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Jan 30, 2016, 02:35 PM
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Mini-HowTo

Durafly Mk1a Spitfire make-over


Hi Guys and Gals

Presented below is a make-over of the very first DF Spitfire MK1a that came out of the mold that Stuart sent me for flight test evaluation. It came to me in bare white foam but in all other ways was representative of a production model in shape and function.

I decided to make this a "B" scheme (mirror image camo of the "A" scheme found on a stock DF spit) Mk1a flown by Robert Stanford-Tuck around May 1940 during the "phony war". GR-P N3249.

First I needed to resize the horizontal tail to match the full scale. It was decided to make the model with a 10% larger tail to make it easier for novice to intermediate fliers to fly. I printed out a scale size tail and cut the stock model one to size in planform first. The I marked the middle of the foam on the LE and TE to give myself something to sand to. I also marked the approximate "high point" of the airfoil on the top and bottom surface.

Sanding EPO is not pretty. You have to use some pretty coarse grit <100. After rough sanding, one can go over this with 180-200grit, but do not be too concerned if you don't get it too smooth.
Last edited by Tom Hunt; Jan 31, 2016 at 09:56 AM.
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Jan 30, 2016, 02:41 PM
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I chose to mount the horizontal tail permanently. Then use light weight acrylic spackle to fill the gaps created by the smaller tail.

Not shown here (because I forgot to take pictures), the raw foam of the horizontal tail was successively paint (with a brush) with Gesso artist canvas primer and sanded. This water based hi-solids primer is a good foam filler and sands easily. Comes in Gray, Black and White for about $10 a 16ounce bottle. It also toughens the "rash" created from sanding to make it easier to sand and smooth after a few layers and sanding. Ity is used full strength the fist couple of times, then can be thinned (I use windex, not water) for the last couple of coats.

Once a decent finish is achieved, recoat with Rustoleum Auto primer.
Jan 30, 2016, 06:55 PM
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Let the painting begin.

I used rattle-can silver on the whole model. Took two coats. Then semi-gloss black and white for the bottom of the wing. I hand brushed the blue-green wheel wheels and cockpit. The Green camo was applied first (full strength flat Behr latex house paint) as the brown goes over the green better than the other way around.

Though technically not the best match to the conversion of the RAF colors to the FS 595B colors for the BoB, the brown and green I chose does match almost exactly to the Eflite Hawker Hurricane. Windsor moss (hey, that's british, isn't it?) and aging barrel from Home Depot are nice colors.

The green is applied full strength with a brush for the first coat and then sanded lightly to remove any high brush marks. The a second coat with 25% windex is applied, then a third with 50% windex. The brown will be added in a similar manor, all hand brushed.
Last edited by Tom Hunt; Jan 30, 2016 at 07:21 PM.
Jan 30, 2016, 10:36 PM
Out of the Past

Behr Paint


Should mention that the Home Depot color matched paints have a harder finish and will take a 400 grit light sand and not pull at edges like the stock paint. Good for a buildup "primer" alternated with spackle between a couple coats which will give u a smooth base for finish painting with a blend between the different paints while sealing the edges on the original paint.
Duck
Did I say that right?
Jan 31, 2016, 09:24 AM
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Tom...

You're a brave man Charlie Brown. You'll probably need that pitch gyro you mentioned...

Great job on the mod...you're quite the modeler. (Actual modelers are a dying breed)

Adam
Jan 31, 2016, 09:57 AM
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Quote:
Originally Posted by Adam Stang
Tom...

You're a brave man Charlie Brown. You'll probably need that pitch gyro you mentioned...
yes, but I suspect the gain will be rather low.

Quote:
Great job on the mod...you're quite the modeler. (Actual modelers are a dying breed)
thanks... more to come.
Jan 31, 2016, 10:01 AM
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probably should have gone flying today as the weather was not that bad but instead:
First coat of brown applied.
Jan 31, 2016, 02:46 PM
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some pics outdoors with full coverage green and brown.

added the antenna mast, top dome light cover and threw the prop and spinner on just cause I could... need to paint the tips yellow though.

I still need to mount the gear doors on the oleo struts I installed.

Waiting for my "new" canopy to come from Int warehouse as that one is a bit tired. also have some decals coming from same warehouse. Not sure how I will do the code letters, may do myself or send to callie.
Jan 31, 2016, 02:50 PM
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oh,... one thing I did not mention.... Though this model was "originally" stock with the right thrust, I printed a new cowl with it taken out and adjusted to motor mount to straight ahead.....

