mercredi 11 avril 2012

The Dewoitine D.520 - Politics and proficiency in complete opposition (Enriched 26 / 11 / 2016)



Any human community having suffered an as great defeat as France experienced in 1940 must analyze thoroughly the reasons which had induced the actual situation. 

This lesson may be shared everywhere.


The example of the fighter Dewoitine D 520 outset seems a very good starting point for the understanding of the fantastic level of incompetence of the technical and the political deciders. 

Among the competences needed to be a politician decider, two are of paramount importance: Detecting the persons who have a true knowledge (independently from any lobbies) and detecting the exact time for action (to avoid the very frequent comment: too late). 

The deciders belonging to the last years of the French IIIème République seemed completely devoid of such competences. 


The Dewoitine 520-02, already a very good fighter


(The data used here have been published in the absolute reference book on this fighter: Le Dewoitine D.520, R. Danel et J. Cuny, Docavia N°4, ed. Larivière.)


The Dewoitine 520 fighter was one of the best fighters of her time. 

Both French politicians and administrative deciders have delayed her appearance on the field during more than 20 months since the end of 1936. 

So, she never reached the maturity achieved by fighters produced by other countries.


The last part of the delay (9 months) was related to the time needed to chose of her engines and of various other devices to be fitted on.


The first official data about the second prototype (D 520-02) were given in a report transmitted by the CEMA the March, 17, 1939.


This fighter was fitted with a Hispano-Suiza engine 12 Y 29 delivering 810 Hp at sea level and 920 Hp at 3,600 m. 

Her takeoff weight was 2,535 kg, giving a wing loading of 158.74 kg/m².

Her top speed was 527 kph at 5,000 m and the altitude of 8,000 m was reached in 13’45”. 


The deciders were OK for the ordering 200 Dewoitine fighters. Both the technical and tactical finalization of the D.520 were actually easy to reach.

The common sense was to build that fighter as she was during trials and the CEMA had no criticism about this fighter.  



Time wasting


French deciders, instead, wanted modifications, especially regarding the kind of engine. 

First, they chosen the Hispano-Suiza 12 Y 31 – the same fitted on the Morane 406 fighter – owing to its instantaneous availability and, mainly, because it did not need the 100° octane fuel (the 85 - 87 octan fuel was the one furnished to the Armée de Terre for its lorries and tanks!).

The 12 Y 31 engine had a power output of 760 Hp at sea level and of 860 Hp at 3,250 m. 

One can calculate the top speed will drop to 507 kph (loss of 12 kph due to the loss of 60 Hp and loss of 7 kph due to the loss of 350 m in altitude).

During the trials with a so-called 12 Y 31 engine in September 1939, the D 520 reached 550 kph at 5,200 m and climb to 8,000 m in less than 13 minutes.

Amazing ? No, clearly dishonest! 

The 12 Y 31 must have been seriously modified to obtain such a result ! 
  • First, if the power is weaker, the speed decreases: It's a physical law. 
  • Second, if the maxi altitude supercharger delivery is lower, the top speed cannot be obtained higher than with a supercharger able to deliver more power 350' higher!

{Parenthesis (26 11 2016): In the French aeronautical review "Les Ailes", published the January 12, 1939, it was written "the D 520 will be fitted with the Hispano-Suiza 12 Y 51 engines". 

Some weeks later, the same review gave an estimation of Marcel Doret about the top speed attainable by the D 520 with such an engine as 550 kph.

It's very likely that the CEMA used of this 12 Y 51 in the September 1939 trials, instead of the 12 Y 31. But, for some insane reason, they persisted to use of the wrong designation of this engine (some hand written texts showed confusing use of a 3 Arabic numeral in place of a 5 one)}


Even before these trials, the official deciders changed their decision again: They now needed another motor, the Hispano-Suiza 12 Y 45, which was similar to the 12 Y 29 but fitted with a much more modern supercharger (Szydlowski-Planiol S39 H3). 

This device used of a very refined internal aerodynamics, inducing a significant lengthening of the engine. 

The power output becomes 850 Hp at sea level and 920 Hp at 4,200 m.


Nobody, among all the distinguished deciders, had measured the length of the new motor with its new supercharger and the canon it was intended to carry!!! 

So, the total length of this package induced a 52 cm lengthening of the fighter. 

The weight of the plane increased to 2,650 kg and, may be, the D 520 was a bit less easy to fly at low speed.


Finally, the Dewoitine D 520 – during her trials of February 1940 - demonstrated :


  • A top speed of 425 kph at sea level, 
  •                           535 kph at 5,400 m,
  •  A climb time to 4,000 m in   5’13”,  
  •                        to 6,000 m in   7’57”
  •                       to 8,000 m in 13’24”.

