# Engine power vs altitude



## Rapecq (Sep 8, 2009)

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.


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## drgondog (Sep 8, 2009)

Rapecq said:


> I would like to ask about differences in the way that engine power decrease with altitude, but first some performance charts:
> 
> BWM 801D2
> 
> ...



Decrease in air density (and temp) with altitude is the reason. 

Getting sufficient mixture of oxygen to fuel is the reasone for superchargers (and all mechanical methods) to bring air into the engine/carburation system


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## Shortround6 (Sep 8, 2009)

It was accepted that most piston engines would loose power with altitude until at about 55,000-56,000ft the engine would only make enough power to overcome internal friction and not be able to provide any power for propulsion.
If you continue the lines on the graphs they will all end at about that altitude. 

It has to do with the air density. The chart I have doesn't go to 55,000ft but only 50,000ft. At 50,000 ft the air is about 15% as dense as sea level so an engine, taking in the same cubic feet of air, could be expected to make 15% of the power at sea level. 
This is gross power and not propeller shaft or 'net' power. Say, as a hypothetical, you have an engine that gives you 1100hp at sea level to the propeller. Such an engine might actually be making an extra 150hp that is used up in friction of pistons and bearings and being used to drive oil and fuel pumps, etc. this gives us a total of 1250hp gross. At 50,000 ft the engine would have 15% of this power or 187.5HP but since the friction and pump dirves still need the same amount of power (150) this leaves only 37.5 hp left for the propeller. 
TO go further let us assume that this engine has no supercharger. In this case it's 1100 hp sea level power would have fallen to about 788hp at just 10,000feet ( 74% air density X 1250 gross - 150 friction/pumps).
Now we fit a supercharger that can give us sea level density at 10,000ft for a cost of 100hp to drive it. This can give us 1000hp at 10,000ft. a very worthwhile improvement. 
But the higher we go the closer the power of the supercharged engine gets to the power of the unsupercharged engine. If I have done the math correctly the unsupercharged engine would give 317.5hp at 30,000ft to the propeller (37.4% air density X 1250 gross - 150 friction/pumps) compared to the supercharged engines 382.5 HP ( 50.6% difference between 10,000ft and 30,000ft X 1250 gross-250hp for friction, pumps and supercharger drive) Still better but both are going to zero out at about 55-56,000ft. 
Adding a second gear to the supercharger or a second stage is going to have a similar effect. At some point the extra boost, which has to be paid for with power from the crankshaft, is not going to be enough to compress the air enough to cover the power needed by the supercharger. 
THe Germans may have made slightly different asumptions about just where the zero point is, and/or used a different density chart. Just how many research flights had been made to 50,000+ feet to measure air density in the late 30s and early 40's

I am not sure if this helps with you question but I hope it does.


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## Rapecq (Sep 8, 2009)

Hello

Thanks for answers, but I still don't know what may cause the difference in power drop beetwen for example BMW 801D/Merlin 66 and Jumo 213 E-1. As I've written before on BWM 801 chart the power goes up from SL till reach FTH of particular gear, then power drops untill 2nd gear is engaged. 

On the other side we have Jumo 213 E-1 chart when at each gear the power of engine is pernamenlty dropping. What may be the reason of this?

Regards


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## red admiral (Sep 8, 2009)

Rapecq said:


> On the other side we have Jumo 213 E-1 chart when at each gear the power of engine is pernamenlty dropping. What may be the reason of this?



I think the difference is because of how the boost is regulated on the two engines. For the Merlin, the available boost is greater below the full throttle height but the engine is limited in how much boost it can make. As a result the throttle isn't fully open below the full throttle height and the engine makes less boost and less power. I imagine the BMW works in a similar way.

I'm not entirely sure about what method the Jumo 213 uses but it seems to keep the boost constant between full throttle heights, maybe some sort of dump valve. Or it might be something to do with the MW-50 boost system, I'm not sure.


