wing loading of a living bird?

[Bob Chiang]

Does anybody know the wing loading of a living soaring type bird?

I watched some kind of hawk in a thermal yesterday. Sunny day, maybe 40 degrees, and very calm. It was circling very tightly (I'd estimate 20' diameter) and gained elevation quite fast. It started at pretty low altitude (not much higher than roof level of the surrounding four story buildngs. It was also interesting because there was another bird circling higher up, not offset very far away, and also circling tightly.

[Mike Taylor]

According to Sibley's book, a red-tail hawk weighs 2.4 lb with a 49" WS. They have ~6:1 aspect ratio, so that works out to ~2.75 square feet, or almost 14 oz/sq foot.

The Americam Kestral is 22" WS, ~7:1 AR, and 4.1 ounces, or about 8 oz/sq foot.

These also have infinitely adjustable wings and on-board real-time inertial nav systems, so your results may differ ;)

If you want to turn with the birds (it is so fun when they come to fly with you), you should add some turbulators to the outer portion of your wings to prevent the inside tip from stalling...

[Highflight]

Mike touched on it; the key to any bird's soaring abilities is not so much it's "raw" wing loading, but it's use of what's in it's head.

Your glider could soar much better too if it had an onboard computer wired to sensors throughout the airframe coupled with optical onboard video, which combined, give constant feedback to the processor which would in turn make infinitesimally fine adjustments of all flight surfaces and moveable ballast to maximize lift on a real-time basis. ;)

Highflight

[Bob Chiang]

Thanks for the info. The way this hawk was going up was really impressive. And it was very interesting to see how narrow the thermal was, and that it remained narrow and hardly drifted as it went up (as shown by the higher bird).

By the way Highflight: they have not only moveable ballast, but also ejectable ballast ; )

[Ollie]

So birds can vary their wing loading two ways. They can vary their wing geometry and aspect ratio by partly folding their wings and they can reduce wing loading by dumping "ballast."

I've watched black vultures working thermals here in Florida. When the conditions are gusty and a vulture gets caught in a developing stall due to a gust, it partially folds its wings momentarily. This increases static margin, provides momentary nose down trim and momentarily increases wing loading. The maneuver takes about one second or a little less but results in killing the stall without loosing much altitude at all.

[Mike Taylor]

Besides the obvious wing changes, I see more minute and sutle changes in the wing tip feathers then in the whole shape of the wing. The ability to adjust camber (selectively in only part of the wing) as well as plan form is pretty easy to see as well. I like living on a hill so the birds are flying at eye level...

[AUBrian]

Also remember most birds have the ability to change the angle of attack of their wings. They can flare them to slow down quickly, and can give a slightly down angle to increase speed. They can also vary the angle of the elevator in relation to the angle of the wings, which most ailplanes aren't able to do on a whim.

[James Frolik]

There is a BBC World television program where a bunch of yuppie-type scientists try to solve or rectify some situation. And last month they tried making a set of wings for the show's host so he could fly like a bird.

This led to an analysis of how birds are designed -- minimal and hollow bones that are interconnected for lightweight and efficient movement -- that was really, really interesting. Showing the skeletal display of a medium-sized bird, like a pigeon, was very revealing. There's not much there, and what is there is ultra-lightweight. Brain is ultra-small; eyes are very big. Feathers make up most of the rest.

Lots of slow-motion shots of various birds in flight too. But what I found most interesting is that a bird's wing produces thrust in both upward and downward swings while lift is the wing's secondary effect.

Needless to say that by nature's way the show's host wasn't designed for flight. No "wing" on his arms could get him off the ground no matter how hard he tried. Although the wing designed for him did get him moving forward (thrust) while suspended from a ceiling trolly.

He was simply too heavy.

[JMP_blackfoot]

My pet pigeon weighs 156 grams. I haven't measured its wing area, but estimate it close to 5 square decimeters. Hence an approximate wing loading of 31 gram/sq.dm or 10 oz/sq.ft.

[Ollie]

There are at least three distinctly different flight modes for bird wings.

There is the non flapping or soaring mode. It is used by the abatross to fly for thousands of miles over the open ocean by extracting energy from the wind shear associated with ocean waves (also known as dynamic soaring). There is slope soaring by many varieties of birds. There is thermal soaring exemplified by the turkey vulture.

Then there is a flapping mode which produces both lift and thrust exemplified by the carrier pigeon and used at one time or another by most birds.

Thirdly there is a hovering mode exemplified by the humming bird in which only lift and no forward thrust is produced.

[JerryHall]

I did a little basic math to see how much wing area it would take to fly my 230 lbs at a wing loading of 10 oz/sq ft...
Seems it would take a wing with a 5 foot cord ( the size of a J-3 Cub wing) and a wingspan of 73.6 ft.. That is not taking into consideration the weight of the wing..
Some have said that if man was intended to fly God would have given him wings...Can you imagine trying to get into a small public restroom with a 90 ft or so foot long set of wings ??? .. LOL

You can tell I don't have anything important to do tonight...

[Ollie]

Doing a little more basic math, a 40.9 square foot wing flying three times as fast ( 66 FPS) would generate the same 230 pounds of lift and have a wing loading of 90 ounces per square foot. For a given coefficient of lift, the lift force increases as the square of the airspeed. Increasing the model's airspeed by a factor of three and wing chord by a factor of about 5 would increase the reynolds number by a factor of 15 and allow a maximum lift coefficient at least 25% greater. This increase in maximum lift coefficient would reduce the airspeed from 66 FPS to about 58 FPS.

[Sail 'n Soar]

Originally posted by Ollie
Doing a little more basic math, a 40.9 square foot wing flying three times as fast ( 66 FPS) would generate the same 230 pounds of lift and have a wing loading of 90 ounces per square foot. For a given coefficient of lift, the lift force increases as the square of the airspeed. Increasing the model's airspeed by a factor of three and wing chord by a factor of about 5 would increase the reynolds number by a factor of 15 and allow a maximum lift coefficient at least 25% greater. This increase in maximum lift coefficient would reduce the airspeed from 66 FPS to about 58 FPS.

Ollie,

Perhaps this is a better way to look at the problem.
For a given weight (i.e., lift), CL, V ~ 1/sqrt(A).
For a constant AR (i.e., similar planform), C ~ sqrt(A).
But Re ~ V*C ~ Sqrt(A)*1/Sqrt(A) = 1
Therefore, for a given weight, CL and planform, Re is constant!

Don't expect to get any max CL change by flying faster with a smaller wing!

Of course, since Power = D*V = L*(D/L)*V, flying faster with that smaller wing just makes you have to work harder to stay aloft.

Gerry

[FlyByMike]

Originally posted by JerryHall
...Can you imagine trying to get into a small public restroom with a 90 ft or so foot long set of wings ??? .. LOL

You can tell I don't have anything important to do tonight... I can't imagine getting unzipped :D
-Mike

[robbie]

anybody built that sailplane turkey vulture?