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 KEAS, Mach Number And Altitude
 Blackbird From , joined Dec 1969, posts, RR: Posted Thu Sep 18 2008 21:01:29 UTC (7 years 8 months 1 week 3 days 20 hours ago) and read 8903 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
 Rwessel From United States of America, joined Jan 2007, 2740 posts, RR: 2 Reply 1, posted Thu Sep 18 2008 21:38:09 UTC (7 years 8 months 1 week 3 days 19 hours ago) and read 8899 times:

 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 From United States of America, joined Dec 2003, 897 posts, RR: 3 Reply 2, posted Thu Sep 18 2008 21:48:48 UTC (7 years 8 months 1 week 3 days 19 hours ago) and read 8896 times:

 Any Astronauts in the forum?
 Booooo Lois, Yaaaa Beer!!!
 Mir From United States of America, joined Jan 2004, 22854 posts, RR: 53 Reply 3, posted Fri Sep 19 2008 09:21:41 UTC (7 years 8 months 1 week 3 days 8 hours ago) and read 8841 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
 Illini_152 From United States of America, joined Jan 2001, 1000 posts, RR: 2 Reply 4, posted Fri Sep 19 2008 09:54:33 UTC (7 years 8 months 1 week 3 days 7 hours ago) and read 8837 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
 BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 5, posted Fri Sep 19 2008 09:58:38 UTC (7 years 8 months 1 week 3 days 7 hours ago) and read 8837 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 dominÃ³s son totalmente pegajosos
 Blackbird From , joined Dec 1969, posts, RR: Reply 6, posted Fri Sep 19 2008 12:30:07 UTC (7 years 8 months 1 week 3 days 4 hours ago) and read 8825 times:

 I don't know if this calculator is entirely accurate as other members have made comments about errors... Blackbird
 Mir From United States of America, joined Jan 2004, 22854 posts, RR: 53 Reply 7, posted Fri Sep 19 2008 15:47:32 UTC (7 years 8 months 1 week 3 days 1 hour ago) and read 8806 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
 Starglider From Netherlands, joined Sep 2006, 690 posts, RR: 43 Reply 8, posted Fri Sep 19 2008 16:16:25 UTC (7 years 8 months 1 week 3 days 1 hour ago) and read 8800 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

 BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 9, posted Fri Sep 19 2008 16:44:52 UTC (7 years 8 months 1 week 3 days ago) and read 8796 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 dominÃ³s son totalmente pegajosos
 Blackbird From , joined Dec 1969, posts, RR: Reply 10, posted Fri Sep 19 2008 17:53:33 UTC (7 years 8 months 1 week 2 days 23 hours ago) and read 8789 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
 Mir From United States of America, joined Jan 2004, 22854 posts, RR: 53 Reply 11, posted Fri Sep 19 2008 18:34:44 UTC (7 years 8 months 1 week 2 days 22 hours ago) and read 8781 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
 BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 12, posted Fri Sep 19 2008 19:18:41 UTC (7 years 8 months 1 week 2 days 22 hours ago) and read 8774 times:

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

That's okay - no problem!

 Todos mis dominÃ³s son totalmente pegajosos
 Tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78 Reply 13, posted Fri Sep 19 2008 19:24:05 UTC (7 years 8 months 1 week 2 days 22 hours ago) and read 8768 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.

 Starglider From Netherlands, joined Sep 2006, 690 posts, RR: 43 Reply 14, posted Sat Sep 20 2008 00:42:04 UTC (7 years 8 months 1 week 2 days 16 hours ago) and read 8750 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

 Blackbird From , joined Dec 1969, posts, RR: Reply 15, posted Sat Sep 20 2008 08:41:21 UTC (7 years 8 months 1 week 2 days 8 hours ago) and read 8723 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
 Tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78 Reply 16, posted Sun Sep 21 2008 23:19:35 UTC (7 years 8 months 1 week 18 hours ago) and read 8652 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.

 Blackbird From , joined Dec 1969, posts, RR: Reply 17, posted Mon Sep 22 2008 10:28:55 UTC (7 years 8 months 1 week 6 hours ago) and read 8629 times:

 Tom, 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 From United States of America, joined Jan 2007, 2740 posts, RR: 2 Reply 18, posted Mon Sep 22 2008 11:45:33 UTC (7 years 8 months 1 week 5 hours ago) and read 8620 times:

 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 From Canada, joined Jan 2006, 12710 posts, RR: 78 Reply 19, posted Mon Sep 22 2008 17:51:54 UTC (7 years 8 months 6 days 23 hours ago) and read 8605 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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