will it take off?

[daTeacha]

Just a couple of points here, gentlemen.

The problem states the conveyor matches the speed of the plane but in the opposite direction. If the plane does not move, neither does the conveyor. The tree sitter cannot simultaneously watch a stationary plane and a moving conveyor. I know this is the basis for most of the fun you are having lately with this thing, but the problem clearly states the plane moves. Not just the wheels, the plane.

I was intrigued by the "time quark" stuff. I enjoy messing with my students minds a bit by telling them that first people thought matter was continuous or analog, then it was eventually shown (to the best of our knowledge) to be made up of small pieces (atoms) which were then shown to be made of even smaller pieces, etc. as we continue to search for the ultimate particle.

Similarly, energy was once considered to be continuous or analog -- consisting of a smooth flow -- then around the turn of the 19th to 20th century was shown to also be made up of pieces (in effect digital), which of course those of you still in this thing will recognize as quanta, whether they be visible (photons) or not.

Then I tell them that sometime before they die someone will find that time is also not the analog thing they perceive it as, but is in fact made up of tiny little pieces. Following that discovery will come efforts to manipulate those little time pieces, which will eventually lead to the ability to travel through time as easily as they now cross the room. Then, just to tighten the screws a little bit, I suggest that the best way to assure that all this happens is for someone from the future to come back here and make suggestions about time being digital, perhaps to aspiring scientists during their formative years.

It takes about 2 or 3 minutes before someone asks me if I'm from the future, to which query I respond with a smile and a non-commital answer.

As a visitor from the future, I can tell you this discussion will continue until the post count exceeds 750. Check back here at that time and remember you saw it here first.

 

[Egon]

This topic is clearly in need of a convention to properly define the problem before setting up another convention to determine who should attend the n ext convention and so on!

Who's got oomph to get funding?

Now I have a faint idea of the planes ability to fly if I am in it. On a bright sunny day with a good weather forecast it will definitely soar into the heavens above. But on a cold windy day with 100 % relative humidity and temperatures at the dew point or slightly below and visibility at about 10 feet I think it will stay on the ground.

 

[MossRoad]

I'm still resisting .....

RESISTANCE IS FUTILE!!! You will run some numbers...

 

[daTeacha]

At this point, Patrick, based on your admitted proclivity to tug on the occasional posterior appendage of those who are sharing space in this thread with you, I find myself wondering if you have intentionally or accidentally changed the description of the aircraft in question to one made of highly processed wood pulp and miscellaneous fibers. One has to wonder just how high the bovine fecal matter can be piled before it tends to succumb to the incessant tug of gravity and bury its originator.

You said "... rendering it stationery". Shall we now consider the various possible configurations of paper airplanes?

Before we venture further into the potential morass of useless verbosity, let us consider the old adage "Exclusive dedication to necessitous chores without interludes of hedonsitic diversion renders John a hebetudinous fellow."

BTW, most of the ways I immediately think of to measure the building involve the use of geometry and proportions and necessitate that the building be other than the one in which your barometer is located when you use it. Do yours?

I'm more of a Model 12 guy myself -- 16" barrel, Polychoke, 7 rounds of slamfire fun per loading.

 

[patrick_g]

Da Teacha, I guess I am more familiar wilth the guy and call him Jack instead of John. WOOD PULP? I don't feed my stock wood and none have ever stayed in one place long enough to bury themselves in the manner you mention.

I am supremely confident that if nothing self destructed and there were suficient traction at the tires that the MCB could accelerate as required to hold the plane stationery +/- a fraction of a mm. I am as sure of this as I am that the wheels in the (will fly) scenario will be rotating at twice the lift off speed when the gear leave the ground.

Yes ratio and proportion would be one way. If you knew the height of the barometer you could go out in the sunlight and set the barometer on the ground and measure the length of the shadow. Then measure the length of the shadow of the building in question and by similar triangles know the height of the building.

You could also work your way up the stairs counting the number of barometers high the building was and multiply times the barometer's height.

You could also take one of your shoelaces and make the barometer into a pendulum and (in theory) measure the difference in its period at ground level and again at the top and calculate the height.

You could walk to the edge of the roof on top of the building holding the barometer in outstretched hands and release it just as it passed the edge. Then note the distance sideways it went by noting the point of impact. You could use this distance and the known lateral velocity to compute the time of fall and then use the equation
S = 1/gt^2 where g is gravitational acceleration and S is distance to get the building height.

If you had a watch you could have just dropped the barometer and timed its fall.

Here is one that gets into the social sciences instead of physics. You go into the basement and knock on the building super's door. When he answers you say something like, "My good sir, do you see this fine presentation model aneroid baromenter, if you but tell me the height of this building it is yours to keep."

There must be lots of other ways but no good ones leap to miind just now.

Differential UV degradation of the plastic or paint of the barometer is different at different altitudes.

You use the standard lapse rate for temp and altitude and measure the dimensions of the barometer to determind delta Temp and compute delta altitude.

These last two are not favored and any number of other "junkie" ones could be formulated but I would love to get some more really good methods.

