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Jan 31, 2019, 06:12 PM
gpw
gpw
“There’s no place like Foam”
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Those Ebeneezer models were first invented by my old Friend and Airplane Mentor Bert Streigler … What a Great guy and Super modeler … I visited often when he lived in SW Houston … It was Mr. Streigler that introduced me to my first Foam wing electric RC airplane made from two yardsticks , with a tissue covered foam wing and tail … Astro 10 … Heavy , but it flew fine … And later we ended up with the original “ Gulf Coaster” … a really Nice size glider … Flew super with it’s Royal radio …
Last edited by gpw; Jan 31, 2019 at 06:18 PM.
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Jan 31, 2019, 06:19 PM
low tech high tech
vtdiy's Avatar
Thread OP
One side through......
Jan 31, 2019, 06:24 PM
low tech high tech
vtdiy's Avatar
Thread OP
And the other side through.

The cowl was marked out and cut the same way. The only difference was there was so little foam to remove that I did it with the sanding block instead of the saw.

This gives us a good start on shaping the block. I'm going to have to leave off for supper, but an hour's work with scraps of foam, and a bare minimum of tools has got us a set of patterns, and almost a kit of parts for this Scientific model conversion.
Last edited by vtdiy; Jan 31, 2019 at 06:30 PM.
Jan 31, 2019, 07:00 PM
Registered User
JSKYVOLT's Avatar
Please delete. Sorry did not notice scratch built foam. Pics were of the balsa block versions. And yes I am near the NH & VT borders, planning on getting back to 1/2a size models, even goo powered! Will put back the pic if appropriate. Cheers. Jim
Last edited by JSKYVOLT; Jan 31, 2019 at 07:46 PM. Reason: Wrong forum/material
Jan 31, 2019, 07:26 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Very nice vtdiy! Keep the momentum going. Will be interesting to see just how long it takes for the build.
Jan 31, 2019, 07:39 PM
low tech high tech
vtdiy's Avatar
Thread OP
Jskyvolt, nice! You're not far form me -- Brattleboro area!

Ruff1, thanks! Will do.
Jan 31, 2019, 09:13 PM
Ken's CAD Models
dz1sfb's Avatar
Quote:
Originally Posted by vtdiy
Thx DZ1, I've designed for a fold-over sheet fuse before -- see my UL "Unfinished Business" bipe thread for a big one. I'm purposely going with the log style carved fuse, and flat wing, just cause I want to try to mimic the original Scientific style of construction for fun.

If anybody else wants to build this or any other Scientific 1/2A C/L plane adaptation with any other type of construction, have at it! Please post here, I'd love to see them!

Back to building......

I cut out the flat pieces using the patterns as guides:
Truth be told, that block insulation is actually very light. That is how I modeled the BD-5J in my avatar. It originally started as just something to do, but then I put some Aero Ace gear on it, and the rest is history. I've been infected ever since.

I did see your "Unfinished Business" thread, and it looked very nice.

Ken
Jan 31, 2019, 09:38 PM
low tech high tech
vtdiy's Avatar
Thread OP
Hey Ken, thanks!

A few small details about this present build I should mention that will also affect flying R/C a bit in the positive direction. I put the wing panels together tonight with 3" total dihedral each.

The flat plate wings shown on the original plan also actually have a radiused leading edge and the last inch of the trailing edge tapers down from the top. Thus there is some camber in the foil and some effective incidence. About 1.25 degrees, even though it lays flat on the fuselage.

Also since I'm using standard 1/4" fanfold foam, the foil is a little thicker than true scale -- which would have been about 3/16". It's actually a resulting 6% thickness on this chord.

I have been considering shimming the upper wing maybe an additional 1/32" for a slight bit of decalage. That combo will mean that the H stab has a small effective negative incidence, even though also seemingly inline.

So this may work out a little more "trim" than might first appear. I'm sure it won't fly hands off on the maiden, but corrections, I hope will be moderate for something entirely new and untried.
Jan 31, 2019, 09:51 PM
Build straight - Fly twisty
Whiskers's Avatar
If it looks right, given your experience and skill, it will be right.
If it does not look right, given your experience and skill, change it until your experience and skill tells you it looks right.
Then it will be right.
Right?
Jan 31, 2019, 09:56 PM
flyin' fool
goldguy's Avatar
I posted about the Ebenezes to show that flat airfoils work on bipes too.
Jan 31, 2019, 10:14 PM
low tech high tech
vtdiy's Avatar
Thread OP
Right on, both of you!

I think this plane will do well. 15 mph stall 33 top, and 1000+ fpm ROC if I'm foolish enough to hand launch full throttle -- a feat I managed to "nearly" pull off a couple times in the past. I just HAVE to remember this time......maiden...launch at half throttle......maiden....launch at half throttle.....

