Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: Traveler on November 22, 2006, 01:50:45 PM
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The speed of sound in dry air is given approximately by
Hyper Physics
Because the speed of a sound in the air is determined by the air itself. It is not dependent upon the sound amplitude, frequency or wavelength and the formula for determining the speed of sound in air is dependent on a constant with only one variable; that being air temperature expressed as Celsius for the altitude.
The speed of sound in dry air is given approximately by
V sound in air = 331.4 + 0.6Tc m/s
I was flying an ME 262 at 25K with a E6B true airspeed of 525 mph which yielded a .76 of Mach. A simple matter of solving for X to determine the outside air temp at 25K.
.76 requires a speed of sound to be around 700 mph which requires an outside air temp of about -31 C or -24 F to attain.
That is great for 25K, so I did it again at 10K , 5K and 20 feet above sea level. The air temptrue at each of these was the same as 25K.
That is not an accurate model for the speed of sound in any aircraft.
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AH's Mach conversion table.
Speed of sound in fps.
1116.89f, /* ALT 0.000000*/
1114.97f, /* ALT 500.000000*/
1113.05f, /* ALT 1000.000000*/
1111.12f, /* ALT 1500.000000*/
1109.19f, /* ALT 2000.000000*/
1107.25f, /* ALT 2500.000000*/
1105.31f, /* ALT 3000.000000*/
1103.37f, /* ALT 3500.000000*/
1101.43f, /* ALT 4000.000000*/
1099.48f, /* ALT 4500.000000*/
1097.53f, /* ALT 5000.000000*/
1095.57f, /* ALT 5500.000000*/
1093.61f, /* ALT 6000.000000*/
1091.65f, /* ALT 6500.000000*/
1089.68f, /* ALT 7000.000000*/
1087.71f, /* ALT 7500.000000*/
1085.74f, /* ALT 8000.000000*/
1083.76f, /* ALT 8500.000000*/
1081.78f, /* ALT 9000.000000*/
1079.80f, /* ALT 9500.000000*/
1077.81f, /* ALT 10000.000000*/
1075.82f, /* ALT 10500.000000*/
1073.83f, /* ALT 11000.000000*/
1071.83f, /* ALT 11500.000000*/
1069.83f, /* ALT 12000.000000*/
1067.82f, /* ALT 12500.000000*/
1065.81f, /* ALT 13000.000000*/
1063.80f, /* ALT 13500.000000*/
1061.78f, /* ALT 14000.000000*/
1059.76f, /* ALT 14500.000000*/
1057.73f, /* ALT 15000.000000*/
1055.70f, /* ALT 15500.000000*/
1053.67f, /* ALT 16000.000000*/
1051.63f, /* ALT 16500.000000*/
1049.59f, /* ALT 17000.000000*/
1047.55f, /* ALT 17500.000000*/
1045.50f, /* ALT 18000.000000*/
1043.45f, /* ALT 18500.000000*/
1041.39f, /* ALT 19000.000000*/
1039.33f, /* ALT 19500.000000*/
1037.26f, /* ALT 20000.000000*/
1035.19f, /* ALT 20500.000000*/
1033.12f, /* ALT 21000.000000*/
1031.04f, /* ALT 21500.000000*/
1028.96f, /* ALT 22000.000000*/
1026.88f, /* ALT 22500.000000*/
1024.79f, /* ALT 23000.000000*/
1022.69f, /* ALT 23500.000000*/
1020.59f, /* ALT 24000.000000*/
1018.49f, /* ALT 24500.000000*/
1016.38f, /* ALT 25000.000000*/
1014.27f, /* ALT 25500.000000*/
1012.15f, /* ALT 26000.000000*/
1010.03f, /* ALT 26500.000000*/
1007.91f, /* ALT 27000.000000*/
1005.78f, /* ALT 27500.000000*/
1003.64f, /* ALT 28000.000000*/
1001.51f, /* ALT 28500.000000*/
999.362f, /* ALT 29000.000000*/
997.251f, /* ALT 29500.000000*/
995.062f, /* ALT 30000.000000*/
992.905f, /* ALT 30500.000000*/
990.743f, /* ALT 31000.000000*/
988.577f, /* ALT 31500.000000*/
986.405f, /* ALT 32000.000000*/
984.229f, /* ALT 32500.000000*/
982.048f, /* ALT 33000.000000*/
979.862f, /* ALT 33500.000000*/
977.672f, /* ALT 34000.000000*/
975.476f, /* ALT 34500.000000*/
973.276f, /* ALT 35000.000000*/
971.070f, /* ALT 35500.000000*/
968.859f, /* ALT 36000.000000*/
968.859f, /* ALT 36500.000000*/
968.859f, /* ALT 37000.000000*/
968.859f, /* ALT 37500.000000*/
968.859f, /* ALT 38000.000000*/
968.859f, /* ALT 38500.000000*/
968.859f, /* ALT 39000.000000*/
