Merlins > Packard vs RR

[FLYBOYJ]

Originally Posted by wmaxt

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!

[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]

Originally Posted by schwarzpanzer

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

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

Originally Posted by schwarzpanzer

Annealed means softened IIRC?

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

Originally Posted by schwarzpanzer

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

Originally Posted by schwarzpanzer

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

Originally Posted by schwarzpanzer

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!

[schwarzpanzer]

I know the tricks that drag racers use to achieve silly hp figures, stress relieving is done after machining.

The only time I've seen annealing used is to soften a copper head gasket.

I think I've seen Merlins with 2 and 4 valves per cylinder, with obvious performance differences, but could be mistaken.

Draw-through carbs reduce the inlet temp and thus density, increasing power, believe me this works with a Garret T3/SU HIF44.

A richer mixture would increase performance/reliability at the expense of fuel economy and is a possibility.

The bolts weren't Whitworth-thread and maybe slight variations did make performance suffer.

At the end of the day, if any engine is blueprinted, it will produce more power than a mass-produced one.

As PlanD said though,

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

This would make a Packard be in the RR's performance league.

Personally, I reckon it's the carb/mixture, this would explain the Merlins supposed higher performance/lower economy.

Adding tetra-ethyl to the fuel would also improve performance if the octanes used were below aprox 90 RON, dunno if anyone knew that then though?

[FLYBOYJ]

Originally Posted by schwarzpanzer

Draw-through carbs reduce the inlet temp and thus density, increasing power, believe me this works with a Garret T3/SU HIF44.

A richer mixture would increase performance/reliability at the expense of fuel economy and is a possibility.

This would only be the case when "flying by the numbers." Remember all of these engines had mixture controls operated by the pilot. If one pilot felt he was operating with a high cylinder head temp., he would simply richen the mixture short of fouling plugs.

[wmaxt]

Schwarz, While your correct in your answer there is more to annealing, stress relief and heat treating. Based on how and what the desired effect is you can relive stress, harden or soften a part depending on how you heat/cool it. There are some machining procedures that also relive stress. A large complicated casting like an engine block needs some ammount of stress relief to stabilize it.

Just richening the mixture or adding octain will not add power by themselves. Coupling mixture and octain to prevent detonation, with more boost, more mechanical compression, more ignition advance will.

The type of carb is not as important as its compatability and efficency in the context of its use.

Blueprinting has to start with a bare block and goes from there. It's the optimizing of balance and clearences to their exact design perameters. Its normaly recognized that a good blueprinted engine will provide 10/12 hp per 500 cu/in or 40/60hp in a Merlin.

Bolt sizes will not affect the relative performance of an engine.

wmaxt

[FLYBOYJ]

Originally Posted by wmaxt

Just richening the mixture or adding octain will not add power, coupling that with more boost, more compression, more ignition advance will.

wmaxt

Yep!

[Parmigiano]

There is also another general consideration : those engines were about the top that technology could achieve at the time, more extreme than today's racing engines. It makes sense that different batches of the engines were a bit different, that even in the same batch an unit was better or worse than the others and that some RR batch was working better than Packard's and vice-versa.
Also there were almost infinite variants, a comparison could make sense only between units belonging to the same development level.
The Pilot impression might be right, but is not enough to state that in general 'RR were more powerful than Packards'

[FLYBOYJ]

Originally Posted by 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."

To go back to the original statement, some other things to consider...

To say the Packard Merlins gave 82% of the RR ones without the benefit of a test cell would say that at least 2 aircraft was flown at a certain altitude, at a certain power setting, and at that point airspeed, rate of climb and service ceiling was probably compared. To accurately achieve a good comparison the airframes would have to be perfect. I doubt any "perfect" Lancaster airframes were available where the asymmetry was right on the money, either from inherent quality lapse from the factory (not taking anything away from the overall quality of the aircraft) or from not being repaired, subject to field abuse (hard landings) or other operational hazards that would of changed they dynamics of the airframe. Without the benefit of test-cell data or comparisons from factory fresh airframes, I would have a hard time believing this if it came from pilots flying operational missions.

