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Oct 16, 2019, 01:11 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Build Log

El Gringo in foam


I like the look of this classic 60s model and its straight forward design (see attached article and plan).
To me there are definite hints of P51B, with perhaps a little Spitfire and BF 109 thrown in too.

Mine will be made up from a single sheet of 50x600x1200 Knauf insulation foam as it is the only stuff that is readily available around here. Not the best stuff to work with but you use what you can get.
Wings will be hotwire cut using a gravity drop arm cutter. The fuse and tail will be made up from 10mm strips (Rotten stuff curls as use hotwire cut it )
The whole lot will be then covered in brown paper and PVA for strength and durability.
Motor will be a 3536 1000kv, ESC 50A, Battery 2200mA 4s and wingspan 1250mm

The original used tricycle LG but this one will be tail dragger with retracts.
There are other slight changes due to the extra room needed in the nose for the electrics and their cooling.
And I will use a more conventional style of canopy.

Hopefully I can keep the weight down to less than 1300 grams but unfortunately I do tend to over build these things.
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Oct 16, 2019, 03:48 AM
2 metre rule applies!
DRAMJET's Avatar
Nice model in the first pic.
El Gringo looks good too!
Oct 16, 2019, 09:36 PM
Build straight - Fly twisty
Whiskers's Avatar
I really like the looks of the El Gringo.
Keep weight out of the tail or you will be adding nose ballast.
Everything that can go forward should go forward. Every gram that can be removed from the tail should be removed.
It'll be a sweet flyer...
Oct 17, 2019, 02:44 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Thanks Whiskers, it is a nice looker and I'll try to do it some justice.
Ballast is for sailing ships not airplanes.
I have left enough room to shove all the electronics as far forward as possible, however the paper covering will add a lot of weight to the tail (1g tail =3grams nose).
I can shift the motor further forward if need be and then extend the length of the cowl. I had to do this on a recent build called the kwiki (see blog).
You never really know with scratch builds until they are near complete. But that's just all part of the fun.
Last edited by brett.c; Oct 17, 2019 at 03:36 AM.
Oct 17, 2019, 07:27 AM
Build straight - Fly twisty
Whiskers's Avatar
I tend to do progressive weight tests as I build, aiming to resolve any CG issues during construction.
Like you, I hate adding ballast.
Oct 17, 2019, 09:46 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
The fuselage is starting to take shape now.
I still haven't quite got he hang of hotwire cutting but after sanding the end results are acceptable.

Installed the main electronics etc and the cg was just ahead of the leading edge. So far so good.

Can't wait to cover it with paper. You just have to look at this foam to ding it.
Not that easy to sand either. Coarse paper just rips it up. I find that shaving it down with a blade and then sanding with a multitool with a 240 grit pad works best.
Oct 17, 2019, 10:49 PM
Build straight - Fly twisty
Whiskers's Avatar

Very nice!


I like it!
Oct 19, 2019, 04:05 AM
Registered User
gogoH2O's Avatar
as always great work bratt. gfy.
Oct 19, 2019, 09:39 PM
Blue Remembered Hills
ShropshireLad's Avatar
Subbed - can't wait to see the finished product!!
Oct 20, 2019, 06:40 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
A bit more progress.
The fuselage is nearly ready for covering with just a few more fiddly items to complete.

The cowl is made from a 50mm thick block of foam. After centralising the spinner with 3deg right and down thrust I hole sawed a 35mm hole through the block. The motor was wrapped with insulation tape such that the block formed a tight fit over it. The block was then sandwiched in place with the spinner base. After a lot of carving, cursing, and sanding the cowl began to slowly take shape. I will cover it in wbpu and 48g glass cloth and then dremel out more foam from the inside.

Once the fuse is covered I will start on the wings.
Oct 20, 2019, 09:22 PM
Build straight - Fly twisty
Whiskers's Avatar
That's the way.
Sand off everything that does not look like part of a beautiful airplane...
Oct 20, 2019, 11:29 PM
Foam is where the heart is
brett.c's Avatar
Thread OP
Quote:
Originally Posted by Whiskers
That's the way.
Sand off everything that does not look like part of a beautiful airplane...
I'm sure there are easier methods that yield better results but to be there is something very satisfying about curving and sanding things into shape.
Kinda like ancient ancestor skill bonding.
Oct 21, 2019, 12:26 AM
Build straight - Fly twisty
Whiskers's Avatar
Yup!
I'm more of a carver than a bender.
Thick foam is still quite light, and because it often does not need other reinforcement, it remains light.
The dust produced by bulk sanding can cause problems.
It's not good to breath, can cause sore eyes and annoy a wife.
My beloved proclaims, "There's foam everywhere!" if there are up to 6 flecks of foam in the house. Above that number, "The house is full of foam!".
I like to share the housework 50/50.
I make the mess and she cleans it up.
Oct 21, 2019, 02:42 AM
Foam is where the heart is
brett.c's Avatar
Thread OP
Quote:
Originally Posted by Whiskers
It's not good to breath, can cause sore eyes and annoy a wife.
Dust mask and eye drops. I once blew the dust out the shed and all over swmbo's washing, so other minor infractions pale in comparison.
Oct 21, 2019, 08:05 AM
Build straight - Fly twisty
Whiskers's Avatar
Oh no! Not the washing! That is a transgression of a very high order indeed.


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