Piston engines power charts

Discussion in 'Engines' started by tomo pauk, Apr 2, 2010.

  1. tomo pauk

    tomo pauk Creator of Interesting Threads

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    People, does anyone has a good (online, if possible) source with charts of engine powers vs. altitudes? Or some kind of tables?

    Appreciate it in advance :)
     
  2. Kurfürst

    Kurfürst Banned

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    Dozens, but it would help if you could tell which one you are looking for ;)
     
  3. tomo pauk

    tomo pauk Creator of Interesting Threads

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    'Mainstream' ones for starter: Merlins, DB-601/605, Allisons, R-1820/1830/2600/2800, Klimov, Shvetshov, Sakae, Homare, BMW-801...
     
  4. Shortround6

    Shortround6 Well-Known Member

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    Simple charts can be done if you know the power at a given altitude, say 1200hp at 16,000ft in high gear.

    plot the 1200hp at 16,000ft on a graph and and plot "0" HP at 55,000ft. Connect with straight line and it should be pretty close at any altitude above the 16,000ft mark.
    Some discrepancy about the "0" point some say 56,000ft or higher but it won't throw things off by that much.
    If you have access to an atmospheric density or pressure chart you can use the percentage change of either density or pressure between a known altitude (as in the above example, 1200hp at 16,000ft) and an unknown altitude (what would the sample engine give at 24,000ft?)to estimate the the power available. as in pressure at 16,000ft is 16.21 in.hg while the pressure at 24,000ft is 11.59in.hg or 71.5% of the pressure at 16,000ft. Our engine should make about 71.5% power at 24,000ft compared to 16,000ft.

    It may not be exact but it should be close.

    Going from the known height to sea level is a lot trickier. The theoretical output of the engine should follow the same line(curve?) but problems with engine strength, cooling, and detonation almost always mean that power output is either held constant from sea level to rated altitude or actually declines from rated altitude towards sea level.
    2 speed engines have two peaks and the DB engines would show a curve rather than a saw tooth as the descend from critical altitude.
     
  5. billswagger

    billswagger Member

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    #5 billswagger, Apr 2, 2010
    Last edited: Apr 2, 2010
    Here is a table and graph for the Allison -33 found in P-40B/C.
    I haven't made much sense of the graph on page two.
    http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/1710-33.pdf


    There are more of these for later Allison versions at the bottom of this page:
    Perils P40 Archive Data

    You might even find info for the Packard built Merlin fitted to later P-40Fs.


    R-2800s is actually a pretty consistent engine in a supercharged configuration up to about 20,000ft, and more so in a turbo configuration up to 30,000+ ft.
    Most power charts i've seen are derived from aircraft performance tests which give these numbers.

    Manufacturers recommended outputs also tend to be conservative for liability reasons, although they also recognize that the expectation of having pilots fly with in recommended conditions may not always suit an emergency situation. They'd rather see the pilot push the engine at the cost of some engine life, rather than risk the pilots life.

    Bill
     
  6. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Yep, I've though to go that way (using 2 known points to construct the curve), but decided eventually to take advantage of any available chart, and then to draw the curve for engines that are left without the charts eventually.
    It's trickier for 2 speed-supercharged, since those have 2 power peaks.
     
  7. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Thanks :)

    That tidbit about R-2800 further reinforces my love towards it :D
     
  8. Shortround6

    Shortround6 Well-Known Member

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    As I understand it the chart shows the sloping lines from upper left to lower right as power at altitude with each line representing a certain rpm. Please note that the lines are converging and should meet and reach the zero power level at around 55-56,000ft should the chart go that high.
    The curved lines that go from upper right to lower left crossing the straight lines are the manifold pressure. At any given altitude-rpm combination you are going to have only one possible manifold pressure and power out put.
    This is both a practical and theoretical chart in that it shows what is possible in practice and (in the upper left part of the chart) what is possible in theory. In practice note the 12,000ft altitude line going up to meet the 2600rpm max continuous speed line and giving the 950? hp at 33.7in pressure noted in the first chart.
    In theory if you gave the engine wide open throttle at sea level it would give you 1700hp at 3000rpm. This is limited in practice by engine strength and detonation limits. But it does show were WEP comes from. It is never available above the rated altitude of the engine because the supercharger is already supplying all the air it can at that altitude. Should the engine be fitted with stronger parts, or shown by experience to tolerate higher out put or a new fuel allow higher detonation limits (or a combination) then a higher boost (manifold pressure) can be used at the altitudes were the supercharger can supply the extra air.
     
  9. vanir

    vanir Banned

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    There's also blower efficiency by altitude to factor in separately, they peak, plateau and flat spot all over the shop. There are specific altitude/flow rates for manifolding. Even valve timing distinctly affects the volumetric efficiency of engines by altitude, so does fuel type ostensibly because of different ignition timing and the dynamic compression ratio changes.

