Mental Rambling - Effects of wing sizes

[geoffbeneze]

Since the kids and I got rained out of the Phx show today I had to satiate my obsession by reading and looking at a bazillion pictures.

This lead to a "mental trigger" and a new crop of questions. I'll throw them out here while I drag out my books to research the subject. In the meantime, I'd love to hear the knowledge, theories and speculation of you guys "out there."

Looking at a variety of plane styles, some with wings 12" in span and cords of 10" all the way out to the UAV Predator with a span of 98 feet (in one model, at least) and a cord of 6'.

Let's assume, for the moment, that engine, fuse and balance problems are all solved, and let's just change wings.

What are the differences in flight and power need characteristics when we change the wing? Let's start with a very short, but deep wing and move out to the extreme example of the Predator.

How would the short, fat wing behave?
How would an intermediate wing, longer span, but shorter cord behave?
How would the LONG, THIN wing behave?

What would the relative differences be?

[vintage1]

Short and fat rolls faster, is stronger and stiffer, and has higher drag.

Ong and thin rolls slower, is far moredifficult to make strng, but will fl faster due to less drag.

You pick the best compromise..

[KLH]

vintage
Very good! That's the short and fat and long and thin of it in a nut shell; However; For the thecnuts out there those explanations could be drug out to fill hundreds and hundreds of pages of finite details which a lot of us would'nt understand anyway.

Kern

[Andy W]

It's called aspect ratio, and "in general" (al KLH hints) the higher ratio (span:chord) is more efficient. Take a look at full-scale sailplanes..
..a

[AmpAce]

The weight factor has to enter into the equation too. Weight has as much to do as anything with how much power us required to fly it. For most conventially constructed models, at least, a long skinny wing will generally be heavier to achieve the required strength.

AmpAce

[Snow Owl]

Wings work best when the air flows over the wing from front to back in a straight line. Out at the wingtips this is messed up by high pressure air under the wing spilling outwards and around the tips into the low pressure air on top. This creates a swirl or vortex of air behind each wingtip. The energy to spin the vortices comes from the energy available to move the wing through the air. Wing tips always lose lift and create drag. Suppose we are talking about wings with the same area. High aspect ratio (long, skinny) wings have more wing that is unaffected by wingtip losses compared to their area than low aspect ratio wings. Also, suppose that the length of wingspan affected by tip losses and the strength of the vortices depends on the length of the chord at the wingtip. The wingtips of a high aspect ratio wing are smaller proportionately, so the losses are proportionately less.
On the downside, when you load a wing at a certain number of G’s, longer wings are longer levers trying to pry themselves off at the root, so if you use the same materials and structural ideas they have to be stronger, hence heavier.
The aspect ratio of a wing almost always depends on what the plane is meant to do. Aerobatic planes and jet fighters with a lot of power available and high g loads have low aspect ratios, and gliders and jetliners that have to minimize power requirements and can limit G loads use high aspect ratios.

[Snow Owl]

Oh yeah, and when ailerons are used to bank into a turn, the aileron that moves down makes more lift, and making lift takes energy. That energy comes from increased drag. The aileron that moves up creates less lift and drag. The unequal drag makes the wingtip which is trying to go up also drag backwards, so the plane is trying to yaw away from the turn you're trying to make. The longer the wing the more the aileron tries to lever the plane around in the wrong direction. That's why the Wright brothers invented three axis control. They needed a rudder to overcome the adverse yaw of their long winged gliders.

[geoffbeneze]

Out at the wingtips this is messed up by high pressure air under the wing spilling outwards and around the tips into the low pressure air on top. This creates a swirl or vortex of air behind each wingtip.

The aspect ratio of a wing almost always depends on what the plane is meant to do. Aerobatic planes and jet fighters with a lot of power available and high g loads have low aspect ratios, and gliders and jetliners that have to minimize power requirements and can limit G loads use high aspect ratios.

How do the various wing tip "end plates" and winglets effect this spilling?

Would it be a fair generalization to say that a high aspect wing is more economical (of power/energy?)

