With wheels & conveyor duking it out down below in a windless environment; no airspeed, no lift, no flight. Just extra blankets & pillows.
Look at it on YouTube. Turn on Captions. Note Caption from :50 - :53. [ame]http://www.youtube.com/watch?v=4r7wHMg5Yjg[/ame]
Not that it matters, but when an RC plane hangs on the prop it is basically a helicopter. The prop becomes the wing and that wing generates lift. So simple a honey badger can do it.... Actually, when the honey badger was asked the original question in post 1 he said: "I don't give a s*@#!". Then he added: "I actually do care, and the original question was so poorly phrased as to its intent, that its a conundrum and therefore can't be answered."
The only answer is to make sure the wheels don't move at all. Place the plane and conveyor belt in a wind tunnel, and strap the plane so it isn't pushed backwards. When there is enough lift created to get the wheels off the ground, add power and slowly back off the tunnel fan until airspeed is maintained by propeller thrust. It's going to be a short flight.
Someone posted earlier a great analogy about a car on a dyno. When a car is on a dyno doing 150mph, the dyno is exactly matching the speed of the wheels. If you put your hand out of the windows of the car while it is on the dyno, there is no wind hitting your hand- the car is sitting stationary on the dyno. Same applies to the plane- no air speed, no lift.
well that is the most basic, no one is arguing that. the argument is whether the plane can move forward. people can't get over in their head a planes wheels not being like those of a driven car. a plane with ski skids will move forward and take off whether the conveyor is going the other direction 80 mph or not.
Ok, don't know if it's been mentioned, but you could put GIANT wheels on the plane so the distance traveled is greater per RPM of the wheel, that way the speed of the treadmill and tire will be lowered significantly by the time the plane takes of. The wheel/treadmill combo will be accelerating exponentially until lift off, but at least we could slow the top end down a bit...
Yep, you are right Einstein. I have several thousand hours pic, and another 500 right seat in Citations. You?
From the original statement" "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." Exactly match speed of wheels in the opposite direction. Read this part again. Power at the wheels like a car ,or not ( as a plane), is irrelevant. If the original statement is upheld, it is impossible to have forward motion, or lift. We all know we rotate when we reach a pre-planned airspeed- not ground speed. As the original statement says,exactly match speed of wheels in the opposite direction, there can be no ground speed. The plane will have no forward motion. There will be no airspeed. There will be no lift. Sure the wheel speed and opposite speed of the treadmill will accelerate exponentially , but this is not addressed in the original statement. Many mathematical equations allow for " infinity and beyond" just as some questions in physics do not take friction into account. If the original question was extrapolated one step further to include seaplanes or snow skids, you would have to include the fact that the snow/ice was on a belt designed to exactly match the speed of the skids at any given time, moving in the opposite direction . Seaplanes- water that comes in contact with the floats would have to be moving like a river ( again, accelerating exponentially) in the opposite direction of the water that contact the floats- just like the wheels in the original question. I think some ( who questioned my knowledge of aerodynamics) incorrectly believe the lift is generated from the speed of the air generated by the propeller moving past the wings ( propwash). This would be a nice time for an apology. If propwash generated enough velocity of air to induce lift, then on our short field take off procedures we could stand on the brakes, go full throttle until the RPMs reach max, release the brakes, and immediately be air born. And we all know this does not happen. The lift comes from airspeed generated by the wings of the plane is it moves forward through the air . No ground speed, no airspeed, no lift. Case closed... again.
the wheels can match the conveyor speed perfectly, but plane can still move forward. it is called skid or slip, not the best for initial friction, but plane can still acquire airspeed. example thousands of posts ago that is relevant, wearing roller skates on a treadmill grab onto a rope, it takes similar energy to pull yourself forward on the rope as it would if treadmill was off.
its hard to see, but there is a conveyor under this plane. [ame]http://www.youtube.com/watch?v=cWTcCtYl5Cs[/ame]
that's not why I used it as an example! I used it as an example as there isn't that much energy to add. if you want to go down that road then the skates wouldn't be moving faster if skid or slip.
