Jump to content

1 mach / in kmh


Lenux

Recommended Posts

I'm just speechless :)

Another off topic question : excepting the water, where the speed of light is about 225.000 kms vs air, 299.972 kms : is the speed of light, too, affected by cold / hot air, density, air pressure, etc??

 

There tends to be two beliefs when it comes to this:

 

1. Light has no mass, and therefore cannot be affected by anything (with the exception of things that have refractive properties, like the water you mentioned)

 

2. Speed of light CAN be affected by temperature, but through the indirect mean of temperature changing the density of the medium the light is traveling through.

 

Either way, the difference is negligible.

 

 

***If someone has a better background in this topic, please feel free to correct me. I'm an aeronautical major, not astronautical:doh:

Link to comment
Share on other sites

Finally, in DCS World when you're using external view speed readings or HUD speed readings, you're reading Indicated Airspeed (IAS) which shows a speed lower than True Airspeed (TAS) because airspeed indicators in aircraft don't compensate for air pressure drop as altitude increases. In other words, airspeed indicators don't actually measure airspeed--they measure ram air pressure in the pitot tube, and are only accurate at one altitude (usually sea level.)

 

Actually, while you're correct in that position error comes into play with speed measurement as you increase your altitude, a lot of that can actually be attributed to highly varying alpha at low speeds, transonic effects inside the tube as well as the inherent inaccuracy of the system itself once you go really fast.

 

The pitot tube itself on a plane is actually a pitot-static system which has two pressure sensors, one for ram air pressure, and one for ambient air pressure, and only both of these values let the instrument in the pit display a halfway decent approximation of the speed you're actually going at.

 

https://en.wikipedia.org/wiki/Pitot-static_system

 

And that said, I believe pitot tubes are actually pretty accurate nowadays as PEC can be incorporated digitally into the displayed reading at all times.

Link to comment
Share on other sites

1. Light has no mass, and therefore cannot be affected by anything (with the exception of things that have refractive properties, like the water you mentioned)

 

 

If light has no mass, why is it affected by gravity? As in black holes and gravitational lenses?

Link to comment
Share on other sites

As gravity is currently defined as curvature in the fabric of space, light affected by gravity isn't deviating, it is still travelling in a straight line.

 

Gravity isn't a force in that sense, and therefore you don't need mass to be affected by it.

 

The speed of light is only a constant in a vacuum, and light can slow if affected by it's environment. The constant is defined as the absolute maximum limit of velocity, not that it will always have the same velocity.

Link to comment
Share on other sites

And that said, I believe pitot tubes are actually pretty accurate nowadays as PEC can be incorporated digitally into the displayed reading at all times.

 

That's right--it should be no big deal nowadays to have a computer use altitude, ambient air temp, angle of attack & sideslip, and even airspeed readings themselves to produce a very accurate readout for the pilot. The system would have to be calibrated and would probably use lookup tables. I wouldn't be surprised if that's how it's done these days.

 

Of course, at whim, the pilot could select between TAS and IAS (or display both if desired).

 

AD

Kit:

B550 Aorus Elite AX V2, Ryzen 7 5800X w/ Thermalright Phantom Spirit 120 SE, 2 x 16GB Kingston Fury DDR4 @3600MHz C16, Gigabyte RTX 3070 Windforce 8GB, EVGA SuperNova 750 G2 PSU, HP Omen 32" 2560x1440, Thrustmaster Cougar HOTAS fitted with Leo Bodnar's BU0836A controller.

--Flying is the art of throwing yourself at the ground, and having all the rules and regulations get in the way!

If man was meant to fly, he would have been born with a lot more money!

Link to comment
Share on other sites

I am almost sure that the F2 will give you your IAS, not your TAS. Using approximations and a few conversions, 780 km/h IAS gives you about 1490 km/h TAS at 6 km of altitude, QNH 760 and -12.4 °C (at ground level I assume, which would give you about -52 °C at 6 km).

