Reshaping top stringer profile for skylight

[Zzz]

I'm curious how many other quickbuilders have done this. As you know, if you are doing a full skylight, removing the 2 middle formers aft of the windshield is necessary to allow the plexi to bridge evenly across the cabin. This also makes the addition of a terminal cross bar at the aft end of the plexi skylight necessary, where the plexi will be anchored and my fuselage fabric will wrap.

Battson did this and had good results, but he reminded me that it makes adjustment of the stringer standoffs down the spine of the aircraft necessary to have a nice straight line without any "humpback" look. Think about how nice the backbone of a Super Cub looks. As you can see in the photos below, I'll have to drop the standoffs to maintain the "green line" which is my proposed top side of the stringer. Also, the mid-run fairlead for the elevator trim cables (not used due to electric trim) will have to be removed.

Current plan is to measure, cut them, internally sleeve the 1/4 x .035 standoff tubing with some 3/16 4130 tubing, and plug weld them in. I've seen others tap and use all-thread, but the sleeve and plug weld seems quicker, and I won't have to risk welding on the actual T-10 or whatever the fuselages tubes are. I have custom brackets already built to terminate the stringers at the crossbar.

Thoughts? Anyone have photos of theirs if they did similar?

[corefile]

Is it really going to run higher towards the tail or is that just because of how you have the green line tied off back there?

[Battson]

Is it really going to run higher towards the tail or is that just because of how you have the green line tied off back there?

Na that'll just be the way he's tied the string off.

[Zzz]

Also, keep in mind the overall height is the top of the stringer once it's nestled in the fork, hence the need to lower the standoffs.

Battson and I can't be the only ones to have done this. Any other full skylights out there?

[Matt K.]

The change in trim system pretty much negates any input I have. I had to leave a little ridge, in the middle to raise the skylight above the trim wheel (could have bent the trim wheel brackets down, but didn't want to).

I wasn't afraid to weld to the square tubing, it isn't structural after all, just a former to match the wing shape. Welding does increase effort to clean/paint. My aft stringers have a slight hump to them, may adjust the standoffs to take some out but there will always be some to get over the passenger area/trim system. The avipro stringers are quite wide, so a lot of adjustment can be made by notching into them rather than cutting brackets.

My .02. -Matt

[Zzz]

The change in trim system pretty much negates any input I have. I had to leave a little ridge, in the middle to raise the skylight above the trim wheel (could have bent the trim wheel brackets down, but didn't want to).

I wasn't afraid to weld to the square tubing, it isn't structural after all, just a former to match the wing shape. Welding does increase effort to clean/paint. My aft stringers have a slight hump to them, may adjust the standoffs to take some out but there will always be some to get over the passenger area/trim system. The avipro stringers are quite wide, so a lot of adjustment can be made by notching into them rather than cutting brackets.

My .02. -Matt

Matt, are you flying yet? Seems like it's been a while since you updated your build blog.

I did want to do my skylight in such a way that the ability to revert to a cable elevator trim is possible. The cable run is impeded by the crossbar, though I guess a guy could fabricate a fairlead into it to allow pass through. I'm pretty dedicated to electric trim but in the event that I sell one day I didn't want to turn anyone away on that detail.

[Zzz]

I'm starting to rethink how I'm going to do this, now that I've realized your can contour plexiglass easily.

[whee]

Z, what part are you rethinking? I took what I saw in Battson's pics and Steve's Aircraft Pacer Skylight pics and came up with my skylight. I origionally planed on having the center section higher like the Pacer skylight but didn't see any benefit so I went with a flat one like Battson.

[Zzz]

It just seemed like a pain in the butt to drop all the standoffs, grind off the mid-fuselage fairlead for the elevator trim cables (despite no needing it) in order to have the plexiglass lay perfectly flat. If I was in a scratch-built transition phase like you Whee I might consider it.

One idea I came up with last night, and mockued up with a piece of aluminum, was just to have a slightly arched crossbar. I will likely build it from 1/2" square steel tubing as used in the wing root formers, maybe 3/4" but very thin wall for lightness, and weld it in. The formers starting at the windshield will be the same elevation as the wing root formers, just not tapering quite as low and they would with a straight aft crossbar.

This allows for a straighter back profile without hugging the fuselage so tightly with the stringers up the back. I've been going through the BH pics on Mark's website (photo 1 and photo 2) to look for examples of how people have done it. Having the standoffs already in place on the quickbuild complicates things a little, but I'm trying to find a solution to work with them instead of altering each one. I may still have to lower them, just not as much.

[whee]

That's what I was going to do so I had room for the trim cable fairleads.

[John Bickham]

I'm probably stating the obvious here. These are some pics of how the Huskies do it. These are pics from the Texas STOL Roundup. I was looking at every skylight I could to help figure out how I might approach mine.
Threw in a pic of Wayne M competing just for fun!!!

Please be so kind to let us know ( with pics ) how you get r dun!

[Zzz]

John, yes those Husky skylights look good, and are obviously contoured on the aft end. I actually emailed with Gavin Chester today who sent me some great photos of how he did his. His positioned his arched crossbar right at the after door post station, and terminated the stringers right on the back side of it.

[Mark Moyle]

Here's the PA20 skylight per Steve's aircraft stc. No modifications to the former centerline or at the outboard edges. Structure was added to the rear edge of the skylight. Uses number six and 8 nutserts. The outer edges are held in place using counter sunk washers...the wing to fuselage fairing covers.


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[Mark Moyle]

To add...aluminum strips are oh three two 2024T3. Down the center and across the back.


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[Zzz]

Mark, are "nutcerts" the same as rivnuts?