1. Member
Join Date
Apr 2005
Location
Odense, Denmark.
Posts
168

## Airspeed

Hello everyone

I am new at this, so one basic question:

I hear that most planes are flying at olmost 1000 kilometres per hour. I can only get mine up to aorund 350 KIAS (e.g. Boeing 747). And whenever I get to around 33000 ft, I can't get any higher. 350 KIAS is not very fast is it?

I've read some of your replies, and you all talk about something called FLXXX, e.g. FL250. What is that.

Please respond, and remember that I am new at this.

Thank you very much - Kenneth

2. Junior Member
Join Date
Mar 2005
Posts
29

## RE: Airspeed

This is because your airspeed is indicated and will not read you true speed through the air. Because airspeed measures the pressure of air being forced in to the pitot tube and then compares it to the pressure of the air in the static ports it will only read correctly at sea level.

This is because as your altitude increases the air pressure decrease which affects the pressure of the air in the pitot tube causing what is known as density error.

350 knots indicated at 33000ft is roughtly equal to 595 knots true airspeed or 1101.94 km/h. So yoiu are flying at the speed you where told.

To work out your true airspeed find 2% of your indicated airspeed times it by your altitude dropping the last 3 zeroes. E.g 35000 = 35. Then add it to your original airspeed.

E.G. 2% of 350 = 7

7 times 35 = 245

350 + 254 + 595

Also FLxxx means Flight Level xxx e.g FL250 is Flight Level 250. A flight level is your altitude using the standard pressure of 1013hectopascals or 29.92 inches of mercury above the transition altitude. This varies from country to country but in FS it is 18000ft which is also used in the U.S. Pilots and Controllers use Flight Levels simply because it makes their lives easier by not having to transfer the correct altimeter setting and also means all aircraft are operating on the same altimeter setting above a certain altitude which ensures correct seperation between them.

Hope that helped :-)

3. Senior Member
Join Date
May 2000
Posts
1,559

## RE: Airspeed

Hint:- Check the learning centre on how airspeed indicators work. Also check true airspeed and ground speed. 1000 km per hour is probably still a bit fast for commercial jets.Remember that air craft speeds are measured mainly in knots. A knot is 1.1 statute miles, and KIAS is knots indicated air speed not kilometers.
Air speed indicators are not that accurate with regard to true airspeed and you will find that generally, as you increase altitude, TAS and ground speed will increase.
Speed is also affected by tailwinds, cross winds and head winds.
Hope this helps.
Ron

4. ## RE: Airspeed

That "2% rule" may give you a ROUGH approximation, but will rarely be accurate, since it doesn't take into account all the variables in the real situation (temperature, lapse rate, etc.). Still, it's somewhat useful to give you a ball-park idea of your speed.

Also, to clarify about flight levels, at the transition altitude (18,000 feet in FS and in the continental U.S.), when climbing you change your altimeter setting to 29.92" Hg (or 1013 millibars). When descending through the transition altitude, you set your altimeter to the correct local altimeter setting, as obtained from ATC (or hitting the "B" key in FS).

Local altimeter settings are of limited utility at higher altitudes, and the 18,000 foot changeover in the U.S. ensures that you will remain clear of the 14,000+ foot mountains in the highest of the continental mountain ranges.

5. Member
Join Date
Apr 2005
Location
Odense, Denmark.
Posts
168

## RE: Airspeed

thank you for taking the time to reply. It really did help me a lot. Nice to speak with enthusiasts instead of looking through the endless manuals

6. Member
Join Date
Apr 2005
Location
Odense, Denmark.
Posts
168

## RE: Airspeed

I started FS2004 and it worked!!

BUT... I always use SHIFT + Z so I can see my airspeed in the windown, since I always fly SPOT PLANE. that title only shows Indicated Airspeed.

Can I change it to show true airspeed? I tried to change it in the realism settings, but SHIFT + Z still only shows indicated....

7. ## RE: Airspeed

Speed is also affected by tailwinds, cross winds and head winds.
Groundspeed is so affected, but airspeed, whether true or indicated, is not affected by winds.

Airspeed indicators are just pressure gauges calibrated to read proper airspeed at sea level under standard conditions: 29.92"Hg, 59º F, 0% humidity. Any variation from those conditions affects the airspeed reading, and accuracy is lost.

But IAS is fairly good as a substitute for an angle of attack indication, under most conditions, and gives a good idea of how close you are to the stall, what your best climb and glide speeds are, etc., since they also vary with pressure changes, and the wing (and prop) see the same pressure changes that the airspeed indicator sees.

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