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## fusbeta (Sep 10, 2009)

what a great info, thanks.
Thanks so much for this. I appreciate the effort. It really helps a lot.
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## Aurum (Sep 18, 2009)

Rapecq said:


> Hello
> On the other side we have Jumo 213 E-1 chart when at each gear the power of engine is pernamenlty dropping. What may be the reason of this?
> Regards


Don't forget that Jumo hydraulic driven second stage that allowed change supercharging smoothly. So line of power between 1st 2nd stage max. power points is not so wavy as other have.


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## Yo-Yo (Nov 9, 2012)

Jumo has vanes before the blower so it can control the boost level preventing from the excessive boosting at low altitude.


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## msxyz (Nov 9, 2012)

Each engine aircraft is built for a critical altitude, that is the altitude at which it can develop the maximum power.

At sea level, manifold pressure must keep below a certain level even if the supercharger could, in theory, pump more fuel air mixture, the limit being the ocurrence of self ignition before the piston reach the top dead center. What's interesting is that power at sea level is usually slightly lower than power at critical altitude becuase air is thinner and thus the expanding hot gases encounter less resistance during their trip down the bore, pushing the piston, and out of the exhaust (this factor is called 'back pressure').

Power curves at a certain altitude are also affected by engine control design: on a car engine you would see power dropping at the same rate of atmospheric pressure. Single speed supercharged aircraft engines start with a certain power, increase it slightly till the critical altitude and, from there on, power will decrease in accordance with barometric pressure. Two speed superchargers follows the same principle of one speed designs except that, above a certain altitude, the engines equipped with them benefit from a higher boost setting.

Daimler Benz designed a hydrostatic, continuos variable coupling controlled by a barometer to use with their engines. The power output of the DB601/5 remains basically flat till about 4500 meters thanks to this automatic compensation system. A simpler, albeit less efficient arrangement, involves variable geometry stators to modify the pressure ratio of a centrifugal compressor by altering the airflow.

Every technical solution to tackle the loss of power at altitude has its pro and cons and influences the engine behavior in a different way.


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## Yo-Yo (Nov 12, 2012)

msxyz said:


> Each engine aircraft is built for a critical altitude, that is the altitude at which it can develop the maximum power.
> 
> At sea level, manifold pressure must keep below a certain level even if the supercharger could, in theory, pump more fuel air mixture, the limit being the ocurrence of self ignition before the piston reach the top dead center. What's interesting is that power at sea level is usually slightly lower than power at critical altitude becuase air is thinner and thus the expanding hot gases encounter less resistance during their trip down the bore, pushing the piston, and out of the exhaust (this factor is called 'back pressure').


Exhaust backpressure is not the only factor reducing the power under critical altitude. The main factor is air (mixture) density. As the manifold pressure regulator keeps MP constant air temperature after blower is higher at low altitude so the density that is proprtional to pressure/abs_temperature ratio drops.


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## tomo pauk (Nov 12, 2012)

> As the manifold pressure regulator keeps MP constant*,* air temperature after blower is higher at low altitude*,* so the density*,* that is proprtional to pressure/abs_temperature ratio*,* drops.



I've inserted some commas - hopefully that's okay?


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## Shortround6 (Nov 12, 2012)

General Motors ( Owner of Allison) published a booklet in 1943(?) describing a number of different intake/supercharger systems and their effects on power at altitude for a theoretical 1000hp engine. Back pressure at 20,000ft was enough lower that the engine would _gain _ 80hp (8%) *IF* the engine could be supplied sea level *AT NO COST* to the engine ( more power to drive supercharger). Please note that this is NOT exhuast thrust and please note that exhaust thrust is not totally free either as the size nozzles needed for exhaust thrust do raise the back pressure some. It does mean that the power to run a Turbo is not totally free however. Balance this against the power needed to compress air at 20,000ft to a sea level air pressure.


