Merlins > Packard vs RR

[KraziKanuK]

Picked this up on another forum:

Ho-Hun
"A small point was made to me by an ex-Lancaster X pilot some years ago, that will advance this thread not one tiny bit. He mentioned that the Packard Merlins, which powered the Lanc X, gave only about 82% of the power of the equivalent Rolls Royce Merlins, and that crews would practically kill to get the RR Merlin Lancs because they took off more quickly, and had a higher ceiling. To aircrews ceiling meant life."

 

[evangilder]

I have not heard that, but there were different versions of the Merlin, so maybe that could explain the difference.

 

[FLYBOYJ]

I seen this on another post. I have a hard time believing this for several reasons.

1. If Packard was to build the Merlin under license, their products would have to comply with the same requirements as a RR built one unless Packard convinced the USAAF for engineering and performance waivers - I doubt that happened.

2. When each engine was finished, it was run in a teat cell, again if RR set the original parameters, I can't see Packard or the USAAF procurement office allowing sub-performing engines to be delivered.

3. I never heard of this problem in the fighter community?!?

Comments anyone else?

 

[KraziKanuK]

RR Merlins were completely re-engineered by Packard to American manufacturing standards, starting with the drawings.

You have never heard of all the problems the Packard Mustangs had when introuduced?

 

[evangilder]

They didn't really re-engineer the Merlins. The drawings that were provided were not the usual customary drawings that American engineers are used to, so they had to tear it down and do the drawings that they expected to build the motors.

Probably the best liquid cooled engine ever developed was the Rolls Royce Merlin. Since 1935 the British had the engine under continuious development. designed to be hand made, however, the enginedid not lend itself to mass-production techniques. On June 24, 1940 Packard was asked by the British goverment to redefine the engine and make it practical for American mass-production. The process required a complete set of new drawings which Packard prepared under the direction of Jesse Vincent. The Rolls Royce drawings from which Packard worked lacked details and specifications and were not in the third angle projection as is the American practice. The Rolls Royce drawings also omitted tolerances which Packard had to develop from an actual engine. It became a matter of taking an actual engine apart and going backwards to develop the needed drawings and specifications. Packard, under the direction of William H. Graves, chief metallurgist for the company, also had to develop the foundry specifications for the Packard-made engine.

 

[DaveB.inVa]

Sounds to me like a case of national pride.

 

[wmaxt]

I've read in several places that the Packard Merlin had some changes like more bolts holding valve covers and crank pan on, to eliminate some leakage due to uneven tension on those parts.
There were also several Blower styles and prop speed reduction setups that affect engine operation, climb, speeds and service ceilings.
It's also possibly that curing/annealing processes had to be adjusted for the rapid pace of manufacturing. Normaly complicated castings require from 6mo. to 2 years to cure before machining and use to avoid stress cracks.
Lastly on the introduction of the P-51s/Packard Merlins in the UK, there were some failures, I've wondered if they suffered, in part, from hand measured/mixed octain adjustments like the first P-38s did.

wmaxt

 

[FLYBOYJ]

You have never heard of all the problems the Packard Mustangs had when introuduced?

I heard there were some, but they were quickly fixed. I remember reading much of the problems involved operating the engine with the right mixture and overboosting. I heard that most of the RR drawings gave measurements in fractions and these had to be converted to 3 place decimal measurements. This coupled with lack of tolerances as previously posted shouldn't of given great problems.....

 

[the lancaster kicks ass]

in service RR ones were found to be more powerful yet packard were found to have slightly better fuel economy.........

 

[FLYBOYJ]

. Normaly complicated castings require from 6mo. to 2 years to cure before machining and use to avoid stress cracks.

Explain that one to me wmaxt? I've worked with aircraft castings and there wasn't no "cure" time on the ones I worked on (both sand and investment castings). After they were poured and cooled they were heat treated and then machined. Maybe the process was different 60 years ago.

The long lead times were uaully due to making moulds on the more complicated parts.

 

[wmaxt]

. Normaly complicated castings require from 6mo. to 2 years to cure before machining and use to avoid stress cracks.

Explain that one to me wmaxt? I've worked with aircraft castings and there wasn't no "cure" time on the ones I worked on (both sand and investment castings). After they were poured and cooled they were heat treated and then machined. Maybe the process was different 60 years ago.

The long lead times were uaully due to making moulds on the more complicated parts.

The heat treating is the key, Flyboy, as in a forging a part, it is anealed (heated) to relive stress in the part. Engine blocks (automotive) are often not heat treated in manufacturing and left to cure naturaly. I learned about it studying manufacturing, in the 60s when Ford came out with its high performance 427/428 engines they would pick the earliest castings they could because the natural heating/cooling relived enough stress to allow the extream machining required (all FE blocks started as 331cid castings), and still not break in use.

This may/may not have anything to do with the Packard Merlin but is more of an "I wonder" on my part.

wmaxt

 

[FLYBOYJ]

. Normaly complicated castings require from 6mo. to 2 years to cure before machining and use to avoid stress cracks.

Explain that one to me wmaxt? I've worked with aircraft castings and there wasn't no "cure" time on the ones I worked on (both sand and investment castings). After they were poured and cooled they were heat treated and then machined. Maybe the process was different 60 years ago.

The long lead times were uaully due to making moulds on the more complicated parts.

