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

"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.

"Peter Dohm" wrote in message
news
Thrust is going to overcome drag and move the airplane forward.

Not in my Cherokee.


Sure it will!

If we can have a treadmill the size of a runway, and [which is] able to
sense the rotation of the airplane's wheels; then we can require it to be
both frictionless and inertia-free.

Whell Hell, if that's the case, 'my' Cherokee runs on H2O!

"Peter Duniho" wrote in message
...
"Richard Riley" wrote in message
...
Sure, any airplane could take off from a treadmill in a wind tunnel.
But climb out is a real pain.

No, it's not. Airspeed is airspeed. If the airplane can take off in the
wind tunnel, it can climb

(to the physical limits of the wind tunnel, of course).

I think that's the 'pain' part.


I was going back to the original premise of a treadmill in still air.

And you were incorrect.

Pete

"Steve Foley" wrote in message
news:NYDfh.5004$%T5.3873@trndny05...
Sure, any airplane could take off from a treadmill in a wind tunnel.
But climb out is a real pain.

No, it's not. Airspeed is airspeed. If the airplane can take off in the
wind tunnel, it can climb
(to the physical limits of the wind tunnel, of course).

I think that's the 'pain' part.

Maybe. Though, if so then I'd say that *any* operation of an airplane in a
wind tunnel could be characterized as "a real pain". I don't see how
climbing is any different than, say, getting to some actual destination for
example.

"Peter Duniho" wrote in message
...
"Darkwing" theducksmailATyahoo.com wrote in message
...
I am a regular on RAP, not a troll.

Then read the extensive thread that we already had on this subject before
you put your two cents in.

Show me video and I will believe it, if the plane is not moving relative
to the wind then the wing isn't making lift.

True.

I have ran on treadmills and I never felt a "wind" blowing in my face.

That's because you're using your feet for propulsion, and the treadmill
was negating your effort. There's no such effect for airplanes, as they
don't use their wheels for propulsion.

Your experience running on treadmills is irrelevant to the question at
hand (except for the intended effect of course, which is to confuse people
like you who haven't thought the whole thing through).

Pete


The plane IS hauling ass in relation to the moving treadmill BUT the wings
see zero lift due to the plane not moving relative to any air in the room. I
really think I am right the plane will not take off. The type of propulsion
is irrelevant. I guess we will have to agree to disagree until someone
actually does the experiement and video records it.

--------------------------------------
DW

The only way the treadmill can stop or slow the airplane is to create
more Drag than Thrust.

The reason the airplane will be able to accelerate is that the
treadmill does not create any significant drag aircraft.

When the treadmill hits 500MPH how much force will it take to hold the
airplane in position?

With perfect frictionless bearings it will take 0 force. If the engine
is generating any thrust the airplane will move forward no matter what
the treadmill does.

Brian.

You propel yourself on the treadmill by the friction interface between your
feet and the conveyor, not by jet propulsion.

mike

"Darkwing" theducksmailATyahoo.com wrote in message
...

I am a regular on RAP, not a troll.

Show me video and I will believe it, if the plane is not moving relative
to the wind then the wing isn't making lift. I have ran on treadmills and
I never felt a "wind" blowing in my face.

----------------------------------------
DW

Come on. You can't be serious.

mike

"Richard Riley" wrote in message
...

And, just to keep it on topic, the only planes that could take off
from a treadmill are the Osprey and the Harrier.

"Brian" wrote in message
ups.com...

The only way the treadmill can stop or slow the airplane is to create
more Drag than Thrust.

The reason the airplane will be able to accelerate is that the
treadmill does not create any significant drag aircraft.

When the treadmill hits 500MPH how much force will it take to hold the
airplane in position?

With perfect frictionless bearings it will take 0 force. If the engine
is generating any thrust the airplane will move forward no matter what
the treadmill does.

Brian.


So lets say I know my little RC plane takes off at exactly 25mph. So I crank
up the treadmill to step up to 25mph so I can keep the RC plane up on the
treadmill, the plane is completely stationary in regards to anyone standing
next to the plane but when the treadmill hits 25mph and my little RC plane
is staying even with the treadmill you are telling me I can pull back on the
elevator stick and the plane will take off? I don't think so.

------------------------------------
DW