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## davparlr (Nov 12, 2012)

This is a good opportunity to compare the strengths and weaknesses of supercharging vs turbo-supercharging. If we compare the turbo-supercharged R-2800-57 used in the P-47N to the supercharged Jumo 213E (used in the Ta-152),

http://www.wwiiaircraftperformance.org/p-47/p-47n-88406-speed.jpg 

we can see that the hp of the R-2800 is basically flat rated up to 33k ft. with none of the saw toothed power levels (note that this graph shows max continuous power. For WEP max power is 2800 hp). Brake Horsepower (BHP) is next to the last graph, right before True Speed. At 33k ft, the Jumo is only generating about 1300 hp, or less than half the power of the R-2800. As pointed out by Shortround6, this is not free. Turbo-superchargers are bulky and heavy, the P-47 engine system is about 400 lbs more on the P-47 than the engine system of the F6F. In addition it does not use exhaust thrust, which other people can discuss.

This does show why turbo-supercharging was such a tempting technology. This also shows that, while the P-47 was never known as a great low level dog fighter, it is known as a formidable fighter at high altitudes.


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## tomo pauk (Nov 12, 2012)

The production engines, mid 1943 to mid 1944 (not the V-1710-117, at least not used in production fighters; here is for comparison). The V-1710-93 and -117 were used in P-63A and -C. V-1710-89/91 are on P-38J.

V-1650-3 weights: Engine + eng. controls + cooling + lubricating: 1670+30+663+101 = 2464
V-1710-93: 1620+105+347+135 = 2207 (no intercooling here); ADI system adds 50 lbs
V-1710-117: 1710+114+346+135 = 2305
V-1710-89/91 weights, same as above + turbo: 2730+321+81+1065+194+613 (turbocharging system) = 5004 for 2 engines; 2502 lbs for 1 engine

TO power: 1380HP* (1490 for the -7) vs. 1325 (both 2 stage Allisons) vs 1425 (for turbo Allison)
max WEP: 1600/1720 HP (low gear) vs. 1500 (1820 with ADI; bot at SL) vs 1600 (for turbo Allison)
max WEP at altitude: 1330* (-3; with ram: at 29000 ft) or 1370 (-7, military power, no ram: at 21400 ft; 1505 HP at 19250 WER, no ram) vs 1150 (no ram: at 22400 or 25000 ft) vs. 1600 HP (no ram: at 25000 ft; with ram: 26500ft)
all data from AHT book. 
Agreed that, while making high speed dash, the non-turboed engines have the exhaust thrust to help them out. They also (at least in P-38 vs. P-51 case) use the ram effect much better. Contrary to that, neither ram effect nor exhaust thrust are of much use when plane is climbing, ie. flying in low or moderate speed.

Fuel consumption, max continous/military power/WER, at altitude: V-1650-3: 140/190/204 USG/hr/engine. In low blower: 115/165/189.
V-1710-89/91: 113/161/187.

* the table for the V-1650-3 gives 1400 for the take off, 1410 @ WER at 23750 ft, no ram.

It indeed took much space weight to have the R-2800 make 2800 HP at high altitude. OTOH, seem like the turbo V-1710 was as good (for the needs of the USAAF) as the 2 stage Merlin.

The single engined fighter with turbo V-1710: a missed USAAF's opportunity?

added: fuel consumption for R-2800-21 (P-47), max cont/mil/WER (2300 HP): 210/275/315 USG/hr
R-2800-8W (F4U), high blower: 250/280/245(???-from the engine table). Low blower: 240/275/245(???)


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## gjs238 (Nov 12, 2012)

tomo pauk said:


> The single engined fighter with turbo V-1710: a missed USAAF's opportunity?


 I think the challenge is where to fit the turbo, and preferably, the intercooler.


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## tomo pauk (Nov 12, 2012)

The best location for non-late-war turbo (ie. the blades are not hollow, for cooling purposes) is where it was for P-47 - within the rear fuselage, down. The intercooler can be a part of the 'cooling group', as it was in the Merlin Mustang, the intercooler here being air-to-air type.


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## Shortround6 (Nov 12, 2012)

Unfortunately the few planes that were built using turbo V-1710s showed a lack of imagination or some rather poor assumptions on drag or perhaps the packaging problem is a bit more difficult than we think.