968.859f, /* ALT 39500.000000*/
968.859f, /* ALT 40000.000000*/
968.859f, /* ALT 40500.000000*/
968.859f, /* ALT 41000.000000*/
968.859f, /* ALT 41500.000000*/
968.859f, /* ALT 42000.000000*/
968.859f, /* ALT 42500.000000*/
968.859f, /* ALT 43000.000000*/
968.859f, /* ALT 43500.000000*/
968.859f, /* ALT 44000.000000*/
968.859f, /* ALT 44500.000000*/
968.859f, /* ALT 45000.000000*/
968.859f, /* ALT 45500.000000*/
968.859f, /* ALT 46000.000000*/
968.859f, /* ALT 46500.000000*/
968.859f, /* ALT 47000.000000*/
968.859f, /* ALT 47500.000000*/
968.859f, /* ALT 48000.000000*/
968.859f, /* ALT 48500.000000*/
968.859f, /* ALT 49000.000000*/
968.859f /* ALT 49500.000000*/
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(http://www.wm-talk.com/images/smiles/shake.gif)
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so in the game it's table driven, but the table was based on a formula, right? I'm, just saying that the air temp woud not be the same at each altitude. The fps is that feet per second, or frames per second?
thanks
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Originally posted by hitech
AH's Mach conversion table.
Speed of sound in fps.
1116.89f, /* ALT 0.000000*/
1097.53f, /* ALT 5000.000000*/
1077.81f, /* ALT 10000.000000*/
1016.38f, /* ALT 25000.000000*/
1116.89f,/* Alt 0.000000*/ yields 762.5588812800001 mph at an air temp of 58F
1097.53f, /* ALT 5000.000000*/ 749.3408025600001 mph 40 F
1077.81f, /* ALT 10000.000000*/ 735.87693312 mph 23 F
1016.38f, /* ALT 25000.000000*/ 693.93547776 mph -32.5 F
That's the number I should have gotten based on the table, however, on the E6B, that's not what I got. Running at each altitued for 3 minutes level flight. The number I got were very different. Also, it appears that the ME262, never stops excelerating at any altitude and would continue to excelerate until it runs out of fuel. There must have been an airspeed restriction to prefent airframe damage, no?
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Traveler:
The me-262 is not supersonic. I think that's your point of confusion with this.
Tango, XO
412th FS Braunco Mustangs
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i can apreciate your stiving for realisim however at some point the devolopers have to stop and use a table that models something like this as close as game mechanics allow. i may be wrong BUT, i beleive its a matter of players pc's over a wide spectrum to be able to do all the extra calculations to provide super uber realism such as temp difference's at altitude with direct correlation to its affects on a particular A/C movement thru the air.
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Originally posted by JB88
(http://www.wm-talk.com/images/smiles/shake.gif)
Me too!!
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Originally posted by WilldCrd
i can apreciate your stiving for realisim however at some point the devolopers have to stop and use a table that models something like this as close as game mechanics allow. i may be wrong BUT, i beleive its a matter of players pc's over a wide spectrum to be able to do all the extra calculations to provide super uber realism such as temp difference's at altitude with direct correlation to its affects on a particular A/C movement thru the air.
Ahh willdCrd, the kicker is that HTC does use air temp differences at alt to correlate to particular a/c movements thru the air. That's what the table HT shows implies.
Don't confuse the use of tables vs. some other way of calculating as less realism. Nothing could be further from the truth :).
Tango, XO
412th FS Braunco Mustangs
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hmm well i didnt know he did.
