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what is this honeycomb transition area?

IowaRV9Dreamer

Well Known Member
This is a picture from inside my pepto pink cowl, with a bright LED light outside. It is looking through the bottom of the cowl, where the air scoop merges into flat cowl bottom.

On the left of the photo is the honeycomb in the flat cowl bottom. The right of the photo is (what is left of) the solid fiberglass air scoop. The dark area between them is the subject of this post.

I'm fitting a removable, larger scoop. I'd like to use #8 nutplates. Ideally, I would put them through the dark band. It appears to be quite thick/strong, but I do not know what exactly it is. Is there some sort of flox, etc? inside?

Will this dark area support the rivets for the nutplates?

Thanks for any info!
 

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IIRC it's the same honeycomb material (cellulose - paper/cardboard) that's been "squished" at that location.
 
Some sort of high density foam (Clark foam?) to edge the honeycomb core.
I ground thru some yesterday while installing some lower louvers.
 
Thanks Ralph - do you think the cowl would hold a nutplate in that area? Or would you recommend a layup on the back side. It seems very thick / stiff there....
 
Your rivets will not set solidly through the foam.
Carefully grind out the foam down to the outter glass skin for a generous area for your nutplate locations. Note the outter glass skin layer is very thin, be gentle. Lay up 3 or 4 layers of glass inside to regain strength and required flatness, the last layer should seal your patch with the other inside cowl skin.
Now you can install the nutplates.
 
Your rivets will not set solidly through the foam.
Carefully grind out the foam down to the outter glass skin for a generous area for your nutplate locations. Note the outter glass skin layer is very thin, be gentle. Lay up 3 or 4 layers of glass inside to regain strength and required flatness, the last layer should seal your patch with the other inside cowl skin.
Now you can install the nutplates.

This is correct----be sure to make smooth rounded corners where you lay the new glass, maybe use a bit of flox to smooth the inner radius.
 
Carefully grind out the foam down to the outter glass skin for a generous area for your nutplate locations. Note the outter glass skin layer is very thin, be gentle. Lay up 3 or 4 layers of glass inside to regain strength and required flatness, the last layer should seal your patch with the other inside cowl skin.
Now you can install the nutplates.

Alternately, rough the area up and use some resin to glue in an aluminum backing plate for the nutplates /rivets.
 
Alternately, rough the area up and use some resin to glue in an aluminum backing plate for the nutplates /rivets.
Randall - will that work? Or will the soft foam inside the fiberglass still squish? Maybe I could use soft rivets? I like the idea though... scraping out and filling in holes for all those nutplates doesn't sounds great.

Why do you need a removable scoop?
I'm converting from carb to fuel injection and the FAB is too low for the O-320 cowl. Rather than buy a new cowl, Vans sold me an O-360-1 scoop. I attached a pic of the new scoop sitting on the old one so you could see the difference. The fit of the new scoop is pretty good.
Haha Mike - I didn't notice you are a cowl expert with the James Aircraft cowls. I'm sure you know way more than I do about cowls :)
 

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I'm converting from carb to fuel injection and the FAB is too low for the O-320 cowl. Rather than buy a new cowl, Vans sold me an O-360-1 scoop. I attached a pic of the new scoop sitting on the old one so you could see the difference. The fit of the new scoop is pretty good.
Haha Mike - I didn't notice you are a cowl expert with the James Aircraft cowls. I'm sure you know way more than I do about cowls :)

You could also just bond the scoop on, to avoid the hassle with nut support.
 
What Ralph said. Remove the inner plies, remove the core, fill with flox, cap with a patch. These are screw locations. You can remove the core by working in from the edge, if your nutplates riveted to glass along a perimeter.
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Dave, If it were me I would just bond the new scoop to the cowl. It will look better and add strength. Removing and reinstalling the cowl will also be faster and easier without the chance of damaging it while it twists and bends.
 
Randall - will that work? Or will the soft foam inside the fiberglass still squish? Maybe I could use soft rivets? I like the idea though... scraping out and filling in holes for all those nutplates doesn't sounds great.

If you made a strip out of .025 or .032 I believe it would distribute the pressure such that that wouldn't be an issue.

But the others' suggestions may be better, I can't really say. In truth its been a long time since I did the fiberglass work on my own cowl.
 
Dave, If it were me I would just bond the new scoop to the cowl. It will look better and add strength. Removing and reinstalling the cowl will also be faster and easier without the chance of damaging it while it twists and bends.

