Air Speed Conversions - IAS to TAS - convert.txt [1/1]
Trips
>
>The following table facilitates IAS to TAS, TAS to IAS
>conversions. Simply multiply IAS or divide TAS by the
>altitude factor to convert. This lets you compare data
>between games, or to real world data.
>
<table snipped>
A quick and dirty conversion is to add 50kts. to the indicated
for every 10K of altitude... not nearly as precise as the table
Jeff posted (thanks Jeff :), but close enough to the ballpark
for most purposes. I got that one from Flush Garden (anyone
remember Flush?), ex A-4 & SLUF driver, and the best damn AW
pilot I ever flew wing for.
Trips
Robin Kim
>jef...@cris.com (Jeffrey Dillman) wrote:
>>
>>The following table facilitates IAS to TAS, TAS to IAS
>>conversions. Simply multiply IAS or divide TAS by the
>>altitude factor to convert. This lets you compare data
>>between games, or to real world data.
>>
><table snipped>
>
>A quick and dirty conversion is to add 50kts. to the indicated
>for every 10K of altitude... not nearly as precise as the table
>Jeff posted (thanks Jeff :), but close enough to the ballpark
>for most purposes.
That's a good tip! For those who desire greater accuracy and are
willing to work for it, I've included below a table of information that
will allow an ambitious reader to make highly accurate conversions for
a standard atmosphere. This level of accuracy is unnecessary for
games, of course, but the table also gives info on the speed of sound,
which is reached at a surprisingly low IAS at high altitudes.
====
Newsgroups: rec.aviation.simulators
From: r...@cactus.org (Robert Dorsett)
Subject: Re: Converting TAS to IAS
In brief, you can get IAS by multiplying TAS by the square root of the
density ratio. The density ratio is the atmospheric density at the altitude
under consideration divided by the atmospheric density at sea level. It
is defined for a "standard atmosphere," which assumes a set temperature
and pressure at sea level, and a constant lapse rate thereafter.
This approach ignores the effects of instrumentation, installation, and
compression error. The worst that all this will contribute is about a 15%
error; you can get away with using the simple approach.
So: IAS = TAS * SQRT(sigma).
The following shows sigma and the speed of sound (feet per second) for
various altitudes. To get your mach number, just convert your TAS to
feet per second and divide by the speed of sound for that altitude.
The following is from the US Standard Atmosphere, 1962.
Altitude Sigma Sound
-2000 1.0600 1124.1
-1000 1.0300 1120.2
0 1.0000 1116.4
1000 0.9710 1112.6
2000 0.9427 1108.7
3000 0.9151 1104.9
4000 0.8881 1101.0
5000 0.8616 1097.1
6000 0.8358 1093.2
7000 0.8106 1089.3
8000 0.7860 1085.3
9000 0.7619 1081.3
10000 0.7385 1077.3
11000 0.7155 1073.4
12000 0.6932 1069.4
13000 0.6713 1065.4
14000 0.6500 1061.4
15000 0.6292 1057.2
16000 0.6089 1053.2
17000 0.5892 1049.2
18000 0.5699 1045.1
19000 0.5511 1040.9
20000 0.5328 1036.8
21000 0.5150 1032.7
22000 0.4976 1028.5
23000 0.4806 1024.3
24000 0.4642 1020.2
25000 0.4481 1015.9
26000 0.4325 1011.7
27000 0.4173 1007.4
28000 0.4025 1003.2
29000 0.3881 0999.0
30000 0.3741 0994.6
31000 0.3605 0990.4
32000 0.3473 0986.0
33000 0.3345 0981.7
34000 0.3220 0977.3
35000 0.3099 0972.8
36000 0.2971 0968.5
37000 0.2843 0968.0
38000 0.2710 0968.0
39000 0.2583 0968.0
40000 0.2462 0968.0
41000 0.2346 0968.0
42000 0.2236 0968.0
43000 0.2131 0968.0
44000 0.2031 0968.0
45000 0.1936 0968.0
46000 0.1845 0968.0
47000 0.1758 0968.0
48000 0.1676 0968.0
49000 0.1597 0968.0
50000 0.1522 0968.0
#
# altitude in feet
# Sigma, density ratio
# Sonic velocity
Jeffrey Dillman
>
>jef...@cris.com (Jeffrey Dillman) wrote:
>>
>>The following table facilitates IAS to TAS, TAS to IAS
>>conversions. Simply multiply IAS or divide TAS by the
>>altitude factor to convert. This lets you compare data
>>between games, or to real world data.
