Airplane on a treadmill

[45Auto]

Re: Airplane on a treadmill

Simplest way I can think to explain it. Anybody doubt that if the winch in the picture is turned on it pull the airplane forward till it hits the winch? Doesn't matter how fast the treadmill is going. If the winch is pulling cable in at 100 mph the airplane will move forward at 100 mph till it hits the winch. It'll take off and fly if it's stall speed is less than 100 mph. If the treadmill is running 100 mph in the opposite direction the wheels will be turning at 200 mph (airplane speed plus treadmill speed) even though the airplane is only going 100 mph towards the winch. Airplane doesn't know (or care) whether the wheels are going 10 mph or 100 mph or 1,000,000 mph. Wheel speed is always airplane speed plus treadmill speed. Has no affect on airplane speed. Unless you have bad bearings or hit the brakes, the airplane moves forward at the speed of the winch.

If you take off the winch and use the propellor it works the same way. The airplane doesn't know if it's being pulled by the winch or the propellor. Either one pulls the airplane forward through the air no matter how fast you run the treadmill. All the treadmill does is make the wheels turn faster which has no effect on the airplane speed (assuming real good bearings). The airplane's speed is independent of the wheel speed or relative ground (treadmill) speed.

Common belief is that the reason an airplane flies and a carb works is the Bernoulli Principle. Says an increase in fluid velocity causes a decrease in pressure. That's why the top surface of an airplane wing is curved (longer) so the air has to travel faster, thus less pressure on top of the wing so the wing lifts. A carburetor venturi is necked down (less area) so the air has to speed up to go through it, giving less pressure so fuel is sucked out of the float bowl.

In reality Bernoulli Principle doesn't explain airplane lift. It is frequently used to analyze it, which is probably where the misconception comes from.

Can you tell I'm kinda bored????

 

[Lakester]

Re: Airplane on a treadmill

Bernoulli's Principle

regards,
lakester

 

[Haut Medoc]

Re: Airplane on a treadmill

Oh no, not again.....​

Bernoulli.......

 

[Lakester]

Re: Airplane on a treadmill

45-

nice graphic!!

ur r right about the ground speed vs the airspeed.

regards
lakester
PVT, COMML, INSTR, MULTI, COMML SES SEAPLANE

 

[jay_merrill]

Re: Airplane on a treadmill

Its called the venturi effect. Now what did I win?

I'll give you 75% - the principal is Bernouli's Principal and it states that as the speed of a moving fluid increases, the pressure within the fluid decreases.

In the case of an airplane, airflow splitting on each side of the leading edge of the wing reaches the trailing edge at the same time but, the upper surface of the wing is curved (longer distance) so the airflow over it must accellerate in oder to meet the "bottom air" at the same time. This causes a low pressure area on the upper surface of the wing, which creates lift. This same principal is what makes a sail on a sailboat work when sailing into the wind and it is also why propellers (airplanes or boats) work.

In the carburetor a similar situation occurs but it is not about airflow matching up. It is simply that the inside of the carb is curved and that accellerates the air, creating a low pressure area, into which fuel is sprayed.

PS: Lakester got it.

 

[waterinthefuel]

Re: Airplane on a treadmill

Airspeed gets a plane airborne. If the winch were pulling the airplane at a higher speed than the stall speed, it would fly, I don't care what you did with the treadmill.

Simple as that.

Anybody know what the prop on a plane REALLY does? Hint: It isn't pulling the plane through the air.

 

[jay_merrill]

Re: Airplane on a treadmill

Here's another way to understand the treadmill brain teaser.

When an aircraft accelerates down a runway, its wheels begin to rotate and increase in rotational speed as the aircraft moves forward faster. In the treadmill scenario, the aircraft will accelerate in a forward direction at essentially the same rate, but the rotational speed of the wheels will increase by a value that is in proportion to the speed of movement of the treadmill.

