Wing Tip shape!  
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Wing Tip shape! - 4/23/2003 4:54:11 AM   
Blue Skyy


 

Posts: 138
Joined: 12/10/2002
From: Charleston, IL, USA
Status: offline 		Aerodynamically, what is the lowest drag wing tip. Should it taper to a clean edge say an 1/8" thick or to cut straight off with a tip 1/2" thick at the widest point.

Also how much will drag increase with thickness of an airfoil. Say an average thickness is 1" vs another wing 1.25" thick. 36" span, 36" root. Actually what we are talking about here is pressure drag. Is it really worth trying to get the thinnest wing possible and just deal with the poor flight characteristics.

The speed we are talking about for this plane is right at 200 mph.

Thanks,

Blue Skyy
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Wing Tip shape! - 4/23/2003 8:26:27 AM   
banktoturn



Posts: 700
Joined: 8/22/2002
From: Bloomington, MN,
Status: offline 		Blue Skyy,

I think that the best tip treatment, especially since high speed is your goal, is a smoothly rounded tip. The main benefit that you could hope to get from any unconventional shape is lower induced drag, and induced drag is negligible for high speed level flight. As you point out, pressure drag is the culprit, and a smoothly rounded shape is where it's at. Regarding thickness, I am guessing that, within the range of thicknesses that you can practically attain, thickness would not be a big factor. The classic reason not to go too thin is that weight will likely increase if you try to make a thin wing strong enough. This is bad, because induced drag is proportional to the lift coefficient, and the lift coefficient increases in proportion to the weight ( for level flight ). For a plane with mandated minimum weight (like a pylon plane), this might not matter. For a plane with unregulated weight, you want to be as light as possible, and an overly thin wing makes that tough.

banktoturn

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Wing Tip shape! - 4/23/2003 10:01:49 AM   
probligo



Posts: 354
Joined: 5/13/2002
From: opononi, NEW ZEALAND
Status: offline 		Surely there is only one answer - elliptical.

All of the theory that I know points toward the elliptical wing being the most efficient on all levels.

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Re: Wing Tip shape! - 4/23/2003 10:05:10 AM   
Tall Paul



Posts: 4655
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: online 		[QUOTE]Originally posted by Blue Skyy
....just deal with the poor flight characteristics.

The speed we are talking about for this plane is right at 200 mph.

Thanks,

Blue Skyy [/QUOTE]
.
What does that mean? Poor at 200 mph? Poor at landing speed?
Poor how?
Who defines "poor" in the first place?

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Wing Tip shape! - 4/23/2003 6:57:37 PM   
Blue Skyy


 

Posts: 138
Joined: 12/10/2002
From: Charleston, IL, USA
Status: offline 		Tall Paul,

You kinda sound like former president Clinton defining "is". I'm sure you have flown planes which are a delight to fly. We all have. Then we have also flown planes that are a nightmare due to poor flight characterisitics whether a rearward CG or a simply bad design.

It seems the thinner the wing tip becomes, the more likely the plane is to tip stall on landings. When you fly a plane with no landing gear, you want to get the plane to slow up as much as possible before touching the ground, because the ground beats the thunder out of the bottom of the plane on landing. In the past the planes where I get the wing tip really thin, show a tendancy to tip stall without any warning. They just radically drop a wing and next thing you know you're an acrobat turning cartwheels.

So lately I have gone with the nicer flying planes and just went with a flat wing tip. I'm not sure how much drag you really get out of this type of wing tip vs. a finely tapered tip to a clean edge. Would you see a noticeable speed increase with the thinner wing tip at 200mph?

I don't like to use washout due to the higher drag with this design, especailly at high speeds.

Blue Skyy

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Wing Tip shape! - 4/23/2003 7:58:46 PM   
banktoturn



Posts: 700
Joined: 8/22/2002
From: Bloomington, MN,
Status: offline 		Blue Skyy,

My understanding of your question is that you have decided on the design of the wing, and are looking to choose the lowest drag wing tip. If this is the case, then the decision is not likely to have a huge effect on the flying characteristics of the plane. A very thin airfoil toward the outboard end of the wing could indeed affect flying characteristics, but only if it represents more of the span than I would consider to be the wingtip. Similarly, to probligo's point, you can't get an elliptical wing by virtue of the wingtip shape. Moreover, the main advantage of an elliptical wing ( actually, an elliptical distribution of lift along the span ), is reduced induced drag, and induced drag, I contend, is not an issue for your high speed plane.

I think you've correctly identified pressure drag as the component of drag to work on. The improvement which is available by working on the wing tip is very limited in any case. Thickness is probably not a big deal. Round those bad boys off to a smooth shape, and feel confident that your wing tip is doing the best it can.

banktoturn

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Wing Tip shape! - 4/23/2003 10:16:33 PM   
Tall Paul



Posts: 4655
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: online 		Blue, you want ideal performance at both ends of the speed range, which happens to be a very speed range for a model.
Ain't gonna happen with a fixed shape.
You have to make the decision... fly very fast very well, land fast, or fly very fast kinda well, land slower.
If I could handle fast airplanes, I'd go for the former, and only fly where a high landing speed can be used.
Look at full-scales... notably the Tomahawk, or even a JDAM. Or an MD-80. What wings there are are so tiny relative to what might be expected you gotta wonder.. But consider the conditions.
Neither the Tomahawk or JDAM have to land at all. The wing/stabliziing strakes work at one speed.
The MD-80 "wings" fall apart for landing.. all those slats and flaps. There's the compromise between good high speed performance and acceptable landing performance.
Don't land at all... Tomahawk. Minimum possible wing, flies very fast.
Have to land (Getting there at all is half the fun of airline flying), so the wing gets fancy, MD-80.
You want both ends of the spectrum without compromise. Well, you can't have them!

