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Title: Puzzle: Airplane take off question Post by: anwar on September 27, 2013, 10:23:33 PM Can a plane which is placed on a sufficiently long treadmill which can run at a speed matching the acceleration of the plane trying to take off (in the opposite direction, of course), finally take off ?
Title: Re: Puzzle: Airplane take off question Post by: prateek13 on September 27, 2013, 10:31:48 PM There won't be enough air passing around the wings to produce lift.
Just like walking/running on a treadmill doesn't get you anywhere. Title: Re: Puzzle: Airplane take off question Post by: VTOLkarthik on September 27, 2013, 10:36:10 PM I guess it wouldnt... the plane has to double its speed so tat it cancels out the deceleration and then it can take-off
or maybe its btr to experiment wit it to conclude wat will happen :P Title: Re: Puzzle: Airplane take off question Post by: saikat on September 27, 2013, 10:36:27 PM no.... planes fly due to the lift generated by the wings which are caused
by the relative air moving over(and under) the wing. in this case as the plane is effectively standing still , the relative airspeed over the wings is zero .... so no lift also if this were to be the case then it would be possible to launch planes simply by putting them on purpose designed conveyors ... so no airports would be required. Title: Re: Puzzle: Airplane take off question Post by: anwar on September 27, 2013, 10:42:46 PM Wrong... it seems !
http://kottke.org/06/02/plane-conveyor-belt http://kottke.org/06/02/planes-conveyor-belt-2 http://kottke.org/13/09/will-an-airplane-on-a-treadmill-take-off http://www.youtube.com/watch?v=YORCk1BN7QY http://www.youtube.com/watch?v=0ul_5DtMLhc Title: Re: Puzzle: Airplane take off question Post by: saikat on September 27, 2013, 10:50:30 PM yes the explanation is correct .... the plane will take off as the thrust of the propeller
will push the plane forward irrespective of the speed the wheels are turning. Title: Re: Puzzle: Airplane take off question Post by: anwar on September 27, 2013, 10:55:20 PM I should have left it open ended for a little while more, to see if other opinions would come in. But I was also worried about people doing the first thing they do these days, which is to google for the right answer.
Title: Re: Puzzle: Airplane take off question Post by: anwar on September 27, 2013, 10:56:35 PM http://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/
Title: Re: Puzzle: Airplane take off question Post by: anwar on September 27, 2013, 10:59:27 PM Apparently there are lengthy discussions, and a lot of people were in the "it does NOT take off camp".
http://boingboing.net/2006/12/11/airplanetreadmill-pr.html Title: Re: Puzzle: Airplane take off question Post by: rastsaurabh on September 27, 2013, 11:01:04 PM If seen closely the plane did not take of from a stand still it was running for 50-60 mtrs.... good enough for a plane of that size to take off.
Title: Re: Puzzle: Airplane take off question Post by: prateek13 on September 27, 2013, 11:05:03 PM The experiment which mythbusters performed was nowhere near precise.
The 'treadmill' was much slower than the plane! It was like running on a treadmill faster than its set speed! This really is a heck of a topic to discuss about. Title: Re: Puzzle: Airplane take off question Post by: prateek13 on September 27, 2013, 11:16:02 PM The pilot in this video never considers that the tyres are not completely friction-less as compared to the plane so even if the tyres are going 200+ the plane wouldn't take off.
http://www.youtube.com/watch?v=Kz8qYGApSUM Title: Re: Puzzle: Airplane take off question Post by: AEROVISHWA on September 27, 2013, 11:19:08 PM its pretty simple if we look into the basic on how the airplane flies.
unlike the car. planes have nothing to do with the contact with the ground( they are not meant to taxi around) and again unlike cars the engines do not produce power at the wheels in contact with the ground. the prop pulls( or push in some cases) the aircraft forward and not turn the wheels so irrespective of what speed the wheels are turning the plane will move forward creating an airspeed enough for takeoff... a lot more explanation can be added i suppose Title: Re: Puzzle: Airplane take off question Post by: AEROVISHWA on September 27, 2013, 11:21:07 PM damn the video came in while i was typing :banghead: :banghead:
Title: Re: Puzzle: Airplane take off question Post by: VC on September 27, 2013, 11:21:43 PM Approximately US $ 25,000 was wasted on this hoax - production / post production, sponsorship and transmission rights.. As is the case with hyped programmes like Mythbusters and Bear Grylls. If the plane had even lifted off the ground for a nano second without the propeller in motion - THAT would have proved something - Pure lift generated by wind flowing over an aerofoil - generated by the reverse motion of the conveyor belt.
