Ok. Basic question. I am planning to purchase an air speed
indicator for my 9a. Should I get knots or MpH on the outer scale?
Thanks. Al
Nautical miles is the standard in US aviation although there seem to be many who will not accept this fact. Some even use just a number, without explaining that they are using a non-standard scale.
Larry is correct, Nautical is the US standard for current production planes......
Knots. Aeronautical charts are nautical measure. Approach plates all use nautical units of measure. Speed assignments from ATC are in Knots. MPH are used when someone asks how fast your airplane is
Personally, I settled on knots because of convention, professionalism and ATC.
However, after reading this thread, I'm considering changing my way of thinking. I've developed a unit of RV-specific speed measurement that equals 100 knots. I call it a "Mock", since it's not real.
Therefore, when cruising around at, say, 160kts, one would then refer to it as "1.6 Mock".
If the larger mph numbers are good for picking up chicks, just imagine what bragging, "Yeah, I can hit 1.78 Mock anytime I want to," would do for you! Eat your heart out, Maverick.
But I said a standard AS indicator. MPH is not standard anywhere.uh oh...what if you are reading it off a MPH A/S instead of a Kt A/S then the MOCK number will be wrong?
Use whatever your car uses!
Left side of my airplane is knots. Ann's GPS (right side) is MPH. She goes faster than I do, but she has further to go.
We usually get there about the same time.
You may as well sell your airplane and drive everywhere.
MPH really have noplace in aviation. It's akin to asking somebody what there airspeed is and they tell you groundspeed.
Does that mean we have to rip out the ASI's in all older airplanes (mph) and have them repainted or replaced? I don't mean to be harsh, but some of you guys sound like you'd make good bureaucrats! Maybe we could help FAA draft up a regulation requiring us all to have ASI's marked only in knots - no mph for us! Then write in stiff penalties (say $1000) for non-compliance. Of course we'd have to redo all old manuals and V speeds to get consistency. A lot of work. And we would have to hire a lot of new FAA personnel to monitor and enforce our new rule. Just kidding. Personally I like the dual scale ASI with TAS. These were in our Commanche, our Lance and one's going in the -8. I think they're very handy. Must admit though that I'm not a professional pilot.
As a general rule, 100kts = 160mph = 180km/hr. Good enough for conversation.