View Single Post
Old 4th Feb 2007, 20:06
  #8 (permalink)  
Mad (Flt) Scientist
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,082
OK,for the question as posed there is no single answer - the result is aircraft dependent, and there are insufficient constraints specified to permit a single solution to be determined.

Consider only the flaps case. The initial stick-fixed transient may be to pitch up OR to pitch down - it depends on the raw pitchingt from the flaps and the effect of the change in downwash on the tail lift. Left's assume the more normal case, where the aircraft pitches down in response to flap deployment.

Next we have to wonder if the increased lift due to flap deployment is offset by the decreased AoA. Again, aircraft dependent. Let's assume the flap effect is greater. So we have a net increase in lift, and of course an increase in drag too. If we do nothing, the aircraft will start to loop upwards, due to being above 1.0'g', and will slow down, both due to the drag and due to climbing. There will be some speed where the increased lift s offset by the reduced speed. There will also be some (other) speed where the drag has reduced enough to be back in trim in the speed axis. The only variable that we have (if we dont change the aircraft configuration) is flightpath angle, which we can adjust to balance the two different speeds (it will affect the drag-trim speed, but not the lift-trim speed).

Whatever that flightpath angle ends up being, its almost certain that it will not be such as to give the original pitch attitude - nothing we`ve done has been towards that end. Therefore in order to maintain the same pitch itude we have to change some other paramet9s) - elevator, or thrust, or speed, or whatever. There will be many many combinations which achieve the desired pitch attitude - some may involve higher speeds and lower AOAs but with a climb - others a low speed and high AOA but a descent. Wheteher the AoA increaes or decreases is a choice, since the question doesn`t constrain what we do to maintain pitch attitude.
Mad (Flt) Scientist is offline  
Reply With Quote