Bf-109 vs P-40 (4 Viewers)

[Shortround6]

The faster you spin the impeller the more air you get per unit of time which equals more power.
However you are also heating up the air more and there is a definite upper limit. Once the impeller tips exceed the speed of sound in the conditions that exist inside the supercharger shock waves are set up that disrupt the airflow.

 

[tomo pauk]

It was the crank shaft, they first improved it using 'peened' metal in early 1942 then used heat treated metal. I think some other components were strengthened a bit. 57" mercury became the standard WEP setting on the P-40K and apparently they could use it for a long time. Prior to that the WEP was 45"

Why does this only confer extra HP up to 5,000 feet?

Overboosting claims up to 70"

Interestingly they also overboosted the Packard Merlin 1650s to 60" apparently.

I never quite understood the 8:80:1 vs. 9.60:1 gearing issue. Can you elaborate on that a bit?

S

Why just under 5000 ft? The lower you get, the S/C can provide more of compressed air. More of that air = greater boost = more power, but all of therse 'more' are good if the engine can stand it. So if we have the V-1710 that will be safely using 56 in Hg at ~4500 ft (like the V-1710-39), and then improve it (streghtnen it) so it can make 60 in Hg, but it will do it at ~2500 ft (like the V-1710-73).
8.80:1 means that for each rotation of crakshaft, the impeller will rotate 8.80 times. 9.90:1 obvously means that impeller will rotate 9.60 times. The 'faster' impeller will be better at high altitudes, shortcoming being that it will also be using more power to be driven, and that it will be compressing and thus heating the air at lower altitudes more than the 'slower' impeller, thus more throttling ust be used. The 8.80:1 gears means that drive toothed wheel used 55 tooth vs. 15 used on the driven wheel; on the 9.60:1 it was 56 vs. 14. So on the V-1710, the impeller was turning to almost 30000 rpm (3000 crankshaft rpm x 9.60).

The dedicated low-level engine ont the A-36 used 53:17, or 7.48:1. The altitude power suffered accordingly, but low level power was improved (15 min power was 1325 HP vs 1150 HP on prevoius engines). The engines with 7.48:1 S/C drive were also used on P-38s, helped out by turbo of course - so there were two stages of supercharging present giving a fine hi-alt power.

Having just one set of gears means that engine has 1-speed S/C. Plenty of superchargers on engines both from USA and abroad used 2 sets of gears, those were called 2-speed S/C. However, there was no in-production V-1710s with 2-speed S/Cs.

 

[Schweik]

Why just under 5000 ft? The lower you get, the S/C can provide more of compressed air. More of that air = greater boost = more power, but all of therse 'more' are good if the engine can stand it. So if we have the V-1710 that will be safely using 56 in Hg at ~4500 ft (like the V-1710-39), and then improve it (streghtnen it) so it can make 60 in Hg, but it will do it at ~2500 ft (like the V-1710-73).
8.80:1 means that for each rotation of crakshaft, the impeller will rotate 8.80 times. 9.90:1 obvously means that impeller will rotate 9.60 times. The 'faster' impeller will be better at high altitudes, shortcoming being that it will also be using more power to be driven, and that it will be compressing and thus heating the air at lower altitudes more than the 'slower' impeller, thus more throttling ust be used. The 8.80:1 gears means that drive toothed wheel used 55 tooth vs. 15 used on the driven wheel; on the 9.60:1 it was 56 vs. 14. So on the V-1710, the impeller was turning to almost 30000 rpm (3000 crankshaft rpm x 9.60).

The dedicated low-level engine ont the A-36 used 53:17, or 7.48:1. The altitude power suffered accordingly, but low level power was improved (15 min power was 1325 HP vs 1150 HP on prevoius engines). The engines with 7.48:1 S/C drive were also used on P-38s, helped out by turbo of course - so there were two stages of supercharging present giving a fine hi-alt power.

Having just one set of gears means that engine has 1-speed S/C. Plenty of superchargers on engines both from USA and abroad used 2 sets of gears, those were called 2-speed S/C. However, there was no in-production V-1710s with 2-speed S/Cs.

So you get no benefit from high boost with these engines above 5,000 feet? It doesn't seem to fit the anecotal evidence though fighter pilots do sometimes seem to get confused on the details.

I find it confusing since i thought the whole (original) point of the supercharger was to compress the thinner air at high altitude so that the engine could operate normally.

 

[pbehn]

So you get no benefit from high boost with these engines above 5,000 feet? It doesn't seem to fit the anecotal evidence though fighter pilots do sometimes seem to get confused on the details.

