TOPIC: Airplane Airspeed/Groundspeed Conundrum?

Rat wrote:
1/10

wolfy wrote:
Sure, we just have to figure out a split off point, im welcome to suggestions, eg give me a post number.

The rest i will get back to you when i have some time.

Rat wrote:
Totally wrong.

its already been explained.

Youd be right if a plane accellerated via driving the wheels.

But it doesnt.

The wheels just freewheel on a plane, they arent joined to any driveshaft or drive mechanism/engine.

A plane accellerates from thrust created from its engine/s ... whether its propellor or jet it doesnt matter, either one is the same effect.

The plane moves by pulling air through, so it pulls through the air... the conveyor doesnt affect the planes speed, it just makes the wheels have to spin faster.

The conveyor has nothing to do with the drive system of a plane, it cant effect it.. it cant effect what the engine and air are doing above it, it has no bearing.

Again, all the conveyor does is make the wheels turn faster.. and since they are just freewheeling, they just turn faster to accomodate.. plane moves forward and takes off.

Youd be correct if it was a car, it would never move.. but not a plane.
Frothy wrote:
Nope thats not what i suggested.

If you were on a power boat in a moving river, and it was caught in the movement of the water moving with it... but you had an exact same power boat 20m infront doing the same thing as you, caught in the water current at the same speed... and one 20m behind doing the same thing as you, caught in the water current at the same speed.. so all 3 boats weighted exactly the same were all moving down the river the same but 20m between each one, and all 3 boats have their engines turned off...... which boat could you reach easier if you turned the engine on...

and lets assume your boat has an identical outboard motor on either end for the experiments sake, so it moves via propellor in the water in either direction, you pick the correct motor to move in the direction you want.

Which boat would take more energy to reach, the one infront of you or behind you, if you try this one way and then the other?

wolfy wrote: If I were on an open roofed train which was travelling at 100 mph .if you looked down into the train as it passed and I was walking back and forth in a carriage in said train, let's say at 4mph, at no point am I travelling at less or more than 100 mph. But within the point of reference I travel at 4mph with the same ease either way.

Novum,
Aeroplanes rely on air flow at the wings in.order to create lift and take off, this would not occur being stationary on a conveyor belt. I don't really know what point your trying to make with the three boats but its surely going to take more energy to power against the current. Hence surfers don't surf away from the shore do they? It's the same as you need to drive harder up hill than down as the gravitational flow is harder, if you go against.anything going.thr other way, it will take more power to travel in that direction at the same speed, than it would going with the flow.

novum wrote:
From post no. 1588 would be good.

Thank you

Btw a plane flying in the atmosphere is like.the man.the train. In otherwords a man.on a train going at 100 mph if he got on a.
motorbike and drove 100 mph.in.the other direction he would not stop he would break through the carraige end at his 100 mph, or have a 100mph crash, only if he left the train would they drift apart at 200mph.

Rat wrote:
Take the front of the train off and see what happens to him.

Rat wrote:
But you arent stationary... soon as you crank that plane engine up, you start to move regardless of the conveyor... youre not getting it.

It doesnt matter what the conveyor is doing... the plane will just move anyway, it dont give a fk what the conveyor is doing, it starts pulling through the air.


But the boat behind you (against the current) is coming at you

I said reach the boat, not reach the same distance upstream to downstream

Novum you're going nuts. the plane is not going forward, the wheels are spinning, the engine is cranked up but the plane is not travelling, its in the same spot on the conveyor. no airflow is being generated on the wings to create lift, its only slipping as if it were on ice, you could stand in front of the conveyor belt with your hand on.the nose of the plane.

wolfy wrote:
But we can't take the front off of the atmosphere. That's the point.

wolfy wrote:
Sure, we agree up to this point, a stationary item wont register anything.

wolfy wrote:
This is where we fundamentally disagree it seems... and now i'll have another go at conveying/explaining whats in my head in a different way...

Lets pick two points from a central starting point, one in the direction of earths rotation, one the other way.

Both points are 1000 miles from the central starting point, and destination B is with the earths rotation, A is against it. And the earth is moving at 1000mph also.

so

[destination A ]<---- 1000 miles ---->[starting point]<---- 1000 miles ---->[destination B]

direction of earths rotation @ 1000mph ---->


Now lets assume we want to get to either point in one hour from our central starting point... so we have to average 1000mph either way (going off ground based reference), lets assume we can do that either way once up in the air because the plane is capable etc.

Lets start with destination A.. you want to travel 1000 miles in one hour, against earths rotation. So you take off, and are not joined to the earth anymore, as you said.

So what do you then have to do to hit our target of destination A in one hour, if you are the plane and not joined to the earth anymore? All you have to do is counter the 1000mph of atmosphere.

If you didnt counter it at all , ie no thrust (for arguments sake, assume the plane could stay up there for our experiments sake) youd stay exactly above your starting point, right? Youd move at 1000mph with the atmosphere, but your starting point is also moving 1000mph with you.. youd stay in the same place relative you your starting point on the ground.

