USAF looking for flying cars. No, seriously.


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1 minute ago, Carborendum said:

So, a VTOL is a quick and dirty solution.

Dirty, yes, but a VTOL is anything but a quick solution. Someone already mentioned Terrafugia as a workable flying car (actually a "roadable aircraft"). To make a robust, reliable, safe, mass-producible VTOL is a tall order, to put it mildly.

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22 minutes ago, Vort said:

Dirty, yes, but a VTOL is anything but a quick solution. Someone already mentioned Terrafugia as a workable flying car (actually a "roadable aircraft"). To make a robust, reliable, safe, mass-producible VTOL is a tall order, to put it mildly.

Terrafugia has two models.  The Transition doesn't even carry three people.  And there is no way for it to land safely in rough terrain.  The TF-X is still concept only.  I may be remembering incorrectly, but they scrapped the Transition as they were pursuing the TF-X manufacturing and marketing.  As far as I know, the TF-X doesn't actually even have a prototype.  It is still awaiting funding to build the first model.

The Aerobmobile can at least land on a fairly flat grassy field.

None of them so far carry more than two people.

Then there's the size issue.  For HTOL aircraft, the wings are the primary lifting mechanism.  When you have a requirement for a flying mini-van, the wings must be very wide.  But with the transitional propeller from VTOL to flight, there can be propeller assist with a shorter wingspan.  The shorter wingspan will be easier to fold up in emergency response situations.

The eventual, mass produced roadable capability will be much easier to achieve with the VToL.  It's a quick solution because it addresses all these issues.  It does, however, make it more expensive.

Edited by Carborendum
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10 minutes ago, Vort said:

Why would this be necessary? A Piper Cub has a takeoff speed of about 50 mph.

Shows how much I know about planes haha.

but in my mind, one can’t consider it a flying car if it requires a runway. At that point they would be nothing more than connection flights one would take from st George to Vegas. It would seem mighty pointless to drive to the runway, fly to another runway, then rent a car to get to your destination.

but perhaps my vision isn’t up to par

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Guest MormonGator
22 minutes ago, Vort said:

Why would this be necessary? A Piper Cub has a takeoff speed of about 50 mph.

Hey, can a plane take off on a treadmill? Not a trick question-I know very little about planes and I've seen this question argued about on Facebook. 

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50 minutes ago, MormonGator said:

Hey, can a plane take off on a treadmill? Not a trick question-I know very little about planes and I've seen this question argued about on Facebook. 

Only if there is vertical thrust.

I'm assuming that your implying that a treadmill means that the plane is not moving horizontally.  A regular aircraft gets its lift by the flow of air across its wings.  Therefore, no horizontal movement =  no vertical force allowing for lift.  So an alternative method of vertical thrust must be provided (VTOL).

But the problem is more complicated than that.

A regular airplane doesn't achieve lift off velocity by wheel force.  It achieves it by its jets or propellers.  Thus the treadmill is irrelevant.

Edited by Carborendum
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47 minutes ago, MormonGator said:

Hey, can a plane take off on a treadmill? Not a trick question-I know very little about planes and I've seen this question argued about on Facebook. 

I know the answer!  It's a wonderful exercise in adaptability.  Folks start out totally convinced you have the right answer, and then you can measure your pride and stubbornness and openness to change and humility, as it becomes increasingly obvious that your answer is not the right answer.

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6 minutes ago, Carborendum said:

I'm assuming that your implying that a treadmill means that the plane is not moving horizontally.  A regular aircraft gets its lift by the flow of air across its wings.  Therefore, no horizontal movement =  no vertical force allowing for lift.  So an alternative method of vertical thrust must be provided (VTOL).

Ooh!  Someone who hasn't run the gamut of this devilish thought experiment!

Here's the setup Carb.  You have an airplane on a treadmill on a nice clear windless day.  The propeller starts like it should.  As the plane moves forward, the treadmill is designed to roll backwards at equal speed.  The intent is to keep the airplane from taking off.  It's a cool perfect quantum treadmill that can measure as accurately, and move as rapidly as it needs to.

So, can the airplane take off?

Everyone feel free to join in.  First person who starts yelling in all caps loses!

Edited by NeuroTypical
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4 minutes ago, NeuroTypical said:

Ooh!  Someone who hasn't run the gamut of this devilish thought experiment!

