Merlin vs. DB601

[Gixxerman]

Wow, some H2 owners here, nice. Always fancied one but never did.
I was ( am) mostly into Suzuki's. I love 2 strokes had all the Gts (except for the 750 triple, which a few friends had so I know them reasonably well). I took a while to get into 4 strokes but the big Gsx11's were ( currently the Gsxr11w) are my thing. Even the 80's Gsx11 weren't exactly the best handling bikes (all that weight basic physics) but the Gsxr's are so much better (more compact, lighter, much better suspension, brakes tyres - despite the power hike - make the big difference I think).

All a carb per pot, the earlier ones ran well enough (nothing quite like a well set up crisp 2 stroke hitting its power-band) but the later ones are harder to set up right but run extremely well at all speeds, the more recent bikes with fuel injection, digital ignition 'closed loop computerised control systems seem much easier to mess with (just get out your laptop, get a Dynojet Power Commander exhaust 'sniffer' when you put it on the rolling road)

 

[GregP]

Gi Gixxerman,

I had a Suzy Water Buffalo. I liked it except when it was decelerating. OK, but nothing to write home about stock. When setup up for drag racing, it was something like a 10-time national champion. About 60 - 75 HP stock, depending on the state of tune. Over 160 HP when setup up for racing, with a LOT of the weight gone.

Doesn't seem like much these days, but it was in the 1970's and 1980's. Heck, a Yamaha TZ750 only had about 160 hp, and won several world titles in road racing. When it came on the pipe, you could NOT keep the front end down ... you had to control the rise with throttle. That assumes you were within 20° of being vertical. If you were leaned over and hit the pipe, you did an instant low-side.

Meanwhile, back to airplane engines .... especially Merlins and DB 601s. I have often wondered why more DB 601/603/605's are not avialable. There were thousands sitting around after the war. Why didn't they save a few more than they did? Hard to imagine just scrapping them ... for no good reason, when they could run and be generators, or whatever. Power is power.

They used Allisons for a few decades as water pump / farm engines in the USA. Why not DB's in Germany?

 

[tomo pauk]

Price of gasoline wrecks the idea for most of the world, let alone in post war Germany.

 

[fastmongrel]

Outside of the US after the war everyone was short of money, raw materials and cash. In Britain people tried to run cars and motorbikes on Petrol mixed with Lamp Oil, waste engine oil, heating oil and other horrible brews because Petroleum was so expensive and rationed. In 1945 Germans didnt have shoes, Coal and food never mind running a gas guzzling aero engine as a generator. A lump of high quality metal scrap was worth a whole lot more.

 

[GregP]

THANKS!

Makes sense now. I always wondered ... seems such a waste to scrap engines that run well ... if nothing else, preserve them for use later. I have several V-8's for cars that are "pickled" for later use in hobby vehicles as I get the time and inclination. One has been pickled for 15 years and , because I treated it well, it has no corrosion and is ready for rebuild. I can turn it over by hand with the spark plugs out.

I have a good friend who JUST rebuilt a Chevrolet 409 (750 HP Version) after the engine had been pickled for 20 years. The car runs GREAT and will do a quarter mile so quickly it will scare you ... if you are riding. If driving, it is just plain old FUN, but hard on the tires.

We should ALL have such problems ...

 

[fastmongrel]

I have a BSA B50 engine thats sitting in a box smothered in grease waiting for the right time and frame. I put it in the box for a few weeks whilst I got on with something else that was 12 years ago.

 

[Deleted member 68059]

Hi,
The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).

P_v=P_comp ((N_in-N_out)/N_out )

Where, Pv is power to oil heating, Pcomp is supercharger impeller compressor drive power and N is shaft speed.

In other words the losses to oil
are highest when the coupling is doing its thing. The slip was around 2.5 %, the power loss
at locked condition was hence less as per equation above. The tests show
that at 0.7/1 (max slip) you`re loosing 42% of the supercharger drive power to oil.

