What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

why MPH instead of knots?

Blw2

Well Known Member
Why does Van's publish performance specs in MPH instead of knots for the RV-12?

Are all the airspeed indicators set-up as MPH?
 
That used to be very common. Quite a few old Cessna and Beech products that are still knocking around with the original mph airspeed indicators.

For the second part of your question; assuming you're going with a glass display, you can set it up however you like.
 
200 MPH sounds faster than 160 KTS.

Also, many people don't know what knots are, and are not interested in hearing that unit.

The other comment about EFIS being your choice is true. For about a year I had my D-100 in KTS, but I switched it back to MPH because my backup analog ASI has MPH on the outer ring and KTS in the (harder to read) inner ring. I didn't want to squint or convert on the fly if my primary failed.

So, I just appear faster in MPH and really only use KTS when I look at the 430W for the GPS ground speed. [having typed this, I think I'll look for a setting there, too]

YMMV
 
I think most of us in the Van's world use knots. Like Rat said, MPH was tried.. but never caught on. I think because MPH is only really used in certain countries anyway.. everyone but us use metric.

However, because a lot of Cessna 150/152s were in MPH, there's an abnormally large number of pilots who expect MPH to be the norm.
 
If you're navigating with highway maps, MPH is appropriate.
If you're navigating with aviation charts or aviation databases, you may find knots more appropriate since all the distances are in nautical miles.
Granted, a 200 mph airplane sounds faster than a 170 knot airplane. It makes good marketing sense to quote speeds in MPH.
 
I think, therefore..

I like to think that knots are preferred because it seems when boat guys get tired of throwing their money into a hole in the water, they buy an airplane.
 
Last edited:
Assuming this thread is now 100% folly:

Some people use MPH because their spouse is KNOT gonna fly in that thang.

[where's the rimshot emoji?]
 
yeah, no....I feel like it's not yet into the folly territory at all.

MPH indication in vintage aircraft...sure. I've got many hours flying those. That used to be common of course....but those aircraft were firmly already vintage when I learned to fly back in the 1990's!!!
I always HATED flying those aircraft only for that reason. Otherwise they were great!

Other than situation where the operating limitations are all published in MPH (such as those vintage aircraft)...but even this seems like a weak reason to me...

or when the instrumentation is calibrated that way so your hand is forced

I can't imagine why anyone in modern aviation would choose to fly in statute miles
winds and pretty much all navigation are based on nautical. ATC works in nautical

oh, looking again I now see that they publish mph for all their aircraft. I was thinking before it was just the 12, for some reason and thought it might have something to do with the LSA regulations. Now I'm even more perplexed!

Why Vans? just why?
 
Someone should ask Van.

Here's my WAG -

WWII Army aircraft used MPH. Navy used Knots.(there is some debate even within those circles, but this is thought)

Ray Stits was an Army Mechanic during the War. It is likely he used MPH in the Playboy. Van was an Airforce Signal man, post war. Although Van could have used whatever he wanted in the Playboy conversion, he chose MPH in the RV1 and that is what it had when I flew it.

So, my guess is, it is what Van was used to and that stuck from the RV1 on forward. ( although I am sure Van was equally proficient in pilotage either way)
 
Van's started producing kits in the mid 1970's. At that time MPH was pretty much the standard for GA airplanes. And apparently they just stuck with it. But use what you want. And the conversion between the two is not difficult. :rolleyes:

Van's aircraft timeline:

i-hDWWdJW-X2.jpg
 
Last edited:
Flying VFR and generally not in the ATC system, I can use whatever. Since my flying experience dates back to the '60s and my other airplane uses mph, my RV-3B will too.

My sailboat uses knots. You would be surprised how many it takes to hold that thing together.

Dave
 
yeah, no....I feel like it's not yet into the folly territory at all.

MPH indication in vintage aircraft...sure. I've got many hours flying those. That used to be common of course....but those aircraft were firmly already vintage when I learned to fly back in the 1990's!!!
I always HATED flying those aircraft only for that reason. Otherwise they were great!

Other than situation where the operating limitations are all published in MPH (such as those vintage aircraft)...but even this seems like a weak reason to me...

or when the instrumentation is calibrated that way so your hand is forced

I can't imagine why anyone in modern aviation would choose to fly in statute miles
winds and pretty much all navigation are based on nautical. ATC works in nautical

oh, looking again I now see that they publish mph for all their aircraft. I was thinking before it was just the 12, for some reason and thought it might have something to do with the LSA regulations. Now I'm even more perplexed!