>>
><table snipped>
>
>A quick and dirty conversion is to add 50kts. to the indicated
>for every 10K of altitude... not nearly as precise as the table
>Jeff posted (thanks Jeff :), but close enough to the ballpark
>remember Flush?), ex A-4 & SLUF driver, and the best damn AW
>pilot I ever flew wing for.
>
>Trips
>
Yep, not bad, I think it is more accurate at about a 450 MPH TAS cruise. I
tried it and it seemed closer at 300 MPH IAS at 20 to 30k. At speeds above
or below that it varied a lot more. Also, don't forget to convert the 50
knots to MPH with sims that are in MPH, like WarBirds. Pretty neat though,
and easy to remember too. Thanks.
Jeffrey Dillman
MJes...@aol.com
>
>In article <4e0c4o$d...@ssbunews.ih.att.com>, op...@marconi.ih.att.com says...
snip
>>This approach ignores the effects of instrumentation, installation, and
>>compression error. The worst that all this will contribute is about a 15%
>>error; you can get away with using the simple approach.
>>
>>So: IAS = TAS * SQRT(sigma).
>>
>>The following shows sigma and the speed of sound (feet per second) for
>>various altitudes. To get your mach number, just convert your TAS to
>>feet per second and divide by the speed of sound for that altitude.
>>The following is from the US Standard Atmosphere, 1962.
>>
>>Altitude Sigma Sound
>
>>20000 0.5328 1036.8
>
>>25000 0.4481 1015.9
>
>>30000 0.3741 0994.6
>
>
>
>Did you check any of your numbers before you posted your table on air speed
>and mach number conversions? I didn't check the mach number stuff, but the
>airspeed conversion factors are wrong. Did you look at my table that started
>this thread? Here it is again.
>
>Jeffrey Dillman
>
>The following table facilitates IAS to TAS, TAS to IAS
>conversions. Simply multiply IAS or divide TAS by the
>altitude factor to convert. This lets you compare data
>between games, or to real world data.
>
snip
>Jeffrey Dillman
>
>
snip - only relevant lines retained
>Alt. factor Alt. factor
>5k 1.078 (1.077) 25k 1.497
>10k 1.167 (1.164) 30k 1.634 (1.635)
>20k 1.373 (1.370) 40k 2.018 (2.016)
The two methods produce the same results, to 3 significant figures.
The first method above matches the values in parentheses quoted in the
second method to 4 decimal places.
- Matt
WB: para
JG14
Robin Kim
>MJes...@aol.com says...
>>jef...@cris.com (Jeffrey Dillman) wrote:
>>>op...@marconi.ih.att.com says...
>>
>>>>So: IAS = TAS * SQRT(sigma).
>
>speed of 270 MPH at 25,000 feet? And you use a sigma of .4481 from the opus
>post?
Yes.
IAS = TAS * SQRT(sigma)
TAS = 404, sigma = 0.4481
SQRT(sigma) = 0.6694
IAS = 404 * 0.6694 = 270.4
QED.
In my original post, I said my table was harder to use than yours.
Now you know why.
>>>Did you check any of your numbers before you posted your table on air speed
>>>and mach number conversions? I didn't check the mach number stuff, but the
>>>airspeed conversion factors are wrong. Did you look at my table that
>>>started this thread? Here it is again.
I sent Jeffrey mail explaining to him that I've used the data in enough
instances to verify its correctness. Of course I don't know for sure that
every figure is exactly right, but it's always given me good results. Plus
the data came from a reputable source.
>>The two methods produce the same results, to 3 significant figures.
>>The first method above matches the values in parentheses quoted in the
>>second method to 4 decimal places.