I find it confusing since i thought the whole (original) point of the supercharger was to compress the thinner air at high altitude so that the engine could operate normally.

As I understand it a single stage supercharger could supply enough boost to be more than the engine could stand at sea level. As altitude increased and the air gets thinner more compression is needed until the limit of a single stage supercharger were reached. Above this altitude, supercharger with a two stage compressor or a turbo feeding a single stage supercharger were needed.

 

[Shortround6]

All engine charts are going to be somewhat similar.
The engine doesn't drop suddenly to 1150hp at 5001 ft, it gradually declines to the 1150hp rate the higher it goes above the 5000ft mark.
Please note that the engine are usually given without any RAM air ( increase in pressure to the carb due to the forward speed of the aircraft which can add several thousand ft to the altitude the engine makes a given power at. However alos note that there can be a several thousand ft difference in climb vrs all out level speed.

Please note that 30 in sea level pressure (rounded off) and please note the different altitudes the same pressure can be achieved using different rpm of the engine ( and the different supercharger speeds resulting from those changes in engine speed. for example 2000rpm will give us 30in (sea level) at just under 12,000ft (but only enough air for about 675hp) while increasing engine rpm to 3000 will increase the supercharger rpm to give sea level pressure at 21,000ft and give 800hp.

 

[tomo pauk]

So you get no benefit from high boost with these engines above 5,000 feet? It doesn't seem to fit the anecotal evidence though fighter pilots do sometimes seem to get confused on the details.

I find it confusing since i thought the whole (original) point of the supercharger was to compress the thinner air at high altitude so that the engine could operate normally.

There was no high boost above 5000 ft to begin with, unless one improves the supercharger system - bigger and/or faster spinning impeller, another stage added, intercooler added. See the chart featuring the Merlin III (over-boost part used boosts between +6.25 psi and +12 psi, note that overboost is a thing of lower altitudes), and effect of two-stage supercharger on Merlin 60 (LX) where altitude power skyrockets.

Point of supercharger is/was indeed to compress the thin air and supply it to the engine. Overboosting was a side effect - taking advantage of supercharger's extra capacity between the sea level and rated altitude, provided that engine gets hi-oct fuel or uses ADI or both (so the knocking is delayed), that engine is strong enough to withstand the mechanical and thermal stress, and that engine is not operated too long in overboost regime.

As I understand it a single stage supercharger could supply enough boost to be more than the engine could stand at sea level. As altitude increased and the air gets thinner more compression is needed until the limit of a single stage supercharger were reached. Above this altitude, supercharger with a two stage compressor or a turbo feeding a single stage supercharger were needed.

The 2-stage superchargers were even more capable to supply too much of compressed air at low level.
Indeed, more than 1 stage of supercharging is a good thing once above 15000-20000 ft.

 

[pbehn]

The 2-stage superchargers were even more capable to supply too much of compressed air at low level.
Indeed, more than 1 stage of supercharging is a good thing once above 15000-20000 ft.

That is why I found and still find some things "counter-intuitive" some improvements in the supercharger or turbo coincided with other engine improvements allowing more boost at all levels.

 

[Schweik]

That is why I found and still find some things "counter-intuitive" some improvements in the supercharger or turbo coincided with other engine improvements allowing more boost at all levels.

So is the 1325 or 1360 hp rating for those versions of the V-1710 accurate and at what altitude is the max HP at 57", Sea Level? 5,000 feet?

Is it as simple as a max power at Sea Level and then it goes down from there, or does is the boost limited at lower altitude?

S

 

[pbehn]

So is the 1325 or 1360 hp rating for those versions of the V-1710 accurate and at what altitude is the max HP at 57", Sea Level? 5,000 feet?

Is it as simple as a max power at Sea Level and then it goes down from there, or does is the boost limited at lower altitude?

S

I see you are suffering the same confusion that I had years ago when I first came here, in all things "supercharger" or "turbocharger" related I would trust Shortround and timo. This is how I understand it, but would be happy to be corrected.
1, The engine block, whatever it is, has a maximum of boost that it can withstand above sea level atmospheric pressure. This is not a constant because for various reasons like heat build up and lubrication it has limits both short and long term.
2. At sea level, it is simply a question of how much boost over atmospheric pressure an engine can withstand and for how long, so you have "take of power" and "war emergency power", "maximum continuous power" etc.
3. As the altitude increases it becomes harder to keep the boost you want because the air is thinner to start with, since compressing air heats it up, if you put hot air and fuel in a combustion chamber it explodes before you want it to. To make a huge increase in the compression it must be done in two (or more) stages with cooling in between. On the Merlin they had a two stage supercharger with an intercooler between, on the P-47 and P-38 there was an exhaust driven first stage turbocharger with intercooling before the normal single stage supercharger driven by the engine. As with everything all these set ups have advantages and disadvantages.
4. in all this, along with advances in turbos and superchargers there were also advances in fuels that allowed more total compression in the cylinder without detonation (octane rating), and advances in materials, bearings and lubricants that allowed running engines with higher pressures for longer.

