Engine power vs altitude
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It's my understanding that variable geometry stators, when employed, were used as for altitude compensation rather than for continuous throttling, with two different levers in the cockpit.
German pilots using the Fw-190 must have greatly appreciated the semplicity afforded by the kommand-gerät of the BMW-801. No longer they had to struggle with 3-4 different levers while keeping a costant, vigil eye on the manifold pressure gauge, tachometer AND, of course, the enemy planes!
German pilots using the Fw-190 must have greatly appreciated the semplicity afforded by the kommand-gerät of the BMW-801. No longer they had to struggle with 3-4 different levers while keeping a costant, vigil eye on the manifold pressure gauge, tachometer AND, of course, the enemy planes!
GregP
Major
A single-stage mechanically supercharged engine will make max power at a some critical altitude determined by the blower size, ratio, and efficiency. Above the critical altitude the power falls off almost linearly in what looks like a "dogtooth" reduction in speed and power. When the power decreases until the excess power can only generate a climb rate of 100 feet per minute, the altitude where that happens is called the service ceiling. Absolute ceiling is the height at which the aircraft will not climb any farther.
When you go to a single-stage, 2-Speed mechanical supercharger, it is the same until some point above the critical altitude of the lower-speed blower gear (the point is a bit arbitrary), then the pilot throttles back, changes gears, and the power again increases until a critical altitude is reached for the higher-speed gear. Above that altitude, power falls off almost linearly. There are two maximum speeds, low-gear max speed and hi-gear max speed for the supercharger, with the hi-gear being at a greater altitude. Betweeen the altitudes for low gear and hi gear highest speeds, the speed is always less then either maximum. The pilot must remember to change gears back to low speed when he descends or he risks overboosting the engine and blowing it up or going into detonation. Much the same as above is true for a 2 -stage mechanical supercharger and a 2-stage, multi-speed (usually 2-speed) mechanical supercharger. The only real difference is the altitude gain by the second stage as opposed to the second speed on the single-stage unit is usually greater by a fair margin. That is, the 2-stage unit usually will maintain power to a higher altitude before power falls off than wikll a 2-speed, single-stage unit.
All WWII major fighter engines were supercharged, most mechanically. If the supercharger, be it first stage or secomd-stage, is driven hydraulically, then it is a different story. The designers usually take the dogtooth into account and vary the slippage and boost to drive the supercharger at progressively higher speeds. It is sort of like "altitude-sensitive supercharging," and the dogtooth usually is MUCH smoother and more gradual, giving both the impression and real-life result of more constant power. The Bell P-63 with Aux-stage blower doesn't have a jagged "dogtooth" power response with altitude. Speed increases to a single maximum and the gradually tapers off.
The trade-offs are complexity, cost, maintenance, weight, size, etc.
The Allison company proposed a 2-stage, 2-speed supercharger on at least two occasions to the USAAF and was turned down due to the situation before WWII in the U.S.A. the first time (we werre not at war) and to the resulting production interruption the second time (and any runored third time). Also, Allison wanted the government, the sole user of the product, to fund or at least help to fund the development costs since the government owned the V-1710 design rights. The government wanted Allison to fund the development in their own, and continue to retain all the rights. Allison demured, as good business would dictate.
If a larger, single stage, hydraulically driven supercharger had been adopted by the Allison, the Merlin, Griffon, etc, then the power drop-off with altitude would have been modified by being more gradual and the curve would have been more lie that of the P-63 Aux-stage units or the Me 109; more gradual at the critical point and a more gradual power drop-off with altitude.
We can second-guess, but in the real war, they did what they did, mostly out of the need NOT to take a chance on losing the war (and thus the country). They went with the conservative decision and prevailed. Had they chosen the bold route and succeeded, they would be heroes of the first magnitude! Had they done so and failed they would be speaking German about now.