Now... consider adding thrust to counter all of the 1000mph atmosphere in its entirety/exactly, so you are then not moving with the atmosphere at 1000mph anymore but staying in the same spot (in this case i say the same spot versus lets say an observer in space that is outside earths rotating system) ... you'd only have to add 1000mph worth of thrust to do this.. to stay in the same spot relative to space.. you add 1000mph to cancel the atmosphere's 1000mph.. and your plane speed indicator would also read 1000mph.

If you do this, just thrust at 1000mph, you will get to A in one hour. Since were not joined to the earth anymore...youre basically thrusting to stay in the same place (versus a fixed reference point in space/outside earths rotating system), youre thrusting to counter 1000mph of atmosphere with 1000mph of your added thrust... with me?

Once youve done this, guess what.. you will be at destination A in one hour, as it rolls towards you once youve simply countered 1000mph of atmosphere with 1000mph of thrust/speed.

Can you understand what im getting at now?

With destination B, you take off, and again if you dont thrust at all (again lets assume for experiments sake the plane can stay up there).. you again stay in the same place relative to the ground, youre above your initial starting point, and destination B stays a constant 1000miles away from you if you never thrust.

In this scenario, you must again add 1000mph, and you will get to B in one hour.

So its the same either way.

I will now try sum this up from a hypothetical vantage point that is outside of earths rotating system (lets say space for arguments sake)...

For destination A:

Atmosphere, destination A, starting point and plane is moving 1000mph this way ---->
You take off and add 1000mph worth of speed/thrust via jet engine to counter the 1000mph atmosphere.

Add them together, obviously its 0 mph. Youre now not moving relative to a fixed observation point in space that is outside earths rotating system, and had to add 1000mph to counter the atmospheres 1000mph to achieve this.

You added 1000mph to basically stay still (versus our space observatory)

But guess what.. obviously the earth is still spinning.

Destination A (1000 miles away) is now still coming at you at ----> 1000mph.

You and destination A will be in the same place in one hour.

From space, it looks like youre standing still, and destination A rolls towards you in an hour.


For destination B:

Atmosphere, destination B, starting point and plane is moving 1000mph this way ---->

You add 1000mph this way ---->

You get to destination B in one hour.

From space it looks like youre moving this way ----> and catch up to destination B in an hour, which is also moving this way ---->

wolfy wrote:
Thats not the same example as a plane moving with the earth and its atmosphere...to be analagous youd have to say you are joined to that 100mph wind, moving with it at the exact same speed. If you then thrusted 100mph in the opposite direction as the wind, youd only feel 100mph of wind.

novum wrote: wolfy wrote:
Does a pitot work in a vacuum?

I'll get back to you on this.. first i will split the thread now.

Rat wrote:
Hmm i wonder you apply the same due diligence to your holocaust research.

Anyway, moving on...

Why isnt the plane travelling frothy?

Why wouldnt it move forward when the engine/s pull air through?

Simple fact is it does move forward.

It doesnt stay in the same spot on the conveyor.

Rat wrote:
Im sure a number of people here would like you to try that out for yourself.

wolfy wrote:
First of all, i know nothing about how shuttles register their speed, so i'll get that out the way for the record.

If you do know then please enlighten me.

But i cant see a pitot tube working in space (vacuum), therefore i doubt they use the same system as planes, at least for the times they are out of the atmosphere.

So if a shuttle did have the same speed sensor as a plane, it wouldnt read the atmosphere.

That said, i know youre also talking about the resistance a shuttle meets when it enters earths system.

Well i see it as apples and oranges vs a plane moving from point A to point B on earth.

If earth is a spinning mass, with a spinning mass of gas attached to it (atmosphere) ... then this mass of gas can exert a rather large force onto anything attempting to enter it. (shuttle in this case).

But if youre already inside that spinning mass of gas you are moving with it.. hence you eliminate the A part of F = MA.

Rat wrote:
This is what I thought Wolfy meant. But he means that the conveyor does NOT slow the plane down because the wheels are freewheeling.

Obviously there are two interpretations because of the imprecise description of the situation given.

rodin wrote:
The description was precise.

Aircraft dont use the wheels the propulsion.

That is all the information you should need.

aircraft don't take off on conveyors. it was always a thought experiment.

the model first suggested to me was one in which something held the plane in situ while the engines were powered up. would there be any lift? no.

I would kindly like to apologize for the inconvenience this may cause, Novum,
but the following comments you excerpted contextually belong completely to
the original thread:



# 2, 6, 9, 10, 11, 12, 13, 14, 15, 16, 18, 28, 29, 69, (71), 72, 73, 78, 95, 96, 97



If you have the time, could you please move them back to where they came from?

Thanks aready!


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rodin wrote:
Yes, because that makes sense!!!

What would the coneyor belt be doing in your scenario?

PFIZIPFEI wrote:
Youre right.. and i'll sort it out now.