>>
>>- Matt
>>WB: para
>>JG14
Matt gets a gold star! :^)
>I sure would like to see how you used his equation and sigma to make 404 TAS
>equal 270 IAS, in MPH, at 25,000 feet. Show me. Remember I'm not talking
>about mach numbers here. I'm only interested in IAS/TAS in MPH.
Hopefully my explanation above will suffice.
Jeffrey Dillman
>
>Jeffrey Dillman <jef...@cris.com> wrote:
>>MJes...@aol.com says...
>>>jef...@cris.com (Jeffrey Dillman) wrote:
>>>>op...@marconi.ih.att.com says...
>>>
>>>>>So: IAS = TAS * SQRT(sigma).
>>
>>So if you plug a TAS of 404 MPH into this equation it will yield an IAS air
>>speed of 270 MPH at 25,000 feet? And you use a sigma of .4481 from the
opus
>>post?
>
>Yes.
> IAS = TAS * SQRT(sigma)
> TAS = 404, sigma = 0.4481
> SQRT(sigma) = 0.6694
> IAS = 404 * 0.6694 = 270.4
>QED.
>
>In my original post, I said my table was harder to use than yours.
>Now you know why.
>
snip.
>
>Hopefully my explanation above will suffice.
>
>Rob
>op...@ihlpf.att.com
I went back and read your original post. I thought your table was labeled
SQRT(sigma) but of course it is labeled sigma so to make it work the square
root of air density must be done.
But my questions are:
1. Why post a table that requires an extra calculation to calculate IAS?
2. Why post a table that requires division to convert IAS to TAS? Most
people are interested in IAS to TAS conversion so they can check sims against
"book" figures. It's no accident that I set up my table so that my
conversion factor could be multiplied to go from IAS to TAS. Multiplication
is much easier using paper and pencil than division. Of course with a
calculator both are easy, but I wanted to keep it simple. I avoided esoteric
discussions of air density, temperature, etc. for the same reasons, I wanted
to keep it simple. Of course I did mention my conversion factors were
determined at a temperature where the density altitude and pressure altitude
were identical, but that was it. And there was a little plug in there for
the E-6B flight computer too. One can often find these at flea marts along
with a 50 cent copy of MARTIN CAIDEN's "Fork-Tailed Devil: The P-38." Yes I
bought both for $5.50 on the same day at KOBE's Swap Meet in San Diego.
3. My last question is since I had already posted a simple, easy to use
conversion table, why post one that is hard to use and confusing to some?
I guess the mach number stuff is an extra goody? I guess you were trying to
help? I am going to save the Mach number stuff minus the sigma part. Thanks
for the info.
Jeffrey Dillman
Jeffrey Dillman
>
>jef...@cris.com (Jeffrey Dillman) wrote:
>>
>>In article <4e0c4o$d...@ssbunews.ih.att.com>, op...@marconi.ih.att.com
says...
>
>snip
>
>>>This approach ignores the effects of instrumentation, installation, and
>>>compression error. The worst that all this will contribute is about a 15%
>>>error; you can get away with using the simple approach.
>>>
So if you plug a TAS of 404 MPH into this equation it will yield an IAS air
speed of 270 MPH at 25,000 feet? And you use a sigma of .4481 from the opus
post?
>>>
>>>The following shows sigma and the speed of sound (feet per second) for
>>>various altitudes. To get your mach number, just convert your TAS to
>>>feet per second and divide by the speed of sound for that altitude.
>>>The following is from the US Standard Atmosphere, 1962.
>>>
>>>Altitude Sigma Sound
>>
>>>20000 0.5328 1036.8
>>
>>>25000 0.4481 1015.9
>>
>>>30000 0.3741 0994.6
>>
>>
>
>>
>>Did you check any of your numbers before you posted your table on air speed
>>and mach number conversions? I didn't check the mach number stuff, but the
>>airspeed conversion factors are wrong. Did you look at my table that
started
>>this thread? Here it is again.
>>
>>Jeffrey Dillman
>>
>>The following table facilitates IAS to TAS, TAS to IAS
>>conversions. Simply multiply IAS or divide TAS by the
>>altitude factor to convert. This lets you compare data
>>between games, or to real world data.
