Merlins > Packard vs RR

[wmaxt]

One thing about the Merlin in the US durring the war. It took an average of 320hrs to overhaul and 198 average to overhaul an Allison. I don't know for sure but this might illistrate the complexity/precision required for the Merlin engines. That would make the Merlin more dependant of careful assembly and would result in a wider variation in power output possible between engines.

wmaxt

 

[FLYBOYJ]

Good point!

 

[wmaxt]

I doubt it. Recips are usually started, run for 5 mins and shut down, provided no defects are observed. Break in times could be between 10 - 20 hours. At that time variable RPMs are avoided.

That's interesting, in smaller recips, cars, bikes the key is to graduly vary thr rpms to avoid "setting" an engine in a particular rpm range. I had a guy bring me an old Honda bike for a tune-up, I found it would not rev beyond 4,500rpm because the owner never reved it beyond that, compression and tune were right on the numbers. The owner confirmed it was never reved higher and was very happy with the job said "It never ran better".

Break in time varies with the pistion ring type but I'll bow to your expertise - I'm ASE certified not A&P. Your much more familiar with aircraft.

wmaxt

 

[wmaxt]

Good point!

Thanks!

wmaxt

 

[FLYBOYJ]

On smaller GA recips it's usually about 10 hours break-in. I think some lycomings want you to avoid certain RPM ranges. Also during break in mineral oil is used in lieu of the regular motor oil....

 

[wmaxt]

On smaller GA recips it's usually about 10 hours break-in. I think some lycomings want you to avoid certain RPM ranges. Also during break in mineral oil is used in lieu of the regular motor oil....

Ya, cars and bikes also have rpm restrictions the first 10 hours, some like Suzuki requires running the engine in top gear (for a load) at ~2,000 and wide open to about 2/3ds red line and then blip the throttle (to cool the pistons) as you coast down. You do that about 10 times to force the rings against the bores. Engine oil is normaly just good oil but is changed at 100 to 600mi the first time.

Interestingly one shop I worked at set up a show in another location, to transport the bikes we rode them. As we were trying to stock the second location, across 15 miles of desert and we were young we ran those bikes hard, much harder than we were supposed to. I watched those bikes for several years (until I went back to school) and the bikes we ran the hardest were the best bikes we ever sold. They got measurably better power, economy and required the least maintenance. Valve adjustments in particular required Half the shim changes (overhead cam shim/bucket adjustment) of any other bikes I ever did!

Sorry I strayed from the topic.

wmaxt

 

[FLYBOYJ]

On smaller GA recips it's usually about 10 hours break-in. I think some lycomings want you to avoid certain RPM ranges. Also during break in mineral oil is used in lieu of the regular motor oil....

Ya, cars and bikes also have rpm restrictions the first 10 hours, some like Suzuki requires running the engine in top gear (for a load) at ~2,000 and wide open to about 2/3ds red line and then blip the throttle (to cool the pistons) as you coast down. You do that about 10 times to force the rings against the bores. Engine oil is normaly just good oil but is changed at 100 to 600mi the first time.

Interestingly one shop I worked at set up a show in another location, to transport the bikes we rode them. As we were trying to stock the second location, across 15 miles of desert and we were young we ran those bikes hard, much harder than we were supposed to. I watched those bikes for several years (until I went back to school) and the bikes we ran the hardest were the best bikes we ever sold. They got measurably better power, economy and required the least maintenance. Valve adjustments in particular required Half the shim changes (overhead cam shim/bucket adjustment) of any other bikes I ever did!

Sorry I strayed from the topic.

wmaxt

You know, very similar with aircraft engines. i knew a gut who had a Grumman Tiger - Ran it close to red line but maintained it accordingly. The engine has a 2000 hr TBO. His went to 3500 hours, still had good compression and hardly burnt any oil.

Maybe this RR/ Packard mystery is in the "break in?"

 

[wmaxt]

You know, very similar with aircraft engines. i knew a gut who had a Grumman Tiger - Ran it close to red line but maintained it accordingly. The engine has a 2000 hr TBO. His went to 3500 hours, still had good compression and hardly burnt any oil.