202 G. "Irish" Machado - AO



[sIGPIC][/sIGPIC]

 

STRIKE FIGHTER SQUADRON 83

http://www.vfa-83.com

Link to comment
Share on other sites

I'd like to have a mod, when i press F10 or some other button, it should show up this little window, with the details, while I'm in the cockpit

 

https://forums.eagle.ru/showthread.php?t=213995&page=3


Edited by Lenux

I9 12900k@ 5 GHz | 32 GB DDR4 | Asus ROG  Strix Z690-A Gaming Wifi d4| RTX 3090 | 6 TB SSD + 8 TB HDD | 4K Samsung Q90R 55" | VKB MK III PRO L | Virpil Throttle MONGOOST-50 | MFG Crosswind | TrackIR5

Link to comment
Share on other sites

Speed of sound is only dependent on temperature in air, not pressure.

[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Varjo Aero, HP Reverb pro, Pimax 8KX] 🙂

[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-14, F-18, FC3, A-10 Warthog II and a few more ]

i9 13900KF@5.8/32Gb DDR5@6400/ Gigabyte Gaming OC RTX4090, ASUS STRIX Z790-F , 2Tb m2 NVMe

Link to comment
Share on other sites

FYI:

Lene Vestergaard Hau (born November 13, 1959 in Vejle, Denmark) is a Danish physicist with a PhD from Aarhus University. In 1999, she led a Harvard University team who, by use of a Bose-Einstein condensate, succeeded in slowing a beam of light to about 17 metres per second, and, in 2001, was able to stop a beam completely.

 

https://en.wikipedia.org/wiki/Lene_Hau

[sIGPIC][/sIGPIC]

Win10 64, Asus Maximus VIII Formula, i5 6600K, Geforce 980 GTX Ti, 32 GB Ram, Samsung EVO SSD.

Link to comment
Share on other sites

I still can't understand why the speed of sound is affected by air temperature, humidity, etc

I9 12900k@ 5 GHz | 32 GB DDR4 | Asus ROG  Strix Z690-A Gaming Wifi d4| RTX 3090 | 6 TB SSD + 8 TB HDD | 4K Samsung Q90R 55" | VKB MK III PRO L | Virpil Throttle MONGOOST-50 | MFG Crosswind | TrackIR5

Link to comment
Share on other sites

I still can't understand why the speed of sound is affected by air temperature, humidity, etc

 

 

Soundwaves are mechanical waves which depends on matter to propagate. As Air is a fluid, it will vary its characteristics depending on the temperature and humidity, behaving as a different propagation media when compared to ISA (International Standard Atmosphere). So it will propagate slower or faster depending on the media it is traveling on, e.g hot air, cold air, water, a peace of iron, etc.

202 G. "Irish" Machado - AO



[sIGPIC][/sIGPIC]

 

STRIKE FIGHTER SQUADRON 83

http://www.vfa-83.com

Link to comment
Share on other sites

...and humidity.

 

But the difference is so small that the normal DCS:er can disregard your post.

 

Between 0 and 100 % humidity in air the sound of speed changes less than 1%.

[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Varjo Aero, HP Reverb pro, Pimax 8KX] 🙂

[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-14, F-18, FC3, A-10 Warthog II and a few more ]

i9 13900KF@5.8/32Gb DDR5@6400/ Gigabyte Gaming OC RTX4090, ASUS STRIX Z790-F , 2Tb m2 NVMe

Link to comment
Share on other sites

Yes it's extremely small. Higher humidity actually decreases the air density. But this effect is considered negligible.

 

And the ISA standard atmosphere actually assumes 0% humidity.

 

If somebody is interested, the quick n dirty formula for calculating Mach 1 speed is 38.95 x sqrt (ambient temp [°K]) => Mach 1 as TAS in knots. Not super scientific precise but for practical purposes (and passing any kind of aviation exams) more than good enough.

 

Going to km/h from there is simple enough not to need an explanation methinks.

| i9 12900K |  64GB DDR5-6000 | STRIX RTX 4090 OC | LG 38GN950 38" |

| Hanns-G HT225HPB | TIR 5 & Varjo Aero | Virpil Throttle & Stick | TM TPRs |

You don't stop playing because you grow old, you grow old because you stop playing.

Link to comment
Share on other sites

But the difference is so small that the normal DCS:er can disregard your post.

 

Between 0 and 100 % humidity in air the sound of speed changes less than 1%.

