mercredi 12 novembre 2014

The Arsenal VG 33 fighter, the ghost of June 1940 (revised 21 / 10 / 2017)


I discovered the Arsenal VG 33 in the early 1960’s, in a very short article in the French review Aviation Magazine

The VG 33 was a derivative of the former VG 30 of 1938, which was a flying mock-up of the VG 10 unconventional heavy fighter which became, in 1944, the all metal VB 10 (too) heavy fighter.

This aircraft was entirely designed by engineer Jean Galtier, of the Arsenal de l’Aéronautique, a government founded establishment dedicated to advanced technologies for the air industries but almost devoid of production capacities.

The chief of this establishment was Ingénieur Général Vernisse (the “V” of VG to designate the VG 33, the “G” being issued from Galtier).

If the first blue prints of the VG 30 were adapted for a lightweight fighter, her Potez 12 D air cooled engine delivered only 485 hp and the cowling being not well designed for a flat 12, induced the use of a Hispano-Suiza 12 X engine of 690 hp (a very reliable engine).

The maiden flight of the VG 30 was done in October 1938, quite simultaneously with the first flight of the Dewoitine 520.

The new fighter was no more a lightweight fighter but performed rather well. 

She demonstrated a top speed of 485 kph at 4,950 m and climbed to 5,000 m in 7’ 15”, performances clearly better than those of the Morane-Saulnier 406 standard fighter of the French Air Force with 860 hp, which was 30 kph slower and climbed at the same altitude in 10’ (these values - very different from the "official performances" - have been carefully measured on all their MS 406 by the Finnish pilots in 1942).

Today, some people wrote the VG performances were disappointing and implicated the "bad" air-screw.

Such a feeling was not relevant at all. 

However, the VG 30 had two main drawbacks: 

·     Her huge radiator was not well positioned, likely to be in same position than the homologous device in the VG 10, a position irrelevantly conserved in the VB 10: This radiator was put in the maximum drag area and had a too large air intake (larger than the hot air exit).

·     She did not use of backward discharging ejector exhaust pipes.

Together, these drawbacks were responsible from the loss of, at least, 20 kph.

Arsenal VG 30  - On the Arsenal VG 33 site of Franck Devillers - Compare the radiator air-intake (for the cooling of a 690 hp engine) to the one of a P 51 Mustang!

If these two points have been fixed, this fighter could achieve top speed between 500 and 515 kph.

In 1939, engineer Galtier was restricted to develop the VG single-engined fighters, and the VG 10 became an all-metal twin-engined fighter, the VB 10, of quite identical silhouette but of very larger dimensions (and weight!) developed by engineer Badie.

The Arsenal VG 33 fighter was the development of the VG 30 with the well-known Hispano-Suiza 12 Y 31 used in the Morane-Saulnier 406 fighter and some aerodynamics refinements.

Arsenal VG 33 on the rain, in Bordeaux – The prototype 01 is in the foreground before a series fighter with a much more sloped windshield.

This fighter appeared as the last and aerodynamically very refined development of the Bernard 20 fighter of the Jockey program (1928).

This older fighter was designed by the same Jean Galtier under the supervision of the famous chief-engineer Louis Béchereau (who designed the Deperdussin monocoque racer, winner of the Gordon Bennett cup in 1913 and designed also, 3 years later, the famous SPAD VII and XIII fighters).

Bernard 20 C1 – 320 kph at sea level with a not supercharged HS 12 Jb 400 hp

As her forerunner, the Arsenal VG 33 was a wooden monocoque. 

Such a choice was the consequence of the irrational fear of some French deciders that France may be short of aluminum.

{One must remind that France was the first producer of this metal up to 1937, only surpassed by Germany the 3 following years. }

Worst, the red spruce of high quality needed to construct the Arsenal fighter was obtained only from Canada, so it must be shipped to France. 

Obviously, once at war, the U-boat hazard would be very present… 

A fast aircraft

The 2 problems seen above on the VG 30 were fixed in the significantly heavier VG 33 of similar overall dimensions.

The wingspan was 10.80 m, the length was 8.55 m and the wing area was 14 m².

The take-off weight was 2,650 kg, quite identical to the one of the Dewoitine D 520 fighter which used a 45 kg heavier engine and a 2 m² larger wing area…

So, the wing loading was ~190 kg/m², 13% heavier than the D 520 and, 20 % heavier than the MS 406.

The first flight was done the April 25, 1939.

The performances of the prototype were good, taking into account the rather weak power delivered (860 hp) by the Hispano 12 Y engine identical to the one used in the Morane-Saulnier 406. 

(Sources: THE reference site - in French - on the Arsenal VG fighters and the excellent series of Fanatique de l’Aviation, #197 and followings, April 1986).

The top speeds were:

·         442 kph at 0 m

·         463 kph at 1,000 m

·         485 kph at 2,000 m

·         508 kph at 3,000 m

·         530 kph at 4,000 m

·         556 kph at 5,000 m

o    Top speed was 558 kph at 5,200 m.