I KNOW how to use the rudder! WARBIRDS did NOT have right thrust... some had down thrust (P-51B/D and Mk12spit and on), some had up thrust (BF-109).... but NONE had right (or left thrust)

Spinner gap now closed up. Motor will run a bit warmer, but I will keep an eye on that!

Tom
Jan 31, 2016, 07:22 PM
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Got to have those rudder skills, and like you ...I have them, but with any full scale plane we make trim adjustments every time we change throttle settings and usually spend long periods of time at a consistent speed and setting...with a model we change throttle settings and speeds constantly. It seems to me (just my best educated guess...please tell me if I'm on to something or not even in the ballpark) that the right thrust in our models is there for a few of reasons - one, our models have wildly lighter wing loadings and much higher thrust to weight ratios so they have the potential to be affected by P factor more. Two, the right and down thrust helps keep our models "in trim" over a broader throttle and speed range, and three...most model pilots have questionable rudder skills and may need the help.

As much as we maneuver and change speeds in a model flight, seems like you will really be compensating much more with the rudder than normal...may very well be what you want and it would be a fun challenge, but it may be more than the average Joe will want to have to constantly correct for.

Nice thread...looking forward to seeing your progress and getting your flight report.

Adam
Last edited by Adam Stang; Jan 31, 2016 at 07:50 PM.
Jan 31, 2016, 09:22 PM
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Adam

the only time P-factor can be noticed enough to do something about it (by the ground based pilot) is during take-off or an emergency punch-out on an aborted landing (when the novice adds too much power too quickly). Many of the other times one gets a bit of P-factor into the flight goes unnoticed when one is flying from the ground (it quite obvious when one is flying FPV though! quite cool!)

Also, P-factor is only around when the prop disk is at an inclination to the flight path (such as the early moments of a tail dragger take-off). Once in the air and the AOA is kept low, there is little to no P-factor. Changes in yaw trim in any air vehicle do to power is more a slip stream effect than p-factor, assuming the AOA is low.

Many ww2 aircraft used offset or cambered fins to help with rudder forces during those hi-p-factor times and is much better than engine offset as it is only speed dependent and not power dependent. sorta like the guy that programs in a little down elevator to keep from ballooning with high throttle instead of using downthrust. Set up right, it can be much more effective.

Low inertias/high power to weight in our models does not help either, that is why i also teach guys to add power slowly during Take-off.

Tom
Feb 01, 2016, 08:34 AM
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Tom,

I use rudder quite a bit during a typical flight...to coordinate turns, etc. I gradually feed in right rudder a good bit during vertical climbs and on the upline towards the top of loops and Cubans (how many times have we seen someone start a big loop and finish well left of their starting line)...I always assumed in maneuvers like that as the plane slowed down, but the power setting stayed high...that the affects of P factor was what I am correcting for. Is this correct or is that caused by something else other than P factor?

Thanks,

Adam
Feb 01, 2016, 02:17 PM
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Looking good Tom, can you convince HK to paint some in the B cammo pattern like you have done?
Feb 01, 2016, 10:29 PM
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Adam

Yes, a "trained" pilot (from the ground or inside the aircraft) will compensate for P-effect during any positive g maneuver, but without a lot of practice it is very difficult to tell how much you need for the AOA change when standing on the ground. No amount if right thrust will compensate EXACTLY for every AOA you choose to do you loop or other + g maneuver that puts the prop disk plane at an inclination to the oncoming flow.

Until I started flying fixed wing FPV, I never realized how much rudder I needed or didn't need to make a coordinated turn or a nice straight ahead round loop,

The argument here is whether right thrust "helps" to maintain a straight heading to correct for ANY yawing moment whether it comes from direct prop effects (yaw due to torque/dihedral coupling, P-effect or gyroscopic) or indirect effects like slipstream swirl.

Since the amount of right thrust required to trim an aircraft varies due to aircraft configuration (long vs short nose), speed and AOA, I say why put it in if it serves no purpose. I have long said that right thrust is a hold-over from the old freeflight days when no human intervention was available!

Quote:
Originally Posted by Adam Stang
Tom,

I use rudder quite a bit during a typical flight...to coordinate turns, etc. I gradually feed in right rudder a good bit during vertical climbs and on the upline towards the top of loops and Cubans (how many times have we seen someone start a big loop and finish well left of their starting line)...I always assumed in maneuvers like that as the plane slowed down, but the power setting stayed high...that the affects of P factor was what I am correcting for. Is this correct or is that caused by something else other than P factor?

Thanks,

Adam
Feb 01, 2016, 10:29 PM
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Quote:
Originally Posted by merlinfan
Looking good Tom, can you convince HK to paint some in the B cammo pattern like you have done?
I doubt it.... more $$$$!


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