 

 

With this statement i assume you wont have a problem with giving me 1% of your monthly income from now on.. :)


Edited by Svend_Dellepude

[sIGPIC][/sIGPIC]

Win10 64, Asus Maximus VIII Formula, i5 6600K, Geforce 980 GTX Ti, 32 GB Ram, Samsung EVO SSD.

Link to comment
Share on other sites

With this statement i assume you wont have a problem with giving me 1% of your monthly income from now on.. :)

 

1) You couldnt handle such amounts.

 

2) Less than 1% stated, for a quick understanding for the average DCS:er.

Try use a calculator to see the difference at, for example the air pressure 200hPa/mbar, put in 20kPa. ( it correlates to roughly 39000 feet, so you are in the tropopaus. Use -56.5 degrees C.

0% humidity gives a speed of sound of 295.65 m/s. Then change to 100% humidity.

Now you are up at 295.66 m/s. Thats 0.0034%. You might be able to handle those percentage actually.

[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Varjo Aero, HP Reverb pro, Pimax 8KX] 🙂

[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-14, F-18, FC3, A-10 Warthog II and a few more ]

i9 13900KF@5.8/32Gb DDR5@6400/ Gigabyte Gaming OC RTX4090, ASUS STRIX Z790-F , 2Tb m2 NVMe

Link to comment
Share on other sites

Didn't say it had a big impact, but stating that the "only" thing that affects the speed of sound is temperature is simply not true. Nitpicking i know. :)

You are clearly more knowledgeable than me so, not trying to lecture you.

How does the calculation look at +40° C?

[sIGPIC][/sIGPIC]

Win10 64, Asus Maximus VIII Formula, i5 6600K, Geforce 980 GTX Ti, 32 GB Ram, Samsung EVO SSD.

Link to comment
Share on other sites

Yes it's extremely small. Higher humidity actually decreases the air density.

 

If you think about it, it's actually logical why higher humidity decreases air density.

 

Well over 99% of the gases in the air have a molar weight of 28 g/mol or more whereas water's is 18 g/mol.

As gas pressure is a function of molecules per volume, their weight is utterly irrelevant, and higher humidity causes the mean molar weight of the gas mixture to drop, which consequently leads to lower air density.

 

n = R * T/(p * V)


Edited by antagonist
Link to comment
Share on other sites

Speed of sound is only dependent on temperature in air, not pressure.

 

Didn't say it had a big impact, but stating that the "only" thing that affects the speed of sound is temperature is simply not true. Nitpicking i know. :)

You are clearly more knowledgeable than me so, not trying to lecture you.

How does the calculation look at +40° C?

 

 

Yes, my "only" was refering to almost every post earlier in the thread stating that the speed of sound is dependent of air density and temperature - which it does'nt, only the temperature.

 

 

I also knew about the humidity, but thought that a white lie would make things easy for the regular DCS-player - which it didnt. :doh:

 

 

For the regular DCS:er, check the excellent picture in post #12. It is easy to se the 100% relationship between temperature and speed of sound. The same temperature simply give the same speed of sound.

 

 

At sea level and +40 c you have your 1% difference between 0 and 100% humidity. The bigger difference comes from the warmer air containing a lot more water than normal temperatures.

Most cases, the highest temperatures give low humidity in air, so +50 and very high humidity is rare, except for in the rain forrests. But I guess not many people travel in high mach numbers in the djungle. :)

[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Varjo Aero, HP Reverb pro, Pimax 8KX] 🙂

[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-14, F-18, FC3, A-10 Warthog II and a few more ]

i9 13900KF@5.8/32Gb DDR5@6400/ Gigabyte Gaming OC RTX4090, ASUS STRIX Z790-F , 2Tb m2 NVMe

Link to comment
Share on other sites

I still can't understand why the speed of sound is affected by air temperature, humidity, etc

 

Because sound is transmitted by molecules banging into each other, so the speed at which they can propagate that macro movement is proportional to their velocity, which temperature is a reflection of.

When you're moving faster than the velocity of the molecules at that temperature, they can't carry the wave forward in front of you, and you're above the speed of sound.

