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KEAS, Mach Number And Altitude  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (5 years 11 months 1 week 1 day 1 hour ago) and read 6420 times:

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

19 replies: All unread, jump to last
 
User currently offlineRwessel From United States of America, joined Jan 2007, 2342 posts, RR: 2
Reply 1, posted (5 years 11 months 1 week 1 day ago) and read 6416 times:
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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/


User currently offlinePilotNTrng From United States of America, joined Dec 2003, 897 posts, RR: 3
Reply 2, posted (5 years 11 months 1 week 1 day ago) and read 6413 times:

Any Astronauts in the forum?


Booooo Lois, Yaaaa Beer!!!
User currently offlineMir From United States of America, joined Jan 2004, 21556 posts, RR: 55
Reply 3, posted (5 years 11 months 1 week 13 hours ago) and read 6358 times:



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
User currently offlineIllini_152 From United States of America, joined Jan 2001, 1000 posts, RR: 2
Reply 4, posted (5 years 11 months 1 week 12 hours ago) and read 6354 times:

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
User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 5, posted (5 years 11 months 1 week 12 hours ago) and read 6354 times:



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.



Todos mis dominós son totalmente pegajosos
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 6, posted (5 years 11 months 1 week 9 hours ago) and read 6342 times:

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

Blackbird


User currently offlineMir From United States of America, joined Jan 2004, 21556 posts, RR: 55
Reply 7, posted (5 years 11 months 1 week 6 hours ago) and read 6323 times:



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
User currently offlineStarglider From Netherlands, joined Sep 2006, 678 posts, RR: 44
Reply 8, posted (5 years 11 months 1 week 6 hours ago) and read 6317 times:



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


User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 9, posted (5 years 11 months 1 week 5 hours ago) and read 6313 times:



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
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 10, posted (5 years 11 months 1 week 4 hours ago) and read 6306 times:

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


User currently offlineMir From United States of America, joined Jan 2004, 21556 posts, RR: 55
Reply 11, posted (5 years 11 months 1 week 3 hours ago) and read 6298 times:



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
User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 12, posted (5 years 11 months 1 week 3 hours ago) and read 6291 times:



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
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (5 years 11 months 1 week 3 hours ago) and read 6285 times:



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.


User currently offlineStarglider From Netherlands, joined Sep 2006, 678 posts, RR: 44
Reply 14, posted (5 years 11 months 6 days 21 hours ago) and read 6267 times:



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


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 15, posted (5 years 11 months 6 days 13 hours ago) and read 6240 times:

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


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (5 years 11 months 4 days 23 hours ago) and read 6169 times:



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.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 17, posted (5 years 11 months 4 days 11 hours ago) and read 6146 times:

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


User currently offlineRwessel From United States of America, joined Jan 2007, 2342 posts, RR: 2
Reply 18, posted (5 years 11 months 4 days 10 hours ago) and read 6137 times:
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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.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (5 years 11 months 4 days 4 hours ago) and read 6122 times:



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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