>>
>snip
>>Jeffrey Dillman
>>
>>
>
>snip - only relevant lines retained
>>Alt. factor Alt. factor
>>5k 1.078 (1.077) 25k 1.497
>>10k 1.167 (1.164) 30k 1.634 (1.635)
>>20k 1.373 (1.370) 40k 2.018 (2.016)
>
>
>
>The two methods produce the same results, to 3 significant figures.
>The first method above matches the values in parentheses quoted in the
>second method to 4 decimal places.
>
>- Matt
>WB: para
>JG14
>
Robin Kim
>op...@marconi.ih.att.com says...
>
>I went back and read your original post. I thought your table was labeled
>SQRT(sigma) but of course it is labeled sigma so to make it work the square
>root of air density must be done.
It takes a big man to admit he's wrong.
>But my questions are:
>
>1. Why post a table that requires an extra calculation to calculate IAS?
Quoting my original post:
= For those who desire greater accuracy and are
= willing to work for it, I've included below a table of information that
= will allow an ambitious reader to make highly accurate conversions for
= a standard atmosphere. This level of accuracy is unnecessary for
= games, of course, but the table also gives info on the speed of sound,
= which is reached at a surprisingly low IAS at high altitudes.
So why did I do it? Because I thought others might find it a useful
reference. I know I've gotten a lot of mileage out of the data in the
table I posted.
>2. Why post a table that requires division to convert IAS to TAS?
Because it was easier for me.
>Multiplication is much easier using paper and pencil than division.
Not to mention square roots! :^) I actually used to know how to do
these with a pencil and paper, but I've long since forgotten the algorithm.
>Of course with a
>calculator both are easy, but I wanted to keep it simple. I avoided esoteric
>discussions of air density, temperature, etc. for the same reasons, I wanted
>to keep it simple. Of course I did mention my conversion factors were
>determined at a temperature where the density altitude and pressure altitude
>were identical, but that was it.
Why are you talking about your motivations when asking me about mine? Are
they supposed to be similar? My post was an addendum to yours, not a
rebuttal. If you didn't like it, ignore it! Or do you take offense at
every post you read that you don't find personally useful?
>3. My last question is since I had already posted a simple, easy to use
>conversion table, why post one that is hard to use and confusing to some?
>I guess the mach number stuff is an extra goody?
Yes, as I stated. Plus the data are more accurate, which, while not useful
for games (as I stated), could be important for other applications. Also,
air density figures are sometimes interesting to know. At least I find
them so as a lowlander planning a skiing trip in the mountains.
David CL Francis
<jef...@cris.com> writes
>--*-*-*- Next Section -*-*-*
>Content-Type: Text/Plain; charset=ISO-8859-1
>
[snipped]
>>
>>Newsgroups: rec.aviation.simulators
>>From: r...@cactus.org (Robert Dorsett)
>>Subject: Re: Converting TAS to IAS
>>
>
>>
>>The following shows sigma and the speed of sound (feet per second) for
>>various altitudes. To get your mach number, just convert your TAS to
>>feet per second and divide by the speed of sound for that altitude.
>>The following is from the US Standard Atmosphere, 1962.
>>
>>Altitude Sigma Sound
>>20000 0.5328 1036.8
>>25000 0.4481 1015.9
>>30000 0.3741 0994.6
We are all straining after gnats here and guilting of excessive quoting
of previous posts as well! We are all quoting variations on the Standard
Atmosphere and its effects. The above figures for relative density
correspond <exactly> with an ancient table of the Standard atmosphere
that I have. The table says 'Based on the Manual of the ICAO Standard
Atmosphere Calculations by NACA. (That dates them!) The booklet was
published August 1962 by Bristol Siddely Engines (later became part of
Rolls Royce).
It must be the same table that Robert Dorsett used!
>Did you check any of your numbers before you posted your table on air speed
>and mach number conversions? I didn't check the mach number stuff, but the
>airspeed conversion factors are wrong. Did you look at my table that started
>this thread? Here it is again.
