Horizons Unlimited - The HUBB

Horizons Unlimited - The HUBB (https://www.horizonsunlimited.com/hubb/)
-   The HUBB PUB (https://www.horizonsunlimited.com/hubb/the-hubb-pub/)
-   -   Welcome to the bar, "down the pub", what have you... (https://www.horizonsunlimited.com/hubb/the-hubb-pub/welcome-bar-down-pub-what-32751)

Dodger 2 Feb 2008 04:17

Not unless there's a bloody big fan at the end of the conveyor belt .

Mr. Ron 2 Feb 2008 05:23

Quote:

Originally Posted by Dodger (Post 172274)
Not unless there's a bloody big fan at the end of the conveyor belt .

Are you sure Dodger??

Dodger 2 Feb 2008 06:21

Quote:

Originally Posted by Mr. Ron (Post 172278)
Are you sure Dodger??

Erhm ?
Yes - [probably]

In order to develop lift an aerofoil section must be moved through air [ by engine thrust ] .
If the thrust from the engines and therefore the planes forward speed is always matched by the speed of the conveyor belt then the plane will not move in air , although the wheels will be spinning at an incredible speed .

Well that's my theory anyway , aeronautical engineers please chime in .

Dodger 2 Feb 2008 06:27

OK Ron ,
Imagine you have a large van travelling up the motorway containing a large Radio controlled helicopter .
The van and contents weigh 2 tons at rest ,with the helicopter standing on the van floor ..
If the helicopter were to hover inside the van as it travels , would the van weigh more than 2 tons , less than 2 tons or remain the same weight ?

Walkabout 2 Feb 2008 13:03

More names
 
Quote:

Originally Posted by SgtMarty (Post 172250)
Cantina sounds less confusing than Bar.

Yes, that's more "international".

How about the "sin bin" or the "last chance saloon" (as in drinking in the last chance saloon)?

I feel a poll coming along.

Walkabout 2 Feb 2008 13:14

Quote:

Originally Posted by Dodger (Post 172280)
Erhm ?
Yes - [probably]

In order to develop lift an aerofoil section must be moved through air [ by engine thrust ] .
If the thrust from the engines and therefore the planes forward speed is always matched by the speed of the conveyor belt then the plane will not move in air , although the wheels will be spinning at an incredible speed .

Well that's my theory anyway , aeronautical engineers please chime in .

No way am I posting as an aero engineer, but your logic is impeccable Dodger: I have never managed to get airborne while on a treadmill either! :rolleyes2:

Your van question is a variation on the decending lift ("elevator" for some people) version.
So, for my two pence, the van still weighs 2 ton - the weight of the helicopter is transferred to the van floor, all in accordance with Newton's laws, by means of the air pressure generated by its' blades.

Mr. Ron 2 Feb 2008 17:31

The plane fly's! Think about it, the plane is driven by a propellar or jet, not the wheels.

Mr. Ron 2 Feb 2008 17:32

Quote:

Originally Posted by Walkabout (Post 172306)

Your van question is a variation on the decending lift ("elevator" for some people) version.
So, for my two pence, the van still weighs 2 ton - the weight of the helicopter is transferred to the van floor, all in accordance with Newton's laws, by means of the air pressure generated by its' blades.

Agreed. The van weighs the same.

Dodger 2 Feb 2008 18:38

Quote:

Originally Posted by Mr. Ron (Post 172345)
The plane fly's! Think about it, the plane is driven by a propellar or jet, not the wheels.


I can't agree , props and jets provide forward thrust to allow sufficient airflow over the wing to provide lift .
Aircraft carriers have steam catapults that launch aircraft , if your logic were true then they would be fitted with conveyor belts .
If an aircraft loses forward speed whilst in the air it is said to stall , lift is lost and the aircraft will fall out of the sky ,lift is regained by diving and increasing speed [ airflow over the wings ] .
Some aircraft can vector thrust to provide lift but the main element of lift is via the wings , otherwise they wouldn't have wings [ they'd be helicopters or Harrier jump jets ] .

Dodger 2 Feb 2008 18:41

In order to remain airborne the helicopter has to generate a downward force as great as it's own weight .

Mr. Ron 2 Feb 2008 20:13

Quote:

Originally Posted by Dodger (Post 172366)
I can't agree , props and jets provide forward thrust to allow sufficient airflow over the wing to provide lift .
Aircraft carriers have steam catapults that launch aircraft , if your logic were true then they would be fitted with conveyor belts .
If an aircraft loses forward speed whilst in the air it is said to stall , lift is lost and the aircraft will fall out of the sky ,lift is regained by diving and increasing speed [ airflow over the wings ] .
Some aircraft can vector thrust to provide lift but the main element of lift is via the wings , otherwise they wouldn't have wings [ they'd be helicopters or Harrier jump jets ] .

Aircraft carriers use catapults to provide near instant exceleration due to the length of the run-way. Aircraft carriers would have to be much longer than they are now if jet fighters only relied on their engines. This is all irrelavent, the plane still takes off. It moves because it is being thrusted foreward by the engines, not the wheels. The wheels only provide a platform for the plane to rest on until sufficient airflow has been produced. The speed of the wheels or the conveyer belt are irrelivant. Imagine if the wheels were powered and the jets are idle. When the wheels accelerate to 50 kph, the conveyer will go 50 kph also, therefor the plane stands still. Turn on the engines and the plane will thrust foreward regardless of the speed of the wheels. Imagine your jogging on the same conveyor belt. As you increase your effort, the belt speeds up and you stand still. Now, imagine you had a rope attached to a tree at the end of the conveyer belt. Although your running your guts out and going nowhere, you can pull yourself foreward with the rope. It is independant of the conveyor belt. Whewh.... thinking is hard :)
Okay, you got me on the helicopter thing.

Walkabout 2 Feb 2008 21:03

Good call
 
Quote:

Originally Posted by Mr. Ron (Post 172345)
The plane fly's! Think about it, the plane is driven by a propellar or jet, not the wheels.

Quite right - we are too "wheel-centric"!

Dodger 2 Feb 2008 21:08

MMn !

Ok, I had assumed that the conveyor was powered and would always travel in a reverse direction so as to counteract the forward speed of the aircraft .
If the belt was freewheeling then the only forces that you would have to overcome would be the weight of the aircraft and friction between the belt and the aircraft wheels.
I notice in your first posting you mentioned "capable of matching the speed." [ Bugger!]I should have read your post more closely .

Redboots 2 Feb 2008 22:55

Quote:

Originally Posted by Mr. Ron (Post 172345)
The plane fly's! Think about it, the plane is driven by a propellar or jet, not the wheels.

I'd say it would not fly...

At take-off, the brakes are applied until the thrust developed by the engine(s) reaches the required power level.
The thrust then pushes the craft forward. The weight of the aircraft causes friction between tyre's and runway. This would set the "conveyor" in motion and the aircraft would remain static while the engine rev'ed and the conveyor conveyed:blink:

John

silver G 2 Feb 2008 23:03

So where is this aeroplane going to - better be somewhere good:scooter:


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