finally they will put an end to this

[jonnymagnum]

ORIGINAL: dodgerules86 I vote a big "no" on it taking off. How is it going to get airspeed when... there is not enough air (that only provided via the engines; see below) flowing over the wing? Why doesn't our aircraft start to lift-up when we do balls-to-the-wall engine runs (w/ brakes set and chalks in place)? If you put your car on a dyno, and "go" 100MPH, and hold your hand out the window, what is the airspeed? Zero. How is your hand going to lift/fall (depending on the angle you hold it at) when there is no air moving over it? I understand the wheels don't move the aircraft forward, but, when the aircraft is on the ground, (now, I might be wrong here...) don't the tires move at the same speed as the fuselage. At least that's what I see day in and day out. wow, I honestly thought you were smarter then that..... I used to look up to you

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[dodgerules86]

ORIGINAL: Jr. Mechanic

OMG I just want to cry!! People are over thinking this just too damn much!! What makes you think the the plane will not be moving? Think of it like this: Planes can take off the back of a moving air craft carrier, correct? The boat is acting like the conveyer belt moving in the opposite direction. I am going to attempt to make an extremely crude model if I can find a prop to use for the plane, will let you guys know in a little bit...

The aircraft carrier isn't moving very fast, first of all (an aircraft can take off in a headwind). Secondly, the actual landing/take-off strip is stationary: you can achieve an airspeed, see below.

The aircraft is on the ground, there is weight on wheels (WoW). So, the wheels need to be moving relative to theair to be at an airspeed. (As I stated in my last post, on the ground, the wheels spin at the same rate as the fuselage moves forward; this assumes the brakes are not applied/set/locked-up; than you have other issues). The wheels on the aircraft on the treadmill are not moving relative to the air, there is WoW, so the aircraft is not moving forward, relative to the air, there is no airflow, and therefor, no lift; except that airflow being generated by the engines themselves, which is not enough to actually lift the aircraft (which is why we can do engine runs at max speed and not lift up off the ground). That is why the wings of an aircraft extend past its engines, because it needs that much surface area to move enough air to make enough lift.

And jonnymagnum... its your own fault for once looking up to me. I never said to do that.

[flamingpinhead]

will the plane be under its own pwoer or just that of a conveyor belt?

a plane will fly. its simple physics. airflow over the wing, with the curved surface on top and flat on the bottom. bernolli's principle (sp?) the air over the top speeds up, thus reducing the pressure above the wing. the higher pressure below the wing seeks the lower above it and vaula, we have liftoff. same reason all the control surfaces such as alierons, rudders work. it changes the 'curvature' and airflow over the surfaces. thats how a plane lands with flaps... it changes the curvature to have a lower stall speed, which also changes the angle of attack... but enough about that.

in short, if you move the wings through the air ata speed above that of the wing's stall speed... it will produce lift.

[minnesotamopar]

Wow, cool topic.

After re-reading the subject--I'll correct myself so nobody else has to.

Since there is no force holding the plane back, I concede that the plane will take off. There is no way to keep the plane on the conveyor belt because it's prop pulls against the stationary air. The plane has to move then.

The thing I had to rethink was that there was nothing holding the plane on the conveyor belt. The wheels are still irrelevant except that they provide a frictionless bearing.

--Matt

[flamingpinhead]

^yeah, if you were using tires to move the vehicle forward, once you reached enough speed that the airflow over the wings was great enough to generate lift, the vehicle would lift off... making the wheels leave the ground and thus unable to generate anymore forward motion. the vehicle would slow down and enough lift would not be generated. now... if you attached a cable to the conveyor belt then to the front of the aircraft, and the conveyor belt continued to generate more and more forward momentum (thrust) on the aircraft, the wings would be able to generate more and more lift and it would be much like trying to fly aone ton kite (assuming a smaller aircraft).

there are 4 forces acting on an aircraft at any given time: thrust, drag, lift and weight (gravity). when the aircraft is in steady flight all 4 are in balance. when going up, there is more lift than weight, etc. if you double the speed, you increase the lift x4. thats why you see soooo many types of wings on different aircraft. they all 'behave' differently given the same airflow. its why they like to teach novice pilots on highwing aircraft, the center of gravity is below the wings making it more stable. you also have a better view of whats 'under' the plane. although the lowwinged aricraft have wings that are 'tilted' in to create balance, imo the high wing is easier to fly

[Burnnout]

I thought the arguement was.... if the planes wheels are going the same speed as the conveyor will it take off.... ? If every time the planes wheels move 1mph the conveyor moves 1mph in the opposite direction, wouldn't that cancel the ground limitation and the plane would still move forward because of the thrust from the engines ? I think people are trying to compare the thrust with the movement of the wheels..... the wheels make no difference. Lets say A= wheels b = conveyor and C= the planes engines. If A=B then B=A... C is left under it's own power thus moving the plane.....correct me if i'm wrong.

[flamingpinhead]

im not familiar with the experiment they are going to do. but, the propeller dosent make the plane fly, the air over the wings does. its the forward motion of the wings through the air. there are two separate things going on: first the propeller is 'pulling' or 'pushing' the entire aircraft through the air. this causes forward motion of the aircraft, or thrust. as thrust exceeds the drag, the plane continues to accelerate though the air. the wing moving through the air, over the curved upper portion of the wing causes an area of low pressue above the wing. this creates lift... high pressure below the wing pushing towards the low pressure above. when the amount of lift exceeds the weight, the plane will rise. the relationship between airspeed and lift is exponential. if you want to go higher, increase thrust and the plane will have a natural tendency to want to go higher. if you want to increase speed and maintain altitude, youll have to keep the plane from ascending by lowering the angle of attack of the wings to maintain present altitude. sometimes things dont always work as they seem.

i did fly planes for a little while when i was a teen, so am alittle famliar with how they work

when flying you can have an airspeed of, say, 100 knots but a groundspeed of 60knots. why? if your in a headwind. your plane is moving faster throught the air than it is 'tracking' across the ground.

[batman13]

it's basic pysics that nobody sees
the prop plane will take off.
for the simple fact...

Nothing is keeping the plane on the belt, the prop will pull it off.

the plane will just roll off the belt even if its spinning double the speed of the planes airspeed,
I play with R/C planes,
plane on a treadmill still takes off

[Sir Hardin Thicke]

quick question, how do some of you know how the test is going to be done? I couldn't find anything that would indicate how it will be tested. According to discovery.com this is what the episode will be about:

MythBusters
Airplane on a Conveyor Belt

In this three-myth blockbuster the team takes a crash-course in remote controlled airplane flying, bug-out by testing the "cockroach survival" theory, then return to fraternity pranks with exploding cans of shaving cream.

[batman13]

ORIGINAL: Sir Hardin Thicke

quick question, how do some of you know how the test is going to be done? I couldn't find anything that would indicate how it will be tested. According to discovery.com this is what the episode will be about:

it's the same way they do all of their big experiments,
start off with a scale test, then, after some brainstorming,
modify a full sized craft to run remotely.
and build what they need

we'll find out for sure when it airs