Hispano-Suiza V8 aero engines

[YavorD]

In this and in the following posts on this thread I will try to put some order in my notes on Hispano-Suiza V8 aero engines and on some aircraft powered with such engines. The focus is going to be engine performance and aircraft performance in my own current best estimate models in comparison with available historical records from various sources.

150 hp Hispano-Suiza V8 aero engine

The first Hispano-Suiza aero engine produced in considerable numbers from 1916 and on is known as Hispano-Suiza type 34, HS 8 Aa, or 150 hp Hispano-Suiza.

Thanks to Paolo Miana, I got an access to an engine maintenance and operation manual published by one of the companies producing the engine under license, Chaléassière St-Etienne Leflaive & Cie. The following figure is an extract from the same manual.



Planche VII Courbes de puissance

Another primary source to be considered comes from the Engine Department of the Royal Aircraft Establishment (formerly Royal Aircraft Factory). The original test report is dated August 8, 1916. The power curve is reproduced as Figure 10 in the Aeronautical Research Committee Reports & Memoranda No. 586, dated July 1921 (thanks to Hugh Baldwin), as shown below.



150 hp Hispano-Suiza engine power curve

Hardly a surprise, there was a considerable interest in Germany concerning the design and performance of the Hispano-Suiza engines. The following picture is an extract from a German test report on captured engines [a lecture presented by Diplom-Ingenieur Otto Schwager, Versammlung der Wissenschaftlicvhen Gesellshaft für Flugtechnik in Hamburg am 19. April 1918. Technische Berichte von der Fluzgeugmeisterei der Inspection der Fliegertruppen, Band III / Heft 5, S. 135].



Abb.4 Bremsergebnisse ... Schwager TB III Heft 5

Yet another, earlier version of the same test data is published by Ingenieur S. Hoffmann, Der "Hispano-Suiza"-Flugmotor, Zeitschrift für Flugtechnik und Motorluftschiffahrt, Heft 3 u. 4, IX. Jahrgang, 23. Februar 1918, S. 27.



Hoffmann - ZFM IX 3&4 27 Fig. 5

[YavorD]

There are many other sources, of course, and some are going to receive more attention later on, in the discussion of the engine altitude performance.

Now, let take a look at the data from various sources presented in one and the same scale, as follows.



150 hp Hispano-Suiza engine data comparison

First of all, let mention German data sets from the previous post (1). German data are placed somewhat below the factory data, particularly at high revolutions. Is it due to engine wear, due to inferior fuel or lubricant quality, or there is another reason? We do not know. The difference, however, is not too large.

An intriguing observation is the shape of the British curves. R.A.E. data from August 1916 show slightly less maximum power at 2000 revolutions per minute, but higher power and maximum torque at 1200 to 1400 revolutions per minute. There should be something about engine induction system or mechanical efficiency (friction loss). Again, we do not know the full answer, but the difference is not too large. In terms of aircraft performance, the British data set can give slightly more power for climb and slightly less maximum level speed.

To be continued.

[AndersJ]

Interesting stuff Yavor, and I look forward to seeing more. Regarding variations in measured engine performance, I fear this is a problem that's very difficult to get around: I find exactly the same problem when trying to reverse engineer aerodynamic data like flat plate drag area from flight tests: You never know if the data you have is from a "lemon" or a top quartile performer. We would need some statistics for that and it's not like there are droves of WW1 flight tests data laying around are there?

That being said, the type of analysis you're doing in this thread is what keeps the science going forward so please keep it coming!

[YavorD]

Originally Posted by AndersJ

Interesting stuff Yavor, and I look forward to seeing more. Regarding variations in measured engine performance, I fear this is a problem that's very difficult to get around: I find exactly the same problem when trying to reverse engineer aerodynamic data like flat plate drag area from flight tests: You never know if the data you have is from a "lemon" or a top quartile performer. We would need some statistics for that and it's not like there are droves of WW1 flight tests data laying around are there?

That being said, the type of analysis you're doing in this thread is what keeps the science going forward so please keep it coming!

Thank you, Anders! Actually there are some data from neglected sources coming out recently thanks to Colin Owers and other authors.

Best regards,
Yavor

[HoHun]

Hi Yavor,

Originally Posted by YavorD

Now, let take a look at the data from various sources presented in one and the same scale, as follows.

Highly interesting, thanks a lot! :-)

It seems the nominal power mentioned in the engine designation isn't really reflected in the power graphs, considering that the "180 HP" engine shows higher power throughout than the "200 HP" and the "220 HP" engine?

With regard to the German tests, it's worth noting that they show three different compression ratios (apparently omitting the figure for on of the four engines shown in the graph) - 4.02, 4.6 and 4.9, with the low compression engine showing the highest power, but also the lowest (tested) rpm limit.

Regards,

Henning (HoHun)

[YavorD]

Originally Posted by HoHun

Hi Yavor,
...

It seems the nominal power mentioned in the engine designation isn't really reflected in the power graphs, considering that the "180 HP" engine shows higher power throughout than the "200 HP" and the "220 HP" engine?