>
Check with what? He quoted them correctly but I am quite willing to
believe that the definition of the Standard Atmosphere, which never
actually exists, has changed over the years. So what? Has any one got an
up to date table?
The main point is that the formula quoted:
>In brief, you can get IAS by multiplying TAS by the square root of the
>density ratio. The density ratio is the atmospheric density at the altitude
>under consideration divided by the atmospheric density at sea level. It
>is defined for a "standard atmosphere," which assumes a set temperature
>and pressure at sea level, and a constant lapse rate thereafter.
is correct!
>
>The following table facilitates IAS to TAS, TAS to IAS
>conversions. Simply multiply IAS or divide TAS by the
>altitude factor to convert. This lets you compare data
>between games, or to real world data.
>
[snipped again]
Well the table by Jeffrey Dillman is a bit different but not so much
that it probably matters much for the things we do with flight sims. I
suppose Jeffrey you did notice that the factors that Robert Dorsett used
were reciprocals of yours, and gave IAS from TAS and not TAS from IAS?
Also that the table you quoted is for sigma and not the square root of
sigma?
>Numbers in parenthesis are from Microprose file f15spd.txt.
>
>
>5k 1.078 (1.077) 25k 1.497
>10k 1.167 (1.164) 30k 1.634 (1.635)
>20k 1.373 (1.370) 40k 2.018 (2.016)
The Microprose figures exactly match the equivalents from Robert
Dorsett's table up to 20k where they diverge slightly:
25k 1.494
30k 1.622
40k 2.015 all rounded to three decimal places.
Storm in a tea cup?
--
--------------------------------------------------------------
David CL Francis E-Mail reply to <da...@dclf.demon.co.uk>
--------------------------------------------------------------
MJes...@aol.com
(snip) ...
>I am quite willing to
>believe that the definition of the Standard Atmosphere, which never
>actually exists, has changed over the years. So what? Has any one got an
>up to date table?
IMO, the Standard 62 atmosphere, the Standard 76 atmosphere,
etc., are intended to provide a reasonable "standard" model of the
atmosphere to be used for performance calculations for aerospace
vehicles.
I can't compare the results of my sim to your sim unless we use
similar inputs. (That having been said, I'm using the Std62 in a
particular sim at work even though I should be using Std76.
No use getting picky until the thing flys. :) The low altitude
stuff isn't much different between them. Higher altitudes are being
improved constantly. The Global Reference Atmosphere Model (GRAM 95)
from NASA's Marshall Space Flight Center is a new computer model
just out that can provide latitude / longitude / altitude / season /
much-more-I-forget dependent and randomized atmospheric data for use
in simulations.
My favorite is the Patrick 63 atmosphere. Based on tracking data of
countless balloons launched from an obscure swamp on the east coast
of Florida. :)
Jeffrey Dillman
snip
>>1. Why post a table that requires an extra calculation to calculate IAS?
>
>Quoting my original post:
>
>= For those who desire greater accuracy and are
>= willing to work for it, I've included below a table of information that
>= will allow an ambitious reader to make highly accurate conversions for
>= a standard atmosphere. This level of accuracy is unnecessary for
>= games, of course, but the table also gives info on the speed of sound,
>= which is reached at a surprisingly low IAS at high altitudes.
>
snip
>Rob
>op...@ihlpf.att.com
Your table is more accurate than a flight computer? I've forgotten a lot of
theory, but I thought air density was temperature dependent. Don't your
figures assume a certain temperature at a given altitude? Doesn't the
temperature actually vary some, changing air density? Of course I'm assuming
computer sims keep the temperature constant at a given altitude, but doesn't
density vary in real life at a given altitude? Wouldn't this throw off the
accuracy of your figures too? I don't know for sure, tell me.
And most intriguing of all, how do skiers use air density tables?
Jeffrey Dillman
Jeffrey Dillman
says...