Take a Hot Wheels car, grease the axles and put it on a 2" inch wide cloth ribbon - 2 feet in length. Place the whole set up on the floor. Now hold each end of the ribbon and move it in a quick reverse flick motion to where the car is facing. Does the car move? Hardly. The wheels spin to move the car forward but the road (the ribbon) moves backwards. Friction = net result = ZERO forward motion. The car practically stays stationary. Now ask a friend to flick the car forward as you drag the ribbon backward. Does it move? You bet it does. Similarly, the undercarriage of the plane would have spun wildly to accommodate the 'reverse treadmill effect' and the aircraft would have hardly moved. Now add the full power of the engine and a spinning prop. Different story altogether. Big deal! Title: Re: Re: Puzzle: Airplane take off question Post by: aniket210696 on September 28, 2013, 12:09:56 AM the case of the jet engine is wrong... the engines are pushing the aircraft forward. the wheels are just to reduce friction. the jet engines exert force on the air to move forward.
direction of force is backward. even if you have a treadmill under the aircraft moving at a 100 m/s, the aircraft still won't go UP into the air, until their is sufficient wind flowing over the wings. that's what wings are for! it is like you standing on a treadmill wearing rollerskates. there is a wall behind the treadmill. let us assume friction is 0. we will stay in one place, while the treadmill moves under us. now push against the wall. you will start moving opposite to the direction of applied force ie:away from the wall. the speed of your wheels will increase a lot. Sent from a potato using a lamp Title: Re: Puzzle: Airplane take off question Post by: VC on September 28, 2013, 12:17:08 AM Jet??? Where did you get a Jet engine from? Who mentioned a jet engine???
Title: Re: Puzzle: Airplane take off question Post by: rohitgupta322 on September 28, 2013, 12:29:25 AM The wording of the question is wrong. If the speed of the airplane is exactly equal to the speed of the conveyor belt, then the plane would stand still with respect to the ground/ air and would not take off.
What they basically mean by the question is that the wheels of the airplane don't slip with respect to the conveyor. Sorry for being technical again, the plane stays still when w(rotational velocity) r(radius) = V(of conveyor) and takes off when wr = V(take off) + V(conveyor) Also, unlike an airplane, a car needs the frictional force of the ground to actually get it to move forward (for cars, bicycles, etc friction on the rear wheels actually help in motion). So, it can't move on a conveyor(moving in the opposite direction). No such problem for an airplane using a propeller to generate thrust. But once again, if the speed of the airplane matches that of the conveyor belt, it won't take off. In the video too, the airplane moves with respect to the ground for takeoff. Hence, its forward speed is greater than the speed of the conveyor moving backwards. Title: Re: Re: Puzzle: Airplane take off question Post by: aniket210696 on September 28, 2013, 01:19:29 AM vc sir it's mentioned in one of the links... along with a picture of a brachiosaur rocketing up into the air on a 747 engine with 2 pterodactyls for stability
Sent from a potato using a lamp Title: Re: Puzzle: Airplane take off question Post by: rcpilotacro on September 28, 2013, 06:29:23 AM for an aeroplane to fly these couple have to exist, for it to climb some of this couple have to change, conveyor , no conveyor, winds equal to take off speed the aeroplane has to balance all these four couples of forces, irrespective, for a drag component, there has to be thrust component, which means the engines have to run. for weight component there has to be a lift component, which means there has to air flowing over the wings. for further reading read the entire thread
