Originally posted by Crumpp
Obviously I need to be more specific.
I was making a general statement. I already know the report states this aircraft increased performance by 12 mph.
You stated that earlier, LRRP2. No reason not to believe you.
This report does NOT make any specific conclusions about the Mustang performance increases due to finish as I stated.
To spell it out. You cannot say the Mustang is only slightly improved by "fit and finish". As the NACA and North American concluded, you cannot get planned performance out of the Mustang under field conditions. It's performance is greatly effected by it's finish.
All the best,
Crumpp
Well Crump, the R.A.E., Boscombe Down, and Wright Field disagree.
What’s your definition of “Planned Performance”? If you mean wind tunnel projections of performance, then you are most likely right. 1940’s production technologies could not produce a surface finish conducive to actual laminar flow. If you mean the NAA/USAAF/RAF figures for clean aircraft performance, then you are almost certainly wrong since reaching the published performance figures didn’t require
actual laminar flow. After all, the test aircraft used to generate those numbers, like squadron examples, didn’t enjoy laminar flow to begin with.
Maybe I need to make
myself clearer: The commonly quoted figures for actual Mustang performance, not preliminary estimates based on wind tunnel tests, were quite attainable by squadron service P-51's. In fact, the RAE’s 12 mph speed loss due to finish fits very well with Wright Field’s test of P-51B 43-24777 from May of ’44. 43-24777 did 364 mph/67” Hg at sea level in full combat configuration (9,680 lbs) with wing racks. FB377 did 383 mph@SL in the same configuration (but probably 9200 lbs) at 81” Hg. Subtracting the 25-27 mph attributed to the increase from 67” to 81” Hg leaves us with 356 to 358 mph@SL for FB377 at 67” Hg- even less than 12 mph estimated by the RAE. The missing 4-6 mph is probably attributable to the fact that FB377 was likely 400-500 lbs lighter than 43-24777, or even just normal variation in airframes or test conditions.
To spell it out. You cannot say the Mustang is only slightly improved by "fit and finish". As the NACA and North American concluded, you cannot get planned performance out of the Mustang under field conditions. It's performance is greatly effected by it's finish.
You are confusing (or combining) the issues of production quality vs. operational wear and tear. Your conclusion doesn't follow from your premise. The only way it
does work is if the Mustang left the factory with a wing capable of true laminar flow. It didn't. Period. No one, including NAA Vice President and Chief Engineer Lee Atwood, believed it did. Did Mustang performance benefit from NAA's high standards for fit and finish? That production quality didn't suddenly disappear in squadron service, however. Like other fighters, paintwork (not overall production quality) degraded in the field, but no more so than other fighters. In other words, paintwork would degrade, but not the underlying production quality of the airframe.
You seem to have a firmly held belief that the Mustang was some how less potent than other fighters under operational circumstances. That's fine, its just that the evidence doesn't support your belief. So far, all you have been able to show is that the Mustang’s wing didn’t achieve the same air flow efficiencies in production as did wooden models in the wind tunnel. You have provided no evidence that production P-51’s were more affected by service wear and tear than its contemporaries. I have provided clear cut evidence that even a heavily degraded surface finish only accounted for a 12 mph speed loss. Like I said, performance numbers were based on actual production finishes, not wind tunnel projections.
The fact is that the Mustang's aerodynamic advantages were based in the cooling design's very effective use of the Meredith Effect, a very slick shape and excellent overall production quality. To what it was not due was actual Laminar Air Flow.
Cheers,
Brent Erickson