When you go to a single-stage, 2-Speed mechanical supercharger, it is the same until some point above the critical altitude of the lower-speed blower gear (the point is a bit arbitrary), then the pilot throttles back, changes gears, and the power again increases until a critical altitude is reached for the higher-speed gear. Above that altitude, power falls off almost linearly. There are two maximum speeds, low-gear max speed and hi-gear max speed for the supercharger, with the hi-gear being at a greater altitude. Betweeen the altitudes for low gear and hi gear highest speeds, the speed is always less then either maximum. The pilot must remember to change gears back to low speed when he descends or he risks overboosting the engine and blowing it up or going into detonation. Much the same as above is true for a 2 -stage mechanical supercharger and a 2-stage, multi-speed (usually 2-speed) mechanical supercharger. The only real difference is the altitude gain by the second stage as opposed to the second speed on the single-stage unit is usually greater by a fair margin. That is, the 2-stage unit usually will maintain power to a higher altitude before power falls off than wikll a 2-speed, single-stage unit.
All WWII major fighter engines were supercharged, most mechanically. If the supercharger, be it first stage or secomd-stage, is driven hydraulically, then it is a different story. The designers usually take the dogtooth into account and vary the slippage and boost to drive the supercharger at progressively higher speeds. It is sort of like "altitude-sensitive supercharging," and the dogtooth usually is MUCH smoother and more gradual, giving both the impression and real-life result of more constant power. The Bell P-63 with Aux-stage blower doesn't have a jagged "dogtooth" power response with altitude. Speed increases to a single maximum and the gradually tapers off.
The trade-offs are complexity, cost, maintenance, weight, size, etc.
The Allison company proposed a 2-stage, 2-speed supercharger on at least two occasions to the USAAF and was turned down due to the situation before WWII in the U.S.A. the first time (we werre not at war) and to the resulting production interruption the second time (and any runored third time). Also, Allison wanted the government, the sole user of the product, to fund or at least help to fund the development costs since the government owned the V-1710 design rights. The government wanted Allison to fund the development in their own, and continue to retain all the rights. Allison demured, as good business would dictate.
If a larger, single stage, hydraulically driven supercharger had been adopted by the Allison, the Merlin, Griffon, etc, then the power drop-off with altitude would have been modified by being more gradual and the curve would have been more lie that of the P-63 Aux-stage units or the Me 109; more gradual at the critical point and a more gradual power drop-off with altitude.
We can second-guess, but in the real war, they did what they did, mostly out of the need NOT to take a chance on losing the war (and thus the country). They went with the conservative decision and prevailed. Had they chosen the bold route and succeeded, they would be heroes of the first magnitude! Had they done so and failed they would be speaking German about now.
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OldSkeptic
Senior Airman
- 509
- May 17, 2010
I would like to ask about differences in the way that engine power decrease with altitude, but first some performance charts:
BWM 801D2
or Merlin 66:
http://www.spitfireperformance.com/merlin66hpchart.jpg
Both engines have 2-speed supercharger. We can see in both cases that the power of engine rise till FTH of the particular gear is achieved, then there is a power drop untill the second gear of supercharger is engaged.
However, on Jumo 213 E-1:
we can notice that there is a constant power decrease with altitude?
Where does these differences come from? Could we use all those charts for direct comparison of engine performance?
Regards
PS. Sorry for my English - isn't as good as I want it to be.
Simply because the 213E ones are wrong. With a supercharged engine it is designed to provide a maximum boost for a particular altitude, for the given gear/stage.
Below that you throttle the engine otherwise you will over boost it. Translated you put a blockage in the supercharger inlet with 'fools' the supercharger into thinking that its inlet pressure is less than what it actually is
Simple, but that throttling causes inefficiencies, such as heat (there are others of course). The temp of the inlet is raised, reducing the supercharger efficiency.
That's why you see, on real charts like Rolls Royce and Daimler Benz, BMW, PW, et al. A slow rise in power until the optimum (totally open throttle) for the particular gear/stage.
Then it drops off with altitude (basically linearly) until the next gear/stage is engaged. Then rises, partially throttled until the throttle is again fully open. And so on through the gears/stages.
Even the variable coupling (like an automatic transmission on a car) DB supercharger showed similar, though smoother power curves. The Jumo 213E used mechanical gears like a Merlin or Griffon.
When you look at those 213E charts you know they are totally wrong. The real give away is the non MW-50 lines or the cruise lines. It is physically impossible for those flat lines to happen in real life.
Jumo had a bit of a history of playing fast and loose with it's claimed power, as well as forecast production, numbers.
Remember also this was an engine with only 3 valves and a very high piston speed (with all the inefficiencies that entails).