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## tomo pauk (Nov 12, 2012)

The second page depicts a non-turbo plane; open exhausts?
Ugly as it was*, the XP-60A was claimed to make 420+ mph. A good info, better/more thorough than one in the 'Vees for victory' would be most welcomed 

*P-47 was seldom, if ever, described as a pretty plane...


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## Shortround6 (Nov 12, 2012)

Curtiss also guaranteed the XP-46 would do 410mph at 15,000ft. The light weight prototype made it, the fully combat equipped 2nd prototype dropped to 355mph at 12,200ft. 

A fire in the XP-60A damaged the exhaust shrouds while ground running, the plane was "repaired" by fitting normal exhausts and the turbo removed with all ducting. First flight was Nov 1st 1942. One source claims a revised turbo installation was installed and tested (ground or flight?) Work stopped Nov 6th and the plane was dismantled with parts used in other aircraft. With only 6 days at best and work going on between flights it seems doubtful high speed runs were done. The XP-60B was supposed to use an Alison engine with a Wright instead of a GE turbo supercharger but was never completed with this engine, being converted to mount an R-2800.

You are correct on the second picture. There seems to be some confusion as to which picture belongs to which version of the P-60. That picture is for the XP-60 with a Merlin 28. (I think?) This airframe was later modified to have a bigger tail and was supposed to have a Merlin 61 installed (becoming XP-60D) Plane is reported to have crashed after the tail was modified but before the engine swap was done.


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## rinkol (Nov 12, 2012)

I think you are referring to the scheme used on the HS 12Y-45 (Planiol supercharger) where throttling was performed using vanes whose incidence could be varied at the supercharger input - http://www.enginehistory.org/Accessories/S-Psc/S-PscTst.shtml. A similar arrangement was used by the Mikulin AM-35 and some other V12s developed in the Soviet Union. Unfortuantely, I don't know much about its applications in the German engines, though it is clear that the Germans would have been aware of the idea.


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## gjs238 (Nov 13, 2012)

VIGV's, variable inlet guide vanes


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## msxyz (Nov 13, 2012)

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!


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## GregP (Nov 13, 2012)

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.


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## OldSkeptic (May 2, 2013)

Rapecq said:


> I would like to ask about differences in the way that engine power decrease with altitude, but first some performance charts:
> 
> BWM 801D2
> 
> ...



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.


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## rinkol (May 2, 2013)

Yo-Yo said:


> Jumo has vanes before the blower so it can control the boost level preventing from the excessive boosting at low altitude.


 
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.


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## Denniss (May 2, 2013)

OldSkeptic said:


> 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.


 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.


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## OldSkeptic (May 3, 2013)

Denniss said:


> 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.




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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## tomo pauk (May 3, 2013)

OldSkeptic said:


> ....
> 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.
> 
> ...



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.


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## Denniss (May 3, 2013)

The graph above is not from a Standard 213A, it's from the 213AG with a special sealevel boost peak. This engine seems to be based on the 1900PS base 213A with erhöhte Notleistung already installed.


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## OldSkeptic (May 3, 2013)

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.


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## tomo pauk (May 4, 2013)

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).


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## Denniss (May 4, 2013)

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.


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## OldSkeptic (May 5, 2013)

Denniss said:


> 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.



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.


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## DonL (May 5, 2013)

OldSkeptic said:


> 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.
> 
> ...



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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## tomo pauk (May 5, 2013)

OldSkeptic said:


> 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.



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.



> 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.



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?



> 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.



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...



> 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).



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.



> 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.



(edit: )Good data covering this? 



> 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.



(edit: )And the numbers would be?



> 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.



As above - until we have better data than one available now, I'll stick to the factory data.



> 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.



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? 



> 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.



Good thing this is still a personal speculation.



> 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.



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.



> 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.



If any German 'aircraft player' can be noted above others, that would be the DB?


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## altsym (May 5, 2013)

DonL said:


> Your whole statement is simply bogus.



I agree completely. If I didn't know better, I would think Mark Williams was writing for OldSkeptic.


