Airplane and Belt Conveyor

[Magdave]

We are going to have to agree to disagree.

The thrust has no speed, its a force. the belt cannot move slower or faster than thrust, only slower or faster than the plane, which you already stated was not moving.....

The net force on the object causes the mass to accelerate. If the thrust alone is not causing an acceleration of the plane, there must be some other force acting on the plane equal and opposite to the thrust. You have yet to tell me where you think that force is coming from. Hint, its not the wheels. And that is the whole point. The conveyor cannot exert a force on the plane opposite of the thrust applied by whatever type of engine is on the plane. The conveyor also cannot effect the air flow over the wings of the moving plane. Prop or jet makes no difference here.

I have consistently stated it is obvious the plane WAS MOVING FORWARD. Look at the MB video again. That is what caused enough airflow over the wings to create lift not the engine. The lift force comes from forward movement of the plane through the air. On a STOL UL it doesn't take much forward movement. If the belt was moving fast enough to keep the plane stationary not enough lift would be generated by the engine alone. That creates dirty air any way. I takes smooth air flow to create lift.

 

[jcthorne]

Your MB post was so bogus. It is obvious the plane was moving forward look at the cones. the belt was not moving at the same speed as the thrust. Once moving forward the engine thrust and forward movement ( causing air flow on the wings) provided lift on the wings. I have seen those UL planes take off in under 100 yrds at our airport just like it does in the video.hyea:

Of course it was moving forward. the belt is powerless to have any effect on the forward velocity of the plane. The belt could have been going 2 or 3 TIMES the plane's velocity in the opposite direction and the plane would still accelerate forward and take off. UL planes use the same physics as larger ones, they just have more wing area per pound of weight so can take off in less distance.

 

[Magdave]

Of course it was moving forward. the belt is powerless to have any effect on the forward velocity of the plane. The belt could have been going 2 or 3 TIMES the plane's velocity in the opposite direction and the plane would still accelerate forward and take off. UL planes use the same physics as larger ones, they just have more wing area per pound of weight so can take off in less distance.

Hmmm I think I get your drift. However I am sure you will agree it takes forward motion to gain lift on a wing. All things being equal if a plane is not moving through clean air it cannot generate lift. In this case the belt moving IS irrelevant because the air is static. That being static allows the prop to pull it forward. Wheel speed is irrelevant. You win. It was an interesting debate though:thumbup:

 

[aeroshots]

Didn't say it wasn't possible with a short forward movement once again a STOL plane. Why doesn't this one magically lift off the ground when the engines are full out. Answer no forward motion to provide airflow over the wings. And for the last time the MB plane WAS moving forward not stationary on the belt.
....

Magic plays only a small factor in this example. Because the dude is not holding his tongue in the correct pitch angle relative to the P-factor doubled in a twin engine recip causing right yaw thereby increasing lift created on the left wing. If he had let go of the Cessna it would have rolled clockwise over onto its back. Or if it was filmed south of the equator then we know everything rotates backwards there and this Cessna model must have been equipped with north of the equator props.:yikes:

 

[aeroshots]

Can you all imagine if the MB pilot had a malfunction during his take off roll that required him to abort the take off? Hint -- what if he applied brakes during an aborted take off while Jeromy continued in his truck?
nojoke

 

[Yazz]

https://youtu.be/g8f3Jto_fjU

Yup, it's going backwards...

To do that maneuver, the plane has to achieve 0 airspeed vertically, then it slides backwards. Once the nose is pointed down, there is proper airflow over the wings and flight is re-established.

http://en.wikipedia.org/wiki/Tailslide

 

[jcthorne]

Hmmm I think I get your drift. However I am sure you will agree it takes forward motion to gain lift on a wing. All things being equal if a plane is not moving through clean air it cannot generate lift. In this case the belt moving IS irrelevant because the air is static. That being static allows the prop to pull it forward. Wheel speed is irrelevant. You win. It was an interesting debate though:thumbup:

No win, just a discussion. And YES, I fully agree that it requires forward motion for the plane to take off in static air. The prop cannot provide the lift. If the plane were pinned to a long rope, such that it could not move forward, ti would not lift off.

