Just saw this over on The Aerodrome forum. https://www.theaerodrome.com/forum/showthread.php?t=75670

IThe book is titled...
WW1 Aircraft Performance Design, Aerodynamics And Flight Performance For The Albatros D.Va, Fokker Dr.I, D.VIIF & D.VIII, Nieuport 28 C.1, Pfalz D.IIIa & D.VIII, SPAD S.XIII, Siemens Schukert D.IV, Sopwith Camel, Sopwith Triplane and S.E.5a.

By Anders F. Jonsson, LuLu Press, Photographs, Charts and Diagrams. Pp.330 pages, ISBN: 97891987748

https://www.theaerodrome.com/forum/showthread.php?t=75670

Very favourable writeup by CjB. I've ordered my copy.

Jonsson, Anders F. WWI aircraft performance: design, aerodynamics and flight performance for the Albatros D.Va, Fokker Dr.I, D.VIIF & D.VIII, Nieuport 28 C.1, Pfalz D.IIIa & D.VIII, SPAD S.XIII, Siemens Schukert D.IV, Sopwith Camel, Sopwith Triplane and S.E.5a. Lulu Press, 2023.

This is a book that some of us have been waiting for! It is probably the first and certainly the most serious quantitative analysis to go beyond the available anecdotal evidence of how some mid- to late-war WWI scouts performed in combat, to 'crunch the numbers' in a C++ model that can provide comparative data that could be incorporated into modern combat flight simulations. The author is active in the 'Rise of Flight' and 'Flying Circus' community under the handle of 'Holtzauge', has an academic and engineering background in the design of mathematical simulations for modern jet combat aircraft (SAAB) and WWII combat aircraft, and certainly appears to know his stuff when it comes to aeronautics and flight modelling (although I will throw my hands up at this point and say that I am no expert in this area, and this important aspect of the book will have to be reviewed by someone else). This book, although it is published first, appears to be the 'little brother' of a similar, though probably larger, book on WWII combat aircraft performance that has yet to be completed or published, and follows on from a couple of papers published online by Anders Jonsson, which are available in full from his website here: https://militaryaircraftperformance.com/documents-1/

This review will concentrate mostly on the engines aspect of his book, as I am not competent to comment on the aerodynamics or the mathematic modelling (which are at the heart of the book), so it can only be a partial review, although I can say that he explains everything very clearly and concisely, so that even a layman can get a basic grasp of this. The book is very well produced in hardback format, well structured and accompanied by both B&W and colour images and easily read diagrams. The first section of the book, after a brief historical introduction into the state of aerodynamic knowledge at the time of the war, looks at general aspects of structure, drag, thrust and lift with further sections on engines, cooling and armament. This is then followed by individual sections dealing in turn with the scouts listed in the subtitle of the book, with a little detail on those parameters and data used to create each C++ model and a reference set of selected historical data (mostly taken from contemporary test flights) which is not used to build the model but is used instead for 'fine tuning' and comparison. The final section of the book takes these C++ models and applies them to a comparative analysis of 'key performance indicators' for ceiling, climb, turn, energy retention and spiral dive, speed, acceleration, dive, handling and structural strength. As you can see, it is a comprehensive attempt to model all the performance parameters that could be fed into a combat flight simulations. This is indeed explicitly presented as one of the aims of the book.

How well does it achieve this? This is a difficult question to answer - in large part as I have, unlike the author, no background in aerodynamics, so a large part of the book is something of a mystery to me and I have to take the author on trust and assume that he has got it right on these most important points. The outcome data from his C++ models certainly appear to provide a close match to the historical reference data that he selects, although it is impossible to know how much the input data has been refined so that the model then matches the reference data that is selected. I think the answer is, looking at some of the small anomalies between the two, that there has been little 'tweaking' of this kind, and I get the impression that the author has been very careful to avoid as best as he can the trap of 'garbage in, garbage out'. The author himself is at pains throughout the book to emphasis that the available reference data for WWI, unlike that for WWII, is sparse and often contradictory, and it is clear that he has done his utmost to find the most detailed and reliable data that is available. Perhaps for this reason he has not relied on these contradictory historical numbers, or the anecdotes of the time, but has gone back to aerodynamic basics and built his models from data on wing area, weight, loading, flat plate drag,sea level power, & etc. and, so far as I can tell, has done a very good job of it. The only area in which I can comment is in power, and I think there are a few anomalies, perhaps some minor misundarstandings, and sometimes some strange choices here. None of this, however, detracts in any significant way from the outcomes (except, perhaps in the low altitude performance for some of the aircraft, which is not dwelt on to any significant extent by the author).