[BMatthews]

This could easily degenerate into a discussion similar to "how many angels can dance on the head of a pin". Geoff, you need to set a task for the model. Short and wide is great for crazy aerobatics and high aspect ratios is better for gliders where efficiency counts for more than maneuvering. And somewhere in between the porridge is JUST the right temperature..... depending on what you want to do with the model. This is why you see funfly models with gobs of low aspect ratio wing area and why gliders are long and slender. And why racers are skinny and why sport models are in between and why.......

[geoffbeneze]

This could easily degenerate into a discussion similar to "how many angels can dance on the head of a pin". Geoff, you need to set a task for the model. Short and wide is great for crazy aerobatics and high aspect ratios is better for gliders where efficiency counts for more than maneuvering. And somewhere in between the porridge is JUST the right temperature..... depending on what you want to do with the model. This is why you see funfly models with gobs of low aspect ratio wing area and why gliders are long and slender. And why racers are skinny and why sport models are in between and why.......

Well THAT part is simple. I'm beginning to draw plans and do the "mind engineering" for a 96-100" span UAV Predator in "WAY stand off Scale". As in rel life, this is to be an Elint ship (i.e. video, stills, most likely gps) for my own entertainment and the consternation of those coming across the border illegally near our ranch.

I'm asorbing as much foam construction knowledge as I'm able as FAST as I'm able. Want to keep the whole thing as light as possible (duh), full controls, flaps, retracts, steering on front plus controls to manage still camera and postion of (dual) camera platorm (zero degrees to 90 degs) both cameras will be "slaved to the same focal point.

Now without fancy footwork, this strikes me as 2 channels for the elerudders, 1 channel for the flaps, one channel for alerons, one channel for retracts, 1 channel for steering, one channel for camera positioning and one channel for still camera control. That's ah (mutter, mutter - take shoes off - splay fingers, mutter, mutter ) AH, 8 channels (and I have an optic six, sigh) so we start paring down what I actually cant live with out.

Ok, do control with the elerudders. (2) stick with the flaps (1) throttle (1), Camera platform (1) Still trigger (1) - Hummmmmmmm SIX but no retracts..... What other things can I juggle and mess with.

BUT, the plane should be stable, it should "float", it should take minimal power ("fuel", "ergs", "watts" , etc) to keep it in the air at something like 1/4 throttle. Speed doesn't have to be great 30-40 mph would do nicely. LONG (LONG) flight times say 1.5 to 2 hours.

STABLE, payload after achieving flight weight of 1.5-2 lb.

[biber]

So, another thing to care about is the reynolds number. Its basicaly the product of the chord multiplied with the airspeed multiplied with at (more or less) constant factor. If calculatet in SI- Units this factor is about 70000 s/m². So if you estimate the plane to fly at about 10 m/s and have a chord of 0.1m you would get re=70 000 e. g. , wich isn't quite much anyway. To prevent bad stalling characteristics and overall draggy aerodynamics you should keep the re-number of the wing at least over about 100 000 or else take care that the used airfoil is capable of the low re-numbers you are expecting to occur during flight. This requirements often limit the aspect ratio for a given wingspan. In terms of Mister Reynolds one could simply say the bigger the better.

[BMatthews]

Use a second radio and operator for the optics. Sort of like the gunner and pilot combo.

For THAT size model glider flyers found that the "optimum" aspect ratio is around 10:1 to 12:1. This reflects the balance between decent reynolds number range for the airfoil and higher aspect ratios for overall wing efficiency.

[Sparky Paul]

Do you want the "surveilled" to know it?
An electric would be very quiet, a glow would be somewhat more noticeable.
Retracts are useless. They contribute nothing but weight and current draw for the flight.
For the slow speeds you want, a tricycle gear is adequate.
Unless there's a need to land steeply and slowly, flaps aren't needed.
Flight endurance tests both the plane and the pilot.
The area to be looked at will not be large unless the pilot can travel with the plane.
This brings in more operators.

