Topic Author
Posts: 365
Joined: Sat Aug 27, 2005 11:14 am

Some Thing About Numbers

Sat Sep 10, 2005 1:57 am

I know that one knot is 1.15mph(that could be wrong). Dose anyone know how to covert mach in to knots or what ever.
"Remember, Remember the 5th of November" from V for Vendetta
Posts: 834
Joined: Tue Feb 08, 2005 6:56 am

RE: Some Thing About Numbers

Sat Sep 10, 2005 2:10 am

Quoting Lastordu (Thread starter):
Dose anyone know how to covert mach in to knots or what ever.

Mach refers to the speed of sound, the speed of sound depends on air density and so varies with altitude. I'm sure someone can put this down a lot better though  Smile
If God had wanted men to fly he would have given them more money...
User avatar
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

RE: Some Thing About Numbers

Sat Sep 10, 2005 2:14 am

First you need to calculate the speed of sound, a. This is proportional to ambient temperature (OAT):

a = SQRT( OAT * 287 * 1.4) m/s (where OAT is in deg K)

Convert this speed into whatever units your true airspeed is in (mph, knots, etc.). Note this must be true airspeed, not indicated.

Mach number = TAS/a

BTW 1.15 is close enough for practical purposes to convert mph to knots.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: Some Thing About Numbers

Sat Sep 10, 2005 2:50 am

Try this.

757 Most beautiful airliner in the sky!
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: Some Thing About Numbers

Sat Sep 10, 2005 3:37 am

There is a much simpler way, valid for subsonic aircraft, that I still use to check my instruments, as it is easily done mentally.

To get a true airspeed (in knots) from a mach number, take as basis a temperature of -35 degrees celsius.At that temperature, the airspeed is exactly equal to the Mach number x 600. Then add or substract 1 kt per degree, rerspectively above or below your -35° basis.
As our mach reading are presented with three digits after the decimal, I just multiply that figure by .6.

Example :Mach .845 and OAT -45° c.
.845 x.6 = 507 kts, from which I substract 10 kts, as -45° c is ten degrees colder than my -35° c basis.

Result : TAS = 497 kts.

It's surprisingly accurate.
Contrail designer

Who is online

Users browsing this forum: No registered users and 16 guests

Popular Searches On

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos