Mach-Number to Airspeed Conversion Above 65,000 Feet [Archive]

PBL

5th Feb 2011, 15:02

Does anybody here have a mach-number to KEAS conversion table for altitudes above 65,000 feet, or a mathematical formula to help perform the conversion?

Jane, you seem to me to be plenty smart enough to figure it out for yourself without a program, but it does need some mathematical background, and I don't know how much you have.

First, a caveat. The speed of sound is functionally dependent only on the square root of temperature in Kelvin. So you need to know what the temperature is at a given altitude - and of course temperature can vary. So speed of sound is not a function of altitude per se and your program is not giving you that. It is probably assuming you are in an International Standard Atmosphere (ISA). Let's make that assumption below.

The speed of sound is sqrt(gamma x R x T), where gamma is the ratio of the specific heat of air at constant pressure to the specific heat of air at constant volume and is usually taken to be about 1.4; R is the gas constant, whose value for "ideal" air is 287 Joules per kilogramm per Kelvin in SI units (or 1716 ft-lb per slug per degree Rankine in English units); T is temperature in Kelvin (you'll have to apply a degrees-Rankine conversion factor in this formula if you are working in English units).

Now, you just need the distribution of temperature with altitude in the ISA. I'm sure there is a nice graph seomwhere on the WWW (it is a linear spline, which is a name for a number of straight line segments joined together at their ends), but I didn't find it. You can get it pointwise from the standard atmospheric calculator at Standard Atmosphere Calculator (http://www.digitaldutch.com/atmoscalc/), but then you can get the speed of sound from it, too, up to 86,000m (about 180,000 ft). To my mind, understanding the relationships of the quantities and using an arithmetic calculator is more fun than plugging numbers into some special computer program.

There is a very nice explanation of the standard atmosphere in Chapter 3 of John D. Anderson Jr.'s Introduction to Flight (6th Edition, McGraw-Hill 2008). This includes the definition of ISA temperature in terms of altitude, given in a graph in Figure 3.4. (Preceding that is a discussion of what "altitude" means!).

You may be wondering about gamma, the ratio of specific heats at constant pressure and volume. That is a matter of (what is called) elementary thermodynamics. Let me spare you the details here, although I seem to remember Pugilistic Animus was inspired to write it down on some other thread, which I forgot. The issue is dealt with quite nicely in Section 4.5 of Anderson. The speed of sound is discussed in Section 4.9.

I think you'll find Anderson quite helpful. If you don't have easy access to a copy, you might think of buying it. It is comprehensive, and Anderson has gone to a lot of trouble over the editions to make it so (it is over thirty years since the first edition). If you need to follow something from very first principles on, you can do it with Anderson. You'll need some facility in following reasoning using differential calculus - I don't know whether you have that.

PBL

Jane-DoH

5th Feb 2011, 20:32

PBL

The speed of sound is functionally dependent only on the square root of temperature in Kelvin. So you need to know what the temperature is at a given altitude - and of course temperature can vary. So speed of sound is not a function of altitude per se and your program is not giving you that. It is probably assuming you are in an International Standard Atmosphere (ISA). Let's make that assumption below.

Okay

The speed of sound is sqrt(gamma x R x T), where gamma is the ratio of the specific heat of air at constant pressure to the specific heat of air at constant volume and is usually taken to be about 1.4; R is the gas constant, whose value for "ideal" air is 287 Joules per kilogramm per Kelvin in SI units (or 1716 ft-lb per slug per degree Rankine in English units); T is temperature in Kelvin (you'll have to apply a degrees-Rankine conversion factor in this formula if you are working in English units).

I can work with Kelvin okay. Which units are you using for pressure?

Now, you just need the distribution of temperature with altitude in the ISA. I'm sure there is a nice graph seomwhere on the WWW (it is a linear spline, which is a name for a number of straight line segments joined together at their ends), but I didn't find it. You can get it pointwise from the standard atmospheric calculator at Standard Atmosphere Calculator (http://www.digitaldutch.com/atmoscalc/), but then you can get the speed of sound from it, too, up to 86,000m (about 180,000 ft). To my mind, understanding the relationships of the quantities and using an arithmetic calculator is more fun than plugging numbers into some special computer program.

