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View Full Version : Why is the P-51D so slow at altitude?



StellarRat
06-17-2005, 10:30 AM
I've looked all over and the max. quoted speed at 25000 feet is 437 mph. I did some testing last night and with less than 25% fuel the best I could at 25000 was 250 IAS (level flight.) By my calculation we should be able to get it to roughly 290 IAS at 25000 ft. We seem to be about 60 mph (TAS) shy. Has anyone been able to get it to a higher speed in level flight at 25K? If you did how did you do it?

LStarosta
06-17-2005, 10:40 AM
290 IAS of what unit?

Heliopause
06-17-2005, 11:07 AM
Any wind conditions to be reconned with?

3.JG51_Stecher
06-17-2005, 11:52 AM
Crimea, 1200, Wind OFF, full throttle w/boost, radiator closed.

25,000 ft (7,620 m)

In level flight, I'm holding the P-51D at 711 km/h TAS, which is 442 mph, almost perfect.

StellarRat
06-17-2005, 12:05 PM
Originally posted by 3.JG51_Stecher:
Crimea, 1200, Wind OFF, full throttle w/boost, radiator closed.

25,000 ft (7,620 m)

In level flight, I'm holding the P-51D at 711 km/h TAS, which is 442 mph, almost perfect. Any prop pitch adjustments or anything else unusual? I'm going try this after work. You are actually exceeding the quoted speed! Is it the D or DNA?

MEGILE
06-17-2005, 12:07 PM
True Air Speed

http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

StellarRat
06-17-2005, 12:13 PM
Originally posted by StellarRat:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by 3.JG51_Stecher:
Crimea, 1200, Wind OFF, full throttle w/boost, radiator closed.

25,000 ft (7,620 m)

In level flight, I'm holding the P-51D at 711 km/h TAS, which is 442 mph, almost perfect. Any prop pitch adjustments or anything else unusual? I'm going try this after work. You are actually exceeding the quoted speed! Is it the D or DNA? </div></BLOCKQUOTE>Oh, yeah, what was your fuel load?

StellarRat
06-17-2005, 12:16 PM
Originally posted by Megile:
True Air Speed

http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif I don't know what you mean with this post, but yes, I know the difference between TAS and IAS. I was calculating 290 mph IAS as the roughly 435 mph TAS at 25K ft. So, my speedbar and gauges should read 290 mph at 25K ft if I want to go 435 TAS.

3.JG51_Stecher
06-17-2005, 12:30 PM
I was using 25% fuel and 100% prop pitch. If I use 100% fuel I get 704 km/h TAS, which is 437 mph. This is the P-51D-20NA.

willyvic
06-17-2005, 12:33 PM
Originally posted by StellarRat:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Megile:
True Air Speed

http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif I don't know what you mean with this post, but yes, I know the difference between TAS and IAS. I was calculating 290 mph IAS as the roughly 435 mph TAS at 25K ft. So, my speedbar and gauges should read 290 mph at 25K ft if I want to go 435 TAS. </div></BLOCKQUOTE>

Are you sure you were not getting 250 KIAS versus 250 MPH indicated? Cause 250 KIAS at 25000 would give ya about 290 MPH indicated or 435 MPH TAS, no?

StellarRat
06-17-2005, 12:46 PM
Originally posted by willyvic:
Are you sure you were not getting 250 KIAS versus 250 MPH indicated? Cause 250 KIAS at 25000 would give ya about 290 MPH indicated or 435 MPH TAS, no? Yeah, I'm sure. You are correct with your math though and someone could make that mistake, but I didn't. It was set to MPH not KIAS. However, I think my problem might have been that I nelected to set the radiator to CLOSED and left it on AUTO. I will re-test tonight with Stecher's settings.

StellarRat
06-18-2005, 12:36 AM
OK, I was able to get it to the listed speed by keeping the rad closed and overheating for a few seconds. It would be impossible to maintain this speed for any length of time, but I wasn't expecting that.

JG5_UnKle
06-18-2005, 04:24 AM
Shhhhh! before those crazy luftwhiners drop in and say the P-51 is too fast at altitude....

Oh hang on http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif