lundi 19 novembre 2012

The French Air Stricking Force: And the winner was... the LéO 451 (revised 06 / 10 / 2013)


The program : a bomber which could be as nimble as a fighter


The French program of November 1934 - designated as B4 for bombing, 4 crews - exacted as fast as possible aircrafts (one wanted initially 400 kph, after what a speed of 470 kph was exacted, 20 kph more than the fighter program published only 4 monthes earlier...).

Another constraint was the use of an engine chosen by some state deciders in place of self chosen engine. Why?

Because all the French aircraft companies were never sufficiently rich for investing enough money in all of the needed equipments, especially regarding the engines. 

The French Republic was always delaying what it was buying. Worst, by the bias of systematic devaluations, the price was automatically lowered... 

In that time, the costliest part of a bomber was the engine, so the French state became the buyer of the engines, implying, obviously, the choice of the engines was in the state bureaucracy instead of  the aircraft designers. Obviouly, also, the state commission of deciders was under strong pressures of various lobbies.


Yes, I did not like the US various lobbies, but, at least, they are well identifyed and they can be defeated by other ones, or combinations of other ones. It was never the case in the France third République where all informations disapeared under the fog of utmost secrecy.

Were the members of these commissions very proficient? Obviously, all of them claimed they were. However, the only perfect validation is, allways, given a posteriori by the History itself. In the actual case, the defeat of June 1940 demonstrated how there claims were illegitime.

A good scholar cursus define only, to any human person, a good level of acquisition of knowledge. That has nothing to do with a proficiency, which is the demonstrated capability to go out the beaten tracks.


A very innovative prototype: A good case to use untested engines for trial flights?


En 1935, attracted by some advertisements, the commission members had chosen to order an radial air cooled engine (HS 14 Aa) developped - but still untested in flight - by Hispano-Suiza and promising to deliver 1300 Cv. This engine was to be fit on all the brand new prototypes of the bombers developped by the various compagnies.

That decision was the worst possible one. Ok, Gnome et Rhône experienced some problems with its own aircooled radial engines 14 Kirs / Kjrs and ordering engines to Hispano-Suiza was a method of pressure on the French specialist of air cooled radial engines. But this order was very shortsighted.

At the origin, the Hispano-Suiza company had bought some licences for Wright radial engines
Contrary to my ancient readings, one of my readers (Thank you Alain) wrote me that it was a true  Hispano-Suiza engine, and not a licence version of the Wright 2600. It was less powerfull but 5 cm narrower in diameter, lighter, and its rotation speed was less important. 
It used, as the US powerfull engines, the 100° octane fuel, implying frequent overheating  when using the standard 85° octane fuel of the French Armies during the developpment of this engine as, also, of the prototypes on whitch it was fitted.

Obviously, it seems that an easy solution could had to prepare 2 sets of engine supports and cowlings, allowing a quiet aerodynamic finishing of the aircrafts. 

The  STAé (service technique de l'Aéronautiquecommissions was lacking completely of any adaptation capability to the real situations.

Nevertheless, after a lot of work, the very good engineers of Hispano-Suiza achieved to finish fairly the 14 Aa engine, which obtained good results on two prototypes: The excellent Latécoère 570 and the Koolhoven FK 58. It was too late.
This history had an adverse consequence on the developpment of the Hispano-Suiza liquid cooled 12 cylinder in Vee, because the very experimented engineers needed to that work have been send to reinforce the team working on the 14 Aa. That explained how long was the time to finish the 12Y51 needed for the Dewoitine 520.


A tactically erroneous conception


The major idea of this bomber program was the new bombers being faster than the projected French fighters, they were absolutely able to outrun all fighters in the world. Amazing !


Even if I acknowledge that some French fighters - as the Nieuport 161, for example - were very well designed, that did not garantees that the ennemy fighters cannot be faster. 

Using the data of some Caudron racers flying at 500kph at sea level with only 300 hp, it was easy to project a 860 hp fighter able to fly at 550 kph at 5000m.

A bomber flying at 550 kph could have been a real solution! A very clean and exceptionnally powerful bomber was the good answer as was the US Boeing B29 (580 km/h), fitted with four 2200 hp engines in 1944. But, in 1936, everywere in the World, it was not a real possibility.  

In 1944, even the B29 might be downed by a fighter diving from above as it hapened some few times over Japan. 

No, a true bomber, once in the air, cannot be sure to go back home: She is the natural prey of the ennemy fighters. General Giulio Douhet was only reasonning as if the bombers were battleships. But they are not...



