Settle a bet: Mach speeds

When knowledgeable people speak of a vehicle going "X Mach" they are
referencing the speed of the vehicle compared to the speed of sound at
local conditions, right?

I ask because I've heard NASA folks mentioning that the Shuttle, at some
point in it's descent, is going Mach 25. I claim that means the vehicle
is going 25 times faster than Mach at that particular pressure and temp
where the Shuttle is, while someone else claims NASA means 25 times the
sea level value of Mach, even though the Shuttle is in the very upper
atmosphere at the time.

I know to discount what reporters say, but I'm referring to engineers
and their official spokesmen.

BTW, I understand the definition of Mach references local conditions.

--
Scott
--------
It's not a coincidence that pictures that would inflame the Americans to
war are not shown extensively while those pictures that undermine our
will to fight are shown ad naseum.

In article ,
"tscottme" writes:
When knowledgeable people speak of a vehicle going "X Mach" they are
referencing the speed of the vehicle compared to the speed of sound at
local conditions, right?

I ask because I've heard NASA folks mentioning that the Shuttle, at some
point in it's descent, is going Mach 25. I claim that means the vehicle
is going 25 times faster than Mach at that particular pressure and temp
where the Shuttle is, while someone else claims NASA means 25 times the
sea level value of Mach, even though the Shuttle is in the very upper
atmosphere at the time.

Upper atmosphere conditions vary quite a bit. The upper atmosphere
absorbs quite a bit of Solar Radiation, and gets relatively warm in
the process. So - the speed associated with Mach 1 varies.
To keep things in the FLight Control System (and the Public Releations
Office) as uncomplicated as possible, but still accurate enough, NASA
uses a sylized value of 1,000 ft/sec as Mach 1 at the very high (Peak
Heating Region) altitudes. The true value for the speed of sound
wanders back and forth across 1,000 ft/sec at those heights, but not
by much.
The Speed of Sound at Sea Leve, on a Standard (29.92"Hg Pressure, 59
Deg F - 1013 mBar/15C) is about 1115 ft/sec.

So, while the number is a little bit arbitrary, it's still related to
local conditions, and not Sea Level conditions.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

thanks Peter

NASA
uses a sylized value of 1,000 ft/sec as Mach 1 at the very high (Peak
Heating Region) altitudes.

This is why I stay faithful to this newsgroup despite all the insane
postings during election years. You never know when you're going to
come across some wonderful, useless bit of information like this.

I wish the people in the local cocktail circuit were more tuned in to
air & space. Then I could ambush somebody with this factoid.

Thank you, Pete!

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

NASA uses a sylized value of 1,000 ft/sec as Mach 1 at the very high (Peak
Heating Region) altitudes.

I wish the people in the local cocktail circuit were more tuned in to
air & space. Then I could ambush somebody with this factoid.

all the best -- Dan Ford

Well, Dan you just have to wait till someone says, "Boy, we've been
having some hot weather recently!"

Whereupon you respond, "Speaking of 'hot,' did you know that at the
Peak Heating Region.....

vince norris

I think that value should be 100 ft/sec. Mach one is about 600 Knots = 1
NM/Min. One NM = 6,000'. Divide 6,000 by 60 (seconds in a minute) and you
get 100, not 1,000.

--

B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"vincent p. norris" wrote in message
...

NASA uses a sylized value of 1,000 ft/sec as Mach 1 at the very high
(Peak
Heating Region) altitudes.

I wish the people in the local cocktail circuit were more tuned in to
air & space. Then I could ambush somebody with this factoid.

all the best -- Dan Ford

Well, Dan you just have to wait till someone says, "Boy, we've been
having some hot weather recently!"

Whereupon you respond, "Speaking of 'hot,' did you know that at the
Peak Heating Region.....

vince norris

1083 fps @ 59F, Sea Level, hypothetically dry atmosphere. STP, Standard
Temperature & Pressure. In std water, about 4800 fps. Al


"Darrell" wrote in message
news:M7Mqc.31369$Md.30236@lakeread05...
I think that value should be 100 ft/sec. Mach one is about 600 Knots = 1
NM/Min. One NM = 6,000'. Divide 6,000 by 60 (seconds in a minute) and
you
get 100, not 1,000.