If my similar size SE5A was any measure, this thing will roll fast with rudder alone, and will have nearly neutral roll stability, so you need to bank it back when you're done turning.

Remind me, guys, when the time comes....
Jan 31, 2019, 10:30 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Quote:
Originally Posted by vtdiy
So this may work out a little more "trim" than might first appear. I'm sure it won't fly hands off on the maiden, but corrections, I hope will be moderate for something entirely new and untried.
Your first cut at this will tell us a lot about the proper setup, thanks for blazing a trail for us.

I already have two Cubs, plenty for the Cub Fly day at the field. The V tail Bonanza is calling, but I'll need to get some advice on setting up the empennage. If i can get it light enough and she flies well would love to put on a coat of Mod Podge or something similar and get a nice coat of paint on it. My paint jobs are sorely lacking and i need to do better. Project show is coming up, one of these would be nice to display; im sure some of the guys in the club will have had one of these models.
Jan 31, 2019, 11:04 PM
low tech high tech
vtdiy's Avatar
Thread OP
Ruff1, I think modge podge is heavy for this kind of small foam plane. I use lightweight spackle watered down, sometimes mixed with a small amount of talcum powder and a few drops of Minwax polycrylic. FreddieB made this well known as "secret sauce" though I used talcum powder and dope the same way back when I was building the original Scientific models, and the change from dope to lightweight spackle and water (which don't attack foam) was well known to foamie folks here a couple decades ago. Freddie did a great job formulating it into one recipe, and letting people know about it.

Anyway it makes a very lightweight easily sandable foam filler which acrylic craft paints adhere to well. Toughest adhesion acrylics, in my experience are Apple Barrel brand -- I've done adhesion and aging tests with it and many others in the Doculam thread.

If you really want to save weight and yet get a fine finish on foam, after filling, you will need to airbrush the final color. I've hand brush painted most of the models I've ever built, and will continue for most, but honestly on the few I've airbrushed, the weight difference opposed to even thin careful brushing of multiple thinned coats is noticeable.

Hope that helps -- I'll show you what I usually do on this model when we get there.
Feb 01, 2019, 06:31 AM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Great, thanks. It has been a real struggle for me to get some kind of attractive finish. I don't have an air brush, I'm simple and like rattle cans. I have done some experimenting with Krylon Shortcuts over coffee filters and tb2/water, and that covers very well. I think if i can get a good lightweight surface prep on the foam I can still go the rattle can route.
I forgot about FreddyBs sauce; never tried that.
Feb 01, 2019, 09:31 AM
low tech high tech
vtdiy's Avatar
Thread OP
Last night I glued the wing panels together with 5 minute epoxy -- my favorite go-to glue for this particular purpose.

I could have done a straight 2 panel dihedral, but that would mean I had to bevel the solid foam fuselage block to fit the wings. Instead I decided to do a 3 piece wing, with a flat section where the wing mates with the fuselage.

Since the fuselage will end up about 2" wide, the center panel would need to be at least that wide. So I marked off a 1" strip of each panel at the root, and cut it off. Two of these were joined together flat first before adding the outer panels at their dihedral angle.

Ideally I'd have thought ahead and drawn the plane with three piece wings instead of two piece, and then the center sections could have been 2" wide, instead of 1" strips glued together. No biggie, and I'll change that when I revise the plans after this thing flies (or doesn't).

The outer panel root edges were beveled slightly to accept the dihedral when joined to the center section, glue applied, panels joined and the tips were raised so that the top of the tip on each side was 1-3/4" off of the table top.

These wings were peeled fanfold from an old bundle I bought many moons ago. Dow blue fanfold is no longer available, as far as I know. But Owens Corning now makes what seems to me the identical product in pink.

Let me clarify that -- Owens Corning used to make a pink fanfold that was about 3/8" thick, and was quite different than the Dow blue fanfold. It was much more uneven, brittler, and more difficult to peel the plastic sheet off of.

However, in insulating under my house this Fall, I bought a couple bundles of Owens Corning fanfold from Hone Depot, and this time it was reduced in thickness from 3/8" to 1/4", and as uniform as the old blue Dow stuff. It seemed as flexible and easy to peel too. In fact it seemed identical in all ways to the old Dow fanfold, other than the fact that it is pink.

So there is a 1/4" fanfold available again, apparently, and Home Depot carries it. It is the single plastic skin type, not the double "Protection Board" type.

Okay enough about fanfold -- back to the model, here are the assembled wings this morning:
Last edited by vtdiy; Feb 01, 2019 at 09:36 AM.


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