Whew, it is time for spyderfest yet! I need a vacation.

 

[ARCTIC]

Hmmm I think I get your drift. However I am sure you will agree it takes forward motion to gain lift on a wing. All things being equal if a plane is not moving through clean air it cannot generate lift. In this case the belt moving IS irrelevant because the air is static. That being static allows the prop to pull it forward. Wheel speed is irrelevant. You win. It was an interesting debate though:thumbup:

I saw the light bulb go on! Glad this could be a entertaining cordial discussion:2thumbs:

 

[Bob Denman]

So if your Spyder is on a treadmill that's going backwards as fast as your wheels are trying to go forward...


How long will it take to get to Albuquerque?

 

[OJ UK]

So if your Spyder is on a treadmill that's going backwards as fast as your wheels are trying to go forward...


How long will it take to get to Albuquerque?

Easy one that, Bob....twice the square root of Thursday...:2thumbs:

 

[bluestratos]

I used to be into large scale Radio Control air craft. If it is a prop driven plane the prop blast can be enough to raise the plane and fly off. If it is a jet there is no air movement until it accelerates. We used to build up to 40lb planes (AMA maximum wieght) and use 20hp engines with huge props. They had enough power to hover vertically like a helipcopter and then accelerate straight up. This requires a very low wieght to horsepower ratio so very diffucult to achieve on full size aircraft but there stunt planes that can do this. The idea of a tread mill would work great since it prevents the plane from moving forward but allows the prop blast to build up until the plane literally would levitat at which point it would shoot forward.

The planes we build were refered to as 3D and used very sofisticated electronics and mutliple high power servos on each control surface to over come the shear power of the prop blast. We flew these with both 2 stroke, fourstroke and electric set ups. The large the aircraft the easier it is to keep the wieght ratio low.

The shape of the wing also has a lot to do with it. A Y-Clark wing has more curve under the wing then over it and generates more lift but it makes inverted flight difficult. Stunt planes either modified or fairly flat surfaces on both sides. The lift is generated by the attitude of the wing and the airlerons. I used to progam the servos to work both in opposite directions or to proved equal movent in both directions which would be controld by a channel on the radio (mine was a 14 channel) or by the elevator. If by a switch this was known as flapperons. This mean no seperate flaps were required.

Flaps act like a Y-Clark wing, causing high pressure under the wing resulting in more lift. Very useful for landing at reduced speed, however we used to kit bash some funky old kits and install huge flaps and airlerons then add 120 size instead of the recommend 40 size engines. These, when pointed into the prevailing wind (as all planes do at take off) would go up like a helicopter or even fly backwards if the wind was a bit stronger. This allowed us to do pin point bombing runs, fly up to the circle, drop the flaps, hover over it then drop a small plastic flour filled bomb. On target evertime. Even though these huge Y-Clark wings did not like being inverted flight, the kit bashing allowed it to fly both inverted and knife edge.

So yes, with a prop driven plane, given the right configuration and horsepower the plane can take off without forward motion.

 

[BajaRon]

I am surprised that this relatively simple questions is giving so many such a difficult time....:dontknow:

 

[Bob Denman]

 

[ThreeWheels]

Well, this thread died quickly.

I was hoping this might pique enough curiosity to keep it active until SpyderQuest.
So I'll just give you all the answer now. I suppose I'll have to buy my own beer in Lake George (sigh).

Drumroll please.................The plane does not take off.
The speed of the belt conveyor is equal and opposite to the speed of the plane. They cancel each other out and the plane doesn't move relative to the earth. If it doesn't move relative to the earth, it's not moving in the air and it doesn't generate lift.

I bet you're thinking "How can that be? It's IMPOSSIBLE for a belt conveyor to match the speed of the plane, and the plane will take off!"
And you'd be right.
Nevertheless, the question is "What If". The question isn't concerned with HOW the belt conveyor matches speed, but asks the question "What if it does?"

