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  #1  
Old 01-07-2017, 09:52 PM
drone_pilot drone_pilot is offline
 
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Default MPH vs Kts

Hello All,

I've done some searching but I'm not finding the answers. I've got dual Dynon Skyviews. I can set the airspeed units to either knots or mph.

The Cessna I currently fly displays both on the gauge but uses mph in the POH. What is the thinking when it comes to setting up the airspeed units on an airplane? Is there any significant advantage to using one unit of measure over the other?

Thanks!

Ben
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  #2  
Old 01-07-2017, 10:13 PM
rv9builder rv9builder is offline
 
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ATC will always refer to speeds in knots. That's a pretty good reason to use knots.

Use mph to impress your non-pilot friends about how fast your plane is!
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  #3  
Old 01-07-2017, 10:22 PM
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RV7A Flyer RV7A Flyer is offline
 
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It's aviation...use knots and nm ATC uses knots, weather reports and forecasts use knots, TFRs use nautical miles, the list goes on and on.

Plus, 1 nm = 1 minute of arc in longitude (at the equator), so it's cooler than the arbitrary distance of a statute mile .

BTW...one of the most cringe-worthy erroneous expressions, IMO, is "knots per hour". Grrr....
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  #4  
Old 01-07-2017, 10:38 PM
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N941WR N941WR is offline
 
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If you have an EFIS, it should be easy to swap between the two with a few button pushes.
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  #5  
Old 01-08-2017, 01:17 AM
dutchroll dutchroll is offline
 
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It's a mystery to most of us living outside the USA and also to quite a few living inside the USA as to why mph is used in aviation at all. Even inside the USA it's normally only experimental or GA which uses mph instead of knots. I've flown US-built military aircraft from the 1970s and they were always in knots. Knots is the international standard for aviation and is the language ATC will always use, the units upon which performance categories are based, with nautical miles being the standard distance unit on charts, and so on.

Suffice to say it's a hangover from days long gone by. I did read a great story about the Mooney 201 which apparently was named because it could reach 201 mph in level flight, and "Mooney 175" (in knots) just didn't have the same marketing "zing"! Maybe they should've gone full metric and named it the "Mooney 323"?
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Last edited by dutchroll : 01-08-2017 at 01:19 AM.
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  #6  
Old 01-08-2017, 04:58 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by dutchroll View Post
...

Suffice to say it's a hangover from days long gone by. I did read a great story about the Mooney 201 which apparently was named because it could reach 201 mph in level flight, and "Mooney 175" (in knots) just didn't have the same marketing "zing"! Maybe they should've gone full metric and named it the "Mooney 323"?
Maybe it was because Mazda had a cart named the 323?
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  #7  
Old 01-08-2017, 05:30 AM
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Plummit Plummit is offline
 
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But (there's always a but) VFR visibility is listed in statute miles! Class D airspace is 5 statute miles IIRC.

-Marc


Quote:
Originally Posted by RV7A Flyer View Post
It's aviation...use knots and nm ATC uses knots, weather reports and forecasts use knots, TFRs use nautical miles, the list goes on and on.

Plus, 1 nm = 1 minute of arc in longitude (at the equator), so it's cooler than the arbitrary distance of a statute mile .

BTW...one of the most cringe-worthy erroneous expressions, IMO, is "knots per hour". Grrr....
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  #8  
Old 01-08-2017, 06:39 AM
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GalinHdz GalinHdz is offline
 
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Quote:
Originally Posted by Plummit View Post
But (there's always a but) VFR visibility is listed in statute miles! Class D airspace is 5 statute miles IIRC.

-Marc
What does visibility have to do with speed?

Quote:
Originally Posted by rv9builder View Post
ATC will always refer to speeds in knots. That's a pretty good reason to use knots.

Use mph to impress your non-pilot friends about how fast your plane is!
IMHO this is the best reason/response. In the end, it will be whatever you want for your airplane.
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  #9  
Old 01-08-2017, 06:44 AM
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BCP Boys BCP Boys is offline
 
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If you are going to talk to ATC, whether it's VFR flight following or IFR, then use knots, no question. If you don't plan on ever speaking with ATC then use MPH to impress.
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  #10  
Old 01-08-2017, 06:51 AM
Sam Staton Sam Staton is offline
 
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Talking Knots 'controversy'

As a retired sailor (Blackshoe navy - nuke subs), I have always used knots, so they're a bit more comfortable. I suspect that the use of mph stems from our early adoption of the English system of measurement. That said, I refuse to switch to metric - just the dinosaur in me, I guess.
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