Here's the setup Carb.  You have an airplane on a treadmill on a nice clear windless day.  The propeller starts like it should.  As the plane moves forward, the treadmill is designed to roll backwards at equal speed.  The intent is to keep the airplane from taking off.  It's a cool perfect quantum treadmill that can measure as accurately, and move as rapidly as it needs to.

So, can the airplane take off?

You're asking for an impossible situation to be analyzed using real-world physics.  Kinda hard to do.  But I'll counter an unrealistic condition with another unrealistic condition that should go hand-in-hand with the condition you submitted.

If the treadmill is a "perfect quantum treadmill" (TM) whatever that's supposed to mean, then I can say that the surface between the wheels and the axles are also completely frictionless.

If those are frictionless, then the treadmill can do whatever it wants, but it applies absolutely no horizontal force to the body of the aircraft.  The wheels and treadmill then divide out of the equation completely allowing the plane to function normally despite whatever the treadmill does.

The reality is that with all these conditions, the treadmill would stand still.

Edited by Carborendum
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5 minutes ago, NeuroTypical said:

Ooh!  Someone who hasn't run the gamut of this devilish thought experiment!

Here's the setup Carb.  You have an airplane on a treadmill on a nice clear windless day.  The propeller starts like it should.  As the plane moves forward, the treadmill is designed to roll backwards at equal speed.  The intent is to keep the airplane from taking off.  It's a cool perfect quantum treadmill that can measure as accurately, and move as rapidly as it needs to.

So, can the airplane take off?

Everyone feel free to join in.  First person who starts yelling in all caps loses!

YOUR RONG!!!!!

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By the way, I have never understood why this is a difficult problem. Granted, my undergrad studies were in physics, so I got used to thinking about things in a particular manner that probably made this setup easy to analyze. But that is clearly not the case for a great many people, including intelligent people who seem to have a pretty good intuitive grasp on mechanics. So this problem, such as it is, seems to be more of a study in psychology and analysis techniques than anything else.

(In my opinion, the bugbear in the "problem" is that it's falsely worded. I note that NT does an admirable job of trying to remedy this difficulty.)

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2 hours ago, Carborendum said:

a "perfect quantum treadmill" (TM) whatever that's supposed to mean

The word "quantum" appears to me to have three basically independent definitions, which are not closely linked at all except in a rough conceptual way. The first two seem almost opposite each other.

1. In careful scientific terms, "a quantum" means "a discrete amount", as in a discrete amount of energy. For example, when an electron in a hydrogen atom falls from an excited orbital state to its ground state, it will release a photon of exactly the energy lost in the transition. This quantum of energy, described as a certain wavelength or frequency of light, is well-characterized and is a sure sign of the presence of hydrogen. The unstated corollary of this is that a "quantum" of energy is almost always a very, very, very tiny amount. This is where the term "quantum mechanics" and other physics-related "quantum" terms (such as "quantum chromodynamics") come from. Such mechanics follow different "rules" from the universe described by Newton, which is what we're used to, so the outcomes seem bizarre and unpredictable, varying widely from our expectations. An example is "quantum tunneling", where an electron passes through what looks like an impenetrable barrier. What?! How is that even possible? Quantum mechanics, that's how.

2. In more casual parascientific speech, "quantum" means "positive change in paradigm or magnitude", as in the phrase "quantum leap" (which lent its name to an '80s TV show with Scott Bakula). This term seems to me to arise from the fact that the "quantum effects" described in the example above defy our expectations, and so end up (conceptually speaking) a long, long way from what we expected. So "quantum" rather ironically takes on the meaning of "a huge change".

3. In very casual, non-scientific terms, "quantum" means something like "magically super-precise to the point that you can assume it's perfect." It is related in spirit to the idea of Unobtanium, the element from which we can build starships or whatever other supertechnological or magical items we want to build, because the Unobtanium has properties we need that are otherwise impossible or unknown. This looks to be the sense in which NT is using the term.

Edited by Vort
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22 minutes ago, Vort said:

By the way, I have never understood why this is a difficult problem. Granted, my undergrad studies were in physics, so I got used to thinking about things in a particular manner that probably made this setup easy to analyze. But that is clearly not the case for a great many people, including intelligent people who seem to have a pretty good intuitive grasp on mechanics. So this problem, such as it is, seems to be more of a study in psychology and analysis techniques than anything else.

