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Wing Aerodynamics Question; Real World

L

Lionheart

SOH-CM-2014
I have a question for anyone that knows about real world aerodynamics and wing lift principals.

The US Airforce experimented with many wings that had reverse dyhedral in them, such as that huge super sonic bomber, the Valkyrie, and a Boeing test plane (fighter concept, really flew). These used a form of lift called compression, where the wings are in a upside-down V shape.

I notice that Seagulls usually fly with half their wings bowed downwards, from the middle on outward, and they glide extremely well...


My thoughts are, and my question is based on this, can wings on a general aviation aircraft, (four passenger type) be able to comfortably use this form of wing layout? Would its lift be improved? Would it be stable in straight on flight?


This is a prototype Gmax sketch I am playing around with presently. In the real world, I can see the tips of the wings striking the ground as being a drawback. Small wheels would help when tips come close or contact, and having a landing gear that is quite high would also help keep the tips away from the ground. But... How would it handle?? That is the question....


One of the things that got me into this concept was the Robin DR221 and Robin DR400. At half way out, their wings angle upwards quite a bit. I would think they lose alot of lift. My thoughts were that if they were reversed, the air coming up the wings would culminate in the flat wing area, like gathering surfaces, like a forward swept wing, but in a different axis angle.

Bill
 
Wing dihedral helps a plane's stability. As one wing dips, that wing becomes flat, or level with the airflow, which increases lift. It's kinda like camber, or toe-in, on a car's front wheels.
Now some fighter planes will have anhedral, or downturned wings, like on a Harrier Jump Jet, Mitsubishi F-1, Jaguar, etc. This makes the plane more manouvorable (could never spell that!).
On your concept plane you got there, it would be too much for the average pilot to handle, and may not fly at all! . Especially with the wing on the fuselage bottom. The planes I mentioned all are high wingers, like seagulls. Aerobatic planes have neutral wings for flight right side up and inverted.
So, moral of the story is, lose those wings, and get some dihedral.
 
What you're referring to is better known as "anhedral", which is the opposite of dihedral (where the wings angle up).

Angling wings upwards (like you see on most low wing singles) doesn't really result in much of a loss of lift (if any), and it adds a great deal of stability in roll, since the low wing will have a higher angle of attack, produce more lift, and therefore roll the aircraft back upright.

Dihedral also has the advantage of being more convenient for things like fuel tanks, since fuel will flow towards the fuselage of the aircraft, where it can be picked up by a fuel pump.

Since both swept wings and a high wing layout add to roll stability, a lot of military transports have anhedral in the wings, since it decreases the roll stability to the point where it doesn't require a massive amount of force to roll the aircraft.

Because modern fighters use "relaxed stability" designs to be more maneuverable, anhedral is often used on fighters to decrease stability and therefore increase maneuverability.

Aside from the ground clearance issues you already mentioned, a small aircraft with that much anhedral would likely be very unstable in roll (not a good thing for GA aircraft), and once in the air, there wouldn't be enough of a lift difference to offset that inherent unstability.

Adding to the stability issues, any fuel in the outer portion of the wings would flow towards the tips, and any imbalance in the fuel quantity would exacerbate the roll instability.

Where anhedral does provide more lift is in ground effect, but flying 10 feet off the ground isn't a terribly practical way to travel.
 
Bill, that wingshape will most probably work better if it was a high-wing.

Im thinking that in the case of seagulls as you mention - the wing acts as a type of parafoil - therefor that wingshape would probably work better for a glider.

Would be interesting to hear from others...

Looks very cool though ! You could have the wheels (or skids) on the wingtips !
 
I like your design and I think you should keep going. I've got a couple ideas on how to make it feasible.


1. Don't change the wings. Move them rearward. Install simple wheels as your main wheels at the tips; maybe even embed them for slick looks-almost like a glider.

2. To stabilize the aircraft, install canards at the front of the aircraft. Incorporate the positive dihedral on the canards.

3. Use a center mounted nosewheel like you normally would.


It should fly stable and fast; plus it'll look awesome!! I like the shape of the fuselage you've got going there. In fact, the whole thing looks sharp. You can even fly with an aft CG for even more instability and speed. That plane will haul butt.
 