As Myth Busters would say .. that chart is Busted. Looks like a PR one for gullible buyers. Any relationship to reality would be totally accidental.
The idea of variable geometry inlet vanes was used in France ( http://www.enginehistory.org/Accessories/S-Psc/S-PscTst.shtml ) and on the AM-35 and later Mikulin engines. The idea was to avoid the situation where the supercharger was producing considerably more boost than could be used (and consuming considerable mechanical power in the process) only to have the pressure reduced by a throttle.
In addition, the Jumo 213e was somewhat unique in having three speeds rather than two or one. It might also be mentioned that the later DB engines had a variable speed supercharger drive - this also smoothed out the variation in power dependence on altitude.
Speed curves for the Fw 190D confirm different characteristics of the Jumo 213 supercharging - the do not lose speed with the supercharged switching to second speed as shown by Fw 190A. Also remember the BMW chart is pure engine power while the 213E chart is "Nutzleistung" - I assume that's called Shaft power, power arriving at Prop.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
That's not how it works. There is no loss of speed when the 2nd gear (or stage) kicks in. The loss is before that as the first gear exceeds its full throttle height.
Then there is a gap with diminishing boost (and hence power) until the 2nd is engaged.
The FW-190D (with the Juno 213A) showed exactly the same characteristics as every other engine around.
Have a look at the results here.
FW 190 D-9 Flight Trials
Click though to the actual test results and you can see the boost (in atmosphere). Follows the same pattern as every other supercharged engine.
So the engine worked (quell surprise) just like every other one.
In terms of aircraft speed it can be complicated by the use of MW-50. This is a charge cooling aid (the methanol is as an anti freeze).
This allows over boosting at lower altitudes.
But this overboost has a far lower full throttle height (since the supercharger can only pump so much air).
So you whack on the MW-50, overboost for take off and climb.
This higher boost will start to drop off quite quickly, but you are gaining altitude so drag is declining. Depending on the aircraft and the various full throttle heights this drop off in speed may be reduced, but never eliminated
You can see this on the charts (focusing on the 1st gear), the full throttle heights of with MW-50 are lower than without it. At altitude climbs eventually they will match.
On the same site you can see this even more clearly on the various impacts of 150 octane and 25lb boost on the Merlin (basically same effect).
The power gains are all below the normal (on 100 octane) full throttle height of the engine. As the altitude goes up the supercharger simply cannot supply the extra boost and the power levels end up matching.
Now the std chart that everyone quotes of the 213E does, correctly show differing full throttle heights for with/without MW-50. And correctly again the non MW-50 is higher than that with MW-50.
Now the reason I say those chart are (hmm how can I say this politely) rubbish is (concentrating again on the 1st gear level and without MW-50) is they do not match the 213A at all, or any other supercharged engine in WW2 (or ever perhaps).
Instead of shallow rise in power because boost is constant but throttling reduced the engine's efficiency, then as you exceed the full throttle height of the gear, boost and power drops fairly rapidly, then the 2nd gear/stage kicks in and you repeat depending on the number of gears/stages (the familiar saw tooth shape, Flight Global archives has one for the 3 speed 2 stage Griffon).
For the 213E charts (ignoring the fantasy top one entirely and the ME-50 ones) you get this gentle curve downwards, until the full throttle height, then it drops until the 2nd gear/stage cuts in.
So Jumo, not used on their 213A, have come up with for a negative efficiency throttling? WTF?
In other words, as you open the throttle (letting in more air to the supercharger) the supercharger efficiency drops????? What is it made of, anti-matter?
The other give away is the short altitude range where the full throttle height is reached, where power drops off before the 2nd gear/stage cuts in.
For a Merlin (depending on boost) this gap was in the 3,000-4,000ft range.
For the 213A is was about (depending on boost and MW-50) 1.5km (roughly 4,500 and a bit feet).
But on the 213E is was about 1,500ft (on all boost/MW-50 settings no less, another give away that this is not very kosher).
In many ways it gets worse with the higher gear/stages and altitudes, with the same negative throttling efficiencies being repeated and very short period of above full throttle power loss.
That's why I think this was that time's equivalent of today's Powerpoint presentation of overblown promises. Translated: "Give us gobs of money and yes we will defy the laws of physics, even we if we fail we still have the money".
