So...about that plane on the treadmill...

Ok, how about this one. Everyone knows pilots love a tailwind.

You have a giant fan mounted on a truck positioned behind the airplane.
The fan blows air towards the airplane, helping it to accelerate down
the runway (literally blowing it down the runway) while the truck
follows, keeping up with the airplane. Pretty soon the plane will be
thundering down the runway and the pilot pulls back on the yoke.

Does the pilot have to wait until the airplane's speed down the runway
is twice Vr before he can take off?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
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Ok, how about this one. Everyone knows pilots love a tailwind.

You have a giant fan mounted on a truck positioned behind the airplane.
The fan blows air towards the airplane, helping it to accelerate down
the runway (literally blowing it down the runway) while the truck
follows, keeping up with the airplane. Pretty soon the plane will be
thundering down the runway and the pilot pulls back on the yoke.

Does the pilot have to wait until the airplane's speed down the runway
is twice Vr before he can take off?

Jose
--
There is not enough beer in the world to fuel such a discussion!!!!

Peter

"Jose" wrote in message
. net...
[...]
Does the pilot have to wait until the airplane's speed down the runway is
twice Vr before he can take off?

As long as the fan is blowing the airplane forward, it will be impossible
for the airplane to take off. The only way for the fan to move the airplane
forward would be for the airplane to be moving more slowly than the air,
which means the airplane has a continuous tailwind.

If, on the other hand, you make the assumption that you can remove the fan
at any time, you can arbitrarily decide to remove the fan at the normal Vr
and the airplane can take off normally.

There are a variety of other assumptions one could make, due to the
incredibly ambiguous nature of your question, and the exact outcome depends
on how those assumptions are made. I simply provided the two "most
reasonable" assumptions that came to mind, for the sake of discussion.

Pete

Jose wrote:
Ok, how about this one. Everyone knows pilots love a tailwind.

You have a giant fan mounted on a truck positioned behind the airplane.
The fan blows air towards the airplane, helping it to accelerate down
the runway (literally blowing it down the runway) while the truck
follows, keeping up with the airplane. Pretty soon the plane will be
thundering down the runway and the pilot pulls back on the yoke.

Does the pilot have to wait until the airplane's speed down the runway
is twice Vr before he can take off?


Down wind takeoffs require a higher ground speed.
--
Gene Seibel
Tales of Flight - http://pad39a.com/gene/tales.html
Because I fly, I envy no one.