Merlins > Packard vs RR

schwarzpanzer · Aug 23, 2005

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 · Aug 23, 2005

schwarzpanzer said:
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 · Aug 23, 2005

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 · Aug 23, 2005

wmaxt said:
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 · Aug 23, 2005

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 · Aug 23, 2005

KraziKanuK said:
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 · Aug 24, 2005

Good points, FBJ!

FLYBOYJ · Aug 24, 2005

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 · Aug 24, 2005

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 · Aug 24, 2005

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.

FLYBOYJ · Aug 24, 2005

schwarzpanzer said:
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!!!!

Click to expand...

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?

I doubt many RAF Maintenance Officer would allow this - it's like allowing your squadron or group to be a "guinea pig."

schwarzpanzer said:
Aircrews would of really noticed the difference during take off and climb and would of screamed bloody murder over this performance lapse.

Click to expand...

Did take off times really matter to Lancs' crews?

Not so much the time, it's the rate. With a certain load the aircraft is expected to climb so many feet per minute. This is usually a "barometer" of aircraft performance....

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

Click to expand...

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?

No - the hp readings and torque are taken right off the crank shaft.

schwarzpanzer said:
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?

That I don't know??? Maybe someone else could shed some light

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

No problem!

schwarzpanzer · Aug 24, 2005

I doubt many RAF Maintenance Officer would allow this - it's like allowing your squadron or group to be a "guinea pig."

Yes, those were my thoughts.

I suppose testing over England would be done?

Maybe this is where the reports came from?

I expect the 1st Packard Merlins would have slight teething trouble?

Also, I heard of a Spitfire fitted with a DB605 engine and an attempt by the Germans to copy the Merlin that went wrong and was scrapped, anymore info on this?

Not so much the time, it's the rate. With a certain load the aircraft is expected to climb so many feet per minute. This is usually a "barometer" of aircraft performance....

Ah, so it's cumulative is it?

No - the hp readings and torque are taken right off the crank shaft.

Well, ram-air effects from NACA cowls and road/air drag etc all cause hp differences.

There's other factors too, but I'm rusty , you sure nothing like this happens with aircraft engines?

That I don't know??? Maybe someone else could shed some light

I can find out about DeHavilland, dunno the rest, I wonder if DeHavilland ever built Merlins for the Mossie, if so I might be able to check that out.

Glad you understand my banter!

FLYBOYJ · Aug 24, 2005

schwarzpanzer said:
I doubt many RAF Maintenance Officer would allow this - it's like allowing your squadron or group to be a "guinea pig."

Click to expand...

schwarzpanzer said:
Yes, those were my thoughts.

Yep!

schwarzpanzer said:
I suppose testing over England would be done?

I would think so. Perhaps the curiosity was raised during missions or after a functional check flight after the engines were installed

schwarzpanzer said:
Maybe this is where the reports came from?

That would be my guess

schwarzpanzer said:
I expect the 1st Packard Merlins would have slight teething trouble?

and that they did!

schwarzpanzer said:
Also, I heard of a Spitfire fitted with a DB605 engine and an attempt by the Germans to copy the Merlin that went wrong and was scrapped, anymore info on this?

Never heard that one!

schwarzpanzer said:
Not so much the time, it's the rate. With a certain load the aircraft is expected to climb so many feet per minute. This is usually a "barometer" of aircraft performance....

Click to expand...

Ah, so it's cumulative is it?

To a point. You would expect a certain time to get to an altitude, or best climb rate vs time, this is referred as 'Vx.' Best climb over a given distance is 'Vy.' These values are usually shown in the pilot's manual and will vary with air temp, altitude, and air density.

schwarzpanzer said:
No - the hp readings and torque are taken right off the crank shaft.

Click to expand...

Well, ram-air effects from NACA cowls and road/air drag etc all cause hp differences.

Yes, on the airframe, but performance values are taken static in the test cell without the benefit of ram air.

schwarzpanzer said:
There's other factors too, but I'm rusty , you sure nothing like this happens with aircraft engines?

Not normally - I've worked on a lot of GA recip aircraft. When "bug-smasher" engines come from the factory, they usually are pretty consistent on their performance when compared to other engines built at the same time.

schwarzpanzer said:
That I don't know??? Maybe someone else could shed some light

Click to expand...

I can find out about DeHavilland, dunno the rest, I wonder if DeHavilland ever built Merlins for the Mossie, if so I might be able to check that out.

I don't think so - most airframe manufacturers stay away from making their own engines

schwarzpanzer said:
Glad you understand my banter!

So sweat!

plan_D · Aug 25, 2005

There was a Spitfire with a DB605, some people have pictures of it on here.

cheddar cheese · Aug 25, 2005

evangilder · Aug 25, 2005

Another point with horsepower/take off. Rate of climb is part of the barometer, but if you have a fully loaded bomber and are coming to the end of the runway fast, the more horsepower, the better. That's not the place to find out you are deficient.

Like our maintenance officer says "There's no replacement for displacement". I know there is a difference, but you get the idea.

FLYBOYJ · Aug 25, 2005

evangilder said:
Another point with horsepower/take off. Rate of climb is part of the barometer, but if you have a fully loaded bomber and are coming to the end of the runway fast, the more horsepower, the better. That's not the place to find out you are deficient.

There is no worse feeling in the world when you have 500' of runway left and you have not lifted off yet!

I could imagine the pucker factor when you're carrying 10,000 pounds of bombs to boot!

evangilder · Aug 25, 2005

Exactly. That will make your sphincter tingle!

wmaxt · Aug 25, 2005

If a casting is not sufficently stress relived before machining it will (if its going to) crack when power (stress) is put to it.

12.6:1 is the ideal for a Lean Burn engine, giving low emisions and fuel economy. 13.7:1 is normaly used/ideal for max power, at least in older engines (pre computer controls and advanced designs). This is why performance carbs have an enrichment circut or "Power Valve". Newer engines use an oxygen sensor and with the computer to adjust the fuel mixture until a minimum oxygen content is reached giving the engine just as much as it can use/needs. Much less than 12.6:1 burns engine components and more than 13.7/14:1 starts fouling plugs, rings, oil, and valves with unused fuel/deposits. Excesively rich mixtures can also damage turbos.

Another thing to consider is that bombers are loaded differently for each mission the differences in weight will also change the relative performance for those loadouts. This is true even within a formation to some extent.

New Reciprocating engines also produce less horsepower when new than after being fully broken in. This added power can be a significant percentage, as much as 10%. Could the RR engines have been broken in better in the test cells, if there really was a difference?

wmaxt

FLYBOYJ · Aug 25, 2005

wmaxt said:
Could the RR engines have been broken in better in the test cells, if there really was a difference?

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.

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