Very interesting thread!
I think we have to look at the NET effect that the component has on the aircraft. For example, a wing produces more lift than it weighs, and an engine produces more thrust than drag.
Now the question is, does a winglet OVERALL produce more thrust than drag? (induced drag reductions don't count as thrust) In cruise flight, is the wing dragging the winglet through the air, or is the winglet helping to push the wing (and the aircraft) through the air? How does this change during the different phases of flight?
This is what, IMHO, would determine wherether or not we can say a winglet produces thrust. What do you guys think? I know mad scientist's opinion, and respect it, but I'm wondering if there is any proven scientific data (if there is any such thing) indicating this. (I believe someone must know, because I'd assume that somewhere in the design process of the structure holding the winglet the engineers would need to know whether its gonna have to resist primarily loads pushing the winglet back, or pulling it forward.)
If all a winglet does is reduce drag, I don't think we could considser it to produce thrust although the effect on aircraft performance is the same, and probably greater. In fact, don't you think that there is little doubt that the greatest contribution that a winglet brings is the reduction in drag rather than an addition, if any, of thrust?
As far as the forward component of force created by the winglet, does it overcome the parasite drag created by the winglet itself or does it merely REDUCE the overall drag produced by the winglets by compensating with some amount or forward force?
KeithWilliams,
First of all I thought the sailboat analogy was excellent, I will definately add that one to my bag of tricks
Not to go off-topic, but regarding the concorde C-D inlet
you wrote:
"
It is often said that the convergent-divergent intakes of Concorde produced more than half of the thrust in supersoinc cruise. The engines alone could not produce this much thrust without using a far greater fuel flow. But if we shut down the engines all of the thrust is lost. The engines need the intakes and the intakes need the engines. Neither alone can produce the extra thrust. But can we really say that the intakes simply reduce drag? No we cannot. "
Why not? We definately can't say the intake creates thrust.... rather, I would say they add drag but are the most efficient compromise between what the intake HAS to do and what it can do. From what I remember, the main purpose of the C-D intake is to slow down the air the air to an acceptable intake velocity (about M.5 if I remember correctly). This is a necessity, not a luxury. By slowing down, speeding up, deflecting or otherwise affecting the air in any way you always loose energy. Now in this case, since you HAVE TO slow it down, you might as well do it in a way that increases the static pressure of the air, since you'll have to do that anyway prior to combustion. In other words, its an efficient utilization of what you have (ie. high speed RAM air) to get what you need (slower-speed air with higher density). But don't forget how you got there (at M2.2)... by burning lots of fuel. Only because you NEED that intake doesn't mean it should receive credit for pushing the aircraft.
I would see the intakes more as as an efficient way of performing a nescessary task rather than a thrust augmentation device.
palgia