For the original poster you CAN get a 262 supersonic, i know cause i've done it!!
was in a dive, had no wings or tail and probly missing some other non-important stuff but, by-god was supersonic. It was the sudden STOP from supersonic that kinda ruined the whole experience:huh
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Originally posted by dtango
Traveler:
The me-262 is not supersonic. I think that's your point of confusion with this.
Tango, XO
412th FS Braunco Mustangs
I know that, Mach is a percentage of the speed of sound. Sound travels at different speeds at different altitudes depending on the air tempture. Supersonic refers to aifcraft that travel faster then the speed of sound.
I was just pointing out that the E6B gives the aircraft speed as a indicated airspeed, true airspeed, ground speed and the Mach number.
When I tested the 262 at see level it yielded a Mach of .67 for a true airspeed of 505 mph. That translated to an outside air temp at see level of -24 F. What I should have gotten was a air temp of 58 F.
that's what I questioned. To have gotten the true airspeeds and the Mach numbers that I received ment that something was wrong.
True air speed increases as you climb. The speed of sound decreases as you climb. The outside air temperature generally decreases as you climb. But according to the numbers yielded by the E6B for the test run I made at sea level. The outside air temperature would have had to have been -24 F.
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Traveler:
The equation you have is for the speed of sound. You can't plug in the 262 velocity into the equation and then get the resulting temperature.
For the equation to yield the temperature the number you have to put in is the speed of sound. So if I take your 262 level speed figures showing 505 mph at mach .67, Mach 1 would then be 753 mph meaning air temp is 48F SL not the 24F that you got.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by Traveler
Sound travels at different speeds at different altitudes depending on the air tempture.
I thought it had as much (or more) to do with air density....
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Originally posted by calan
I thought it had as much (or more) to do with air density....
Then you thought wrong, go to Google search speed of sound.
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Originally posted by dtango
Traveler:
The equation you have is for the speed of sound. You can't plug in the 262 velocity into the equation and then get the resulting temperature.
For the equation to yield the temperature the number you have to put in is the speed of sound. So if I take your 262 level speed figures showing 505 mph at mach .67, Mach 1 would then be 753 mph meaning air temp is 48F SL not the 24F that you got.
Tango, XO
412th FS Braunco Mustangs
You are correct about "you can't plug in the 262 volocity into the equation" however, you take true airspeed and calculate for velocity. Search Google for speed of sound. The forumla is there.
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Originally posted by Traveler
Then you thought wrong, go to Google search speed of sound.
ummm... I don't think so (but we may have a communication gap going here). The density of air does affect it, but the density is determined (mostly) by temperature.
For any given temperature, the pressure and density will remain constant and cancel out of the equation, thus making it possible to say that it is only dependent on temperature. But in affect it is still the density of the air that determines how many molecules are available to transmit molecular motion.
Or I could be full of crap... I dunno... :lol
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Originally posted by calan
ummm... I don't think so (but we may have a communication gap going here). The density of air does affect it, but the density is determined (mostly) by temperature.
For any given temperature, the pressure and density will remain constant and cancel out of the equation, thus making it possible to say that it is only dependent on temperature. But in affect it is still the density of the air that determines how many molecules are available to transmit molecular motion.
Or I could be full of crap... I dunno... :lol
if you look at the formula for speed of sound you will see that air density is not part of the formula only air temp. So while your statement about pressure and density is correct and I agree with you. It is not part of the formula. if you know of a different formula for the speed of sound that includes pressure altitude , what is it?
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From wikipedia:
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In general, the speed of sound c is given by
(http://www.jcsautomation.com/images/speed of sound.png)
where
C is a coefficient of stiffness
p is the density
Thus the speed of sound increases with the stiffness of the material, and decreases with the density. For general equations of state, if classical mechanics is used, the speed of sound c is given by
(http://www.jcsautomation.com/images/speedofsound2.png)
where differentiation is taken with respect to adiabatic change.
*****************
I'll agree to disagree :)
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Originally posted by JB88
(http://www.wm-talk.com/images/smiles/shake.gif)
OH MY GOD! AH has the same temperature at all altitudes??? That's it, I quit, I am never playing this CARTOON game again. I just can't handle the lack of REALISM!
:p
:rofl
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I'm an expert on the relative air temperature at different altitudes in AH...
I have fallen through all of them MANY times with nothing but a chute above me. And it was very cold on my widdle toes until I got closer to the ground.