>
>In article <4e44ev$3...@spectator.cris.com>, Jeffrey Dillman
><jef...@cris.com> writes
>>--*-*-*- Next Section -*-*-*
>>Content-Type: Text/Plain; charset=ISO-8859-1
>>
snip
>We are all straining after gnats here and guilting of excessive quoting
>of previous posts as well! We are all quoting variations on the Standard
>Atmosphere and its effects. The above figures for relative density
>correspond <exactly> with an ancient table of the Standard atmosphere
>that I have. The table says 'Based on the Manual of the ICAO Standard
>Atmosphere Calculations by NACA. (That dates them!) The booklet was
>published August 1962 by Bristol Siddely Engines (later became part of
>Rolls Royce).
>
>It must be the same table that Robert Dorsett used!
>
snip
>Check with what? He quoted them correctly but I am quite willing to
>believe that the definition of the Standard Atmosphere, which never
>actually exists, has changed over the years. So what? Has any one got an
>up to date table?
>
Exactly, and it's not more accurate than using conversion factors obtained
from an E-6B flight computer, it's just harder to use the formula.
>The main point is that the formula quoted:
>
>>In brief, you can get IAS by multiplying TAS by the square root of the
>>density ratio. The density ratio is the atmospheric density at the
altitude
>>under consideration divided by the atmospheric density at sea level. It
>>is defined for a "standard atmosphere," which assumes a set temperature
>>and pressure at sea level, and a constant lapse rate thereafter.
snip
Jeffrey you did notice that the factors that Robert Dorsett used
>were reciprocals of yours, and gave IAS from TAS and not TAS from IAS?
>Also that the table you quoted is for sigma and not the square root of
>sigma?
>
I misread the table. I thought the figures given WERE the square roots of
air density. I still can't believe he didn't convert them for those of us
who are easily confused. <G> Of course he said it was more work to use his
table!
>>Numbers in parenthesis are from Microprose file f15spd.txt.
>>
>>
>>5k 1.078 (1.077) 25k 1.497
>>10k 1.167 (1.164) 30k 1.634 (1.635)
>>20k 1.373 (1.370) 40k 2.018 (2.016)
>
>The Microprose figures exactly match the equivalents from Robert
>Dorsett's table up to 20k where they diverge slightly:
>25k 1.494
>30k 1.622
>40k 2.015 all rounded to three decimal places.
>
>Storm in a tea cup?
>--
>--------------------------------------------------------------
>David CL Francis E-Mail reply to <da...@dclf.demon.co.uk>
>--------------------------------------------------------------
You also notice my figures agree within .001 to .003 of Microprose's figures?
At 20k that gives a speed of 391 MPH TAS rounded off to 3 significant
figures, using Microprose's and my factor. Not bad for reading it off the
E-6B with 50 year old eyes. You say results are different with the table
using sigma above 20k? Thank you for pointing that out. Actually except at
30k they are virtually identical. I would advise people to use my table
which sticks to the Microprose figures. It would seem that the E-6B computer
and Microprose would be more reliable. The other table which some might
consider more "scientific" just introduces error between flight sim
comparisons, at least at 30k as you point out. It turns out 30k is one of
the main altitudes for checking top speed and cruise, along with 20 and 25k.
The "Sigma" table is certainly a pain in the ass to use. As far it being
more accurate than Microprose's figures, I dont think so.
I'll post convert.txt again when all this dies down. It should have been
allowed to stand alone in the first place to prevent confusion.
Jeffrey Dillman
Jeffrey Dillman
>>believe that the definition of the Standard Atmosphere, which never
>>actually exists, has changed over the years. So what? Has any one got an
>>up to date table?
>
>etc., are intended to provide a reasonable "standard" model of the
>atmosphere to be used for performance calculations for aerospace
>vehicles.
>
>I can't compare the results of my sim to your sim unless we use
>similar inputs. (That having been said, I'm using the Std62 in a
>particular sim at work even though I should be using Std76.
>No use getting picky until the thing flys. :) The low altitude
>stuff isn't much different between them. Higher altitudes are being
>improved constantly. The Global Reference Atmosphere Model (GRAM 95)
>from NASA's Marshall Space Flight Center is a new computer model
>just out that can provide latitude / longitude / altitude / season /
>much-more-I-forget dependent and randomized atmospheric data for use
>in simulations.