    Only a very comprehensive computer model of a specific engine setup and atmospheric conditions could return anything remotely accurate. Or otherwise recorded flight test data, not projected manufacturer data like most graphs available.

    For example Thunderbolts reportedly had overspeeding problems with the turbo at high altitude which killed performance that should've been available. So you need to go by actual test flight records and stick to those figures, without projecting imaginary lines outside their specific range or it's just fantasy.

    With all this in mind each aero engine sort of has a distinct and unique character of performance by altitude which cannot be represented in a simple one-two calculated line graph projecting by guess work.
    To outline, the character of the Merlin is given at 2000m, that of the Daimler at 1000m. The BMW under 1000m, the Jumo 213 at 5000m and the Allison is the most interesting disparity between published figures and actual performance, it's character is given at 12,000' but it was a completely different animal under 5000' which many are not aware of, I've talked to RAAF vets who rated it as highly as a Spit at that height.

    They're like personalities. A properly modelled graph using comprehensive data input would be filled with kinks and troughs for every aero engine type.
     
  10. Shortround6

    Shortround6 Well-Known Member

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    While a good part of what you say is true it does not affect things to extent you are saying.

    as an example let us take the Allison you mentioned. There is a very good reason it performed so well at 5000ft and it is reflected in the charts. The squadrons ignored the manufactures recommendations as to manifold pressures and ran the engines at what would become WEP settings later in the war. Look at the chart. there is plenty of extra supercharger capacity at 5000ft. The American chart was developed using AMERICAN 100 octane fuel which in 1939/40 did not have a rich mixture octane/performance number and did not act like British 100 octane fuel. Feed the engine 100/125 fuel in 1941/42 with it's high aeromatic content and you can use more manifold pressure before detonation occurs. Please notice that on the chart provided a manifold pressure of 50in (roughly 10lbs of boost) will give a theoretical 1400hp at that altitude. what do you think is going to happen with an extra 300hp+ at 5000ft?
    Remember what happened to the Merlin III when they went from 6lbs to 12lbs of boost? ZERO improvement at 16,000ft and above but several hundred HP at lower altitudes. Pretty much like such a chart would show.
     
  11. billswagger

    billswagger Member

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    #11 billswagger, Apr 3, 2010
    Last edited: Apr 3, 2010
    Overspeeding of the turbo was not a problem unless the pilot wasn't monitoring his inputs, but yeah, max RPM for the turbo was 22,000 and its reached in the low 20,000ft range.
    Correct me if i'm wrong, but didn't the D models have turbos with their own governing system that automated turbo inputs so all the pilot had to do was throw the lever forward and the turbo was on. The proper RPMs were governed by the technology in the plane. It actually may not have been introduced until the bubble top models, but i know that the B and C turbos had to be governed by the pilot.

    The R-2800 lent itself well to water injection, which when it came to boost pressures it was limited to the capacity of the turbo or supercharger ability to feed the engine the air. More on the R-2800 and WEP back ground,.
    http://enginehistory.org/Frank WalkerWeb1.pdf
    If you refer to page nine, it outlines the engines capacity to produce 150" in a test lab.

    Bill
     
  12. vanir

    vanir Banned

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    I know you're very knowledgeable and say only respectfully, in part my point would be that it is not reflected by projecting performance given at other heights, but by postulating different conditions which may not be available at given heights for various reasons and involve detailed modelling. Conditions that a simple extension of line graphs wouldn't encompass.

    The charts you're referring to are given the knowledge of its high low alt WEP tolerances, which is extra curricular information.

    Charting the Allison performance at low altitude by extending the graph from its performance at 12,000' doesn't give you its WEP tolerances (for the F-series motor) at 5000' which is the difference between ostensibly 1150hp and 1650hp. You'd never come up with the latter figure if you didn't know about the WEP potential of the motor under 5000' since about the most you can squeeze under WEP at throttle height is 1200hp. Any simplistic graphical extension would project this for maximum sea level performance.

    It is because what Allison Div called throttle height (12,000' for F-series) was for the military rating, which under European standards is the climb setting. The throttle height for WEP, which under European standards is take off and emergency, is actually closer to 5000'. And you'd never know this by simply extending charts unless the additional power setting for under 5000' was stipulated.

    If this disparity was not specifically mentioned in a given chart and only the military setting figures graphed, then you would need to model the engine itself using a comprehensive engineering software like Engine Analyzer Pro before you ever suspected it. How would you know otherwise, lucky guess?
     
