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

NOW BE HONEST....

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Old 08-07-2009, 07:40 PM
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combatpigg
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Default NOW BE HONEST....

Hey you Monkey Spankers, I need some honest opinions here. Is this sucker gonna be a DOG?

I've got a .46 SJ on the way and figured that a Scimitar type plane would be a good fit for it.
The trouble is, it is begining to look like a very disappointing delta I built back in 1990, for a Webra .50.
It was a DOG. But it was built way too heavy and the wing was somewhat thicker.

What I have here is a 1.625" thick airfoil [with 1/16" sheeting] that will have about 20" of root chord.
The span is 56 inches, the tips will have 10" of chord.
Depending on how the design gets executed, I can't see it weighing over 4 pounds.
So be honest, compared to the .60 sized ME 163, what do you think I have here? There isn't much time invested so far. No matter what, the fuselage will do just fine. It was designed around a 6 oz tank and the SJ .46.
Pictured is a Rossi .45 which is more like the size of a .60......I just put it in there for reference.
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Old 08-07-2009, 08:23 PM
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Default RE: NOW BE HONEST....

Looks interesting,I would be tempted to clip the wing tips though.
Danny
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Old 08-07-2009, 08:23 PM
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Default RE: NOW BE HONEST....

Don't know if it will be a dog or not, but it looks cool.

My friend had a .049 powered Bill Evans wing ~5' it was pretty fast for a .049.
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Old 08-07-2009, 10:25 PM
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Default RE: NOW BE HONEST....

I like your version of CAD. Same one I use.
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Old 08-07-2009, 11:31 PM
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Mike Connor
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Default RE: NOW BE HONEST....

I think it will fly very well slow at 11 oz ft^2 wing loading and also be fairly quick with an 8% wing. The SJ 46 is a great engine but that 840 sq. in. is a lot of wing for for really high speed. If speed was my goal I would cut the root cord to 12 or 15 in. (from the back) and the wing tip cord down to 7" for a little higher aspect ratio and maintain the 8% thickness. That would still give you over 500 sq. in. I do not think it will be a dog the way it sits but not sure if you will make it much past 100 mph. Those are my thoughts.
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Old 08-08-2009, 12:02 AM
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Default RE: NOW BE HONEST....

I think you're right Mike. I'm going to clip some span from it, but it will still be a pretty big wing.
I think I'll finish it like a AMA fast combat plane, which means no balsa sheeting, just limited fiberglass on the surface and seal-lamen or fascal or doculam for covering. Those planes stand up to quite a bit. The key to this plane having any chance at all will be to keep it light.
I made a full depth spar out of 1/8" balsa sheet with a layer of CF cloth on both sides. Kind of a pain to get everything lined back up after making the drastic cuts to pass the spar through the fuselage and into each wing panel. In Gorilla Glue we trust.

Tom, we don nee no steenking CADs..[sm=pirate.gif]
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Old 08-08-2009, 07:53 AM
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Default RE: NOW BE HONEST....

Keep the span but cut the cord and add a tail to get proper pitch and yaw stability.

I also have the same version of CAD you do.
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Old 08-08-2009, 09:15 AM
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Default RE: NOW BE HONEST....

combatpigg

What you have is a plank flying wing which is basically a one speed airplane, fast or slow whatever you make it. The fact that it uses a airfoil with reflex make it very speed sensitive. If you use a airfoil without reflex you pretty much have to sweep the wings forward or backwards to get the pitch stability, but they aren't so speed sensitive.

I just flew my friends scratch-build 120" sailplane flying wing yesterday, it was very touchy on the CG. The plane went from what we both agreed was a little nose heavy to OMG I can't control this in a 1/4" on a 15" chord.
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Old 08-08-2009, 09:48 AM
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Default RE: NOW BE HONEST....

Hey Evan..........You want a tail? Man, you're a tough customer. And a CF fuselage too, I'll bet? The nerve of some guys, ask for an honest opinion and see what you get? Well, if you're gonna make me build a real plane, I'll have to get one of those CAD deals, take a night class in aerodynamics....

