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Oct 10, 2013, 04:10 AM
Another one on the way...
ysolomon's Avatar
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Thanks, P901. We actually started with those plans, it those are only the 2D plans. He didn't post the 3D ones... You have all the parts you need to build it out of ply and balsa. I was also a bit concerned with the scale of some of the things. We spent a lot of time online until we found/bought the 3D plans we now have.

We are now printing them in 1:1 scale for the plane we will be building (WS 54.7"). Yesterday we bought R4, 0.75" blue foam sheet. We are starting by building a "test plug", actually for the laser targeting pod on this airplane. We would rather "shave" on that part and practice how to make the molds on something small and simple before we do the fuse.
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Oct 10, 2013, 06:21 AM
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p901P901's Avatar
Thought it was a good start to begin with. I find the 3 view posted online are not dimensionally correct and see that a good quality image is a must. I usually would take former section from dxf into devfus or devfus foam and create the sections. I like seeing a good 3D image and would do all this if I had a good 3d program that had lofting abilities.
Anyway sounds like your going in the right direction and will see how develops.
Oct 16, 2013, 03:10 PM
Another one on the way...
ysolomon's Avatar
Thread OP

Exhaust pipes too small!!!


First SNAFU... Printed the model in 1:1 scale. Looks great. But wait! The exhaust pipes are 52mm... On the outside! For JetFan 90 to work well and not draw too much current, I need 78-79mm. On the inside! I have experienced with this fan with 75mm, and it draws too much current. So, we need to modify the design a bit to accommodate for slightly larger exhaust pipes... Learning how to do that with nanoCAD.
Oct 16, 2013, 03:31 PM
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p901P901's Avatar
So are you going to scale the plane up 1.5x for 2 90mm fans? Or are you thinking of 1 90mm?
Found an interesting site http://igor113.livejournal.com/259634.html
Oct 16, 2013, 04:59 PM
Another one on the way...
ysolomon's Avatar
Thread OP
Hey P901. No, I'm not going to scale it up. My plan was to have a ~15lb plane, and I think that at 54.7" wingspan and 64.6" length, I will get a 15lb plane... Just about... So, what I intend to do it to increase the nozzles. It will not be exactly scale, but what RC plane really is?...

Yes, thanks for that site. I saw it before. Someone really took a lot of shots of that plane...
Oct 19, 2013, 07:21 PM
Another one on the way...
ysolomon's Avatar
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As stated before, we will start with the laser targeting pod to get our process nailed down before we spend some serious hours on the fuselage. Took 3x 0.75" thick blue foam. Glued them together with 3M 77 spray glue. Now we will use hot wire to carve the right shape, and then continue to finish it.
Oct 20, 2013, 05:11 AM
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D_FAST's Avatar
not knocking your process, but how are you gonna get a cigar shape? from just 2 circles on either side? That is unless your cutting that blank into sections.

just in case ive done many of these types of builds smaller yes but the concept is the same.

https://www.rcgroups.com/forums/show....php?t=1722906
https://www.rcgroups.com/forums/show....php?t=1747669
https://www.rcgroups.com/forums/show....php?t=1800930
https://www.rcgroups.com/forums/show....php?t=1681958
https://www.rcgroups.com/forums/show....php?t=1984555
Oct 20, 2013, 06:59 AM
Another one on the way...
ysolomon's Avatar
Thread OP
D_FAST, thanks for your ideas. This is a first scratch build for us, so every idea can help. Doing it in sections is what we plan for the main fuse. Since we are using 3/4" foam on a 64.5" fuse-- 86 of them... I thought that doing such a small part would not be as challenging... We'll see very soon... If it doesn't work simply, we'll do it using slices.

By the way-- you have some beautiful builds there!!!
Last edited by ysolomon; Oct 20, 2013 at 07:05 AM.
Oct 20, 2013, 02:43 PM
Another one on the way...
ysolomon's Avatar
Thread OP
OK, the 3M 77 spray glue "ate" through the blue foam. What glue do others use for blue foam?
Oct 20, 2013, 03:03 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
That happens sometimes when it's put on to heavy.

Check out some of these by Loctite-- several suggest they do foam.

http://www.menards.com/main/paint/ad...ves/c-7923.htm

Easier to post whole page than separatly.
Oct 20, 2013, 03:12 PM
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ysolomon's Avatar
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Thanks!
Oct 21, 2013, 06:09 PM
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p901P901's Avatar
Your L-39 mods should be about the same as this one and you can make this one much better. Have you figured the internal structure to support all the stress of the gear, wing and airframe? This will help greatly in figuring the design of the foam as well as the wood support frame.
I use Mat board http://www.michaels.com/24%22-x-36%2...efault,pd.html for the templates with CA clue on the edges. I use this http://www.michaels.com/aleene%27s-r...efault,pd.html to glue the mat board to the foam. It takes about 1 minute to tack up before applying to the foam. To same time just use the plans from post 30 to make the templates. You can use most of the supporting structure also.

Glue foam sections with Gorilla Glue white or 3M™ FoamFast 74 Spray Adhesive
Last edited by p901P901; Oct 22, 2013 at 10:27 AM.
Oct 22, 2013, 10:13 AM
EDF Jet Jam 2019, June 13-16
eatond's Avatar
Quote:
OK, the 3M 77 spray glue "ate" through the blue foam. What glue do others use for blue foam?
Hi ysolomon,
Try WBPU. I saw somebody mention it being used for glue on foam somewhere and decided to give it a try when I glued up some blue foam blocks for a nose cone. Dang if it didn't work great.

Dan Eaton
Oct 22, 2013, 12:59 PM
Another one on the way...
ysolomon's Avatar
Thread OP
Thanks, Dan. What I realized based on the replies that I got (on this and other threads) was that I wasn't using the incorrect glue, I was using the glue incorrectly... I sprayed the glue on the foam until it was almost running (too much) and immediately stuck the two pieces together. The Acetone in that glue had to go somewhere... It went into the foam. Since then I did a second block. This time I sprayed it lightly on both sides from a distance of 8". Allowed it to dry a bit for a minute or two until it was tacky. Then I stuck the two pieces together. Seems to be holding great now! Wrong procedure. Not wrong material, apparently...
Oct 23, 2013, 01:37 AM
Registered User
Yea, I've had the same experience with the 77, just have to spray it light. Also, the strongest bond with it is if you let both sides dry completely tack free, then press them together. It's counter-intuitive but it's actually a contact cement. Just make sure it's aligned, you won't get a second shot!


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