Of course -- It's important to understand the concept as well as just the answers

There is a very nice explanation of the standard atmosphere in Chapter 3 of John D. Anderson Jr.'s Introduction to Flight (6th Edition, McGraw-Hill 2008). This includes the definition of ISA temperature in terms of altitude, given in a graph in Figure 3.4. (Preceding that is a discussion of what "altitude" means!).

That's a real expensive book...

There is a very nice explanation of the standard atmosphere in Chapter 3 of John D. Anderson Jr.'s Introduction to Flight (6th Edition, McGraw-Hill 2008). This includes the definition of ISA temperature in terms of altitude, given in a graph in Figure 3.4. (Preceding that is a discussion of what "altitude" means!).

My calculus skills are kind of rusty...

Checkboard

5th Feb 2011, 21:13

What on Earth are you intending on flying?? ;)

mm43

5th Feb 2011, 21:34

There's an ISA Chart to 70,000 feet at:-

ISA Chart (http://countjustonce.com/a330/isa-chart-div.html)

It is an adaption of stuff floating around on the web.

PBL

6th Feb 2011, 06:51

I can work with Kelvin okay. Which units are you using for pressure?

What a very odd question!

...John D. Anderson Jr.'s Introduction to Flight (6th Edition, McGraw-Hill 2008).
That's a real expensive book...

That depends on how much knowledge is worth to you. I think it's cheap.

My calculus skills are kind of rusty...

Rusty? Would you care to be more precise?

PBL

selfin

6th Feb 2011, 23:17

The International Standard Atmosphere and the 1976 US Standard Atmosphere agree up to 32 kilometres. The latter standard is included in the references to the Wikipedia entry on ISA. Working with altitudes greater than this will require taking account of changes to R (gas constant for air). At sufficiently high Mach numbers account may need to be taken of changes to gamma.

Use the Barre de Saint-Venant equation for Mach numbers below 1, and for Mach 1 and above use the Rayleigh supersonic equation. Both are derived in Anderson referenced by PBL above, and are elsewhere located on the Internet. Build your tables for Mach -v- CAS. While EAS is a physically meaningless quantity the step in determining it from TAS is straight forward.

The equations you'll need can be found in NACA Report 837. Aiken, William S, Jr. (1946.) NACA Report 837: Standard nomenclature for airspeeds with tables and charts for use in calculation of airspeed. Langley, VA. NACA UK Mirror report description page (http://naca.central.cranfield.ac.uk/report.php?NID=2451)

Jane-DoH

7th Feb 2011, 02:30

PBL

What a very odd question!

Well, one measurement for pressure is PSI, another is pascals. I'm just wondering which one should be used

That depends on how much knowledge is worth to you.

True enough

Rusty? Would you care to be more precise?

I haven't used them in a long time...

selfin

The International Standard Atmosphere and the 1976 US Standard Atmosphere agree up to 32 kilometres. The latter standard is included in the references to the Wikipedia entry on ISA. Working with altitudes greater than this will require taking account of changes to R (gas constant for air). At sufficiently high Mach numbers account may need to be taken of changes to gamma.

Okay, so just to make sure I have all these variables right
q = dynamic air pressure
R = gas constant for air
rho = ambient air density
gamma = ratio of specific heat at a constant pressure to specific heat at a constant volume

The equations you'll need can be found in NACA Report 837.

I'll have to give it a look. I'm not particularly an expert on greek characters, so I'll have to find the greek-alphabet for that purpose.

Brian Abraham

7th Feb 2011, 02:51

See Equivalent airspeed - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Equivalent_airspeed)

PBL

7th Feb 2011, 05:52

Well, one measurement for pressure is PSI, another is pascals. I'm just wondering which one should be used

Used, Jane? I didn't need to use either.

This looks to me very much as if you performed a keyword search on my reply. I grant you, the word "pressure" was in there.

Rusty? Would you care to be more precise?
I haven't used them in a long time...

So you think "calculus" is plural. Could be.....

The equations you'll need can be found in NACA Report 837.
I'll have to give it a look. I'm not particularly an expert on greek characters, so I'll have to find the greek-alphabet for that purpose.

