Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

A new summer hat for demons

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Old 07-01-2009, 01:54 AM
  #1  
MJD
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Default A new summer hat for demons

Hi folks,

Time to hit the sack! But I had a late night creative surge, so I drew up cowl templates on AutoCAD, which have been grafted around drawings of the Jett 60LX (actually, all Jett .40 block series I suppose) and a Nelson FISE .40. Grafted those to a ply spine, added blocks to the side, did a little jig with the scroll saw, then sanded merrily away for a few minutes and voila. The blocks for the engine apron and tank cover are seen there in rough form where they shall stay overnight. So.. this is supposed to end up being a plug for a neat little accessory fiberglass cowl to set on top of a Screamin Demon to cover up it's big ugly metal head but let a little air through to cool its nostrils. Whatchoo think so far? I get the first 5.

'nite all [sm=sleeping.gif]

MJD
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Old 07-01-2009, 03:19 AM
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soarrich
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Default RE: A new summer hat for demons

Looks good. You might want to increase the fin size to compensate for the forward area.
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Old 07-01-2009, 07:38 AM
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Default RE: A new summer hat for demons

That plane is going to look Great!
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Old 07-01-2009, 07:39 AM
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Default RE: A new summer hat for demons

Making some good progress there, lookin good.
Thanks for the pics.
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Old 07-01-2009, 10:12 AM
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Mike Connor
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Default RE: A new summer hat for demons


ORIGINAL: soarrich

Looks good. You might want to increase the fin size to compensate for the forward area.
I would think this would add to the Vertical Tail Volume Coefficient.
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Old 07-01-2009, 12:16 PM
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Default RE: A new summer hat for demons


ORIGINAL: Mike Connor


ORIGINAL: soarrich

Looks good. You might want to increase the fin size to compensate for the forward area.
I would think this would add to the Vertical Tail Volume Coefficient.
It's adding a bit of side area yes, with about half the moment of the fins. Whether it matters or not depends on the margin of stability it started with, but the engine and tank have side area and not too clean at that, so I am not sold on how much net destabilization there really will be. I plan to toss it as is. If it isn't enough I'll fix it.

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Old 07-01-2009, 12:31 PM
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Default RE: A new summer hat for demons


ORIGINAL: MJD


...so I am not sold on how much net destabilization there really will be. I plan to toss it as is. If it isn't enough I'll fix it.

MJD
My point is there shouldn't be any destabilization. Unless I am missing something here.
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Old 07-01-2009, 12:50 PM
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Default RE: A new summer hat for demons


ORIGINAL: Mike Connor


ORIGINAL: MJD


...so I am not sold on how much net destabilization there really will be. I plan to toss it as is. If it isn't enough I'll fix it.

MJD
My point is there shouldn't be any destabilization. Unless I am missing something here.
Vertical area ahead of the cg/cp is destabalizing.
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Old 07-01-2009, 01:05 PM
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Default RE: A new summer hat for demons

MJD, your cowl looks real good. I'd think it would be pretty tough to make any money off hand laid cowels? By the time you go through all the steps, you could have laid up half a purpose built speed plane's fuselage. At the rate I get stuff done, I'd have to charge $300 just to break even
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Old 07-01-2009, 01:06 PM
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Default RE: A new summer hat for demons

I've got a scratch built delta almost identical in size to the SD with a pretty massive cowl and the plane flys just fine.
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Old 07-01-2009, 02:10 PM
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Default RE: A new summer hat for demons


ORIGINAL: Lownverted

Vertical area ahead of the cg/cp is destabalizing.
Yes we know - but the fact is there was vertical area there before, not zero, and a lot dirtier at that. So the question was simply whether the cowl would represent a net destabilizing effect or not. The aircraft is not hanging on the ragged edge of lateral stability so I'm am not even worried about it. If it swaps ends into the ground after launch, I'll deal with it..

Mike C - oh yeah, you did mean you thought it would improve the picture didn't you? Now I get it.. ;-)

CP - you are quite right, unless I charge enough money to scare people. I want them myself though - always a good motivator - and I'll find out if I can offer them for a reasonable figure. I'll call it R&D for now.. not fooling around.. [8D]

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Old 07-01-2009, 02:52 PM
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Default RE: A new summer hat for demons

anything that keeps the dreaded drag down is cool
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Old 07-01-2009, 03:08 PM
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Default RE: A new summer hat for demons

Even though there was area there, (albeit dirty) the fact is by cowling it in, you are adding substantial area ahead of the cp/cg. Simply by the addition of the area, there will be some affect on stability. You have also reduced drag, so likely it will be a wash. There is plenty of tail, I'll bet probably won't notice any difference, but make no mistake there is a change.

