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na85
12-16-2007, 08:36 PM
I was having a good time breaking the wings off various planes in high speed dives (ever spawned an i-16 at 10000m in FMB and hit fly? It's hilarious. Drops like a stone http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif ) and I decided to see if I could break the sound barrier in IL2.

The closest I got was with the corsair. The wings had long been shredded off, but I was still about 1km or so above the ground when the aircraft simply exploded. I was at 1100km/h IIRC.

I did this a few times and concluded that the engine probably just can't handle something going that fast at sea level.

Since the speed of sound decreases with temperature, which decreases with altitude, my next goal is to try and break it up high where the speed of sound is slower.

I remember reading that the atmosphere is not properly modelled in IL2... is this true? How did Oleg model his atmo?

Bartman.
12-16-2007, 09:21 PM
Dont forget to take your headphones off if or when you succed .

Bartman .

Cajun76
12-16-2007, 09:51 PM
http://img.photobucket.com/albums/v30/Cajun76/IL2M_W040209_180538_C04020918053832.jpg

Can't get much lower and faster than that in one piece, and if your still bookin by the time you hit 3000m, 3000m will hit you. http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

na85
12-16-2007, 10:00 PM
Sweet!

cawimmer430
12-17-2007, 03:33 AM
I've been meaning to ask. Sometimes when I cruise around in the Go-229, it just explodes in dives at around 800 km/h+. http://forums.ubi.com/images/smilies/16x16_smiley-surprised.gif

Oh well, I've tried spawning with a Messerschmitt Me-163B at 10,000 meters with unlimited fuel and vulnerability turned off, then climbing to the highest possible height before the rocket engine losses its thrust. Then I dive! It's quite fun and difficult to control that sucker. I'm not sure the ailerons can be trimmed. Will give it another go tonight. http://forums.ubi.com/images/smilies/25.gif

joeap
12-17-2007, 04:33 AM
Originally posted by na85:
I remember reading that the atmosphere is not properly modelled in IL2... is this true? How did Oleg model his atmo?

Cool, oh and that is not true...the atmosphere is modelled correctly...up to 10000 M. Then it doesn't change.

Viper2005_
12-17-2007, 05:56 PM
A few patches back it was possible to take the Go229 up to massive altitudes and attain TAS corresponding to Mach numbers considerably in excess of 1.0 if you were determined enough to sit around for ages whilst it climbed.

Quite a lot of aeroplanes are erroneously supersonic in IL2 if you dive them from high altitudes. Indeed, lack of reasonable transonic modelling causes major balance issues in high altitude combat (consider the relative performance of P-47s & P-51s at altitude for example).

This affects all aeroplanes; my 190 has certainly been supersonic a few times during offline testing assuming that the atmosphere on the crimea map at noon isn't hugely removed from standard.

If you want to calculate your Mach number then to a first order of magnitude, on a Standard Day at (geopotential) altitudes less than or equal to 11 km:

Mach Number = TAS/(1225*((288-((ALTITUDE*6.5)/1000))/288)^0.5))

TAS in km/h, ALTITUDE in m

Once you've put in the numbers you can paste this directly into Google.

Fork-N-spoon
12-18-2007, 01:02 AM
Originally posted by Cajun76:
http://img.photobucket.com/albums/v30/Cajun76/IL2M_W040209_180538_C04020918053832.jpg

Can't get much lower and faster than that in one piece, and if your still bookin by the time you hit 3000m, 3000m will hit you. http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

Further proof that Kay-jun's cheatin... :\/ Yea, 1,200 something was always the limit for me as well. As Cajun76 so admirably stated, if you don't pull out by 3,000, it hits you, literally...

Save a Kanadian, Daiichidoku fund drive. He's being held Kaptive in the People's Republik of Kanada without Internet.

Viper2005_
12-18-2007, 09:31 AM
BTW - If you put the data from the screenshot into the formula I posted, the Mach number comes out at 1.038 on a standard day...