Make it a bi-plane with the anhedral on top wing and the dihedral on the bottom wing. Make the top wings wider with the flaps in the top ones close to the fusealage where the air is funneled to so you get more lift from them at slow speeds. You might get great low speed handling and lift then but mantain good stability at all speeds. Keep the bottom ones slightly forward of the center of gravity from the top ones to spread out lift across the body of the plane at low speeds for a gentler more controlled stall at an even lower speed.

Or maybe use the same wing design with dihedral from the fusealage to 2/3rd out and then anhedral for the last third to keep ground clearance and still create two forces of air building up against each other under the middle of the wing. ie moves away from fuselage to wing center and in from wing tip to center.

At least that is what I would try. Sorry about my spelling.
 
The Anhedral wing has a very negative effect of being more unstable in flight and harder to control. So why do seaguls have this? Well technically, all birds' wings tend towards downward tips simply because of the finger bone geometry. (Yes, tip feathers may well curl up due to their flexing - this is "Washout" on a human constructed wing). The thing is, land birds can land and take off on land and they flap more. A sea bird glides and eats at sea level. So land bird wings have more "up" at the shoulders to give that dihedral stability. Besides - birds are not technological creatures. They FEEL the air, so it doesn't matter to them, if their wing is whateverhedral ;) they have much better control than we humans had (before fly by wire).

Anhedral is perfect for a gliding creature because the drooping tips help enclose the ground cushion effect if it has to nab it's prey from the water while on the wing. Look at albatrosses.

And besides - even with the anhedral, a seabird has it's C of G below it's shoulders still, so the pendulum effect is still there. Your design suffers a severe stability problem with such a high C of G

Fast jets will use the advantage of anhedral for shaping the supersonic flow - the Valkyrie, for instance, had wing tips that folded down in flight. Look at how a falcon shapes its wings in a high speed attack flght. The wings shorten inward - well actually the elbows tuck back and in, the wrists forward and the fingertips down and rearward.

Human designed aircraft are mostly merely a poor copy of one aspect of the avian art of flight.

Some problems with your wings, Bill, start with the risk of damaging the tips during ground movement. The plane will rock around the wheel contacts - the longer your wings, the higher the legs will have to be. A low wing monoplane with anhedral will be very top heavy and unstable around the longitudinal axis. In flight, your stall and spin characteristics could easily put you in an inverted flat spin with high RPM.

There are anhedral low wing possibilities - put the landing gear in the wing tip? Wasn't there a Rutan design? (Weight penalty for reinforcement though) - but there will always be more conventional designs that will outperform this.

Anyway - for all who are more interested, here is an excellent presentation of understanding flight by a man who really does. You have to think "Newton" when designing a mechanical wing.
 
Give it 2 or 3 small engines and we can test the theory that several small engines are cheaper to maintain than 1 big engine. Make them jets too (looks like a high flyer).
 
The low COG of high wing military jet transports such as many US and Russian examples allows sufficent stability with anhedral. A high wing and dihedral would make engine access very difficult and would loose some of the advantages of ground effect for takeoff. The "nohedral" C-130, which I have flown a lot, was quite a stable aircraft, again to the low COG effect.

Cheers: T.
 
"Meant to echo the look of the X-Wing fighters from the movie Star Wars, according to Burt Rutan the principle designer, it appears to be a modified canard design or biplane but in reality is a tandem wing aircraft. The majority of the lift is developed in the front wing which is fitted with elevators and the forward landing gear. The aft wing, located on the upper part of the fuselage behind the cockpit serves also as the horizontal stabilizer."

http://www.museumofflight.org/aircraft/rutan-model-54-quickie

Another thing to consider (thanks for the reminder Tom) is that a lot of the large aircraft (AN-124, C-5, B-52) and in other ways, helicopters, are actually a "flex-wing" that starts our with significant anhedral at zero-low speed for structural purposes that shifts to neutral or dihedral as lift increases (in the Buff's case, about 11 ft of tip movement). Not something that can be duplicated in a smaller span or lighter structure.
As always, we find aircraft design to be simply a matter of finding the right compromises or experiments in rather narrow flight regimes (ask any F-104 pilot).

Rob
 
F104... Wings.

We don't need no stink'n wings....

B47 was the first of the large flexi flyers....

T.
 
Rob,

That Runtan Quickie does look a bit like an X-Wing if you think about it, lol.. Love it.


