---------TOP SPEED -------> [Speed Records Leaderboard]

[Oznerol256]

I have a question: AfkMan's screenshots from the F-15C show 800 knots. How is that 2600 km/h? google states that 800 knots is 1400km/h. According to google 2600km/h would be 1400 knots. What am i doing wrong? (Yes, i tried nautical miles per hour.)

[VincentLaw]

I have a question: AfkMan's screenshots from the F-15C show 800 knots. How is that 2600 km/h? google states that 800 knots is 1400km/h. According to google 2600km/h would be 1400 knots. What am i doing wrong? (Yes, i tried nautical miles per hour.)

That gauge is probably not calibrated for supersonic speeds. Check the bottom of the external screenshot here: http://cs313928.vk.me/v313928532/38ea/EUNm3aHpvmo.jpg

 

The interface is in cyrillic, so CK is the speed in km/h and BC is the altitude in meters.

[Oznerol256]

That gauge is probably not calibrated for supersonic speeds. Check the bottom of the external screenshot here: http://cs313928.vk.me/v313928532/38ea/EUNm3aHpvmo.jpg

 

The interface is in cyrillic, so CK is the speed in km/h and BC is the altitude in meters.

 

So a supersonic jet doesn't have a speed gauge that can measure supersonic speeds correctly? Makes sense :thumbup:.

 

The last entry of the gauge seems to be Mach 2.4 which doesnt make any sense at all. The maximum speed of the F-15C according to Wikipedia is mach 2.5. The speed gauge of the A-10C goes 20% above the Never exceed speed (which is 450 knots). The F-15C's gauge should therefore go to at least Mach 2.90.

 

So is this a bug in FC3 or am i doing something wrong?

[Winfield_Gold]

to get extra beans, crank up the the wind direction and up the wind speed. Make sure you are flying with the wind...... not into the wind after takeoff

[Weltensegler]

to get extra beans, crank up the the wind direction and up the wind speed. Make sure you are flying with the wind...... not into the wind after takeoff

 

I thought we're talking IAS not ground speed!?

[hitman]

My record was set with default mission editor settings, and I would recommend everyone else does the same.

 

Changing the wind speed would let you improve your ground speed but not your air speed. I think F5 view shows 3D ground speed though. Lowering the air pressure and raising air temperature would reduce density, which would reduce drag at low altitude, but higher air temperature will also reduce engine performance. The speed of sound is also roughly a function of temperature, so higher air temperature means wave drag effects are delayed until higher speeds.

Its more due in part by pressure. Exhaust gases have a higher rate of expansion with cold atmosphere, while lower pressure creates less parasitic drag on the air frame. The amount of water vapor (relative humidity) in the atmosphere also affects sound speed.

[8core]

we have to wait AFM module.

DCS will only be able to correct all errors with the help of a real pilot of F-15 ...

I hope that a real pilot helps develop DCS F15C-AFM module.

English made in google tradutor :)

Edited February 6, 2014 by 8core

[Roadrunner]

505kmh / 275knt with a huey without loosing the blades?

 

did they change so much on the huey?

 

i'd like to understand how you did it, as for me the blades say goodbye between 190 and 220 knt usualy.

 

 

 

regards,

RR

[Jerkzilla]

505kmh / 275knt with a huey without loosing the blades?

 

did they change so much on the huey?

 

i'd like to understand how you did it, as for me the blades say goodbye between 190 and 220 knt usualy.

 

 

 

regards,

RR

 

AFAIK you have to set your power to idle and collective as low as possible. Then you basically just free fall.

[Roadrunner]

AFAIK you have to set your power to idle and collective as low as possible. Then you basically just free fall.

 

i did try low collective, havent tried power to idle, will try it now, thanks.

 

regards,

RR

[Roadrunner]

ok, i managed 512 kmh / 281 knt without loosing the blades now, so that was the thing i did not try ;)

 

sidenote: on my attempt i had an engine flameout, i did not try to restart it, as i only wanted to see if the blades wood go off or not ;)

 

have fun breaking the speed records gents ;)

 

regards,

RR

Edited February 6, 2014 by Roadrunner

[ZaltysZ]

Shouldn't the weather settings be fixed for this competition? :smartass:

[BitMaster]

Just wondering,

 

do you take in consideration that the Mach speed differs greatly between altitudes and density of matter ? Mach speeds do not tell you how fast you actually fly, neither in IAS or SOG, it only shows the relation from your speed to the speed of sound at your altitude, air density and temps.

Mach-1 and Mach-1 do not necessarily mean the same actual speed in km/h or knots/h or mph..whatever.

 

Also, fairly unrealistic to have the huey in free fall to get that speed... thought it's a Sim, not an iOS 2.99 game LoL

 

Bit

[muffler]

Without wind:

Speed record MiG-29S Swifts.zip

with wind:

Edited February 7, 2014 by muffler

[VincentLaw]

Its more due in part by pressure.

