Originally posted by Pilgrum
reply to post by weedwhacker
If I can call on your experience actually flying these beasts and not that you'd ever consider doing such a thing, but try to picture the disputed
757 coming in cleanly at high speed and descending in order to hit its intended target. At what point would the blast of the engines at full throttle
be directed at an angle toward the ground?
To my knowledge of flying, admittedly limited, the engine blast could only be directed at the ground if the plane was stalling or attempting to gain
altitude again. At the suggested speed the attitude of the plane would be a little nose-down to overcome ground effect which would angle the blast
upward from the horizontal which is logical as you need a vectored downward force to overcome the resistance to descent so close to the ground.
Or am I way off target here?
Pilgrum, the exhaust forces from the engines will never be directed downwards. The exhaust forces from the engines are particularly noticable during
ground operations, and only affect nearby objects, say a few dozen feet behind.
In flight, of course, what is encountered is the 'wake turbulence'....this is a common term to describe the wingtip vortices, produced while in
Think of them as horizontal tornados, rotating off of each wingtip....left wingtip rotates clockwise, right wingtip rotates counter-clockwise.
If you boat, you know that your boat leaves a 'wake'. This is similar, except it is in the air, not the water.
Also, if you boat, you'll know that other wakes, or the prevailing current, can affect YOUR wake. Not the best analogy, except to say....a wingtip
vortice will be produced, and will descend approx 300 - 400 feet behind the airplane, and will tend to spread out, and away... They can persist for
several minutes. If you are looking at an airplane that is taking off, or landing, and if there is a prevailing crosswind, then the wingtip voritce
that is 'Upwind' could be 'blown' back over the runway surface, and 'linger'.
This is why, and it's a very simple rule when you fly small airplanes, always land BEHIND the point of a larger airplane's lift-off point, if
landing behind a large jet that just took off. AND, always land AFTER the landing point, stay above the path of a larger jet, if you are landing
behind a large jet.
As professional aviators we are taught to land within the 'landing zone'...this is the first 3000 feet of the runway...the 'touchdown zone' is
designated at the first 1000 feet, and when you look at runway markings, you will see and understand.
BUT, as I said above, if you are flying a small airplane, and landing behind a big jet, then you are landing on a long runway, and avoiding wake
turbulence is more important than landing in the 'landing zone', since you're a small airplane, and only need about 1500 feet of runway at most, to