Who made the better Merlin?

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Hot Wings

Grumpy Cynic
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My father worked on both versions when they were current production. Had nothing good to say about the RR version. "Too picky to build....and they leaked"
Point of interest: The airbase here got a significant portion of it's electricity from the dyno testing of the rebuilt engines.
 

Hot Wings

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Regarding the oil leaks my understanding was that Packard simply used better seal material.
Never worked on either myself, but my father said the RR had no/few seals. A lot of hand lapping on a table to make flat surfaces - thus the extra work and leaks.
 

Aesquire

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Packard produced Merlins got ( after some time ) an improved supercharger. Rolls Royce didn't because they didn't feel they had the luxury of interrupting production when the engine was in such demand. Other improvements were introduced by Packard.

It wasn't unusual for Lancaster bombers to have a mix of Rolls Royce & Packard engines. They were interchangeable. Same Quick Change packages. Reviews from the time are mixed. Some said one type ran rougher, others the other.

Merlins for Mustangs built by Packard used a different prop shaft but otherwise were identical to the same mark built for British planes. ( note that different models used different supercharger setups. Single and two stage, & various gearing )

Lovely engines.

Ford in England and Packard engines also had "tighter tolerances" on parts to ease assembly, while Rolls Royce engines needed more hand fitting.

Iirc, a visitor to a P&W plant in WW2 commented that the assembly line didn't have a vise on each station, as was common practice in other plants, and was told the reason was they did not hand fit parts. If it didn't fit, the part was sent to be reworked or scrapped.

Interchangeability is a challenging task. We take it for granted today. As a former QC guy in machine shops, I can tell you a LOT of effort goes into precision, if only to make labor costs less.
 

crusty old aviator

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During the war, the RR engines were considered superior, but after production ended, the Packards became the more valued engines because of their readily interchangeable parts, especially in the US (Yanks aren’t into hand-fitting everything: build it right the first time).
 

Riggerrob

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Modern Reno Air Racers prefer bomber engines because the crank cases are a bit stronger. Then they mix and match RR and Packard parts. Allison piston rods are often installed because they are stronger than Merlin piston rods.
Then racers boost super-chargers to obscene pressures (more than 50 inches of mercury) and try to finish the race before parts melt.
 

Tiger Tim

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I wonder if the RR Crecy (think two stroke Merlin with twice the power) could have seen the same development potential that the Merlin has had.
 

Vigilant1

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you forget that the rolls were made under enemy fire,take a look at pictures from the plant at the time to see just what fierce determination looks like
Amen. No need for motivational speeches from management, no time for offsite teambuilding exercises. Those machinists, fitters, clerks, and janitors traveled through bombed out neighborhoods to get to their jobs--they knew exactly what the stakes were.
 

Deuelly

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Modern Reno Air Racers prefer bomber engines because the crank cases are a bit stronger. Then they mix and match RR and Packard parts. Allison piston rods are often installed because they are stronger than Merlin piston rods.
Then racers boost super-chargers to obscene pressures (more than 50 inches of mercury) and try to finish the race before parts melt.
They run the standard block but the heads are what they refer to as "transport" heads. They're a lot beefier and handle the higher combustion pressures better.
Stock Allisons and Merlins could pull 50 inches during WWII with no trouble. That's at or below take-off power for those engines. The guys racing at Reno are seeing in the neighborhood of 120 inches.

Brandon
 

pictsidhe

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The insatiable demand for their engines meant that Rolls Royce had to introduce changes without interrupting production. Clearly, this made major changes in design or production tricky to implement. Some other war manufactuers weren't allowed to change hardly anything on established lines, for fear of disrupting the flow of their badly needed materiel. The UK had it's back up against the wall for a large part of the war, better was most definitely second to 'that'll do, but could you make them three times faster?'.

The Crecy was one of many victims of resource shortages. It showed huge promise, but was not allocated much development. With the Merlin and Griffon working, the government gave them lions share of development resources. RR Heritage has a good book on the Crecy, BTW.
 

Aesquire

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Ditto on demand for production over improvement. Allison had the same problem. Without being under threat.

Allison is often criticized for not making 2 stage mechanical superchargers like the Merlin later versions ( as used in the P-51B,C,D ) & P&W, soon enough, but Air Corps specs were for single stage supercharged engines under the assumption that turbos would provide a more efficient second stage. Unfortunately only the P-38 would be produced in large numbers with the desired combination. The turbochargers just were either not ready yet, ( P-39 ) and/or Too hard to package in a small single engine fighter. ( P-39, XP-37, P-40, P-51a )

And the P-38 also suffered from "good enough, make more" and had extensive trouble with turbocharger control, overspeeing & exploding. And cooling control, oil concealing to goo, fuel dropping out of suspension from over cooling, etc. Problems over cold Europe at high altitude that weren't an issue in the Pacific.

Possibly the most missed opportunity was the Allison variants of the B-29.
https://en.m.wikipedia.org/wiki/Boeing_XB-39_Superfortress

Arguably building this version would have saved countless lives as the Wright powered B-29 was underpowered and had a staggeringly high engine failure and fire rate. Nearly half???? of all B-29s lost in the war were from engine related issues, not enemy action.

I'd say those numbers are unbelievable, but from what I've read about Wright corporate rigidity and poor QC, ( in some Quality Control advanced classes Wright is cited as "How not to" ) I buy them.
 

Toobuilder

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...which also begs the question of a P-38/Merlin package. If they could only slow production down enough to develop this combo, I'll bet it would have been something spectacular.
 

Kyle Boatright

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...which also begs the question of a P-38/Merlin package. If they could only slow production down enough to develop this combo, I'll bet it would have been something spectacular.
The P-38K was an experiment with the Merlin. Performance was supposed to be outstanding, but that might have been the result of the prop change (IIRC).

If you wanna go up high, the Allison w/turbo was a better engine. The P-38's biggest fundamental limitation was its airfoil which was a relatively low speed airfoil but gave good low speed and climb performance for such a large aircraft, at the expense of speed and limiting mach. I doubt Kelly Johnson saw the mach limit thing coming when he picked the airfoil...

The other airplane with a turbo was the P-47.
 

Deuelly

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I've had the pleasure of rigging a P-38 turbo system many times. It's an amazing combination of cables, pulleys, bellcranks and push/pull tubes. It's amazing they kept as many running as they did. That being said, I'd have picked that combination over the Merlin any day. When set up right, and with the late model turbo controller it's a good solid system.

Brandon
 
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