  13. Shortround6

    Shortround6 Well-Known Member

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    I am sorry for the confusion, perhaps my choice of the phrase" reflected in the chart" wasn't the best. What I am trying to say is that the chart does offer an explanation as to why service squadrons were able to get more performance from their engines at lower altitudes than the 1040 at 14,000 would suggest. Since surplus supercharger capacity is available at lower altitudes and the chart does show pretty much just how much extra capacity is available at any given altitude (or how much less is available at higher altitudes) you can use the chart to predict performance of the engine SUBJECT to the strength of the engine, the detonation limits of the fuel it is being fed, and the ability of the engine to maintain cylinder and oil temperatures within limits. Now the last three, the actual limits of the engine, may only be determined by experience and test running. So the limit may very well be less than the chart show but it should never be more. It is known from squadron reports that a number of squadrons using the P-40s with the engine in question were using higher manifold pressures than were officially authorized by the factory. The chart will show about (if perhaps not EXACTLY) what level of power they could get at what altitude using a given amount of extra boost.


    You are quite right in this case, The Allison was not going to hold together (at least not for very long) trying to give 1650hp-1700hp at sea level which the chart says is theoretically possible.

    However the chart does show that 1400hp was possible at 5000ft without resorting to either overspeeding the engine or using a really ridiculous amount of manifold boost. It also doesn't require any strange or mysterious change in the airflow of the engine. Given the change in the fuel situation between when the engine was adopted by the US and when it went into service with the British and British commonwealth the extra performance available at 5000 ft or so is perfectly understandable. the 1400hp figure could be reached using about 5lbs (10 in) less boost than than 1650hp figure. Wither the 1400hp setting could be held for a full 5 minutes without exceeding the the cylinder or oil temperature limits might be another story, especially in the North African or Southern pacific heat. I don't know exactly what limits the squadrons were using but like I said to begin with, the chart does show how the extra performance at lower altitudes can be explained and also shows why there there was no extra performance to had at altitudes over 12-14,000ft. The supercharger simply wouldn't supply anymore air without over speeding the engine.
    I believe there is some confusion here. The Military rating for this engine was full throttle, 5 minutes only, This, I don't believe, under European standards is a climb setting. Many European countries used a 30 min setting for climb. The US, pre-war and in the early part of the war had take-off and military settings which were basically the same for most engines, a 5 minute rating. A few engines had a shorter time limit. The US very often had no 30 minute rating. The "rated" power of the engine was maximum continuous, in this case 930hp at 2600rpm at 12,000ft. using 33.7in manifold pressure. This power fell to about 840hp at sea level at the same rpm and manifold pressure because as the plane descended the throttle had to be closed to a smaller opening which raised pumping losses and the air got warmer which, especially after going through the supercharger reduced it's density. This line is shown on the chart. The full power ratings were established during the type testing and bench testing. the engine had to run at so many hours at full power (take-off/military) during the 150 hr type test with t he bulk of the time at max continuous . Later in the war when WEP ratings were established (or standardized) a test engine had to perform for 7 1/2 hrs at the WEP rating before this rating was authorized. What squadron commanders, pilots and mechanics may have done is something else:)
    The disparity (or WEP power level) has to fall somewhere in the chart and not outside of it. The Chart will tell you what manifold pressure (power level) is available at a given altitude using a certain rpm. The chart will not tell you if that combination is actually usable without blowing the engine up and I doubt that Engine Analyzer Pro will either.
     
  14. vanir

    vanir Banned

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    I fear we're becoming too complicated that succeeding point matter will cause a thread detraction.
    To simplify my initial point, the real world performance of an engine is not going to be reflected in a simple chart of the kind being discussed in the thread. It requires proper modelling.

    The difference between a comprehensively modelled performance graph by altitude and a simplistic chart of idealistic and ultimately unrealistic figures is more than dramatic, one has no relationship with the other, unless all you're doing is charting actual test results without projecting outside the immediate scope of those figures.

    This business of using a sliding scale to project aero engine performance is very loose measure even in the hands of manufacturer engineering departments. I'd cite the tremendous disparity between Focke Wulf graphed performance of the Jumo 213E compared to pilot reports (both in flight test and during service evaluation). There is more than 4000m worth of altitude performance which just plain didn't exist in the real aircraft, which is on the graphs marked by FW letterhead.
    There is a similar story with the 213A but it's not as dramatic and will again get complicated in discussion, plus there are more actual flight test data for the 190D.

    These manufacturer engineering departments did use a sliding scale for projecting performance, but it was based upon some crucial distinctions and even then as can be shown was at times in dramatic error. Firstly they designed and built the engine with spanners in hand, and having such intimate familiarity gives a reasonable amount of "instinctive estimation" for them when projecting the limitations and performance of that particular engine family. Secondly their projections are based on actual bench test performance data to which they apply this "instinctive" kind of performance modelling using engineering guidelines as a rule of thumb.

    You're talking about taking a third party chart and getting a ruler, then drawing a line on the graph and claiming a performance figure.
     
  15. vanir

    vanir Banned

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    apolegise, double post
     
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