Well, I forged ahead last night and lopped off some span, framed the front and back with balsa sticks and will now spend an hour sanding it into shape. Are there any CAD programs to help with the sanding?

I'm going to stock up on materials to build another version after this one is done. I'd still like to stick with the flying wing idea, just work the idea down in size to what is just right.

I sure wish I could still come up with cheap laminating film. It came on big rolls that were enough to do about 12 combat planes. I think they call it Avery paper now. It's a clear plastic film with a sticky glue on one side. It should shrink slightly with low heat and it worked real well directly over foam.
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Old 08-08-2009, 10:16 AM
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Mike Connor
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Default RE: NOW BE HONEST....


ORIGINAL: evan-RCU

Keep the span but cut the cord...
Yep, those pesky aeronautical engineers keep telling me to consider a high aspect ratio wing for less drag.
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Old 08-08-2009, 10:37 AM
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Default RE: NOW BE HONEST....

Woof!

Still looks like fun, its all in how fast you want to go, I don't see much more than 150mph with that engine. The wing is too thick, and the Chord is two wide, although you may stuggle with stability if you cut the chord without a tail.
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Old 08-08-2009, 11:22 AM
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Default RE: NOW BE HONEST....

Hey Dave...150 is about what a Nelson .36 powered combat plane looks to be going after it gets cut loose and the fuel shutoff SNAFUS.....then it's time to grab a lawn chair and hope that the plane doesn't have a taste for human flesh, just dirt.

One thing about high aspect with flying wings is you can never find stability unless you put in a bunch of sweep. Sweep introduces structural challenges to keep light.....so then you're back to square one with compact designs. I've had good results with 4:1 flying wings, I don't know what the practical limit is before you start running into pitch stability issues. I'm a firm believer in low wingloadings to make any design idea more forgiving and easier to work with. I can see right now that some glassing will be needed on this plane to stiffen up the wing and this is where weight can really add up. In the past I've sprayed 3M-77 on the foam first to act as a barrier so the foam doesn't drink up a bunch of epoxy resin. I've even glassed over the foam after it was sealed with packing tape with good results.

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Old 08-08-2009, 03:41 PM
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Default RE: NOW BE HONEST....


ORIGINAL: combatpigg
I sure wish I could still come up with cheap laminating film. It came on big rolls that were enough to do about 12 combat planes. I think they call it Avery paper now. It's a clear plastic film with a sticky glue on one side. It should shrink slightly with low heat and it worked real well directly over foam.
Looks like a Q500-speed range aircraft to me, with the 1-5/8" thick wing. Bet it turns tight! Hope the wings stay on.

Is Doculam a possibility? Tyvek and contact adhesive? Tool handle dip..?

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Old 08-08-2009, 05:25 PM
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Default RE: NOW BE HONEST....

Someday I'll have to try Tyvek. It would also be nice to just dunk the plane in something and let it drip dry.
At this point the plane weighs 12 ozs. I think it could easily take 8 ozs worth of glass and resin to make it stiff enough. The plane is pretty rubbery right now. The RTF weight should end up being in the low 3 pound range with a nice glass job, plus I wouldn't have to use covering anywhere.
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Old 08-08-2009, 07:58 PM
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Default RE: NOW BE HONEST....

ORIGINAL: combatpigg

I sure wish I could still come up with cheap laminating film. It came on big rolls that were enough to do about 12 combat planes. I think they call it Avery paper now. It's a clear plastic film with a sticky glue on one side. It should shrink slightly with low heat and it worked real well directly over foam.
I got a closeout roll of laminate flim from these guys for about $15.00

http://www.usi-laminate.com/?source=...FRJM5QodIQ98eA
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Old 08-09-2009, 07:58 AM
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Default RE: NOW BE HONEST....

I wonder if you could cover it with .005 fiberglass sheet from aerospace composites?? epoxy and bag it to the foam??

Maybe, just an idea, looks like its coming along nicely.

