Skybolt flanges and Cowl Stiffening

[Webb]

Good explanation. I wasn’t exactly clear when I said sides. I wasn’t referring to area C but to the side as in the lateral joint between cowl halves.

My RV-7 experienced hinge failure in area B like you described.

 

[Webb]

No pucker or chainsaws allowed.

Did I mention I do not like fiberglass work. I promise I will never build a glass airplane. And I still have some sanding left to do on the glass layer on top of the carbon fiber.

 

[Lucmac]

No pucker or chainsaws allowed.

Did I mention I do not like fiberglass work. I promise I will never build a glass airplane. And I still have some sanding left to do on the glass layer on top of the carbon fiber.

Did you first file out material before you added the carbon fiber so it was the same original thickness when it was all said and done?

 

[Webb]

No. I added a 0.32” spacer between the flange and firewall. 3 layers of carbon fiber tape and 1 of glass. Came out a good match.

 

[Lucmac]

No. I added a 0.32” spacer between the flange and firewall. 3 layers of carbon fiber tape and 1 of glass. Came out a good match.

Did you do the carbon addition before or after you drilled the individual pilot holes? Curious how well the magnet method used to align the pilot hole jig works with that carbon layer in the way.

 

[hoyden]

Here is how I found the grommet hole centers. I made a small adapter that provides a center for the compass. Then drew several arcs to find the grommet hole center.

 

[Webb]

No magnets for me since I used strips. I used a steel drilling jig I made that matched the receiver hole pattern locations and drilled the flange for the receivers. Drew a line and marked 2” from the hole and marked the drill spot on the cowl 2” from the reference mark. Since I couldn’t see thru the carbon fiber strip, drilled first with a #40 bit and wallowed out the fiberglass hole since glass is softer than aluminum. Then drilled it round with a #30 And put a cleco in it.

For the sides, using what I learned about predrilling the flanges before fitting the cowl, I will drill a #30 pilot hole thru the cowl and flange for a perfect match, and then using the jig, drill the receiver rivet holes In the flange. Had I known this before, I would have done the firewall flanges this way and saved a day’s time Instead of trying to hit the hidden flange hole thru the cowl.

When it comes time to drill the large holes, I will unibit both cowl and flange together with a 1/2” bit, then remove cowl and finish both holes with a larger unibit. To ensure the cowl doesn’t move as the big holes are drilled, I will drill between the Skybolt locations and use a temporary #40 cleoco, filling in the extra holes in the cowl afterwards.

 

[Freemasm]

Here is how I found the grommet hole centers. I made a small adapter that provides a center for the compass. Then drew several arcs to find the grommet hole center.

Have used this technique many times. Geometry works.

To the OP; if you employ this technique, make you marks on tape versus the aluminum. Graphite will cause local corrosion to the aluminum.