This really depends upon the imposed weather limitations of the simulator, but we can check with a quick calculation. First, the drag equation is D = 0.5ρv^2 CdA. Drag is related to temperature and pressure by the equation of state P = ρRT. Combining these we get:

 

D = 0.5 P/(RT)v^2 CdA

 

The default temperature in the game is 20 C (293.15 K) and the max temperature is 50 C (323.15 K). The default pressure in the game is 760 mmHg (1.0132E5 N/m^2) and the minimum pressure is 720 mmHg (9.599E4 N/m^2).

 

For simplicity, we can assume that the reference area is 1 m^2, the Cd is 1, and the velocity is 1 m/s because that won't make a difference in the comparison. So our equation simplifies to:

 

D = 0.5 P/(RT)

 

First we can fix temperature and vary pressure:

D1 = 0.5 * 1.0132E5/(287.058*293.15) = 0.602 N

D2 = 0.5 * 9.599E4/(287.058*293.15) = 0.570 N

 

(0.602 - 0.570)/0.602 = 0.0531

 

So you can shed 5.3% of your drag by minimizing pressure in DCS.

 

Now to vary temperature and fix pressure:

D1 = 0.5 * 1.0132E5/(287.058*293.15) = 0.602 N

D2 = 0.5 * 1.0132E5/(287.058*323.15) = 0.546 N

 

(0.602 - 0.546)/0.602 = 0.0930

 

So you can shed 9.3% of your drag by maxing out temperature in DCS. This means drag reduction (in DCS) is more due to temperature than pressure. and that is not accounting for wave drag reduction by increasing the speed of sound.

 

If you combine the two then you get:

 

D = 0.5 * 9.599E4/(287.058*323.15) = 0.517 N

 

(0.602 - 0.517)/0.602 = 0.141

 

That is a 14% reduction in drag for messing with the weather settings in DCS.

 

Exhaust gases have a higher rate of expansion with cold atmosphere

The simplified thrust equation is:

 

mass flow rate*(exit velocity - free stream velocity) + exit area*(exit pressure - free stream pressure)

 

There is no temperature in that equation, and over/under expansion depends only on exit pressure. Lower temperature improves thrust by allowing more energy to be added in the combustion chamber before reaching material limits.

while lower pressure creates less parasitic drag on the air frame.

Correct, and so does higher temperature.

The amount of water vapor (relative humidity) in the atmosphere also affects sound speed.

Sound speed is approximately (γRT)^(1/2). The specific heat ratio γ can change due to changes in gas composition such as humidity. γ also varies slightly with temperature.

 

 

If you compare the speed of sound at about 0% humidity and 100% humidity and 30 C, you get:

 

T = 30 + 273.15 = 303.15 K

a1 = (1.3995*287.058*303.15)^(1/2) = 348.980 m/s

a2 = (1.3968*287.058*303.15)^(1/2) = 348.642 m/s

 

(348.980-348.642)/348.980 = 0.000968

 

so the max % difference in sound speed due to humidity is about 0.1%

 

In contrast, the maximum temperature in DCS is 50 C, while the default temperature is 20 C. Since γ doesn't change much with temperature, we can assume it is a constant 1.4 when comparing the change due to temperature.

 

T1 = T = 20 + 273.15 = 293.15 K

T2 = T = 50 + 273.15 = 323.15 K

a1 = (1.4*287.058*293.15)^(1/2) = 343.237 m/s

a2 = (1.4*287.058*323.15)^(1/2) = 360.372 m/s

 

(360.372-343.237)/360.372 = 0.0475

 

The best % difference in sound speed due to temperature in DCS is 4.75%

 

This shows temperature is much more important than humidity in reducing wave drag, but if you really want to minimize drag, dry air is the best.

Just wondering,

 

do you take in consideration that the Mach speed differs greatly between altitudes and density of matter ? Mach speeds do not tell you how fast you actually fly, neither in IAS or SOG, it only shows the relation from your speed to the speed of sound at your altitude, air density and temps.

Mach-1 and Mach-1 do not necessarily mean the same actual speed in km/h or knots/h or mph..whatever.

Mach is mainly a function of temperature, not density, but temperature varies with altitude, which is why the speed of sound is slower at higher altitudes. The competition has never used Mach as a parameter. We were just talking about it in relation to wave drag effects.

Also, fairly unrealistic to have the huey in free fall to get that speed... thought it's a Sim, not an iOS 2.99 game LoL

Terminal velocity is higher at higher altitudes because of lower density. I climbed to 20000 ft before making that dive. Relevant:

Shouldn't the weather settings be fixed for this competition? :smartass:

TLDR: Yes, it should.
Edited February 6, 2014 by VincentLaw

[hitman]

 

The simplified thrust equation is:

 

mass flow rate*(exit velocity - free stream velocity) + exit area*(exit pressure - free stream pressure)

 

A more simplified answer to this would be a higher compression capacity within the compressor chamber. Cold, dense air with moisture has a higher rate of expansion than warm, less dense air without moisture. I wouldnt put moisture into play because it also affects lift, but comparing volume by volume of the two varieties of atmosphere, the cold and moist dense air provides the greatest rate of expansion for thrust producing turbofans.