It is evident from just the subtitle that the author is interested only in the performance of single-seat scouts, not in two-seaters, and the book covers a limited selection of mid to late war scouts. Some of the choices are a little strange (to me) and I think reflect the interests and enthusiasm of the author rather than presenting a more balanced selection of early war, through to mid war and then to late war examples - although there is, I think, a good balance between Entente and German scouts. The author is also at pains to point out that this just a quantitative model of aircraft performance, and takes no account of 'human' elements when it comes to aircraft performance and engine management, and clearly recognises and accepts that this is a limitation. How can you, for example, provide a 'real' comparison of the dive performance of any of these aircraft without taking into account the extent to which the individual pilots will be more or less 'risk averse' when it come to pushing the aircraft beyond it's known (or unknown) 'safe' limits in combat? The author accepts this limitation, pointing out that he can only present the data on the potential performance of the aircraft, as a 'tool of the trade', but it is then up to the competence and experience of the pilot to use this to best advantage. This does result in some curious choices, however, which are not always entirely consistent: the choice, for example, to base the performance of the Fokker D.VIIF on the 'emergency power' of the engine available, to some extent, at low altitude resulting in the decision to give the BMW IIIa engine an output of 209 hp up to a Full Throttle Height of 1,700 m instead of the 185 Ps prescribed by the engine manual to a FTH of around 3500 m. The author has acknowledged that the choice of output was a dilemma, that in his opinion 185 hp up to the 3500 m FTH would be too conservative, whilst the even higher figure of 234 hp from SL up that is advanced by some others is too optimistic, and that 209 hp has been arrived at as a figure based on those that he has seen in contemporary historical sources and was achievable. I think that this choice may also have been made because the model, based on more modern engines, does a good job for the Allied engines, all of which are 'conventionally' altitude compensating, but cannot easily accomodate the peculiar features of either the BMW or some of the other German engines - and the output chosen is the one that will give the correct output with which to calculate the most important mid- to high altitude performance of the aircraft. In the context of the book, I think this does not matter - as the emphasis is, correctly I think for most of the aircraft selected, on the mid- to high altitude combat environment. It does mean, however, that if the same model were to be used to simulate low altitude performance of this aircraft (and probably the Siemens Schukert D.IV as well) it would endow these aircraft with low-level superpowers that they did not have (or did not have as more than a 'war emergency power' for a few minutes only). To be fair, this is a dilemma that has also faced the developers of all WWI combat flight simulators, all of which have in varying degrees only partially or not at all been able to resolve this. After reading the book I also asked the author if his C++ model takes into account the lack of manual mixture control for some of the aircraft modelled in the book - the most obvious being the Albatros D.Va and Pflaz D.IIIa, which were both powered by a Mercedes D.IIIa engine that had no manual mixture control - and if it took into account the extent to which most German engines of the period started with a lean rather than the conventional stoichiometric air fuel mixture at ground level (severley so, in the case of the D.VIIF with the BMW engine, less severley but still, I think, significantly so in the case of the Albatros and the Pfalz D.IIIa). He said that the C++ model does not model the actual fuel/air mix, but only power with altitude, the numbers in the simulation corresponding to a properly managed engine. This means that in every case the power will simply drop in proportion to altitude (from sea level in the case of most engines, from the the Full Throttle Height in the case of the overcompressed German engines). Again, the effect of this on the model is going to be minimal in most cases, as the main emphasis is on mid- to high altitude performance. But it might explain why the models for the Albatros D.Va and Pflaz D.IIIa predict a slightly lower service ceiling and slightly poorer climb at mid- to higher altitudes than the historical reference data would suggest.