There was no other supercharged British, German, American or even another Jumo engine that behaved this way.
Search the Flight Global archives section for the Griffon 130 and see how a real 2 stage, 3 speed engine works.
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Hello, OldSkeptic,
Seems that Jumo-213A has the same shape for it's power vs. altitude curves (minus one supercharger speed, of course) - gently dropping downward until FTH, then sharply dropping until the 2nd supercharger gear is engaged. BTW, Jumo-213E should not be able to engage/disengage 2nd stage - it was always engaged. Much like 2 stage Merlin, and unlike 2 stage P&W.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
Hi Tomo,
Here's a better one based on measurements: http://www.wwiiaircraftperformance.org/fw190/002rep2-level.jpg
There are some others linked to FW 190 D-9 Flight Trials but I think that's the clearest one.
You can actually see the dots and crosses of the measurements, then the lines drawn to fit.
In the middle you can see the boost pressure. Straight up to about 1.7km, then drops off linearly until the 2nd gear is engaged at about 3.7km.
If the boost is constant up to the the first FTH (exactly as in every other engine)... why is the power decreasing as shown in some of those other charts?
In a real engine, the supercharger efficiency is going up because throttling is being reduced (hence power goes up), until you hit FTH.
If those other charts were correct then the 213A (and 213E) would have had to have negative supercharger efficiency. That is they get less efficient as you get closer to FTH.
Here's a better one based on measurements: http://www.wwiiaircraftperformance.org/fw190/002rep2-level.jpg
There are some others linked to FW 190 D-9 Flight Trials but I think that's the clearest one.
You can actually see the dots and crosses of the measurements, then the lines drawn to fit.
In the middle you can see the boost pressure. Straight up to about 1.7km, then drops off linearly until the 2nd gear is engaged at about 3.7km.
If the boost is constant up to the the first FTH (exactly as in every other engine)... why is the power decreasing as shown in some of those other charts?
In a real engine, the supercharger efficiency is going up because throttling is being reduced (hence power goes up), until you hit FTH.
If those other charts were correct then the 213A (and 213E) would have had to have negative supercharger efficiency. That is they get less efficient as you get closer to FTH.
Thanks for clarification, Denniss 
OldSkeptic,
I can follow the logic about the constant boost, decreased throttling until FTH is reached etc. However, we have 3 Jumo-213 charts posted, and indeed all of them seem to do things their own way, so to speak. So until someone, who really researched Jumo history, speaks, seem to me that best thing is to go with official source(s).
OldSkeptic,
I can follow the logic about the constant boost, decreased throttling until FTH is reached etc. However, we have 3 Jumo-213 charts posted, and indeed all of them seem to do things their own way, so to speak. So until someone, who really researched Jumo history, speaks, seem to me that best thing is to go with official source(s).
Maybe they had a different design philosopy in mind when developing the 213 - not a short big spike and dropping off considerably but a constant power generation over a larger altitude band. May increase engine life and decrease fuel consumption.
Hmmm, we need someone with a complete description (or a book about Jumo engines) of the 213 to understand the supecharging system of these engines.
Hmmm, we need someone with a complete description (or a book about Jumo engines) of the 213 to understand the supecharging system of these engines.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
No they didn't, as the most famous engineer in history said" ya canna defy the laws of physics Captain".
The give away is actual performance figures of the 190D, which showed the normal 'saw tooth' speed shape with altitude.
If RR, Packard, Allison, Wright, Pratt and Whitney, BMW, DB, Napier, Bristol, et al, et al all show, with a supercharger the same performance shape ... then the logical thing to do is question the Jumo ones.
Answer: They are bogus.
And if Kurt Tank, who made it clear he didn't like the 213 engines and wanted the DB 603, was skeptical then it was he had been burned by Jumo a bit too often, both on performance and production.
For example I'm doing an analysis of the 213A (not finished yet). The post 2nd gear figures (non MW-50 and non GM-1) are exactly -100PS per 1km of altitude ...a bit too convenient.
This was from an engine with so-so supercharger efficiency and pressure ratio and only 3 vales per piston? With a very high piston speed (so internal engine friction would have been high).
The reality was the 190D never made the performance numbers predicted and that was largely, not entirely though, because the Jumo never produced the 'predicted' numbers.