For a 601-E, at 1.3Ata at GND>5000feet zone the coupling looses 39bhp in pure oil heating alone,
at 1.15ata (hence lower compressor pressure ratio) its reduced to 24bhp. So it doesnt take
long to imagine whats happening with fairly moderate boost increases. Going up 0.15 Ata
boost puts 61% more power to oil.

Once you`re at 17,000feet or above thats reduced to nominally insignificant (in the case
of this particular engine in that particular condition, it depends on how the secondary
control pump is set to come online).

Not too bad as long as you`re just going up and down once. But evidently if you do any sort of
time in the band between min and max slip, you need a much bigger oil cooler. I do not
know much about air operations as I`m just an engines man - but just saying that is the
case with this type of drive. Conversely it was stated by other studies that in a pure intercept
and return home scenario the coupling was actually quite nice, as it warmed the engine up
fast, and then the losses become small above rated height. So it all depends (like all
engines) on deciding what the exact nature of the application is.

Geoffery Wilde at Rolls did a study on the coupling for Stanley Hooker, as he had worked
previously with these couplings and knew their workings. Because the Merlin was a smaller
engine they knew they would have to boost it considerably higher than the DB in order to
have a chance. This means higher compressor air power, hence in a Merlin with a higher
pressure ratio compressor, the power lost to the coupling will go up and up.

Geoffery worked out that a Merlin equipped with a fluid drive (there are layout drawings
and a complete theoretical set of curves), that with projected boost developments,
that the drag of the required oil cooler would almost nullify the advantage of the
coupling (which is basically that it "fills-in" the area under the "saw-tooth"
pattern of a gearbox equipped supercharged aero engine).

This is further complicated by the characteristics of the Fottinger coupling,
which follows this mathematical behaviour.

Pt=ρ x d^5 x n^3 x c

Where Pt = power transmission capacity (Watts), d= outer diameter of coupling (m), ρ= oil density (kg/m^3), n= shaft speed (rads/sec) and c=a geometry constant (depending on the shape of internal ribs of the particular coupling and so on).

To get a compact installation Geoffrey worked out that running it off the back of a crank (like a automatic gearbox in a modern car) you`d need a huge toriod.
So (like Benz) realised it needed to be speeded up (see the n^3 term). However once you do this the viscous heating losses go up further.

This tended to sludge up the couplings, because the oils were pretty awful back then compared to what we run now, so you would often find the superchargers
on the DB not performing to factory spec at the mid-end of their lives. I`ve got a coupling here thats in "as used" condition and it extremely gummed up
inside. Not a design error really, just something that one aspect of tech. of the day didnt quite deliver on in real life. I think if Geoffery had
done the study for Stanley 6 months prior, they would definetly have at least built a test-stand.

Geoffery and Stanley hooker both visited Sinclair Fluid Drives in person to discuss
developing the coupling into the Merlin - but within a month hostilities officially
started and all efforts swung into "get the most out of what we`ve got now".

Hence the Merlin with fluid drive never happened for these two reasons.

In other words, if you want a larger lower boosted engine the fluid drive is better,
because the losses into oil are less and hence smaller oil cooler = lower drag = more speed.

If you study the Merlin vs DB series compressor power - you`ll see the Merlin expends
considerably more shaft power driving its impeller. Which it would as it was nearly
always running at a higher pressure ratio than the DB. Another very good reason
why DB used methods to increase power late-on that didnt involve running
extremely high pressure ratios in their compressors (eg Nox), as
that power comes from direct chemical energy not increasing the compressor
pressure ratio.

Kind Regards

Calum

 

[fastmongrel]

Good first post and I learnt something new.

 

[stona]

Well done! Even I managed to follow the arguments and learn something new and I am definitely not an engines man.
Cheers
Steve

 

[Deleted member 68059]

For your interest, this is a rather well used DB605-A fluid drive
supercharger coupling. Dismanted for your delectation under laboratory
conditions (my PC desk).

 

[bobbysocks]

if you have that kind of stuff laying around I would love to dig through your attic!!

 

[gjs238]

Hi,
The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).

P_v=P_comp ((N_in-N_out)/N_out )

Where, Pv is power to oil heating, Pcomp is supercharger impeller compressor drive power and N is shaft speed.