Well, I think that clinches it for me. I thought I'd be able to get you if it were true, but it turns out you got yourself. You have done very, very well so far. You ask great questions, and it is a lot of fun thinking of the answers. Considering you are only a few years old, you are doing pretty well.

Do you by chance have a big date at the end of the month? Do we by any chance have a mutual friend called Eliza, whose Dad died almost three years ago now?

Credit, BTW, must go to mike-wsm, who guessed in mid-January. I couldn't believe anyone would go to the trouble of figuring out their way around PPRuNe syntactic tasks, but obviously one of your friends has done so.

PBL

Pugilistic Animus

7th Feb 2011, 17:41

the SR71:{...used a direct EAS indication for operations and many items such as spike position were in terms of EAS...

the POH has since been declassified...good stuff:ok:

mutt

7th Feb 2011, 17:52

the POH has since been declassified I got one on Ebay for about $50.....

Mutt

Pugilistic Animus

7th Feb 2011, 18:33

Mutt is this you?
R_SHozxzwqs

:p

we are all just grown up children after all :}

Jane-DoH

7th Feb 2011, 18:36

PBL

Used, Jane? I didn't need to use either.

What units do you use? I'm not just asking this stuff to be difficult

This looks to me very much as if you performed a keyword search on my reply. I grant you, the word "pressure" was in there.

The two units of pressure I could readily think of was PSI and pascals.

So you think "calculus" is plural. Could be.....

No. I said that my calculus skills were rusty -- skills are plural.

Well, I think that clinches it for me. I thought I'd be able to get you if it were true, but it turns out you got yourself. You have done very, very well so far. You ask great questions, and it is a lot of fun thinking of the answers. Considering you are only a few years old, you are doing pretty well.

My knowledge of the greek alphabet is limited because, I'm not fluent in Greek. Yes, some greek characters are covered in math class, but it's been quite awhile since I've taken a math-course.

I can tell you an alpha looks like an "a" drawn as if you were trying to make it look like a fish; beta as if it were a "B" drawn in some kind of calligraphy; a gamma looks like a "y"; a delta like a triangle; an epsilon like a curvy "E";

I know alpha looks like a fish, beta looks like a really fancy B, I can tell you that gamma looks like a y, Delta looks like a triangle, Epsilon like an "E"; a sigma like a jagged "E"; a Pi looks kind of like two "T's put together with the horizontal line up top kind of curvy; a chi like an "x
; a Mu like a backwards "u" with a curvy tail; an Omega looks kind of like two legs with a loop drawn to connect them.

That does cover a number of the characters, but I don't remember what a "rho" looked like and a number of the other greek characters.

LH2

7th Feb 2011, 19:18

Jane,

What units do you use? I'm not just asking this stuff to be difficult

I guess the answer is in the very first sentence of PBL's reply:

"The speed of sound is functionally dependent only on the square root of temperature in Kelvin." (my emphasis)

Your task is to determine the temperature (real or assumed, as befits your problem) for where you (hypothetical) aircraft is, then you call that 'T' and plug it into the formula that PBL gives you in his third paragraph.

Simple as that. Your real problem is not in calculating a Match number given an airspeed, your real problem is in finding the value for the local speed of sound. PBL goes on to suggest that you might deduce a nominal figure for that variable from tables available on the internet (and in books), which will give you an LSS (or the elements needed to calculate it) from an atmospheric model. Up until that point, pressure has nothing to do with what you're attempting to solve.

Jane-DoH

7th Feb 2011, 21:06

LH2,

To convert TAS into IAS you need to know the atmospheric pressure... that's why I asked what units of pressure you need.

FullWings

7th Feb 2011, 21:59

You're in a desert, walking along in the sand, when all of a sudden you look down...

Jane-DoH

8th Feb 2011, 03:05

FullWings

You're in a desert, walking along in the sand, when all of a sudden you look down...

What does this have to do with the topic?

PBL

8th Feb 2011, 05:37

Jane-DoH,

To convert TAS into IAS you need to know the atmospheric pressure... that's why I asked what units of pressure you need.

I could ask you, as you did to FullWings, who is as aware as I am:

What does this have to do with the topic?

If you want to carry on playing the game, I am willing because it's fun gradually finding out what you know and how, but you need to answer my questions if you want me to answer yours.