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Originally posted by calan
I thought it had as much (or more) to do with air density....
Air density decreases as altutude increases, so you wouldn't need both. Alt assumes a given density, more or less.
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I think the key word was...dry.
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I may be a little off base here but......
WHO CARES????????????:huh
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BOOOOOOOMMMMMM!!!!!!!!
I'm pretty sure that's what he was lookin for in the first place:p
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Originally posted by Hornet33
WHO CARES????????????:huh
I don't... but I always enjoy expanding my knowledge and learning something a bit more complex than which hat button fires the whoopie bombs.
But to each his own.
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Originally posted by Traveler
You are correct about "you can't plug in the 262 volocity into the equation" however, you take true airspeed and calculate for velocity. Search Google for speed of sound. The forumla is there.
Traveler -
TAS is the velocity. That's what E6B is telling you. No other conversions needed. The speed of sound is measured on TAS as well. You also can't come up with mach numbers without TAS. Trust me. Stop for a second and think about what I have said above. I'm not trying to prove you wrong, just trying to illuminate the subject.
Thanks for pointing out google, but I have several aero text books btw so no need to look it up on the net :).
Tango, XO
412th FS Braunco Mustangs
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Originally posted by Traveler
When I tested the 262 at see level it yielded a Mach of .67 for a true airspeed of 505 mph. That translated to an outside air temp at see level of -24 F. What I should have gotten was a air temp of 58 F.
You are also assuming the .67 and 505mph are distinct and exact. Most likely they are neither, thus you have errors due to rounding. For example:
505.49mph / .665 Mach = Approx 760.1mph speed of sound
505mph / .67 Mach = Approx 753.7mph
504.5mph / .6749 Mach = Approx 747.5mph
Plus you appear to have a small conversion error based on HiTech's table. You posted:
Originally posted by Traveler
1116.89f,/* Alt 0.000000*/ yields 762.5588812800001 mph at an air temp of 58F
1097.53f, /* ALT 5000.000000*/ 749.3408025600001 mph 40 F
1077.81f, /* ALT 10000.000000*/ 735.87693312 mph 23 F
1016.38f, /* ALT 25000.000000*/ 693.93547776 mph -32.5 F
Converting fps directly to mph (perhaps you converted to meters/second then back to miles / hour?) yield the following results:
1116.89 fps * 3600 seconds (1 hr) / 5280 feet (1 mile) = Approx 761.5mph
1097.53 * 3600 / 5280 = Approx 748.3mph
1077.81 * 3600 / 5280 = Approx 734.9mph
1016.38 * 3600 / 5280 = Approx 693.0mph
All about 1 mph less than what you have.
This, of course, assumes the Bill Gates product I am using is error free, which could be a stretch. :lol
At any rate, the combination of small rounding / conversion / etc. errors that creep into formulas like this will often give unexpected results.
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e2580:
He's making a much bigger error. If it was creep etc. then the SL temp would be 48F, not the -24F he came up with. That's a big difference. Infact for -24F the SL speed of sound should be around 699 mph.
HTC know's their aero physics. Very doubtful there are holes that big in their employment of the physics model.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
e2580:
He's making a much bigger error. If it was creep etc. then the SL temp would be 48F, not the -24F he came up with. That's a big difference. Infact for -24F the SL speed of sound should be around 699 mph.
HTC know's their aero physics. Very doubtful there are holes that big in their employment of the physics model.
Tango, XO
412th FS Braunco Mustangs
I'm barking up the wrong tree, then . . . :aok
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what? Is Stephen Hawking playing this game?
He does have a joystick built into his wheelchair, don't he?
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which hat button fires the whoopie bombs?
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Originally posted by JB88
which hat button fires the whoopie bombs?
dunno... haven't learned that yet :)
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i broke the sound barrier in a 262 WITH wings!
45 degree dive down 20 k or something like that and 247 (whatevers) of wind behind me! .99, .98, .99, 1.0, 1.1,0 zero you say???? A mountain :rofl
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:O
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Originally posted by JB88
(http://www.wm-talk.com/images/smiles/shake.gif)
lol
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Originally posted by calan
From wikipedia:
*****************
In general, the speed of sound c is given by
(http://www.jcsautomation.com/images/speed of sound.png)
where
C is a coefficient of stiffness
p is the density
Thus the speed of sound increases with the stiffness of the material, and decreases with the density. For general equations of state, if classical mechanics is used, the speed of sound c is given by
(http://www.jcsautomation.com/images/speedofsound2.png)
where differentiation is taken with respect to adiabatic change.