The brilliant result, after 9 months of "brain" storming (?), was a gain of 8 kph in top speed and 21” to reach the altitude of 8,000 m. LOL!

OK, this fighter was a very good fighter, equal to the best of her times.  


But the 9 months wasted to chose the best motor was catastrophic: If ordered and build as was the 02 prototype, the original D 520 (version 1) was able to be really operational since the Fall of 1939.

Her build time was 8,000 hours each.


With all her modifications, the technical and tactical finalization of the D 520 (version 2) was impossible before the May 10.

The deciders were under lobbies influence and have forgotten the lessons of Darwinian evolution: Competence is forged every day on the field of the realities, not in lounges, clubs or so on. 

French pilots and also French and Allied soldiers were killed owing the incompetence of these men !


I did not accept such behaviors for my country – but I did no more accept them for other countries, especially when they are friendly... 





6 commentaires:

  1. Good day and thanks for this precise article.

    If I'm not going off thread, I would like to ask a few details that could help me to better understand operational behaviour and capabilities of this fighter.

    1.Could the flaps be set at any angle between "raised" and "landing" position, so to get also an help in combat and for takeoff?
    2.Did have its engine (Hispano-Suiza 12Y45) problems with negative G's?
    3.Was its Ratier propeller automatic (I mean, in same fashion of the Bf 109)?
    4.Was its mixture variable in flight, so to lean it to reduce consumption?

    Thanks for any help!

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    1. Hello !

      Your 4 questions are all relevant.

      The only one I can answer clearly is the #3: Yes, the D 520 used full automatic propellers, the Ratier electric one in a first time, a more easy to adjust Chauvière one later (which was unfortunately nos as good for speed performances as the Ratier).

      Regarding the three other questions, I have no such precise answer.

      For the #1 question, I never read anything about the use of the flaps during combat.

      Nevertheless, the concept of combat flaps was known in the French aeronautic reviews at least from 1936, because the Mureaux 190 and the Hanriot 220 were explicitly fitted with!

      Perhaps, the victories of Adj. Pierre Le Gloan against 4 Fiat 42 biplanes in June 1940 were explained by such a practice ?

      The #2 question is very interesting, but I never read any mention of G cut in any French pilot combat account.

      Moreover, in the beginning of the 20's, the French pilots were frequently confronted, in aerobatic competitions, with the excellent German pilot Gerhard Fieseler who was demonstrating inverted looping.

      So, the French carburetors used in aerobatics engines were adjusted for inverted flight.

      It's difficult to believe that the French combat engines were not using such carburetors.

      Question #4: The EGT was known since 1934-1935 in the transport companies.

      But I do not know if such a device was fitted on D 520. Sorry...



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  2. Good evening and thank you very much for your kind answers!

    It's a pity not to have a D.520 flight manual to check about the use of flaps.

    I guess that inverted flight and negative G's are not quite the same thing, and, as such, managed in same way. I think negative G's were definitely dealt with by injection carburetor, having no float chamber (the one flooded with fuel in such condition). I read an earlier version of HS 12Y (that mounted on VG.33) had float carburetors...

    Again, a flight manual would have helped also about leaning the mixture, as well as a detailed description of cockpit left side (was there a mixture lever?).

    Again a big thanks for your cooperation.

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    1. As you know certainly, France was completely occupied by Germans in November 1942 in retaliation for operation Torch.

      The Germans used of D 520 for the training of their young pilots and recovered all the flight manuals. The Armée de l'Air in French North Africa used some surviving D 520 but, after the Libération, the D 520 flew back to France.

      Very few were in good conditions and their flight manuals where not sufficiently conserved.

      I do not agree with you for inverted flight, which is a -1 G flight.

      On the flight panel of this fighter, there was no EGT nor mixture lever.

      Remember, for French deciders, the only enemy was Germany, and the target of the French bombers were at most at 500 km from the French bases...

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  3. Hi Drix and thanks again for further info.

    You are right: inverted flight is just one of negative G conditions; I was wrong, sorry.

    Lack of mixture lever, as well as of EGT, looks like a good hint to guess an automatic device to adjust mixture.

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  4. Good day and sorry to be insistent.

    I would just to inform you and who reads this blog that I got a complete answer for first three questions:

    https://ww2aircraft.net/forum/threads/dewoitine-520-technical-details.45909/#post-1299631

    that I would share here.

    So D.520 pilots could take advantage from slightly deploying flaps during combat and, maybe, shorten takeoff run by a further extension.

    Oddly, there's no record of their complaints about negative-G cutoff while following Bf 109 in sudden dives, like did their British collegues about Spitfire and Hurricane.

    At least, now we have a more complete historical picture, I think.

    Thanks for all the help,
    greybeard

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