Aluminum stringer help wanted

[Pbruce]

FB7886F9-ED09-448D-87EA-C5E175840823.jpeg I’m having difficulty visualizing the final product, which is problematic since the stringer placement (in or out) defines the final product. In the attached picture you can see that I’ve had to move the bottom left-side stringer way out to create a smooth flow from the door jamb to the stringer. (green circle).

Moving aft, I have notched the stringer 3/16” at the attachment in order to prevent having to force it in at subsequent attachment stations (yellow circle). I had to do this at three stations and the stringer now has a nice arc, to my eye.

The upper stringer fit fairly well, but it seems that it has to be curved inward at the front so that the fabric surface will be flush with all the tubing. (Red circle).

My questions are: Does this seem right? Specifically, will it correctly allow for window frame placement? How do you terminate the fabric at the doors? Does it wrap around , or what? I’ve riveted the aluminum frames on already.

Thanks, fellow patrol kit builders.

[noema]

I am at a similar stage in the build and glad you ask this question. Unfortunately I have no definitive answers. For the green stringer mount I came to a similar conclusion. The stringer needs to align with the door frame. This means the U-tabs are very short and some piece has to be machined to make it all connect (or be fine with it only mounting to the door frame).

Screenshot 2021-07-19 093006.jpg

For the red stringer mount I also align it with the frame. From what I can tell the window frame mounts flush to it and the rest of the frame. I haven't though of notching the stringer but I can see how it helps the vertical line (the window frame does not protrude as far outward as the lower stringer).

Screenshot 2021-07-19 093237.jpg

Generally I found the stringers need a lot of bending to nicely fit into the mounts. Initially I build a rig similar to Mark's but found I don't have good control with it especially at the ends of the stringers.

Screenshot 2021-07-19 094351.jpg

Screenshot 2021-07-19 093109.jpg

My final bending rig works much better and allows for very gradual bends all the way to the end. It is even simpler to make.

Screenshot 2021-07-19 094640.jpg

Looking forward to hear how others aligned the stringers.

[Mark Goldberg]

The formers on the fuselage sides can be adjusted if it helps the fit. They are just temporarily pop riveted in place. Mark

[Pbruce]

The formers are already tight to the tubing at both the top and bottom. Mark, are you saying I can just kind “squash” the center part of the former inward and re-rivet so the stringer will engage in the clip?

You’re right Stefan. Mine looks pretty much looks pretty much like yours. Once I notched a bit of material out of some of the stringer locations, I was able to spring them into place without bending, except the last 2 feet which will require slight bending.

Can anyone verify if the top stringer should lie in a perfect straight line? I can do that. On the other hand, if I place it in the clips at the bottom of each one, it curves. I know this is only cosmetic, but I would like to know that my Bearhawk isn’t going to end up looking like something else.

[Bcone1381]

I installed my top stringer so that it is in a straight line. Inserting the stringer material all the way down into the clip did not result in cosmetic look I desired, so I made adjustments to get the look I think that is appealing and intended.

[davzLSA]

My stringers are straight until the aft end where they terminate. But I had to weld all my clips on. So I could be sure they were all straight. I guess that is one of the differences between plans build and kit build.

[N942VT]

What you've done is fine. Rivet an extension on that forward tab to reach the stringer or move the door former in to match (maybe). The flow of the stringers is mostly personal aesthetics, try to make them flow as smoothly as possible. Use masking tape to check how the fabric will eventually lay from one surface to the other. The window frames can be riveted directly to the stringers or to L brackets off of the stringers. Some brackets and spacers may be needed to make the flow right. Fabric will eventually be wrapped into the door jamb, all the way to the inside edge or meet the fabric from the inside if that's what you're doing. The stringers are not perfectly straight. Pic 86.jpgPic 91.jpgPic 91.jpg

[davzLSA]

That looks really good, great job!!

[Pbruce]

Great pictures! Worth thousands of words. Thank you! For anyone else at this stage of kit construction, here’s my current plan to finish this task:

It looks like I’m going to move the front end of the top side stringer (red circle) outward 1/4” proud of the tube cluster. There is another short section of stringer which runs a couple of feet forward from that point This should provide a straight line or slightly convex line for the bottom of the window frame to mount against. If I left that stringer flush with the tubing cluster (as in the picture) the bottom of the window would be pinched inward visually near the halfway point. I will use aluminum sheet to shim the stringers as required. Looks like the same treatment is needed on both sides.

[Pbruce]

Does anyone know if the purpose of this little steel strap across the aft end of the fuselage is intended for terminating the bottom stringers? FC62DD2F-7AEA-464C-96A5-E783C115DE84.jpeg

[Bcone1381]

That is what I used to terminate my bottom stringers.

[Pbruce]

Thank you. I’m going to do that. If it gets in the way of something else, I can cut them any time prior to cover.

[Bcone1381]

My kit is several years old and my formers required adjustment to make them fit.

The L aft former shown below was trimmed to marry it with the stinger so that it does not draw the stringer away from the stinger clip and the fuselage tubing. Below is a photo I found. On the left side I added an orange line on the photo to help show how I trimmed it.

Screen Shot 2021-08-11 at 6.47.58 PM.png

[Pbruce]

Turns out the stringers are a little too short to reach that strap. I’ll rivet an aluminum holder onto it and terminate the stringers just ahead of it. Thanks all. Very helpful.