*****************
I'll agree to disagree :)
only that p/ro ~ T and so c~sqrt(T).
The speed of sound may weakly depends on the density through change in mean molecular weight (change of chemical composition) or if the adiabatic polytrope (power relation between density and pressure for adiabatic compression) changes.
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Originally posted by dtango
Traveler:
The me-262 is not supersonic. I think that's your point of confusion with this.
Tango, XO
412th FS Braunco Mustangs
depends.... ive "broke" 1.12mach i think it was..... however there was a big bang a few seconds later as i crashed into the ground straight down....lol
on another note to hitech.
i was chasing a con yesterday in my 262 and unknown to me he was AFK, on auto climb. a 109k.... my 262 stopped climbing at almost exactly the service ceiling of 37565ft. However for some reason the 109k was at 44k when i broke off... a bit odd (its ceiling is 41k).
anyway on my decent i got upto 0.96mach, but theres no way id push it further than that (it was already almost totally out of control).... try it in offline mode.
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Sorry fellas. I was being obtuse about the me262 being non-supersonic.
In level-flight, max-top speed of the 262 isn't above mach 1 meaning without the help of gravity the 262 on it's own power can't reach or break the speed of sound.
That's the classic definition of being supersonic. Otherwise we could call different planes supersonic including the P-47 or the P-51 that I believe have recorded hit or exceeded mach 1 in dives.
Tango, XO
412th FS Braunco Mustangs
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yeah but , what is the air speed of a unladen swallow?
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Originally posted by john9001
yeah but , what is the air speed of a unladen swallow?
African or European? :D
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
African or European? :D
Tango, XO
412th FS Braunco Mustangs
Dtango, you beat me to it. :D
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LOL - i love that movie!
Tango, XO
412th FS Braunco Mustangs
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Traveler: FPS = Feet per sec. have no idea why you think it would relate to any thing else.
I have no idea where you went wrong on your calculations.
But did a real quick test of the e6b with a p51.
300 mph 200 Ft showed mach 0.39
300 mph 25k Ft showed mach 0.43
So now if you think my speed of sound table is incorrect please show your work and why.
HiTech
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I think a lot of you guys are mixing up m/s for mph or C for deg. F or both.
For example, applying the formula at sea level with Traveler's data:
Originally posted by Traveler
When I tested the 262 at see level it yielded a Mach of .67 for a true airspeed of 505 mph. That translated to an outside air temp at see level of -24 F. What I should have gotten was a air temp of 58 F.
.67 Mach at 505 mph means the E6B is thinking speed of sound is 754 mph. That's 337 m/s. Using the formula, that would give sea level temperature of (337 - 331.5)/0.6 = 9.2 C, which is 49 deg. F -- reasonably close given that the formula is an approximation and that the table likely uses more-accurate data.
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Originally posted by dtango
Otherwise we could call different planes supersonic including the P-47 or the P-51 that I believe have recorded hit or exceeded mach 1 in dives.
In WWII there were prop planes that, by looking at the indicated speed on their airspeed indicators and correcting to true airspeed, indicated that they were going past Mach 1. I think, though, that the pitot-tube-based airspeed indicators of WWII became inaccurate as they approached Mach 1 in ways that were not corrected by the standard correction tables and that the aircraft were thus not actually travelling at Mach 1 or higher.
I think I remember reading that people have done some research that shows that the WWII prop fighters could not have gone faster than Mach 1, even in a vertical dive with full power from 45,000 ft straight down. The airframes and propellers created too much drag at higher speeds for the terminal velocity to get that high.
Airflow over the wings, though (airflow over the top of the wing is faster than true airspeed of the aircraft), and tip speed of the propellors did become supersonic at high enough speeds in dives. The supersonic airflow over wings is the cause of compressibility for WWII fighters and was worse for wings with thick cord (faster air over the top), like the P-38, than for those with thinner cord (like the P-51). Thick-cord wings hit compressibility at lower speeds than thin-cord wings.