(In my opinion, the bugbear in the "problem" is that it's falsely worded. I note that NT does an admirable job of trying to remedy this difficulty.)

Maybe it is just supposed to be a "fun" question that gets all funned-out when applying analytical physics to the problem.

I have a "geek club" that I used to meet with before the quarantine.  As part of the process of admittance, they asked the following question:

Quote

If we take the function y=1/x and rotate that graph about the x-axis, we end up with a 3-d shape.

The surface's rate of increase tends to decrease, the further we go out from the origin.  However, the volume decreases at an even greater rate.  So, which is greater?  The total surface area?  Or the total Volume?

They had apparently been arguing that for the past three weeks.

I thought about it for about three seconds and decided, 

Quote

Volume is infinity^3.  Area is infinity^2. Therefore Volume is greater.

They welcomed me into the club.

Edited by Carborendum
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7 minutes ago, Vort said:

The word "quantum" appears to me to have three basically independent definitions, which are not closely linked at all except in a rough conceptual way. The first two seem almost opposite each other.

1. In careful scientific terms, "quantum" means "discrete", as in a discrete amount of energy. For example, when an electron in a hydrogen atom falls from an excited orbital state to its ground state, it will release a photon of exactly the energy lost in the transition. This quantum of energy, described as a certain wavelength or frequency of light, is well-characterized and is a sure sign of the presence of hydrogen. The unstated corollary of this is that a "quantum" of energy is almost always a very, very, very tiny amount. This is where the term "quantum mechanics" and other physics-related "quantum" terms (such as "quantum chromodynamics") come from. Such mechanics follow different "rules" from the universe described by Newton, which is what we're used to, so the outcomes seem bizarre and unpredictable, varying widely from our expectations. An example is "quantum tunneling", where an electron passes through what looks like an impenetrable barrier. What?! How is that even possible? Quantum mechanics, that's how.

2. In more casual parascientific speech, "quantum" means "positive change in paradigm or magnitude", as in the phrase "quantum leap" (which lent its name to an '80s TV show with Scott Bakula). This term seems to me to arise from the fact that the "quantum effects" described in the example above defy our expectations, and so end up (conceptually speaking) a long, long way from what we expected. So "quantum" rather ironically takes on the meaning of "a huge change".

3. In very casual, non-scientific terms, "quantum" means something like "magically super-precise to the point that you can assume it's perfect." It is related in spirit to the idea of Unobtanium, the element from which we can build starships or whatever other supertechnological or magical items we want to build, because the Unobtanium has properties we need that are otherwise impossible or unknown. This looks to be the sense in which NT is using the term.

I'm aware of these definitions.  But I tend to roll my eyes whenever anyone uses definition #3.  Not that it is "perfect."  But that it is "magical."

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1 hour ago, NeuroTypical said:

Ooh!  Someone who hasn't run the gamut of this devilish thought experiment!

Here's the setup Carb.  You have an airplane on a treadmill on a nice clear windless day.  The propeller starts like it should.  As the plane moves forward, the treadmill is designed to roll backwards at equal speed.  The intent is to keep the airplane from taking off.  It's a cool perfect quantum treadmill that can measure as accurately, and move as rapidly as it needs to.

So, can the airplane take off?

Everyone feel free to join in.  First person who starts yelling in all caps loses!

35rsff.jpg

 

 

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2 hours ago, Carborendum said:
Quote

If we take the function y=1/x and rotate that graph about the x-axis, we end up with a 3-d shape.

The surface's rate of increase tends to decrease, the further we go out from the origin.  However, the volume decreases at an even greater rate.  So, which is greater?  The total surface area?  Or the total Volume?

They had apparently been arguing that for the past three weeks.

I thought about it for about three seconds and decided, 

Quote

Volume is infinity^3.  Area is infinity^2. Therefore Volume is greater.

They welcomed me into the club.

They welcomed you into the club because they liked how you thought. But you were wrong. 😁

In a way, the question itself is flawed. You can't ask whether a volume or an area is "bigger". They're two entirely different things, and cannot be directly compared. But the volume of the funnel you describe is finite (as long as you use a positive value for the left-hand x value), while the area of the same bounded funnel is infinite.

