Blackbird
Topic Author
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KEAS, Mach Number And Altitude

Fri Sep 19, 2008 4:01 am

I'm wondering if anybody could help answer these two questions...

1.) What mach number would you be traveling at, if at an altitude of 165,000 feet if you had an indicated airspeed of...
- 390 kts?
- 450 kts?
- 585 kts?
- 650 kts?
- 750 kts?
- 900 kts?

2.) What mach number would you be traveling at, if at an altitude of 191,000 feet if you had an indicated airspeed of...
- 390 kts?
- 450 kts?
- 585 kts?
- 650 kts?
- 750 kts?
- 900 kts?


Blackbird
 
rwessel
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 4:38 am

Where on earth do you come up with these questions? And did you even try looking for an answer yourself?

Here's a nice online calculator that will give you all the numbers you want:

http://www.aerospaceweb.org/design/scripts/atmosphere/
 
pilotntrng
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 4:48 am

Any Astronauts in the forum?
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Mir
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 4:21 pm



Quoting Blackbird (Thread starter):
What mach number would you be traveling at, if at an altitude of 165,000 feet if you had an indicated airspeed of...



Quoting Blackbird (Thread starter):
What mach number would you be traveling at, if at an altitude of 191,000 feet if you had an indicated airspeed of...

In both cases, not enough information to answer the question.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
Illini_152
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 4:54 pm

A big one.

BTW- that calculator is wrong. 440 KTAS at FL410 and -56C is NOT .891 Mach, and .780 Mach at FL360 at -56C is considerably faster than 385 KTAS.
Happy contrails - I support B747Skipper and Jetguy
 
BAE146QT
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 4:58 pm



Quoting Rwessel (Reply 1):
Here's a nice online calculator that will give you all the numbers you want:

That's fantastic - I've had almost as much fun playing with that as the "What would the damage be if you dropped a nuclear weapon of yield x over location y" calculator!

I tried 191,000ft @ 900ktas and got a figure of 19.6kcas. The sort of figure you might see in a Piper Cub with a headwind, but in a black-project spybird! Marvellous.
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Blackbird
Topic Author
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 7:30 pm

I don't know if this calculator is entirely accurate as other members have made comments about errors...

Blackbird
 
Mir
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 10:47 pm



Quoting BAe146QT (Reply 5):
I tried 191,000ft @ 900ktas and got a figure of 19.6kcas. The sort of figure you might see in a Piper Cub with a headwind, but in a black-project spybird! Marvellous.

It may not be exact, but I wouldn't be surprised if that were close. CAS goes down with altitude.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
Starglider
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 11:16 pm



Quoting BAe146QT (Reply 5):
I tried 191,000ft @ 900ktas and got a figure of 19.6kcas.

Good, then a yaw string will suffice as an airspeed indicator me thinks. Comes in handy too if you encounter any cross wind up there . . . .


Starglider
 
BAE146QT
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RE: KEAS, Mach Number And Altitude

Fri Sep 19, 2008 11:44 pm



Quoting Mir (Reply 7):
It may not be exact, but I wouldn't be surprised if that were close. CAS goes down with altitude.

Wait - It wasn't me criticising it for lack of accuracy and I understand how CAS fluctuates. I was just having fun with it.

Quoting Starglider (Reply 8):
Good, then a yaw string will suffice as an airspeed indicator me thinks.

It could also be one of the few time you could measure your speed with a whistle. You could hold it out the window and see how fast you're going by the pitch of the noise it made!
Todos mis dominós son totalmente pegajosos
 
Blackbird
Topic Author
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RE: KEAS, Mach Number And Altitude

Sat Sep 20, 2008 12:53 am

From what I remember, the X-15 at high mach numbers produced enough lift with it's fuselage alone to support the whole aircraft even at fairly high altitudes.

This sounds like a tricky question, so I'm not sure how to ask it -- basically at what mach number, or at what altitudes, or what combination of mach number and altitude could the plane basically fly simply on the lift produced by it's fuselage and chines?


Blackbird
 
Mir
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Joined: Mon Jan 05, 2004 3:55 am

RE: KEAS, Mach Number And Altitude

Sat Sep 20, 2008 1:34 am



Quoting BAe146QT (Reply 9):
I was just having fun with it.