Those minor and rather abstruse 'niggles' aside I highly recommend this book to anyone with more than a passing interest in the combat performance capabilities of WWI mid- to late war single-seat scouts! And, of course, to any developers of WWI combat simulations.

Disclaimer: although I supplied Anders Jonsson with some of the historical sources that he used to produce some of the data and references for the book, and I am acknowledged as a source, I had no other input into the writing of the book and recieve nothing from the sales (although Anders did very kindly send me a complimentary copy, upon which this review is based).

Although I don't think the book is available yet from Amazon or other booksellers, it is now available for purchase online via the author's website (see link above at the end of the first paragraph).

I do hope you will enjoy reading the book PipsPriller and do not hesitate to contact me if you have any questions about the book or its contents!

And Bletchley, thanks for the review! To answer some of the questions you bring up and beginning with the choice of power both for the Entente and German aircraft: I’m not sure I would describe it as I have selected “war emergency power” for the Germans scouts since I have not assumed that the German engines are being run at higher “WEP” rpm. E.g. for the BMW IIIa, the simulation assumes that the engine is run at 1400 rpm and not 1600 rpm which would then have yielded even better performance for the Fokker D.VIIF. However, what does of course complicate matters was that I had to select a power level for the German aircraft with over-compressed engines without automated altitude compensation like on the Mercedes D.IIIaü. Again, in the book I refer to trial and test data for aircraft powered by both the Siemens Halske Sh.IIIa and BMW IIIa engines, and the power levels I have selected for these engines in the simulations gives speed and climb times that tab quite well with the results from the flight trials I have referenced. But I am of course open to new data and if you consider that other data would be more representative for these aircraft.

Regarding the point about mixture control not being modeled in the simulation and that this poses a problem, I’m not sure I understand the issue? True, I do not model the inner workings of the engine, but I do not see that I need too? Instead the way my simulation works is to model the engine’s power output with altitude and this will of course vary if there is a mixture control, and if this is set properly or improperly by the pilot. On the other hand, if there is no way for the pilot to control the mixture at all, then the power output will of course be according to whatever setting is used. However, all this must in the end result in the engine giving a certain power level at a certain altitude just as I have modeled, and the crux as I see it is to model the power variation with altitude correctly. Connected to this then is then the point you brought up about the ceiling and climb rate for the Albatros D.Va and Pfalz D.IIIa, and that in your opinion my estimates are lower “than the historical reference data would suggest”? I am not sure which data you are thinking about here? I list references to the historical data I base my C++ models on, and as far as I know these are the best available, but as I say in the book, if new data surfaces I may revise those numbers. What are the higher historical ceiling and climb rate values you are thinking about and what are the sources?

Hi Holtzauge,

It is quite likely that I am misunderstanding something. If so, I apologise

With respect to the Albatros D.Va and Pfalz D.IIIa, it appeared on first reading that the historical reference data set in both cases is for aircraft powered by a Mercedes D.III, and in your model you use the power output of a Mercedes D.IIIa. But on second reading I am not sure, it is not clear! Maybe I am just confused!