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## OldSkeptic (May 6, 2013)

altsym said:


> I agree completely. If I didn't know better, I would think Mark Williams was writing for OldSkeptic.



Who's Mark Williams?


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## altsym (May 6, 2013)

OldSkeptic said:


> 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.


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## OldSkeptic (May 6, 2013)

altsym said:


> 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.



Where?


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## altsym (May 6, 2013)

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.


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## Jabberwocky (May 6, 2013)

If you're going to criticise someone, at least have the common courtesy to spell their name correctly.

*Mike* has put up hundreds (if not thousands) of original documents on WWII Aircraft Performance and made them freely available for all to look at and share. In doing so, he's performed a valuable service to almost all who use and enjoy this forum.

What have you done?


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## altsym (May 7, 2013)

Yes Mike, thank you. No doubt he has provided us with original documents, a great service. He has also made glaring mistakes in HIS _analysis_ of some documents, NOT the documents themselves.


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## RCAFson (May 7, 2013)

altsym said:


> Yes Mike, thank you. No doubt he has provided us with original documents, a great service. He has also made glaring mistakes in HIS _analysis_ of some documents, NOT the documents themselves.



OK, I'll bite. Where exactly does Mike insult der fuhrer's uber fighter?


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## OldSkeptic (May 7, 2013)

Jabberwocky said:


> If you're going to criticise someone, at least have the common courtesy to spell their name correctly.
> 
> *Mike* has put up hundreds (if not thousands) of original documents on WWII Aircraft Performance and made them freely available for all to look at and share. In doing so, he's performed a valuable service to almost all who use and enjoy this forum.
> 
> What have you done?




I agree. You may or may not agree with his analysis, but his work in putting up data has been invaluable.
And that's the nice thing about it. You can make your own interpretations, it's all there for you to do it.


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## Tante Ju (May 7, 2013)

I often wonder why never been an "evaluation" of 109F and Spit 5 on ww2performance site.  I guess Mike was not yet able to find bad enough graphs for 109Fs...  Seriously, the bias of those articles are legendary in aviation community.. the errors (manipulations?) are well known.

The originals are good though. I prefer to read those and ignore these silly articles completely. I am sure everybody can find in originals what is interesting for him.


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## OldSkeptic (May 7, 2013)

All Data from WWII Aircraft Performance, in their FW-190 section. Plus the Jumo 213A charts shown here.

I took various 801D numbers (all at max settings without C3). 
Two sources agreed well. The USAAF tests, which I think were on a static rig to NACA specs. There are 2, with and without the geared fan.
These agree quite well with FW's own climbing numbers, that is without any (or minimal) RAM air.
The FW numbers are on level flight, that is with ram air increasing boost. This increases power and delays FTH.
I suspect the very high altitude ones (30,000ft+) are a bit high, because by that point IAS would be getting very low.

A very important factor often forgotten, especially with Merlins on high boost, they couldn't always get the 25lb boost without high speeds ramming air into the intakes.

Basically the BMW numbers look good, excepting the very high altitude with ram air, and overall cross check quite well.

Now the Jumo 213A numbers, taken from charts shown here with no MW-50 or GM1, but at 3,250 rpm, thus basic maximum power numbers without power boosting.
I assume they include ram air, but then again? Confirmation from anyone would be nice. If they are static then the correct comparison would be with the 801 static (or climbing) numbers.

Now I took the numbers at min/max values and back calculated the in between ones, to enable like by like comparisons.
PS is corrected for to BHP. KM to feet.
The X-axis is chosen to shown to various FTH and min value heights, so it is not linear (hence the shape is a bit different from the normal ones). Later I'll write a program to calculate it all at every 100 feet or so to give nicer charts.
Plus all numbers can move +/- 1% or so because I am converting charts to numbers for calculations.


But the results, I was bemused by them (so I double and triple checked them, _no guarantee of course, if anyone finds an error please let me know and I'll fix it_).
The 190D was developed as an interim design to give better high level performance to the 190. Needed for interceptions of the USAAF bombers and escort fighters.
The 213A was chosen for this, but the 801D was superior or equal in that 20,000-30,000ft region. Only at 35,000ft does it pull ahead and not by much.

