Then, Biplanes Can't Fly Upside Down!

[Xema]

Some radio-controlled helicopters can hover inverted - indeed, it’s a fairly common (& cool) advanced maneuver.

I’m a trifle skeptical that any full-sized helicopter can do this. The thing would need to be specially engineered in a number of ways, which would certainly add weight and cost. In return, you get nothing of real use (except the chance to impress the hell out of anyone who sees it). It would make for a terrific airshow act, but that’s about the limit of its application.

(Of course, there have been plenty of planes built just for their airshow capabilities.)

[Xema]

@micco

The point is they have about the same lifting surface (i.e. span) without having to have the structural support for a wing twice as long.

Well, wingspan is pretty much universally understood as the linear distance from one wingtip to the opposite one. When you say “same lifting surface” it sounds as if you’re talking about wing area, not span.

in every real aircraft I recall examining, the wing was mounted on the fuselage with a positive angle of attack.

This is generally called the angle of incidence. The angle of attack is the angle between the wing’s chord line and the relative wind.

…but it still has a positive angle which makes inverted flight less efficient.

Agreed - the angle of incidence is almost always set with upright flight in mind, at the expense of inverted flight efficiency.

Of course the various control surfaces can be used to vary the angle and, especially in the case of flaps, their effect may be much greater than the angle caused by the fixed design, but that doesn’t eliminate the fact that there is a permanent positive angle of attack in the basic construction …

Again, this would be an accurate statement if “incidence” is substituted for “attack”. As it stands, it’s wrong. The angle of attack is controlled the same way in upright flight as in inverted flight - basically, by the elevator (though flaps, when present, do play a role). It need not always be positive.

[micco]

@Xema

Again, this would be an accurate statement if “incidence” is substituted for “attack”. As it stands, it’s wrong.

The angle of incidence contributes, either positively or negatively, to the angle of attack. The point I was trying to make is that most planes are built so that, all other things equal, the structure by itself creates a positive angle of attack in normal flight. I never said the angle of attack was solely due to this factor. I never said it couldn’t be offset by control surfaces. I was trying to point out that this was one big factor in why inverted flight is less efficient than normal flight.

[Xema]

@micco

The angle of incidence contributes, either positively or negatively, to the angle of attack.

I don’t really think it does. If you mount the wings on the fuselage at some strange angle, you’ll end up flying with much the same angle of attack, while dragging the fuselage through the air at some inefficient orientation. This is pretty much the point you have made about inverted flight.

The point I was trying to make is that most planes are built so that, all other things equal, the structure by itself creates a positive angle of attack in normal flight.

It would be more accurate to say that most planes are build so that normal angles of attack during upright flight cause the fuselage to be at a reasonably efficient angle to the relative wind.

I was trying to point out that this was one big factor in why inverted flight is less efficient than normal flight.

And that part of your post is quite accurate.

[micco]

@Xema

It would be more accurate to say that most planes are build so that normal angles of attack during upright flight cause the fuselage to be at a reasonably efficient angle to the relative wind.

That’s exactly what I was tring to say. Thanks for saying it better.

[David_Simmons]

@micco

The question was rhetorical.

Semantics. The point is they have about the same lifting surface (i.e. span) without having to have the structural support for a wing twice as long.

I deal mostly with theory and wind tunnels, but in every real aircraft I recall examining, the wing was mounted on the fuselage with a positive angle of attack.

The angle the wing has relative to the fuselage centerline is the angle of incidence. This angle is set so that in level flight at optimum airspeed the fuselage is aligned at the position of minimum drag if you are after most economical performance. This was particularly noticable with the Martin B-26. The angle of incidence on the G model was increased to lower the nose in level flight and in a formation the difference in fuselage angel for the G from all previous models was apparent. In landing you could also tell because the nose was noticably lower for the G.

The Chance-Vought F-8 had a variable incidence wing in order to give the pilot visibility forward on takeoff and landing. Pilots said that on the first flight in an F-8 you got the feeling that you were going to stall out on climb-out when you “lowered” the wing because you didn’t really lower it. The wing maintained nearly the same angle of attack and the fulselage lifted to meet it. This gave the impression that you had suddenly increased your climb angle and took a little getting used to.