But they can't skid because it is easier for them to roll. Therefore their speed would just keep increasing.
good point, but it is possible to skid, either poor bearings, pilot applied brakes, poor traction, etc. 1) plane needs airspeed to fly. 2) this version of the question in post #1 is the "matching speed" one, many versions of the question without "matching speed" is an absolute it will fly. 3) the only way plane can have wheels "match speed" and plane move forward for airspeed is for there to be slip or skid on the tires. It is possible, that is all that matters for the answer.
I wish I knew someone local with a plane, say a Cessna 400, that would not mind using his plane as a guinea pig... Mythbusters style. Hook up a slick piece of plastic the length of 52F, attach it to a trailer hitch of implied plane's owners Maserati... :0
maybe a 360 would be better as faster than a GranSport. yesterday the groundspeed of 400 over Oklahoma was 225 kts, yes Oklahoma was moving backwards as always!
K here's the original question. I've read some of this thread but not all of it so please excuse me if I'm just repeating something. It says a couple things, more importantly, it's what it DOESN'T say that matters. It doesn't say the wheels have to be in contact with the conveyor. SO, what if you place the plane on a sled with its own wheels? The plane wheels don't move, and the conveyor belt stay stationary. The plane takes off
*sigh* The whole argument here is due to the incorrect phrasing of Opie. If the conveyor matches wheel speed, then wheels and conveyor tend to go to infinite speed. The proper phrasing of this riddle had the conveyor matching plane speed, which is trivially simple: plane moves forward, wheels turn twice as fast as they would, plane takes off. If you really insist on the wrong question, then the answer is that the conveyor and wheels go insanely fast until bearing friction exceeds the friction of the rubber tires on the belt, and the wheels start to skid. Then one of two things happen: the plane has enough power to drag the skidding wheels down the runway, or it doesn't.
A motorized, backward-accelerating conveyor is perfectly capable of providing a rear-ward force to the plane (through friction at the wheel/conveyor interface), that can balance the forward thrust of the engines .... keeping the plane perfectly still relative to surrounding air, preventing lift. YES ... the conveyor needs to be constantly accelerating to do so. Which means that the rotational speed of the wheels will constantly increase. BUT, the forces involved are finite, and therefore so is the acceleration. SO, it takes an infinite amount of time to reach a conveyor (and wheel rotation) speed of "infinity". So ... is the original "spirit" of the question answered, if the plane is unable to lift for a ... minute? For an hour? I would say YES Certainly, there are practical considerations that (perhaps) extend beyond the simple problem statement of the original question : how long before wheel bearings overheat? how long before the plane runs out of fuel, while it's standing still relative to still air? how long before the circuit breaker trips, that powers the motorized conveyor? In my view, such concerns are incidental to the "spirit" of the original question. EDIT : Alternatively, i'm happy to say that : As long as the original premise of the question (as i interpret it) is satisfied ... for as long (in time) as the original premise of the question is satisfied ... the plane does not take off.
In my opinion, the question is meant to be theoretical, therefore there is no bearing failure, no limit to the speed the conveyor belt is capable of, etc. To be non-theoretical would require a bunch of extra information and the result would be calculated (and obvious) from that information. In this theoretical situation, there are 2 answers (again IMHO) you can follow the concept of the question and the planes wheels spin forever faster and faster and the plane never moves or you can say the wheels can be locked up by the brakes, therefore the conveyor belt doesn't move, and, if you have a big enough engine, the plane gets pushed down the runway, skidding the whole way, until it reaches a speed high enough for it to take off.
I think we sterotypical type A Ferrari owners have over analyzed this to death. I think the original intention of the question was to expose those that incorrectly believe that the propwash provides sufficient airflow over the wings to cause lift. And to keep the dead horse down, I thought of this last night. Call it question #2. 1. Seaplane ( say 172 on floats). Rotates at 55 kia 2. River moving 55 mph 3. No wind 4. Plane faces upstream, full throttle 5. Ignore the water velocity limits of the water on the floats Will plane be able to take off? This should draw some interesting similar comments. Another 108 pages?