BTW..it looks super cool
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Old 07-01-2009, 04:52 PM
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Default RE: A new summer hat for demons

ORIGINAL: Lownverted

Even though there was area there, (albeit dirty) the fact is by cowling it in, you are adding substantial area ahead of the cp/cg. Simply by the addition of the area, there will be some affect on stability. You have also reduced drag, so likely it will be a wash. There is plenty of tail, I'll bet probably won't notice any difference, but make no mistake there is a change.

BTW..it looks super cool
Why, thank you! Of course, cool factor is what really counts.

Yeah, I guess I can see how the cleaned up and greater side area would be more efficient at generating "bad" lift (ahead of the CG) in the lateral plane, wouldn't it? I was thinking about drag in the lateral direction being less.

Progress pics: The plug so far sitting in top of the fiberglass apron I molded to the top surface earlier. These will be bonded together now, and fairing puttly blathered in all the junctions and squidged into shape with my best old white TF nylon 10-6 filleting tool.

MJD

re: the brick - I really didn't want the wind to blow it off the sawhorses again.
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Old 07-01-2009, 04:56 PM
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Default RE: A new summer hat for demons

I meant to point out - it is a PITA thinking about a nice cowl nose shape, when you have to consider the big ugly blobs that R/C carbs really are on the front of the engine. I'd have to carve a goiter into the front of the cylinder jacket to allow for every size and shape out there I think.. So anyhow I stretched the top profile forward, leaving it perhaps overall a bit fatter than optimum (no kidding?) but certainly not all that bad, and I am fairly sure it will be a net improvement. The cylinder jacket is a NACA 0035 btw. Not a great speed airfoil for wings.

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Old 07-01-2009, 06:28 PM
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Default RE: A new summer hat for demons

MJD, don't forget that some of the real goooood APC props have blades that extend to the rear of the spinner backplate.
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Old 07-01-2009, 06:56 PM
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Default RE: A new summer hat for demons


ORIGINAL: combatpigg

MJD, don't forget that some of the real goooood APC props have blades that extend to the rear of the spinner backplate.
Okay, maybe I'm suffering from lacquer thinner fumes CP - are you meaning the pickle forks out front? I just haven't trimmed those yet. Or what are you cautioning me about? [sm=confused.gif]

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Old 07-01-2009, 07:15 PM
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Default RE: A new summer hat for demons

It will most likely be a nice fit between the LE and the back of one of those props after you trim the forks off. When you were talking about clearance for a carb, I thought you might be talking about making the cowl bigger up front......then there would be a clearance problem.
The best solution of course is to remove the carb and sell it to a 90 year old speed freak, then set the plane up with a venturi.
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Old 07-01-2009, 09:06 PM
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Default RE: A new summer hat for demons


squidged into shape with my best old white TF nylon 10-6 filleting tool.

Lol...I thought I was the only one who had one of those!!
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Old 07-01-2009, 09:09 PM
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Default RE: A new summer hat for demons


ORIGINAL: combatpigg

It will most likely be a nice fit between the LE and the back of one of those props after you trim the forks off. When you were talking about clearance for a carb, I thought you might be talking about making the cowl bigger up front......then there would be a clearance problem.
The best solution of course is to remove the carb and sell it to a 90 year old speed freak, then set the plane up with a venturi.
I didn't think you were that old, dude! Oh.. [sm=red_smile.gif].. you meant someone else.

Some more progress pics. The goo is too plastic to sand yet, but a good time to snip and trim a few things. So far it fits nicely. There's gotta be a couple of mph in this thing, I hope.

MJD
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Old 07-01-2009, 09:25 PM
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Default RE: A new summer hat for demons

Looks just a little bit nicer than a stretch of lumpy Monokote directly over the fuel tank.....
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Old 07-01-2009, 10:22 PM
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Default RE: A new summer hat for demons

I Like It.
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Old 07-02-2009, 11:15 AM
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Default RE: A new summer hat for demons

Sanded second coat of fairing putty, shot some primer on to look for all the booboos. I didn't zoom in enough for you to see them..

Now I'm liking it. It should even look cool with a rear header poking out coupled to a pipe. If this works out I will mess with the full meal deal, i.e. fully enclosed pipe. As is should be perfect for any of those old nitro guzzling AMA pylon engines with mini pipes. Wish I had one. Wish I knew someone who wanted one of aircraft so bad (yeah right ) they'd barter for one. Dream on buddy.

MJD
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Old 07-02-2009, 12:11 PM
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Default RE: A new summer hat for demons

Looks very studdly. If you showed up at our club field with that beast the parking lot would be empty before you could spit.

I'll bet your plane will need an air filter to keep chunks of Cermark F-16s out of it's stool.

Keep up the faith looking for old F-1 engines, they're out there.
In your travels if you see a K&B 6.5cc P/L set, let me know!
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Old 07-02-2009, 09:23 PM
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ORIGINAL: combatpigg
I'll bet your plane will need an air filter to keep chunks of Cermark F-16s out of it's stool.
Even with a .46FX and a 9-8 I think...
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