JtD
12-18-2007, 11:11 AM
Full mission builder is your friend:

http://mitglied.lycos.de/jaytdee/screens/fast.jpg

JG53Frankyboy
12-18-2007, 11:22 AM
Originally posted by Viper2005_:
BTW - If you put the data from the screenshot into the formula I posted, the Mach number comes out at 1.038 on a standard day...

well, the "proplem" is that that what we call here in general TAS (the speed on the comicgauges) is not that TAS that is needed in that formula............
the speed showed in the speedbar is here the deserved source. And i dont think this speed can go supersonic in game...............

jadger
12-18-2007, 11:36 AM
I've gotten to about 1200 km/h in a ME163. I was bored and put her into a dive to see what a highspeed crash was like.... I hit the ground at said speed, but my plane bounced, although at a severely reduced speed (about 400 km/h I think it said), unharmed and I went flying again... and yes, vulnerability was turned on.

Bremspropeller
12-18-2007, 11:43 AM
I have experienced the same.

Viper2005_
12-18-2007, 11:54 AM
Nope JG53Frankyboy; speedbar speed is EAS. The speed of sound essentially independent of air density so you need to work with TAS.

There is a problem if you use WW altitude since that tells you your height AGL rather than your altitude above MSL. Speedbar altitude exposes you to rounding errors, but this isn't a big deal given how slow the lapse rate is, and the fact that the speed of sound is proportional to the square root of the absolute temperature.

The formula I used is based upon TAS, and assumes that you're in the troposphere of a standard atmosphere* (lapse rate -6.5 K/km).

You can check it against
http://aero.stanford.edu/StdAtm.html

If you look at the TAS gauge in the screenshot, you'll see 1211 km/h.

1211 km/h = 336.388889 m/s

In this case, the speedbar altitude of 4100 m is less than the WW altitude of 4121 m, so the chances are that the screenshot was taken over the sea. Therefore we should use the WW altitude.

So now set the applet to use metric units and input the data. You'll see a Mach number of 1.0379, as predicted by my simple formula.

Now you can check this against the speedbar EAS.

Note down the dynamic pressure from the applet:

Q = 45756.6 Pa

Now set the altitude to zero and change the speed until you get back to this value of Q:

Speed = 273.321 m/s = 983.9556 km/h

This is reasonably close to the speedbar EAS of 970 km/h. Since the speedbar truncates to the nearest 10 km/h, since I can't remember if this applet includes compressibility effects and since we don't know how exactly Oleg's atmosphere replicates standard day conditions, I feel reasonably happy saying "QED" at this level of accuracy. We are, afterall, within 1.5%...

*There are lots of standard atmospheres. Mostly I use the US standard atmosphere myself because its definition is freely available. However it is essentially identical to the ISA at the altitudes aeroplanes fly.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19...09539_1977009539.pdf (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf)
(17 Mb)

Cajun76
12-18-2007, 01:34 PM
Originally posted by Fork-N-spoon:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Cajun76:
http://img.photobucket.com/albums/v30/Cajun76/IL2M_W040209_180538_C04020918053832.jpg

Can't get much lower and faster than that in one piece, and if your still bookin by the time you hit 3000m, 3000m will hit you. http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

Further proof that Kay-jun's cheatin... :\/ Yea, 1,200 something was always the limit for me as well. As Cajun76 so admirably stated, if you don't pull out by 3,000, it hits you, literally...

Save a Kanadian, Daiichidoku fund drive. He's being held Kaptive in the People's Republik of Kanada without Internet. </div></BLOCKQUOTE>

The dirty secrets of my lack of success, REVEALED!! http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

If you notice, in the shot I've just deployed my combat flaps. I'm also about to reduce the throttle and gently pull out before I hit the Wall.

If not, at that speed, there's barely a shudder as the wings flutter away... http://forums.ubi.com/images/smilies/winky.gif