Nieuport 161 - A Stronger French Air Force in May 1940

stevep ,

Not completly of subjet as the LN 161 demonstrated that although engine power is fundamental, aerodynamics makes sometime bigger difference. LN 161 with 860 HP Hispano-Suiza 12Y 31 had better performances than Dewoitine D.520 with 920 HP H-S 12Y 12Y 45, and even more the 545 km/h of the CAO.200 with the same 860 HP engine.

Ten per cent power more on the Spitfire would have given some 3 to 5 % more speed, it would have reached nearly 600 km/h. This would have saved some lives but probably not as many as improving tactics (Vic vs Four fingers, Big Wing controversy...) or pilots skills.

French engines didn't had fuel injection and, as far as I know, little effort was made on it. One German fuel injection pump have been secretely obtained but officials shown no interrest in it (I have to check my sources).

Anyway, the main concern on the French engines was the low octane rating fuel used in French Armée de l'Air wich lead to a hudge loss of specific power. Other concerns was poor reliability of engines due to design issues according to some authors (including less bearing than in equivalent foreign engines) but I suspect more the low quality of manufacturing, regularly reported in some companies including Gnome & Rhône or Marcel Bloch Aviation, as no reliability issues has been reported on foreign licensed engines in Switzerland, Romania, Czhechoslovakia... On the other hand, Szydlowski-Planiol variable supercharger used on H-S 12Y 45 was the most efficient of the time. Engine industry in France, as many other, was a mix of leading technology and below state of the art.

Uchrony Nieuport 161

The Contest

All the following is the real history.

A program to select the future standard single-seater fighter (C1, Chasseur) for the French Air Force (Armée de l'Air, AdA) was issued on July 3rd, 1934. The re-equipment plan foresaw 355 online fighters plus one third in reserve.

The program called for a single-seat aircraft with closed cockpit, retractable landing gear, equipped with radio, propelled by an 800 to 1,000 HP engine, capable of 400 km/h, with an autonomy of 2.5 hours at 330 km/h, i.e. 825 km, a ceiling of 11,500 m and climb times of 6 minutes for 4,000 m, 15 minutes for 8,000 m and 19 minutes for 10,000 m [this last value is surprising and need to be checked because it gives 4 minutes for the last 2,000 m where the previous 4,000 m would have taken 9 minutes]. The armament should consist of one or two 20 mm cannons and two machine guns. The required top speed will be increased to 450 km/h in November 1935.

The Morane-Saulnier 405, powered by a Hispano-Suiza 12 Ygrs engine developing 850 HP at 4,000 m, made its first flight on August 8, 1935. The aircraft seemed promising, but the top speed reached was lower than 400 km/h.

Each design department of Loire-Nieuport, former Loire and former Nieuport, presented its own prototype.

On September 28, the Loire 250, powered by a 980 HP Hispano-Suiza 14 Ha-79 air-cooled star engine, made its first flight. It lacked stability, and the engine had tuning problems that prevented it from reaching its calculated speed.

A few days later, on October 5, the Nieuport 160 took off. It only had a Hispano-Suiza 12 Xcrs engine of 680 HP at 4,500 m driving a two-bladed wooden propeller with a fixed pitch. Despite the lack of power and a fixed landing gear, it quickly reached 440 km/h. Like the Loire 250, it has a canopy with 360° visibility which has the particularity of being monobloc, shaped like a water drop. Unfortunately, this ultra-modern canopy has vibration problems at high speeds.



Nieuport 160. Air Mag - Collection S. H. A. A.

After manufacturer's tests, the Nieuport 160 returned to the factory in January 1936 to be modified: it received a Hispano-Suiza 12 Ycrs engine of 860 HP at 4,000 m with a three-blade variable pitch propeller, its landing gear became retractable and the wing has a slightly higher dihedral, but the bubble canopy was replaced by a faceted one to solve the problem of vibration, which should result in a slight increase of drag.

On February 20, 1936, the MS 405 entered the Centre d'Essai des Matériels Aéronautique (CEMA) for official tests, which it completed in April; it was quite healthly and very maneuverable, but its maximum speed, as well as its climb times and ceiling, were far below the program requirements. Moreover, its engine tends to overheat and will have to be changed several times; no modification of the radiator will ever solve the problem.

The modified LN 160, now Loire-Nieuport 161, made its first flight in March and entered CEMA on May 9 until the end of July. Its behavior was good and its performance better than required.

However, in June 1936, even before the LN 161 tests were completed, a pre-production run of 16 MS 405s was ordered, even though none of its performance was acceptable in view of the program requirements.

In August, LN 161 went to Cazaux to realize firing tests on air and to the ground...

The Fate

Still real history.