In other words the losses to oil
are highest when the coupling is doing its thing. The slip was around 2.5 %, the power loss
at locked condition was hence less as per equation above. The tests show
that at 0.7/1 (max slip) you`re loosing 42% of the supercharger drive power to oil.

For a 601-E, at 1.3Ata at GND>5000feet zone the coupling looses 39bhp in pure oil heating alone,
at 1.15ata (hence lower compressor pressure ratio) its reduced to 24bhp. So it doesnt take
long to imagine whats happening with fairly moderate boost increases. Going up 0.15 Ata
boost puts 61% more power to oil.

Once you`re at 17,000feet or above thats reduced to nominally insignificant (in the case
of this particular engine in that particular condition, it depends on how the secondary
control pump is set to come online).

Not too bad as long as you`re just going up and down once. But evidently if you do any sort of
time in the band between min and max slip, you need a much bigger oil cooler. I do not
know much about air operations as I`m just an engines man - but just saying that is the
case with this type of drive. Conversely it was stated by other studies that in a pure intercept
and return home scenario the coupling was actually quite nice, as it warmed the engine up
fast, and then the losses become small above rated height. So it all depends (like all
engines) on deciding what the exact nature of the application is.

Geoffery Wilde at Rolls did a study on the coupling for Stanley Hooker, as he had worked
previously with these couplings and knew their workings. Because the Merlin was a smaller
engine they knew they would have to boost it considerably higher than the DB in order to
have a chance. This means higher compressor air power, hence in a Merlin with a higher
pressure ratio compressor, the power lost to the coupling will go up and up.

Geoffery worked out that a Merlin equipped with a fluid drive (there are layout drawings
and a complete theoretical set of curves), that with projected boost developments,
that the drag of the required oil cooler would almost nullify the advantage of the
coupling (which is basically that it "fills-in" the area under the "saw-tooth"
pattern of a gearbox equipped supercharged aero engine).

This is further complicated by the characteristics of the Fottinger coupling,
which follows this mathematical behaviour.

Pt=ρ x d^5 x n^3 x c

Where Pt = power transmission capacity (Watts), d= outer diameter of coupling (m), ρ= oil density (kg/m^3), n= shaft speed (rads/sec) and c=a geometry constant (depending on the shape of internal ribs of the particular coupling and so on).

To get a compact installation Geoffrey worked out that running it off the back of a crank (like a automatic gearbox in a modern car) you`d need a huge toriod.
So (like Benz) realised it needed to be speeded up (see the n^3 term). However once you do this the viscous heating losses go up further.

This tended to sludge up the couplings, because the oils were pretty awful back then compared to what we run now, so you would often find the superchargers
on the DB not performing to factory spec at the mid-end of their lives. I`ve got a coupling here thats in "as used" condition and it extremely gummed up
inside. Not a design error really, just something that one aspect of tech. of the day didnt quite deliver on in real life. I think if Geoffery had
done the study for Stanley 6 months prior, they would definetly have at least built a test-stand.

Geoffery and Stanley hooker both visited Sinclair Fluid Drives in person to discuss
developing the coupling into the Merlin - but within a month hostilities officially
started and all efforts swung into "get the most out of what we`ve got now".

Hence the Merlin with fluid drive never happened for these two reasons.

In other words, if you want a larger lower boosted engine the fluid drive is better,
because the losses into oil are less and hence smaller oil cooler = lower drag = more speed.

If you study the Merlin vs DB series compressor power - you`ll see the Merlin expends
considerably more shaft power driving its impeller. Which it would as it was nearly
always running at a higher pressure ratio than the DB. Another very good reason
why DB used methods to increase power late-on that didnt involve running
extremely high pressure ratios in their compressors (eg Nox), as
that power comes from direct chemical energy not increasing the compressor
pressure ratio.

Kind Regards

Calum

What is that playing on the TV in the background?

 

[GregP]

Looks fairly easy to clean up and make good again. That assumes it isn't magnesium.