[geoffbeneze]

Use a second radio and operator for the optics. Sort of like the gunner and pilot combo.

For THAT size model glider flyers found that the "optimum" aspect ratio is around 10:1 to 12:1. This reflects the balance between decent reynolds number range for the airfoil and higher aspect ratios for overall wing efficiency.

Biber, Bmatthews,
NOW we're starting to jell a bit. It's always amazing to me how one simple (and clarifiying) explanation leads to hours of reading (G).

Someday I'll take up an SIMPLE interest (Nah......)

[geoffbeneze]

Do you want the "surveilled" to know it?
An electric would be very quiet, a glow would be somewhat more noticeable.
Retracts are useless. They contribute nothing but weight and current draw for the flight.
For the slow speeds you want, a tricycle gear is adequate.
Unless there's a need to land steeply and slowly, flaps aren't needed.
Flight endurance tests both the plane and the pilot.
The area to be looked at will not be large unless the pilot can travel with the plane.
This brings in more operators.

"No Sir, my intentions are strictly honorable" (he said, while gently patting the daughter's hinter regions).

The original idea was to use the thing as an elk spotter, or maybe even a hunter spotter, since it's a bad idea to walk into the areas where noobs and those of unknown experiences are (G)

Most elk I've encountered don't do much sky gazing (G).

The other application (excuse) would be to spot illegals in the vincinity of our ranch. We've been broken into four times and had one of the corrals set fire. I'm not too concerned that the see or know that they're "Under the Eye," as a matter of plain fact, it's probably BETTER if they know about it.

Maybe I should put a small player and speakers in it and play the "Ride of the Valkeri?" (Well, and Wagner would do)

Re: retracts & Flaps. I understand they're most likely NOT needed and are extra complications. However, this is the "dream design" (one I've wanted to do since I was 10'ish, before the technology to even think about it existed) so I'll throw all that crap on my "list" and shed it as the design actually solidifies. Ultimately, it seems likely that I'll end up with fixed landing gear and be happy with that (G) Endurance time is the same situation. Less a matter of wanting to do one LONG flight, but one of being able to do several without having to recharge (etc).

Original concept dictated that there would be a "Data Operator/Monitor" along with the pilot AND that, very likely, the pilot would have to be mobile (meaning more "ground crew").

OTOH, if that results in the GC rolling an elk with relative ease, I doubt I'll have to much bitching on my hands (G).

[geoffbeneze]

Use a second radio and operator for the optics. Sort of like the gunner and pilot combo.
.

Now THERE's a forehead slapper!

The Original Concept has always called for a "data operator/monitor" all along. I'd ALWAYS been thinking of two people to run the show. I just flatly hadn't though of using a second radio (well, duh, geoff).

Thanks for steering me. But then, that's why I ask questions here while at the same time doing "hard" research.

thanks guys.

[biber]

I would say Wagner is pretty good choice. Maybe won't even need any rc-plane at all if you just turn on your hi-fi loud enough :D . Hope yours goes up to eleven ;) . (And if you want to go for sure, use yoko ono music to prevent any darkmindet evil person from wanting to break in, even if he is a real hard guy :eek: )

Ok, just kidding. :D

[geoffbeneze]

I would say Wagner is pretty good choice. Maybe won't even need any rc-plane at all if you just turn on your hi-fi loud enough :D . Hope yours goes up to eleven ;) . (And if you want to go for sure, use yoko ono music to prevent any darkmindet evil person from wanting to break in, even if he is a real hard guy :eek: )

Ok, just kidding. :D

No 11's on mine, sadly (G). Actually, I like the overture to Flying Dutchman more, but don't think it would have the impact. I sat through four consecutive performances of it in Stuttgart.

THEN, I lost my mind and saw Yoko in Frankfurt. And I though RAP was bad!

But if I played that for them, it might start an international incident with Mexico (G)

[biber]

LOL

When did you get to germany? I guess you didn't come the long way just to hear some music :rolleyes: ?

Neither did i expect you to have already suffered of a yoko ono performance.

Hope you didn't need a treatment by psychiatrist after that to recover.