I think if you are behind on your competence with the greek alphabet, you are going to have a hard time dealing with airspeed and Mach, because all that is so dependent on the greek alphabet, as you remarked.

PBL

Jane-DoH

8th Feb 2011, 06:25

Okay, so you want me to be able to make sure that I can compute the mach-number figures based on air-temperature?

PBL

8th Feb 2011, 07:22

Jane,

no, I want you to answer my questions.

PBL

DERG

8th Feb 2011, 16:31

you single Jay?:hmm:

Turbine D

8th Feb 2011, 19:00

Jane,

To find the Greek Alphabet, Γοογλε ιτ !:cool:

CliveL

8th Feb 2011, 21:34

I posted this once, then pulled it because Jane Doh is almost certainly an anti-sciolist, but for those who are genuinely interested, the speed of sound expressed in EAS is independent of temperature. You only need to know pressure altitude and then multiply by Mach Number to get the flight EAS.

Values:
Press.Alt Speed of sound
65000 ft - 156.02 kts EAS
70000 ft - 138.35 kts EAS
75000 ft - 122.69 kts EAS
80000 ft - 108.8 kts EAS

Turbine D

8th Feb 2011, 22:04

CliveL

Thanks for your post, I was interested as to the correct answer.:ok:

John Farley

8th Feb 2011, 22:11

If that means does not read, consider and properly respond to what is sent to them then I agree.

Jane-DoH

8th Feb 2011, 23:47

PBL

sqrt(gamma x R x T)

Okay gamma is the ratio of specific heat at constant pressure vs ratio of specific heat at constant volume. What are the formulae for specific heat at constant pressure and specific heat at constant volume?

Turbine D

To find the Greek Alphabet, Γοογλε ιτ !:cool:

I've already went online to find it...

PBL

no, I want you to answer my questions.

Which questions? I explained what the reason I was asking about the units of pressure because I was trying to convert the TAS figures for mach (sea-level) into IAS readings at altitude.

CliveL

Jane Doh is almost certainly an anti-sciolist

Sciolist means an amateur, right?

You only need to know pressure altitude and then multiply by Mach Number to get the flight EAS.

Pressure altitude means the pressure at a given altitude?

CliveL

9th Feb 2011, 06:31

Sciolist means an amateur, right?Just look at the small green text at the bottom of the page!

Pressure altitude means the pressure at a given altitude? No - look it up

keith williams

9th Feb 2011, 09:01

You only need to know pressure altitude and then multiply by Mach Number to get the flight EAS.

Values:
Press.Alt Speed of sound
65000 ft - 156.02 kts EAS
70000 ft - 138.35 kts EAS
75000 ft - 122.69 kts EAS
80000 ft - 108.8 kts EAS

I'm probably being a bit thick this morning, but it looks like you have missed something out.

If I am reading you correctly you are saying that the EAS in the right hand column is the local speed of sound (Mach 1) at the pressure altitude in the left hand column.

How do we get from the pressure altitudes that you have quoted, to the EAS values by multiplying by Mach 1?

CliveL

9th Feb 2011, 09:43

If I am reading you correctly you are saying that the EAS in the right hand column is the local speed of sound (Mach 1) at the pressure altitude in the left hand column.

How do we get from the pressure altitudes that you have quoted, to the EAS values by multiplying by Mach 1? Yes, the RH column is the speed of sound at that pressure altitude.

I didn't say multiply by Mach 1, I said multiply by Mach Number; i.e. the EAS at say Mach 1.4 at 65000 ft would be 218.4 kts

Perhaps I should have written "you only need to know the pressure altitude to get the speed of sound in kts EAS and then multiply that by Mach Number to get the flight EAS"

CliveL

http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/statusicon/user_online.gif http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/report.gif (http://www.pprune.org/report.php?p=6233278) http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/reply_small.gif (http://www.pprune.org/newreply.php?do=newreply&p=6233278&noquote=1)

keith williams

9th Feb 2011, 12:36

Sorry Clive,

When I read you post I thought that you were saying "Multiply the pressure altitude by the mach number and you get the EAS at that mach number".

For one fleeting moment I thought that this was going to be one of those really magical moments like the day I was first introduced to Calulus all those decades ago.