·         554 kph at 6,000 m

·         543 kph at 7,000 m

·         530 kph at 8,000 m.

The altitude where the top speed was obtained was 700 m higher than the one used for the best speed of the Morane 406 (4,500 m) which used exactly the same engine with the same supercharger (the HS 12 Y 47 differed from the HS 12 Y 31 only by the carburetors and the fuel pump).

So, the difference of the operational critical altitude (2,000 m) - which is very higher than the one observed in the laboratories owing the influence of the dynamic pressure induced by the speed of the aircraft – might result from the more efficient position of the supercharger air intake, of same fashion than in the Nieuport LN 161-03 of 1938 and the CAO 200. 

The climb times were:

o    1,000 m in   1’ 17”

o    2,000 m in   2’ 34”

o    3,000 m in   3’ 51”

o    4,000 m in   5’ 07”

o    5,000 m in   6’ 26”

o    6,000 m in   8’ 02”

o    7,000 m in 10’ 11”

o    8,000 m in 13’ 26"

The service ceiling was better than 9,500 m, the maximum permissible IAS was 620 kph (= a true speed of 750 kph at 4,500 m).

You may found other values published in the C.J. Ehrengardt study (Aéro-Journal #46, December 2005) on this fighter:

o    455 kph at sea level

o    554 kph at 6,000 m

o    545 at 8,000 m.

Two climbing times were also published (as also an amazing service ceiling of 11,000 m):

o    5,500 m in 6’ 06”

o    8,000 m in 10’ 16”.

This author gave a take-off weight of 2,450 kg, which may explain partly the better performances.

Nevertheless, these more recent values are questionable because the speed at 6,000 m is exactly the same as the one published in 1986, a bit inconsistent. 

Two orders totaling 700 fighters were quickly decided (and other followed).

The mass production was transferred to the CAMS factory, near Paris, which was a former flying boat company merged with the Potez one and, latter, was part of the nationalized SCAN.

Nevertheless, the VG 33 issued from mass production were a bit slower (540 kph), owing, probably, to the omission of the main landing gear hatches of the VG 33-01 prototype... 

The individual ejector exhaust pipes appeared as a new device, the pipes being very short and not completely backward.

The same device was fitted on the Loire-Nieuport 402 fighter-bomber prototype. Maybe, such device was cheap, perhaps not the most efficient!

Flying qualities

In accordance with the comments of Ingénieur-Général Louis Bonte (Histoire des Essais en Vol, Docavia #3), the flying qualities of this aircraft were superlative: Far better than those of all other fighters.

However, this assessment was devoid of any precise description of the so-called qualities.

Luckily, Mathieu Comas (in: La Chasse Française Inconnue, hors série #7, Lela Presse), published a more comprehensive picture of how the VG 33 behave.

The first positively acknowledged quality was the total absence of swing tendency during take-off.

Such a characteristics is of paramount importance for inexperienced pilots, but became less crucial for veterans.

The stall speed was 120 kph (aircraft clean) at full power and 130 kph with no power in the same configuration.

During the stall, the VG 33 had no tendency to begin a spin.

The optimal speed for climbing was 240 kph (to be enhanced by 30 kph in case of overheating).

Compared to the Dewoitine D.520, the minimum speed for aerobatics figures were a bit faster with the Arsenal fighter: For example, the vertical loop must be started at 400 kph for the Arsenal fighter against 380 kph for the Dewoitine D 520.

However, the handling was easy at any speed.

I take the opportunity to destroy a legend which stay about all the French fighters: In several papers about them, you can read the spin was prohibited.

That was only a “fossil” of the “bureaucratic viscosity” developed in France.

This rule was decreed for all military aircrafts, likely just after WW I, when the aircrafts, worn by an intensive war usage, were frequently crashed, killing their pilots.

Obviously, this rule was never known by the pilots who were carefully trained to spin start and recovery, especially the fighter pilots!

But, because it appeared in the service book of all fighters, some authors recopy it.

The only known shortcoming of the Arsenal fighter was her too large air intake of the radiator, which, in summer, gathered an impressive amount of plant stalks, not very good for cooling the engine ;-).

A tremendously short operational career

The first Arsenal VG 33 fighters issued from the CAMS factory were delivered to the CEAM (center dedicated to military tests) in April 1940.

That was about one year after the maiden flight of her prototype (to be compared with the 4 years spent between the maiden flight of the Morane fighter and the delivery of the first series MS 406!).

Unfortunately, some of the following aircrafts were not fitted with their gun-sights (OPL 39 or Baille-Lemaire 40), so they were quite useless.

However, the operational pilots who saw these fighters loved her instantly.

For some unknown reason, the well experienced pilots of the Grp I/2 – in which was embedded the famous SPA 3 of Georges Guynemer – who were scheduled to obtain the first dozen of VG 33 fighters, were never equipped with.