[geoffbeneze]

LOL

When did you get to germany? I guess you didn't come the long way just to hear some music :rolleyes: ?

Neither did i expect you to have already suffered of a yoko ono performance.

Hope you didn't need a treatment by psychiatrist after that to recover.

We were there from 60 through 70. Went to the German schools till '68 when college credit issues arose. Lived first in Doffingen (near Stuttgart, or rather Boblingen) then Weisloch (near Heidelberg).

I calculate that Yoko was a learning and character building experience. After a trauma like that, you're always MUCH stronger (G)

[Snow Owl]

I remember Burt Rutan explaining that when you consider factors like increased torsional amd bending loads, Whitcomb winglets offered very little as compared to a wing of greater span that imposed the same loads. Didn't keep him, and Boeing from using them, though. Tip plates may be slightly better than a square wingtip with no plate, but anybody could come up with a better shape. Cessna liked the aftermarket drooped wingtips people were selling for their airplanes so much they put them into production.

[geoffbeneze]

Because I've got this fixation on the Predator going for the moment, I started searching for the "real" airfoil they used on the thing.

Lots and lots of discussions about development, but I couldn't find anything that said what the actual shape WAS.

Frustrating (not that it matters for this [potential] model).

Now it's become a mission to find out that little bit of trivia (G)

[BMatthews]

Pick one that works for YOUR mission profile. You'll be happier with it that way. Obviously for a model that has a payload and will be upright pretty much all the time you want a nice cambered one. Thicker, within reason, also seems to take higher wing loadings better. The bonus is that a thicker airfoil makes it easier to make the wing strong but still light. I used the Eppler 201 on a 2 meter glider and it didn't do that well until I made an electric power fuselage for it. The weight gain from 36 to 56 oz made that wing REALLY perform. It floats nicely but penetrates super well. The Selig S4233 is in the same boat thickness and camber wise and would also be a good choice for an all 'rounder. Slower would benifit from more camber but trust me, these two when loaded to 10 to 12 oz/sq foot will smoke so there's no need for anything faster.

[Scaledown]

For an ambitious project like this, you might want to build and fly a crude prototype first to find the bugs before you add all the gadgets.

[geoffbeneze]

For an ambitious project like this, you might want to build and fly a crude prototype first to find the bugs before you add all the gadgets.

Amen Brother! Indeed, I'm planning a 48" "proof of concept [i.e. "Can THIS Bozo Build In Foam Effectively") before we dive into the "real" thing.

Figured to use coin rolls or lead bars as ballast to emulate the payload through development.

THEN, we'll start working on the full sized beast.

I have built several "own design" scratch planes in the past, I've just never gone quite this big, nor have I used foam for the construction.

[Sail 'n Soar]

Short and fat rolls faster, is stronger and stiffer, and has higher drag.

Ong and thin rolls slower, is far moredifficult to make strng, but will fl faster due to less drag.

You pick the best compromise..

This long discussion seemed to build around the assumption that Vintage1 summarized it all here. While comments relative to roll rates and stronger/stiffer are correct, the comments relative to long and thin flying faster because of lower drag for reasonably powered models is not true. At higher speeds lift coefficients, hence induced drag, becomes MUCH less significant to the point that the stubbier wing has less total drag as a result of lower profile drag as a result of a higher Reynolds number.

Before the "experts" on this forum start challenging my comments, let me give an example with one arbitrarily chosen test case - these were the first and only combo's I tried, so I did not choose a set of assumptions that would support my hypothesis.

For this example I assumed:
W/A = 16 oz/sq ft.
A = 400 sq in
CL = .1

Calculating flight speed from those inputs I get:
U = 91.7 fps
= 62.5 mph

I then choose two wings, one with AR = 4 and the second with AR = 8
For AR = 4,
C = 10 inches cord
CDi = .0008 for elliptical lift distribution
Re = 487,000

For AR = 8
C = 7.07 inches cord
CDi = .0004 for elliptical lift distribution
Re = 345,000

Assuming an NACA 0012, I used XFoil to calculate CDp for the two wings.
For AR = 4 (Re = 487,000)
CDp = .0064, or
CD = CDp + CDi = .0071

For AR = 8 (Re = 345,000)
CDp = .0074, or
CD = .0078, which is greater than the ..71 for the stubbier wing.