At the same time, I doubt the Air Ministry would of accepted Packard Merlins (even at the height of the bombing campaign) that were 17% deficient in performance when compared to their British cousins!!!!

[evangilder]

Good points, FBJ!

[FLYBOYJ]

Thanks!

Some other things to consider. I believe the RR Merlin put out 1,280 HP. A 17% reduction in my calculator comes out to 1,062 HP. That's a big reduction! Aircrews would of really noticed the differance during take off and climb and would of screemed bloody murder over this performance lapse.

[FLYBOYJ]

One more point.....

As some of you know major components of an aircraft come with logbooks (airframe, engine and propeller) The format of aircraft logbooks were basically the same. On engines, the usual first entry is the data gathered at the test cell when the engine is completed and at that time the engine is checked on a dyno and results annotated. These log book entries would of showed any variances in the engines......

Additionally if a crew complained to a maintenance officer about engine performance problems (especially after an engine change utilizing brand new Packards) the first place one would look is in the engine log books to see what the factory annotated about that particular engine.

Either the dyno results were wrong or falsified (I really doubt either)

or the engines put out as advertised and the deficiencies in performance were inherent in the airframe

or another variable was present that gave the RR Merlins better performance (someone tweaking them in the field, factory mods not shared with Packard, etc....)

In either case I doubt any of these gave a 17% variance between RR and Packard Merlins!

[schwarzpanzer]

Remember all of these engines had mixture controls operated by the pilot.

Didn't know that! Kinda throws the mixture point, damn!

There are some machining procedures that also relive stress.

Seriously??

On the stress-relief thing, if blocks were used but not stress-relieved from the factory. The 'use' would stress relieve them anyway.

Just richening the mixture or adding octain will not add power by themselves.

It depends I suppose, adding octane reduces inlet temps usually if it's under a bonnet, dunno about in a fuselage?

I know 12.6:1 air/fuel is optimal, though that's after twiddling for me (usual is 13-14:1), do planes usually run that?

Any higher would cool the exhaust, reducing scavenge? and that thingy that uses the exhaust heat to increase speed (what is it called? It slips me!)

Its normaly recognized that a good blueprinted engine will provide 10/12 hp per 500 cu/in or 40/60hp in a Merlin.

Bloody Yanks, why don't you use cubic centimetres like everyone else? - only kidding!

Bolt sizes will not affect the relative performance of an engine.

Actually, they can! ARP are great as are the now deceased(?) Whitworth thread.

Also:

Finally, note that Peugeot changed the bolt that holds the cam pulley on from a 12mm diameter bolt on early engines to a 10mm bolt on later ones. As with the crank bearings, why on earth they messed around with something which was fine to start with I have no idea. Maybe the smaller bolt saved 0.1 of a penny per engine and they were going through hard times. All Kent and Piper cams use blanks with the original 12mm thread in them so if you have an engine with a 10mm bolt you'll need to go and buy the 12mm one from a Peugeot dealer to be able to fit the new cam.

(Taken from Pumaracing.co.uk)

Also variations is true, look at the Sierra Cosworth, it's '205' blocks were specially selected standard '205' Pinto blocks allowing more power, whilst being 'the same'.

At the same time, I doubt the Air Ministry would of accepted Packard Merlins (even at the height of the bombing campaign) that were 17% deficient in performance when compared to their British cousins!!!!

To see were they were going wrong maybe?
More likely on a dyno than in combat that though?

Or to see if the drop in hp would be noticeable in combat?

Aircrews would of really noticed the differance during take off and climb and would of screemed bloody murder over this performance lapse.

Did take off times really matter to Lancs' crews?

Either the dyno results were wrong or falsified (I really doubt either)

Well, I know dyno readings, rolling road-readings and actual real-world readings can (and do) differ in cars, maybe it's the same with aircraft?

Maybe the piston tops/combustion chambers were polished in the Rolls etc?

The ports gasflowed etc.

If they were hand built it's likely, I know DeHavilland components were surface-ground etc, maybe RR's were too, but Packards weren't?

Is there any way to find this out?

Hope someone here understtands me, I know I'm having a hard time communicating, sorry.