Now I see that what you were really saying was "If you have a table of pressure altitudes against the EAS for local speed of sound, then just multiply this EAS by any given mach number and you will get the EAS for that mach number at that pressure altitude".

CliveL

9th Feb 2011, 14:29

Now I see that what you were really saying was "If you have a table of pressure altitudes against the EAS for local speed of sound, then just multiply this EAS by any given mach number and you will get the EAS for that mach number at that pressure altitude".

Not a problem!

Clive

Pugilistic Animus

12th Feb 2011, 19:55

tfbHMxnlbfI

:=

Jane-DoH

12th Feb 2011, 22:14

John Farley

I'm sorry that I didn't properly read your messages. I should have paid more attention.

BTW: In regards to the video that Pugilistic Animus showed, you're a very good narrator

Pugilistic Animus & John Farley

Fascinating video. I never knew the Harrier used reaction control systems

TEOTWAWKI

13th Feb 2011, 23:05

PBL, who on earth do you think would have any interest in building such an incredibly sophisticated system as Jane-Doh ... and come up with the idea to of all things test it on an aviation forum? I can see only one logical conclusion: Jane-Doh is Skynet!

Jane-DoH

14th Feb 2011, 00:56

TEOTWAKI

PBL, who on earth do you think would have any interest in building such an incredibly sophisticated system as Jane-Doh ... and come up with the idea to of all things test it on an aviation forum? I can see only one logical conclusion: Jane-Doh is Skynet!

Yeah, that's it :rolleyes:

Ex Cargo Clown

14th Feb 2011, 10:25

What are the formulae for specific heat at constant pressure and specific heat at constant volume?

You don't ask for much do you !

I'm not entirely sure what you mean by specific heat, are you attempting to apply pV=nRT to this or something else?

Jane-DoH

15th Feb 2011, 03:33

Ex Cargo Clown

I'm not entirely sure what you mean by specific heat, are you attempting to apply pV=nRT to this or something else?

Yes.

DERG

15th Feb 2011, 04:46

your my kinda women Jay....always asking questions...most don't ask..you single?

Brian Abraham

15th Feb 2011, 04:50

you single?Pointless question DERG, she's married to a keyboard.

DERG

15th Feb 2011, 11:24

you win some..sometimes:E

Ex Cargo Clown

15th Feb 2011, 14:58

I'm not a huge fan of thermodynamics, I hate physical chemistry.

you could quite easily use pV=nRT, the more accurate equation though would be the Van der Waal equation

(p+(n^2a/v^2)) * (v-nb)=nRT

you can easily find the a and b constants for air as you know the mole fractions, I'll help you out here, as I have the text in front of me with a nice table. a=1.3725 b=0.0372 and you can class air as having a molecular weight of 28.85 at those figures.

You can now plug your figures into the equation.

Jane-DoH

16th Feb 2011, 03:40

Ex-Cargo Clown

That formula provides the gamma figure?

Ex Cargo Clown

16th Feb 2011, 14:14

You can get the gamma value from the ratios, but you are still making assumptions. I don't know how many accurate temperature and pressure readings there are at 70,000ft.

I'd suggest you are looking at a gamma value of between 1.3-1.4, as soon as you get that high you can use pV=nRT a little better as the air is so "thin" there are less molecular collisions and so these are negated, but are still present.

You might want to email NASA, I'm sure they have some data on this. You can get up to 80,000 ft on here, temp there is 199K :eek: U.S Standard Atmosphere (http://www.engineeringtoolbox.com/standard-atmosphere-d_604.html)

Don't forget when you do your calculations to use only SI units, ie Pa, K etc

Jane-DoH

16th Feb 2011, 22:13

DERG

your my kinda women Jay....always asking questions...most don't ask..you single?

First of all, before we go any further my name isn't Jane or Jay -- it's Robyn. I did intend to register under that name but when I did, the e-mail message to activate the account never came. When I attempted to create another account, it wouldn't let me claiming that I already had an account (one that I couldn't activate). So, I then created an account called Jane-DoH, which was effectively a parody of Jane Doe pronounced as if Homer Simpson was saying it.

Secondly, yes I am single.

Ex Cargo Clown

You can get the gamma value from the ratios, but you are still making assumptions. I don't know how many accurate temperature and pressure readings there are at 70,000ft.