Mid-September, the pre-production order for 30 LN 161s was ready. But due to the accident of the prototype at Cazaux, it was not placed to Loire-Nieuport. Only three new prototypes and a sample of tools for the construction of a small series were ordered at the end of December.

Although the LN 161 was once again in the spotlight in the spring of 1938 due to MS 405-406's production delays, the Bloch MB 151 and the Curtiss H-75 were ordered instead and the history of the Nieuport 161 was over. In May 1940, the French Air Force had to fight with outdated aircraft that were far too few in number: 328 operational fighters against Germany (excluding the defense of Paris and the lower Seine Valley, groupement 21), including 196 MS 406s, 99 H-75s and 33 MB 151-152s.


What was the actual performance of the two competitors?



It should be noted that the maximum speed of the MS-406, with the radiator raised, could not be maintained for more than a few minutes (2 minutes according to the testimonies of the pilots of the time) under penalty of burning out the engine. The maximum speed of the LN 161, on the other hand, was continuous.

(1) Official rejection values for serial aircraft. The values vary according to the type of mounted propeller.

(2) The top speed of 480 km/h or sometimes 486 km/h (298 or 302 mph) could be found in various newspapers of this era but does not appear in any official documents.
See Pierre-Yves Hénin's blog (in french):
sam40.fr/le-morane-406-des-handicaps-connus-des-performances-occultees/

(3) With additionnal fuel tank on top of the main one that slowed down the filling.

My Comments

It's obvious that such a huge difference and such a shortcoming compared to the program requirements makes the MS 406's choice simply beyond any understanding. It should be noted that the third prototype of the Nieuport had better performances than the prototype of the famous Dewoitine 520 at the same time (480 km/h in 1938, and a lower rate of climb than LN 161) while having a less powerful engine (860 hp vs 920 hp)! The mere installation of propulsive exhaust pipes on the LN 161-03, as on the D.520 in the spring of 1939, would have given it a speed of more than 510 km/h, enough to hold its own even against the Bf 109E (560 km/h for 5 minutes only, 520 km/h continuous) which also had a lower climb speed; not to mention the switch to a 920 hp engine and the aerodynamic improvements proposed at this time by the Nieuport design team.

In my opinion, the decision to choose the Morane and to reject the Nieuport was based on serious collusion between Morane-Saulnier and the CEMA, or even other high responsible of the AdA or the Air Ministry. Nothing else can explain the lies about the performance of the two aircraft and the systematic denigration of the Nieuport, including during official meetings (Comité du matériel, Conseil supérieur de l'Air). I have no proof of what I am saying, it is simply for me the only plausible explanation of the facts. If you have another one, I'll be happy to hear it.

About the Cazaux accident

Louis Bonte and Jacques Lecarme (in "Histoire des Essais en Vol, Docavia #3") indicate that the origin of the accident would be a stall of a part of the wing induced in certain configurations [of flight, I imagine] by the air outlets of the radiators on the extrados.

Without going into technical details, this is doubtful for several reasons:
- The message informing the minister of the accident specifies: "the accident does not seem to be attributable to the material", not an evidence but to be considered;
- The dive-bomber Loire-Nieuport LN 40-401-411 had the same radiators and was used in operational configurations that were far more challenging than those of the LN 161 (dive-bombing, landing on carrier) without any accident despite being heavier (2,835 kg vs. 2,278 kg fully loaded) with a smaller engine (Hispano-Suiza 12X 690 hp); there is even a photo showing an LN 40 on final approach on the carrier Béarn with one of the wing flaps extended (on the left) and the other not, without apparently causing the slightest problem of stability;
- Michel Detroyat stated in January 1938, during the discussions intended to choose a complementary aircraft to the MS 406: "There is no possible comparison between them [LN 161 and MB 151]: because of its ease of piloting, the Nieuport 161 is the only aircraft likely to be entrusted to the majority of military pilots";
- Despite intensive test in wind tunnel following the crash, the radiators did not evolve on the subsenquent prototypes of the LN 161 whereas this was the case for many other aircraft, including the MS 405-406 and the D.520; the simple fact of moving the outlets from the upper to the lower surface of the wing would have eliminated the problem if such was the case, modifications which are extremely easy to carry out and do not modify the structure of the wing.



LN 40 landing on the carrier Béarn. Note the internal right flap not lowered. Source Clausuchronia.



LN 161 radiator installation diagram. L'Aéronautique - December 1937 - BNF

So, here again, we are most likely in face of a FUD campaign (Fear, Uncertainty, Doubt) to justify and legitimize a posteriori the dismissal of the Nieuport and the choice of the Morane.