Maybe this RR/ Packard mystery is in the "break in?"

Maybe, or maybe a combination of detailing and break in OR it isn't really there in the first place.

wmaxt

 

[FLYBOYJ]

You know, very similar with aircraft engines. i knew a gut who had a Grumman Tiger - Ran it close to red line but maintained it accordingly. The engine has a 2000 hr TBO. His went to 3500 hours, still had good compression and hardly burnt any oil.

Maybe this RR/ Packard mystery is in the "break in?"

Maybe, or maybe a combination of detailing and break in OR it isn't really there in the first place.

wmaxt

Yep! I'll state again; "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!"

 

[KraziKanuK]

posted by Buzzsaw on the UBI Il-2 forum

"Couple comments on the Packard Merlin:

I am currently doing a documentary on a Canadian Ace James Edwards, who got most of his kills in the Desert as a Sergeant pilot in Kittyhawks in '42.

However, he was later promoted to Wing Commander, and commanded a Canadian wing of 4 Squadrons of Packard engined Spitfire XVI's in 2nd TAF in the spring of '45.

He says that they ran the Packards at 81 inches MAP, (+25 boost) for most of 1945, but found there were issues with reliability which they could not deal with in the temporary airfields they were operating out of at the end of the war, so he made a decision to downrate the operating boost at the very end of the war, (last few weeks) back to 72 inches MAP, +18 boost. At that level of boost, they had no reliability problems at all.

He said the British manufactured Merlins in Spit IX's had a better reliability record at +25 boost than the Packards in the Spit XVI's, perhaps because of Rolls Royce's more stringent manufacturing standards. He also mentioned that the RAF Mustang Squadrons based out of Britain continued to use +25 boost, since they could deal with the relibility issues more successfully in their better equipped permanent facilities. These Squadrons also often used Merlin engines as replacements in their Mustangs when the original Packards went over their max. operating hours."

 

[FLYBOYJ]

That's good but one thing was left out - at 81" what was the RPM? I find a lot of folks talk about MP and boost but always exclude engine RPM in the discussion. By keeping the throttle at a certain setting, the MP can be varied by using prop control. When operating an aircraft with a controllable pitch propeller, the two are related in their operation and many charts in the POH show the relationship in climb and cruise performance.

That tells me that when they were operating out of these temp airfields, they were probably doing "short field takeoffs" because of field length, or the field might of been at a higher elevation above sea level requiring more power for take off.

Again, while I believe your source, they only way to prove that RR Merlins were "tighter" built is to actually examine drawings and compare the two.

I would also like to know what components were failing. Valves? Piston Rings? Bearings? Cylinder heads? Knowing that will also provide more information of how the engines were being operated and what components were inferior. Many times pilots won't concern themselves with the root cause of the problem.....

 

[wmaxt]

While there were some reliability issues on the early production Packards, that the RR Merlins were significantly more precise isn't likely. Plus, were talking short field, max power, poor maintenance and lots of dust as contributing factors.

Recently a DB crank from a Bf-109 was taken to RR. After anyalizing the crank, RR gave it back with the warning: "Take care of it WE can't duplicate it" . With an additional 50/60 years advancement in experiance and technical know how it's unlikely they were much better in the '40s, not to mention in a war.

Like Flyboy has mentioned these differences are pretty subjective. Do we have any comments from US pilots that might have had both engines, as a counter point?

wmaxt

 

[FLYBOYJ]

Recently a DB crank from a Bf-109 was taken to RR. After anyalizing the crank, RR gave it back with the warning: "Take care of it WE can't duplicate it" . With an additional 50/60 years advancement in experiance and technical know how it's unlikely they were much better in the '40s, not to mention in a war.

wmaxt

I heard about that! I guess the DB tolerances were amazingly tight and the crank, when measured fell right at nominal!

 

[Gemhorse]

Alex Henshaw commented in his book, ''Sigh for a Merlin'';
''The new Merlin engines came from Packards and although they were beautifully finished, they had cut out one of the machining processes on the piston skirt, the result of which was that on many of the machines one would get one or two distinct thuds as if the engines were about to seize up. Mostly, however, they settled down...''