Consider the funnel from the point x=1 out to infinity. To calculate the volume, you will divide the funnel into infinitesimal disks of thickness dx and of face area π f2(x), where f(x) is our function—in our case, f(x) = 1/x (or x-1). Integrating between 1 and ∞ gives

V(x) = ∫ [ π f2(x) ] dx [taken between 1 and ∞]
= π  (x-1)2 dx [taken between 1 and ∞]
= π  x-2 dx [taken between 1 and ∞]
= π [ x-1 / (-1) ] [taken between 1 and ∞]
= -π/x [taken between 1 and ∞]
= -π [1/∞ - 1/1]
= -π [0 - 1]
= π

The volume is π (finite).

The surface area of the same funnel is found by integrating the infinite disks of thickness dx that have an external (rim) circumference of 2πx. Integrating again between 1 and ∞ gives

A(x) =  2π f(x) dx [taken between 1 and ∞]
= 2π  x-1 dx [taken between 1 and ∞]
= 2π [ln(x)] [taken between 1 and ∞]
= 2π [ln(∞) - ln(1)]

But ln(x) as x→∞ is ∞. That is to say, the area of the funnel is unbounded.

So your funnel could hold π cubic feet of paint, but if you actually tried to paint the inside surface of the funnel, you couldn't do it, because it would take infinite paint. Go think about that one for a while.

PS Would they let me in your geek group?

Edited by Vort
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1 hour ago, Vort said:

They welcomed you into the club because they liked how you thought. But you were wrong. 😁

In a way, the question itself is flawed. You can't ask whether a volume or an area is "bigger". They're two entirely different things, and cannot be directly compared.

Yes.  We were all aware of that.  But the way the question was worded was that if we ignore units and just look at the number, which would have a bigger number.

Quote

But the volume of the funnel you describe is finite (as long as you use a positive value for the left-hand x value), while the area of the same bounded funnel is infinite.

Consider the funnel from the point x=1 out to infinity. To calculate the volume, you will divide the funnel into infinitesimal disks of thickness dx and of face area π f2(x), where f(x) is our function—in our case, f(x) = 1/x (or x-1). Integrating between 1 and ∞ gives

...

The volume is π (finite).

The surface area of the same funnel is found by integrating the infinite disks of thickness dx that have an external (rim) circumference of 2πx. Integrating again between 1 and ∞ gives

...

But ln(x) as x→∞ is ∞. That is to say, the area of the funnel is unbounded.

Now perform the same calculation for the volume and area for the range { 0<= X<=1 }.   You'll not only notice that the volume→∞ as x→0, but you'll also notice that the ln(x) does some pretty funky things.

1 hour ago, Vort said:

PS Would they let me in your geek group?

I'll put in a good word for you. :) 

Edited by Carborendum
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4 minutes ago, Carborendum said:

Now perform the same calculation for the volume and area for the range { 0<= X<=1 }.   You'll not only notice that the volume→∞ as x→0, but you'll also notice that the ln(x) does some pretty funky things that look great on paper, but don't pass the reasonable test.

This is the problem with considering a nonpositive boundary. The question is clearly unsolvable and meaningless in any real sense if you allow nonpositive x, which I personally don't find interesting. Limiting it to positive-only values of x gives a meaningful (and quite interesting) problem.

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10 minutes ago, Vort said:

This is the problem with considering a nonpositive boundary. The question is clearly unsolvable and meaningless in any real sense if you allow nonpositive x, which I personally don't find interesting. Limiting it to positive-only values of x gives a meaningful (and quite interesting) problem.

Now that we've talked this thing to death.  The flying cars... wow... they're not here yet.

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6 hours ago, mordorbund said:

You can totally see the wires. Very clever of him to spin it as a "one string teather (sic) test".

I can't tell when you're joking or not.  But I didn't see any wire that you're talking about other than the throttle controls and the netting.

Don't be my childhood friend who told me about the North Koreans coming down over the mountains.

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4 hours ago, Carborendum said:

I can't tell when you're joking or not.  But I didn't see any wire that you're talking about other than the throttle controls and the netting.

Don't be my childhood friend who told me about the North Koreans coming down over the mountains.

I'm joking. You (well, I) can see it at 2:39 going from the vehicle off to the upper-left somewhere.

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