In short, its a bit complicated

 

[Schweik]

I see you are suffering the same confusion that I had years ago when I first came here, in all things "supercharger" or "turbocharger" related I would trust Shortround and timo. This is how I understand it, but would be happy to be corrected.
1, The engine block, whatever it is, has a maximum of boost that it can withstand above sea level atmospheric pressure. This is not a constant because for various reasons like heat build up and lubrication it has limits both short and long term.
2. At sea level, it is simply a question of how much boost over atmospheric pressure an engine can withstand and for how long, so you have "take of power" and "war emergency power", "maximum continuous power" etc.
3. As the altitude increases it becomes harder to keep the boost you want because the air is thinner to start with, since compressing air heats it up, if you put hot air and fuel in a combustion chamber it explodes before you want it to. To make a huge increase in the compression it must be done in two (or more) stages with cooling in between. On the Merlin they had a two stage supercharger with an intercooler between, on the P-47 and P-38 there was an exhaust driven first stage turbocharger with intercooling before the normal single stage supercharger driven by the engine. As with everything all these set ups have advantages and disadvantages.
4. in all this, along with advances in turbos and superchargers there were also advances in fuels that allowed more total compression in the cylinder without detonation (octane rating), and advances in materials, bearings and lubricants that allowed running engines with higher pressures for longer.

In short, its a bit complicated

Thanks I do understand the basics- what i don't grasp is how to translate that into different max HP at different boost ratings / RPM at different altitudes.

Somebody a few times in this and other threads claimed that at 57" or some other boost number a V-1710 could reach ~1,500 hp, I'd like to know if that is even possible and if so, how much risk of detonation and other issues would there be, how long could you get away with that for, and etc. Or is the max really what they indicate as the official max takeoff rating.

Like you say though other factors come into play like the fuel and the type of oil and so on so it is probably hard to pin down.

S

 

[pbehn]

Thanks I do understand the basics- what i don't grasp is how to translate that into different max HP at different boost ratings / RPM at different altitudes.

Somebody a few times in this and other threads claimed that at 57" or some other boost number a V-1710 could reach ~1,500 hp, I'd like to know if that is even possible and if so, how much risk of detonation and other issues would there be, how long could you get away with that for, and etc. Or is the max really what they indicate as the official max takeoff rating.

Like you say though other factors come into play like the fuel and the type of oil and so on so it is probably hard to pin down.

S

As I said I am no expert on this, but it is certainly possible because the Merlin did it and more, and the Allison V-1710 was in some ways a stronger engine with a bigger swept volume. The Allison and Merlin engines as conventionally aspirated engines were not much different, it was the various superchargers and superchargers with turbos that makes the difference.

In the "turbo era" of Formula 1, cars were restricted to 1.5 litres swept volume but produced a maximum power of circa 1000 BHP. That is how far advanced materials and fuels can take things. They were made to last at that output for a maximum of 2 minutes on absolute maximum and 2 hours at "max continuous" interesting in a way but no use for an aircraft.

 

[Shortround6]

Confusing things is the
1.max the engine would actually make
2. and what they allowed to make to leave a safety margin
3. and what they allowed it make and still achieve a certain "engine life/time before overhaul".

On an Allison with 8.80 gears (and this pretty well covers the long nose -33 engines used by the Flying Tigers)
You might be able to get 70 in of manifold pressure at sea level on a stationary engine. It might depend on the day
This is around 1700hp ( I am not looking at the books). How long the engine lasts depends on the particular engine, how many hours on on it already (wear), how hit it gets and maybe the phase of the moon.
WEP power was tested by running a test engine at the desired power rating for 5 minutes at a time ( or longer if the engine maker was really confident.) with cooling off periods in between ( run at max continuous or "normal" power) until the engine had accumulated 7 1/2 hours at the WEP rating without breaking.
Once one engine on a test stand had done that then all engines of that type/model could be rated at that power.

go back to the chart posted in # 625
or

engine gets to 66in at sea level (?). Getting to 70in in flight is possible, due to forward airspeed increasing pressure in the inlet before the supercharger (the supercharger multiplies the pressure coming into it. In the case of the Allison here the supercharger is operating at about 2.2 to 1 so if you can get the pressure in the duct before the carb up to 31.8 inches instead of 30 inches then you got it. however as soon as you climb it gets harder and harder.
You can also get to 70 inches by overspeeding the engine, running 3100-3200rpm instead of 3000rpm. Perhaps easy to do in the heat of combat?
You also have the pilot, in the heat of combat, trying to look at his pressure gauge anad judge if the needle was really on 70 or just on 69?
This assumes that the P-40 in question even had a pressure gauge that went over 50lbs.

