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Maple_Tiger
02-22-2004, 12:20 PM
In game when you go to the View Objects and click on aircraft. Scroll down to the P-51D.

Notice it says?

Speed at WEP

Sea level 578kmh TAS
7,600m 703kmh TAS

Well i havent found one sight that said it needed WEP to reach its MAX speeds.


I know you know alot more then i do about aircraft.

I also beleave that Oleg and team have the P-51D FM so that it can only reach its MAX speeds using WEP.

My point is that i am having trouble finding information on whether or not the P-51D needed or used WEP to reach it MAX speeds.

Please help if you can. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Capt. 361stMapleTiger.

http://www.imagestation.com/picture/sraid78/pd6c878f0006c224805da6c9645408b41/fb291d3e.jpg

[This message was edited by Maple_Tiger on Sun February 22 2004 at 11:51 AM.]

Maple_Tiger
02-22-2004, 12:20 PM
In game when you go to the View Objects and click on aircraft. Scroll down to the P-51D.

Notice it says?

Speed at WEP

Sea level 578kmh TAS
7,600m 703kmh TAS

Well i havent found one sight that said it needed WEP to reach its MAX speeds.


I know you know alot more then i do about aircraft.

I also beleave that Oleg and team have the P-51D FM so that it can only reach its MAX speeds using WEP.

My point is that i am having trouble finding information on whether or not the P-51D needed or used WEP to reach it MAX speeds.

Please help if you can. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Capt. 361stMapleTiger.

http://www.imagestation.com/picture/sraid78/pd6c878f0006c224805da6c9645408b41/fb291d3e.jpg

[This message was edited by Maple_Tiger on Sun February 22 2004 at 11:51 AM.]

plumps_
02-22-2004, 12:25 PM
Lol, this must be "Skychimp's Ready Room"!

I guess you were going to post this in your private topics or send an email to Skychimp, did you?

A.K.Davis
02-22-2004, 12:44 PM
Ski Chimp?

http://www.barenaked-music.ch/ski-chimp.jpg

--AKD

http://www.flyingpug.com/pugline2.jpg

KIMURA
02-22-2004, 12:48 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by A.K.Davis:
Ski Chimp?

http://www.barenaked-music.ch/ski-chimp.jpg

--AKD

http://www.flyingpug.com/pugline2.jpg <HR></BLOCKQUOTE>

Skiing Chimp...............http://www.schildersmilies.de/schilder/nothatway.gif http://www.schildersmilies.de/schilder/closed.gif http://www.dooya.schildersmilies.de/youreright.gif

Jippo01
02-22-2004, 01:11 PM
If a plane reaches it top speed at a given throttle setting less than 100%, what does it do at higher throttle setting?

Decelerate???? http://ubbxforums.ubi.com/infopop/emoticons/icon_rolleyes.gif


-jippo

LeLv28 - Fighting for independency since 2002
http://www.lelv28.com

Falkster's Ju-88 fan site:
www.ju88.de.tf (http://www.ju88.de.tf)

hop2002
02-22-2004, 01:52 PM
I have heard references to the P-51 needing slightly reduced rpm for max speed at critical altitude. The reason was at max rpm at high altitudes the propellor tips were supersonic, causing a loss in thrust.

I've never seen any proper documentation of it though.

SkyChimp
02-22-2004, 01:54 PM
WEP = War Emergency Power = Combat Power.

Most sources say that top speed of 437 mph was reached at Combat Power.

The confusion may come into play here: There is no such thing as Combat Power in the P-51D Mustang at 7,600m (24,934 feet).

Combat Power in the P-51D is defined as 67" hg of manifold pressure at 3,000 rpm. The V-1650-7 was incapable of maintaining 67" hg of manifold pressure at 24,934 ft. The best it could do was something like 45" hg.

19,300 feet was the critical altitude of the P-51D at WEP. That was the highest altitude where true WEP could be maintained - 67" hg @ 3,000 rpm. Anything over that and the Hg begins to drop off.