--

B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"vincent p. norris" wrote in message
...

NASA uses a sylized value of 1,000 ft/sec as Mach 1 at the very high
(Peak
Heating Region) altitudes.

I wish the people in the local cocktail circuit were more tuned in to
air & space. Then I could ambush somebody with this factoid.

all the best -- Dan Ford

Well, Dan you just have to wait till someone says, "Boy, we've been
having some hot weather recently!"

Whereupon you respond, "Speaking of 'hot,' did you know that at the
Peak Heating Region.....

vince norris

In message M7Mqc.31369$Md.30236@lakeread05 - "Darrell"
writes:

I think that value should be 100 ft/sec. Mach one is about 600 Knots = 1
NM/Min. One NM = 6,000'. Divide 6,000 by 60 (seconds in a minute) and you
get 100, not 1,000.


I think you made a mistake at the very beginning:

600 knots = 600 MN/Hour = 600 NM/3600 Sec = 1/6 NM/Sec = 6000/6 ft/Sec =
= 1000 ft/Sec.

BTW, I think at sea level Mach 1 is around 660 Knots (at some "average"
temperature).

HTH,
************************************************** ****************************
* Arie Kazachin, Israel, e-mail: *
************************************************** ****************************
NOTE: before replying, leave only letters in my domain-name. Sorry, SPAM trap.
___
.__/ |
| O /
_/ /
| | I HAVE NOWHERE ELSE TO GO !!!
| |
| | |
| | /O\
| _ \_______[|(.)|]_______/
| * / \ o ++ O ++ o
| | |
| |
\ \_)
\ |
\ |
\ |
\ |
\ |
\ |
\ |
\_|

In article M7Mqc.31369$Md.30236@lakeread05,
"Darrell" writes:
I think that value should be 100 ft/sec. Mach one is about 600 Knots = 1
NM/Min. One NM = 6,000'. Divide 6,000 by 60 (seconds in a minute) and you
get 100, not 1,000.


Darryl, It's a good thing they had somebody behind you with the map

600 Kts is 10 Nautical Miles/minute, not 1.

BTW, you'd probably know this: Is theere any truth to the story that
a B-58 got itself into some manner of perdicament up over Alaska, near
one of the airbases. (For the same of Argument, I'll say Eielson, but
I don't know) The Pilot was busy trying to keep teh airplane flying,
and things were kinda touchy. While things were gyrating, the Nav
tried calling the Pilot & DSO, and for some reason (Either they were
busy trying to save the airplane, or the ICM wasn't working too well)
didn't answer. The Nav got nervous & punched out, right near one of
the Base Rescue helicopters, which scooped him up & ran for home.
In the meantime, the Pilot got things under control, & managed to get
it on the ground at this Alaskan base. As he clumb down teh ladder,
he was met by the irate Nav, who was screaming at him "Why didn't you
tell me where we were! I'm teh Navigator, dammit, and I have a right
to know!"


--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

"Al Gerharter" wrote in message ws.com...
1083 fps @ 59F, Sea Level, hypothetically dry atmosphere. STP, Standard
Temperature & Pressure. In std water, about 4800 fps. Al

SNIP
For quick and dirty (in one's head) cruise calculations I always used
1.0 Mach = 600 kts. (It's closer to 610 at -57F) but that let me, for
example, say .8M was 8 miles a minute. On the deck, about 670 (11
m/min). That and using fuel flow per minute (3000pph - 50ppm) gave me
rough figures. Of course, if things looked tight, then I used the
whiz-wheel. BTW, on the deck 760 mph is close to .1M (STP), so when
your car is showing 76 mph, you're buzzing along at about .1M. (For
interstate travel, 75 mph is 12.5 miles in 10 minutes . . . we just
completed about 6000 miles of driving where I used this sort of mental
T=D/R to predict ETAs thus boggling my better half. Same sort of calcs
can be used ina light plane such as C152 . . . 6gph = 1 gal in 10 min,
90KTS = 1.5 nm/min; 120(tailwind)=2 nm/min. As above, use the
calculator if things look tight. (If they do you've screwed up.)
Walt BJ