Quite an interesting read on the RR thoroughbreds....

Gemhorse

 

[FLYBOYJ]

Alex Henshaw commented in his book, ''Sigh for a Merlin'';
''The new Merlin engines came from Packards and although they were beautifully finished, they had cut out one of the machining processes on the piston skirt, the result of which was that on many of the machines one would get one or two distinct thuds as if the engines were about to seize up. Mostly, however, they settled down...''

Quite an interesting read on the RR thoroughbreds....

Gemhorse

Ah-ha! Now here getting somewhere!

 

[helmitsmit]

I heard a report from an ex Mk1X and XV1 pilot that Packard used it metric measurements which might make a difference. There was also a dead spot on the Packards when at a certain RPM, I think 2400rpm. He also said the is fellow pilots couldn't keep up with his older Mk1X when they had XV1s.

 

[Twitch]

Christ, Packard brought the Merlin into the modern world of production line assembly that RR never had at that point. Packard was able to improve reliability due to standardizing manufacture and assembly proceedures instead of assembling engines in a one off atmosphere of the quaint little shop. This standardization learned in automobile assembly line operation ensured that parts were actually interchangable in the field to a far higher degree than they were before. The ability to produce LARGE NUMBERS of engines of equal quality was the key that Packard brought to the mix.

The Merlin was a great engine and Packard's production of it by no means diminished it.

 

[helmitsmit]

Well, there are so many things I've heard all pointing the same way.

 

[chris mcmillin]

I read a book by Don McVicar that had an experience with his Mosquito MK25 with Packard Merlins. He was going to race in the 1948 Bendix from Long Beach, CA to Cleveland, OH. He was based in Montreal and was ferrying the airplane to LB, when they had an exhaust stack go bad. They stopped in Wichita KS and had the stack repaired. On climb out after a harrowing overweight take off, one of the Merlins threw a rod out of the crankcase. He didn't mention the power setting, but I assume it was high. The mechanic he had with him explained that this Merlin was one that didn't incorporate "blended rods", like RR. There was some stress riser in the shape of the connecting rod that Rolls blended out, Packard hadn't yet done it. The mech said that airplanes with Packards had a reputation for this and some CO's sometimes pulled the engines and had them replaced with RR.

I assume that sometime down the line the problem was rectified. At that same Cleveland race, a National Airlines pilot named Anson Johnson won the Thompson Trophy in his Mustang that had been modified to accept the Packard Merlin 225 low altitude engine used in the Mosquito MK 25! He used water injection to keep the induction temps low and turned the prop governor up to allow an overspeed of 3200 rpm, getting about 90 in hg at 650 feet msl.

Those speaking of mixture controls on these big recips. They aren't like a small light airplane. The are ACM. Automatic Mixture Controls. They set the mixture for the barometric and manifold pressure needs sensed by the carbs myriad of diaphrams. The only mixture control selections on any Mustang I have ever seen is Run and Idle cut-off, and Rich, Auto Lean, and Idle Cut Off. The B-25 had Auto Rich, Auto Lean, and Idle Cut Off. Same with the DC-3.

The 81 inches on take off was I'm sure perilously close to detonation inducing induction temperatures without the aid of water injection. I am not suprised that there were reliability problems. Only the low altitude engines could make this MP because of the way the blower was set-up, a high altitude engine will only make about 67 at 3000rpm with the auto regulator blocked off. And by the way, the rpm was set by the propeller governor and it is 3000 rpm on a Merlin, also the only way to spin the blower fast enough to get 81 inches is to turn that rpm. (Any attempt to get high manifold pressure by using high blower down at low altitude will only increase induction temps and reduce hp to the prop because of the power used to turn the too dense air through the too coarse gearing for the conditions.)
Great thread guys.
Chris...

 

[helmitsmit]

I think RR used similar techniques in 1940 with the speed Spitfire and a modified merlin III that also ran at 3200rpm and gave 2130hp.