A fast good bomber may kill the naughty fighter by shooting strait between the twin rudders...


Another exacting was the twin fins-and-rudders of the B4 bombers to allow the rear shooting of a 20mm cannon.

The only one French aircarft designer who found a true good twin fins-and-rudders solution was engineer Moine for the Latécoère 570, exceptionnally easy to fly, very well adapted to the futur strugles but never ordered. 

If you observe the bombers of the WWII, you can see that the most famous were not fitted with the twin fins-and-rudders, for some reasons :
  • At low speed, with important angles on wind stream, the fins-and-rudders were masked by the engine cowlings, or the landing gear box, that giving a very difficult aerodynamic stiring control.
  • The twin fins-and-rudder  was mechanically a complicated structure, because they are situated downstream the engines cowling. At high speed, the vortices induced by the engines produce vibrations which are dangerous from a structural point of view. To overcome these vibrations, on must strengthen the assembly of the tail, then one increases substancially the mass of the bomber.
All the US bombers bought by the French government in 1938 (Douglas DB 7 Boston and Martin 167 Maryland), used a classical tail and they had good flying characteristics. The French deciders were happy with them. 

So, the twin fins and rudders was not so crucial for them. But they accepted to buy these US bombers without self-protected fuel tanks the French-build bombers had.

At last, I need a cannon!


The French bureaucracy had decided another juicy nugget: The rear defense used a cannon! 
The chosen weapon, the Hispano-Suiza HS 404 was indoubtedly a very good one, with a impressive destructive power and very good ballistic properties. 

Ok, but the actual reasonning was biased as if the deciders were allways stuck in a two-dimmensionnal universe. In an air combat, the decision depends, in most of the cases, by the intantaneous speed difference in all of the three dimensions. So, any fighter, even the poor Morane 406, was able to manoeuvre quickly in an unexpected direction. The 5 times heavier bomber was never able to escape such a manoeuvre, owing to her own inertia.

If that weapon had a muzzle velocity twice as great as the one of a machine-gun, a gunsight allowing a very great precision, the bet may have been a winner one. It was not the case.
Worst, the number of shells was to small. Initially, the cannon had 60 shells (6 seconds!) in the drum, after, it had only 30 shells drums (14 kg). In a bomber, which is manoeuvring to escape ennemy firing, the number of g might increase from 1 to 3, even 4, increasing the drum weight up to 60 kg. The French gunners were not Hulk!

One or two belt-fed riffle machine-guns were a very better solution.


The perfect bomber?...!



That bomber was the Lioré-Olivier 451 or LéO 451. 

An aircraft I saw personnaly in a hangar of an airfield (Boufarik, in Algeria) when I was 6 or 7 (1952). 

Around me, the peoples were chating together, mezzo vocce, and said "it is a warplane". 

Obviously, I did not understand anything, but she appeared me as malicious.

The aerodynamics study of the LéO 451 was up to date, with very thin wings (15 to 11% relative thickness), the engine cowlings designed by engineer PE Mercier were very optimized for the highest possible speed (allowing 40 kph more than the previous ones). 

The fuselage was elegant allowing a good visibility to the pilot, the bomber and the gunner.


 LéO 451 in flight on this site wwiivehicles



The performances were outstanding for its time, achieving, with a bomb load of 1350 kg and all fuel, 502 kph at 5100 m and 640 kph IAS in very shallow dive (the finish of the tested bomber was particularly good, the others flying at 495 kph). 

That was 25 kph faster than a Ju 88, 55 kph faster than a He 111, etc.

The climb  to 5000 m in 14 minutes displayed that this bomber was a bit too heavy. 

The reason for that was the suggestion made by Jacques Lecarme, a skilled engineer and test pilot who thought that a bomber could be used as a fighter (!).

The flying qualities were very good in flight, with an outstanding manoeuvrability. 


A big take off concern!


Nevertheless, some problems occurred when taking off. 


The origins of these problems were in the weight excess, in the too small fins-and-rudders and in the landing gear box.

A little power assymetry between the two engines when taking off induced a crash, deadly when the aircraft was full loaded. 

From the Septembe3, 1939 to the Mai 10, 1940 (included), 20 crashes destroyed at least one bomber. 

So, the losses, without any ennemy action, accounted ~20%. 

The test pilots - too skilled to be representative of common operationnal ones (?!) - never anticipated such a behaviour. 

Lately, since the March 18, 1940, Mr Jacques Lecarme went in the bomber squadrons to explain the pilots his own take off method. 