I hope you have the rest of it around somewhere.

 

[Balljoint]

Since the DB 601 et al was the larger engine but weighed about the same as the Merlin it would seem to be the better execution of a V -12 design. For a given fuel flow the larger displacement allowed for greater conversion of heat energy to power. Conversely, the Merlin would have a hotter exhaust that saw low efficiency in power extraction as through exhaust thrust and such. Both greater stress through higher boost and larger components tend to drive engine weight. Just an opinion but I see the Merlin as the result of evolution that involved compromises (of spec creep) while the DB was more of a clean sheet of paper design.

 

[gjs238]

Wonder what the DB series would have been capable of with US fuel.

 

[tomo pauk]

Provided they fulfil the original specs, that was not the case always, the power at lower and mid altitudes would've increased with higher oct fuel.

 

[Aozora]

Hi,
The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).

P_v=P_comp ((N_in-N_out)/N_out )

Where, Pv is power to oil heating, Pcomp is supercharger impeller compressor drive power and N is shaft speed....

....Geoffery and Stanley hooker both visited Sinclair Fluid Drives in person to discuss
developing the coupling into the Merlin - but within a month hostilities officially
started and all efforts swung into "get the most out of what we`ve got now".

Hence the Merlin with fluid drive never happened for these two reasons.

In other words, if you want a larger lower boosted engine the fluid drive is better,
because the losses into oil are less and hence smaller oil cooler = lower drag = more speed.

If you study the Merlin vs DB series compressor power - you`ll see the Merlin expends
considerably more shaft power driving its impeller. Which it would as it was nearly
always running at a higher pressure ratio than the DB. Another very good reason
why DB used methods to increase power late-on that didnt involve running
extremely high pressure ratios in their compressors (eg Nox), as
that power comes from direct chemical energy not increasing the compressor
pressure ratio.

Kind Regards

Calum

Thanks for that, even I understood! For comparison, attached is an interesting article from AEHS (Aircraft Engine Historical Society), describing Rolls-Royce's methods for testing the Merlin's power and supercharger efficiency in 1940 and comparing the results with NACA tests.

 

[gjs238]

Hi,
The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).

P_v=P_comp ((N_in-N_out)/N_out )

Where, Pv is power to oil heating, Pcomp is supercharger impeller compressor drive power and N is shaft speed.

In other words the losses to oil
are highest when the coupling is doing its thing. The slip was around 2.5 %, the power loss
at locked condition was hence less as per equation above. The tests show
that at 0.7/1 (max slip) you`re loosing 42% of the supercharger drive power to oil.

For a 601-E, at 1.3Ata at GND>5000feet zone the coupling looses 39bhp in pure oil heating alone,
at 1.15ata (hence lower compressor pressure ratio) its reduced to 24bhp. So it doesnt take
long to imagine whats happening with fairly moderate boost increases. Going up 0.15 Ata
boost puts 61% more power to oil.

Once you`re at 17,000feet or above thats reduced to nominally insignificant (in the case
of this particular engine in that particular condition, it depends on how the secondary
control pump is set to come online).

Not too bad as long as you`re just going up and down once. But evidently if you do any sort of
time in the band between min and max slip, you need a much bigger oil cooler. I do not
know much about air operations as I`m just an engines man - but just saying that is the
case with this type of drive. Conversely it was stated by other studies that in a pure intercept
and return home scenario the coupling was actually quite nice, as it warmed the engine up
fast, and then the losses become small above rated height. So it all depends (like all
engines) on deciding what the exact nature of the application is.

Geoffery Wilde at Rolls did a study on the coupling for Stanley Hooker, as he had worked
previously with these couplings and knew their workings. Because the Merlin was a smaller
engine they knew they would have to boost it considerably higher than the DB in order to
have a chance. This means higher compressor air power, hence in a Merlin with a higher
pressure ratio compressor, the power lost to the coupling will go up and up.

Geoffery worked out that a Merlin equipped with a fluid drive (there are layout drawings
and a complete theoretical set of curves), that with projected boost developments,
that the drag of the required oil cooler would almost nullify the advantage of the
coupling (which is basically that it "fills-in" the area under the "saw-tooth"
pattern of a gearbox equipped supercharged aero engine).

