RV tip-up builders,
I have been working on fitting the tip-up front canopy skin and drilling the hinge blocks. Twenty years ago (man I'm getting old) I fought with my RV-4 canopy frame and canopy to fuselage skin fits. There was no part symmetrical or straight back then and shimming was routine.
I thought that twenty years later things would be a bit better. Better tooling, builders experience etc. might have changes things for the better. No so. So last night I came to the following conclusion. Shim as required.
I spent a great deal of time fitting the canopy front skin, checking and triple checking the curves and the forward canopy frame bow doesn't match the forward bulkhead assembly. After drilling the hinge blocks, the skin contours matches reasonably well on one side but the other side needs shimming (about 0.030-0.040") under the fuselage front skin to match the canopy skin (at the 2:00 position when sitting in the airplane). I am a pro at making tapered shims for this occasion after all I went the RV school of hard knocks (1980's RV-4 building-Old School).
I also had to shim under the hinge weldment flanges where they meet the front canopy frame bow. The shims varied in thickness from 0-0.060". One might be thinking that I must have had things out of position or something, not so. I spent hours checking removing, installing, checking etc before drilling any holes in the canopy frame. But the end result was the hinge holes were within 0.020" of center. I ended up with a gap between the front skin and the canopy top skin of 0.050-.060". I was shooting for 0.040" but things must have moved when drilling and reaming the bushing holes (another area for improvement-trying to ream bushing holes perpendicular by hand with a hand drill is not a very good technique).
A few builders posted similar problems with the skin fits. One mentioned that even the factory RV-7 tip-up has a misfit. The solution recommended was to bend the offending skin down with an edge-rolling tool. This was not acceptable to me. So I started shimming to fix the problem. One new fast shimming technique to determine the length, thickness and taper of the shims required was to use laminations of aluminum tape (found in the ducting department of Home Depot). I just cut strips of aluminum tape and laminated them over the offending bulkhead or frame. I kept adding tape starting with a longer piece with each additional piece a little smaller to simulate a gradual taper. Re-installed the skin to determine if I had achieved the results I was looking for. If not I removed the skin and added or removed layers of tape. Then I removed the laminated shim and measured the varying thickness and lengths and created a taper shim for permanent installation.
For those interested I can post some pictures of the shimming or fit achieved.
Feedback is always welcome.
Paul
RV-4/RV-7A finishing kit
I have been working on fitting the tip-up front canopy skin and drilling the hinge blocks. Twenty years ago (man I'm getting old) I fought with my RV-4 canopy frame and canopy to fuselage skin fits. There was no part symmetrical or straight back then and shimming was routine.
I thought that twenty years later things would be a bit better. Better tooling, builders experience etc. might have changes things for the better. No so. So last night I came to the following conclusion. Shim as required.
I spent a great deal of time fitting the canopy front skin, checking and triple checking the curves and the forward canopy frame bow doesn't match the forward bulkhead assembly. After drilling the hinge blocks, the skin contours matches reasonably well on one side but the other side needs shimming (about 0.030-0.040") under the fuselage front skin to match the canopy skin (at the 2:00 position when sitting in the airplane). I am a pro at making tapered shims for this occasion after all I went the RV school of hard knocks (1980's RV-4 building-Old School).
I also had to shim under the hinge weldment flanges where they meet the front canopy frame bow. The shims varied in thickness from 0-0.060". One might be thinking that I must have had things out of position or something, not so. I spent hours checking removing, installing, checking etc before drilling any holes in the canopy frame. But the end result was the hinge holes were within 0.020" of center. I ended up with a gap between the front skin and the canopy top skin of 0.050-.060". I was shooting for 0.040" but things must have moved when drilling and reaming the bushing holes (another area for improvement-trying to ream bushing holes perpendicular by hand with a hand drill is not a very good technique).
A few builders posted similar problems with the skin fits. One mentioned that even the factory RV-7 tip-up has a misfit. The solution recommended was to bend the offending skin down with an edge-rolling tool. This was not acceptable to me. So I started shimming to fix the problem. One new fast shimming technique to determine the length, thickness and taper of the shims required was to use laminations of aluminum tape (found in the ducting department of Home Depot). I just cut strips of aluminum tape and laminated them over the offending bulkhead or frame. I kept adding tape starting with a longer piece with each additional piece a little smaller to simulate a gradual taper. Re-installed the skin to determine if I had achieved the results I was looking for. If not I removed the skin and added or removed layers of tape. Then I removed the laminated shim and measured the varying thickness and lengths and created a taper shim for permanent installation.
For those interested I can post some pictures of the shimming or fit achieved.
Feedback is always welcome.
Paul
RV-4/RV-7A finishing kit