I disagree with this. The added layers of reinforcement glass for the flange adds plenty of strength to the cowl and when done right, there is no ugly transition between the removable snorkel and the cowling,,just a nice looking clean line with some nice flush 1/4 turn SS Camloc's. This really made things easy for me to remove/re-install the lower cowling on my -10 by myself. You can also easily do an oil and filter change without the need to remove the lower cowl just by removing the snorkel. I liked it so much on my -10 that I am doing the same on my -9A. A lot of modification work for this mod, but well worth the effort IMHO.
 
Dave, If it were me I would just bond the new scoop to the cowl. It will look better and add strength. Removing and reinstalling the cowl will also be faster and easier without the chance of damaging it while it twists and bends.

This one has nearly 1000 hours on it. No problems. The exit panel goes on with screws and nutplates, so it is more or less structural, but the air intake fasteners are just quarter-turns. Both are handy. I've built four exit panels while exploring cooling flow, without ever modifying the cowl itself. And the intake pops off every time I drop the cowl.
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Thanks to all, great suggestions. I want to make the snout removable for several reasons:
1 - I have an idea I might be able to make a better / less leaky connection between thee snout and the fab
2 - It is easier to remove/install the lower cowl since I won't have to struggle between the gear leg and spinner backplate. So far it doesn't seem that the lower cowl with the big cutout is floppy, fragile, or difficult to handle.
3 - I have an idea that I can have no gap ahead of the gear leg, thus having a tighter lower cowl.
4 - Ease of maintenance / inspection access for the servo and exhaust
5 - Sadly, I have literally zero fiberglass skills so if I try to bond it on it'll look worse than nicely screwed on (ok this is the real reason haha)​

Dan - thanks for helping me with your pictures. I see your exit is screwed / nutplated on, and without a flange (i.e. it isn't flush with the cowl) if I am seeing the pictures correctly. I think that is what I'm going to try for.

I'll take a good look at possible screw locations but if I have to put them through the honeycomb area I guess I'll have to figure out how to clean out the core and replace it. I was hoping an aluminum backing would work but I want the attach to be solid.

I've not yet used flox so I gues this will be a learning experience! I'm not sure how much flox to add to the epoxy, and how to get it nice and smooth/flat prior to putting the inner cloth layer on it. At least it doesn't have to be pretty since it will be on the inside.... I will do some experimenting this weekend.
 
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Sadly, I have literally zero fiberglass skills...


We all learn anything we wish, if we want it. Sex is a pretty good example.

I see your exit is screwed / nutplated on, and without a flange (i.e. it isn't flush with the cowl) if I am seeing the pictures correctly. I think that is what I'm going to try for.

Dave I used lap joints because I intended to pressurize the lower cowl to a level somewhat higher than typical. Flush mounting would have required a thick flange for bending stiffness; here the "flange" is the cowl itself, a thick, cored layup. The exposed edges of the fastened parts are not optimum from the standpoint of drag. Done again, I think I'd build a flange for the cowl cored with Soric, a material I didn't know anything about (or maybe didn't exist) more than a decade ago. Then I'd bond a Soric/glass strip around the perimeter of the scoop, both for stiffness and to equal the thickness of the original cowl. Result would be flush.

That said, simply lap jointing that scoop with nutplates and screws, or even 1/4 turns, might cost you a whole 1.5 knots ;)

I've not yet used flox so I gues this will be a learning experience! I'm not sure how much flox to add to the epoxy, and how to get it nice and smooth/flat prior to putting the inner cloth layer on it. At least it doesn't have to be pretty since it will be on the inside.... I will do some experimenting this weekend.

Buy Rutan's instructions, read it three times, then actually build the practice parts.

https://www.aircraftspruce.com/catalog/bvpages/moldless.php?clickkey=23413
 
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"I have literally zero fiberglass skills"
Neither did I, but with a little instruction, buying the Rutan book DanH recommended, and some experimentation, its easily learned. This was our scratch build.
 

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We all learn anything we wish, if we want it. Sex is a pretty good example.
Well, I'm in trouble then!

That said, simply lap jointing that scoop with nutplates and screws, or even 1/4 turns, might cost you a whole 1.5 knots ;)
I hope not! But never getting it done will cost me over 100!

Buy Rutan's instructions, read it three times, then actually build the practice parts.
https://www.aircraftspruce.com/catalog/bvpages/moldless.php?clickkey=23413
WOW - that looks fantastic! Book ordered! Thanks so much! I had bought an old video but it didn't help that much. I'm glad to hear there is a good book available!
 
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