Sign in to follow this  
Guest enave

Something to think about (warning large images)

Recommended Posts

note to mods: please let me know if this many images violates forum rules. If so, I'll space them out over several posts, or just link to the powerpoint slides here:http://seaofcrisis.com/ext/avsim/airplanetreadmill.ppthttp://seaofcrisis.com/ext/avsim/slide1.gif------------------------------http://seaofcrisis.com/ext/avsim/slide2.gif------------------------------http://seaofcrisis.com/ext/avsim/slide3.gif------------------------------http://seaofcrisis.com/ext/avsim/slide4.gif------------------------------http://seaofcrisis.com/ext/avsim/slide5.gif------------------------------http://seaofcrisis.com/ext/avsim/slide6.gif------------------------------http://seaofcrisis.com/ext/avsim/slide7.gif------------------------------http://seaofcrisis.com/ext/avsim/slide8.gifI'll leave these slides up until my bandwidth is all gone. I'll attach the powerpoint slides to this message so that you can download them if the images don't work.http://forums.avsim.net/user_files/135886.zip

Share this post


Link to post
Help AVSIM continue to serve you!
Please donate today!

Great presentation! Entertainting, quirky and, not least, correct.-

Share this post


Link to post

Yeah, I don't know why I got so focused on the wheels part, I've taken aerodynamics courses through my college training so I should have known better, but for some reason I was focusing on the wrong forces. In my mind, the aircraft was receiving friction on the wheels, thus adding to net drag. But looking at it, the friction shouldn't be so much that it over powers the prop.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

Share this post


Link to post

So the original poster is saying that the airplane will fly? I guess so, if you take the route of saying that the transmitter is tied to the airspeed indicator. We're talking about relative motion to the ground here though; in my opinion, the transmitter should be tied to the tires. You say that the airplane is not like a car in that the power applied is not directly transferred to the wheels. I say thats bologna, it may be an indirect transfer, but it does transfer; without power applied, the airplane is not moving forward. If you tie the transmitter to the wheels in the airplane, as soon as power is applied, the wheels will begin to spin, and the treadmill will spin in the opposite direction. We are talking about instantaneous reaction here aren't we?

Share this post


Link to post

RiddlePilot, would you kindly apply your reasoning to the analogy of a guy wearing roller skates and pulling himself forward by grabbing monkey bars. Thanks.

Share this post


Link to post

I'm imagining the friction forces causing his skates to drag a bit behind him, and him having to use more arm strength because of it. This is a little deeper into physics nuances than I really know of though, so it's conjecture.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

Share this post


Link to post

My reasoning for the guy with the monkey bars...If he is to move forward along the treadmill, the wheel speed of the roller skate wheels has to be greater than the counteracting treadmill speed. If, again, the transmitter is tied to the wheels of the rollerskates, and instantaneous reaction is still present, the speed of the treadmill will always match the speed of the wheels. The person's arms WILL move forward along the monkey bars, but the skates will remain stationary.Like I said before, this whole situation depends on what you choose to say the transmitter is tied to.

Share this post


Link to post

>> 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.I actually devised a little thought experiment for people who think the way you do. I posted it in the other thread:http://forums.avsim.net/dcboard.php?az=sho...00&mesg_id=2380"Here is another, similar, physics problem for you: there is a butterfly sitting on a set of railroad tracks 20 meters in front of a locomotive. If the locomotive starts moving, the butterfly will flap its wings. The faster the locomotive goes, the faster the butterfly will flap."Applying your logic, the butterfly will stop the train, because that's what you would read into the problem. What I'm trying to make you understand, is that it is inappropriate to read certain things into the problem. It is silly to think that a butterfly could flap its wings hard enough to stop a locomotive, and it's silly to think that a treadmill can stop and airplane.The two problems are exactly the same. They both present a situation with a simple feedback loop. As one thing happens, another thing happens to counteract it. You jump to the conclusion that the counteracting thing is successfull.I give up.

