Merlins > Packard vs RR

[FLYBOYJ]

Originally Posted by schwarzpanzer

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."

Originally Posted by schwarzpanzer

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....

Originally Posted by schwarzpanzer

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.

Originally Posted by schwarzpanzer

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

Originally Posted by schwarzpanzer

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

No problem!

[schwarzpanzer]

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]

Originally Posted by schwarzpanzer

Originally Posted by schwarzpanzer

Yes, those were my thoughts.

Yep!

Originally Posted by schwarzpanzer

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

Originally Posted by schwarzpanzer

Maybe this is where the reports came from?

That would be my guess

Originally Posted by schwarzpanzer

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

and that they did!

Originally Posted by schwarzpanzer

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!

Originally Posted by schwarzpanzer

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.

Originally Posted by schwarzpanzer

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.

Originally Posted by schwarzpanzer

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.

Originally Posted by schwarzpanzer

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

Originally Posted by schwarzpanzer

Glad you understand my banter!

So sweat!

[plan_D]

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

[cheddar cheese]

Yep!

[evangilder]

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]

Originally Posted by evangilder

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]

Exactly. That will make your sphincter tingle!

[wmaxt]

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]

Originally Posted by wmaxt

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.

[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]

Originally Posted by FLYBOYJ

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]

Originally Posted by FLYBOYJ

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....