posted on Oct, 22 2006 @ 05:47 PM
Originally posted by Valhall
The main reason for a longer take-off with low-mounted wings is because of the ground interference. I'm not sure I'm in on the "low-wing is more
efficient at cruise" statement yet. I'm going to have to think about that a bit.
Yeah sorry, dropped the ball with the low-wing/cruise statement, correction is above.
Originally posted by Flight Master FIN
What is it in the "cobra" manouver that makes it so hard to perform? Does it have to do with pressure on the wings or what? If anyone can explain I
would be happy.
OK, the cobra is into deep post stall manouvering, so aircraft stall angle doesn't really matter that much. What is important, is pitch control
The cobra as performed by the original Su-27 was purely momentum based. Heave back on the stick, get as much upward momentum into the nose as
possible. As the aircraft pulls up sharply it stalls, as its AoA increases, the horizontal tailplanes and wing are inducing a nose down pitching
moment through pure wind resistance (drag) - this is what restores the aircraft to controllable flight. Its totally outside of the pilots control
beyond around 25 deg - its all momentum and wing/tail drag from then on.
However, the later aircraft, like the MiG-29 OVT and F-22 can all do controlled cobras - through use of TVC. This allows the pilot to negate the nose
down moment from the tail/wing - and hold the 90/120 deg AoA - then pitch down in his/her own time.
The reasons for aircraft not being able to do the cobra are (all or some of the following):
- not enough elevator input to get the nose momentum up to sufficient levels
- not high enough polar moment of interia in the longitudinal axis
- not right wing/tail planform to get sufficient nose down moments to restore controllable flight [you can do the "cobra"... once, then yer deep in
the brown stuff]
- no TVC
[edit on 22-10-2006 by kilcoo316]