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

Airfoil selection help

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Old 03-01-2003, 01:02 AM
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corey-RCU
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Default Airfoil selection help

Hey guys, I am building a 40 size speed plane and could not decide on an airfoil to use. What would be a good high speed airfoil to use but will still slow down nice? My plane has a wing shape sorta like an F-5 with about 400sq. in. area....any ideas?
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Old 03-01-2003, 02:06 AM
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ChuckAuger
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Default Look here...

There are several here:

http://www.mh-aerotools.de/airfoils/index.htm

I don't know which one will be right for your application.
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Old 03-04-2003, 12:43 AM
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Troy-RCU
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Default Airfoil selection help

If you want a fast plane that slows down well you need to keep it light. Otherwise, you'll need flaps. Having said that, airfoil selection can do a lot to how a plane performs but there are give-and-takes for everything. Personally I wouldn't go with anything above 8% thick and you can even go down to 7%. The MH33 is a good foil, so is an RG-14, RG-15, and SD8000. It is important to keep the integrity of the airfoil's profile as much as possible so it doesn't develope nasty separations, stalls, etc. One thing to note is that while a thin airfoil is great for speed, parasitic drag can undo all of that hard work if you aren't careful. Retracts, sharp trailing edges, cowled engine, and so on can clean up an airframe quite a bit. Have fun!
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Old 03-04-2003, 04:39 PM
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Default Airfoil selection help

corey,

The need to go fast and "slow down nice" is shared by a lot of full sized aircraft. The airfoil selection can only do so much to help you. To go fast, you want an airfoil with fairly little camber, maybe none. To fly slowly, you would ideally want fairly high camber. The "right" solution to this problem is flaps, which essentially give you variable camber. The traditional model aircraft solution to this problem is huge wing area, which does add drag and limit speed. My advice is to use flaps inboard, with ailerons outboard. The flaps don't need to be fancy; 20% to 25% of wing chord, sturdy hinges, about 30 deg. deflection, pretty beefy servo. You might want to mix elevator to deal with the pitch-down that will likely occur. This could be determined by some test flights with successively increasing deflection.

Good luck,

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Old 03-04-2003, 06:50 PM
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Default Airfoil selection help

On my scratch built speed plane I used an S6063 at about 360 sq inches. For a delta configuration I would use a SD8020.
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Old 03-06-2003, 12:13 AM
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corey-RCU
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Default Airfoil selection help

Lots of good info guys! I think I will build my plane and build a few wings for it with different airfoils and see what works and what doesn't.
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Old 03-06-2003, 08:08 PM
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Default Airfoil selection help

Since we're on the subject, what's a good all round aerofoil for a 53 powered 36 inch span propjet. The full size model had BLC which greatly increased the lift during landing and takeoff. I'm going to have to increase the wing to begin with coz the wing area is only about 100 sq in! I don't want to be landing at 50 mph!!

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Old 03-06-2003, 08:19 PM
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Default Airfoil selection help

DIPSY,

If the full sized aircraft required boundary layer control for landing, then you are unlikely to get the lift you need by airfoil selection. Increasing wing area is one fix. As for esanger, flaps is the 'natural' one.

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Old 03-06-2003, 09:09 PM
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Default Airfoil selection help

I was hoping the propwash over the inboard flaps would help. I'm beginning to think I've bitten off a bit more than I can chew!
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Old 03-06-2003, 09:35 PM
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Default Airfoil selection help

DIPSY,

The propwash will definitely help. It may not be enough to let you land as slowly as you want.

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