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Topic: Texas and OU to where?!?!

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utee94

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Re: Texas and OU to where?!?!
« Reply #588 on: August 12, 2021, 05:21:43 PM »
Yeah, and when you think about how they work, it's basically electromagnetic forces balanced against a spring. The electromagnetic forces may not be perfectly proportional to actual speed, and the resistance of the spring is going to be non-linear as well (as much as they want it to be linear). I'll bet that inaccurate readings are probably found both at the low speed and the high speed ends, due to the spring resistance nonlinearity. But we only care about the high end because that's where we get in trouble with the law...
That reminds me, I'll need to get the speedo recalibrated in the Jeep when I throw the 35s on.

You can mitigate this somewhat by designing the system such that the relevant measurements are taken in the middle of the spring's travel, where it is the most closely approximate to linear.  When I worked at Eaton doing final test engineering for ion implanters (particle accelerators), we had similar instrumentation, and it was designed that way.  Of course, each ion implanter sold for several million dollars, so...
« Last Edit: August 12, 2021, 05:51:05 PM by utee94 »

betarhoalphadelta

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Re: Texas and OU to where?!?!
« Reply #589 on: August 12, 2021, 06:05:02 PM »
You can mitigate this somewhat by designing the system such that the relevant measurements are taken in the middle of the spring's travel, where it is the most closely approximate to linear.  When I worked at Eaton doing final test engineering for ion implanters (particle accelerators), we had similar instrumentation, and it was designed that way.  Of course, each ion implanter sold for several million dollars, so...
Yes, which frankly is how that type of speedometers work. They'd be calibrated such that their optimal accuracy is going to be in perhaps the 35-65 mph range, and the springs used will be most linear there. Accuracy below or above those ranges are less important.

CWSooner

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Re: Texas and OU to where?!?!
« Reply #590 on: August 12, 2021, 06:29:25 PM »
Yeah, and when you think about how they work, it's basically electromagnetic forces balanced against a spring. The electromagnetic forces may not be perfectly proportional to actual speed, and the resistance of the spring is going to be non-linear as well (as much as they want it to be linear). I'll bet that inaccurate readings are probably found both at the low speed and the high speed ends, due to the spring resistance nonlinearity. But we only care about the high end because that's where we get in trouble with the law...
That reminds me, I'll need to get the speedo recalibrated in the Jeep when I throw the 35s on.
What are 35s?  Are you talking profile ratio or overall diameter?
If the former, why would you do that on a Jeep?
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Cincydawg

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Re: Texas and OU to where?!?!
« Reply #591 on: August 12, 2021, 06:30:40 PM »
F = kx.  The Hooksters discovered that.


betarhoalphadelta

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Re: Texas and OU to where?!?!
« Reply #592 on: August 12, 2021, 06:31:43 PM »
What are 35s?  Are you talking profile ratio or overall diameter?
If the former, why would you do that on a Jeep?
Diameter. 35" tires on a 17" rim.

CWSooner

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Re: Texas and OU to where?!?!
« Reply #593 on: August 12, 2021, 06:33:38 PM »
Got it!  That makes sense.  ;)
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utee94

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Re: Texas and OU to where?!?!
« Reply #594 on: August 12, 2021, 06:48:45 PM »
For various reasons, Jeep and pickup truck people tend to refer to overall diameter of the wheel/tire combination.

Car people tend to talk about the wheel diameter by itself, and then the tires with respect to the width/tread profile ratio/inside diameter.

I found it quite confusing too, when we first got the Jeep and I was wondering what the next set of tires should be on my 17" wheels and people started talking 33s, 35s, etc.

Anyway, the next set on the Jeep will definitely be 35s.  On the Rubicon I can run 35s without any additional lift (Rubis come with a modest lift from the factory compared to base trim levels).

« Last Edit: August 12, 2021, 06:54:58 PM by utee94 »

Cincydawg

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Re: Texas and OU to where?!?!
« Reply #595 on: August 12, 2021, 06:52:56 PM »
I used to hear folks bragging about doing 130 mph in a Dodge Dart with a 6 in it.  Not a chance, it's speedo error and hyperbole.

And those old cars were not designed for such speeds of course and could turn briefly into aeroplanes as air gets underneath them.  CWS knows about this.

I have read that airplane pilots have difficulty learning to operate rotary wings because the controls are so different.  I am only vaguely familiar with terms like "collective" except as applied to The Borg.

An airplane gives you three basic controls, throttle, stick/yoke, and pedals.  The pedals turn the rear of the plane, and oddly enough steer it when on the ground.  I and others found it challenging to hit and maintain a specific altitude, it takes a lot of work to do that.

betarhoalphadelta

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Re: Texas and OU to where?!?!
« Reply #596 on: August 12, 2021, 07:18:13 PM »
Principles of flight for helicopters are really interesting... I learned a fair bit about it from my brother who was a CH-53E pilot before he became a fixed-wing flight instructor and now airline pilot.

MrNubbz

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Re: Texas and OU to where?!?!
« Reply #597 on: August 12, 2021, 07:43:20 PM »
Yup, they do say that.  All five of them. 
They only need 5 the Canadians or Russians aren't hopping the fence
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CWSooner

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Re: Texas and OU to where?!?!
« Reply #598 on: August 12, 2021, 07:56:09 PM »
I used to hear folks bragging about doing 130 mph in a Dodge Dart with a 6 in it.  Not a chance, it's speedo error and hyperbole.

And those old cars were not designed for such speeds of course and could turn briefly into aeroplanes as air gets underneath them.  CWS knows about this.