With regard to the German tests, it's worth noting that they show three different compression ratios (apparently omitting the figure for on of the four engines shown in the graph) - 4.02, 4.6 and 4.9, with the low compression engine showing the highest power, but also the lowest (tested) rpm limit.
...
Henning (HoHun)

Hi Henning!

Concerning the power rating, it may be a good idea to post the figures from the Leflaive & Cie manual.

HS 8 Aa ... 150 hp @ 1450 rpm (Courbe I)
HS 8 Ab ... 180 hp @ 1540 rpm (Courbe II)
HS 8 Bb ... 200 hp @ 1870 rpm (Courbe III)
HS 8 Bc ... 220 hp @ 1970 rpm (Courbe IV)

One must keep in mind the timeframe.

• HS 8 A (Aa) first generation, low compression, conservative rating "1600 rpm for a few minute4s only"
• HS 8 B (Bb) first generation, low compression, geared, conservative rating "1800 rpm for a few minutes only"
• HS 8 Bc second generation, increased compression, geared, "revolutions not to exceed 2100 rpm"
• HS 8 Ab second generation, increased compression, revolutions limited by the propeller advance ratio, but during 1918 going well above 2000.

Also, the high compression engine without gearbox can easily produce a few percent more power than geared version, later rated at 235 hp @ 2150 rpm. This topic will be discussed later concerning HS 8 Ab, Wright E and Wolseley Viper performance.

"4.02" is just a reproduction error, is should be "4.92" (see Hoffmann figure), compare with 4.7 compression ratio stated by Hispano-Suiza.

Best regards,
Yavor

[YavorD]

After looking at power curves in posted above (posts 1 and 2), it is necessary to look for performance data at altitude.

There are very few altitude performance data for aero engines before 1917. The best source known to me for the 150 hp Hispano-Suiza aero engine is the "Air Board Engine Data Chart" revision from August 1917. The document notes slight difference between "Hispano-Suiza (French)" and "Hispano-Suiza (Wolseley)". Both engines are rated at 150 hp at 1600 rpm, maximum 1800 rpm. The Wolseley version [Python] is listed as 455 lb dry [+15 lbs] and 556.4 lbs in running order [+18.9 lbs]. Estimated B.H.P. at 6000 / 10000 / 15000 / 20000 feet are listed as follows.

Hispano-Suiza (French) ...... 129 @ 6000 / 114.1 @ 10000 / 97.5 @ 15000 / 83.8 @ 20000.
Hispano-Suiza (Wolseley) ... 129 @ 6000 / 114 @ 10000 / 97.5 @ 15000 / 83.5 @ 20000.

There is no clear statement about the method used. However, there is an evidence in the Air Board documents and the Advisory Committee for Aeronautics documents of 1917 about the method used.

Looking at the "Technical Report of the Advisory Committee for Aeronautics for the Year 1917-18, Volume II. Airscrews and Full Scale Work on Aeroplanes, Reports and Memoranda, No. 324. March, 1917", page 590, one can read.

The density at any point can be determined immediately barometer and thermometer readings are taken, and the Meteorological Office has supplied the results of a long series of observations of temperature and pressure up to a maximum height of 20,000 feet. This has led to the construction of a standard density curve, the standard density at a given height being the mean value of ρ calculated from a series of observations at that height.*

* This standard is now in use at the Testing Squadron R.F.C. Martlesham, and also, it is believed, in the R.N.A.S.

Few pages through the same volume, Reports and Memoranda 474, Figs. 4 and 4a.





The following graph is an Air Board commissioned version of the function plotted on Fig. 4 above with a reference to one Harry Ralph Ricardo, an engineer.

[AndersJ]

Originally Posted by YavorD

After looking at power curves in posted above (posts 1 and 2), it is necessary to look for performance data at altitude.

There are very few altitude performance data for aero engines before 1917. The best source known to me for the 150 hp Hispano-Suiza aero engine is the "Air Board Engine Data Chart" revision from August 1917. The document notes slight difference between "Hispano-Suiza (French)" and "Hispano-Suiza (Wolseley)". Both engines are rated at 150 hp at 1600 rpm, maximum 1800 rpm. The Wolseley version [Python] is listed as 455 lb dry [+15 lbs] and 556.4 lbs in running order [+18.9 lbs]. Estimated B.H.P. at 6000 / 10000 / 15000 / 20000 feet are listed as follows.



There is no clear statement about the method used. However, there is an evidence in the Air Board documents and the Advisory Committee for Aeronautics documents of 1917 about the method used.

Looking at the "Technical Report of the Advisory Committee for Aeronautics for the Year 1917-18, Volume II. Airscrews and Full Scale Work on Aeroplanes, Reports and Memoranda, No. 324. March, 1917", page 590, one can read.



Few pages through the same volume, Reports and Memoranda 474, Figs. 4 and 4a.





The following graph is an Air Board commissioned version of the function plotted on Fig. 4 above with a reference to one Harry Ralph Ricardo, an engineer.

Thanks Yavor, this is very good data indeed. Especially for those cases one only has data for one altitude (usually the rated power at SL) and has to make estimates for the rest.

