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  #1  
Old 08-11-2014, 12:37 PM
aerosmitty aerosmitty is offline
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Default Front seatbac longeron cutout edge glassing

I just started building an Aerocanard and am trying to figure out if the cutouts for the longerons need to be glasses. Per the plans, I'm suppose to glass the forward side with 2 layers of uni at opposing 45 degree angles then cutout longeron profiles on the edges. When I glass the aft side with 1 layer of bid, I'm suppose to wrap the bid around the edges per a cross sectional view. The vague part is wether or not the longeron cutouts require glass as well. If it does, that would require wrapping glass over a 90 degree cutout edge which doesn't seem right to me. I'd end up with a corner that has glass butted up to each other but not overlapping. Doesn't seem like that would make a strong structural corner which is why I'm wondering if it's the proper way.
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  #2  
Old 08-12-2014, 11:11 AM
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Default Re: Front seatbac longeron cutout edge glassing

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The vague part is wether or not the longeron cutouts require glass as well.
They do not. Later on you will add tapes to structurally attach the seatback to the sidewall and Longerons which will provide the required strength.

Remember to peel ply the areas of the seat that you intend to bond to. That will save you the headache of sanding and you'll end up with a stronger part as a result.
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Old 08-12-2014, 11:42 PM
aerosmitty aerosmitty is offline
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Default Re: Front seatbac longeron cutout edge glassing

Will do. Thanks for the tip.
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Old 03-19-2016, 09:32 AM
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Default Re: Front seatbac longeron cutout edge glassing

I had the same question about the longeron cutouts. Was glad to see the answer here.

Additionally, what about the bottom rounded corners of the seatback? Does the BID wrap around them also, or can it just be cut off flush with the edge? Seems like that would be a difficult, if not sloppy corner trying to wrap the BID around it. I would think it would cause the BID on the rear to buckle up.
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  #5  
Old 03-19-2016, 01:43 PM
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Default Re: Front seatbac longeron cutout edge glassing

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Additionally, what about the bottom rounded corners of the seatback? Does the BID wrap around them also, or can it just be cut off flush with the edge?
Same answer. Cut it flush to the edge. There will be other areas like this.
The tapes secure it in place and create the structural bond.
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  #6  
Old 03-19-2016, 01:50 PM
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Default Re: Front seatbac longeron cutout edge glassing

Thanks for the information. This forum really fills the gaps where the plans leave off.

Thanks to all that have gone before and paved the way for the rest of us.
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  #7  
Old 03-20-2016, 10:43 PM
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Default Re: Front seatbac longeron cutout edge glassing

Ok, so I ended up scrapping the seatback due to way too many bubbles. Finally figured out through lots of reading and some testing that I was removing too much epoxy from the layup. My technique was a little too aggressive.

I figured the technique out while glassing F-22. Another scrap, not because of air bubbles. The layup was perfect, except I made it out of UNI instead of BID. Realized my mistake as I was going to cut the strip of UNI for the doubler.

Some time and money burned, but the education was worth it.

Fortunately some of the ASS chapter kits have excess material, so I have foam for another seatback. Before I build the second and final seatback though, I wanted to ask what everyone did for the BID on the rear of the seatback. The instructions tell us to lay BID butted up against adjoining pieces and to overlap UNI. The seatback only has a single ply of BID. So do we overlap, or just butt them up?

Also, the instructions call for the UNI and BID on the seatback to be laid at 45 degrees. Of course, the pictures in the instructions show a square seatback, which would be easy to do with a single piece of fiberglass. I went both ways on the first seatback. Another reason I'm scrapping it. I laid UNI at 35 degrees on the front, which enabled me to put it down without a splice.

It got the best of me by the time I did the rear layup of BID, so I spliced it, but due to my concern of a single ply, I did overlap it about an inch or so.

Chapter 4 has been Chapter 3B for me so far, but I think I've got the technique of micro, stippling and squeegeing down now.

So two questions on the seatback: is 35 degrees ok? If not, does a single ply of BID on the back get an overlap if more than one piece is used?
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Old 03-20-2016, 11:32 PM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: Front seatbac longeron cutout edge glassing

Quote:
Originally Posted by turbo View Post
I wanted to ask what everyone did for the BID on the rear of the seatback. The instructions tell us to lay BID butted up against adjoining pieces and to overlap UNI. The seatback only has a single ply of BID. So do we overlap, or just butt them up?
Backwards. You overlap BID and butt UNI. Read the instructions again.

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Originally Posted by turbo View Post
So two questions on the seatback: is 35 degrees ok?
For a seatback bulkhead, it would be, but marginally so. But please, when fabricating structural parts, do what the plans say. Angles are important for load transfer and stress requirements - if it says 45, make it as close to 45 as you can. If you need to cut more glass, cut more glass.

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If not, does a single ply of BID on the back get an overlap if more than one piece is used?
See above. BID ALWAYS is overlapped if you need more than one piece to cover a layup. Generally 1/2" - 1" of overlap.

UNI is only overlapped if you need more length in the UNI fiber direction, but I can't think of one place on the plane where that's done. If you need more WIDTH, than you just butt the UNI up next to the previous piece - this happens in many places.
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Old 03-21-2016, 08:25 AM
turbo turbo is offline
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Default Re: Front seatbac longeron cutout edge glassing

Thanks for the clarification. Going to remake seatback and F-22. I had the instructions for BID and UNI completely backwards in my head. About 12 hours of time and materials burned. Won't forget that again. F-22 looked good too. I'm going to hang it in the shop as a grim reminder.......

