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 Post subject: Engine power by date
PostPosted: Wed Jul 20, 2016 5:17 am 
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I posted this in the Med-Light thread but thought it might be better here.

The first shows how specific power (power/displacement) was affected as a function of time- some engines you will see as a vertical stack where I do not have dates for the first flights or test runs of later derivatives of that engine.

The second shows how available power for fighter a/c developed over time, the major inflection point comes in '43-'45 as jet turbines took over from piston engines. NB for propeller-driven a/c, 1HP gives fairly close to 1lbf thrust from the prop, so I have assumed that this scales alongside jet turbines. I know it doesn't, I'm not allowing for constant-speed or multi-pitch vs fixed pitch props here but at the engine powers that fixed pitch props operated with, it's not really relevant.

The step up in the trend lines for late war onwards represents around 2000lbf equivalent, so moving from piston to jet had the net effect of almost doubling engine power.

The screaming obvious outlier bottom right of the second chart is the EJ200, very low power output considering its contemporaries.

What I find interesting is in the early piston engines (top chart), the Hispano-Suiza 8 of the SE5a and the Rolls-Royce Falcon III of the Bristol F2b have significantly higher specific power than their German contemporaries, around 35% more. That lends more weight to Stuart's initial conclusions about German scouts having powerful but big/ inefficient engines in comparison to their Allied counterparts for comparison here, the BMW IIIa produced 185hp from 1164 cu in, the Mercedes D.III 160hp from 903 cu in. H-S 8b produced 200hp from 718 cu in and the Falcon III 275hp from 867 cu in).


Attachments:
F piston engines sp power vs date.png
F piston engines sp power vs date.png [ 107.56 KiB | Viewed 505 times ]
F piston and jet engines-1.png
F piston and jet engines-1.png [ 86.09 KiB | Viewed 505 times ]

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 Post subject: Re: Engine power by date
PostPosted: Wed Jul 20, 2016 7:59 am 
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Thank you Craig, the data here is extremely interesting. One thing that explains a lot is that the German WW2 engines rate fairly poorly towards the end of the war. That explains the lack-luster rating of their aircraft. One factor here is fuel; by the end of the war, the Allies were running on 130/150 octane fuel while the Germans and Japanese were running on 87 with 100 being a special item. That makes a huge difference. The Russians were running on 87 octane as well. It's an interesting thought that if the USAAF had been on the Russian Front, they'd have brought their high-octane fuel with them and the Russians would have started using it as well (remember in this scenario, no fuel deliveries to the UK). So, Russian aircraft performance would have improved significantly.

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 Post subject: Re: Engine power by date
PostPosted: Wed Jul 20, 2016 8:04 am 
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No problem, that second chart is now having a tweaked version due in a few minutos. What I'd also like to do if I ever find the time is to plot power vs time within engine series, somewhere from my aviation days I have a lot of data on the R-1830 and R-2800 power ratings for different subset models and fuels and I recall that there were service bulletins issued within the manuals addenda that showed various hundreds of HP were being added every month or two as either fuel or design was improved.

Edit- and here it is. Split jet era into early (<10k lbf), mid (10-20k) and late (>20k). Interesting how the Spey and Avon have almost the same power output but a significant period of development between them, I presume this shows the development potential of the Spey and that the Avon was reaching its limits.


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F piston and jet engines-2.png
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 Post subject: Re: Engine power by date
PostPosted: Wed Jul 20, 2016 9:42 am 
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This shows the specific power development during the engine's lifetime. For the date I have taken the first test run or test flight of the original model of each engine.

interesting the limited development potential of German aero engines in comparison to their competition. I've not added any of the lovely Bristol radials yet, not had the time.


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F piston engines sp power vs date-1.png
F piston engines sp power vs date-1.png [ 39.76 KiB | Viewed 487 times ]

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 Post subject: Re: Engine power by date
PostPosted: Thu Jul 21, 2016 10:10 am 
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This shows the development potential of the Rolls-Royce Merlin, beginning as its Private Venture start and ending up as the slimline installation in the Hornet. I have plotted the petrol octane rating and max allowable boost too, something often overlooked. E.g. german superchargers often ran at 28-30psi boost, even by war's end for the Merlin to obtain >2000hp we were running at 22, and actually derated back to 18psi post-VJ Day.


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Merlin power v time.png
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 Post subject: Re: Engine power by date
PostPosted: Thu Jul 21, 2016 4:20 pm 
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Fascinating stuff!

I wonder what a "Merlin vs Griffon" chart might look like?

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 Post subject: Re: Engine power by date
PostPosted: Fri Jul 22, 2016 6:58 am 
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That's next on my list of things to do. The Griffon was derived from the Type R and a substantially bigger engine than the Merlin. As always there are a great many "soft stats" not shown in any of these figures which go even further into explaining things; Stuart has touched on petrol (I had cause to delve into the guts of a DB601 once (their 83/87 octane fuel was really horrid stuff, it didn't like aluminium or magnesium castings at all) and the condition of it was awful in comparison to the P&Ws, Rolls-Royce, Bristol, Alvis and various de Havilland lumps of the same era I was used to. So, things like Time Between Overhaul for the German engines I'm suspecting at something like 10-15hrs running time, Merlins/ V1650s had a minor inspection at something like 65hrs and total rebuild at about 120. P&W radials about 10% greater than that. Fast forward 10 years and the T56/ 501D jet turbines had TBO periods of 600 hours, one of the many hidden strengths of axial flow turbines when properly designed.

What it does show here is the potential incremental improvements that were available in some engines. I don't have data on the V-1710 but have some reason to believe that it had broadly similar potential to the Merlin/ V-1650.

The R-1830 was always a ereally low-stressed/ low BMEP engine so power output was never stellar for its size and displacement; the R-2800 was designed with many of the results of the 1830 already built in so started life at a higher output than would "normally" have been the case.

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 Post subject: Re: Engine power by date
PostPosted: Fri Jul 22, 2016 7:20 am 
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The Bushranger wrote:
Fascinating stuff!

I wonder what a "Merlin vs Griffon" chart might look like?


Your wish is my command.

The skewy bits on the Merlin line are where different marks for different applications came out- bombers or specialized low-altitude fighters for instance, max TO power might be lower but max power upto 10-12k would be maintained. "Clipped and cropped" for example.

Some Griffons ended up putting out over 3000hp with water/ methanol injection.


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Sir Humphrey Appleby: Bernard, Ministers should never know more than they need to. Then they can't tell anyone. Like secret agents, they could be captured, tortured.
Bernard Woolley: You mean by terrorists?
Sir Humphrey Appleby: By the BBC, Bernard.
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