At low altitudes the Jumo appears more powerful (but has that funny 'defying the laws of physics' shape again) up to about 17,000ft (more with MW-50 of course).

And yet this was supposed to improve high altitude performance?

Starts to explain why the 190D performance numbers, without power boosting, were not that great (still good though).

Any ideas anyone?


Nice thing about this, once I have written my program (those numbers were just done in Excel), is that later I will be able to overlay all sort of different engines.


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## OldSkeptic (May 7, 2013)

Tante Ju said:


> I often wonder why never been an "evaluation" of 109F and Spit 5 on ww2performance site.  I guess Mike was not yet able to find bad enough graphs for 109Fs...  Seriously, the bias of those articles are legendary in aviation community.. the errors (manipulations?) are well known.
> 
> The originals are good though. I prefer to read those and ignore these silly articles completely. I am sure everybody can find in originals what is interesting for him.



And you should thank him for the work he has done in providing them. While, _politely_, disagreeing with his analysis and interpretations.
I think that is only fair, given the (obviously) tremendous work he has put in.
Nothing wrong with saying " I disagree, I think based on these numbers such is such", not so good to claim "bias", manipulation" or "silliness".

Hey, here is an opportunity for you .. you write an 'evaluation' of the Spit V vs the 109F, with all supporting materials of course (original sources only). 
Naturally we will all agree or disagree "politely" of course, naturally no one will accuse you of "bias", manipulation" or "silliness".

I like honest analysis. I have my own personal disagreements with some of Mike's analysis, but I truly respect the work he has done, and the honesty of providing all the material.
If I have an issue that I care a lot about then I will contact him directly. Perhaps you should do so too.

*I will not ever go behind his back saying anything about him , except "I respectfully disagree, this is what my analysis shows".*.


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## DonL (May 7, 2013)

> Now the Jumo 213A numbers, taken from charts shown here with no MW-50 or GM1, but at 3,250 rpm, thus basic maximum power numbers without power boosting.
> I assume they include ram air, but then again? Confirmation from anyone would be nice. If they are static then the correct comparison would be with the 801 static (or climbing) numbers.



Your calculation is *without ram air* as you can see at Denniss graph.
The graph from Denniss shows (only) the performance with ram air for "Steig und Kampfleistung" (3000rpm). The red marker.






So you have a poweroutput/performance of 1480PS at 22300ft with normal "Steig- und Kampfleistung" at 3000rpm.

Edit:

Here the graph for the BMW 801D with ram air and normal Steig- und Kampfleistung at 2400 rpm





So you have a poweroutput/performance of 1320PS at 19600ft with normal "Steig- und Kampfleistung" at 2400rpm.

Now you can see, why the FW190D-9 was a major improvement for higher altitudes.


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## tomo pauk (May 7, 2013)

Hello, OldSkeptic. Some remarks:



OldSkeptic said:


> ...
> I took various 801D numbers (all at max settings *without C3*).



The would be 'without C3 acting as anti-detonant'?



> Two sources agreed well. The USAAF tests, which I think were on a static rig to NACA specs. There are 2, with and without the geared fan.
> These agree quite well with FW's own climbing numbers, that is without any (or minimal) RAM air.
> The FW numbers are on level flight, that is with ram air increasing boost. This increases power and delays FTH.
> I suspect the very high altitude ones (30,000ft+) are a bit high, because by that point IAS would be getting very low.



The lines for engines with ram and without fan would just throw more confusion IMO.
Here is the BMW 801D chart, it, conveniently, has altitude expressed in ft. Thick lines are for static engine. The lines are for figures without fan, subtract 100-50 PS to get real power available to the prop (as from table attached below).













> ...
> Basically the BMW numbers look good, excepting the very high altitude with ram air, and overall cross check quite well.



If you will be so kind to make another chart (containing the data posted above, and without ram take into account), we might get a slightly different results. The results at high altitude would be comparable, both engines were single-stage anyway.



