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Old Aug 14, 2013, 12:14 AM
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Australia, SA, Adelaide
Joined Jan 2009
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70mm L-39 foam to composite build

Hi all,
I am embarking on an extremely ambitious project...scratchbuilt composite F-86 (or another if convinced otherwise) 70mm or 90mm jet. Ambitious because I have only been flying for just over 5 years with a couple of years in the middle not doing any flying because of young family duties, and second I have no experience in designing using CAD nor with composite moulds, but hey, you have to start somewhere
What I do have experience in is scratch building balsa from a plan (Tony Nijhuis Hurricane and Spitfire 62" WS for both, and a RBC kits F-22 Raptor which is in the final stages of completion). I am also fairly handy with building in general and am keen to learn from you kind people that will subscribe to this thread and hopefully help me out.
I have been inspired by the builds of Acesimmer, Kanji, Matt Halton and Odysis and thus decided to give it a go myself. I have just emailed someone I know who owns the Classic Jet Fighter Museum in Adelaide www.classicjets.com as I want to make a jet that he has on display because I figure that is the best resource having the real plane their and access to it for design and detailing. He does have an f-86 and several other jets on display.
My plan is to meet up with him and see what info I can get (hopefully 3 direction drawings and cross sections as they do restoration work as well) and start designing from there.
Over the last couple of days I have downloaded sketchup which I plan to use as my 3D CAD program and viewed lots of tutorials and tried to get my head around the program and how to make the 3D design.
I hope this thread will not only help me with this build but anyone else who wishes to "scratch build" but doesn't know where to start ( because I really do not know where to start!)
I hope you subscribe and follow my progress as any help will be greatly appreciated!

Sandy
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Old Aug 14, 2013, 01:44 AM
“Do it Right The First Time!”
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United States, MN, Hermantown
Joined Dec 2008
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Don't even pi$$ around with a 70mm fan, go right to a 90mm!!

This might give you a head start.

When I get done with my Scorpion build, http://www.rcgroups.com/forums/showthread.php?t=1819176
it's back to this:
http://www.rcgroups.com/forums/showthread.php?t=1635049

http://static.rcgroups.net/forums/at...8-DSCN0228.jpg

This might be of use:
http://www.rcgroups.com/forums/showthread.php?t=771365

http://www.rcgroups.com/forums/showp...&postcount=628

same plane --motor change Kv-
http://www.rcgroups.com/forums/showp...postcount=1219

If you want to do this right and proper, it's going to be a hell-of-a-lot more work and money than you think!!!
And save up some serious cash!

Which reminds me I need to order these for the my F-86F.
http://www3.towerhobbies.com/cgi-bin...8&I=LXAYM7&P=K
Don't recall if I have this or the 105° one? It's been a while.
http://www.robart.com/products/100-d...obostrut-ready
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Old Aug 14, 2013, 06:21 AM
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United States, NV, Fernley
Joined Oct 2011
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Sandy.... I agree with cool. Use 90mm fan. The F-86 is an easy to build airframe for the first time out and also fly's really good and very stable. You may need to extend the elevator and stab from scale depending on finished size.

Another way of saving time and money when venturing in to composites is to start with a proven foam kit airframe and pull the moulds off that. I did this with an FMS T-28 and it worked out great. Saved a lot of time and flew better than the original. Heres the link ---> http://www.rcgroups.com/forums/showthread.php?t=1767143

One tip is to use a heavier glass cloth if the base model is foam of any kind. I experienced handling issue with my Euro build cause I used a 2oz/yard cloth over the foam plug. Two layers would have been better. The issue shows up later in the build when finishing ready for layup. I kept finding dimples and low spots after each fill pass. They seemed excessive and I could not understand why I kept missing them. I finally figured it was when I handled it to sand etc. I could have saved two weeks off my build if I had used the heavier cloth.

Anyhow, I've subbed this thread and looking forward to it.

Cheers Jim
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Old Aug 14, 2013, 06:42 AM
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i get those finger dimples every single build!
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Old Aug 14, 2013, 06:53 AM
Life begins at transition
Australia, WA, Perth
Joined May 2007
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And don't waste time with the resin from Adelaide Moulding and Casting (R180 or West). I was amazed at the difference when I switched to L3600 - much easier, which means layups are much faster.

Are you planning on CAMing the whole thing, just formers, or hand-building the whole lot? I've gone down the rabbit hole before where I made a great 3D model, but then just hand-cut the formers. All this work getting sub 1mm accuracy in the computer, then had 1mm+ thick lines on the printer

Do you have your heart set on learning moulding, or would a lost foam fuse float your boat?
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Old Aug 14, 2013, 07:21 AM
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Lake Charles, Louisiana
Joined Jun 2009
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Quote:
Don't even pi$$ around with a 70mm fan, go right to a 90mm!!
+1

70's are great, I built several.
With 70mm jets things are very cramped in the fuse, the retracts that do fit are not sturdy enough for the speeds these jets land at, they get small real fast.

And power systems max out at 6s.
90mm fans can run anywhere from 6s to 12s. Makes for lots of choices.

If you fly at a smallish grass field (belly landings) 70mm would make some sense.
But 90mm is where it's at.
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Old Aug 14, 2013, 08:27 AM
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Australia, SA, Adelaide
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wow, thanks for the input so far everyone! After playing with sketchup for a few hours I now realise that learning a CAD program overnight is NOT going to happen, and as Odysis pointed out if you are going to create the model by hand (which I am) it is not necessary to have a perfect 3D model, just the cross section outlines.
Ace, I have read your thread on making a foam model into a plug, and this is the way I am leaning ATM as I have skinned plenty of models with epoxy and glass so am very familiar with the process of making the plug and adding details (panel lines etc). I think I will keep trying to learn about CAD, but while doing that actually make a plane I will heed your advice on thicker glass for the plug too. do you think 2 layers of 2 oz would suffice or go with a light first layer with a heavier second layer?