Look the 211 (which with better cooling and smaller physical size was the 213, though with the same piston size and overall design) was inferior in most (not all though) altitude regimes of the Merlin X on the same fuel.. pre Hookers supercharger improvements.
Suddenly Jumo, out of the box and in unexplained ways, came up with a design that behaved like no other supercharged engine built by anyone else in the whole World (as I have said before, with negative supercharger efficiency). Something that no one else ever managed (then or now), basically because it is impossible.
This is my personal speculation, is that Jumo trying to get performance out of a so-so design (it wasn't a bad design, just sort of average for the time, with low supercharger efficiency and pressure ratio), realised that it had to use power boosting to meet the demands, therefore concentrated on incorporating MW-50 and GM-1 for various altitudes.
It then back calculated, for presentation purposes at least, the non boosting figures .. and fudged the power curves. Looked good to say the RLM who were paying the bills.
And, being a competitive private company, held off DB, who had stolen a march on them getting that (forgotten the name) specialised factory for 603 production, which DB had lied about and also never delivered.
Translated: corporate politics.
That was Germany at the time, a shambolic mess. Where at the corporate level patriotism never, ever, got in the way of making a buck.
Poor old Focke Wulf and Tank and BMW, which of all of the German aircraft players, definitely seemed to try their best to get the best pieces of kit for their country.
DonL
Banned
Your whole statement is simply bogus.
I advise you read some good researched book for example:
Flugmotoren und Strahltriebwerke: Amazon.de: Kyrill von Gersdorff, Helmut Schubert, Kurt Grasmann: Bücher
There you can find your answers.
By the way the claim that Tank didn't want the Jumo 213 is a myth nothing else.
Edit:
An other advise for good researched books:
http://www.amazon.com/dp/0764318764/?tag=dcglabs-20
http://www.amazon.com/dp/0764308602/?tag=dcglabs-20
There you can find primary sources and charts (from E-Stelle Rechlin) about the performance of the Jumo 213 and the a/c's powered by this engine and not some selected tendentious crap from your posted biased homepage.
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Until you either buy the 213 and run it on the appropriate instrument, or unearth present better data than the existing ones, such claims of your can be named the same.
Some data, backing up the claims about Tank's dislike of 213, then about the Jumo burning him too often (when? by what products?), and then about performance production would be good.
There was one thing 603 was 'better' - it was available earlier. However, if someone was to blame about non-availability of the 603 for Fw, that should be RLM?
Would that be post 2nd gear FTH figures? Mentioning of the MW-50, Jumo-213A and altitude above 2nd gear FTH in the same sentence might point out towards the credibility of the man doing the analysis...
Out of interest, what was the efficiency of the supercharger of the Jumo-213A? Pressure ratio - ditto? Very high piston speed was a product of stroke (long) and RPM (high) - the high RPM made the 213 a much more powerful engine than 211. Price was the increased weight - the 'no free lunch' rule applies as ever.
(edit: )Good data covering this?
(edit: )And the numbers would be?
As above - until we have better data than one available now, I'll stick to the factory data.
Again, as above - please post the creditable figures about supercharger efficiency pressure ratio of the 213. What does the 'use of power boosting' mean??? Should we now all think, that people that struggled to have their engines use water-methanol injection, were inept in their job?
Good thing this is still a personal speculation.
Few god words can be indeed said about the German war management, even small hiccups can retaliate when one is confronted against 3 world powers.
If any German 'aircraft player' can be noted above others, that would be the DB?
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I agree completely. If I didn't know better, I would think Mark Williams was writing for OldSkeptic.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
Who's Mark Williams?
Mark Williams is a self proclaimed 'expert' who specializes in hand picking and choosing DATA about ME 109's FW 109's that suits his needs.
Check Mark Williams claims about 109's and 1.98ata.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
Where?
Right here:
Spitfire Mk XIV versus Me 109 G/K
I'm not saying one was superior to the other, but the data that Mr. Williams presents is snips bits of 109 testing to try and prove his own agenda,
of the 109K being vastly inferior to the Mk XIV.
Spitfire Mk XIV versus Me 109 G/K
I'm not saying one was superior to the other, but the data that Mr. Williams presents is snips bits of 109 testing to try and prove his own agenda,
of the 109K being vastly inferior to the Mk XIV.
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