I have read that airplane pilots have difficulty learning to operate rotary wings because the controls are so different.  I am only vaguely familiar with terms like "collective" except as applied to The Borg.

An airplane gives you three basic controls, throttle, stick/yoke, and pedals.  The pedals turn the rear of the plane, and oddly enough steer it when on the ground.  I and others found it challenging to hit and maintain a specific altitude, it takes a lot of work to do that.
Heh!  You asked for it!

I'll talk about a helicopter with a simple single main rotor (rotating counterclockwise as seen from above--the American way) and a tail rotor.
The collective stick ("collective" for short) sits to the left of the pilot and adjusts the overall pitch of the main rotor blades.  In a turbine-engine helicopter, it's sort of analogous to the throttle.  The throttle is like a sleeve on the outside of the collective, which pivots in a housing that is mounted to the floor at its aft end.  At zero pitch it sits at maybe a 15-30-degree angle upward to where you hold it.  When you are starting and running up the helicopter, it is twisted clockwise (to of your hand moving inward) to that position.  When you are ready to taxi or take-off, you twist in the other way to max rpm and a governor takes care of it when you make more demand on the engine by pulling the collective stick up.  If the power is by a piston engine, the governor may not work very well (as it does not on a TH-55) and you will need to increase throttle as you increase collective pitch, and reduce it when you decrease collective pitch.  Between the throttle (w/ or w/o a governor) and changing the overall pitch of the main rotor, the collective is effectively the power, analogous to the throttle on an airplane.

The cyclic stick ("cyclic") variably (cyclically) alters the pitch of the main rotor blades as they rotate around the mast.  This effectively tilts the thrust of the rotor so that some of it is going in a direction other than pure vertical.  To do this, the rotor blades, either by hinges or their inherent flexibility, "flap" up and down as they go through each rotation around the mast.  (In most rotor designs, the blades can "hunt" a little bit forward ("lead") or a little bit aft ("lag"), but this does not require any pilot input, so it's just something to know about as you do pre-flight inspection of the rotor head.)  In forward flight, for the pilot, it is very much like the "control stick" on an airplane.  If you push the cyclic forward, a combination of pitch-change rods and upper and lower swash plates will cause each blade, as it comes past 9 o-clock (strait out left) to be at its highest pitch (given how much collective you are pulling) and as it comes past 3 o'clock (straight out right) to be at its lowest pitch.  Because of gyroscopic precession, the effect of max and minimum pitch inputs does not take effect until 90 degrees later.  So the rotor disc is tilted up at the back and tilted down at the front.  The pilot will also have to adjust the collective to maintain level flight as he moves the collective around.  As the helicopter reaches effective translational lift (ETL--lift by way of fresh air rather than rotor-wash being sucked into the top of the disc) at 25-ish knots, it will require a reduction of collective to stay at the same altitude.  As you increase speed further, it will require more collective the more you push the cyclic forward, or you will descend.
In forward flight the pedals are analogous to rudder pedals on an airplane.  They control the tail rotor.  In a simple single-rotor helicopter, the fuselage will want to rotate around the mast in the opposite direction as the rotor blades are moving.  So, for this example, the nose of the helicopter will want to turn to the right, and more strongly as the pilot pulls in collective.  The tail rotor applies lateral thrust to the aft end of the helicopter to compensate for that.  In slow or hovering flight, you apply pressure to the left pedal to keep the nose pointed the way you want it pointed.  At higher speeds in forward flight, you apply pedal as necessary to keep the aircraft in trim.  There's a trim ball--usually associated with the turn-and-bank indicator that you use to monitor this.
That's it in a nutshell.  All in all, once you're at 40-50 knots in a forward direction, flying a helicopter is a lot like flying an airplane as far as control inputs go.
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CWSooner

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Re: Texas and OU to where?!?!
« Reply #599 on: August 12, 2021, 08:03:33 PM »
Principles of flight for helicopters are really interesting... I learned a fair bit about it from my brother who was a CH-53E pilot before he became a fixed-wing flight instructor and now airline pilot.
Heh!  As you know, a CH-53 is a monster of a helicopter.
Most of my time was at the opposite end of the spectrum--OH-58 Scouts (very similar to a Bell Jet Ranger), UH-1 Hueys (in flight school and during my year as a "staff aviator" in Korea, and AH-64 Apaches.  The Apache was the biggest, and IIRC, we usually flew it weighing about 16,000 lbs at takeoff.  The CH-53E has a max gross weight of 73,500 lbs.  Going from an OH-58 to that would be like going from an Mazda Miata to a Kenworth hauling two trailers.
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FearlessF

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Re: Texas and OU to where?!?!
« Reply #600 on: August 12, 2021, 11:02:04 PM »
not sure anyone asked for it
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Cincydawg

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Re: Texas and OU to where?!?!
« Reply #601 on: August 13, 2021, 07:40:21 AM »
I found it interesting, and rather complicated.  But that stands to reason.  I suppose every helo in the world has standardized on those control parameters.

I'd guess even an ultralight AC has the same basic control features as a Cessna, as does a 747.

I watch videos at times of a commercial heavy landing at some airport, apparently today they enter the desired altitude digitally on the panel and the plane goes there.

And you apparently can land an F-18 on a carrier deck hands off.

The next gen of military AC likely will not have a human pilot, or you might have one piloted AC in a group of say 8 drones he controls.

Automation is really amazing today.  That could be the barrier to having flying cars.  There are others of course.

 

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