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-   -   Knots or MPH?? That Is The Question (https://vansairforce.net/community/showthread.php?t=81947)

longranger 01-30-2012 09:01 AM

Quote:

Originally Posted by Jamie (Post 622874)
Virtually every single reference to speed and distance in every aeronautical document, chart, sectional, AIM, FAR, not to mention every controller uses nautical miles.

It's the unit for the system. Anything else is just for bragging rights.

THE system for bragging rights is furlongs per fortnight, eighths of a mile (statute:D) per two weeks.

Flying at 7500ft is fairly handy in my 170 as the indicated mph is pretty close to true knots.

MarkW 01-30-2012 09:33 AM

Knots
 
Learned to fly in an old 172 with MPH. My instructor told me to use the inner numbers (knots) not the outer ring with the wrong numbers. Since then I have been flying newer 172's with knots. Learned to fly IFR using knots. Started visiting this site and many RV'ers were using the MPH and I am thinking "What the heck".

John Clark 01-30-2012 11:55 AM

"Back in the day" when I bought my used B-55 Baron, it was equipped with a dual scale A/S with knots on the inside ring. I sent the gauge off to the instrument shop where they rescreened the face to show only knots. Come to think of it, the last airplane I had with an MPH A/S was my J3 Cub, which I sold in 1970 :rolleyes:

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

dutchroll 01-30-2012 11:30 PM

Quote:

Originally Posted by longranger (Post 623553)
THE system for bragging rights is furlongs per fortnight, eighths of a mile (statute:D) per two weeks.

Flying at 7500ft is fairly handy in my 170 as the indicated mph is pretty close to true knots.

I was wondering how long it would take for "furlongs" to be mentioned! ;)

Flying Scotsman 01-31-2012 12:14 AM

Quote:

Originally Posted by dutchroll (Post 624011)
I was wondering how long it would take for "furlongs" to be mentioned! ;)

I like slugs as the unit of mass, too. :)

MauiLvrs 01-31-2012 12:34 AM

Quote:

Originally Posted by MarkW (Post 623571)
Learned to fly in an old 172 with MPH. My instructor told me to use the inner numbers (knots) not the outer ring with the wrong numbers. Since then I have been flying newer 172's with knots. Learned to fly IFR using knots. Started visiting this site and many RV'ers were using the MPH and I am thinking "What the heck".

The numbers are bigger:confused:

dutchroll 01-31-2012 12:45 AM

Heh, I vaguely remember "slugs" from my aerodynamic days at uni. But I don't think I ever did understand why someone came up with such a unit! :)

Hey Vlad, if it's any consolation, I like the metric system and think it makes emminent sense (we converted down under several decades ago, and I speak "both" languages despite my public disdain for mph). But I think the hotchpotch of "standard" aeronautical units is here to stay for a while! ;)

Flying Scotsman 01-31-2012 01:21 AM

I've actually never understood why certain manufacturers (certificated or experimental) would mark their systems in mph. The *system*, at least in the U.S., uses knots and nautical miles. I've never heard an ATC specialist ask for or assign any speed in miles per hour.

As some of us know all too well, mixing measurement systems can be a recipe for disaster...

At least nautical miles and meters are related to measurements of the earth...1 nm = 1 minute of arc, 1 meter = 1/10,000,000th of the distance from the equator to the pole). Statue miles are essentially arbitrary. :)

(BTW, a Roman pace was *two* steps, not one...)

(I don't know if it's actually true or not, but my physics prof asserted that if you use the furlongs/fortnight/slug system, virtually all physical constants end up being approximately 1 x 10^some power :) I suspect he just made that up to see if we were listening!)

Can you tell I'm up late and bored tonight? LOL!

RV8R999 01-31-2012 04:29 AM

The ATC already mixes systems...

Wx is reported in statute miles and therefore the visibility portion of approach minima are published in statute miles...

why do we use Feet instead of meters?

sailvi767 01-31-2012 06:51 AM

Quote:

Originally Posted by RV8R999 (Post 624032)
The ATC already mixes systems...

Wx is reported in statute miles and therefore the visibility portion of approach minima are published in statute miles...

why do we use Feet instead of meters?


I think the feet verses meters issues was decided by Pan Am. Much of the worlds conventions on how we fly date back to their early days where there were no standards. Not all nations however use the ICAO standard of feet. Its a pain in the ____ flying in countries that do not with a aircraft set up for feet. Leveling at 11100 meters is one thing but when they ask you your altitude passing and its 26,700 feet by the time my slow brain has done the conversion to meters the number is history not where we are at the moment. Approaches get especially tricky because they often convert from meters standard to local altimeters at very low altitudes like 1200 meters. Add in another conversion since the same countries often use QFE instead of QNH for altimeter settings and things get interesting for the math inept among us.

George


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