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 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.
Her takeoff weight was 2,535 kg, giving a wing loading of 158.74 kg/m².
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!).
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).
- 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!
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)}
This device used of a very refined internal aerodynamics, inducing a significant lengthening of the engine.
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.
- 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”.
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 !