30.06.2010, 17:46
Ok, I guess I might have come across as a bit harsh. But I must say that you have been making some obvious annotations simply for the sake of arguing.
Most light aircraft have one main spar (there are obviously smaller spars in the wing as well). When an aircraft has more than one "main spar" (if you still want to call it that), then it will obviously not have multiple centers of gravity; the center of gravity will be between them. I think it is pretty obvious and truly didn't think it even needed mentioning, but apparently you didn’t consider it to be obvious. When discussing these basic aerodynamic principles it is also absolutely absurd to hammer on about every little variation in design just in order to be argumentative. The center of gravity also shifts slightly as cargo and passengers are loaded on the aircraft, but let’s not fret about it shifting a few cm to this side or that side just for the sake of arguing. And let’s not get into every slight center of gravity variation for each aircraft on the planet, please.
The reason a tailplane is not curved at the top and flat underneath, is because the function of the tailplane and elevator combination is to create either positive or negative lift at the tail in order to control pitch. Bulging it at the top would produce constant positive lift at the tail, which will make constant up trimming necessary just to keep the nose level (getting worse as speed increases). It would also increase induced drag and make it difficult to pitch the nose up. There are exceptions to this - caused by certain aircraft designs, but let’s please not hammer on about that either.
Most of what you said previously I can agree with (pretty basic principles that didn’t need mentioning in the first place), but at least it supports what I've been saying all along. However, you still don't seem to understand that when the elevator is deflected it causes both the angle of attack and the camber of the combined tailplane and elevator surface to produce either a lift or down force, depending on the deflection of the elevator. When the elevators are lowered -> increasing the camber, it creates an upward force called lift at the tailplane. When the elevators are raised -> decreasing the camber, it produces a downward force (negative lift) at the tailplane.
How do you think flaps work? Notice how a wing with lowered flaps looks similar in profile to a tailplane with a lowered elevator. Flaps work on the same aerodynamic principle as lowered elevators... When the flaps are lowered they increase the camber of the wing, which increases lift (the same applies to the tailplane and lowered elevator combination). On the other hand, when the elevator is raised it acts similar to an inverted flap, causing negative lift at the tail. The same principle applies to all the control surfaces of an aircraft. If you don't agree with that then I don't see any further use in continuing this discussion. In fact, if you want to continue this discussion at all I suggest we do it through PM since I think we've gone off this threads intended topic enough as is.
Ps. Before you PM me, please read up a bit on how the elevator changes lift at the tailplane by altering its camber.
I thank you.
Most light aircraft have one main spar (there are obviously smaller spars in the wing as well). When an aircraft has more than one "main spar" (if you still want to call it that), then it will obviously not have multiple centers of gravity; the center of gravity will be between them. I think it is pretty obvious and truly didn't think it even needed mentioning, but apparently you didn’t consider it to be obvious. When discussing these basic aerodynamic principles it is also absolutely absurd to hammer on about every little variation in design just in order to be argumentative. The center of gravity also shifts slightly as cargo and passengers are loaded on the aircraft, but let’s not fret about it shifting a few cm to this side or that side just for the sake of arguing. And let’s not get into every slight center of gravity variation for each aircraft on the planet, please.
The reason a tailplane is not curved at the top and flat underneath, is because the function of the tailplane and elevator combination is to create either positive or negative lift at the tail in order to control pitch. Bulging it at the top would produce constant positive lift at the tail, which will make constant up trimming necessary just to keep the nose level (getting worse as speed increases). It would also increase induced drag and make it difficult to pitch the nose up. There are exceptions to this - caused by certain aircraft designs, but let’s please not hammer on about that either.
Most of what you said previously I can agree with (pretty basic principles that didn’t need mentioning in the first place), but at least it supports what I've been saying all along. However, you still don't seem to understand that when the elevator is deflected it causes both the angle of attack and the camber of the combined tailplane and elevator surface to produce either a lift or down force, depending on the deflection of the elevator. When the elevators are lowered -> increasing the camber, it creates an upward force called lift at the tailplane. When the elevators are raised -> decreasing the camber, it produces a downward force (negative lift) at the tailplane.
How do you think flaps work? Notice how a wing with lowered flaps looks similar in profile to a tailplane with a lowered elevator. Flaps work on the same aerodynamic principle as lowered elevators... When the flaps are lowered they increase the camber of the wing, which increases lift (the same applies to the tailplane and lowered elevator combination). On the other hand, when the elevator is raised it acts similar to an inverted flap, causing negative lift at the tail. The same principle applies to all the control surfaces of an aircraft. If you don't agree with that then I don't see any further use in continuing this discussion. In fact, if you want to continue this discussion at all I suggest we do it through PM since I think we've gone off this threads intended topic enough as is.
Ps. Before you PM me, please read up a bit on how the elevator changes lift at the tailplane by altering its camber.
I thank you.