It's more an exercise in out of the box thinking. Can you accept a premise that might be counter to your everyday experience. Once the premise is accepted, it's simply a matter of two speeds in opposite direction canceling themselves out. All the talk of planes going faster, wheel speed, friction etc. are accurate, but all irrelevant given the conditions of the question.

Here, I'll give you the exact same question, but in a way that's more plausible to those stuck on the answer:

A float plane is travelling in a river upstream at 20 mph. The river is flowing downstream at 20 mph. Does the plane move relative to someone standing on the riverbank ?

 

[Magdave]

I was hoping this might pique enough curiosity to keep it active until SpyderQuest.
So I'll just give you all the answer now. I suppose I'll have to buy my own beer in Lake George (sigh).

Drumroll please.................The plane does not take off.
The speed of the belt conveyor is equal and opposite to the speed of the plane. They cancel each other out and the plane doesn't move relative to the earth. If it doesn't move relative to the earth, it's not moving in the air and it doesn't generate lift.

I bet you're thinking "How can that be? It's IMPOSSIBLE for a belt conveyor to match the speed of the plane, and the plane will take off!"
And you'd be right.
Nevertheless, the question is "What If". The question isn't concerned with HOW the belt conveyor matches speed, but asks the question "What if it does?"

It's more an exercise in out of the box thinking. Can you accept a premise that might be counter to your everyday experience. Once the premise is accepted, it's simply a matter of two speeds in opposite direction canceling themselves out. All the talk of planes going faster, wheel speed, friction etc. are accurate, but all irrelevant given the conditions of the question.

Here, I'll give you the exact same question, but in a way that's more plausible to those stuck on the answer:

A float plane is travelling in a river upstream at 20 mph. The river is flowing downstream at 20 mph. Does the plane move relative to someone standing on the riverbank ?

Wrong The belt speed IS irrelevant all that does is roll the wheels. The wind is static therefore the prop will provide forward thrust. The wheels may be rolling twice as fast as normal at take off but wind speed is what counts not ground speed. it will move down the belt and take off just as the MB video shows. Now if the wind speed moved the same speed as the belt IN THE OPPOSITE direction (same direction as plane is going to take off) it would not provide lift and stall on the ground never to see the sky.:thumbup: The float plane would lift off too even if it did not appear to be moving forward because the prop would provide wind speed over the wing providing lift. I t would eventually over come the river speed to and begin to move just as the plane on the Mythbusters video does.

 

[aeroshots]

Can you all imagine if the MB pilot had a malfunction during his take off roll that required him to abort the take off? Hint -- what if he applied brakes during an aborted take off while Jeromy continued in his truck?
nojoke

 

[jcthorne]

I was hoping this might pique enough curiosity to keep it active until SpyderQuest.
So I'll just give you all the answer now. I suppose I'll have to buy my own beer in Lake George (sigh).

Drumroll please.................The plane does not take off.
The speed of the belt conveyor is equal and opposite to the speed of the plane. They cancel each other out and the plane doesn't move relative to the earth. If it doesn't move relative to the earth, it's not moving in the air and it doesn't generate lift.

Magdave is right. The speed of the conveyor is irrelevant. Could be going many times the speed of the plane and the plane will still take off. The forward speed of the plane is completely unaffected by the mythical moving runway. It cancels out nothing. The thread died because the issue was determined.

 

[ThreeWheels]

Magdave is right. The speed of the conveyor is irrelevant. Could be going many times the speed of the plane and the plane will still take off. The forward speed of the plane is completely unaffected by the mythical moving runway. It cancels out nothing. The thread died because the issue was determined.

As I said in my answer. You are discussing physical reality vs a what if scenario. You are saying that the belt conveyor could be going many times the speed of the plane. The question is worded in a way that makes that impossible.

"A plane is standing on a runway that can move (some sort of belt conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

The Mythbusters video is also incorrect in that they did not match the speeds.

You may, of course, choose to ignore any and all of the scenario. The simple fact is, you are answering a question different than the one that's postulated.

Nevertheless, I'm thinking it's time to end this before you guys turn this into a silly flame war.