firstly in level flight weight= lift =CL ˝ σ V˛ S. CL is coefficient of lift, which depends on your wing angle of attack (position of the nose in level flight) shape, camber etc, ˝ σ V˛ is called the dynamic pressure, simply put, number of air molecules for a given time, ALSO CALLED THE INDICATED AIRSPEED, 'S' is your wing area. Now, aeroplane has lift and weight acting as one couple (noseup or down will in RC language, will depend on the cg, because weight acts along it, and position of wings because centre of pressure through which the lift acts). It also has thrust and drag couple acting on it. nose up or down will depend on position of your engine and wings, which if you are not designing, is pretty much taken care of, Couple of Forces. For aeroplane to fly in level unaccelerated flight all these couple have to balance so that the residual is zero. If the aeroplane is say designed to get airborne at 30 kmph, it will get airborne at 30 kmph, if the wind that is blowing is 30 kmph, the ground speed at which will get airborne will be zero. But remember the thrust drag couple will have to be zero, which means, you have to open power normally as you do in nil wind condition. If the winds are 40 kmph the aeroplane after getting airborne into wind will travel rearward at 10 kmph. With respect to ground, however with respect to air it is still travelling at 30 kmph. Bottom line CL and S being same it is the ˝ σ V˛ (the number of air molecules for a given time above and below the wings) which matter. another post http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg53691/#msg53691 Title: Re: Puzzle: Airplane take off question Post by: anwar on September 28, 2013, 04:07:42 PM Hmmm.. should this be a poll now ? :giggle:
Title: Re: Puzzle: Airplane take off question Post by: aniket210696 on September 28, 2013, 04:46:53 PM Hmmm.. should this be a poll now ? :giggle: why not? :)Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 28, 2013, 05:25:38 PM Interesting question; but insufficient data for a clear answer.
We know that the relative velocity of the plane from the ground frame of reference is zero. But our interest is the Relative Velocity from the air frame of reference. For which we lack data. Title: Re: Puzzle: Airplane take off question Post by: girishsarwal on September 28, 2013, 08:02:35 PM How is the conveyor adding to the airspeed? its not. Its only adding to the ground speed. Probably a little due to cohesion of air on the surface of the conveyer but thats too less to make any laminar flow on the surface of the wing. If it were a wind tunnel, and ir blown, things would be different
A related question "will a plane flying from east to west reach faster than the one moving from west to east, because the earth below is moving west to east" Title: Re: Puzzle: Airplane take off question Post by: anwar on September 28, 2013, 08:21:33 PM Interesting question; but insufficient data for a clear answer. ... But our interest is the Relative Velocity from the air frame of reference. For which we lack data. Whaaaaaaaaaat ? ;) I thought the question is simple and straight forward ! Will the plane take off, from the eyes of someone who is not on the treadmill and not on the plane... both of which are obvious 8-) :P Title: Re: Puzzle: Airplane take off question Post by: rcpilotacro on September 28, 2013, 08:30:33 PM "will a plane flying from east to west reach faster than the one moving from west to east, because the earth below is moving west to east" get onto a balloon and stay still, once earth moves past land wherever you want to land, Simple !! :giggle: (only catch is, it has to be on the same latitude, because earth moves only west to east not north to south or any other combo ) :banghead: Title: Re: Puzzle: Airplane take off question Post by: AnjanBabu on September 28, 2013, 08:58:21 PM As sikat bhai mention,
planes fly due to the lift generated by the wings which are caused Considering that lift acts perpendicular to the direction of airflow, irrespective of whether the plane is standing still or in motion, as long as there is some airflow over the wing, in a tractor setup, the plane should experience a certain amount of lift. For it to take off, the wings must genetate lift that's more than the weight of the plane; if that much lift can be produced, then the aircraft should take of vertically up like a VTOL craft before moving forward. by the relative air moving over(and under) the wing. I derive my understanding from experimenting with a small wind tunnel. A while ago, i was fiddling around with some wing sections and a weighing scale to measure lift. The wings produced lift even while stationary, all it needs is airflow over the aerofoil section. The same cannot the true with pusher setup and jet engines. there the airflow over the wing is generated by the motion of the aeroplane. or I could be wrong too. :D Title: Re: Puzzle: Airplane take off question Post by: Sb_Maharana on September 28, 2013, 09:15:49 PM I had very similar thought when I was a kid, I had my own ideas shipping parcels to America, make a small rocket which will launch straight up and design such way that it will come down to the earth after 12 hours, by this time parcel will land safely in America.
