Something to think about (warning large images)

[Guest]

I don't think it would fly still.The aircraft would get a forward momentum from the engine of course, but an identical rearward momentum is imparted on it by the treadmill keeping it in place (assuming a perfect thought experiment here).Only if those 2 force vectors are not identical in both direction and size would the aircraft move.So it would take some very careful callibration...Think of a a carrier aircraft on a moving carrier.Let's say for argument's sake that the carrier is steaming not into the wind but with the wind so there is no airflow over the deck (not standard procedure, but say we were able to convince the US Navy to do our experiment for us).Place an aircraft on the bow facing aft.We now have a deck moving back under the aircraft at a certain speed, say 35 knots.Make that aircraft one that can take off at 35 knots or less.According to the theory that an aircraft can take off from a moving treadmill this aircraft would now need no thrust from its engine(s) to get airborn despite there being no airflow.

[mgh 89]

"The person's arms WILL move forward along the monkey bars, but the skates will remain stationary."If his hands and arms move forward and the skates stay stationary the person will expand and get taller?

[Guest Adverse Yawn]

Oh lordy :)Everybody forget wheel friction, it is a total red herring and has nothing to do with the experiment (see note below). The solution is an explanation of the relationship between Ground Speed and TAS.The understand the problem you first need some assumptions to simplify the problem without invalidating the solution:1) No wheel friction.2) The experiment is conducted at mean sea level (i.e. TAS = IAS).3) The airspeed indicator is perfect and without error.4) An ISA atmosphereAeroplanes fly through air; the propeller pulls the aircraft forward through the air. The rolling road matches the aircraft's forward air speed but in reverse, the rolling road will fail to prevent the aircraft from moving through the air. Instead the wheels will spin at exactly twice the airspeed of the aircraft's TAS/IAS. In effect, the rolling road creates the same conditions as a tailwind the same as the aircraft's instantaneous TAS. If the rolling road worked in reverse (forwards), then the wheels would be motionless as the rolling road matches the aircraft's instantaneous TAS. The same conditions as taking off in a headwind.***** The Note Below ******Wheel Friction 1: If you chose to include wheel friction in the problem, then all that would happen is the aircraft would take longer to accelerate to take-off speed. It does not alter the result one iota. If the wheel friction prevents the aircraft from reaching take-off speed, then it doesn't take off, BUT, it still moves forwards along the rolling road and through the air and the wheels will still spin at twice the aircrafts true air speed.Wheel Friction 2: I can easily push my airplane around the hanger all day, it needs only a few pounds of force to move. A propeller produces attached to my little 65hp Continental engine produces hundreds of pounds of thrust.TAS = IAS: If you ran this experiment above sea level, then TAS is more than IAS. If you run this experiment below sea level then IAS > TAS. So, above sea level, the airplane at take-off would be moving faster through the air than the IAS displays. Therefore, the wheels would spin and more than twice the IAS but at exactly twice the ground speed. Visa versa if the aircraft is below sea level.

[mgh 89]

Yes - if the teacher finds it necessary to test Newton's Laws of Motion.

[Guest]

You're still assuming that the aircraft will attain an airflow over the wing, which I think we've shown well enough will never happen.On a frictionless surface you might be correct, but then on a frictionless surface the aircraft would not even notice that the surface were moving so it would behave identically whether it were on a treadmill or not.Altitude and barometric pressure are also irrelevant, as there will never ben any airflow.Similarly the airspeed indicator. If the aircraft were to achieve takeoff velocity it would take off, but as it doesn't achieve any airflow we know the IAS and TAS to be zero under all conditions (not taking wind into account here).

