Conveyer Belt Takeoff- Mythbusters jumps in!!!

[michal 44]

>What would be truely>interesting is to see the "wheelspeed" paradox version>addressed with an answer other than declaring it a poorly>worded paradoxical question.Ok, I see it.I don't see anything very illuminating in addressing this 'paradox'. The only solution to such stated problem is VA (airspeed) = 0 (see my complete explanation well above - post #59) so airplane can't fly.I tend to agree with Craig's statement: "Again, people get on wheel speed because they get the wrong answer first, then try to shape the problem to make their answer work.". I think it sumps up the situation very well.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

[KevinAu 441]

>>I don't see anything very illuminating in addressing this>'paradox'. The only solution to such stated problem is VA>(airspeed) = 0 (see my complete explanation well above - post>#59) so airplane can't fly.>>>Michael J.So wait, are you saying the airplane can't fly?

[michal 44]

>So wait, are you saying the airplane can't fly?With the nonsensical restriction imposed on the movement on the conveyor belt/wheels it can't fly. However real airplane moving on real conveyor belt (regardless who and how controls its speed) isn't subject to such restriction. I repeat - it is a nonsensical restriction (see my comment about it in post #59).Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

[KevinAu 441]

But that is why this question wastes so much bandwidth. The question is easy if you use real airplane and real conveyor belt. It is the nonsensical restriction in a what-if question that makes it fun.So I'll mark you down under "can't fly."

[michal 44]

>So I'll mark you down under "can't fly."Kevin, please mark me down under "have no time for nonsensical problems". :-lolMichael J.

[Guest NeXTer]

Nonsense indeed... "Matching the wheel speed" makes no sense whatsoever, since the speed of the wheels can be defined as the speed of the belt surface relative to the aircraft. So if that constraint was in place, the speed of the belt could be just about anything. Or you could simply accellerate the belt until either the belt or wheel bearings gave up. Unless such a failure occured, no change in the outcome would happen.

[Guest Zevious Zoquis]

Well, I can't take the time to read this entire thread, but I will say this - the only way that the plane WON'T take off is if it's tied by a good length of rope to a tree at the tail end of the treadmill. If it's not, then as soon as it's prop starts to generate any sort of pull on the air, the plane is going to start to move forward - it's wheels spinning madly no matter how much the treadmill speeds up - and will quickly roll off the treadmill and continue on it's merry way into the wild blue yonder. :)

[Guest]

Oh man, I've seen this debate on three forums, reaching over 50 pages. I'm not reading this thread but the plane would obviously take off.

[Guest Shalomar]

Hope it's not another false alarm... saw an advert that what they call "Big belt takeoff" will air next Wednesday, the thirtieth as someone mentioned was the actual air date. I mainly want to see how they handled the technical challenges without breaking the bank, I have no doubt the aircraft will take off.Best Regards, Donald T :-waveFLYing? It's cool. Trillions of birds and insects can't be wrong.

[tf51d 284]

>Hope it's not another false alarm... saw an advert that what>they call "Big belt takeoff" will air next Wednesday, the>thirtieth as someone mentioned was the actual air date.>> I mainly want to see how they handled the technical>challenges without breaking the bank, I have no doubt the>aircraft will take off.>>Best Regards, Donald T :-wave>>>FLYing? It's cool. Trillions of birds and insects can't be>wrong.Nope this is it, they even showed a brief clip. It looks like some how they managed to do a full scale test, so this should be interesting, no matter what the result!!

[Guest rmce]

Einstein Rules!Anyway, I was on a cruise recently to Canary Islands, and about 500 miles from land a Hawk appeared on my balcony.He takes off and flies around ship which is the Navigator of the Seas, a rather large cruise ship!American swallow (I know this is the bird I have photos) walks around deck, and flies around superstructure. Now, at what point to these stowaways, cease to have a relevant speed to the ship travelling at around 24 knots, and take to their 'own' relevant airspace controlling their flight with pinpoint accuracy.One of the ships officers told me that they follow ship at night, and can fly from ship to alongside the ship, and still catch scraps thrown, and fish in ships wake at will.Makes ultralights and such stuff rather sad in comparison!(lol)Then again its our feather friends that are the real professionals.