 

If I remember my physics correctly (and its been a while), temperature is directly proportionate to pressure. I would think that sound wouldnt be able to travel in a zero pressure environment, but I cant back that assumption up. You are correct about temperature being regulated mainly by the temperature.

 

<---not a physicist.

Edited February 7, 2014 by hitman

[Revan]

This really depends upon the imposed weather limitations of the simulator, but we can check with a quick calculation. First, the drag equation is D = 0.5ρv^2 CdA. Drag is related to temperature and pressure by the equation of state P = ρRT. Combining these we get:

 

D = 0.5 P/(RT)v^2 CdA

 

The default temperature in the game is 20 C (293.15 K) and the max temperature is 50 C (323.15 K). The default pressure in the game is 760 mmHg (1.0132E5 N/m^2) and the minimum pressure is 720 mmHg (9.599E4 N/m^2).

 

For simplicity, we can assume that the reference area is 1 m^2, the Cd is 1, and the velocity is 1 m/s because that won't make a difference in the comparison. So our equation simplifies to:

 

D = 0.5 P/(RT)

 

First we can fix temperature and vary pressure:

D1 = 0.5 * 1.0132E5/(287.058*293.15) = 0.602 N

D2 = 0.5 * 9.599E4/(287.058*293.15) = 0.570 N

 

(0.602 - 0.570)/0.602 = 0.0531

 

So you can shed 5.3% of your drag by minimizing pressure in DCS.

 

Now to vary temperature and fix pressure:

D1 = 0.5 * 1.0132E5/(287.058*293.15) = 0.602 N

D2 = 0.5 * 1.0132E5/(287.058*323.15) = 0.546 N

 

(0.602 - 0.546)/0.602 = 0.0930

 

So you can shed 9.3% of your drag by maxing out temperature in DCS. This means drag reduction (in DCS) is more due to temperature than pressure. and that is not accounting for wave drag reduction by increasing the speed of sound.

 

If you combine the two then you get:

 

D = 0.5 * 9.599E4/(287.058*323.15) = 0.517 N

 

(0.602 - 0.517)/0.602 = 0.141

 

That is a 14% reduction in drag for messing with the weather settings in DCS.

 

The simplified thrust equation is:

 

mass flow rate*(exit velocity - free stream velocity) + exit area*(exit pressure - free stream pressure)

 

There is no temperature in that equation, and over/under expansion depends only on exit pressure. Lower temperature improves thrust by allowing more energy to be added in the combustion chamber before reaching material limits.Correct, and so does higher temperature.Sound speed is approximately (γRT)^(1/2). The specific heat ratio γ can change due to changes in gas composition such as humidity. γ also varies slightly with temperature.

 

 

If you compare the speed of sound at about 0% humidity and 100% humidity and 30 C, you get:

 

T = 30 + 273.15 = 303.15 K

a1 = (1.3995*287.058*303.15)^(1/2) = 348.980 m/s

a2 = (1.3968*287.058*303.15)^(1/2) = 348.642 m/s

 

(348.980-348.642)/348.980 = 0.000968

 

so the max % difference in sound speed due to humidity is about 0.1%

 

In contrast, the maximum temperature in DCS is 50 C, while the default temperature is 20 C. Since γ doesn't change much with temperature, we can assume it is a constant 1.4 when comparing the change due to temperature.

 

T1 = T = 20 + 273.15 = 293.15 K

T2 = T = 50 + 273.15 = 323.15 K

a1 = (1.4*287.058*293.15)^(1/2) = 343.237 m/s

a2 = (1.4*287.058*323.15)^(1/2) = 360.372 m/s

 

(360.372-343.237)/360.372 = 0.0475

 

The best % difference in sound speed due to temperature in DCS is 4.75%

 

This shows temperature is much more important than humidity in reducing wave drag, but if you really want to minimize drag, dry air is the best.

Mach is mainly a function of temperature, not density, but temperature varies with altitude, which is why the speed of sound is slower at higher altitudes. The competition has never used Mach as a parameter. We were just talking about it in relation to wave drag effects.Terminal velocity is higher at higher altitudes because of lower density. I climbed to 20000 ft before making that dive. Relevant:

TLDR: Yes, it should.

 

 

 

TOO MUCH MATHS!!!!!!!!!!

[H-var]

I like this thread, but some ground rules need to be set. A 90 degrees vertical dive with full afterburners will probably produce the highest speed, before ejection and/or death ;)

you have to land after the speed record was made.

[H-var]

---> Please read the updated rules!

Edited February 11, 2014 by H-var