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Nov 20, 2015, 10:41 AM
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Started on the Hellcat (Blue Bullet)

...going for round 2 on building these cartoon warbirds. Learned a bunch from building the P-40 so hopefully this one will go a little smoother. Lots of new techniques to learn but very fun!

- I replaced Formers 1 and 2 with 9mm EPP. Found out the hard way on my P40 how fragile the nose section can be and broke those on almost every landing(derp.. crashing), so beefing up this area this time around.

- I am also using Foam Tac for most of the construction(contact method) which makes for a much quicker build but partly due to my lack of weights to hold the pieces in place for the 2 hour dry time(and attention) of PU.
Last edited by Sethorus; Nov 20, 2015 at 11:02 AM.
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Nov 21, 2015, 07:43 AM
When cows fly!
Originally Posted by sparks
Before we get to the ailerons there is some time consuming steps to do.
If you have not done it already it is time to trim and sand the edges of the wing to shape. We are looking for a smooth radius that blends into the sheeting. I start with 120 grit and finish with 280. Sharp leading edges stall a wing quickly.
The sanded portion may feel smooth but when it is painted it will look fuzzy. To fix this I coat the sanded areas with wood workers glue spread with my finger. This fills the open cells of the foam and gives the wing a crust for ding protection. After the glue has dried it will feel very rough; sand it once more with 280 grit and reapply and you are done.
Have you tried WBPU/Spackle/BP for this step?
Nov 21, 2015, 07:44 AM
When cows fly!
Or just Water Based Poly?
Nov 21, 2015, 10:16 AM
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Spackle will appear flat when the paint goes on because it will soak it up.
WBPU does not sand as smooth, sort of balls up and feels like rubber when tapped.
Also if you get glue on the smooth portion of the foam you can wipe it off with a damp rag.
Nov 21, 2015, 05:42 PM
When cows fly!
Makes sense!
Nov 22, 2015, 10:54 AM
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again, no weights, but the contact-cement method with Foam-Tac worked great and I didn't have to use the leading edge spacer. Just coated the surfaces with FT, rolled the top sheeting from back to front, press down evenly, roll back like a hinge on the trailing edge, wait 5 minutes, hinge back over, roll the sheeting back down and voila! instant set....
Nov 25, 2015, 10:44 AM
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WBPU vs Thinned Tightbond

after trying Sparks tip on using glue for the leading edge I wanted to do a test on which coating would protect depron the best from paint(Rustoleum in this case)

Hands down, thinned tightbond brushed on(2 coats) worked great while 2 coats of WBPU still let the solvent penetrate and ripple the foam. Ouch, wish I would have tested on scrap, but will just spackle this mistake and paint over with glue.

So don't be afraid to use light weight spackle. As long as you cover it with thinned glue, it will take paint well...
Last edited by Sethorus; Nov 25, 2015 at 12:33 PM.
Nov 26, 2015, 05:14 PM
When cows fly!
Thanks for this test. I have tried wbpu as a barrier before and was less than pleased with the results. Now I know
Nov 29, 2015, 05:16 PM
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Looking great!
I'll have to try the foam tack to see how it holds up for the spars, Should work great.
Nov 29, 2015, 05:17 PM
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Special tail feather notes.

Before the epoxy sets up flex the controls to be sure you have plenty of throw.
Also note the bottom rudder hinge is larger than the rest. This is so it can take the load of the tail wheel.
Set them aside and do the glue coating to the edges as you get the ailerons ready.
Nov 29, 2015, 05:18 PM
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To install the elevator cross over wire.
Bend the wire to match the plans then put it in position and press down to leave a dent in the foam.
Use a heated wire to melt slots into the foam panel and epoxy the wire in place .

Note the offset in the wire, this is to save space for the control horn .
Nov 29, 2015, 05:21 PM
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Locate the aileron hinge line strip in the wing by holding it up to a bright light.
Mark the half way point of its width. (should be the same width that is on the plans)
Cut slots at the inboard ends of the ailerons. I prefer using my Scroll saw for this step because it leaves a little gap and I know it is 90 degrees to the bottom of the wing.

While holding a hobby knife at a slight angle toward the trailing edge cut the ailerons free from the wing. Several light weight cuts will give you a cleaner cut.

When there is a left and right surface; I mark them with a highlighter pen to keep a check on myself.
Nothing more aggravating than beveling a surface the wrong direction.
Nov 30, 2015, 11:09 AM
When cows fly!
As usual, learning a lot!
Dec 03, 2015, 05:50 PM
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Sand an equal angle into the ailerons bottom leading edge that you cut with the knife in the wing.
This will allow the aileron to move downward after the hinges are in place.
A small amount of sanding will be needed for the strip above the hinge line as well.
The hinge line is easy to find, it is where the top sheeting and spar strip meets if you used a dark highlight pen during the sanding step it is easy to see.

Note the use of the wood strip. The strip is used to hold the aileron straight against the pressure from the sanding bar. and gives us a good straight angle.

Use light sanding pressure and count your strokes to give you a sense of how much material you are removing.

Wait for the next steps Before you hinge the ailerons . . . .
Dec 03, 2015, 05:54 PM
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Aileron servo

This is where there is a major difference from all the other Cartoon planes.

The servo mounts are on the bottom of the wing.
This does three things for the plane. It allows us to make adjustments easily, Keeps the weight low for a more stable airframe lay out and keeps us from putting a hatch above the wing.
(Hatches weaken a fuselages.)

So, get out the wing pattern again and cut the hole locations.
Hold the wing up to the light to find the spar that separates them to be sure you put the holes in the right place.
Mark the holes for the servos and cut.
the servo wire will pass thru the spar and the top sheeting will require a cut to allow the servo seat completely.

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