Why Vans? just why?

My Bucker is in "Klicks" (KPH). Try that on for size.
I have a conversion table glued near the instrument panel. I can do most of it in my head, (close enough) but it comes in handy at times.
KPH, KTS, MPH chart with about 10 different airspeeds.
 
A nautical mile is used for navigation because it is 1/60 degree of latitude. For anyone else still using sectionals, any vertical line of longitude will have mile tick marks that are to scale. It makes it easy to find distance quickly when flying, (but in nautical miles).
 
I fly from the left side and have everything set up in knots. My Wife flies from the right seat and has her side set up in MPH.

She goes faster than I do but has farther to go, so we both get there about the same time!
 
I fly from the left side and have everything set up in knots. My Wife flies from the right seat and has her side set up in MPH.

She goes faster than I do but has farther to go, so we both get there about the same time!

Ha Ha!! Good one Mel. I’m going to use that one too. It’ll make her feel good
 
As long as you use consistent units it does not matter, MPH, KTS, KPH, MACH, Speed of light or Furlongs Per Fortnight.

Obviously MPH sounds better as it is 15% more than Knots. So 190 knots is plenty fast for a single engine sky scooter. However 220 MPH (218.5 MPH rounded up) sounds better doesn't it? Being experimental (EAB) planes we can use what units we want. The conversion is easy to make either way.

Back in the day all planes were in MPH before 1969. After 1969 they progressively transitioned to knots/hr for airspeed and knots for distance.

Mile or MPH is an archaic unit based on the British Imperial units. WIKI: "The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 English feet, or 1,760 yards."

Why knots? It is way easier to do navigation for boats and planes that fly in reference to Lat and Long. WIKI "The nautical mile is based on the Earth's longitude and latitude coordinates, with one nautical mile equaling one minute of latitude.
 
Last edited:
They didn't name the Mooney 201 because it's top speed was in knots.

201MPH was an easier number to reach.


Question..... Why is the speed of sound in MPH.
 
Last edited:
Back in the day all planes were in MPH before 1969. After 1969 they progressively transitioned to knots/hr for airspeed and knots for distance.

.

Partially correct. WWII US Navy Aircraft used Knots, just look up their operations manuals. There is some debate on whether the instrumentation was in Knots or MPH. I have seen panels with both, inner and outer rings, as is pretty common still. 1969 was when the FAA finally standardized Airworthiness directives. The IOAC started working on standardization in the late 40's, whereby aircraft used MPH, Knots, and KPH. It took a long time to reach standardization, or have we?

My Bucker was built in 1961 and still used "klicks". German design built by CASA in Spain. It has Spanish, English, and German placarding. It doesn't know it has an identity crisis.

How they standardized on "feet" for altitude so much earlier is beyond me.
 
Partially correct.

I think this is totally correct.... in the context of the lighter side of general aviation anyway.

The POH for a 1975 C-150 was still in MPH.
It wasn't until a year or two later that Cessna had switch all of the new production aircraft over to Kts.
 
Decades ago, there was a big push to switch aviation from miles and MPH to knots. Guess which side won...

BTW, Class D airspace is now 4.7 nm (5 miles) because an expansion to 5 nm would have grabbed a lot of airspace where it would have been inconvenient for GA operations.
 
I'll jump in here.... Per the OP’s question regarding RV-12…. I believe when Light Sport Category was enacted back in 2004, the thinking was to make flight instruction less costly with simple airplanes requiring less instruction (read - less knowledge). If I remember, some of the rationale was to make things less confusing, mph would be used for speed designation because it was already used for US ground transportation and well engrained.

I earned my PPL/ASEL in 1970. I fly my RV-12 as hybrid… airspeed is mph and navigation is nm. I have to confess… I like seeing higher number for speed...
 
Aviation is not only in knots.

Temperature and dew point will always be reported in degrees Celsius. Visibility will always be reported in statute miles. RVR will always be reported in feet. Wind Speed will always be reported in knots.

-Marc
 
I think this is totally correct.... in the context of the lighter side of general aviation anyway.

The POH for a 1975 C-150 was still in MPH.
It wasn't until a year or two later that Cessna had switch all of the new production aircraft over to Kts.

You can find examples of both way earlier than this. Doesn’t matter though.
I think Van stuck with it and the factory just kept the convention going. If he was a Navy guy, they would most certainly have been in Knots ;)
 
You can find examples of both way earlier than this. Doesn’t matter though.
I think Van stuck with it and the factory just kept the convention going. If he was a Navy guy, they would most certainly have been in Knots ;)

My understanding is that it had nothing to do with Airforce vs Navy.