Here if we make the example something different like tying a rope to a small glider and to the casing of a table fan, by the wind flowing, lift will be generated and glider will fly, but there is no momentum in the glider (as it is in a static position) and in real scenario it will be very difficult to control the aeroplane. With conveyor belt system the run up distance can be shortened, but plane should have it won momentum to control it. Title: Re: Puzzle: Airplane take off question Post by: girishsarwal on September 28, 2013, 11:30:58 PM Quote The wings produced lift even while stationary, all it needs is airflow over the aerofoil section. Exactly what I feel. It is the same case if iron man is travelling at the speed of the airplane,.,for ironman the airfoil is stationary but still producing lift. In our case, there is no effect on the airflow, but only the ground speed, by the conveyer, if the conveyer had any substantial effect on the airflow, the plane would levitate (and someone will have to firefight to control it perhaps, because sooner or later it will fall out of the direction of airflow. Whereas with a prop the airflow is always directed along the longitudnal axis of the plane.) The theory of relativity talks about frames of reference. Gusty sir, I've never tried that in a balloon ;D but afaik, with planes the rotation has no effect, of course some fluid laminars/jet stream have a part to play, but the rotation does not have any direct implications because all us observers are in the same time space and it will not have any significant, observable effect. Title: Re: Puzzle: Airplane take off question Post by: VC on September 29, 2013, 12:22:03 AM "will a plane flying from east to west reach faster than the one moving from west to east, because the earth below is moving west to east" get onto a balloon and stay still, once earth moves past land wherever you want to land, Simple !! :giggle: (only catch is, it has to be on the same latitude, because earth moves only west to east not north to south or any other combo ) :banghead: The balloon has to be flying higher than the Exosphere or 320 km above the Earth (or beyond into deeper space). Anything at a lower altitude else will cause the balloon to move along with the earth's rotation due to its gravitational pull. Title: Re: Puzzle: Airplane take off question Post by: VC on September 29, 2013, 12:27:31 AM God, why am I even indulging in such meaningless balloonist discussions???
Title: Re: Puzzle: Airplane take off question Post by: anwar on September 29, 2013, 01:31:19 AM This seems to be the most interesting topic in a while ;)
Title: Re: Puzzle: Airplane take off question Post by: rohitgupta322 on September 29, 2013, 02:14:08 AM The balloon has to be flying higher than the Exosphere or 320 km above the Earth (or beyond into deeper space). Anything at a lower altitude else will cause the balloon to move along with the earth's rotation due to its gravitational pull. No it won't. Gravity will only pull it along the line joining their centers. Not all satellites move along with the earth's rotation (some move faster others slower, infact you can also make it stationary, but then it would fall down as there is nothing to generate lift in a satellite). Also, the moon is about 400,000 kms away. So, being higher than 320km will not diminish the gravitational pull. Title: Re: Puzzle: Airplane take off question Post by: rcpilotacro on September 29, 2013, 07:09:39 AM ... the plane would levitate .... The aeroplane (and the passengers in it, if there are) could Meditate to Levitate >:D :giggle: Title: Re: Re: Puzzle: Airplane take off question Post by: aniket210696 on September 29, 2013, 09:13:10 AM the wind blowing at the wings can be experienced when you try to make your bixler take off in a windy day. it holds its position and just goes straight up, even though there is no treadmill.
