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Vacuum Bagging and 3M 78 adhesive


TMann

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I was making the wheel cover for my nose gear yeserday and made an interesting discovery.

 

I had drawn out my profile and cut it out of a scrap of wingfoam which I was going to use as a mold. In the process I ralized I had made a miscut with my hotwire bandsaw so I corrected it by gluing the piece back together with 3M 78 spray adhesive.

 

After glassing the part I stuck it in a vacuum bag and turned it on. Later in the day, I pulled it from the bag an popped it into the DAU (domestic autoclave unit) that I keep in our kitchen for 2 hours @ 180F.

 

In the process of transfering it to the DAU I noticed that the area where I had sprayed the adhesive was indented. It appears as though the adhesive weakens the foam.

 

I encountered the same problem when I was making the nose shell. I ended up doing it over WITHOUT the vacuum bag. I'm now convinced that the problem lies with the adhesive.

 

I'm glad that I discovered this prior to glassing my wings. The wing skins will be carbon fiber and it will also be vacuum bagged. I can just imagine adding up the cost of such a mistake.

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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I'm glad that I discovered this prior to glassing my wings. The wing skins will be carbon fiber and it will also be vacuum bagged. I can just imagine adding up the cost of such a mistake.

Will the spars be carbon fiber too? Otherwise you may have bit of mismatch between more flexible spars, less flexible skins. Would eventually lead to cracking.

 

Also -- have you priced this out? CF is really friggin expensive, and you won't save hardly any weight, using the same # plies as UNI.

 

If you just have to have stronger wings, I'd recommend using S2 glass.

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Will the spars be carbon fiber too? Otherwise you may have bit of mismatch between more flexible spars, less flexible skins. Would eventually lead to cracking.

 

Also -- have you priced this out? CF is really friggin expensive, and you won't save hardly any weight, using the same # plies as UNI.

 

If you just have to have stronger wings, I'd recommend using S2 glass.

One thing I noticed about carbon wings on a Berkut is the ruff ride in turbulance . the wings don't soak up the bumps as well. also the carbon transmits any vibration all the way through the aircraft and different things buzz at different frequencies. also screws tend to come loose faster from the vibration. carbon also wears out around screw holes and under the tinnerman washers a lot faster then glass. even though it is stronger and stiffer, it is not as durable as glass.

Evolultion Eze RG -a two place side by side-200 Knots on 200 HP. A&P / pilot for over 30 years

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Tom, Give Dennis Oelman a call, He can provide a wing that is stable to 290mph+ using thicker spar caps and etc. All with the better 'glass ride than CF. Using CF entirely for all the wing structures is a bunch of dough for a harse ride. When Chris E did his out of CF, I thought that was what I had to have for the added stress, but then I found out about Oelman's layup schedule...

Self confessed Wingnut.

Now think about it...wouldn't you rather LIVE your life, rather than watch someone else's, on Reality T.V.?

Get up off that couch!!! =)

 

Progress; Fuselage on all three, with outside and inside nearly complete. 8 inch extended nose. FHC done. Canard finished. ERacer wings done with blended winglets. IO540 starting rebuild. Mounting Spar. Starting strake ribs.

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Will the spars be carbon fiber too?

 

Yes

Also -- have you priced this out? CF is really friggin expensive, and you won't save hardly any weight, using the same # plies as UNI.

I already have the tapes. For those looking ..... www.defender.com had the best price.

As far as the plies go ... it's a different schedule than it is for the EZ.

 

One thing I noticed about carbon wings on a Berkut is the ruff ride in turbulance . the wings don't soak up the bumps as well. also the carbon transmits any vibration all the way through the aircraft and different things buzz at different frequencies. also screws tend to come loose faster from the vibration. carbon also wears out around screw holes and under the tinnerman washers a lot faster then glass. even though it is stronger and stiffer, it is not as durable as glass.

Well .... if it's good enough for Dick Rutan.......

 

What is really odd about your responses is they did not have anything to do with:

Wing Foam

3M 78 Adhesive

Vacuum Bagging

 

........ but thanks for playing.

 

As long as nobody wants to stay on-subject ..... I got my Infinity Retracts last Thursday. I'm building with these while I wait for the new set to come in so ....... they will end up being for sale eventually.

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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Hi Tom,

 

When you glued the 2 pieces of foam together, did you give the adhesive plenty of time to dry and release its solvent into the atmosphere? One thought is if this isnt done, and the release (tape?) and glassing is done pretty much immediately, then the 3M adhesive solvents may be 'trapped' inside the bonded area and absorbed into and weaken the foam. This becomes evident when the vacuum is applied and the foam compressed.

 

I love the spray adhesive as well, but after your noting this point, I will be cautious in my technique if vacuum bagging.

 

Just my 2 bobs worth, and thanks for sharing your experience mate.

 

Cheers,

 

Bruce.

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