will it take off?

[TomKioti]

If the conveyer matches the approximate ground speed in relation to a real world takeoff speed and matches it through all the V speeds to within a few digits then in reality the plane ain't moving forward through the air. It is remaining virtually still. The wings need air velocity (as I and others stated) to produce the required lift. I still say myth busted. But what do I know I'm an audio engineer by original trade. Ask me what a Munsen curve is next time. We actually need to send this to mythbusters don't we?

 

[jk96]

Tom,
I'm with you on this one. At full throttle, the plane will still be standing still with relation to the ground and its surroundings. The only thing moving is the conveyer and the wheels of the plane. The conveyer may be moving at 500 mph though. Without the plane moving there is no way for air to move accross its wings at the speed needed to create lift.

For example, on take off. The plane starts out at full throttle but does not magically lift into the air until there is enough airspeed moving accross the wings.

 

[jk96]

Well Tom,

I'm sorry to say I retract my last post after discussion with a friend of mine, I'm now in the "it will fly category"

It doesn't matter how fast the conveyor is moving. The wheels on the plane are free spinning. Therefore, regardless of how fast the conveyor is moving, thrust from the plane will move it forward. The plane will not remain in place regardless of the speed of the conveyor. It will move forward, gain speed, and either leave the conveyor, or if the conveyor is say 4000' long, will travel the distance needed along the conveyor to gain proper air speed and take off. The only thing the conveyor will do is make the wheels spin faster at the point it leaves the ground. Looks like spark man was right clear back on post #4, I just didn't read his post close enough. I just couldn't get over the vision in my head of the plane sitting still due to the conveyor when in reality, there's no way the conveyor can keep the plane from moving forward in increasing speed just like a normal takeoff.

I'm laughing now. I bet you guys in the "it will fly" category are just getting a kick out of us in the "it will not fly" category.

jk

 

[MossRoad]

Tom,
I'm with you on this one. At full throttle, the plane will still be standing still with relation to the ground and its surroundings. The only thing moving is the conveyer and the wheels of the plane. The conveyer may be moving at 500 mph though. Without the plane moving there is no way for air to move accross its wings at the speed needed to create lift.

For example, on take off. The plane starts out at full throttle but does not magically lift into the air until there is enough airspeed moving accross the wings.

No. The conveyor can't move at 500 without the plane moving forward at 500. The problem states the conveyor matches the plane's forward speed. One of two things will probably happen.

1. There will be a tremendous humming sound (think power applied to an electirc motor that cannot turn) until the struts get ripped off the plane, or:

2. The conveyor and plane will spin at opposite directions to infinite speed instantly (think starship Enterprise leaving in a flash). Both will probably disentigrate (sp?).

 

[jk96]

I think the problem here is everyone has a problem getting over the idea that the plane is stationary. It's the same problem I had. I've been racking my brain trying to fine a way to illustrate this visually to show that the plane is moving. I the best way I can think of is a helicopter. I've crudely attached a set of wheels to the drawing to show this.

Let's say the helicopter begins lifting off of the ground at 5 miles per hour. The belt that the wheels are touching moves in the opposite direction at 5 miles per hour. Does anyone think that the helicopter will remain on the ground? Of course not, it will fly regardless of what the belt is doing.

Now let's put some weight on the wheels. Please dont give me some long explanation that the helicopter couldn't balance at this angle, etc. Its for illustration purposes only. Will the helicopter still move off of the ground.

Now you probably know where I'm going with this last image. On end, the helicopter cannot remain in the same place, it will travel along the runway and eventually off of it. No differenty than if it was verticle, and no different than an airplane. The plane will fly

 

[rback33]

JK,

Thanks for the illustrations. I think you proved the point perfectly. Now about your artwork..... J/K it was a great idea...

 

[jk96]

Rback,

Yeah I know, the artwork could use a little work. Hopefully the illustration makes up for my stupidity on post #442 though.

One other note on this subject. One person I talked to had a good point. There have been several people converted from the "no fly" to the "fly side", but no one I know of has been converted from the "fly side" to the "no fly" side.

jk

 

[bluecon1]

Well, I've watched this thread for a couple weeks, and must say I've not responded because of the great arguments from all camps. I have to say, that as a pilot, and of course reading the question a few times, that I am in the "will fly" camp.

The question states that the plane begins to move forward, the belt moves backwards at the same speed. Therefore plane moves 5 mph forward, conveyor moves 5 mph backwards, the wheels spin at 10 mph. We still have 5 mph winds going over the wings. The situation escalates as the speed of the plane increases, so at 70 mph forward airspeed, belt is 70 mph backwards, wheels are spinning 140 mph.........a small plane would be lifting off at this point. Somewhere way back, someone gave the example of a float plane lifting off on water, going against the current-this was a great example. Of course, everyone knows that helicopters are the way to go My 2 cents.

 

[daTeacha]

Is there some way to take a poll and put the results in one post? How many (and who) are in each camp?

If someone knows how to do it, put me in the "Will fly" crowd.

 

[patrick_g]

So long as you can have the magic in the MCB you can have magic wheels and bearings that can witstand spinning at relativistic speeds. So as long as the MCB can accelerate as required to continuously provide a counterforce to the thrust of the Aircraft (propellor, pure jet, turbo prop, rocket, series of small A-bombs set off in a strong (magic) dish mounted at the tail... it just doesn't matter how propelled so long as the propulsion is by thrust not by rotating the wheels) by definition the plane will remain stationery.

Why? Because the MCB accelerates as required to couple rearward force onto the aircraft through imparting kinetic energy to the spinning wheels (and using the frictions available) in exactly the same amount as the propulsive thrust applied to the aircraft by the engine(s) so as to cancel the thruyst with equal and opposite force.

Most folks with a modicum of mechanical understanding or training in elementary physics should agree to the above, in principal.

Now, as the MCB accelerates faster and faster the aerodynamic drag on the MCB's contact with the air causes the air nearest the MCB to be accelerated rearward. There will be some shear which will reduce the speed of this accelerated air depending on how far above the MCB you test. Still at some point as the MCB approaches the speed of light sufficiently the air at the elevation of the wings of the aircraft will eventually be accelerated in excess of the minimum needed to produce lift equal to the weight of the plane. Then the plane will rise above the MCB and accelerate forward with respect to the ground the MCB is sitting on.

What happens next is not well specified in the problem statement as we know little of the A/C characteristics or the length of the MCB. There are various possibilities. If the MCB controller were "perverse" it might immediately brake the MCB to a halt as soon as the weight of the A/C was sensed to be removed. The moving air current would stop and the A/C would most likely fall immediately back down on the MCB. If the MCB were short (not extending too far in front of the plane) as the plane accelerated forward after lifting off it would rapidly leave the zone of accelerated air and again stall and settle back to the ground or the MCB. If it made it past the end of the MCB it could then make a normal takeoff, assuming available runway and no obstructions.

So, what do we know for sure? The A/C will eventually take off (it will rise above the MCB at least a little bit for a little while) but we don't have enough given information to predict what happens next.

I got lost in a bunch of stuff about chocks and other red hearings that don't seem to have come from the problem statement and only provide more confusion which was already available in excess.

Pat