Sent from a potato using a lamp Title: Re: Puzzle: Airplane take off question Post by: girishsarwal on September 29, 2013, 12:40:29 PM Hahaha, Gusty sir, seems like Hyderabad has been more of a relaxing experience rather than flying ;)
Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 01:41:39 PM Talking of balloons, Col. S Sundaram will soon be making a RC Hot Air balloon using a Propane Soldering Iron as the heat source, and small ducts with servo controlled valves for direction :D :D
Anyone else ready for it? Title: Re: Puzzle: Airplane take off question Post by: rcpilotacro on September 29, 2013, 04:53:55 PM (http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/?action=dlattach;attach=634633;image)
Alright! to put matters to rest (you can continue the levitation stuff though ;D). Look at the image on top. these forces have to balance for an aeroplane to fly. AIr has to flow on top of the wings (This can be achieved by keeping aeroplane in a wind tunnel, or putting it against the wind etc) Whenever there is wind (even the slightest amount) there will be Drag. Now this drag has to be compensated with (a) Thrust (i.e. Engine) (b) by trading Gravity by putting the nose down (In slope soaring the aeroplane w.r.t wind is always descending, however the air is climbing faster than that that's why relatively she is climbing). Lift is generated due to the wind that blows over the wings, when it equals weight the aeroplane lifts. Once again see the diagram and understand the conotations, PS you will have to read this post carefully, may be once twice and imagine, whatever i am trying to say Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 06:01:22 PM Precisely Gusty sa'ab. Which is why one needs additional data in the form of the air condition around the wings as created by the environment. Without that the question is in the "insufficient data" category ;)
Title: Re: Puzzle: Airplane take off question Post by: sundaram on September 29, 2013, 06:18:36 PM Hmmm.. should this be a poll now ? :giggle: Definitely Anwar Bhai would be interesting to see the results. :rofl: Sanjay Sir :hatsoff: :hatsoff: How the hell did I get roped into middle of this balloon discussion :rofl: Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 07:06:56 PM Jallandhar has a very conducive environment for ballooning, Col. Saheb ;) ;D
Title: Re: Puzzle: Airplane take off question Post by: sundaram on September 29, 2013, 07:10:42 PM :hatsoff: :hatsoff: Nevertheless it was a great idea of Balloon with Butane torch Sanjay Sir. Very Practical idea worth a try.
Title: Re: Puzzle: Airplane take off question Post by: rcpilotacro on September 29, 2013, 07:15:16 PM ..great idea of Balloon with Butane torch Sanjay Sir. Very Practical idea worth a try. true ! the more i think about it, more plausible it sounds Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 07:20:45 PM 3 servos controlling 3 valves - for left, right (Ducts or pipes to directionally release hot air from the ballon....will need a neutral too to control excessive height) plus one for regulating the flame...higher or lower.
Apron (like hovercraft) material to make the balloon. Or parachute material :) Title: Re: Puzzle: Airplane take off question Post by: rcpilotacro on September 29, 2013, 07:34:13 PM .will need a neutral too to control excessive height no need ! atmosphere does that ! it equalizes temp very fast, in fact to maintain height you need to keep pumping in some hot air every now and then Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 07:38:48 PM How about landing, eg in an emergency (on-board Rx Battery low?)
Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 07:39:56 PM And Sandy will have to keep a sharpshooter handy....in case it goes out of control. Don't want to lose the Radio equipment :D :D :D
Title: Re: Puzzle: Airplane take off question Post by: sanjayrai55 on September 29, 2013, 07:46:42 PM And now, to bring back the original question in a modified form : will Sandy sir be able to fly and control this balloon while running on a treadmill? ;) ;) ;)
Title: Re: Puzzle: Airplane take off question Post by: Sb_Maharana on October 02, 2013, 12:11:00 AM I am still unable to understand the concept of treadmill takeoff :headscratch:
Just want discuss more on that, e.g. when we running on open ground, if the prime resistance is air, then the resistance is quite low when we are on a treadmill, or the automobile factories test the engine power/ wheel balance etc. on similar type of treadmills, my point is can they test the aerodynamic characters of a particular vehicle (its body shape) by running it on a treadmill, I think No. because the vehicle is moving relative to the surface but not against the wind. At present I am using the laptop and unable draw a diagram what I was trying to explain previously (the table fan and glider part). At low wind speed the glider will remain nose up (drag + weight > thrust + lift) (here thrust is the tension in the rope). Nose down on heavy wind ( drag + weight < thrust + lift). Now at this point if we have engine (thrust) greater than (drag+weight+lift) it will move forward. So what I am trying to conclude is there is no role of treadmill while taking off but entirely depends the engine power. I may be wrong… or there is something wrongly presented in the video ………. chalta hey. |