Please educate me on the Airspeed Mach Indicator

[S. Low]

I can't figure out how to read my airspeed, please help my brain noodle out these hieroglyphics.

 

So as I read and understand it, the first 3rd of the dial shows knots (times 10). This seems pretty straight forward in that when the arrow points at 15 the Airspeed is 150 knots. And this section ends at 200 knots, right before the .7 mach. Correct?

 

Now my confusion: .7 mach is 466 knots according internet converter. Is there a way it is reading to me the Airspeed in between 200 and 466, or am I misunderstanding the calculator?

 

Also, I think the inner dial reads knots. So when it says 40 I assume that means 400 knots, but this doesnt correspond correctly with the mach number unless I'm calculating incorrectly. Further, if when the inner dial is at "40" it means 400 knots, then why when I check map does my airspeed say 529ish? 529, as I recall, actually would correspond correctly to the mach number according to the calculator. But I'm a bit corn fused by which thing I'm reading incorrectly

[razo+r]

Mach number depends on altitude. If you are high enough, you could get a Mach 1 reading with 200 knots (just an example). So, 400 knots can mean Mach .8 at the current altitude, and lower down it could mean Mach .5 (also just an example).

 

And about the difference in knots, your gauge in cockpit shows Indicated Air Speed (I believe), and on the map you can choose between True Air Speed (Which is probably the one you selected back then) and Indicated Air Speed.

 

Some links:

 

https://en.wikipedia.org/wiki/Airspeed

 

https://en.wikipedia.org/wiki/Mach_number

 

Another tipp: Fly the aircraft and look at how the gauge behaves. That should solve most of your questions.

Edited September 27, 2019 by razo+r

[S. Low]

Oh man, that helps a bunch. Thanks!

[QuiGon]

The indicator also shows knots above 200, but it will then be displayed on the inner side of the Mach scale. Keep in mind though, that it shows Indicated Airspeed (IAS) and not True Airspeed (TAS).

Edited September 30, 2019 by QuiGon

[r4y30n]

Is it just IAS or is it CAS? The CADC has enough data and power to compute calibrated speed, doesn't it?

[draconus]

It's IAS.