So, the best way to describe it would be that the P-51D Mustang achieved top speed at 24,934 ft at Full Throttle, but not technically Combat Power.

Regards,
SkyChimp
http://members.cox.net/rowlandparks/skychimp.jpg

Maple_Tiger
02-22-2004, 02:22 PM
Ok, so to keep it at 67" 3000rpm at 7600m you needed WEP.

I alwasy thought CombatRPM was 32000. I guess it could be that the gauge in FB is not quite right or im an idiot.

Capt. 361stMapleTiger.

http://www.imagestation.com/picture/sraid78/pd6c878f0006c224805da6c9645408b41/fb291d3e.jpg

SkyChimp
02-22-2004, 02:27 PM
No, there was no way to keep that engine at 67" hg at 7600m.

Like I said, the critical altitude of the P-51D at WEP was 19,300 feet. That was the highest altitude at which 67" hg could be maintained - the supercharger was in high gear and the throttle was all the way forward. There was no way to generate more power. Going over 19,300ft and power drops, there is nothing you can do about it.

So, at 24,930 feet (7600m), you are at full throttle, the supercharger is in high gear, but manifold pressure is at about 45" hg - that's as high as it can go at that altitude.

3,000 was max allowable rpm.

Regards,
SkyChimp
http://members.cox.net/rowlandparks/skychimp.jpg

Maple_Tiger
02-22-2004, 02:40 PM
ok, i think i now see what you mean lol.


I noticed 10,100 was normal take of wheight for the P-51D.

Do you know if that is the wheight that the speeds tests where performed or that Max seed could be acheived at altitude.

If so would this include 1880 rounds of amo and 269 gallons of fuel?

Capt. 361stMapleTiger.

http://www.imagestation.com/picture/sraid78/pd6c878f0006c224805da6c9645408b41/fb291d3e.jpg

hop2002
02-22-2004, 02:44 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Combat Power in the P-51D is defined as 67" hg of manifold pressure at 3,000 rpm. The V-1650-7 was incapable of maintaining 67" hg of manifold pressure at 24,934 ft. The best it could do was something like 45" hg.

19,300 feet was the critical altitude of the P-51D at WEP. That was the highest altitude where true WEP could be maintained - 67" hg @ 3,000 rpm. Anything over that and the Hg begins to drop off.
<HR></BLOCKQUOTE>

I still think that's unrammed, or with partial ram (ie ram at climb speed)

The Spit LF IX, with essentially the same engine, tested by the A&AEE kept 67" up to a shade over 22,000ft.

If the same chart shows 45" at 25,000ft, then I'm convinced it's with little or no ram, as the Spit LF IX managed close to 60" at 25,000ft, and didn't drop to 45" until just over 32,000ft.

The Mustang had a higher top speed, and should therefore have had slightly higher critical alts, not considerably lower.

EDIT: a drop in manifold pressure of 22" in 6,000ft or less is wierd. It should take 10 - 11,000ft for map to drop that much, if 3000 rpm is maintained.

[This message was edited by hop2002 on Sun February 22 2004 at 02:06 PM.]

hop2002
02-22-2004, 02:50 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>I noticed 10,100 was normal take of wheight for the P-51D.

Do you know if that is the wheight that the speeds tests where performed or that Max seed could be acheived at altitude.

If so would this include 1880 rounds of amo and 269 gallons of fuel?
<HR></BLOCKQUOTE>

Weight doesn't have much effect on top speed, because weight only increases induced drag, which is a tiny proportion of overall drag at high speed.

A British test gives the weight of a P-51 D combat equipped but with the rear tank empty as 9,480 lbs. (It says this weight is typical)

Fuel for the rear tank should be 6 lbs per US gallon, 7.2 per imp gallon.

