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        Build Log He-219 UHU

#1 pmullen503 Jan 07, 2013 01:02 PM

He-219 UHU
 
2 Attachment(s)
I've wanted to build an He-219 ever since I saw the last remaining "UHU" at the Air and Space Museum, Udvar Hazy Center a couple years ago.

There are a couple aspects about the plane that made me hesitate. The nose gear for one. The small wheel and long strut made it look questionable for flying off of grass, at least at the scale I'd planned. Secondly, the 219 doesn't have a huge wing to haul around that long fuselage and nacelles.

The solution was to make it a hand/catapult launched belly lander and just eliminate the landing gear to keep it as light as possible.

I'll be using heat molded foam for the fuselage and nacelles, and the "laser method" to make the wings just like my last several builds.

Specs:
WS 52"
Area 400 sq in
length 44"
Weight 44 oz
Power 350 watts

#2 **neons** Jan 07, 2013 01:22 PM

Nice museum picture there. I hope they have the rest of the plane. Where is it being shown?
Thanks,
**Neons** Bob

#3 turbonut Jan 07, 2013 01:44 PM

See top line in his post!

#4 pmullen503 Jan 07, 2013 02:00 PM

Quote:

Originally Posted by **neons** (Post 23741090)
Nice museum picture there. I hope they have the rest of the plane. Where is it being shown?
Thanks,
**Neons** Bob

They have the rest of the airplane and its undergoing restoration. Udvar Hazy is near Dulles airport in Virginia and is really worth the trip if you are anywhere near the area.

#5 **neons** Jan 07, 2013 02:28 PM

My overlooked it. My eyes were focused on the pictures.

#6 pmullen503 Jan 07, 2013 08:27 PM

5 Attachment(s)
The first step is to blow up a 3 view to the proper size. I trace over it (in Coreldraw) to get the drawing into an editable form and fair up the lines. That way I can print out full size templates.

The backer boards are made from 1/2" plywood. Blocks of foam are rough cut to size with a hotwire using cardboard templates and then glued to the boards. There is a gap between the blocks the width of the cardboard templates so I can slide them in while shaping to check progress. Rough cutting the blocks is the most time consuming part of the process.

Dead straight 1x2" spines are screwed to the backers. These not only allow me to clamp the form in a bench vise to hold it while shaping, but also keep the form from bowing when baking it in the oven.

First, I shape the foam with a drywall sanding mesh tool to quickly to bring it to shape. Once I get it to within about an 1/8" of the final dimensions I stop worrying about matching the templates exactly and concentrate on getting nice fair curves and making both sides match each other. There's no guarantee that the 3 view (or my tracing of them) is correct. So when in doubt, I try to match photos. Shaping the forms takes me about an hour.

Once I'm satisfied with the forms, I give them a heavy coat of WBPU to harden them up a bit and make them more dent resistant.

#7 pmullen503 Jan 07, 2013 10:15 PM

4 Attachment(s)
Now that the forms are made I'm ready to form the fuselage shells. This method is based on techniques worked out by Harpye several years ago. The key innovation was the use of packing tape as the female mold. The main benefits are that the formed foam is inherently stiff for it's weight, it's easy to build from a simple 3-view or even just photographs, it's cheap, and once you have the forms made, additional copies can be made quickly.

I'm using 1/4" fanfold foam but I've used Dollar Tree foam and depron too. The taping of the foam (and the oven I built) has been covered in detail is these threads:
http://www.rcgroups.com/forums/showt...ighlight=ki+46
http://www.rcgroups.com/forums/showthread.php?t=1454109
http://www.rcgroups.com/forums/showthread.php?t=1300153
http://www.rcgroups.com/forums/showthread.php?t=1549389
so I won't bore you by repeating it here.

Once the foam is taped to the form it's baked at 100C for 15 minutes. Thinner foam takes less time and you have to be careful not to cook it too long or the form can be damaged. After it comes out of the oven I trim the shells flush with the top of the backer board and mark the former locations using the saw cuts in the backer boards. From this point everything is done in situ so I draw an accurate reference line as shown below to make the wing and stabilizer cutouts.

This is the 8th model I've done with this technique and I've successfully(?) destroyed 3 of them so I've seen how they fail. The formed shells make a very stiff fuselage so no structure is needed for that. And whether covered with fiberglass, paper, or Styrospray 1000 (aka liquid sheeting) they don't fail under tension. The weakness of the foam is compressive strength: on impact the foam collapses under the skin. This is harder to repair than a clean break. So I've been experimenting with adding carbon or bamboo rods or sheet balsa to add some compressive strength to the system.

On the He-219 the sides are almost flat so I glued in a piece of 1/16" balsa from nose to tail. This will also form part of the wing saddle. I placed the shell with the glued balsa stiffener back on the form (covered in plastic wrap) and wrapped it more plastic wrap to clamp the balsa stiffener tightly to the fuselage while the glue set.

I made new templates for the formers by slipping cardboard into the form slots and tracing the form. After cutting out the formers I glued them into one side. Then I added the flexible pushrod sheath for the elevator. After checking that both sides would come together tightly and after tweaking a couple oversized formers, I glued the halves together.

The weight of the fuselage at this point is about 120g (minus the tape) after covering with Styrospray 1000 and adding the wing saddle and battery hatch, it should come in well under 200g. I'll leave the tape on the outside to protect it until I'm ready to coat it with Styrospray.

#8 Smokin' Beaver Jan 08, 2013 04:44 AM

Nice work - I'm sub'd!!

Phil

#9 Quorneng Jan 08, 2013 03:05 PM

A nice build.
The He 219 is an interesting subject and has an impressive appearance. I still have an unfinished 60" span control liner sitting in the roof!
The main concern about the wing is not so much its area but its massive taper towards the tip which is likely to promote the tip stalling well before the root!
I shall watch with interest.

#10 J Morgan Jan 08, 2013 04:39 PM

Nice work Pat

J

#11 pmullen503 Jan 08, 2013 04:53 PM

Quote:

Originally Posted by Quorneng (Post 23752669)
A nice build.
The He 219 is an interesting subject and has an impressive appearance. I still have an unfinished 60" span control liner sitting in the roof!
The main concern about the wing is not so much its area but its massive taper towards the tip which is likely to promote the tip stalling well before the root!
I shall watch with interest.

The wing will have washout. It's about the same size as the Aeronaut He-219 kit and those seem to fly OK. Plus, I hope to bring it in at about 2/3 the wing loading of Aeronaut's version so it should be fine
.

#12 pmullen503 Jan 08, 2013 05:03 PM

Quote:

Originally Posted by J Morgan (Post 23753601)
Nice work Pat

J

Thanks John, really enjoyed your AC-119K build. My 219 fuselage would just about fit inside your 119!

#13 floss Jan 09, 2013 04:11 AM

There are numerous He219 scratchbuilds of various sizes on different RC sites and they always seem to fly fine.

#14 pmullen503 Jan 09, 2013 07:14 AM

2 Attachment(s)
I cut out for the tail section and made a quick mock up of the tail just to see how much room I'll have for linkage in the fuselage.

Plan A was to hot wire cut the stab and sheet it with 1/32" balsa with Sullivan S507 flexible pushrods inlaid under the skin and external linkages. Now that I have the mock up in hand, it looks like there's room to completely bury the rudder linkage inside a built up and sheeted balsa stabilizer. I'll have to think about it some more.

#15 Rekitter Jan 09, 2013 02:44 PM

Cool project and interesting building technique. Looking forward to following your progress.


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