 

There tends to be two beliefs when it comes to this:

 

1. Light has no mass, and therefore cannot be affected by anything (with the exception of things that have refractive properties, like the water you mentioned)

Actually, light has a mass.

Anything with a non-zero kinetic energy and a non-zero velocity has a mass that can be derived from E=MC^2

 

Have you ever seen those evacuated spheres with a suspended cross that has flags at the end of each arm - one side black the other silver.

If you put them in the sun, the cross spins away from the silver side of the arms, because the dark side just catches the photons, but the silver side has to stop them, then turn them around and throw them back.

The difference in the kinetic energy transferred to the device when catching (on one side) and reflecting (on the other) causes the spin.

That there is kinetic energy shows there is mass (hence the "wave / particle duality ")

 

Light is also an electromagnetic wave, and so is impacted by electromagnetic fields - like gravity waves.

 

It just goes so fast that under normal circumstances you don't notice it bending (like you don't notice that the ground beneath your feet is curved if you just look at the bit you can see around you).


Edited by Weta43

Cheers.

Link to comment
Share on other sites

Because sound is transmitted by molecules banging into each other, so the speed at which they can propagate that macro movement is proportional to their velocity, which temperature is a reflection of.

When you're moving faster than the velocity of the molecules at that temperature, they can't carry the wave forward in front of you, and you're above the speed of sound.

 

 

Actually, light has a mass.

Anything with a non-zero kinetic energy and a non-zero velocity has a mass that can be derived from E=MC^2

 

Have you ever seen those evacuated spheres with a suspended cross that has flags at the end of each arm - one side black the other silver.

If you put them in the sun, the cross spins away from the silver side of the arms, because the dark side just catches the photons, but the silver side has to stop them, then turn them around and throw them back.

The difference in the kinetic energy transferred to the device when catching (on one side) and reflecting (on the other) causes the spin.

That there is kinetic energy shows there is mass (hence the "wave / particle duality ")

 

Light is also an electromagnetic wave, and so is impacted by electromagnetic fields - like gravity waves.

 

It just goes so fast that under normal circumstances you don't notice it bending (like you don't notice that the ground beneath your feet is curved if you just look at the bit you can see around you).

 

 

 

What makes you think the movement has to be caused by kinetic energy?

I'd really like a better source that photons have mass, I have never heard anyway say it has mass. It behaves like a particle at times but a massless particle.

Link to comment
Share on other sites

What makes you think the movement has to be caused by kinetic energy?

I'd really like a better source that photons have mass, I have never heard anyway say it has mass. It behaves like a particle at times but a massless particle.

 

Discussing the photon having mass or not might be considered a slight thread drift from ”Why does mach 1 only read 1270 kph” :)

 

Most common explanation to black holes is that gravity is so strong that even the light cant overcome it.

[T.M HOTAS Warthog Stick & Throttle + T.Flight pedals, Varjo Aero, HP Reverb pro, Pimax 8KX] 🙂

[DCS Mirage 2K; Huey; Spitfire Mk IX, AJS 37, F-14, F-18, FC3, A-10 Warthog II and a few more ]

i9 13900KF@5.8/32Gb DDR5@6400/ Gigabyte Gaming OC RTX4090, ASUS STRIX Z790-F , 2Tb m2 NVMe

Link to comment
Share on other sites

I'd really like a better source that photons have mass, I have never heard anyway say it has mass. It behaves like a particle at times but a massless particle.

 

light has zero rest mass but contributes to the inertia (and weight in a gravitational field) of any system containing it.

 

Inertia is one of the primary manifestations of mass.

 

A photon moving at the speed of light has a mass of 1x10^-18 electron volts.

 

Given that practically, you will never meet a stationary photon, all the photons you ever meet will have a non zero mass of about 1E-18 EV

 

What makes you think the movement has to be caused by kinetic energy?

That was how it was incorrectly explained to me - the actual reason is here:

https://en.wikipedia.org/wiki/Crookes_radiometer#Explanations_for_the_force_on_the_vanes

 

That the phenomena does exist as I explained it is explained here:

https://en.wikipedia.org/wiki/Radiation_pressure

 

This has drifted OT though, so I'll stop :)


Edited by Weta43

Cheers.

Link to comment
Share on other sites

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...