>
>My favorite is the Patrick 63 atmosphere. Based on tracking data of
>countless balloons launched from an obscure swamp on the east coast
>of Florida. :)
>
>
>- Matt
>WB: para
>JG14
>
>
based on, probably that air density table!! As long as we use the same
figures between our sims here we'll come out all right too. It's not like we
are doing anything high powered here. That stuff you are doing at work
sounds like another matter, things sure are getting technical. That NASA
stuff is something else!
Jeffrey Dillman
Sean A. Long
: Thanks for the input Matt. It makes me wonder what the E-6B "whiz wheel" is
: figures between our sims here we'll come out all right too. It's not like we
: are doing anything high powered here. That stuff you are doing at work
: sounds like another matter, things sure are getting technical. That NASA
: stuff is something else!
: Jeffrey Dillman
My understanding of the E-6B is that as a true circular slide rule, it
performs "real" calculations for any input set rather than using a lookup
table. Accuracy is then dependent on the accuracy of the mark placement
on the wheel, on the ability of the user to correctly set the arrows in
the proper locations, and the resolution possible reading figures off the
disk.
FWIW, in "real life", approximations are quite useful, and my instructors
taught me how to nit-pick my calculations to the nearest 1 or 2
miles/knots/pounds of fuel/etc, then laughed at me when I actually USED
numbers that accurate. I generally round to the nearest 5 knots, 5 or 10
miles, and 50-100 pounds of fuel, usually choosing to err on a
conservative side (5 knots slower, 5 miles farther, 50-100 more pounds of
fuel burned, etc.) That way I "make gas" and "make time" during a flight
and get a nice warm fuzzy feeling. If I can do the flight plan on paper
in a conservative fashion, the real world tends to cause less anxiety
when the 10 knot forcast headwind is really 50 knots or whatever.
Just a couple of thoughts after seeing the decimal places on the airspeed
calculations (almost died laughing ;). It's hard to keep airspeed within
5 knots let alone .5 knots ;)
eagl
--
sl...@netcom.com
Robin Kim
>>
>>Quoting my original post:
>>
>>= For those who desire greater accuracy and are
>>= willing to work for it, I've included below a table of information that
>>= will allow an ambitious reader to make highly accurate conversions for
>>= a standard atmosphere. This level of accuracy is unnecessary for
>>= games, of course, but the table also gives info on the speed of sound,
>>= which is reached at a surprisingly low IAS at high altitudes.
>
>theory, but I thought air density was temperature dependent.
Most sims do not model air temperature variations. I'd even hazard a
guess and hypothesize that they use a "standard" atmosphere model.
>Of course I'm assuming
>computer sims keep the temperature constant at a given altitude, but doesn't
>density vary in real life at a given altitude?
I'm sure it does.
>Wouldn't this throw off the
>accuracy of your figures too? I don't know for sure, tell me.
Yes, you are correct. It was not my intent that the figures be assumed
to be correct for all conditions in the real world, and I never implied
this to be the case. Your numbers were not universally applicable
either, were they? I didn't think so.
>And most intriguing of all, how do skiers use air density tables?
To satisfy one's curiousity of how thin the air is up in the mountains,
silly! If others couldn't figure it out either, then I'm sorry I did not
explain myself more clearly.
Gavin Hewins
<snip>
>Check with what? He quoted them correctly but I am quite willing to
>believe that the definition of the Standard Atmosphere, which never
>actually exists, has changed over the years. So what? Has any one got an
>up to date table?
The International Standard Atmosphere (ISA) has not changed much over
the years. this is because it is used to calibrate the aircraft
instruments of all commercial aircraft and most military aircraft in
the Western World. It is required to ensure that the instruments of
aircraft flying in the same airspace are calibrated to the same
standard. If for example an aircraft is flying on a non standard day
(as most are) it does not matter if his altimeter is reading an
altitude 100 feet less than the true altitude because all other
aircraft in the same airspace will be subject to the same error. e.g.
if one aircraft is assinged an altitude of 1000ft and an another is
assinged 2000ft the first aircraft actually be flying at 1100ft and
the second aircraft will be flying at 2100ft. Although they are both
flying 100ft above their assinged altitudes the 1000ft seperation is
maintained. The reason that ISA tables still date back to the sixties
is that we still have aircraft from the sixties flying in commercial
airspace and the aircraft obviously have to be flying to the same
calibration standard as the modern aircraft of today.