The heat treating is the key, Flyboy, as in a forging a part, it is anealed (heated) to relive stress in the part. Engine blocks (automotive) are often not heat treated in manufacturing and left to cure naturaly. I learned about it studying manufacturing, in the 60s when Ford came out with its high performance 427/428 engines they would pick the earliest castings they could because the natural heating/cooling relived enough stress to allow the extream machining required (all FE blocks started as 331cid castings), and still not break in use.

This may/may not have anything to do with the Packard Merlin but is more of an "I wonder" on my part.

wmaxt

OK- I remember seeing a company I used to vist do that for landing gear forgings. "Menasco" had a division in Burbank, Ca., they made lots of civilian and military landing gear. On some of the Boeing stuff they would let some of their forgings sit for awhile before they started machinig them, but they always got heat treated first. I thought they did this for schedueling.

 

[wmaxt]

OK- I remember seeing a company I used to vist do that for landing gear forgings. "Menasco" had a division in Burbank, Ca., they made lots of civilian and military landing gear. On some of the Boeing stuff they would let some of their forgings sit for awhile before they started machinig them, but they always got heat treated first. I thought they did this for schedueling.

For lower output/stress castings heat treating is not always criticle. In more important castings heat treating is a must and I would think landing gear fits that catagory.

You are also right in that with heat treating a part may be worked anytime. It's also true that the plant you saw the castings in the yard, were probably just setting up a slight backlog for scheduling purposes.

My original thought was maybe the first Packard Merlin engines weren't heat treated and that changed when the cracks were found.

wmaxt

 

[FLYBOYJ]

OK- I remember seeing a company I used to vist do that for landing gear forgings. "Menasco" had a division in Burbank, Ca., they made lots of civilian and military landing gear. On some of the Boeing stuff they would let some of their forgings sit for awhile before they started machinig them, but they always got heat treated first. I thought they did this for schedueling.

For lower output/stress castings heat treating is not always criticle. In more important castings heat treating is a must and I would think landing gear fits that catagory.

You are also right in that with heat treating a part may be worked anytime. It's also true that the plant you saw the castings in the yard, were probably just setting up a slight backlog for scheduling purposes.

My original thought was maybe the first Packard Merlin engines weren't heat treated and that changed when the cracks were found.

wmaxt

Agree wmaxt - I don't know, until someone could produce test cell data showing that RR built Merlins put out more power than Packard Merlins, I think it was "all in the pilot's head."

 

[wmaxt]

Agree wmaxt - I don't know, until someone could produce test cell data showing that RR built Merlins put out more power than Packard Merlins, I think it was "all in the pilot's head."

Your most likly right, there were so many prop reductions and supercharger combinations that comparisons must be taken with a grain of salt.

There is a test of two Spitfire IXs and a P-38F. The P-38F was right in the middle performance wise between the Spits. The only difference in the Spitfires was the prop reduction ratios.

wmaxt

 

[FLYBOYJ]

Agree wmaxt - I don't know, until someone could produce test cell data showing that RR built Merlins put out more power than Packard Merlins, I think it was "all in the pilot's head."

Your most likly right, there were so many prop reductions and supercharger combinations that comparisons must be taken with a grain of salt.
wmaxt

I think this is where part of the mystery lies, aside from a pilot's over-active imagination.

CASE IN POINT: Years ago I worked on this guys airplane. After about a month he claimed he wasn't getting the right "fuel burn." I cleaned his carb., removed and re-timed his mags, inspected all the fuel filters and there was nothing wrong. Finally I flew with him and he was going by the position of the fuel needle on the gage based on time in the air. When we actually did a fuel tank 'top off' and computed the fuel used based on the time in the air, the fuel burn was right where it should be. When he argued about the gage, I told him the FAA only required the fuel gage to be accurate reading empty in a level-flight attitude!

The moral of the story?!? Pilots will believe 'things' based on inaccurate sources and here-say, those 'things' will sometimes find their way into assumed law and operating procedures that no one could remember where it was written! 8)

 

[schwarzpanzer]

I guess that the RR's were stress-relieved, the Packards weren't?

Annealed means softened IIRC?

For the Packard the carb was changed and I think the supercharger.

The carb was draw-through in the RR, one of the keys to it's power! But may have been blow-through with the Packard, like the DB605's FI?

The simplest possible explanation is just that the RR's carbs were set up for a richer fuel/air mixture than with the RR's?

 

[FLYBOYJ]

I guess that the RR's were stress-relieved, the Packards weren't?

That shouldn't have anything to do with engine performance.

Annealed means softened IIRC?

Yes - it is used to relieve stresses, and to soften metal for additional processing (machining)

For the Packard the carb was changed and I think the supercharger.

Later models had a pressure carb in lieu of a float carb. if anything this should of enhanced perfromance

The carb was draw-through in the RR, one of the keys to it's power! But may have been blow-through with the Packard, like the DB605's FI?

This still should not make a difference

The simplest possible explanation is just that the RR's carbs were set up for a richer fuel/air mixture than with the RR's?

????

I think until someone produces flight test or test cell evidence, i think this is a myth!

 

[plan_D]

I don't know the exact facts but I would imagine it would all come down to what the engineers did with the hand-built ones. We must remember that there are people out there that can just tweak a piston-engine off his own back. Surely, in the RR factory they could have had some of these people that played with these engines to increase their power. It could even have been possible in the Packard built engines but they were mass-produced and wouldn't really be tinkered with.

But then, the engineers on the line could have done it when it was in the aircraft.

 

[FLYBOYJ]

Good point D!