Some other things that would be interesting to see, is first of all if there are systematic differences between rotaries and more conventional engines, and secondly, how do Central and Entente engines compare on this point?

However, that question is of course a bit off topic seeing the title of this thread, but it is anyway something that I've always wondered about. But that maybe will become clearer later on, if you plan to do similar threads for other engines later on (which of course would be just as interesting as this thread.

Best wishes,

Anders

[YavorD]

Originally Posted by AndersJ

...
Some other things that would be interesting to see, is first of all if there are systematic differences between rotaries and more conventional engines, and secondly, how do Central and Entente engines compare on this point?

However, that question is of course a bit off topic seeing the title of this thread, but it is anyway something that I've always wondered about. But that maybe will become clearer later on, if you plan to do similar threads for other engines later on (which of course would be just as interesting as this thread.

Best wishes,

Anders

Hi, Anders!

The question is not much off topic because one need to compare successive modifications of the engine chosen for this thread, too.

Generally, as stated by Victor Gage, altitude performance of the engine, if not restricted by the induction manifold and carburettor, depends strongly from mechanical efficiency (friction loss). While most of the loss is proportional to the density of the charge, so much that decrease with altitude in a proportion similar to the power output, a part of friction loss remain almost constant from ground to ceiling. This part is a function of speed of rotation (average piston speed), number and size of cylinders and bearings, but does not change with air density, as much as oil temperature remains within certain limits. The significance of this part is increasing with altitude and is the most important factor limiting the output of normally-aspirated engine with altitude.

Just to mention, a spur gear reduction of the propeller shaft speed can almost double the friction loss of the whole engine, which is the case with HS 8 B geared engines.

For the rotary engines, windage loss is present but it is proportional to the air density and speed of rotation (power two). Limiting factor for rotary engine altitude performance is the relatively long stroke, lower compression ratio and the total loss lubrication.

German engines were usually running at lower engine shaft speed (with a notable exception of Siemens & Halske) but about the same average piston speed. One result is somewhat less power per unit of swept volume or per unit of weight. Increase of engine speed and compression ratio is a function of materials, production tolerances, and quality of fuel and lubricants. All this became a problem after about 1916 while the need for mechanical power in all forms was increasing exponentially and the theory of the internal combustion engine was ready to provide answers but at a high cost in man power, production capacity and precious resources.

It was not much different about 25 years later, by the way.

Best regards,
Yavor

[AndersJ]

Originally Posted by YavorD

Hi, Anders!

The question is not much off topic because one need to compare successive modifications of the engine chosen for this thread, too.

Generally, as stated by Victor Gage, altitude performance of the engine, if not restricted by the induction manifold and carburettor, depends strongly from mechanical efficiency (friction loss). While most of the loss is proportional to the density of the charge, so much that decrease with altitude in a proportion similar to the power output, a part of friction loss remain almost constant from ground to ceiling. This part is a function of speed of rotation (average piston speed), number and size of cylinders and bearings, but does not change with air density, as much as oil temperature remains within certain limits. The significance of this part is increasing with altitude and is the most important factor limiting the output of normally-aspirated engine with altitude.

Just to mention, a spur gear reduction of the propeller shaft speed can almost double the friction loss of the whole engine, which is the case with HS 8 B geared engines.

For the rotary engines, windage loss is present but it is proportional to the air density and speed of rotation (power two). Limiting factor for rotary engine altitude performance is the relatively long stroke, lower compression ratio and the total loss lubrication.

German engines were usually running at lower engine shaft speed (with a notable exception of Siemens & Halske) but about the same average piston speed. One result is somewhat less power per unit of swept volume or per unit of weight. Increase of engine speed and compression ratio is a function of materials, production tolerances, and quality of fuel and lubricants. All this became a problem after about 1916 while the need for mechanical power in all forms was increasing exponentially and the theory of the internal combustion engine was ready to provide answers but at a high cost in man power, production capacity and precious resources.

It was not much different about 25 years later, by the way.

Best regards,
Yavor

Hi Yavor!

Interesting info about the friction losses being so high on the HS 8 B engines. I didn’t know about that. I have of course heard about the reliability problems of early propeller reduction gear systems. But I always put that down to quality control issues such as poor tolerances, or that the tempering or surface treatment of the cogs was off somehow, given that reduction gearing is not exactly rocket science and should have been a pretty mature technology even back then.

AFAIK typical losses in a reduction gear unit should be in the order of 1-2% of the power, so while certainly resulting in some heat that needs to be cooled off, this should be quite manageable compared to the roughly 70% that needs to be cooled off due to combustion. So a doubling of friction losses on the HS 8 B sounds high.

I would expect the old gearing to be quite noisy though, since they probably used straight gears. I was fortunate enough to be present one time when Mikael Carlson fired up his Siemens Halske on his Pfalz D.VIII, and you could clearly hear all the gearing in that engine “sing” on top of the exhaust noise. In addition, IIRC then he said that the bevel gearing connected to the counter rotation was worn out even after just a few hours running. And since he does not overexert his engine and uses best quality castor oil, my bet is that it had to do with the quality of the gearing, and probably not much he could have done anything about.

Best wishes,

Anders