Might be faster than we think.
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Old 08-09-2009, 09:00 AM
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Default RE: NOW BE HONEST....

Dave, I've never tried that stuff. There are some compound curves here out by the wing tips where they got hand sanded to shape.
I'll give what you are talking about a look.

Rich, thanks for that link. They sure do have a selection! I need to figure out how thick the old stuff was. I used to buy it and all other combat supplies in bulk from Bear Mfg.
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Old 08-09-2009, 11:52 AM
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ORIGINAL: daven

I wonder if you could cover it with .005 fiberglass sheet from aerospace composites?? epoxy and bag it to the foam??

Maybe, just an idea, looks like its coming along nicely.

Might be faster than we think.
If yer gonna do that, check McMaster for it and compare. They have G-10 / FR-4 "films" that are laminates in the .010" +- range.

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Old 08-09-2009, 04:48 PM
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Default RE: NOW BE HONEST....

I think the .010 might be too thick...?? Just a thought, never tried it, the .005 is pretty flexible.

I know Gary James was thinking of trying it on a Quickie wing, not sure if he had.
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Old 08-10-2009, 12:30 PM
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ORIGINAL: daven

I think the .010 might be too thick...?? Just a thought, never tried it, the .005 is pretty flexible.

I know Gary James was thinking of trying it on a Quickie wing, not sure if he had.
I agree - I couldn't remember if they had .005".

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Old 08-10-2009, 02:09 PM
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Default RE: NOW BE HONEST....

I read that the .010" is the same as Flite Skin, the product that has detailed markings printed on it. It is designed to replace balsa and FG skin, but will not cover compound curves.

The plane I'm working on here was glassed last night on the underside. I first laid down a 4 inch wide strip of 4 oz cloth from wingtip to tip, then laid down 1.5 oz cloth over the entire underside. No vacuum bag, just allowed to lay there and ferment. The end result was dozens of little bubbles that formed sometime during the night.....now I can see why bagging is SOP. I don't have this problem on smaller projects where the cloth is tacked with 3M77 before the epoxy is spread out.
So...this plane isn't going to be finished up with too much attention to detail. I'm just going to slam the rest of it together and fly it. I was trying to see if a project like this could be done without $30-40 worth of balsa skin....not be me I guess.
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Old 08-10-2009, 05:21 PM
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Default RE: NOW BE HONEST....

No, the glass sheet will not do compound curves at all. But on a straight tapered wing should work like a champ. It needs to have the surface gloss sanded off, the bond to that surface is suspect if not due to residual mold release and the gloss finish.

Did you do this one with 3M-77? If so, was it completely gassed off? I've helped some foam/glass jobs by smoothing and pulling the cloth out, then tacking strategic points with thin foam-safe CA.

A layer of release film heat shrunk over it could help - that window insulating film for example. Or cut it into 2" wide ribbon, and spiral wrap the wing after glassing to smoosh it all down flat. Just some hair-brained ideas I've used in various forms in the past.

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Old 08-10-2009, 07:09 PM
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Default RE: NOW BE HONEST....

No, I didn't use any 3M77. I positioned the cloth on the wing panels dry and used a soft brush to smooth it out. Then I drizzled epoxy over it and spread it out with a credit card. Once the cloth was saturated I scraped the excess resin off and scrutinized the work with angled lighting. I didn't stress the cloth during any portion of the process. I thought that things went very well.
As it turns out, the bubbles seem to be surface beads of resin, not hollow spots where the cloth lifted like I first feared. So, outside of slight flaws in the foam work underneath...it's going to turn out OK.
Still no substitute for doing it the right way with balsa skin and a vacuum.
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Old 08-10-2009, 08:40 PM
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ORIGINAL: combatpigg

if you don''t fold one every now and then....you''re building too heavy.
That's the truth, anyone that said he never folded a wing isn't trying hard enough, either in the building or the flying.
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Old 08-10-2009, 08:58 PM
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Default RE: NOW BE HONEST....

Is that some sort of prerequisite, to be a "True" speed freak or something?[8D]
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