Field Mod for P-51 Escorts

[Chalenge]

Field mods? I know. HTC doesn't usually go this route. I'm posting this here as a general question.

I found this video that indicates that the Merlin Engine -7 had a supercharger that was most efficient at it's cruise altitude (obviously) of 19,000 (plus a little bit). Because escort duty at the time occurred at 25,000 feet the US Army included a field modification (listed in either the crew manual, or erection manual) to modify the supercharger from the -7 to the older -3. This allows the P-51D to perform at its best at 28,800 feet. The video also has other comments concerning other improvements and advantages which I do and do not agree with. Apparently, the mod was done to deal with aircraft that the P-51D was engaging in escort duty, rather than low altitude performance.

My question is: How popular was this field mod? Will we ever know?

https://www.youtube.com/watch?v=sTD7DqXfRno

[lyric1]

Interesting Video thanks for posting.

[save]

Maybe when the German AS-engines show up in the 109's.

Do you have any numbers of how many where upgraded ?

[Brooke]

That was an interesting video and great find.  Thanks, Chalenge! 

[Chalenge]

Maybe when the German AS-engines show up in the 109's.

Do you have any numbers of how many where upgraded ?

My question is: How popular was this field mod? Will we ever know?

Still haven't looked it up, yet.

[drgondog]

Field mods? I know. HTC doesn't usually go this route. I'm posting this here as a general question.

I found this video that indicates that the Merlin Engine -7 had a supercharger that was most efficient at it's cruise altitude (obviously) of 19,000 (plus a little bit). Because escort duty at the time occurred at 25,000 feet the US Army included a field modification (listed in either the crew manual, or erection manual) to modify the supercharger from the -7 to the older -3. This allows the P-51D to perform at its best at 28,800 feet. The video also has other comments concerning other improvements and advantages which I do and do not agree with. Apparently, the mod was done to deal with aircraft that the P-51D was engaging in escort duty, rather than low altitude performance.

My question is: How popular was this field mod? Will we ever know?

The 'field mod' was occasionally replacing the 1650-7 with a 1650-3 when a spare -7 wasn't in inventory. The FTH with ram air for the -7 was at ~ 24K whereas the -3 FTH was 29K with ram.  The future -9 was basically a beefed up -3 with better bearings and Carb (when functioning correctly) plus WI in the P-51H. The FTH of the -9 with ram, WI and 90" boost was about 22K.


The fundamental change between the -3 and -7 was the supercharger gearing/ratio

https://www.youtube.com/watch?v=sTD7DqXfRno

[icepac]

Then we also need the I153, turbocharged, with a pressurized cockpit.

[nrshida]

Greg's got some great videos I've watched them all. Spit14'd have to perked if HTC heard what he said about 150 octane & manifold pressures.

[eddiek]

Recalling my lengthy visit with the gentleman who flew Jugs with the 9th AF during the Second World War, remember him telling me that oftentimes before a new aircraft was released or delivered to a squadron, it went through a "depot"(his words, not mine) where it was set up for the particular theater it would be operating in.
Here is the closest description to what he described:
https://en.wikipedia.org/wiki/List_of_United_States_Army_Air_Force_modification_centers

Not exactly a field mod, it is still interesting that the USAAF had to made adjustments to it's aircraft before sending them into combat. 

[drgondog]

Recalling my lengthy visit with the gentleman who flew Jugs with the 9th AF during the Second World War, remember him telling me that oftentimes before a new aircraft was released or delivered to a squadron, it went through a "depot"(his words, not mine) where it was set up for the particular theater it would be operating in.
Here is the closest description to what he described:
https://en.wikipedia.org/wiki/List_of_United_States_Army_Air_Force_modification_centers

Not exactly a field mod, it is still interesting that the USAAF had to made adjustments to it's aircraft before sending them into combat.

Depots primarily installed production level updates sent to field as kits because a.) the production line would not be stopped to retrofit on the line, b.) the upgrade was deemed necessary for theatre combat operations, or c.) modification were made because they were necessary (wiring Harness, Radios, etc) and manufacturer Field Service reps communicated the mods as Change Requests.

Depots also performed Division wide - or block of airplanes within Division - maintenance, engine overhauls, major repairs not available at Service groups attached to fighter/bomber wings, etc.

[Squire]

Too bad re field mods. The trouble is though there were many such "tweaks" in the field for many WW2 a/c. It's kind of hard to go down that road because every fan of every plane is going to dig up something. I think HTC did it right by trying to stick to the "stock" planes as much as they could.


...ya interesting vid.

[seano]

Fly the B.  It does very well above 28k

[Chalenge]

Too bad re field mods. The trouble is though there were many such "tweaks" in the field for many WW2 a/c. It's kind of hard to go down that road because every fan of every plane is going to dig up something. I think HTC did it right by trying to stick to the "stock" planes as much as they could.


...ya interesting vid.

Actually we already have the biggest field mod there was in the war. Every B-29 was produced in unusable condition and then field modified and upgraded before it could perform any mission. The B-29 was not suited to fly from India or Iwo as it was produced, but modified in the field to perform its duty.

Many of the fighters were like the P-51 in that they were assembled in forward areas, like England, and this mod was just part of that process.

[DaveBB]

Actually we already have the biggest field mod there was in the war. Every B-29 was produced in unusable condition and then field modified and upgraded before it could perform any mission. The B-29 was not suited to fly from India or Iwo as it was produced, but modified in the field to perform its duty.

Many of the fighters were like the P-51 in that they were assembled in forward areas, like England, and this mod was just part of that process.

Very interesting! What did they do to B-29s after they rolled off the assembly line to get them ready for combat?

[Shuffler]

Very interesting! What did they do to B-29s after they rolled off the assembly line to get them ready for combat?

Waxed them