ORIGINAL: Daryl Martel
Dick, someone is going to have to advise all those Boeing and Airbus engineers that they've got it all wrong! All along they've been thinking flaps add lift. They've been adding all that extra weight, mechanical complexity and cost to airframes all these years building in flaps when you say it really doesn't create lift. What were they thinking! :^) Maybe we need to use a different angle here - if you can land slower with flaps, they must be adding lift right. After all, you're supporting the same weight at a lower air speed. Do they add drag? Of course flap deployment does - you're sticking more surface out into the airstream. You compensate by adding power. Simple physics says that you don't get something for nothing right. Dick, I'm no engineer, but I've been formally trained as an aircraft mechanic (for whatever that's worth), and we were taught flaps add both lift and drag. Makes sense I think. I think any credible book on aerodynamics will back this up.
You are correct. It is amazing to see the conclusions people come to. Flaps change the shape (and sometimes enlarge the area) of the wing. The new shape generates more lift at a given speed; the speeds associated with T/O and landing. So why not fly with flaps extended all the time? Because their lift/drag ratio is worse than a clean wing. Once speed is sufficient, the lower lifting ability of a clean wing is able to do the job because it is moving faster, and of course is also more efficient.
I flew B737's out of short slippery runways. That meant that one wanted to get off at the lowest possible speed, in case one needed to abort T/O. Yet one couldn't just select the largest flap setting, because drag would become a factor. You have to be able to maintain a minimum climb gradient in case you lose one engine right at V1 decision point. We would get into the books to select the highest flap setting that would allow a one engine climb out.
Conclusion: Flaps are used to make up for the inadequate lift supplied by a clean wing at landing speeds. The clean wing is suitable for cruise, not landings.