1. iainwallace Guest

## Re: Didnt ask the right questions huh!

747-400 and has a cruise speed of
460kts I can only get 241kts at FL410.

What does the Mach number represent and how does it work in
regards to flying? The above mentioned 747-400 has a mach value of 0.9 which
means nothing to me.

Thanks Robin
Hi Robin
The Mach is the speed of sound ie mach 1 is about 600kts however at altitude
your airspeed indicator becomes a little inacurate due to the very thin air. at
sea level this is at average 1013hpa droping 2hpa every 1000ft so at 40000ft
you have a air pressure of 933hpa. So it shows about half of true airspeed at
40000ft.

The 747 400 has a crise of M0.84 and a max altitude of 45100ft.
when you are climbing say at 310kts watch the Mach value (this should be the
little window on the asi) when it reaches M0.76 select that speed and continue
to climb and at the cruise you may select M0.84 and continue with that.
when decending when your desiged airspeed ie 290kts then select back to
ias(indicated air speed)

hope this helps

Iain

2. alastairmonk Guest

## Re: Didnt ask the right questions huh!

Well since the last post was unanswered I'm going to ask some more questions.

1. How does one increase the crusing speed of an aircraft? I am using FSNav4.4
and made my flight plan using it the A/C is a 747-400 and has a cruise speed of
460kts I can only get 241kts at FL410.

2. Why do the aircraft on takeoff roll begin to rotate early at around 50kts?
I have to hold the nose down until at least 115 to 125 kts.

3. I have Chuck Domes program for overspeed adjusting, and I am wondering about
the Mach number. What does the Mach number represent and how does it work in
regards to flying? The above mentioned 747-400 has a mach value of 0.9 which
means nothing to me.

Thanks Robin
Hi Robin,

The 241kts you see is the Indicated rather than the True Airspeed. The formula
for converting between the two is as follows:

TAS=((IASx2%)x(Alt/1000))+IAS

Thus you have ((241x0.02)x41)+241 = 438.6

As the 747-400 cruises at around 490kts, you're in the right ballpark.

Cheers,

Alastair

3. iainwallace Guest

## Re: Didnt ask the right questions huh!

Well since the last post was unanswered I'm going to ask some more questions.

1. How does one increase the crusing speed of an aircraft? I am using FSNav4.4
and made my flight plan using it the A/C is a 747-400 and has a cruise speed of
460kts I can only get 241kts at FL410.

2. Why do the aircraft on takeoff roll begin to rotate early at around 50kts?
I have to hold the nose down until at least 115 to 125 kts.

3. I have Chuck Domes program for overspeed adjusting, and I am wondering about
the Mach number. What does the Mach number represent and how does it work in
regards to flying? The above mentioned 747-400 has a mach value of 0.9 which
means nothing to me.

Thanks Robin
Hi Robin,

The 241kts you see is the Indicated rather than the True Airspeed. The formula
for converting between the two is as follows:

TAS=((IASx2%)x(Alt/1000))+IAS

Thus you have ((241x0.02)x41)+241 = 438.6

As the 747-400 cruises at around 490kts, you're in the right ballpark.

Cheers,

Alastair

Hi Robin
Alastair's answer is a lot better than mine as I gave some incorrect info.
the drop in hPa is 1 hectopascal for each 30 ft. Its temp that drops 1 degree
every 500ft

Iain

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