Flying that freeware Quickie the other night had me doing alot of thinking, as I was watching it fly along in Spot Plane Mode. Just think, two sets of full size wings.. Not one... Two...!

I had always wondered why the Caproni super liner didnt fly and often wondered why more aircraft didnt show up with same size dual wings (biplane?) one in front of the other, didnt show up more throughout history..

With the Quickie, it must have all sorts of lift going on...



Back to this little prototype, I will not be putting wheels in the wingtips, or small jet engines. ;) I want it to be as real as possible. Lancair woudlnt let me make one of their planes, so I am making my own design in a similar size. Working on the instrument panel layout right now.. I want it very 'automototive/concept car' looking..



Bill
 
Lionheart said:
Rob,


I had always wondered why the Caproni super liner didnt fly and often wondered why more aircraft didnt show up with same size dual wings (biplane?) one in front of the other, didnt show up more throughout history..


Bill
Click to expand...

I'm certainly not an aerospace engineer but ...I would have to imagine that the front wing would probably disturb the airflow headed back to the rear wing unless there is some staggering in elevation.
 
I'm certainly not an aerospace engineer but ...I would have to imagine that the front wing would probably disturb the airflow headed back to the rear wing unless there is some staggering in elevation.
Click to expand...

In normal flight the airflow to the rear wing would be at a different angle than that to the front, it's in the downwash of the front wing. That would hold for pretty much any elevation you could sensibly have it at, however all that means is that you'd rig the aft wing at a different angle of incidence so the angles of attack of both wings are pretty much the same.
What you'd also want to do is ensure the front wing would stall first so the nose would lower allowing you to pick up speed, rather than tailsliding. I'm not totally sure balancing both those requirements is feasible although I don't see why not. I'm wondering if it's not just because such an aircraft would be less practical from a ground handling aspect?
 
Airplane design is as much about economics as well - if you can build one wing cheaper than two smaller, why build the two smaller ones - unless you need the hangar floor space. And despite the wonderful performance of Rutan's canards, people still fly the less stable shoulder wing / standard empennage airplanes.

Think of all the innovations we could have... and then look at the very basic planes that are built.

They are made that way because the concepts work and 99.99% of all people with the budget can learn to fly a "standard" plane. Flying isn't difficult - that's why even serious professionals can learn to fly.

But don't let that ever stop innovation Bill. Go for it!
 
CBris said:
Airplane design is as much about economics as well - if you can build one wing cheaper than two smaller, why build the two smaller ones - unless you need the hangar floor space. And despite the wonderful performance of Rutan's canards, people still fly the less stable shoulder wing / standard empennage airplanes.
Click to expand...

It's also, in some cases, about customer/public perception. A lot of buyers and their passengers have trouble breaking away from the Bleriot style even if the innovative designs are better - or older. Over the years a lot of "new" concepts have received the dreaded: "I wouldn't fly in that - it looks wierd (or dangerous)!"
- monoplanes (not enough wings)
- nose-wheeled airplanes (won't it break off when we land?)
- canards (does it fly backward? where's the tail?)
- pusher engines (see 'canard')
- composites (it will come unglued like my ___)

So, like the auto industry we keep seeing more of what granddad taught us was "right"

Rob
 
Well.. I could make two versions of wings for this baby. The 'classic' style, and my radical Seagull wings.

I can see though that in turns, they would be hard to handle as the inner wing in a turn would lose a 'lot' of lift, almost pointing down, but only by an extra 10 or 12 degrees over normal. Perhaps shedding about 5 degrees off the anhedral would be a good compromise and increase distance of the wingtips from the tarmac when on the ground.

I love innovation and new idea's. For a while, in General Aviation, its like, all we had were Cessnas and Pipers here in America. Nothing else. Nothing cool.. All 1940's designs...

At least now, we have Cirrus, Diamond, Cessna's new Columbia. (I am sure I missed some there). Some good modern designs finally sprouting up.



I agree Chris on Economics. I used to work in a small aircraft factory in my younger days; Sadler Aircraft Company. I was the landing gear guy. Good fun watching them roll slowly from the frame zone through the wing fittings area, and finally to the 'prep for flight' area in front of the main door. Sure was labor intensive though.


Roger that Rob on new idea's being introduced and how they can scare away customers. I do think though that now people are more drawn towards innovations, so long as the innovations work properly and are for good reason.




Bill
 
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