 

[bassboy1]

Re: Airplane on a treadmill

Anybody know what the prop on a plane REALLY does? Hint: It isn't pulling the plane through the air.

Here's my guess. Solely an educated guess.

The prop is basically 3 wings (assuming it is a three blade prop) On an airfoil (plane wing, prop blade etc), the distance over the top, is more than the distance under the bottom. Now, when, pulled at speed, the air has to move faster over the top of the airfoil, which creates a lack of pressure on the top. This pulls the airfoil upward, and is what is called "lift." Each blade of the prop is an airfoil. Spinning it is doing the same as pulling the wing through the air. The air in the front has to go faster than that behind it. Now, since the "wings" are horizontal, the prop is sent forward. Now, because this is horizontal, this is called "thrust." So, the prop isn't pulling the plane through the air. The lack of air pressure in front of the prop, is pulling the prop through the air.


Alright, that is my guess. How right, or wrong am I?

 

[Lakester]

Re: Airplane on a treadmill

PS: Lakester got it.

...blush!!

regards,

lakester

 

[Lakester]

Re: Airplane on a treadmill

Here's my guess. Solely an educated guess.

Alright, that is my guess. How right, or wrong am I?

lakester sez:

"solely an educated guess?? sure, sure... " but in any event, aside from a few lil issues with ur comments on prop aerodynamics... i would give u an:

A

not bad for solely an educated guess. the word i am having probs with is educated. for anyone educated in aircraft aerodynamics understands prop aero, also.

regards
lakester

 

[Nandy]

Re: Airplane on a treadmill

that is a big treadmill!

 

[Lakester]

Re: Airplane on a treadmill

that is a big treadmill!

hello,

almost a mile!

regards,
lakester

 

[bassboy1]

Re: Airplane on a treadmill

not bad for solely an educated guess. the word i am having probs with is educated. for anyone educated in aircraft aerodynamics understands prop aero, also.

I was educated on how the wings cause lift. None of my previous education taught me about props. I before assumed the just pulled the plane through the air, solely because no one had taught it to me, and there never was a reason for me to research it. But, what told me to question it, was waterinthefuels hint. Then, I put what I know about lift, into an explanation about a prop. But no, I had 0 previous education on props. BTW, I feel that public school technology departments are somewhat lacking.

 

[Lakester]

Re: Airplane on a treadmill



regards
lakester

 

[i386]

Re: Airplane on a treadmill

Since airplanes were brought up. I heard this on the radio today, just a question to ponder.

If you put an airplane on a treadmil, ( the treadmill can be any length let's say 5000' )When you throttle up the plane you start the treadmil in the opposite direction. Will the airplane get air borne ?

Let's say we have a 5000' treadmill. That's about a mile. That's a nice runway for a small plane.

When you throttle up the plane you increase RPMS on the propeller.

The plane is going to move forward and take off (assuming the control surfaces are set to do so).

Because the runway (treadmill) is moving in the opposite direction, the plane's wheels will be spinning faster than if they were on a stationary runway but it's irrelevent in this example.

 

[jay_merrill]

Re: Airplane on a treadmill

Just for some more fun ... what do the upturned wingtips on some modern aircraft have in common with a once famous sailboat?

 

[SpinnerBait_Nut]

Re: Airplane on a treadmill

It's cold outside, 9?

 

[SpinnerBait_Nut]

Re: Airplane on a treadmill

Whoops, wrong thread, my bad.

 

[Lakester]

Re: Airplane on a treadmill

hello,

am i allowed to answer?

wondering...

regards,

lakester

 

[SgtMaj]

Re: Airplane on a treadmill

WAIT A MINUTE!!! You said it didn't matter what size treadmill, but if the treadmill is too small, the plane will NOT get airborne, it will hit the front of the treadmill and depending upon the size of the front of the treadmill and the size of the plane, may explode in a firey crash, or just run it over and destroy the treadmill.

So there.

Yeah.

That's right.

I went there.