Having perfect pitch I can thump the barometer and note the resonant freq at ground level and at the top of the building. The frequency will be changed by the difference in gravitational attraction (relativity) . not a really good one either.

Give it a whorl, maybe someone will come up with some novel and nice alternatives.

Pat

 

[daTeacha]

Well, Patrick, you missed the point of the reference to "stationery", I guess. Here I thought you were trying to refer to a plane made of writing paper (stationery) while talking about one that wasn't moving (stationary). Sigh, another missed opportunity for humor.

I was trying to restrict my uses of the barometer to those not involving precision instrumentation. A watch relying on human reflexes, for example, will not give you a sufficiently accurate means to time the fall of the barometer.

Climbing the stairs and laboriously measuring the height of the building in barometers would work up to a point, but it wouldn't get you to the top of the exterior of the building and is rife with opportunities for accumulating small errors every step of the way, so to speak.

Seeing how far from the building it landed would ignore the slight but present gravitational attraction between the barometer and the mass of the building as it fell, plus it ignores the possibility of Coriolis effect, depending on the orientation of the building. Further, it presumes the building is falt sided from top to bottom, which is rather rare these days.

The tonal variations in the barometer might take something more than even an ear with perfect pitch, but being essentially tone deaf and suffering from partial hearing loss resulting from too much shooting and tractoring without sufficient ear protection makes that whole line pointless for me.

I have students about to come in, so will leave this short.

 

[HTWT]

S = 1/2 gt^2
S = 0.5(32) t^2 or
S = 16 t^2
In Patrick thread missed the 2 when typing

 

[patrick_g]

Da Teacha, Sorry but I am an aural speller (awful speller??) at best. I appreciate the chuckle now that you have explained it to me. I know the diff between paper and being still but didn't note whch word meant which. Thanks.

I noted a sign above the door between the pilot house and the radio room on a Portuguese tuna clipper. It said, "No one aloud in the radio room." I figured it was library rules so my bud and I whispered while there checking out the radio and sat nav.

My wife still kids me about a note I sent her over 40 years ago with rabbit spelled rabit.

My claim to fame is not in being a good speller. I think that the writers of the best spell checkers deserve the Nobel prize.

I am a graduate of the Christopher Columbus school of touch typing where I look for, discover, and land on the keys one at a time. Frequently they are the key I want but are the wrong key. Other times my larger than standard fingers hit multiple (or wrong) keys even when I know the right key.

I took a typing class in the USAF and the final "graduation" exercise was a speed test where I scored 15 WPM before correcting for errors. I can copy morse code faster with fewer errors in all caps long hand with a pencil!

About your objections regarding error and precision of my suggested measuring techniques... what part of "IN THEORY" do you need explained in detail?

One other thing... I tend to forget to

Pat

 

[daTeacha]

You need some guidelines regarding accuracy and precision else you could just look at the barometer, then at the building, and guess its height based on your visual estimate of how many barometers tall it appears to be. -- sort of like a forester using his Biltmore stick but with a lot less accuracy. For that matter, you could use your thumbnail like a Biltmore and get some vague idea, too.

Which in a roundabout way brings us back to the original problem, I think.

We really need to define what is meant by motion of the plane. I maintain that motion OF the plane is not the same as motion within the plane. I.E. the whole thing has to move to be counted as motion. Therefore, if it can move at all, it can move enough to lift off, unless one insists on claiming the wheels are being rotated by the engine as in a tractor rather than by friction with the ground.

Both of my analogies (the rubber band and the dyno) were attempts to emphasize the point that the motion of the plane as a whole is caused by something other than the motion of the wheels. Rather, the wheels turn as a result of the motion of the plane. The wheels could turn (on a dyno for example) without causing the plane to move enough to fly. Conversely, the plane can fly without regard to the motion of the wheels on the dyno, which is nothing more than our MCB wrapped around a cylinder.

 

[patrick_g]

daTeacha, No! Let me repeat for emphasis N O contest if you want to take the "will fly" assumptions (and be bored stiff.) As has been repeated MANY times the plane will take off almost normally with the biggest noticible difference being the wheels will be rotating at twice the plane's lift off speed. (This assumes as has also been said, the wheels don't come apart at 2x takeoff speed)

If you take the "extended" assumptions of the "Won't Fly" argument and nothing comes apart and there is sufficient traction on the wheel-conveyor interface and such then the plane's CG doesn't move more than an arbitrarily small distance forward and back (averaging zero) as the MCB may not be perfect. For our purposes, since any motion is of short duration, extent, and velocity that it is of no more importance that the molecular motion of the atoms comprising the plane's structure which are above absolute zero in temp. IF you take the will fly assumptioins the plane will fly. I don't want to work on the design team responsible for the MCB unless I get paid up front not on completion and successful testing.

Pat

 

[Egon]

Use rollers!

 

[NorthwestBlue]

Pat,

I too enjoy the mental stimulation, although I'm obviously outmatched. My degree in Aerospace Engineering has gone unused as I took the unenviable course of a career of directing high speed aluminum tubes. A once glorious occupation regarded highly by many and rewarded with wonderful perks and compensation. Alas, it has now been relegated to the bowels of the mass transportation system. So you might call me a frustrated something or other, or not.