> Now the Jumo 213A numbers, taken from charts shown here with no MW-50 or GM1, but at 3,250 rpm, thus basic maximum power numbers without power boosting.
> I assume they include ram air, but then again? Confirmation from anyone would be nice. If they are static then the correct comparison would be with the 801 static (or climbing) numbers.



As noted from DonL, all lines are for static engine, bar the lines highlighted in red by him.



> Now I took the numbers at min/max values and back calculated the in between ones, to enable like by like comparisons.
> PS is corrected for to BHP. KM to feet.
> The X-axis is chosen to shown to various FTH and min value heights, so it is not linear (hence the shape is a bit different from the normal ones). Later I'll write a program to calculate it all at every 100 feet or so to give nicer charts.
> Plus all numbers can move +/- 1% or so because I am converting charts to numbers for calculations.



Okay.



> But the results, I was bemused by them (so I double and triple checked them, _no guarantee of course, if anyone finds an error please let me know and I'll fix it_).
> The 190D was developed as an interim design to give better high level performance to the 190. Needed for interceptions of the USAAF bombers and escort fighters.
> The 213A was chosen for this, but the 801D was superior or equal in that 20,000-30,000ft region. Only at 35,000ft does it pull ahead and not by much.
> 
> ...



The (not only high altitude) performance was improved, not because the Jumo-213A was an uber engine, but because it was offering two important things - less drag and better use of ram effect. We can note that, even the 190A-9, with improved BMW-801S, way paying the price in drag, and with more HP it was slower than D-9. It was also featuring the internal air intakes (= less able to capitalize on ram effect), a major handicap for fights above 20000 ft.
The 190A, when tested with external intakes, was found to be faster at high altitudes than the regular 190A with internal intakes.



> Starts to explain why the 190D performance numbers, without power boosting, were not that great (still good though).
> Any ideas anyone?



I guess you speak about 190D-9? That one was flying with engine featuring single stage engine, and any good plane with two stage engine will be faster climb better where the air is thinner (=hi-altitude), no sweat.


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## tomo pauk (May 7, 2013)

Another thing where the 213A was better than 801 was exhaust thrust - static engines were making, eg. at 7km, 126 kg vs. 100 kg of exhaust thrust. Or, 150kg vs. 125 kg at ~5,5 km. Also, the D-9 was having 2 cannons less, along with 2 ammo chutes less - less drag.


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## DonL (May 7, 2013)

Also note thas all graphes from the Jumo 213A/E *except the one from Denniss* shows performance datas *without* ram air.

The graph from Denniss shows also exactly which exhaust thrust (kg)was generated from the Jumo 213A, with which outputperformance (Sondernotleistung, Start/Notleistung and Steig- und Kampfleistung)


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## OldSkeptic (May 7, 2013)

Thanks for all that everyone, I'll update. Yep, makes a lot of sense about the drag issues and exhaust thrust being a factor.


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## tomo pauk (May 7, 2013)

Until something more professional looking is posted, here is my contraption - the red line is for Jumo 213A from the graph Denniss kindly posted, the blue line is for BMW 801 based upon the values from the table from post #49. The 100 PS difference above 5,7 km is apparent. Denniss' chart also nicely shows that 213A can add another km to the critical altitude via taking advantage of ram effect, the 'regular' 801 fares less well in that area.


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## DonL (May 7, 2013)

Tomo ist this for static engine or with ram air?

Because I think Start/Notleistung with ram air (Jumo 213A) would be much smoother and better at higher altitudes?

My interpretation of the Jumo 213A with Start/Notleistung and ram air, taken from the chart with Steig and Kampfleistung.






Edit I see you have already answered my question


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## Denniss (May 8, 2013)

On the 801 the fan was consuming 70-80PS at 2700rpm and down to 20-30PS at 2000rpm, varied a bit with engine version. BMW graphs show 25-70 for the 801S/TS and 20-82 in the 801Q/TU


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## Tante Ju (May 8, 2013)

70-80 PS to drive a fan...?! Seems unbelievable.


