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