The 1150hp rating was the max they figured the engine could run at for 5 minutes at a time (later 15) without seriously degrading the life of the engine.
This is on the -35/39 engines and later, the -33 was limited to 1090hp (?). ANY use of WEP called for notations in the aircraft log books and discussions with the squadron engineering officer on what extra maintenance procedures might be needed or not needed. 1942 and up engines would take a lot more abuse than the early ones but it also took time to accumulate the knowledge of how much abuse they could really take and not break down on the next flight or the one after.

Now please note that ALL Allison engines with 8.80 gears ( or 8.77) are going to follow pretty much the chart above as far as ability to make power. It is just a question of how strong the different models were that affected the limits that were placed on using that power.

 

[Dan Fahey]

Regarding comments by Japanese Pilots!
Type in Japanese Aces on YouTube. You will see several interviews.
One conversation was about a ace being taught to fly the F80 and had a asshole teacher.

 

[Dan Fahey]

If you want some interesting history on Allison Engines.
Look up Yancey Allison Engines....
The Russians ran the Allison as high as 3500rpm to get more power out of it.
Engines did not last long but much longer than the Merlin and Russian redesigned Hispano Suiza engines.

 

[tomo pauk]

So is the 1325 or 1360 hp rating for those versions of the V-1710 accurate and at what altitude is the max HP at 57", Sea Level? 5,000 feet?

Is it as simple as a max power at Sea Level and then it goes down from there, or does is the boost limited at lower altitude?

S

If we're talking about 1-stage 1-speed S/Ced engines like many V-1710s or Merlins in service, then an ideal version of those engines woud've have the power 'curve' turned into a line, as it can be noted at graphs kindly provided by Shortround6. But, indeed the power is indeed limited at lower altitude, with S/C providing too much of boost. The boost lines can be seen as curved lines, where the same boost equals to ever slightly higher power until some altitude is reached (due to ever cooler intake air benefiting it) and then slowly going down. So we will have engine doing 1300 HP at 57 in HG at sea level, and same engine doing 1410 HP at 9800 ft (all of that is war emergency power, with ram effect, ie. aircraft in full power horizontal flight) - link
That engine was still rated to 1200 HP for take off - there is no incoming ram air to help the impeller, so the engine designers need to be on the safe side here.
I've managed to find two tables, that can show the difference between the two V-1710s, -33 and -73, note the take-off and WER are different, but military power is still the same. Also note that rated altitude is typed in the wrong column, it should've been typed under 'no ram' column:



What is not noted on those tables is that -33 wil be making 1500+ HP at 56 in at 4500 ft, and the -73 will emulate that, while also doing some 1590 HP at 60 in at 2500 ft, no ram.

Thanks I do understand the basics- what i don't grasp is how to translate that into different max HP at different boost ratings / RPM at different altitudes.

Somebody a few times in this and other threads claimed that at 57" or some other boost number a V-1710 could reach ~1,500 hp, I'd like to know if that is even possible and if so, how much risk of detonation and other issues would there be, how long could you get away with that for, and etc. Or is the max really what they indicate as the official max takeoff rating.

Like you say though other factors come into play like the fuel and the type of oil and so on so it is probably hard to pin down.

S

It was possible to beat 1500 HP mark on the V-1710s, unofficially it was done before 1942, officially it was done some time in second half of 1942. link

 

[Schweik]

If we're talking about 1-stage 1-speed S/Ced engines like many V-1710s or Merlins in service, then an ideal version of those engines woud've have the power 'curve' turned into a line, as it can be noted at graphs kindly provided by Shortround6. But, indeed the power is indeed limited at lower altitude, with S/C providing too much of boost. The boost lines can be seen as curved lines, where the same boost equals to ever slightly higher power until some altitude is reached (due to ever cooler intake air benefiting it) and then slowly going down. So we will have engine doing 1300 HP at 57 in HG at sea level, and same engine doing 1410 HP at 9800 ft (all of that is war emergency power, with ram effect, ie. aircraft in full power horizontal flight) - link
That engine was still rated to 1200 HP for take off - there is no incoming ram air to help the impeller, so the engine designers need to be on the safe side here.
I've managed to find two tables, that can show the difference between the two V-1710s, -33 and -73, note the take-off and WER are different, but military power is still the same. Also note that rated altitude is typed in the wrong column, it should've been typed under 'no ram' column:

View attachment 490629 View attachment 490630

What is not noted on those tables is that -33 wil be making 1500+ HP at 56 in at 4500 ft, and the -73 will emulate that, while also doing some 1590 HP at 60 in at 2500 ft, no ram.



