mithrandir
03-09-2004, 08:14 PM
Anyone care to take a stab at explaining the dynamics of a Harrier? (Deep Stall)? Why does an aft CG make such a huge beneficial difference?
Dave Robelen
03-15-2004, 06:40 PM
Hi,
You have a couple of things going on here. As you move the CG back, it comes closer to the neutral point for the aircraft. This requires less force from the stab/elevator to maintain the high AOA condition. Once the wing goes to a high angle of attack (well beyond the primary stall) it becomes prettty well damped in roll. NASA did a study with a Schweitzer glider that was fitted with a "pop-up" horizontal tail that showed the importance of rapidly pitching the wing to a high angle to avoid the typical roll-off associated with the basic stall. This was a method being considered for the recovery of certain UAV machines at one time. Our free flight cousins have been using a "pop-up" stab for many years to put the model in the deep stalled condition. A very handy way to drop a model out of a thermal.
Cheers, Dave