They finished the Battle of France with their old, worn out, Morane 406...

Evacuation by inexperienced pilots

When Paris was on the point to be seized by the Wehrmacht, these VG 33 fighters were given to quite inexperienced pilots to evacuate these aircrafts from Paris area in a hurry (as, also, a lot of other fighters: Morane-Saulnier 410, Bloch 152, and so on)!

Due to the emergency situation, most of them were just qualified as fighter pilots.

The most advanced fighter they could have flown previously was the Morane 406 or only Dewoitine 500 family fighters designed between 1929 and 1930...

They discovered this fighter without any serious briefing. 

When they flew this brand new fighter - very fast by comparison with all the aircrafts they had flown previously (100 to 200 kph faster!) – they were confronted also with her high wing loading.

So, some of these pilots said “she flew like an iron”… 

Similar negative opinions have been expressed each time a real evolution affected the French fighters (as also, in several Air Forces of other countries). 

It is likely that the opinions of experienced pilots would have been very different.

Anyway, these pilots were first gathered at Etampes (at 50 km SW of Paris).

A very good potential fighter 

The June, 13, they went to Orleans before they flew to Bordeaux with a heterogeneous collection of fighters (Morane 410, Bloch 152 / 155 and 6 Arsenal VG 33)!

During their journey to Bordeaux, two pilots of VG 33 strafed a Wehrmacht infantry column,  demonstrating the confidence they had in their Arsenal Fighter. 

They suffered no Flak damage nor German fighter attack, in a sky entirely controlled by the Luftwaffe, though, a confirmation of the high speed of the Arsenal fighter.

The June, 17, they became part of the newly constituted Grp I/55.

The pilots take part successfully to some combat against enemy air raids over Bordeaux, but we don’t know if they used of their Arsenal VG 33. 

The Bordeaux airfield was overcrowded by French military aircrafts without any flight control: What a mess!

Nevertheless, none among the pilots of VG 33 was injured and none of their fighters crashed in such an emergency situation.

It appears, for me, as a consistent proof of the very good handling qualities of the VG 33 fighter!

Three of the Arsenal fighters stayed in open air on the Bordeaux airfield until November 1942, after what they were scrapped by the Germans invading the so-called Vichy "free zone".

Evolution of the Arsenal VG 3x family

Something was awkward in the management of the finishing process of the Arsenal fighters. 

The ordering of the VG 33 was not following the classical way: The order was directly given to the SNCAN, a nationalized company technically managed by his former leader, Mr. Henry Potez.

So, the team of the engineers who conceived the VG 33 had no direct information about the perception of the pilots!

Instead, they were encouraged to develop as quickly as possible the VG 30’s family: During the full year following the maiden flight of the VG 33, four more powerful derivative prototypes were built:  VG 34, 35, 36, 39.

The VG 34 was a VG 33 airframe fitted with the same Hispano-Suiza 12 Y 45 engine than the Dewoitine 520. 

She achieved 570 kph at 6,000 m and climbed to 5,000 min less than 6’.

The VG 36 was the most interesting fighter of this family, with a completely redesigned air intake of the radiator and a Hispano-Suiza 12 Y 51 engine delivering 1,100 hp for take-off and 1,000 hp at an altitude of 3,250 m. 

It was said that she flew at 590 kph at 7,000 m in May 1940.

Arsenal VG 36 

This variant will be introduced in mass production at the Fall of 1940.

The last derivative to fly was the VG 39, which was a test bed for the new engine: This aircraft was fitted with the new Hispano-Suiza 12 Z engine, with 4 valves for each cylinder, and designed to deliver 1,600 hp (but actually limited to 1,150 / 1,200 hp).

She flew the May 3 and, some days later, achieved 625 kph at altitude.

VG 39 at Bordeaux - A more streamlined nose and quite optimal ejector exhaust pipes

The definitive fighter was using the long nose of the VG 39 (induced by the elongated reduction gear box of the HS 12 Z), the fuselage of the VG 36 with her shallow radiator air intake and new wings of longer wingspan (11.6 m) and larger area (16.5 m²), in order to take into account the new take of 2,800 to 3,000 kg. 

The fuel tank will carry 170 liters more than the previous one (400 liters) and the armament was supplemented by 2 machine guns.

The wood: Not a real problem!

You can read in the literature complaints about the fire hazard for a wooden fighter essentially. 

To these professional mourners, it may be useful to remind that the aluminum is used as solid fuel for some very powerful missiles carrying strategically thermonuclear head.

The pilots who tried to burn down one of the Arsenal fighters did not had success!
From the other hand, the wood had the advantage to be quite transparent to the actual radars.

The war experience of the Mosquito crews and of the Yak 3 pilots confirm that, yes, any war is dangerous, but not especially the wood (at speed staying well below the trans-sonic barrier).

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