I'm doing an independent study with some of my friends and we're trying to think of what to build. We're all aerospace engineering majors, well most of us, and want to do an independent study related to our major. One guy suggested we try building a plane with an "X" wing. He described it as a plane with two wings perpendicular to eachother. Our whole group agrees that we have never seen this before and we don't think it really exists. If this is true, why doesn't it exist? Why won't such a wing design work? The guy who proposed the idea said that the advantages of having such a design would mean that the plane wouldn't have to bank to turn.

Any ideas to help us?




P.S. I'm a total beginner to r/c planes and aerospace engineering so try to explain in layman's terms please.

A couple X-Wing designs have been posted in the X-Plane groups. X-Plane simulates aerodynamic forces and does a reesonable job of sorting flightworthy shapes from duds.

The best guess I can offer on x-wing planes might be that they do best in high-speed planes that need to manueuver a lot and that depend more on power than on the size of their wing to stay aloft. The reason: Biplane wings of most sorts cause disturbances in the air, especially downwash, that interfere with wings behind and below the top wing. Downwash might be more critical near the middle for several reasons that I wouldn't write about without doing some reasearch first.

A purely perpendicular planform would always want to favor one plane or the other. A more practical geometry places the wings closer to each other, like a tall, leaned-over X. A more practical anhedral/dihedral configuration for lower speed flight puts the wings the other way, so the most downwash is at the tips - more like <>, but with the tips separated a little bit. I think this, <>, is a very nimble, though somewhat less stable than a double dihedral biplane configuration.

Theres even a very low tech X-wing plane that has been built from coroplast signboard. Essentially four 2 ft X 1 ft panels put together with an engine and controls strapped on, its square from top or side view. These things fly OK... but are not for beginners.

http://spadworld.net/viewtopic.php?t=780

If the purpose is to build something that looks different, I'm sure it can be done and will fly after a fashion. However if the only gain is the ability to turn without banking, where is the advantage in that? By banking into a turn, the force on the occupants remains normal in their seats, while if the turn is done without banking a side force will be generated that will be quite uncomfortable.

First off, I'm not discouraging you. Inquisitiveness is the first step to becoming good at this stuff. And it does seem like a really neat wing configuration (especially if you watched a little too much Star Wars) [img]i/expressions/face-icon-small-smile.gif[/img] . BUT:

Such an aircraft would be EXTREMELY aerodynamically and structurally inefficient.

Just look at the top half of the X for now. Viewing the aircraft from the front or the back, you see one right and one left wing, just as on a standard aircraft, but with a 45 degree angle between each wing and the horizontal. This angle is called dihedral. Most manufacturers of light aircraft include some degree of dihedral, but it's usually on the order of 3 or 4 degrees. Visualize the lift pointing out the bottom of each wing (really simplifying the matter, but that's the point). Each wing will generally develop the same amount of lift, which can be mentally split between a horizontal and vertical component.

If the aircraft is banked, the low wing approaches horizontal, and the high wing gets further from it. Keeping it simple, the low wing's lift now points more vertically, which causes that wing to rise, making the plane return to straight and level flight. Thus, the manufacturer is accepting a little loss of lift (because in straight and level flight, there's still some horizontal component of lift from each wing) to gain stability. Generally, since lift is lost, dihedral is added only until the aircraft's stability goals are met.

If the wings of the aircraft angle down below the horizon (as on an F-104), that's called anhedral, and has the opposite effect (if you visualize the lift again, you'll see why). That's done on fighters to enhance maneuverability. But it also involves some loss of lift. However, the benefits outweigh the problems for that particular application.

What you're suggesting puts the lift from each wing equally up and to the side. The dihedral of the top half of the wing assembly is effectively canceled by the anhedral of the bottom half, so you gain neither the stability of dihedral nor the maneuverability of anhedral, and lose an IMMENSE amount of lift.

In order to reclaim that lift at a particular speed, you can either increase the total wing area (which increases drag), change to a higher-lift wing section (which increases drag), or fly the aircraft more nose-high (which increases drag).

Finally, the wings still need to lift the airplane. But only about 70% or so of the total lift generated by the wings goes to lifting the airplane (that's trig on the 45 degrees). So the TOTAL force generated by the wings has to be 41% greater than with a conventional design. The wings correspondingly have to be built strongly enough to resist ALL of the force that they generate. And strength = weight. And weight = bad.

Keep thinking, keep dreaming, and keep brainstorming. You might even still feel like making this thing, just for the sake of making it and having something completely different. But it has little practical application.