In the case of the D.VIIF my understanding is that the BMW produced 185 Ps (or thereabouts) with the main throttle fully open at ground level. That is why it is rated at 185 Ps. But it was 'leaned down' to that power output by the carburettor from a higher 'nominal' figure only achieved if the mixture had been stoichiometric and not very lean at around 20:1 (when the British tested the engine they used a 'blower' to get around the leaning imposed by the carburettor, to find this otherwise nominal output, which is why they gave it a higher rating).This 185 Ps was maintained up to c. 2000 m without any need to adjust either the main throttle or open the high altitude throttle. If the high altitude throttle was opened below 2000 m then the engine would produce more than 185 Ps, but as this throttle was advanced the mixture became weaker still, as the side chambers of the carburettor pulled in more fuel but in a weaker mixture thus increasing the likelihood of both detonation and pre-ignition. Benzol in the fuel could suppress the detonation, but not the pre-ignition (in fact it made it more likely, as benzene is one of the least pre-ignition resistant of the hydrocarbons). So opening the high altitude throttle at low altitude was always going to be a gamble - more power for a short period of time, but also more chance of the engine being badly damaged, which is why I would describe it as a kind of War Emergency Power. It is not meant to be done other than in rather exceptional circumstances, and even then 'for a few minutes only'. In normal use the power would be maintained at a steady 185 Ps on the main throttle alone below c. 2000 m, then gradually opening the altitude throttle above c. 2000 m to maintain that 185 Ps up to around c. 3500 to 4000 m. At some point after this Full Throttle Height was reached, opening the altitude throttle further would not draw in any more fuel, as the fuel jets will be delivering fuel at full capacity - just air, to prevent the air fuel mixture from becoming too rich (very much like the Mercedes D.IIIaü carburettor at that point).

This is all explored in much more detail in my posts, and the discussion that followed, on German altitude compensating carburettors at The Aerodrome: https://www.theaerodrome.com/forum/showthread.php?t=75618

In the end it makes no difference at the medium to high altitudes that you focus on in your book, as it is all smoothed out at those altitudes, but again, if I have misunderstood something, then I apologise!

As I have said, I think it is an excellent book, and I highly recommend it! .

B.

Hi Bletchley,

No need to apologize, and maybe I instead should be apologizing for not being more clear in the book! You are quite right about there being two data sets for the aircraft in the book, the Albatros included:

One is in the chapter where I describe the aircraft models and how those have been tuned. The second data set is in the chapters where the actual performance data is presented in charts. And you are quite right that the tuning of the Albatros model has been done with an earlier D.III engine: The data which seems most reliable was from a French STAe test of a captured specimen but which was tested with a lower weight than standard (no ammunition for obvious reasons!). So when I did the tuning of the C++ model, I use this lower weight in combination with the lower assumed power for the D.III engine to derive aircraft fixed parameters like Cdo etc.

Then when I was satisfied with the model, I entered the typical T/O weight with armament and used a power more consistent with a D.IIIa engine instead and it is those numbers that are behind the values in the charts. So if you meant that it was the Albatros performance numbers that was in the tuning data that was lower than historical values, then I understand and of course agree with that but for a typical standard aircraft with the D.IIIa engine, those numbers are to be found in the charts.

About the use of WEP I now see your point and I agree: I was thinking more in terms of rpm when considering if WEP was used or not and for the BMW I was connecting this to 1600 rpm and not 1400. But I can see your point about the “pilot” in the simulations not following the BMW user manual recommendation of only using around 185 hp from SL up to the FTH and that this could also be construed to be using WEP. Since I have assumed that they are engaging “Höhengas” earlier and taking more out of the engine, this is a valid point. However, the reason I have done so was that it looked to me like the pilot could get away with squeezing a bit more power out of the engine without detonation as per the NACA data, and secondly, the only way to reconcile the climb times the Germans in the Fokker D.VIIF (Udet included) seems to have been able to reach 6000 m in (I mention this in the book), was to assume a bit more power than 185 hp in the early stages of the climb. So this was why I assumed 209 hp at SL which I agree in some sense can be seen as WEP being applied if we look at the BMW user manual.

Regarding the thread on The Aerodrome forum you linked where you analyse German altitude compensating carburetors, I have read that and it’s a good read and very informative! I fact, I am now looking into the Albatros D.Va equipped with the over-compressed Mercedes D.IIIaü engine, and I have some ideas about that that I would like to share with you but that is off topic here and I will do that via mail instead!

Finally, I would like to say that I recently acquired WoFF (I only had RoF and Il-2 Sturmovik FC before), and while all simulators have their strong and weak points, I really like the environment in WoFF and especially the single player campaign mode. And the scenery is really top notch! Flying a really immersive S.E.5a campaign right now!