Odysis, thanks for the advice on Adelaide moulding as that's where I have got stuff from before (I normally use z poxy for skinning with fibreglass) where do you get the other stuff in Adelaide?

There seems to be an overwhelming nod towards the 90mm fan so that would seem the go. As for making a plug, what do people think about FlyFly's F-86. I could get one shipped for around A$130 which is pretty reasonable. Any other suggestions would be appreciated.
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Old Aug 14, 2013, 08:30 AM
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United States, MN, Hermantown
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Gentlemen, thanks for your replys, the F-86 is a great bird!! shoey's post promted me to add the previously mentioned retracts to my order. Do it while I can!! Winter is not far away.

shoey, I'd suggest reading Ace's and look up John Morgan's build threads.
Here's alink to John's threads, pick and choose. http://www.rcgroups.com/forums/searc..._%20J%20Morgan

John has done many plug to fuse builds. Keep us informed of your progress, most here are more than willing to help out where and when we can.

How and what ever size you decide to build---DO NOT make it a big mouthed bass! http://www.rcgroups.com/forums/showp...10&postcount=4 LOL.
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Old Aug 14, 2013, 08:37 AM
“Do it Right The First Time!”
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Quote:
Originally Posted by shoey View Post
There seems to be an overwhelming nod towards the 90mm fan so that would seem the go. As for making a plug, what do people think about FlyFly's F-86. I could get one shipped for around A$130 which is pretty reasonable. Any other suggestions would be appreciated.
Contact AIR SALLY, he may have a FG intake/nose for that , to make it much more scale. Not entirely sure on it though.?


Thr FlyFly F-86 is just a touch ovet 1/8th scale, a very nice size!! Had I seen it before I had started mine, I would have went that way.

If you hav'nt already checked it out--- http://www.rcgroups.com/forums/showt...ht=flyfli+f+86
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Old Aug 14, 2013, 03:29 PM
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United States, NV, Fernley
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Sandy

A few of our guys fly several 90mm F86 foamies and they fly great once the internals are updated to quality stuff. All of them had to extend the elevator 1/2" to make it work right. I'm not sure who makes it but can get the info if you want to go that way.

Just realize that the 86 uses a straight through intake and exit duct. So you want to take particular care that you have enough room for the electronics and bats. I know that all the 86's at the club have very tight spacings between the ducting and bats. The bat location is just below the canopy along with RX. Looking forward...
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Old Aug 14, 2013, 05:53 PM
Life begins at transition
Australia, WA, Perth
Joined May 2007
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Sandy, not sure where you'd track down more epoxies in Radelaide, I switched after I moved over West (my local fibreglass shop here carries West and Araldite, so it was an easy choice)

The FF "plug" sounds good, but if you're after 100% scale, it can go a bit awry. I was going to go down that route (flying though, not plug) with the Mirage, but the wings and fuselage are all stretched, skewed and contorted when compared to a 3-view. To correct it would require just as much work as a scratch built plug...

On the plus side, it would make a perfect training / test platform for you and the gear going in the composite one!
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Old Aug 17, 2013, 09:07 PM
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Australia, SA, Adelaide
Joined Jan 2009
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Ok, I have decided to to take Ace's advice to convert a tried and tested foam frame and make that into a plug for moulding. 90 mm it is and I will go with the Flyfly f-86 as that should be fairly easy to work with. I WILL do a mod on the intake though to make it look more scale!
I was thinking of making a plug of the inside by taping together the fuse and lining the inside with cling wrap (glad wrap) and spraying expandable foam inside. I could then use that to make a plug of the ducting and do another to make templates for any formers needed. Does this sound like a reasonable idea or is there a better way of designing the ducting without 3d software?
I will make it a replica of the f-86 at the museum I mentioned previously which is the Australian version of the sabre. Will take pics when I go there.
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Old Aug 17, 2013, 10:22 PM
Life begins at transition
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Joined May 2007
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If you go down the expanding foam route, be careful with spray foam. It tends to not cure when done inside a confined space. To make it worse, when you sand or cut into the uncured bit, it then expands! Even a week or two later... Go slow, lots of thin layers.
Or use two part foam - it doesn't rely on atmospheric moisture like the spray stuff

My last duct plug for a foamy I made from a chunk of blue foam, slit, bent and sanded until it fit like a glove. About 3 hours work on the foam, then same again for fairing and paint. It worked because the duct in the foamy was way too big
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Old Aug 18, 2013, 03:27 PM
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I would do what Odysis suggest. You could use small bits of blue or pink foam and carve and sand until you get the general shape then smooth it off. It would be better to do this once you have a composite structure which is open inside. For my Euro I'm waiting until the end to do my ducting.
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Old Aug 18, 2013, 05:23 PM
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United States, MN, Hermantown
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To get an idea of how to make them, check out a little of AIR SALLY's handy work here:::
Interest in T-38/F-5 CNC kit?????

Scroll down about 3/4 of the page and just look for the ducting pics.

http://www.rcgroups.com/forums/thumb...=threadgallery

http://www.rcgroups.com/forums/showp...&postcount=638

I agree with Ace, on the ducting, I also will wait till the end for mine. Once I get closer to being finished, and have all the components in the right places, then I can figure out where exactly the fan/motor will go for balance. Hard to know how long the ducting needs to be, untill you know where the fan will end up.
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