mcjohn said:
Had a student ask me how aerodynamic braking works the other day and I blanked out. I said something stupid like "I dunno, it just makes the mains press into the runway better." I used to spit out a great reason but it has slipped my mind. We're talking about the full back yoke right? Anyone care to refresh my memory?
mcjohn said:
Oh wait, I think I have it........It takes weight off the nose gear and transfers it to the main gear. By putting on brakes the weight of the airplane is thrown foward toward the nose gear which has no brakes so the full aft yoke will attempt to pull some of that weight off the nose and put it back on the mains where the brakes are.
Patting myself on the back.
Your aerobrake comments are interesting -- I"ve not really heard that term in quite a while (since military days). We'd aerobrake the F-15 and 16, and T-38 down to about 80 knots, then fly the nose down and wheel brake. Saved the brakes for sure. Early turn-offs were seldom an issue.
I've not seen it used by design in 16 airline years. It's generally not as effective on the higher cambered, low swept jets. They don't fly very fast (relatively) on final either, so not that much speed to dissipate. I don't do much GAA time, but haven't seen it used that much there either.
The following short article is an interesting take on the aerobrake. Maybe too much info, but interesting (from Aero-News):
Aerodynamic Braking and Lightplanes
The Air Force is big on “aerodynamic braking”, especially in fighter aircraft. Holding the nose high exposes a larger cross-section of the aircraft to the relative wind, increasing drag and helping to slow it down. The practice apparently came along with the advent of swept-wing fighters and reconnaissance aircraft, which tend to have very high stalling speeds and therefore long landing rolls (
Note: increasing stall speed requires a faster landing speed for stall avoidance; faster speeds in turn require longer runways to dissipate landing energy). Aerodynamic braking is an alternative to ungainly drag ‘chutes that appeared with the introduction of these same airplanes.
Will aerodynamic braking reduce your landing roll in typical light airplanes? Probably not. Drag is an exponential function of airspeed, and at usual landing speeds of prop-driven airplanes simply aren’t moving fast enough for additional drag to be much of a factor. There are, however, several tangible advantages in holding the nose up during the landing roll (in tricycle gear aircraft) until minimum control effectiveness speed:
- Improved controllability. If too much airplane weight is borne on the nosewheel at high speeds, a nosewheel shimmy or vibration may develop and steering may overpower aerodynamic (rudder) directional control.
- Less stress on structure. Nose gear mountings, engine mounts and engine firewalls may all incur undue stress if lowered to the ground at a high speeds.
- Aircraft longevity. There’s evidence in some cases that letting the nose down at high speeds initiates a bending force along airplane fuselages, perhaps accelerating fatigue in other parts of the airframe.
- Nose tire life. Keep the nosewheel off the ground at high speeds and the tire lasts much longer.
- Adoration of pilots and nonpilots alike, as you provide a smoother landing experience.
Aero-tip of the day: Maybe not for the same reasons as fighter types, in most cases holding the nose up until it gently settled to the ground is an good technique in light airplanes