Last edited by turbo : 03-21-2016 at 09:23 AM.
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  #10  
Old 03-22-2016, 08:40 PM
Marc Oppelt Marc Oppelt is offline
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Default Re: Front seatbac longeron cutout edge glassing

These are just transverse bulkheads. I wouldn't remake them.

You could lay 2" wide BID tapes over where you butt-jointed the BID layers. Sand first for good adhesion. Peel ply the edges. The overlapped UNI isn't going to hurt anything on these bulkheads. Neither is the 35 degrees, not on these parts.

You learnt your lesson, so you'll get it right next time. And when you start making the critical parts, it needs to be right.
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  #11  
Old 03-23-2016, 11:58 AM
turbo turbo is offline
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Default Re: Front seatbac longeron cutout edge glassing

i actually did overlap the BID on the seatback, but was thinking that was wrong (again, had it backwards in my head). I ran UNI on the front, but ran it at 35 degrees.

Then, I made F-22 out of UNI instead of BID. Realized it when it was time to put a strip of UNI across the doubler.

*doh!*

I have an extra piece of H45, so i'm only out a few yards of glass and two pieces of clark foam. I really didnt get the technique down good on the glassing till F-22 anyway. Had a lot of dry spots on the seatback (<10%), but too much stippling (I think the plans OVER emphasize this) and not enough epoxy so a lot of micro got pulled up. Noticed it when I was squeegeeing and the bead in front of the squeegee was turning milky white. The finished layup shows a lot of white in it.

F-22 looked great. After I realized the mistake, I used it as a test piece. I intentionally put too much epoxy in some areas just to see what it looked like cured. I now have physical examples of most types of layup errors to compare with.

Both pieces could probably be salvaged, but I really dont want to start like that. I'm also big on what Marc said about "the margin belongs to the designer" -to the point that I'm building a pretty much "plain vanilla" cozy without any mods beyond what may improve safety so I can get this thing built in a reasonable time.

Thanks again for the advice. Glad I can check in here for guidance and opinions.
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Old 03-23-2016, 12:42 PM
Marc Zeitlin Marc Zeitlin is offline
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Default Re: Front seatbac longeron cutout edge glassing

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Originally Posted by Marc Oppelt View Post
These are just transverse bulkheads. I wouldn't remake them.
While the seatback bulkhead is not highly loaded, F-22 holds the canard on to the rest of the plane. Screwing with the structural integrity of a bulkhead that's responsible for keeping you from becoming a lawn dart seems a bit cavalier.
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Old 03-23-2016, 01:42 PM
Marc Oppelt Marc Oppelt is offline
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Default Re: Front seatbac longeron cutout edge glassing

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Originally Posted by turbo View Post
i actually did overlap the BID on the seatback, but was thinking that was wrong (again, had it backwards in my head). I ran UNI on the front, but ran it at 35 degrees.

Then, I made F-22 out of UNI instead of BID. Realized it when it was time to put a strip of UNI across the doubler.

Quote:
Originally Posted by Marc Zeitlin View Post
While the seatback bulkhead is not highly loaded, F-22 holds the canard on to the rest of the plane. Screwing with the structural integrity of a bulkhead that's responsible for keeping you from becoming a lawn dart seems a bit cavalier.
Obviously. IIRC, initially he didn't say he used the wrong type of glass on F22. I had the impression he just did the overlaps wrong. F22 is pretty damn critical. That one would need to be redone.
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Old 03-23-2016, 07:10 PM
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Default Re: Front seatbac longeron cutout edge glassing

Turbo is the 4th builder I have heard of that is not happy with the seatback. I don't think it is a good bit to start the build on, even with me having some experience from work on other people's aircraft. I started with F-28, thinking I could build about 4 until I was happy with the result without buying any more foam or glass, then F-22, THEN the seatback.

I discovered some defects in the resultant F-28, but also thought they were not a failed part when I followed the inspection guidelines. Decided to build on, and make a final decision when I had made some more parts. Ended up being happy and using it.

When I attempted the seatback I was surprised how much harder it was than the previous, the flox corners and large area seemed to soak up time and gallons of epoxy compared to F-22/28. I felt the urge to heat-gun it majorly to squeegee the epoxy out, but restrained myself as I was happy with the result I had with the smaller parts. Result was lovely!
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Old 03-23-2016, 10:22 PM
turbo turbo is offline
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Default Re: Front seatbac longeron cutout edge glassing

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Turbo is the 4th builder I have heard of that is not happy with the seatback
I agree. Going from the small CH3 layups to the seatback kind of threw me off on the scale of things and found me experimenting with epoxy batch sizes, exotherming a cup of micro and doing a large quantity of micro, epoxy and flox right from the get go and right in the middle of the layup.

I found F-22 a lot easier than the seatback even with adding the doubler and micro'ing it with everything still wet, trying not to let it move around. Despite screwing it up with the wrong fiberglass, the layup itself came out well. I know both fiberglass materials by look and feel now.

Perhaps the thought process was risk-based with the seat being less critical than F-22. The seatback looks pretty simple, but its a lot of area to cover, and some large pieces of fiberglass to try and manage keeping the fibers straight and oriented compared to the practice section.

My recommendation would be F-28, then instrument panel, F-22, then seatback IMO.
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