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## altsym (May 8, 2013)

That's only 4%. My old 1966 427 big block Chevy mechanical fan uses about 25hp @ 4800rpm. That's 6%.


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## tomo pauk (May 8, 2013)

Denniss has posted the graphs covering that here.


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## Tante Ju (May 8, 2013)

tomo pauk said:


> Denniss has posted the graphs covering that here.


 
Thank Tomo, its hard to believe at first but its there on the graph, black and white! 

Thanks also altsym. I did not know even cars "waste" so much power on driving a fan... thats something like 18 000 Watt for a car fan... what sort of electric motor is that and why does it need to be so powerful?


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## rinkol (May 8, 2013)

"Thanks also altsym. I did not know even cars "waste" so much power on driving a fan... thats something like 18 000 Watt for a car fan... what sort of electric motor is that and why does it need to be so powerful?"

Up until the 1980's automobile engines had fans that were operated via a belt drive running off of the engine crankshaft. The problem was that a fan that was configured to provide adequate cooling for an idling engine in a stationary vehicle took a considerable amount of power when the engine was operating at a speed corresponding to its rated output or anything close to it, even though the flow of cooling air resulting from the vehicle motion would have been more than sufficient. Consequently, newer vehicles have a thermostatically controlled electric motor driving the fan. This arrangement only operates when needed and gives a significant improvement in net engine output and overall efficiency.


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## Shortround6 (May 8, 2013)

The electric fans replace clutch fans which were an intermediate step. The fan de-clutched at high rpm or when the airflow through the fan over-drove it. Unfortunately the clutches tended to fail after awhile and start to wobble. Since the fan was often mounted on an extension shaft of the water pump a wobbling fan could take out the water pump bearing seal causing the engine to loose coolant.


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## Mike Williams (Jun 2, 2013)

Jabberwocky said:


> Mike has put up hundreds (if not thousands) of original documents on WWII Aircraft Performance and made them freely available for all to look at and share. In doing so, he's performed a valuable service to almost all who use and enjoy this forum.



Thanks Jabberwocky, I'm glad you find the material on WWII Aircraft Performance of interest.

Here's a couple of primary source documents concerning the Fw 190 D with Jumo 213 engine that tie in with this discussion:

Flugbericht FW 190/170003 V 53 Nr. 1
Flugbericht Fw 190 D-9/210001 Nr. 1
Flugbericht Fw 190 D-9/210001 Nr. 2
Flugbericht Fw 190 D-9/210001 Nr. 3
Flugbericht Fw 190 D-9/210002 Nr. 1
Flugbericht Fw 190 D-9/210002 Nr. 2
Flugbericht Fw 190 D-9/210002 Nr. 3
Flugbericht Fw 190 D-9/210002 Nr. 4
Fw 190 D-9, Climb and Level Speed Performance with C3 Fuel (calculated estimate)
Flugbericht FW 190/0043 V 21 Nr. 1

For translations see: FW 190 D-9 Flight Trials


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## Aozora (Jun 2, 2013)

altsym said:


> No doubt he has provided us with original documents, a great service. He has also made glaring mistakes in HIS _analysis_ of some documents, NOT the documents themselves.



Looking forward to you spending thousands of hours and and a small fortune finding the original documents; you can then develop your own website and present them all with your analysis and conclusions, so some anonymous dweebs on various forums can claim that you are extremely biased/don't know what the hell you are talking about. But then some people just find it easy to gripe and complain about other people's hard work.



Tante Ju said:


> I often wonder why never been an "evaluation" of 109F and Spit 5 on ww2performance site.  I guess Mike was not yet able to find bad enough graphs for 109Fs...  Seriously, the bias of those articles are legendary in aviation community.. the errors (manipulations?) are well known.



Guaranteed that you have examples of your high quality analysis and unbiased opinion available for us all to read on your own website? Or is this more to your tastes? Kurfürst Discussion Boards • View topic - Nuther quote minus a source ...well informed and completely unbiased.

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