Will it fly?

aircooled said:

Jesse Ransom (FFS) said:

... the issue is that the problem says that the instant the plane moves AT ALL then the wheels have traveled faster than the treadmill, thus breaking the stipulation.....

Explain this part.  This is the part that does not seem to be in the question (to me).  (Curtis can also, you seem to think alike... maybe that's good...)

I guess I could also ask what your interpretation of "moving in the opposite direction" means in the question.

We will get to the bottom of this... then we need to talk about your relationship with your mother.... 

I can't really put words to it this late, but I need to re-read the meme and re-read the original.  It's possible I'm conflating the two when in fact they are different.

You may have just burst my bubble.

If we think THIS alike, maybe we should discuss YOUR relationship with my mother.  Are you my dad?

Theory of flight. Ground speed is irrelevant to airspeed. How fast the wheels go is not a factor in take offs. It's the speed of the wind over the wings that matter for flight. That's why airplanes usually take off into the wind. Multiplies the wind speed over the wings at a lower ground speed. Same principle with landing, usually into the wind also. If you compare ground speed to airspeed, a plane can actually have a higher ground speed than air speed with a tail wind and inversely a lower ground speed than air speed with a head wind.

Now taking physics in mind. One theory is the plane wouldn't move at all because of the treadmill going the opposite direction of the wheels. Another theory is the treadmill doesn't matter since the propulsion isn't at the wheels but at the wings and a jet or prop engine (either one same theory applies) may move the aircraft anyway regardless of treadmill. Would have to ask a mathematician/aero engineer. I'm just an aircraft tech with limited experience at the controls and work with engineers. Understand forces and stresses but can't calculate how much.

Given enough head wind an airplane can lift of the ground with zero ground speed. But may take more than tornado type wind to lift an airliner. Have seen helicopter rotor wash cause a light Cessna 152 get light and lift a little off the ground. Had to hold them down when ground taxiing past with our big helicopters before.

In reply to aircooled :

I'm also going to have to pick this up in the morning, and as others have noted, there are multiple interpretations of the problem, and I was more addressing that interpretation than the problem itself, but I do think after sleep and coffee I can take a stab at articulating my understanding of that interpretation.

I do think that the problem may be that the problem sort of allows your choice of misinterpretations, but there is no sane interpretation.

wlkelley3 said:

Theory of flight. Ground speed is irrelevant to airspeed. How fast the wheels go is not a factor in take offs. It's the speed of the wind over the wings that matter for flight. That's why airplanes usually take off into the wind. Multiplies the wind speed over the wings at a lower ground speed. Same principle with landing, usually into the wind also. If you compare ground speed to airspeed, a plane can actually have a higher ground speed than air speed with a tail wind and inversely a lower ground speed than air speed with a head wind.

Now taking physics in mind. One theory is the plane wouldn't move at all because of the treadmill going the opposite direction of the wheels. Another theory is the treadmill doesn't matter since the propulsion isn't at the wheels but at the wings and a jet or prop engine (either one same theory applies) may move the aircraft anyway regardless of treadmill. Would have to ask a mathematician/aero engineer. I'm just an aircraft tech with limited experience at the controls and work with engineers. Understand forces and stresses but can't calculate how much.

Given enough head wind an airplane can lift of the ground with zero ground speed. But may take more than tornado type wind to lift an airliner. Have seen helicopter rotor wash cause a light Cessna 152 get light and lift a little off the ground. Had to hold them down when ground taxiing past with our big helicopters before.

That's the way I always "interpretated" the question.Curtis's response went to philosophy, and mentions the "original," but I've heard versions of that question for 40 years, and Im sure its older than that! I feel folks are reading way to much into miswording by someone that doesn't understand how airflow past the wings affects lift. The question (at least how I've always heard it asked) states the wheel speed = treadmill speed. That makes ground speed = 0 - but that is irrelevant. This is the first time I've personally come across it on the internet; it suprises me its made 3 pages!

In reply to 03Panther :

Well, the way this meme is worded, it never mentions ground speed, only treadmill and wheels.  So, by the wording of this meme, the plane could be traveling at 50 mph ground/air speed while the wheels and treadmill operate at 100mph.

Back in my Physics days (when I was actively in classes and retaining this stuff) the example we used DID correlate groundspeed which meant very large deltas in speeds and acceleration which shot huge holes in the question itself.

Still processing.

Mr_Asa said:

The best explanation I've read.  Also, it's XKCD, so you know its good

Basically you can have three interpretations of the problem.  Whether it takes off depends on the interpretation and how far you're willing to compromise physics and mechanical limitations

https://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/

My #1 takeaway is that this question is designed to troll message boards to get pedantic nerds exactly like us to argue exactly like we're doing.

In reply to Beer Baron :

Who you callin' pedantic?

Nerd, yes.

Curtis73 (Forum Supporter) said:

In reply to Beer Baron :

Who you callin' pedantic?

Nerd, yes.

Literally everyone who has responded in this thread.