But that ratio covers specific heat at constant pressure vs specific heat at constant volume right?

Don't forget when you do your calculations to use only SI units, ie Pa, K etc

Thank you.

DERG

17th Feb 2011, 08:15

Robyn

Thanks for your reply. May I ask if you are a formal student of aviation?

Upper Air

17th Feb 2011, 09:08

Why not just calc Machno to get your TAS, then convert your TAS to EAS using your whizzwheel computor. . ?

The formula for Machnumber, as you know is (grab a calculator - its sssooooo easy)

the sqrt of 273 (+/- T) x 38.94

So stab in 273 add or subtract you outside temperatur (+/-T)
sq rt the result

then times it by 38.94 (you van prob do it by calculas too . . . but I really don`t wanna know, ok?)

then - you will have a number whic is you True Airspeed, ok?

Now, take this True Airspeed and using your metal or plastic flight computor you can calculate the EAS from the Tas.

Happy?

Jane-DoH

18th Feb 2011, 01:34

DERG

Thanks for your reply. May I ask if you are a formal student of aviation?

No, I'm just an aviation enthusiast. Still I've always been fascinated by how things work.

Upper Air

The formula for Machnumber, as you know is (grab a calculator - its sssooooo easy)

the sqrt of 273 (+/- T) x 38.94

So stab in 273 add or subtract you outside temperatur (+/-T)
sq rt the result

then times it by 38.94

So at 273 K, you get 643.3944 kts, correct?

DERG

18th Feb 2011, 07:21

I am a big fan of the USN. Do you like military aviation?

This link is a good read:
http://compass.seacadets.org/pdf/nrtc/fn/14104_ch6.pdf

Regards

Upper Air

19th Feb 2011, 09:43

So at 273 K, you get 643.3944 kts, correct?

Yes and that is TAS, just one more step and slide for EAS then.

But, after about 36,000 feet its -56.6*C

Concord flew backwards and forwards regularly at 70,000ft

mm43

20th Feb 2011, 07:57

Upper Air;

This may be getting pedantic, but when you start quoting the Speed of Sound as 643.3944 kts at standard sea level, something didn't look right.

Standard Sea Level conditions according to the ISA are:-

101.325kPa and 15°C / 288.15°K, and the accepted speed of sound is 661.4788kts / 340.2941m/sec. Just refer to the ISA Chart (http://countjustonce.com/a330/isa-chart-div.html) in Post #5.

It would appear that a digit or two got transposed in your "magic" multiplier and the standard temperature of 15°C got left behind in the calc.

√ 288.15 * 20.0468023 = 340.2941m/sec
or
√ 288.15 * 38.9678655 = 661.4788kts

So 38.97 seems closer for a memory number.

Jane-DoH

20th Feb 2011, 22:04

mm43

So 38.96 seems closer for a memory number.

No wonder my result didn't seem right. Off memory, Mach 1 ~ 660 kts.

DERG

21st Feb 2011, 07:07

Robyn...

Do you know how many decimal places the crew use when they enter the "numbers" into the flight computer?

Well I always round mine to 2 decimal places for general use, but I could imagine the third decimal place might make a difference on long flights.
In civil engineering we work to plus or minus 5mm over a 6000m distance, well we did when I was trained, but these days they user lasers and GPS stuff..so maybe even "tighter".

So the question is... how many decimal places are used when a crew inputs the data for mapping the flight?

Regards

p.s. the laser spelling came out like that when I entered the text..I mean LASER. done it again..why does it do that?

HazelNuts39

21st Feb 2011, 08:19

So at 273 K, you get 643.3944 kts, correct?
Correct, but ... the SLStd temperature is 15 °C or 288.15 K

regards,
HN39

john_tullamarine

21st Feb 2011, 11:04

the l@ser spelling came out like that when I entered the text..I mean l@ser. done it again..why does it do that?

The site has some background text checks for various reasons .. l-a-ser becoming l@ser is one of them. Hopefully no-one has a need to know as I would then have to dig deep to find out the specific reason.

mm43

21st Feb 2011, 17:32

Laser pinpoint accuracy in cutting steel is ...