Share this post


Link to post

I was under the opinion the the plane would not be able to take off and I still am, sort of. While your display is convincing it does not fit the physics I was thinking of. In fact before you posted this I asked a physics teacher and she agreed that the plane could not take off for lack of airflow over the wings. We actually decided to test this theory to be sure we were right. When we get the details worked out and tested I will post the findings here along with a video. Ok, in my mind I was under the assumption that thrust is the key. You know that an engine produces X amount of thrust so based on your throttle setting the treadmill will move to counter act that amount of thrust instantaneously. Consider this for a moment, place a toy car, like a MatchBox car on a treadmill, turn on the treadmill and the car will be pushed back until it goes off of the treadmill. Now leave the treadmill off but push the car and the car will "drive" off the end. Now if you apply equal force to the car and the treadmill the car will remain in place. Can anyone dispute this? Now the same goes for an aircraft, there is no driving force exerted by the wheels in the toy car nor the aircraft so the result will be the same, equal force and the object remains stationary. If the aircraft remains in place then there is no airflow over the wings, no lift and no take off. The experiment that we will do will involve an RC aircraft but the trick will be to create something that will provide equal force to counter the thrust provided by the airplanes engine. It may take some time for us to properly prepare and conduct this exeperiment but we are going to do it. I admit there is a chance that I might be over looking something and could be wrong but I kind of doubt it at this point. So for now I will have to say that while that the images are interesting and convincing, for me they do not fit what I know of physics so therefore I will test it in the real world. Either way I will be very interested to learn the truth as this is a very interesting puzzle. I will also post here just before we expect to perform the experiment just in case anyone wants to come and witness it. In the mean time wish me luck as this is going to take a lot of work and money! Actually for now the physics teacher will be doing a lot of the work as I am still recovering from my cancer treatments.Philip Olsonhttp://www.precisionmanuals.com/images/forum/supporter.jpg

Share this post


Link to post

>fact before you posted this I asked a physics teacher and she>agreedStrange people are teaching physics these days. If I were you I would be looking for a different school ;). If the teacher got mixed up on complex issues of the Maxwell theory or special relativity I would understand, but not being able to handle elementary Newtonian mechanics circa 1700 it is something else.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

Share this post


Link to post

> The experiment that we will do will involve an RC aircraft>but the trick will be to create something that will provide>equal force to counter the thrust provided by the airplanes>engine.Did you ever consider that it is impossible to build such a machine. You cannot counteract the thrust, because the wheels rotate with negligible friction. If for no other reason, your machinery will break down at some point, as the running speed of the threadmill and wheels would have to approach infinity.-

Share this post


Link to post

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?

Share this post


Link to post

the plane couldn;t take off unless there was airflow over the wings. yes the prop would produce forward thrust keeping the plane stationary on the tread mill. Unless the prop was producting enough air current over the whole surface of the wing no lift would be produced... or not enough. what comes to mind is this: If the thrust was strong enough, the craft (missle i would say) could fly. wings have no purpose in the experiment as i see it. but i think you did a great job explaining this time. i'm simple i like the picturesmark

Share this post


Link to post

Yes, anyone who disagrees with your warped ideas knows nothing right?So a teacher who wants to put your theories to the test is a poor teacher...

Share this post


Link to post

The aircraft will take off, and you need a new physics teacher!Consider the basic physics. If a thrust is applied to the aircraft it must accelerate in the direction of the thrust unless there is an equal and opposite force to stop it. (Newton's Second Law of Motion). There isn't such an equal and opposite force. The only source could be the rolling resistance of the wheels and, in any, realistic aircraft, this will be a fraction of the thrust. The wheels will rotate twice as fast as they would normally. This would absorb a little more rotational energy reducing the acceleration a little. However, the rotational energy in the wheels will be fraction of the energy in the rest of the aircraft so the take off would be only slightly delayed.The analogy of the car on the treadmill doesn't go far enough either. "Now if you apply equal force to the car and the treadmill the car will remain in place. Can anyone dispute this?" No, I don't dispute it, but if you then increase the force of your finger you will push the car forwards.You can't escape Newton's Laws.

Share this post


Link to post

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.

Share this post


Link to post

"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?

Share this post


Link to post

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.

Share this post


Link to post

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

Share this post


Link to post

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).

Share this post


Link to post

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

Share this post


Link to post

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

Share this post


Link to post

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?

Share this post


Link to post

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

Share this post


Link to post

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 ;)

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this