Imboring25, while I agree with most of your comments, the explanation of dihedral effect is not correct. When an aircraft banks, a portion of the lift pulls the aircraft to the side, while the vertical component of lift is no longer equal to weight, so the aircraft begins to descend. The net result is a decending sideslip. If the wing has dihedral, this sideslip changes the angle of attack of the wing such that the low wing angle increases and the high wing angle decreases. This produces a rolling moment to roll the airplane away from the sideslip (back toward level). This tendency to roll away from a sideslip is the dihedral effect, and will occur in any attitude regardless of the direction of gravity.

This lateral stability interacts with directional stability since the sideslip that produces the corrective rolling moment also tends to swing the nose toward the sideslip. An airplane with a big rudder, and little dihedral will tend to proceed into an increasingly steep spiral dive, while one with a small rudder and a lot of dihedral will tend to rock a lot and the nose will wander.

Dihedral effect is sometimes called "rudder coupling" since the sideslip introduced by rudder application will cause a roll response also.

So I'm not an engineer or anything special really, and quite a bit of what's said I'm not sure I understand, but I'm just thinking of one minor point people have been overlooking.

Everyone's focused on how this thing would fly. I'd seriously consider first.... how this plane can even roll around on the ground. Supposing a large wingspan, if the wings are perpendicular to each other, that fuselage will be really high off the ground. So that you'd need to either put the main gear on the bottom wings, or have them incredibly long to have the wings clear the ground!!!

We're creative about the landing gear.... sometimes we just leave them off and slide in on the wingtips. [img]i/expressions/face-icon-small-wink.gif[/img] With the planes built from corrogated plastic sign material... you won't hurt a thing this way.

The "Star Wars" X-wing has appx 30 to 40 deg between the wings... or about 15 to 20 deg off horizontal wings. If the fuselage could be made light enough... then a flyable R/C model would work out operating similarly to a flying wing. In the late 1970's or early 1980's someone built a X-Wing by adding a clear plastic (lexan) canard near the nose. It worked Ok, but was somewhat unstable (inadequate canard surface and no rudder... it had problems getting out of spins.)

The more you think of trying to do... the more you find has already been done. [img]i/expressions/face-icon-small-wink.gif[/img]

Lots of X-wings are flying...check it out Here!

Thanks for the replies guys!

Yea our group decided that an X wing is not the best idea for a project at the moment, but i'll probably try taking a look at it again when i take some damn aerospace courses.


We're now trying to build a solar powered glider that will stay up all day and all night. Meh we heard NASA was trying to do something like this and everyone knows i would love to beat NASA at something...*sigh* it'll never happen...

will, There is a Big chance you could beat NASA to some kind of solar powered, 48 hour glider. Who would have ever dreamed that the military would come to us modelers for such things as ornithopters that chase birds away from air strips, because birds do not make good feed for a Bombers Turbine jets. Consider the radio controled "snoop" and "spy" planes. Modelers have been taking pictures (and very good ones) from their RC models for years. 25 years ago I went to a RC fly-in at the Wright Patterson Air Force Museum. They tried to fly an experimental RC plane by watching a black and white TV screen, receiving a projected picture from a camera mounted in the airplane. The pilot got it up in the air, and switched his view to the TV and lost it. [img]i/expressions/face-icon-small-sad.gif[/img]
You guys there in Aerospace Enginering have too much going for you to even think "It'll never happen." It is guys and gals like you that will MAKE IT HAPPEN!

<blockquote>Quote
<hr>Originally posted by: member Bill
will, There is a Big chance you could beat NASA to some kind of solar powered, 48 hour glider. Who would have ever dreamed that the military would come to us modelers for such things as ornithopters that chase birds away from air strips, because birds do not make good feed for a Bombers Turbine jets. Consider the radio controled "snoop" and "spy" planes. Modelers have been taking pictures (and very good ones) from their RC models for years. 25 years ago I went to a RC fly-in at the Wright Patterson Air Force Museum. They tried to fly an experimental RC plane by watching a black and white TV screen, receiving a projected picture from a camera mounted in the airplane. The pilot got it up in the air, and switched his view to the TV and lost it. [img]i/expressions/face-icon-small-sad.gif[/img]
You guys there in Aerospace Enginering have too much going for you to even think "It'll never happen." It is guys and gals like you that will MAKE IT HAPPEN!<hr></blockquote>


Thanks for the pep talk man, i feel all confident now! heh

Right now, we're trying to figure out where we can find some damn solar panels that aren't heavy as hell. We know that there are solar panels that come in thin films;we could even replace some of the wood with solar panels too, but at the same time we still have a budget. This damn campus is too damn stingy.

One more thing about aerodynamics, i should make another thread but whatever: Sandpaper on the wings. I was told by someone that if i put some sandpaper under the wing, close to the leading edge or something. The point is that it would help us fly at high angles of attack without stalling. What do you guys think?