Since i have an actual pilots licsense i'll tell it to you like this. There is no way you would want a game (AH) to acurately simulate every aspect of real life flying. In terms of airspeed these are the airspeeds i remember as i haven't flown in about 8 years.
Indicated airspeed - As Widewing said measured by static pressure and ram air pitot tube pressure. Basically it's your aircraft calculating the difference between how fast your moving using the still air pressure as a reference. However since the static pressure changes with altitude it's not totally acurate. The geater the difference the higher your speed will read. Hence if you get a blocked static port in instrument conditions you will get wild inacurate readings. Pitot tubes even have a little heater in them called pitot heat to prevent icing.
True airspeed - Basically a true measurement of your aircraft's speed through the air, corrected for atmospheric temperature and pressure.
Calibrated airspeed - It's been awhile but i believe this was airspeed corrected from indicated airspeed corrected for atmospheric pressure.
Groundspeed - Your speed over the ground corrected for headwinds and tailwinds. Very important in navigation. I have been in cessnas flying and navigating and even though my indicated airspeed was reading say 100 -120 mph. When i calculated groundpeed with predicted winds aloft, i was only going 50 or 60 mph over the ground. lol
Than you have knots and mph and the differences there. A knot is longer than a statute mile so you may be going 250 knots. But that could correlate to say 300 mph.
If you think the Aces High planes don't match up to real life speeds take a plane up to altitude, look at a real life performance chart and you'll see it's right on the money. Be sure to read true airspeed. I have done extensive testing to check. A P-47N WILL do 470 tas at about 25k or so. A P-38 will do about 417 to 421 tas at 22 to 25k. Reading True airspeed.
If your're looking at indicated airspeed which is the reading off that little speed dial in your cockpit you're getting the wrong interpretation. So it's not Aces High it's you.
That's all i remember from passing that FAA exam and checkride in July of 1997 at the age of 19. It's been awhile but i think i'm pretty much right about it.
Cheers !