Beer Baron said:

Mr_Asa said:

The best explanation I've read.  Also, it's XKCD, so you know its good

Basically you can have three interpretations of the problem.  Whether it takes off depends on the interpretation and how far you're willing to compromise physics and mechanical limitations

https://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/

My #1 takeaway is that this question is designed to troll message boards to get pedantic nerds exactly like us to argue exactly like we're doing.

Admittedly, that's why I posted it. There's lots of plane nerds here, and I can't tell a 737 from a 747, or a MIG 25 from an F16.

I assumed because wheel speed didn't really matter, it could take off, but some arguments I'd read elsewhere brought in air deflection and pressure/speed changes from the giant rolling treadmill. My aerodynamics knowledge starts with "wedges are good" and ends with "tear drops are better".

The sea plane comparison from earlier in the thread caught me off guard and got me thinking I've never seen a jet powered sea plane, which is an interesting thought in itself.

Well... now you have:  F2Y Sea Dart (experimental only).  The only jet fighter amphibian I believe.  The basic explanation as to why no (or few) jet powered amphibians is that sea planes where on the way out because of aircraft carriers, longer range planes, inflight fueling, more airfields, etc, as jet where coming in. 

As Curtis I think correctly concluded, the questions as posted in this thread is more about interpretation of the question and how someone reasons out a problem.

My suspicion is that the OP question is a weird hybrid of the Russian question Curtis mentioned, and the one Mythbusters tested (which is just put a plane on a 100 mph treadmill, what happens... it of course will slowly roll off the back from rolling friction).  I suspect it was not intentionally worded so poorly, just a quick development to generate discussions (arguments).

The interesting aspects of how people answered the question seemed to be heavily related to the above.  Some assumed the Mythbusters question, others seemed to be influenced by the Russian one.

The question, as presented, really does not make any sense, and does require assumptions, but that is not at all uncommon for many real questions.

In reply to aircooled :

Yarp. And don't forget that we were given a specific version of the problem by the OP, which is not really the one I (kinda) answered; neither is the one at the start of this thread exactly the Mythbusters one or the original, I'm guessing.

I also want to take a moment here to agree with Beer Baron.

The question, as it appears here, immediately gives us multiple choices of interpretation. If this were a sane question, these are the sort of things that either could be gleaned from context, or one would ask follow-up questions about.

1. By "match the speed of the wheels" do they mean that the conveyor belt travels to match the hub's location, so that the wheels never spin? Do they mean that however fast the wheels are rolling, the treadmill goes that fast in the direction that agrees with the tires' interface with the treadmill? Do they mean that the ground speed of the treadmill and the treadmill speed of the wheels are always the same (meaning that the plane can never move w/regard to the ground/air/larger frame of reference)?
2. By "opposite direction" do they mean that the treadmill travels with the plane's nominal direction of travel, or against it?

The central problem is that we don't know what the original questioner (any of them) actually means.

Many of the options have built in impossibilities, while others are trivial.

If the treadmill is traveling in the direction of travel, matching the velocity of the wheels' hubs, then the plane could accelerate normally and take off without the wheels rotating, and without colliding with the word problem.

If the idea is that however fast the wheels are rotating, the treadmill will travel against the plane's direction an equal speed, then we have mathematically prevented the plane from moving. The issue is that there's no reason in the actual world for our word problem to keep that constraint. The issue here is that the word problem says that treadmill speed = wheel speed (or negative wheel speed, depending on how you want to look at it), but we also know that wheel speed = treadmill speed + airplane ground speed. Because wheel speed = treadmill speed, the latter equation is only true for airplane ground speed = 0;

As long as I'm playing with the ways people have trouble modeling this one, I think another way of basically proving (EDIT: why would a recreational pedant use "prove" here? This is not a proof. Sloppy...) the question is fundamentally broken is that what we have are two systems which are basically unrelated, but which each contain the airplane. There's the airplane/treadmill/ground system, and the airplane/air (or even airplane/air/ground) system. Making stipulations that bind them together in ways that don't have a basis in reality is just going to cause a bunch of us dingbats to waste time on the Internet.

I think one thing that you guys are missing from explaining it is the air resistance that would come from the treadmill as the boundary layer expands.

Therefor, I think that you can only consider this scenario in a vacuum.  

If you removed all the air and had the plane on an exactly speed-matching treadmill, would the plane take off?!?  Hmmmmmm!?

In reply to WonkoTheSane (FS) :

I'll bet a plane ride in a vacuum would be very smooth.  A little unpleasant with the not-breathing thing, but smoooth

Generating lift might be somewhat difficult, but I think that's a secondary problem to not being able to breathe.

Curtis73 (Forum Supporter) said:

In reply to WonkoTheSane (FS) :

I'll bet a plane ride in a vacuum would be very smooth.  A little unpleasant with the not-breathing thing, but smoooth

*psssstt* This is your captain mouthing... We're now descending at approximately 9.82 m/s^2.