[Guest Philip Olson]

Ok, if we agree on the car thing we can discuss this. Granted if you increase the force on the car it will move forward but we have to assume that any increase of force on the car is equally and instantaneously balanced by the treadmill or this whole thing is meaningless. If you increase the force of both once again the car will remain motionless. There is no difference between a toy car and a plane, yes different methods of propelling it, but the end result will be the same because it is all a question of force, or thrust. In your arguement you say that an aircraft must accelerate in the direction of thrust, this is also true of the car, the same rules apply whether it is a jet engine or a finger or any other source of thrust. Also I would like to say that the wheels do indeed have a factor in all of this. Friction! Remember that the wheels interaction with the treadmill provides friction, additionally the wheels turning also have a small amount of friction with the bearings. This friction does factor into this equation. Of course the wheels are not providing any driving force but they do provide friction. Again I say that there is a chance that I could be wrong, I am one who will admit this. At least I am willing to actually prove or disprove this. While some people, me included may have some knowledge of physics I fear that without actual proof all we have are opinions and assumptions. Since I am no expert in the field I can and will not say that I am 100 percent right, if I did I would be a fool. Does anyone know if this experiment has actually been done by anyone? Philip Olsonhttp://www.precisionmanuals.com/images/forum/supporter.jpg

[Guest Adverse Yawn]

MGH is spot on, you are wrong Peter. Read my post on the irrelevant wheel friction issue.

[Guest Adverse Yawn]

It hasn't been shown because the car analogy is invalid. The original question what an aeroplane, aeroplanes measure speed relative to airflow. Cars measure speed relative to ground speed indirectly via wheel revolutions. The car, no matter how much thrust it generates will never move. In fact, there is no thust with a car, merely torque. Torque will be negligible with zero air speed (zero wind resistance) and no rolling resistance. In fact the puzzle simply makes no sense at all if you consider a car.The aeroplane will obviously generate more (much more) foward thrust than rearward friction (unless you put the brakes on!). How can an aeroplane take-off in real life otherwise? What is this other mysterious force holding the aeroplane back?

[Guest Philip Olson]

While you so easily dismiss friction, this is supposed to be a real world experiment, granted friction is not a big factor in this but it is a part of the equation. You can not arbitrarily take things in and out of the equation and have it remain true to life. Maybe you misunderstand what I said, I do not say that friction is the key in this, I just say that it is a factor and that can not be dismissed. My point is simply that I think the plane will not take off. I may be wrong, at least I am willing to admit that, but I am going to try and prove what the truth is with an experiment. In my opinion it is almost worthless to argue the physics of it here because I am not a physics expert and many here have been completely wrong in their arguments anyway, on both sides. Even scientists, experts in their field routinely argue points for years believing that they are right only to be proven wrong when someone gets more data or can physically disprove it. Belief in something does not make it fact, at least that is how I approach life. Sadly many people can not make the distinction between what is their opinion or belief and what is truly a fact, people don't like to be wrong. I am simply curious about this, no matter how my experiment turns out I'll be happy as I learned something. I mean no disrespect to anyone but rather I am just curious as to their backgrounds in physics or science. Who here has any real training or experience in this sort of field? I ask this in case I need any advice or information on how to conduct this experiment outside of the people I have already talked to. It never hurts to have several sources of information. Just for giggles does anyone want to place any friendly wagers on the outcome? Remember I am looking at this as fun, not a "I am right and you are wrong" type of deal.Thanks,Philip Olsonhttp://www.precisionmanuals.com/images/forum/supporter.jpg

[Guest Adverse Yawn]

Philip,I didn't disregard friction, I merely said that to get to the core of the problem you can remove it. I then wrote about 100 words on how friction would affect the aircraft. Did you not read it? Also, you asked if you were wrong. It can be difficult writing something without sounding blunt sometimes. IMHO, you are...incorrect :) The physics and maths required to understand this problem are truely elementary so that isn't the problem. The problem is that some people need a factual grounding in how airplanes work.Physics and Maths background? Not much, I even failed high school. However I do have 20 years in IT and defence industries. Also a JAA CPL holder with a few hundred hours TT.I bet you a flight in my PA-17 that the treadmill does not prevent the aircraft from taking off ;)

[Guest RiddlePilot]