Then I interpreted your post entirely incorrectly, and I apologize.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
BAE146QT
Posts: 981
Joined: Sun Sep 24, 2006 4:58 am

RE: KEAS, Mach Number And Altitude

Sat Sep 20, 2008 2:18 am



Quoting Mir (Reply 11):
Then I interpreted your post entirely incorrectly, and I apologize.

That's okay - no problem!
Todos mis dominós son totalmente pegajosos
 
tdscanuck
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RE: KEAS, Mach Number And Altitude

Sat Sep 20, 2008 2:24 am



Quoting Blackbird (Reply 10):
This sounds like a tricky question, so I'm not sure how to ask it -- basically at what mach number, or at what altitudes, or what combination of mach number and altitude could the plane basically fly simply on the lift produced by it's fuselage and chines?

Any altitude, and essentially any mach number, for the right combination of fuselage shape, engine, and weight.

Tom.
 
Starglider
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Joined: Sun Oct 01, 2006 12:19 am

RE: KEAS, Mach Number And Altitude

Sat Sep 20, 2008 7:42 am



Quoting BAe146QT (Reply 9):
It could also be one of the few time you could measure your speed with a whistle. You could hold it out the window and see how fast you're going by the pitch of the noise it made!

LOL, it would whistle in the airflow alright, but would there be enough (static) air between you and the whistle to hear it?


Starglider
 
Blackbird
Topic Author
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RE: KEAS, Mach Number And Altitude

Sat Sep 20, 2008 3:41 pm

Tom,

I'm talking about the X-15 fuselage-shape... and at the various weights the X-15 operates at (34,000 to 35,000 empty IIRC)


Starglider,

If I recall, the higher the mach-number, the higher the pitch of the airflow right? Because the sound of wind-noise shortly after takeoff is lower in pitch than when flying at high-subsonic speed, and supersonic airflow is higher in pitch than subsonic...


Blackbird
 
tdscanuck
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RE: KEAS, Mach Number And Altitude

Mon Sep 22, 2008 6:19 am



Quoting Blackbird (Reply 15):
I'm talking about the X-15 fuselage-shape... and at the various weights the X-15 operates at (34,000 to 35,000 empty IIRC)

I don't know enough about the X-15 aerodynamics to answer this, but you can figure out a Cl curve for any shape, not just airfoils. So it's a question of how much angle of attach can the fuselage take before stalling, what's the slope of the lift curve (can't use 2-pi here, the shape is too far off), and how fast are you going (and how high you are). Just like with a normal jet, you could trade angle of attack against airspeed to get the same overall lift.

Tom.
 
Blackbird
Topic Author
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RE: KEAS, Mach Number And Altitude

Mon Sep 22, 2008 5:28 pm

Tom,

http://membres.lycos.fr/wings2/3vues/x15_3v.jpg


Wingsweep is 20-degrees, 22-feet in span, area 200-square feet (I can't seem to find the thickness to chord ratio), airplane is shaped like a big missile with a semi-blunt nose and thick highly-swept chines.

Weight is 34,000 pounds fully loaded and 14,600 empty...

Now I'm not sure if you can do anything with that...


Blackbird
 
rwessel
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RE: KEAS, Mach Number And Altitude

Mon Sep 22, 2008 6:45 pm



Quoting Illini_152 (Reply 4):
BTW- that calculator is wrong. 440 KTAS at FL410 and -56C is NOT .891 Mach, and .780 Mach at FL360 at -56C is considerably faster than 385 KTAS.

For -56C, did you enter -56 or zero? The field is a differential from standard conditions, not the actual temperature. IOW, assuming -56C at standard conditions at 41kft, another -56C would be an actual temperature of -112C.
 
tdscanuck
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Joined: Wed Jan 11, 2006 7:25 am

RE: KEAS, Mach Number And Altitude

Tue Sep 23, 2008 12:51 am



Quoting Blackbird (Reply 17):
Now I'm not sure if you can do anything with that...

Not really. Not that it can't be done, just that I can't do it. This thing is so far from being a nice thin supersonic airfoil that I don't think you can do it analytically. You'd either need to model it in 3D and run a CFD code on it (easily done with the right software, but I don't have the right software), or model it in a wind tunnel (and, much as I'd like one, I don't have a supersonic wind tunnel).

Tom.

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