I have just about finished writing a simple windows based on the
calculations used in a commercial aircraft Air Data Computer. If any
body is intersted in this I will E-mail them a copy as soon as the
first version is finished (hopefully in the next week or to). I would
welcome any critism or suggestions as to how it may be improved. If you
are interested E-Mail ghe...@minster.win-uk.net
Regards
Gavin
Jeffrey Dillman
Sean do your calculations as close as you can and then round off to whatever,
it could save your life. I remember the picture of an F-86 setting in a
field, beautiful wheels up landing, no gas. One other thing, get out of that
hunk of junk when it decides to quit flying. I'm tired of hearing about dead
pilots that waited too long to eject. And besides ICI needs you as a
customer!!!
About the E-6B flight computer the way I used it was pick an IAS, set Density
altidude to desired value and read TAS opposite IAS. An example is at 20k,
300 MPH IAS divided into 411.8 gives a conversion factor of 1.372666667.
That's a lot of numbers, but it's a calculation number, so to be correct you
should multiply that by the particular IAS at 20K. I was making a table so I
rounded off the conversion factor to make it fit and look better. Once you
are done with the calculations the answer should be rounded off to 3
significant figures like 401 MPH or whatever. Really that's a stretch for
the E-6B as its graduated in 5 MPH increments, but you can estimate between
the lines. Remember we are not trying to fly at a set speed here, we're
trying to see how fast it will go and then compare it with real life
published figures and with other sims.
At present a certain online sim has a P-51D that only goes about 281 MPH IAS
at 25k. By using the conversion factor I get "about" 420 MPH TAS, not even
close. It should be very close to the real life published figure of 437 MPH
IAS. I say about because it's hard to read that "digital" analog
speedometer. Anyway this is the kind of information I am looking for, I NEED
those tiny numbers to make the conversion work.
Jeffrey Dillman
Jeffrey Dillman
35...@We.Turn.190's.Into.Lawn.Darts says...
>
>> jef...@cris.com (Jeffrey Dillman) writes:
>>
>> At present a certain online sim has a P-51D that only goes about 281 MPH
IAS
>> at 25k. By using the conversion factor I get "about" 420 MPH TAS, not
even
>> close. It should be very close to the real life published figure of 437
MPH
>> IAS. I say about because it's hard to read that "digital" analog
>> speedometer. Anyway this is the kind of information I am looking for, I
NEED
>> those tiny numbers to make the conversion work.
>
>guns in the wings? If so, 281 may be a little too fast.
>
>Next time I'm up, I'm going to load 15% fuel, fire off my ammo, and check
speed at
>25k. I'll post my results here.
>
>-Squid-
I don't know where the figures come from, or how they were obtained. It does
make sense that guns and ammo would be included though, along with a
reasonable fuel load.
You have an excellent idea, I'm going to try the WarBirds P-51D the same way
offline with no ammo and low fuel. I'm going to try Air Warrior the same
way. Air Warrior has the option of IAS or TAS read out too, so that makes it
easier. I just wish it were easier to read the "digital" analog speedometer.
By the way, anybody know how fast the P-38J in WarBirds is at 20,000 feet?
The P-51D won't quite reach 300 MPH IAS at 20,000 feet.
Anybody got anything on Fighter Duel P-51D at 25,000 feet?? I don't have
that sim.
Jeffrey Dillman
-Squid-
Jeffrey Dillman
snip
>At present a certain online sim has a P-51D that only goes about 281 MPH IAS
>at 25k. By using the conversion factor I get "about" 420 MPH TAS, not even
>close. It should be very close to the real life published figure of 437 MPH
>IAS. I say about because it's hard to read that "digital" analog
>speedometer. Anyway this is the kind of information I am looking for,
snip
The above quoted speed of 437 MPH is TAS not IAS. My error, I was tired.
Jeffrey Dillman