It was possible to beat 1500 HP mark on the V-1710s, unofficially it was done before 1942, officially it was done some time in second half of 1942. link

Fascinating, thank you. So were DB 601, Sakae, Merlin XX etc. also achieving ~300 hp over "rated for takeoff" rating?


EDIT: I thought I'd seen that memo before but it must have been a shorter one specifically about the 70" setting. It is news to me that they were routinely doing 66" and that Allison had already approved 60" by Dec of 1942. The highest i had heard was 57. All very interesting. Also the difference between the (I gather slightly higher altitude rated) 9.6 ratio vs. the 8.8 ratio blowers etc.

Next question is, why was this such a secret if it was so widespread?

And how fast does a P-40 go at ~1,700 hp!!!?


S

 

[Shortround6]

Here things get a bit more complicated. The later aircraft with the 9.60 gears heated up the intake mixture hotter than the 8.80 gear engines did and started getting detonation in the cylinders at lower pressure. This restricted them from using the higher pressures that had been being used unofficially in some service squadrons. There is no free lunch. Allison was rather emphatic about the 9.60 gear engines sticking to the guide lines as they knew that if the pilots tried to use the same pressures over 57in that they had been being using there were going to be a lot more wrecked engines and pilots not making it back from missions due to engine failure.

Engines ability to make the extra power depends on surplus supercharger capacity and the ability of the fuel to resist detonation at high boost levels.
The Japanese and German fuel was, on average, well below the Allied fuel in this regard.
The British certainly made use of this. A Merlin running 12lbs of boost was running 54in of manifold pressure.

So the old Merlin III which could make 1030 hp at 16,250ft (6lbs boost=42in) was rated at 1310hp at 9000ft (12lbs boost=54in) and in Sea Hurricanes 1440hp at 5500ft (16lbs boost=62in). The Sea Hurricane use was well after the BoB, required newer fuel and since they didn't really expect long life out of Sea Hurricane in any case shorting up the engine life a bit probably wasn't a problem.

 

[Juha2]

Yeah I didn't include La 5FN in the "greats" list because I just thought La 7 was kind of the definitive version of it. when did La 5FN become widely operational and relatively 'bug free"? I know some kind of La 5 were available in late 1942 or early 1943 right?

S

Summer 1943 and from autumn 1943 onwards more or less in the final form with appr. 620 km/h max speed.

 

[tomo pauk]

Fascinating, thank you. So were DB 601, Sakae, Merlin XX etc. also achieving ~300 hp over "rated for takeoff" rating?
EDIT: I thought I'd seen that memo before but it must have been a shorter one specifically about the 70" setting. It is news to me that they were routinely doing 66" and that Allison had already approved 60" by Dec of 1942. The highest i had heard was 57. All very interesting. Also the difference between the (I gather slightly higher altitude rated) 9.6 ratio vs. the 8.8 ratio blowers etc.

Next question is, why was this such a secret if it was so widespread?

And how fast does a P-40 go at ~1,700 hp!!!?


S

Not that fast, the P-40 with 1700 HP, since that power was availabe at low level where the air is thick = plenty of air resistance. Though the climb would've been excellent.
Any military matter, no matter how well spread, will be deemed as secret in official docs in a time of war.
As for the over-boosting their respective engines, one needs hi-oct fuel to help out. Allies were in better position there, Axis forces not so much. So we can see many late-war German and Japanese engines outfitted with ADI systems instead, so over-boost can be achieved, and with it the engine power. The BMW 801D and S, as well as Jumo 213 were taking advantage of ever-higher rich rating of the German hi-octane C3 fuel in later part of the war.
Granted, people can use the hi-oct fuel and ADI in the same time for the best result.

 

[Juha2]

Maybe you can answer a question for me on this - I had read that the Spit VIII etc. was a "long range" version of the Spit, but in googling it recently i saw range figures of ~650 miles which sounds like 'medium' range at best. A little less than most US fighters except the Wildcat. Is that the right number? What is the actual range of the Spit VIII?

S

Yes, Mk VIII was a long range Spit and has a reasonable range for an European air superiority single-engine fighter, according to RAF its range with max internal fuel was 660 mls, according to RAAF 740 mls. US and Japanese fighters tended to be longer ranged than their European counterparts.