Laser pinpoint accuracy when cutting steel .... , aah, looks like more to do with keyboard idiosyncrasies than anything else. The top line was pasted in from a text editor, and the next line was typed into the text-box. In fact the "L" was entered as "upper-case", but was also changed - to "lower-case".

Further investigation seems to confirm that laser is a reserved word in the program - as JT has already indicated.

Solution: Use a text editor.

chris weston

21st Feb 2011, 21:51

Sorry all, coming to this late.

pV=nRT is a longish wave length Clupea Harengus

Watch V - its m3

Trust me - I'm a chemist

Units of pressure?

Try N/m2 or Pa or kPa or mmHg or inches / feet of water or Bar or mBar or Atmospheres or psi etc ad nauseum

We use kPa mostly where 1 Bar/Atmosphere = 101.3 kPa

Mods will decide if this adds anything!

CW

Upper Air

22nd Feb 2011, 13:04

Jane-Doh was confirming Mach 1 at 273K - nobody was talking about ISA or AMSL! If you took the time to look at the previous text you would have seen this and Jane, yes you are right, that is the Local Speed of Sound (LSS) at 273K - and mm3 - it is 38.94 because the Captain says so.

Insulting words removed by UA.

bits deleted - we really don't need to be gratuitously insulting ? JT

HazelNuts39

22nd Feb 2011, 13:35

Obviously, Hazelnut 39 if you apply the ISA temp of 15*C then K will be plus 15 higher - duh. Sorry, you missed the point of my post, which was twofold: First to point out that Jane's sonic speed was for 273 K, not 288.15 K (hence the title: Confusion?), and second that the standard sealevel temperature is 15 °C per definition, not 15.2. Thought that would be obvious.

regards,
HN39

Jane-DoH

22nd Feb 2011, 23:29

DERG

Do you know how many decimal places the crew use when they enter the "numbers" into the flight computer?

Well I always round mine to 2 decimal places for general use, but I could imagine the third decimal place might make a difference on long flights.
In civil engineering we work to plus or minus 5mm over a 6000m distance, well we did when I was trained, but these days they user l@sers and GPS stuff..so maybe even "tighter".

So the question is... how many decimal places are used when a crew inputs the data for mapping the flight?

Two to three decimal places when mapping the flight depending on the length of the flight.

p.s. the l@ser spelling came out like that when I entered the text..I mean l@ser. done it again..why does it do that?

Well, I think you just think I'm a chatterbot so you are entering odd characters and text as well as switching the topic midway into civil engineering, using ambiguous measurements (m can be in meters or miles though in this case it's obviously meters), then switching back to the original topic in some bizarre attempt to "screw me up".

I'm not a robot. Sure, I can be odd, and be socially inept, kind of quirky sometimes, and take things a bit too literally but those things are all the product of having a pervasive developmental disorder such as asperger syndrome, high functioning autism or PDD NOS (which means you have a pervasive developmental disorder which does not neatly fit into any of the following). I've been diagnosed, at different times, over the past 14 years with one of the three (PDD NOS was the most common diagnosis that came up).

HazelNuts39

Correct, but ... the SLStd temperature is 15 °C or 288.15 K

So at 273 K, Mach 1 = 643.3944 kts, and at 288.15 K, is 661.4788 kts.

john tullamarine

The site has some background text checks for various reasons .. l-a-ser becoming l@ser is one of them. Hopefully no-one has a need to know as I would then have to dig deep to find out the specific reason.

That's a really weird quirk. I honestly just thought DERG thought I was a chatterbot and did that as some kind of "test". Still, I'm going to leave what I wrote to him anyway.

chris weston

We use kPa mostly where 1 Bar/Atmosphere = 101.3 kPa

Even though 1 atm and 1 bar are supposed to be 1 atmosphere, why does a bar translate out to 100 kPa, and an atm translate out to 101.3 kPa? (I checked the defintion of 1 bar to make sure it was the same as 1 atm)

BTW: As you have "second law" written as a title under your name, I assume you mean entropy. Here's something that's rather fascinating. Being that the total amount of energy in a closed system is zero, and gravity being negative potential energy, this actually means that given enough time every unit of positive energy which includes energy and matter, and every unit of negative energy will actually neutralize out to nothing (if our universe is a closed system, which I wouldn't be surprised if it is).