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Wing Tip shape! - 4/23/2003 11:06:14 PM   
banktoturn



Posts: 700
Joined: 8/22/2002
From: Bloomington, MN,
Status: offline 		Tall Paul,

I understand what you're saying about tradeoffs, but I guess I didn't get the impression that Blue Skyy was looking for an optimum solution in all flight regimes.

banktoturn

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Wing Tip Shape - 4/24/2003 5:38:46 AM   
Blue Skyy


 

Posts: 138
Joined: 12/10/2002
From: Charleston, IL, USA
Status: offline 		What I'm looking for is optimum high speed wing tip shape with a plane I can safely land.

Is it really that much of a drag reduction advantage to make the wing razor sharp at the wing tip vs just leaving it cut straight off with a 1/2" thick airfoil. The attached image is the Wing planform. Sorry I don't have a better photo of the wing tip.

If the there is sizeable drag reduction in the trade off, it would be worth it. If I'm knocking off 2 MPH at 200mph, I'd rather opt for the nice handling thicker wing tip.


So how important is it to have a thinner over all wing in terms of pressure drag.

How much will drag increase with thickness of an airfoil. Lets say plane "A" has a mean thickness is 1" vs Plane "B" with an average 1.25" thick. Both planes are 36" span, 36" root.

Actually what we are talking about here is pressure drag. Is it really worth trying to get the thinnest wing possible. I guess what I asking is, Is it more the smooth airfoil that's going to make the difference in overall speed or is it actually how thick the pressure drag that predetermines how much drag is created?

Thanks to all who have answered!

Blue Skyy

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Wing tip shape/wing planform! - 4/24/2003 6:32:57 AM   
Daryl Martel



Posts: 595
Joined: 2/10/2002
From: WinnipegManitoba, CANADA
Status: offline 		If you check out this link to the Polish designed PZL-130 "Orlik" advanced miltary turboprop trainer, I think you'll be impressed by the wing tips: http://www.pzl-okecie.com.pl/orlik.htm This type of wing planform (although the aspect ratio is obviously stretched considerably) is often used in high performance gliders where streamlining and drag reduction is crucial. This is one very efficient low drag wing tip and overall wing planform. Cool looking plane in my opinion!

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Nemesis Tip Shape - 4/24/2003 7:54:36 AM   
Blue Skyy


 

Posts: 138
Joined: 12/10/2002
From: Charleston, IL, USA
Status: offline 		Daryl Martel,

Very Unique shape! Kinda reminds me of a giant scale formula one racer I had a few years back call "Nemesis". That wing tip would look very cool on a delta. The new Nemesis has that same look.

I never really considered putting this type of wing tip on a Delta!

Nice Idea.... I think?

Here is the latest Nemesis NXT wing tip, but I don't understand the configuration by looking at it.

Thanks,

Blue Skyy

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Nemesis Wing Tip - 4/24/2003 8:03:24 AM   
Blue Skyy


 

Posts: 138
Joined: 12/10/2002
From: Charleston, IL, USA
Status: offline 		Here is a shot of the old Nemesis wing tip. I think you've got a great idea here Daryl!

Opinions?

Blue Skyy

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       Post #: 12

Scheumann? Platform - 4/24/2003 9:49:15 AM   
Daryl Martel



Posts: 595
Joined: 2/10/2002
From: WinnipegManitoba, CANADA
Status: offline 		Thanks Blue Skyy. The Germans in many of their advanced gliders have been using a multi step swept leading edge terminating in a raked tip giving the wing a "scimitar" look. This Scheumann planform is noted for its high efficiency. I've even seen some airliners employing this wing type - I think it was one of the newest Fokkers or a Dornier. What you see with the PZL is similar but simpler. Bizjets are another example where you see some pretty slick aerodynamics. If you look at Lancair and Dymond airplane wing tips they're pretty slick as well. That new Nemesis is an excellent example of very advanced aerodynamic design. The newer carbon fiber design wing seems to employ a flexible trailing edge skin! Wow - I'm sure that's been done on military prototypes but I've not seen it done like that before! I look at some of the more advanced propellor shapes, like APC props, being a good example of optimised airfoil design. Trouble with a lot of these shapes is their not easy to accurately build, that's why we see the move to glass and carbon fibre molds. I guess if you have lots of time and patience, anything can be carved from balsa!

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Ground effect - 4/24/2003 10:47:57 AM   
a088008



Posts: 404
Joined: 6/14/2002
From: San Diego, CA, USA
Status: offline 		I'm not an expert as far as ground effect goes, but here is my educated guess.

You can bring the plane in at a safe speed for a landing, then just above the ground flare out and keep the plane just above the ground (less than a foot). The ground effect will induce a pitch down effect so you need to feed in a little more elevator. The ground effect will also increase effective lift and allow you to increase your angle of attack, futher increasing your drag and slowing the plane down. As the plane slows the lift will decrease and the plane will descend onto the ground.

Sound reasonable? This is all assuming you can fly the plane well enough to accoumplish the task.

-Q.

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-Q

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       Post #: 14

Nemesis Nxt - 4/24/2003 11:06:01 AM   
Daryl Martel



Posts: 595
Joined: 2/10/2002
From: WinnipegManitoba, CANADA
Status: offline 		Wow - your pictures of the carbon fiber Nemesis follow on got me looking for their website. Found it at: http://www.nemesisnxt.com/ Hot diggety dog that's some high tech kit concept they have going there. Amazing that a person will actually be able to buy and assemble this as a kit plane! This is about as slick as a personal aircraft can get. see image

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