|Quoting Speedracer1407 (Reply 2):|
...I guess where I get hung up is when i consider the percieved fact that control surfaces on the trailing edge of a B2 or Concorde are integral with the primary lift-providing wing. Thus any change to the shape of that wing via pitch control surfaces seems like it should effect the overall lift, and provide little pitch control.
Dear Speedracer, I think that I can explain it.
When on a delta plane the pilot pulls elevator up, then the total lift of the wing will indeed DEcrease.
But the lift decrease is entirely at the trailing edge of the wing. At the leading edge the lift will not change (yet).
Since the trailing edge is behind the center of gravity (CG) then the tail will drop slightly. When the tail drops, then it increases the overall angle of attack (AOA) of the wing. This AOA increase increases the total lift all over the wing far more than the local lift decrease at the traling edge. The plane will pitch up and climb.
Same the other way around. Pushing down elevator will INcrease the total lift, but only on the trailing edge. The tail will lift, the AOA will decrease (maybe become negative), and the plane will dive.
It's all a question about balance.
A tailless plane must be balanced a lot more precisely than an ordinary plane with a tail. That's the reason why they have never been popular as civil transports. In fact most transport planes have a generously sized horizontal tail so the flight crews don't have to worry so much about fat pax in one end of the plane and empty seats in the other end. Anyway, all planes have certified forward and rearward balance limits, a generously sized tail only makes the limit range wider.
Look at old bomber planes which are similarly configured to modern transport planes, such as B-47, B-52, Tu-16, Tu-20/95 etc. They all have a relatively smaller horizontal tail. They were all designed to carry one nuke bomb at their CG, and balance calculation was piece of cake. Very unlike a Ryanair B737 with no booked seating and no known weight of each individual passenger.
Then how could the Concorde be operated without a tail?
I'm sure that exactly balance calculation was a big issue before each Concorde flight. And then the pax payload was relatively small, only 4.5% of TOW. On a 737 it can easily be well over 20% of TOW.
The Concorde also had the capability to adjust it's CG during flight by shifting fuel between forward and aft tanks. That was also needed to adjust for changed aerodynamics and wing lift distribution when shifting between sub- and supersonic speed, but that's a different story.
Many modern transport planes can also adjust CG inflight, but that's only for efficiency reasons. When the tailplane can fly with the smallest possible negative AOA, then the total drag - and fuel burn - is minimized.
Yes, a tailplane on a transport plane always flies with a negative AOA, although a small one. That produces what is called stability on the pitch axis.
When a plane is disturbed in flight by a turbulence, then let's assume that it creates a one degree pitch up. It may mean that the wing AOA will increase from, say, 8 to 9 degrees, while the tailplane has it's AOA reduced from, say, minus 2 to minus 1 degree. That will increase the wing lift only slightly, while the negative lift of the tail will be cut in half. A proportionally much greater change of force on the tail. The result will be that the tail will lift more than the rest of the plane and stabilize the original AOA values. Same (only opposite) when a turbulence forces a pitch down.
That stability is much harder to produce on a tailless plane, but it is done in much the same way, only by shaping the wing profile in a special way. (That does not count for the B-2 which rilies on artificial - computer controlled - pitch- (and yaw-) stability).
There has been a lot of talk about BWB transports - Blended Wing-Body planes, which are essential tailless planes. They could potentially be more fuel efficient than ordinary tailed planes. I don't believe in them, not because they could not be enonomically efficient and safe, but because they would be too complicated to operate because of too narrow CG range. They could be made with a quite wide CG range, but that would call for a very stangely shaped wing profile, and then all the efficiency gains would be gone due to increased drag.