This is further complicated by the characteristics of the Fottinger coupling,
which follows this mathematical behaviour.

Pt=ρ x d^5 x n^3 x c

Where Pt = power transmission capacity (Watts), d= outer diameter of coupling (m), ρ= oil density (kg/m^3), n= shaft speed (rads/sec) and c=a geometry constant (depending on the shape of internal ribs of the particular coupling and so on).

To get a compact installation Geoffrey worked out that running it off the back of a crank (like a automatic gearbox in a modern car) you`d need a huge toriod.
So (like Benz) realised it needed to be speeded up (see the n^3 term). However once you do this the viscous heating losses go up further.

This tended to sludge up the couplings, because the oils were pretty awful back then compared to what we run now, so you would often find the superchargers
on the DB not performing to factory spec at the mid-end of their lives. I`ve got a coupling here thats in "as used" condition and it extremely gummed up
inside. Not a design error really, just something that one aspect of tech. of the day didnt quite deliver on in real life. I think if Geoffery had
done the study for Stanley 6 months prior, they would definetly have at least built a test-stand.

Geoffery and Stanley hooker both visited Sinclair Fluid Drives in person to discuss
developing the coupling into the Merlin - but within a month hostilities officially
started and all efforts swung into "get the most out of what we`ve got now".

Hence the Merlin with fluid drive never happened for these two reasons.

In other words, if you want a larger lower boosted engine the fluid drive is better,
because the losses into oil are less and hence smaller oil cooler = lower drag = more speed.

If you study the Merlin vs DB series compressor power - you`ll see the Merlin expends
considerably more shaft power driving its impeller. Which it would as it was nearly
always running at a higher pressure ratio than the DB. Another very good reason
why DB used methods to increase power late-on that didnt involve running
extremely high pressure ratios in their compressors (eg Nox), as
that power comes from direct chemical energy not increasing the compressor
pressure ratio.

Kind Regards

Calum

So I guess one is faced with the choice of a multi-speed geared supercharger drive, a torque converter driven supercharger, or a turbo charger.
The latter seems to avoid some of the issues of the former, while creating some of its own.

 

[fastmongrel]

Since the DB 601 et al was the larger engine but weighed about the same as the Merlin it would seem to be the better execution of a V -12 design. For a given fuel flow the larger displacement allowed for greater conversion of heat energy to power. Conversely, the Merlin would have a hotter exhaust that saw low efficiency in power extraction as through exhaust thrust and such. Both greater stress through higher boost and larger components tend to drive engine weight. Just an opinion but I see the Merlin as the result of evolution that involved compromises (of spec creep) while the DB was more of a clean sheet of paper design.

It doesnt quite work that way on a supercharged engine, its not about fuel, compression ratio or capacity though bigger is often better. Its all about how much Air you can move into and out of the engine and thats down to the air compressor and the intercooler.

Take a look at BMWs M12 Formula 1 engine of the 80s, it was a 1500cc 4 cylinder engine with an Iron block from a saloon car that ended up producing 1,400 hp in practice trim and 1,000 hp in race trim with the boost wound back to save fuel. The Turbo just got bigger and bigger and the engine became almost a gas generator bolted to a Turbine. If BMW had kept on strengthening the engine (it was Iron because Aluminium technology couldnt cope) and making the Turbo bigger and the radiators bigger its mind boggling to imagine what power they could have achieved if the FIA hadnt changed the regulations to try and slow the cars down.

 

[tomo pauk]

So I guess one is faced with the choice of a multi-speed geared supercharger drive, a torque converter driven supercharger, or a turbo charger.
The latter seems to avoid some of the issues of the former, while creating some of its own.

Both the multi-speed and torque converter are supercharger drive systems, they add flexibility, not altitude capability. Compare Merlin III vs. Merlin X, or Merlin 45/50 vs. Merlin 20 series.
The addition of turbo adds another impeller, thus it adds capability.