I liked your question about the barometer and immediately thought of most of the methods you described with the exception of the trade and the staircase (I seem to always overlook the obvious). Another way would involve turning it into a fluid dynamics problem. Place two interconnected buckets filled with water next to the building. On one place a float just the right size to fit inside (kind of like a plunger). Drop the barometer on the float. The displacement of water will allow you to determine the kinetic energy at impact, etc. Or an optical method… place a mark on the ground and move the barometer until the mark is barely visible behind the barometer when looking down from the top of the building. Now use that angle and distance to calculate the height. Or another audio method… drop the barometer on the ground and measure the time it takes for the sound to reach the top of the building. Of course, you could also melt the barometer down and make a nice long wire out of the metal.

I don’t share your feelings on “real world” being un-fun or boring. Anytime you through people into the mix it often times makes fantasy or fiction seem dull in comparison.

Da Teacha,

Your idea about using the giant rubber band is intriguing. Start out with a large force that decreases with distance. That wouldn’t be unlike a rubber band powered balsa airplane. I wonder how many turns it would take to wind up enough to generate 70 kN of thrust. Of course if we discount the fact that the rubber band would eventually break, then we could get an unlimited force to deal with that pesky MCB.

 

[SPYDERLK]

No. If the tires have enuf traction to overcome engine thrust the magical conveyor could hold the plane stationary by applying a force, equal&opposite to engine thrust, to the tires. This thrust would rotationally accelerate the mass of the wheels. As long as the wheels, tires and bearings could withstand the increasing rpm the plane would not move.

NorthwestBlue, thank you for the good physics. I will review it in some depth later to refresh my education.

Above is my first post on this thread. Id like to point out that your numbers have shown the truth of the post.

-- Traction coefficient 0.8 x weight ~7.8KN = ~62.7KN
Engine thrust reduced by this number [70KN - 62.7 = 7.3KN] is quite close to the 7.2KN force you calculated, based on traction limited max possible rotational acceleration of wheel mass, to be left over to push the plane forward. Since the numbers dont match exactly there are probably some small errors of approximation that crept in.
Larry

 

[Egon]

small errors of approximation that crept in.
Larry

That's sorta like a fudge factor to adjust to whatever you need?

 

[NorthwestBlue]

Larry,

Good catch. Thanks for keeping me honest. At least someone was looking at the numbers. Correct values were 70000 N - 62784 N = 7216 N.

Egon,

If you don't like the numbers I first give you, I got a lot more where those came from. Just tell me to stop when you like them.

 

[daTeacha]

Northwestblue -- the rubber band I had in mind would be more akin to a slingshot. When I was a kid you could spend a quarter and buy a plane that had a prop spun by a rubber band, or a bit less and get one that you launched with a rubber band attached to a stick. Of course of all you had was a dime, you had to settle for the one you through, supposedly a model of the Sabre Jet, an F-86 if memory serves.

 

[NorthwestBlue]

daTeacha,

I guess I wasn't clear, but I did understand that you meant a slingshot. I was just making the comparison. Force is force whether you get it from pulling, pushing, thrust, gravity, etc. How many rubber bands would it take to make the non-believers believe?

Its funny you mention the planes you bought when you were a kid. I loved those little planes as a kid. They played a big part in fostering my fascination with flight. I wanted to buy some recently to play with my boys, however they are not easy to find and cost a lot more than a quarter.

 

[patrick_g]

I had several of the throw it yourself balsa gliders profiled and printed to be a Saber jet F-86 and later super saber F-100. May have had some F-80 as well (single seat fighter version of the T-33 two place trainer Straight vs the saber's swep[t back wings.)

Oh yeah... I am builty of working out from under the umbrella of a precise degree field. Although physics required more math then a math minor (a couple three classes short of a major) I never worked as a mathemetician. I never held a job title of physicist either but used physics a lot. I once had a job title with a small startup of Wizard, receiving mail so addressed. Actually I worked more realistically as an EE with my physics background and then after going back to school to be retread as a computer scientist and softwarre engineer I actually had job titles to match for a while. My last trip back to grad school was for Instructional Technology where you engineer training solutions. I needed that paper to be a manager of a team of courseware developers for Naval warfighting systems. The lab where my wife and I worked, NCCOSC, RDT&E (Naval Command Control and Ocean Surveilance Center, Research Development Test and Evaluation) abbreviated NRAD, we were the NRadicals. This place had very broad bins for labeling folks. My job title was Scientist (not rocket scientist.) I had friends who were labeled Engineer. Pretty non descriptive. What we actually did was whatever needed to be done. Besides, if I told you too much about what I did I'd have to shoot you.

Pat

 

[daTeacha]

Maybe, but since your plane won't take off, you could never get here from there.


I just had a thought regarding the rapidly spinning wheels -- air friction, friction in the bearings, etc. would bring about some serious amount of thermal expansion as the rpm of the wheels approached near infinity. The result would be that the wheels expand to a size large enough to contact the wings and tear them off, hence it won't fly.