIGHT in the right position. These shims should be.025 or.032 aluminum about 1.5 high by ¾ wide. The need a small 3/16 slot in them to allow them to slide into the fittings past the 3/16 bolts you have pinning the wings to the fuselage. Try and move the wings up and down to see that they are indeed held tight. Again, if you tried to move them and they moved you will need to check it all again to make sure all is OK before drilling. If you still are not happy after trying your best to get everything aligned properly for drilling PLEASE give me or Bob a call to discuss before drilling. Some of the holes have easy access. But there are some spots where it is tight and hard to get a drill close to where you are drilling. If that is the case there are two options. One is to buy a drill bit extension from the hardware store is enough. The other option is to insert your drill bits into a piece of 4130 tubing where the bit is snug inside the tubing. Then put some good tack welds to hold it in place. It is probably preferable to start with a smaller drill bit and work your way up to final size. Best practice (but not required) is to drill to 1/64 undersize and then finish off with the correct reamer. The drill guides we provide assure the holes are going in straight. If the center of the aluminum wing spar hole is very far out of the center of your steel fuselage hole you need to make sure that you don t let the drill get off by following the hole in the wing. Starting with smaller diameter bits is a good way to go in this case. Having a piece of

5 3/8 O.D. tubing (for use on main spar holes) with an I.D. of say 5/16 is a good way to do this. A slow turning electric drill is the way to drill steel. Drilling/tapping fluid is useful also. With the drill guide pinned firmly in place you can drill some from the front and some from the back side if it works best. Drilling your wing struts is another operation. It is well described in the manuals and Bob s BearTracks newsletters. Drilling procedure for the perfectionist in you: Bush the drill guides to 1/4, drill the fittings to 1/4"; Put the 5/16" drill guide on the front spar fitting and drill a 5/16"; Put the 3/8" guide on and drill to 1/64" under 3/8"; Then ream to 3/8". Drill the rear spar fittings with the 3/8" guide bush to 1/4" Then drill the 5/16" with the 5/16" guide. You can make a couple little step plugs with a #D bit size tit on the end of the plugs to drill the first holes in the fuselage fittings to hold the rear of the guides in position while the drilling was being done. The drill bit will push them out as it goes through.