It was what has always been mentioned, that it looks like a higher speed.
It wasn't that many years ago that even a lot of the pilot population wasn't used to Kts and didn't have a good feel for what the relationship between Kts and MPH was (a lot of them still don't).
 
My understanding is that it had nothing to do with Airforce vs Navy.

It was what has always been mentioned, that it looks like a higher speed.
It wasn't that many years ago that even a lot of the pilot population wasn't used to Kts and didn't have a good feel for what the relationship between Kts and MPH was (a lot of them still don't).

I was teasing Scott.
I think your explanation makes the most sense, and as others stated, it looks faster!
 
My left panel is in knots and my right one is in statute miles. This allows me to speak either with a glance, I’m getting used to the conversion relationship this way also.
 
I think most of us in the Van's world use knots. Like Rat said, MPH was tried.. but never caught on. I think because MPH is only really used in certain countries anyway.. everyone but us use metric.

Technically you're using metric too: All the American units of measure are officially defined as fractions of SI units these days.

Dragged kicking and screaming :)

- mark
 
Hmm, faster in MPH, slower in Knots

Maybe the RV-15 will have a cruise speed in MPH and a stall speed in Knots

Just throwing it out there
 
We laugh about knots versus mph but last year going into Oshkosh for AirVenture I got stuck behind two high wing aircraft who were obviously flying 90 mph @ 1,800’ for the arrival and not 90 knots. I slowed down to 78 knots and did s turns trying to stay behind them to no avail. I asked several times “high wings - push it up” and after the third “push it up” he said: “I’m doing 90” to which I replied: “knots or mph.” I eventually broke out, did a turn around Groom lake” and then re-entered the conga line. Very frustrating after already having held for two and a half hours waiting for the airport to open back up.

My point being those aircraft whose airspeed is measured in mph need to be cognizant of the difference when flying the AirVenture arrival. It would also help if the published arrival procedure mentioned something about this issue in their NOTAM.
 
Funny turn in this thread - another less than obvious connection between marine and air craft are the datum of the drawings. Drawings have to have a datum line, and engines begin at the center of the crank (ok that is logical) but then (at a different job) when a major aircraft manufacturer showed our engineering group a fuselage and I pointed to the datum and asked why is it there? I was informed it is not called the datum but the "water line" and it is lower than the centerline as the marine architects were the draftsmen (ok persons) that had the necessary experience to become aircraft designers . . .thus the water line.

That is probably not odd to VAF, but it was to me.
 
You think MPH vs Knots is bad? I used to have a Yak-52 with an airspeed indicator in KPH. I got good at cutting in half and adding 10% to get knots when ATC asked.😝 it also had an AI with brown on top and blue on the bottom. When I did my transition training the CFI said, “Just remember what ever color is in front of the marker on the AI is what you’re pointed at!”
 
At one airshow way back when, Dick Rutan and Jeana Yeager were showing a VariEze, or maybe Long Eze, with cruise speed listed in MPH and stall speed in knots.
 
Airspeed indicators should be scaled from 0-100.

0 = Vso
100 = Vne

fight me. :)





(kidding, if you can't tell)
 
Airspeed indicators should be scaled from 0-100.

0 = Vso
100 = Vne

fight me. :)





(kidding, if you can't tell)

If you're going that way, you might as well go all in and just do a 5 star scale.

5 Stars = Vne (awesome, great experience!)
0 Stars = Vso (would not recommend)
 
All relative

They are all just numbers with a unit. The mix of units would be an issue if we needed to do calculation converting altitude to airspeed or use air density to determine rate of climb. But since we don’t do that when flying (maybe some OCD pilot may) not too much of issue as long as we all are consistent, which we are not due to primarily the difference in airspeed units discussed here.

Knots and nautical miles are the modern standard and used by ATC so I use Knots. (Based on day job, my RV cruises at 0.2565M but over the fence on landing at 70kts)
 
Last edited:
Airspeed indicators should be scaled from 0-100.
0 = Vso
100 = Vne
fight me. :)
(kidding, if you can't tell)

I might propose:

0 = Sitting still (Need to verify "Airspeed Alive" on take off roll)

Min = Vso

Max = Vne
 
KPH

If statue miles sounds faster than knots then logically we should all change over to KPH (1000 meters per hour).

Unfortunately most analog gauges in the US is in mph or knots :(
 
Back
Top