Can a Plane on a Treadmill Take Off?

Actually conveyor belt would decrease the length of runways if operated
in the direction of take off???

Instead of wasting all that energy to power the conveyor belt, why not
add that power to the plane itself?

The Monk

Darthpup,

Actually conveyor belt would decrease the length of runways if operated
in the direction of take off???


The point the question makes is that the speed of the belt is completely
independent of the airspeed of the plane, so you just CAN'T make the belt
keep the airspeed at zero.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:

Alexy,

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

Absolutely, if you CHANGED the problem, and restated it as above, then
it wouldn't fly.


Actually, you couldn't do that - which is another point the question
makes.

True, from a practical standpoint. As far as the thought experiment
goes, you could if the conveyer moved fast enough that the rolling
friction of the tires plus the bearing friction of the wheels exactly
offset the thrust of the plane's propulsion system. My initial
calculations indicate that the speed needed for that to happen is
somewhat below the speed of light, but significantly beyond the speed
at which the wheels and tires would disintegrate. g
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Alexy,

My initial
calculations indicate that the speed needed for that to happen is
somewhat below the speed of light, but significantly beyond the speed
at which the wheels and tires would disintegrate. g


Concur. g

--
Thomas Borchert (EDDH)

alexy wrote:
Thomas Borchert wrote:

Alexy,

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

Absolutely, if you CHANGED the problem, and restated it as above, then
it wouldn't fly.


Actually, you couldn't do that - which is another point the question
makes.

True, from a practical standpoint. As far as the thought experiment
goes, you could if the conveyer moved fast enough that the rolling
friction of the tires plus the bearing friction of the wheels exactly
offset the thrust of the plane's propulsion system.

The question, though, says that the wheels are built to take it. They
must have frictionless bearings. g

How about this, you chain the plane to the ground with a 120kt headwind and
six 600HP engines mounted on a 172 all developing max thrust. Will it fly?

The answer, of course, is yes because no tiedown at any airport I've ever
seen would keep that on the ground. By the way the tires and wings are
irrelevant to the puzzle.
--
-------------------------------
Travis
wrote in message
oups.com...
If you restate the problem as follows the aircraft will obviously NOT
fly.

The aircraft is on a conveyor belt.

The conveyor is programmed to move in such a way as to maintain the
aircraft at an airspeed of zero as measured at the pitot.

propwash?

No - It's a Skymaster and the examiner cut the front engine.

Oh-wait - It's a jet...

a.


cjcampbell wrote:
Saw this question on "The Straight Dope" and I thought it was amusing.

http://www.straightdope.com/columns/060203.html

The question goes like this:

"An airplane on a runway sits on a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward. Does the airplane take off?" (Assuming the tires hold out, of
course.)

Cecil Adams (world's smartest human being) says that it will take off
normally.

cjcampbell wrote:
Saw this question on "The Straight Dope" and I thought it was amusing.

http://www.straightdope.com/columns/060203.html

The question goes like this:

"An airplane on a runway sits on a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward. Does the airplane take off?" (Assuming the tires hold out, of
course.)

Cecil Adams (world's smartest human being) says that it will take off
normally.

Yes.
The problem states '..moves in the opposite direction at exactly the speed
that the airplane is moving
forward..' So the plane is moving forward, thus it will fly. The wheels
are just spinning at 120mph instead of the usual 60mph.

"pilot" wrote in message
oups.com...

cjcampbell wrote:
Saw this question on "The Straight Dope" and I thought it was amusing.

http://www.straightdope.com/columns/060203.html

The question goes like this:

"An airplane on a runway sits on a conveyer belt that moves in the
opposite direction at exactly the speed that the airplane is moving
forward. Does the airplane take off?" (Assuming the tires hold out, of
course.)

Cecil Adams (world's smartest human being) says that it will take off
normally.

Exactly right.

In the end we'd have to say it's a nicely phrased question. My first
instinct was to say the ariplane had zero speed relative to the ground
the moving belt is on, but that is NOT the condition the problem
stated.

So, under the usual circumstances (not having a significant tail wind,
for example) you'd lift off assuming the wheels are not going to self
distruct turning at twice their usual takeoff speed.

"Tony" wrote in message
oups.com...
Exactly right.

In the end we'd have to say it's a nicely phrased question. My first
instinct was to say the ariplane had zero speed relative to the ground
the moving belt is on, but that is NOT the condition the problem
stated.

So, under the usual circumstances (not having a significant tail wind,
for example) you'd lift off assuming the wheels are not going to self
distruct turning at twice their usual takeoff speed.

The plane would take off from the treadmill even if there were a tail wind
equal to Vr (though in that case, the wheels would be turning at *four*
times their usual speed).

--Gary