Plane on a conveyor belt

[pott]

I don't get why people are still arguing that the plane won't take off if it doesn't move... No shit sherlock :| That is NOT the argument at stake here...



Aircract carriers with conveyor belt... come on... jesus christ...

[SeventhSon]

For example, if I drive my car at 40 mph and I stick my hand out the window, I would get alot of wind buffering my hand. Now if I was driving my car on a belt at 40mph but not moving anywhere, my hand would not meet any resistance when I stuck it out the window. No wind, no lift IMO.

True, but if some chain was tied to your front bumper and pulled you forward at 40 mph (while your car was in neutral). it wouldn't matter if the conveyor belt was going backwards at 40 mph. you'd stick your hand out and feel a 40 mph wind. the fact that the chain is moving your car forward at 40mph is unaffected by the fact that your wheels are spinning on a conveyor belt that's moving backwards at 40 mph.

similarly, the jet engine is the chain that is unaffected by the existence of a backwards moving conveyor belt.

[Ralph E.]

T minus 1 hr 26 minutes

[LouSiffer]

Alright, the questions and scenarios are all over the place.....lets look at the 2 possible questions in a way that makes sense:

1: Can the thrust of the engine overcome the revrse speed and direction of a conveyor belt in a manner to achieve flight? Meaning, if a takeoff speed for a plane was 300MPH and the conveyor was moving in the opposite direction at 300MPH, would it still move forward and gain lift.

Answer: Absolutely it can. Again, as I said earlier, if this were not the case, no plane would ever gain flight off a runway taking of in a East to West direction since the earth rotates at about 3600 miles per hour. The wheels will spin at 600MPH, but, it will still move on as normal. Case closed...no more arguing about that scenario.

2: If a plane is on a conveyor belt and kept still with its thrust, will it achieve lift?

Answer, Absolutely not. The trick is matching the thrust speed to compensate for the friction of the wheel bearings. And that is all you are matching. Lets say you are turning the conveyor at 300MPH. You would not need 300 MPH of forward thrust from the plane, you need just enough to overcome the friction from the wheel bearings. Hypothetically, you may need only 100MPH of thrust to hold it still. Again, as it is sitting still, there is no lift and drag created.


Now, lets say hypothetically, these guys get lift off trying to achieve question#2, it is still inaccurate as they are using a RC plane. The horsepower to weight ratio between the RC plane and the real deal is very far off and it favors the RC plane.

It really depends on which one of these 2 questions that is being asked as to what the answer is. -Lou

[fuel0707]

Guys - for a plane with a fixed engine (i.e. not a Harrier or a V-22 tiltrotor), all that matters in getting a plane to fly is the so-called "relative wind" as it relates to the wing in question.

In classic aerodynamics, the wing is usually modeled as being static (not moving) while the air "flows" around it. As such, the wing doesn't care if it's moving relative to the ground or not as long as the airflow over and under it is at a sufficient speed to produce the necessary lift.

My father learned to fly in a Piper Cub in Texas in the '60's. That plane is capable of flying at very slow speeds. Given the winds in Texas, it was possible to slow the airplane up to the point where its airspeed was less than the speed of the wind. If you do that pointed into the wind, the aircraft will appear to be flying backwards to an observer on the ground. Yet, the aircraft is still flying forward through the air itself. My Dad said they would sometimes go out with new pilots and show them that you could fly "backwards".

It should be noted that some planes are designed to fly at very low speeds. This is done by using specially-chosen airfoils (wing cross-section shapes) and usually by using a relatively large wing. As a result, the wing needs very little airflow to produce enough lift to overcome the weight of the aircraft itself. With model airplanes (like I'm guessing we'll see during the early portion of the experiment on "Mythbusters"), the correct airfoil paired with an ultra lightweight plane could appear to fly with very, very little forward speed or, hence, airflow.

Someone brought up the issue of the propellor blowing air over the wing. Again, the wing doesn't care what causes the airflow, only that it exists. So "prop blast" can indeed produce lift over a wing. Going back to something like a Piper Cub, the prop blast can produce enough airflow that the horizontal portion of the tail will generate enough force to lift the tail off the ground. Some of you may have seen this old trick at an airshow - it's a classic.

So bottom line: a conventional aircraft is going to fly if it gets sufficient airflow around the wing (and tail). With a specially-designed aircraft (or model airplane), a plane can appear to fly with almost no "ground speed" built up.

[SeventhSon]

the whole ground speed vs. air speed thing is a moot point as well.

if a plane needs to achieve 300 mph air speed to get lift AND it takes 3000 feet from point A to point B on the ground to achieve that air speed, then it will still need 3000 feet of ground from point A to point B even if point A to point B is covered with a magic conveyor belt that moves backwards (or in the case of mythbusters, a backwards moving tarp).

fuck, my comcast cable guide says a repeat is coming on! no-o-o-o-o-o-o!!!

[fuel0707]

I'm not sure that I follow what you are saying about the A-to-B distance and the conveyor belt. However, without sufficient airspeed, you can have 100 miles of magic conveyor belt and the aircraft will not fly. Airspeed is what matters. If you doubt this, then why are aircraft operating speeds noted with reference to airspeed?

[SeventhSon]

i didn't say airspeed was NOT important. it is everything.

i just said that the existence of a backwards moving conveyor belt does not change the A to B distance on the ground that the plane will need to achieve an air speed necessary for lift.

[fuel0707]

Let's watch the episode and talk later.

[JACKS0NESP]

Wow...

The plane will NOT take off. There is no LIFT by the wind as the plane is more or less, stationary.

In a NORMAL SITUATION, the wheels ONLY get the plane up to speed so the "wind speed/strength" causes lift under the wings. A helicopter would, as the propellors are pushing the helicopter UP, away from the ground....but the plane needs the wind factor to create ANY lift. Thrust is only there to get the plane up to speed.

I guess there are a lot of stupid people on this planet. :S


I hope adam and jamie are laughing all the way thru this mith...it is the most stupid one I've seen yet.

[Bengal]

Fuck these cockaroaches. Get to the damn plane...

[SeventhSon]

Wow...

The plane will NOT take off. There is no LIFT by the wind as the plane is more or less, stationary.

In a NORMAL SITUATION, the wheels ONLY get the plane up to speed so the "wind speed/strength" causes lift under the wings. A helicopter would, as the propellors are pushing the helicopter UP, away from the ground....but the plane needs the wind factor to create ANY lift. Thrust is only there to get the plane up to speed.

I guess there are a lot of stupid people on this planet. :S


I hope adam and jamie are laughing all the way thru this mith...it is the most stupid one I've seen yet.

hey RETARD BOY, how about putting your money where your mouth is?

$20 says that the toy plane and the real plane on the mythbusters show both TAKE OFF and FLY.

loser pays the winner $20 via paypal. loser also wears the title RETARD BOY for a year on the JCF.

what say you?

[Bengal]

Well, the remote control plane moved foward. I think that's a good sign of what's to come. It didn't fly because the belt was too short...

Anyone wanna change their minds???

[z1n]

Fuck these cockaroaches. Get to the damn plane...

Amen to that brotha!

[z1n]

OK I think I see now. For a person, when you walk you push foward off the ground which is why you stay still on a treadmill but for a plane, it pulls itself foward via the air/prop so no matter if it's on a treadmill or not, it should pull itself foward. I think oh but what if... lol

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