Now, if I take advantage of the wider cord and shorter span and use an NACA 0009, while still having a stronger and stiffer wing than the AR =8 wing with the 12% foil,
For AR = 4 (Re = 487,000)
CDp = .0056, or
CD = .0064, which translates to 18% lower drag from the stubbier wing.

Now if you take into account that the wing with the stubbier wing can be built lighter, then the total drag (i.e., drag = weight/(L/D)), then the stubbier winged plane will have a lower drag, hence higher speed, yet.

[geoffbeneze]

Lord, the more I look, the deeper I fall in.

Can anyone recommend a source ('net would be great) that EXPLAINS various foils, their effect and use? I've located good data and good "backward lookup" (i.e. "what does XYZ airplane use?") but I'm wading in without understanding why one foil is chosen over another.

[BMatthews]

SnS, you data is 100% right as long as the desire for lift is kept under control. A pure speed model will do well with a relatively stubby wing and not much area. However pylon racers need GOBS of lift in the turns and where permitted we see the trend being back to higher aspect ratios. The class that shows this the best is the FAI pylon event where the model design is much more free.

The bit about Reynolds numbers also showed up in an issue of Soartech way back when where they discussed an optimum aspect ratio. Turns out it should have been titled "An Optimum Wing Chord". The final results being that only open class models can benifit from higher aspect ratios and the span limited events are better off with stubby wings with lots of area to keep the wing section wide and thick enough to remain in the minimum efficiency Re range.

Geoff, wander in, the water is fine.... :D There's lots of fine airfoils out there and truth be told if you have an internal combustion engine as part of the equation then any number of them will work fine. Even for gliders if the list of expectations are decently limited it's hot that hard to find one.

The ones to watch for are the ones where the shape is critical to the tune of requireing tooling that can produce the ideal shape within a 1% error. Typical modelers will have trouble with that. So basic shapes are good.

Oddly enough an old DOS based sailplane performace program I have that used the original Selig data predicted that the sad old ClarkY is often as good and no worse than 95% of the fancy stuff. There's been a few new shapes since then but for simplicity and ease of building you can't beat the ClarkY. We're talking TRUE ClarkY here. Not a 10% shoe sole flat bottom shape.

[biber]

geoff,
I guess you still understand some german? Try this link:

http://www.aerodesign.de/profile/profile_n.htm

I think there is no english version except for tailless wings airfoils:

http://www.aerodesign.de/english/profile/profile_s.htm

wich is nevertheless quite intersting to read.

But to shortcut this, I think Bruce's suggestion of a clark-y is perfectly right. Certainly the best choice to make.

[geoffbeneze]

geoff,
I guess you still understand some german? Try this link:

http://www.aerodesign.de/profile/profile_n.htm

But to shortcut this, I think Bruce's suggestion of a clark-y is perfectly right. Certainly the best choice to make.

Coincidence! I found that one last night and have been reading it. I read (german) pretty well still. I'll not even attempt to write it now, though I understand spoken just about as easily as 'Mercan. What I find is that I've lost the "flow" of speaking and lots of vocabulary.

[Sail 'n Soar]

SnS, you data is 100% right as long as the desire for lift is kept under control. A pure speed model will do well with a relatively stubby wing and not much area. However pylon racers need GOBS of lift in the turns and where permitted we see the trend being back to higher aspect ratios. The class that shows this the best is the FAI pylon event where the model design is much more free.

I kept the wing areas constant in my calculation so that the stall speeds would be approximately the same. For the speed model, the challenge is to balance speed down the straights - which pushes you toward the low AR wing - and induced drag in the gobs of lift turns - which drives toward higher AR.

As Ollie so frequently emphasizes, aircraft design is a compromise.