Cruise speed

[EHM-2404 Jigishu]

In the climbing and descending graphs are the speeds IAS. If not what is it then? Is there anyway to convert that speed to IAS?

Also in the fleet page (e.g. http://www.euroharmony.com/site/fleet_docs/version2/f_b1900.html) is the cruise speed IAS?

Can anyone explain the different types of speed?

Which speed is shown in my aircraft gauges then?

Thanks for your help

[EHM-1001 Robert]

Hello Jigishu !

We are talking about 3 kind of speeds:
- IAS: indicated airspeed
- TAS: true airspeed
- GS: ground speed

1. IAS is measured on the base of current air pressure, so it is changing according to the pressure. As you climb higher at a constant speed IAS is decreasing slowly. A plane flying with the same absolute spped at ground level at 600 kts, it is flying with some 300 KIAS at 30000 feet. IAS is not an absolute speed, but it came from the traditional structure of early gauges. IAS is also used to check your stall speed. For example an airplane stalls at 180 kts near ground, will also stall at 180 KIAS at high flight level... although it is flying with a 500 kts absolute speed at so high.

2. TAS is the relative air speed. It is regardless pressure and flight level, but it always contain wind components too, therefore not real if seen from the ground. Your aircraft "feels" it is the true airspeed as the airplane moves in the air mass. Because it is relative to the winds we do not really use it.

3. GS is the speed you can see relative from the ground. We can calculate the airplane flying time and schedule according to GS. GS equals TAS if wind is zero, and all 3 are equal on the ground with no wind.

You can see several forms, like "KIAS" (for IAS) or "kts GS" (for GS) or simply "kts". But you always need to know which system it is mentioned. On the fleet pages speed data are all GS. Although it is mixed in charts... the aim was to draw speeds in IAS, but it seems it is true only for jets. For turboprops the charts are rather show GS. Sorry for inconveniences.

Although you may see there are weaker/stronger airplanes that can fly slower/faster according to those graphs. You will see IAS on your gauges, but if you turn on your GPS (or luckily it is shown in some advanced panel) you can read GS there.

Also the graphs are there just for early help flying those planes, so novice pilots can avoid many confusions and crashes. Those data are not written in stone, you can fly as you wis, as long as the aircraft is capable to do that.

[EHM-2155 Mariano]

Originally posted by EHM-1001 Robert

Also the graphs are there just for early help flying those planes, so novice pilots can avoid many confusions and crashes. Those data are not written in stone, you can fly as you wis, as long as the aircraft is capable to do that.

Thats very important to mention... If you look at the graph:



It says "Class 1 graph"... But you might have to fly the Beech and the Sukhoi differently. For example the Sukhoi is almost twice as heavy as the Beech, but it doesnt have twice the power, so it wont climb as well

[EHM-1001 Robert]

Sure ! It is always a matter of weight, fuel amount, payload, climate, etc. Everything have effect on the plane, but I did not want to create a whole book with tons of charts for each airplanes. These are just average data.