[slashed2 53]

Everytime I see this question my hands begin to shake, not sure why but my brain begins to bleed and my eyes water.I'll tend to agree with those who state it's a trick question because the whole wheel speed etc...and frictionless bearings just goes way to deep. Unfotunately, I haven't any idea what the answer is and I've gone back and forth from initially thinking it wouldn't take off to yes it will and back again....Here's where my thinking is anyway...A float plane on a river that is flowing at 60 knots against the forward motion of the plane would hamper takeoff because to negate the weight of the plane it would need forward airspeed of what, 70 knots to lift off depending on overall weight and since it's airspeed is -60 against the airflow it would require 140 knots thrust to takeoff (considering wind wasn't a factor)? Is that a correct assumption or way off?Let's say an aircraft like a Cessna is on a variable incline. If you let off the brakes you roll backwards at 10 knots and would need to increase thrust to maintain 0 knots, sort of like applying throttle in a car on a hill. Increase the incline to negate thrust and you reach a point where the cessna can't maintain 0 knots, obviously it wouldn't take off.Is that comparable to the weight vector for a treadmill despite the fact that the force pulling against the aircraft is no longer straight down?These are the bloody things driving me nuts on this, obviously you can prevent an aircraft from taking off by applying forces against it's forward thrust but can a large treadmill apply enough force to prevent the aircraft from acquiring the needed airspeed to negate it's own weight?I think it comes down to how the question is worded, matching wheel speed or airspeed although it should be interesting to see how the Mythbusters do it on Tuesday.

[michal 44]

>I'll tend to agree with those who state it's a trick question because the whole wheel speed etc...and frictionless bearings just goes way to deep.It is NOT a trick question. And you do NOT have to assume that bearings are frictionless. >weight and since it's airspeed is -60 against the airflow it>would require 140 knots thrust to takeoff (considering wind>wasn't a factor)? Is that a correct assumption or way off?Not exactly correct. The drag forces in the water are enormous and a typical sailboat would indeed feel substantial differences in such forces with speed but a sea plane is not a sailboat, once it gets on the "step" (this is the term used for water takeoffs) the drag forces diminish and we have situation similar as on the treadmill. If you don't want to get into idiosyncrasies of water takeoffs it is better to forget about this example.>Is that comparable to the weight vector for a treadmill>despite the fact that the force pulling against the aircraft>is no longer straight down?Not sure what it all means but there is no analogy between your variable-incline takeoff and our problem with a treadmill. If you insist on this line of thinking the friction forces on the treadmill could be emulated by a takeoff from a slightly inclined runway but please bear in mind such incline would be minimal and the "variable" part has no place here.>how the question is worded, matchingIt is possible to state the problem without using the word "matching". Therefore as I stated in one of my posts above the ambiguity of what "matching" means can be easily eliminated.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

[kerosene31 349]

Reminder- this episode is going to finally air this Wednesday (Jan 30th). 9:00pm eastern. It is listed on TVguide.com and I also saw a tv promo for it the other day, so this looks like it is really going to be on now!

[michal 44]

>Reminder- this episode is going to finally air this Wednesday>(Jan 30th). 9:00pm eastern. It is listed on TVguide.com and>I also saw a tv promo for it the other day, so this looks like>it is really going to be on now! I think it is going to be at 9:00 pm (local) for every time zone in the US. I am afraid however this is not going to be a human operated aircraft - from the very brief description it sounds like they are going to use a radio controlled model airplane. At the very least I want everyone to be ready for such eventuality. Do thye have budget, know-how desire to build a treadmill for a real size even an ultralight .. I doubt it.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg