Replacing Leading Edge Skins - Drilling Question

[kyleb]

At the gathering at Nathan's place last weekend and through some private e-mails, a couple of us discussed how to drill new wing skins onto previously used ribs. You can't use the old skin as a pattern and access is tight for backdrilling. Someone (me) mentioned offsetting a new set of holes to maintain edge distance, but I hate adding new holes into these old ribs. I think the bottom line was that we couldn't come up with a method that any of us really liked.

So, does anyone have a tried and true procedure for this?

Thanks,

Kyle

[Jerry Jackson]

I had success in doing this when replacing the LE on my Citabria.

My method involved installing small magnets over the screw holes and then using a sharpened scribe to find the magnets and mark the LE. The method was a little slow but it was highly accurate.

I bought some super-magnets from Radio Shack. They are about 3/16 inch diameter discs and are about 1/16 inch thick. Using 1/4 inch wide masking tape, I taped the magnets exactly over the center of the rib holes. Then I strapped the new LE in place. I used a sharpend piece of 1/16 inch music wire, about 4 inches long, to find the magnets and mark the LE. Marking the LE involves two different operations: (1) Finding a magnet and (2) Finding its center. To find the magnet, gently hold the back end of the wire and lay it down to be nearly parallel to the LE surface. Slowly sweep the LE surface until you feel a magnet tugging at the wire. To find the center of that magnet, gently hold the wire near its middle and hold it normal to the LE surface but not quite touching the surface. You will find that the magnet will draw the sharpened wire towards the center of the magnet, which is centered (you hope!) over the old hole. Then you simple mash the sharp tip against the LE to mark the new hole position. That mark will be tiny and should be highlighted by drawing a small circle around it using a suitable marker. I removed the new LE before drilling and then de-burring the holes.

The accuracy of this method is dependent on (1) the accuracy of placing the magnet over the center of the old hole, and (2) avoiding undue pressure on the wire when you are trying to let the magnet attract the wire to its center. I made a few trials to determine how much random error there was in perceived hole location. With the magnet remaining in a fixed location, I made a few attempts to mark the LE and then I measured the amount of scatter between those locations. I found that the scatter was so small that it was hard to measure--the diameter of a circle that would encompass all trial locations was less than 1/32 inch.

The Radio Shack magnets are not cheap but I did not attempt to find another source. I bought 18 magnets, which is not enought to mark all holes in one LE section. I marked 18 holes in one installation and then move the magnets to mark the other location during a second installation.

I was totally satisfied with the resuts.

Jerry Jackson
7ECA & 65TC
8T8

[Kif]

Working with metal has never been one of my gifts but couldn't you use a hole finding tool. They are thin and u shaped and slide over the piece that needs drilled. The under side goes in the hole to line up the tool and the top end has a bushed hole for the drill bit.

[Kif]

Try this site. http://www.yardstore.com/browse.cfm/2,388.html

[Captgrumps]

Spruce, Aircraft Tool and many more sell hole finders..Old timey tool.
Doug

[Nathan K. Hammond]

Will a hole finder work though? Because of the curve and the thickness of the tool; won't that affect hole placement to a degree? (I've used them before, but always on flat surfaces.)

nkh

[kyleb]

Will a hole finder work though? Because of the curve and the thickness of the tool; won't that affect hole placement to a degree? (I've used them before, but always on flat surfaces.)

nkh

Me too. My results using a hole finder or a strap duplicator have been pretty discouraging.

[Paul Agaliotis]

Kyle,
On the lower holes I use a hook scribe to find the hole. The higher up holes I use a bow drill. Just get a long (12") drill and put a piece of of brass tubing to use as a hand hold and bow the drill to the remaining holes. Make sure it's pulled up tight to where you want the skin.
Paul

[kyleb]

Kyle,
On the lower holes I use a hook scribe to find the hole. The higher up holes I use a bow drill. Just get a long (12") drill and put a piece of of brass tubing to use as a hand hold and bow the drill to the remaining holes. Make sure it's pulled up tight to where you want the skin.
Paul

Paul, what do you think about this:

1) Strap a skin in place.
2) Backdrill the row of holes nearest to the spar on the top surface of the wing.
3) Cleco or screw those holes to keep everything in place. (Do cleco's go through a #44 hole?)
4) Backdrill the next row and cleco them.
5) Repeat until the geometry prevents more backdrilling.
6) Unstrap the skin so you have better access from the bottom and finish backdrilling all of the holes in the top of the skin. Cleco row by row as you go and find a way to hold the skin in place as you backdrill.
7) Remove several rows of clecos towards the aft edge of the top skin. This gives access to backdrill the bottom of the skin.
(note, this is supposed to be an "8", but it gets turned into an emoticon - bizzarre).Find a way to hold the bottom skin tight against the ribs and backdrill the bottom skins, beginning at the leading edge. Cleco the skin in place as you move aft.

Thoughts? Criticisms?

[seaheli]

Kyleb,

In tough areas like skins we backdrill all accessible holes, then use lexan to transfer none-accessible holes.

What type of drill motors are you using; straight, 90 degree, 45 degree?

Sometimes we use drill bits 12" or longer and flex them into position.

Charles

[kyleb]

Kyleb,

In tough areas like skins we backdrill all accessible holes, then use lexan to transfer none-accessible holes.

What type of drill motors are you using; straight, 90 degree, 45 degree?

Sometimes we use drill bits 12" or longer and flex them into position.

Charles

I've got both 90 degree and conventional motors in addition to standard and long bits.

[John Welna]

I've had some luck using a sharp scribe. Push through the hole from the back to make a small dent and then drill there with a sharp drill that won't wander.

[Lostdutchman]

I used a piece of masking tape and marked all the holes on the ribs and drew a line through all the holes. When I got the leading edge strapped in, I placed the tape over the leading edge and drilled the hole with a #60 drill. When I could tell which side of the rib hole I was at I could adjust the drill to size. It came out close enough for me. I also counter sunk(dimpled) my holes and put in rivets to clean up the leading edge.