SkyChimp
02-22-2004, 03:13 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by hop2002:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Combat Power in the P-51D is defined as 67" hg of manifold pressure at 3,000 rpm. The V-1650-7 was incapable of maintaining 67" hg of manifold pressure at 24,934 ft. The best it could do was something like 45" hg.

19,300 feet was the critical altitude of the P-51D at WEP. That was the highest altitude where true WEP could be maintained - 67" hg @ 3,000 rpm. Anything over that and the Hg begins to drop off.
<HR></BLOCKQUOTE>

I still think that's unrammed, or with partial ram (ie ram at climb speed)

The Spit LF IX, with essentially the same engine, tested by the A&AEE kept 67" up to a shade over 22,000ft.

If the same chart shows 45" at 25,000ft, then I'm convinced it's with little or no ram, as the Spit LF IX managed close to 60" at 25,000ft, and didn't drop to 45" until just over 32,000ft.

The Mustang had a higher top speed, and should therefore have had slightly higher critical alts, not considerably lower.<HR></BLOCKQUOTE>

I think you are right Hop, but I don't have a chart that shows MP with rammed air, only no ram.

Now, the P-51B/C with the V-1650-3 could maintain 67"hg to 23,000 feet and it dropped to around 45" hg at around 30,000 feet.

The engine in the Spit LF IX, was it equivalent to the V-1650-3 or the V-1650-7.

Regards,
SkyChimp
http://members.cox.net/rowlandparks/skychimp.jpg

hop2002
02-22-2004, 03:24 PM
The LF IX had the Merlin 66, which was the equivalent of the V-1650-7. The earlier Spit F IX used the Merlin 61, which had a smaller supercharger and was limited to 15 lbs boost, about 61" iirc, so it wasn't really equivalent to the -3 engine.

67" at 19,300 doesn't exactly look unrammed to me, more like less ram, but individual engines and aircraft could vary by 2000ft or more, so it's hard to tell from isolated examples. But the difference between 67" at 19,300 and 45" at 24,934 seems extreme, as if the higher figure is at reduced rpm.

Dropping 22" in 5,600 ft is almost 4" per 1,000ft. At that rate, the ceiling wouldn't be much over 30,000ft

SkyChimp
02-22-2004, 03:42 PM
Here are a couple of charts I have on it:

MP @ altitude
http://members.cox.net/rowlandparks/dash3_1.jpg

HP @ altitude
http://members.cox.net/rowlandparks/dash3_4.jpg

Regards,
SkyChimp
http://members.cox.net/rowlandparks/skychimp.jpg

Maple_Tiger
02-22-2004, 05:40 PM
Why do i get the feeling im beating a dead horse? Im also running out of horses to beat.

From the MP chart it does look like the D's MP at 24,500 is about 45"

But i just don't have the technical background or experaince make any use of this information.

If i had a real P-51D in my back yard then i could take it for a speed test.

What if i took P-51D in FB of course for a spin at 7600m with 99% throttle and write down the actual MP.

But then it would be easier to just walk across the street to the farm next door, find a horse, kill it and beat it for a while.

Capt. 361stMapleTiger.

http://www.imagestation.com/picture/sraid78/pd6c878f0006c224805da6c9645408b41/fb291d3e.jpg

SkyChimp
02-22-2004, 06:15 PM
Maple:

Don't get all hung on manifold pressure.

At 24,930 feet the P-51D should do 437mph at full throttle and 3,000 rpm. What the manifold pressure is is moot.

Your question was "is top speed obtained at combat power." My answer is is that it is achieved at full throttle.

It's not that hard.



Regards,
SkyChimp
http://members.cox.net/rowlandparks/skychimp.jpg

Bremspropeller
02-23-2004, 09:11 AM
I've got one question:

why does the "Low Fighter" Spit perform better (I assume since the manifold is higher) than the Fighter @ high alts ? http://ubbxforums.ubi.com/images/smiley/16x16_smiley-surprised.gif

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"Once upon the time..there was an aircraft that ruled the skies of Europe..."
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