Airplanes and Conveyor Belts - Mythbusters

Hallo Michael Ash, Du schriebst am 01.05.2008 17:42

Werner Schmidt wrote:
2.) If both begin to accelerate at the same time, it makes no
significant difference to a usual start. The rolling drag of the
undercarriage wheels pulls the airplane a *little* backwards, but this
effect is negligible. - The wheels just turn faster (as above).

In standard Newtonian dynamics, rubbing (or rolling) friction is
independent of speed, so long as you're moving at all. So the extra speed
of the wheels is no penalty at all, barring problems with extra heat as
you mentioned.

But same friction at higher speed releases more energy (=heat).

Why does a spaceship need a heat shield and a ASK13 doesn't? And special
gearboxes do need cooling (air may suffice). Bearings become hot if
rotation speed is high and cooling not adequate. A too hot bearing may jam.

Regards
Werner

Ugh, this old topic again? :-P

I understand why you say "the answer is in the wheels". But that's
exactly the wrong attitude to take, and it illustrates why so many
pilots (IMHO) don't fly well.

The answer is in the wing!!! :-)

The answer is ALWAYS *the wing* when it comes to flying!
(OK, some smartass will point out that its sometimes *the tail* - but
that's really just another wing!)

If more pilots could think about their aircraft in terms of "what is
the wing doing right now" or "what is the wing __feeling__ right now",
there would be a lot more pilots who were a lot more skilled (and
possibly a lot fewer accidents!)

Take care,

--Noel

"noel.wade" wrote:
I understand why you say "the answer is in the wheels". But that's
exactly the wrong attitude to take, and it illustrates why so many
pilots (IMHO) don't fly well.

The answer is in the wing!!! :-)

Maybe it would help by simply saying "The answer is in the air."

Jim Logajan wrote:

The answer is in the wing!!! :-)

Maybe it would help by simply saying "The answer is in the air."


The answer


My friend


is blowin' over the wing

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...aring/200805/1

Werner Schmidt wrote:
Hallo Michael Ash, Du schriebst am 01.05.2008 17:42

Werner Schmidt wrote:
2.) If both begin to accelerate at the same time, it makes no
significant difference to a usual start. The rolling drag of the
undercarriage wheels pulls the airplane a *little* backwards, but this
effect is negligible. - The wheels just turn faster (as above).

In standard Newtonian dynamics, rubbing (or rolling) friction is
independent of speed, so long as you're moving at all. So the extra speed
of the wheels is no penalty at all, barring problems with extra heat as
you mentioned.

But same friction at higher speed releases more energy (=heat).

Right, that's why I mentioned extra heat.

Why does a spaceship need a heat shield and a ASK13 doesn't? And special
gearboxes do need cooling (air may suffice). Bearings become hot if
rotation speed is high and cooling not adequate. A too hot bearing may jam.

The comparison with the spaceship isn't quite apt. Aerodynamic friction
increases with the square of the speed so the total rate of generated heat
increases with the cube of the speed. Rolling friction is constant so the
total rate increases linearly. In any case, if the extra heat is enough to
cause problems then that would certainly make a difference, but I think
the original question more or less assumes that it's not a factor.

--
Michael Ash
Rogue Amoeba Software

Hello Michael Ash, you wrote at 02.05.2008 05:12

Werner Schmidt wrote:
[...]
Why does a spaceship need a heat shield and a ASK13 doesn't? And special
gearboxes do need cooling (air may suffice). Bearings become hot if
rotation speed is high and cooling not adequate. A too hot bearing may jam.

The comparison with the spaceship isn't quite apt. Aerodynamic friction
increases with the square of the speed so the total rate of generated heat
increases with the cube of the speed. Rolling friction is constant so the
total rate increases linearly.

Correct.

In any case, if the extra heat is enough to
cause problems then that would certainly make a difference, but I think
the original question more or less assumes that it's not a factor.

I just wanted to mention that a jamming wheel bearing (caused by extra
heat due to higher rotation speed) might cause an accident.

Regards
Werner