>wow. All I can say is just wow.Hey enave, thanks for your understanding of both opinions. Let me break it down for you one more time. THIS WHOLE THING DEPENDS ON WHAT YOU CHOOSE TO TIE THE "TRANSMITTER" TO. Yes, if the transmitter is tied to the airspeed indicator, the plane will fly. If its tied to the wheel speed, no, it won't fly. If the transmitter is tied to the wheels, the treadmill will instantaneously counteract the forward movement of the wheels, thus keeping the airplane stationary until either the wheels or treadmill spin so fast that they self destruct.Now, the boy on the monkey bars with the roller skates. Again, if tied to the wheels on the roller skate (and I don't see what else it COULD be tied to), the treadmill would instantaneously set its speed to match that of the roller skate wheels. And no, the person wouldn't "stretch" They'd continue reaching for the next farthest bar until they couldn't reach any further...I didn't mention that in my previous post, I thought it would be simple logic.And what in the world does the butterfly/train analogy have to do with any of this. That one was so far out in left field I chose to ignore it.

[Guest enave]

>And what in the world does the butterfly/train analogy have to>do with any of this. That one was so far out in left field I>chose to ignore it.And that is why you don't understand.>If (the transmitter is) tied to the wheel speed, no, it won't>fly. If the transmitter is tied to the wheels, the treadmill>will instantaneously counteract the forward movement of the>wheels, thus keeping the airplane stationary until either the>wheels or treadmill spin so fast that they self destruct.wrong. And that's why I made the butterfly analogy. The speed of the butterfly's wings is tied to the speed of the locomotive. If the locomotive tries to accelerate, the butterfly will instantly beat its wings faster.Nonetheless, the butterfly will not stop the train.If the airplane increases its speed, the treadmill will instantly increase its speed.Nonetheless, the airplane will continue to accelerate.You made up your mind about this issue too fast, and then you closed your mind and refused to let people educate you. You made an assumption, that a treadmill could stop free-spinning wheels. That assumption was incorrect.

[michal 44]

>am not a physics expert and many here have been completely>wrong in their arguments anyway, on both sides. on one side only.> I mean no disrespect to anyone but rather I am just curious>as to their backgrounds in physics or science. I am M.S. in Physics (Quantum Optics). Yes, you can still fail me on some problems in electrodynamics but I claim to have a pretty good grasp of Newtonian physics.> Just for giggles does anyone want to place any friendly>wagers on the outcome?No, we don't want to place friendly wagers, we know what the solution is. If you opted however for a real monetary wager (say some FS9 addon?) then I would be interested - why not make a buck or so? Find some bona fide physics teacher and ask him/her and then come back and place a real wager. ;)Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[michal 44]

>> The person's arms WILL move forward along the monkey bars, but the skates will remain stationary.>wow. All I can say is just wow.>Hey enave, thanks for your understanding of both opinionsNobody is having understanding of your 'opinion'.Enave said "wow. All I can say is just wow." because it is such an utter nonsense in your sentence above, how else to react. Maybe you should grab a pair of roller skates and do the experiment it should not be that difficult to find out if the skates move or remain stationary. Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[Guest enave]

>The original question made no mention of any transmitter>arrangement but only mentioned the fact that the treadmill>could match the speed of the aircraft. If the aircraft is>moving forward then is the treadmill not moving at a slower>speed and therefore invalidating the experiment?And for the answer to that, we look to the rollerskates/monkey bar analogy. The only "thrust" that the guy can produce is by pulling on the monkey bars. If he pulls on the bars, he goes forward and the treadmill turns on. If he doesn't pull on the bars, then he doesn't move, and his wheels don't move, so duh, obviously the treadmill would turn off therefore invalidating the experiment.Those are your two options. 1) the guy doesn't pull on the bars. The treadmill is therefore off. The experiment is invalidated.2) the guy pulls on the bars and moves forward.Those are your options. Please pick one. Functionally, this analogy is an exact copy of the airplane problem.I've been doing this for a while guys. I really have thought of everything you're going to say. This is the third forum where I've seen this posted. I find it a little sad that people who study flight are no smarter than the people in those other forums.