Nevertheless, there was still some crashes, but post-take off and probably due to air screw problems or excess of weight.


Another problem was the huge manufacturing time of this bomber (60,000 hours!). 

The first 5 LéO 451 were built in 4 months. 

And none were ready to fight. From September 1, 1939 and May 10, 1940, about LéO 451 were taken into account by the French Air Force, an average of 12 bombers a month.

It's impossible to see that as a sucessful result of our nationalization. 

Even if Jacques Lecarme answered to an article published during the 60's in Aviation Magazine, that the SNCASE company had delivered 450 bombers at the June 24, 1940, only the half part of these aircrafts were taken into account by their operational aircrews.

So, the other ones were not usable in combat.


The efficiency?... only average




Among the 247 LéO delivered for Mars 1st, 1940, only 108 were accepted! So, the May 10, 1940, few pilots and crews were able to use this bomber with the maximum skill. 

Ok, this aircraft allowed loops and roll, but that was quite useless.

Some extraordinary pilots, in team with excellent gunners, were able to survive very difficult situations, even downing about 12 German fighters. But it was not the job of this aircraft!

One know that, for the 10 days between the May 10 and the May 20, among 128 take off, only 95 sorties go to the objective. This is the proof the LéO 451 was not perfected enough.

The losses rate was 31 bombers among the 63 bombers available (49%). 


That was the same rate as the one for the Bréguet 693 and similar to the one of the RAF Fairey Battle. 

It was the direct translation that nobody, among the Allieds, was knowing how to strike the Wehrmacht.


For all the Battle of France, 80 Léo 451 were lost (for any reason) among the 180 used in operational units. 

The rate of losses was progressively lower.


Most of the times, the Léo bombers were sent to attack by small groups (3 to 4 !) at low level, favouring the Flak.

Facing the Wehrmacht, the results of such bombing were likely a bit disapointing

.

That was the hard lesson of the hasty order of an unperfected bomber.


Just after the French defeat, the fins and rudders of all LéO 451 bombers were enlarged with the amazingly very fast agreement of the German commission.



After the invasion of the Vichy France, the Germans captured hundreds of these bombers they transformed as cargo for fuel or as troops transporter, each LéO 451 carrying up to 17 soldiers in their modified bomb bay.



After the French Liberation, the remaining LéOs were used to various tasks (mostly in Sea Air Rescue duties) and the lasts were flying up to 1956.


2 commentaires:

  1. L'obligation d'utiliser des moteurs non mis au point est je pense l'illustration de la lutte sourde qui opposait les Services Officiels et les constructeurs privés (chose qui s'est curieusement poursuivie après les nationalisations, mais c'est une autre histoire).

    Au début des années 30, il était clair que le marché des moteurs était en train de se partager "équitablement" entre les deux leaders - à Hispano les moteurs à refroidissement liquide, à Gnome-Rhône ceux à air. L'annonce de la mise en chantier de moteurs à air de forte puissance par Hispano dut apparaître aux Services Officiels comme une bonne occasion de donner un coup de pied dans la fourmilière et de casser une forme (supposée) d'entente anti-concurrentielle. D'où cet engouement déraisonnable pour un moteur qui n'existait que sur le papier, et toutes les déconvenues qui s'en suivirent.

    Le plus triste est qu'après avoir imposé aux avionneurs contre toute logique, un moteur qui ne marchait pas, les Services Officiels s'en désintéressèrent brutalement, et Hispano dépensa en pure perte beaucoup d'énergie pour "fiabiliser" son 14Aa, dont les versions 14Aa 12/13, qui marchaient bien, ne volèrent jamais que sur des prototypes... Le tout, comme vous le dites bien, au détriment du développement des moteurs qu'Hispano savait faire, les V-12 dont la version 12-Z fit si cruellement défaut en 1940.

    Bien cordialement, and sorry for my bad english.

    Alain Breton

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    1. Je vous remercie de bien documenter un mécanisme de cette viscosité administrative qui repose sur les idées préconçues de bureaucrates qui croient savoir des choses et généralisent des actions qui obtiennent l'inverse de ce qu'ils pensaient obtenir.

      Thank you to illustrate the "administrative viscosity". I use this concept for a set of bureaucratic actions of persons who acted following unproved beliefs to obtain some wanted results. These persons are never able to forcast the real effects of there actions, but other bureaucrats acting in another direction, the main result is a blockade of all avance.
      I'm writing for the 1940 France.
      May be some people would, in the future, write about some similar problems in the US Pentagone...

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