Other operational issues of the MS 406

The wing's machine guns freezed at high altitude (above 4,000 m). Even though it's impossible to say the LN 161 would have been immune from it, the constant developpement of this plane should have made it fixed by May 1940 (on the opposite, very few work has been done on the MS 406).

The machine guns mount had some looseness which increased the dispersion of the weapons. And the reflector-sight was subject to vibration (due to its installation out of the cockpit, this having be changed on the last examples of Morane) which made the sighting not very precise. On the opposite, the LN 161 was declared "good shooting platform" in Cazaux.

These points, added to the poor top speed, climbing rate and the overheating was the main criticisms raised by the pilots from September 1939 until the end of fight in June 1940; commandant Maurice Arnoux replied to his superior about MS 406: "Our fighters, but they make us excellent turkey shoot for the enemy!". It is noticeable that the manufacturing of the Morane-Saulnier 406 was stopped in March 1940 even before the Dewoitine 520 production was nominal and despite the dramatic lack of modern fighters. All MS 406 was to be replaced before the end of the year.

LN 161 was considered as a good plane without vice "the only able to be put in hands of all AdA's pilots" (Michel Detroyat famous testing pilot).

Did the Swiss not solve the engine overheating problem in their versions of the Morane?

Why was the reflex gunsight not shock mounted? 

The MAC 1934 tended to seize up at minus 10 Celsius at any atmospheric condition or altitude. The pawl was rather weak and the drum feed was another jam event waiting to happen. In many respects it suffered the same feed faults as the Browning .303 or its American cousin, although the Reibel seems to have operated without the inverted gravity misfeed problems of the British and American machine guns.

Electro-pneumatic gun trigger and drum feed was AdA's technical services requirements in 1935, not Morane-Saulnier's fault.

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General comments on fighter selection and support in an air campaign.


1. The air campaign is an attrition affair. It is not jousting between two aircraft.  The fighter in the air campaign exists to kill bombers and to deny the enemy the use of the air to reconnoiter, bomb and move through the air to harass your own forces below his aircraft while you scout, bomb, strafe and harass his forces, denying him the ability to hide or even move against you in the land or sea campaigns.

2. In regards to 1: the most important aspect of fighter choices for production is quantity, availability, ease of production, pilot use and ground crew maintainability. To take the RAF example of the era, the Spitfire was a far superior technical achievement to the Hurricane, but the key qualities of the Hurricane were that it was easier to make, easier to fly, had a higher availability rate, less intensive ground crew work load was cheap and was good enough, when present  in good numbers to shoot down Dorniers and Heinkels.  The Spitfire was a niche fighter used to chop out the German air superiority fighters at the time. 

3. In reference to 2: the AdA might have used the LN161 and the De520+ series, in a hypothetical France 1940 to chop away the BF 109s, but it would still need numbers of other fighters to go bomber and Stuka hunting. And this gets to the real problems with the French air establishment as it existed.

a. Planes were delivered to frontal aviation units incomplete without radios, gunsights, guns or even essential spare parts for routine flight familiarization and check rides.

b. Air crew were not given sufficient flight hours to learn the quirks of what they had.

c. There was no competent ground observer corps, radar net, ground controlled intercept or AIR STAFF to direct either air attack or air defense in either the immediate battlefield support or battlefield interdiction sense. The RAF had an air defense staff and ground controlled intercept service system with radars, but they did not have any competent trained air staff for tactical air or strategic operations either. About the only air forces who did, were the Japanese and the Republic of China as regards air offense and air campaign but they learned it the hard way from 1937 to 1940. It would be remarkable if anyone else had a clue before a couple of years of learn by failure as the RAF did. 

d. In the critical category of aircraft sortie rates, the Germans were cycling each aircraft in their tactical air campaign once every six to eight hours or about 3 times a day. French air sortie rates were about once per day per available aircraft. This was a ground crews and spare parts problem. Add the difference of 35% French aircraft actual availability as opposed to 70% German as to "paper aircraft on hand" and the numerical odds the AdA faced were not 2 to 1 in air combat. it was more like 6 to 1. The good news for the AdA, what little there was, was that their fighter pilot corps was deadly. They accounted for between 2/3 or 3/4 of Luftwaffe aircraft destroyed in the air campaign via air combat in France 1940 and might have been the difference in the Battle of Britain as the French pilots killed the best of the German bomber crews and may have seriously dented LW mid level in the air leadership thereby.

The point in MS 406 vs LN 161 contest was that the first had too many shortcuts to be a good fighter while the last was promising and the only to meet AdA's requirements.

MS 406 was ordered while not having achieved required top speed. Its climbing rate was disastrous and its ceiling 1,500 m less that requested. And the construction technics (welded tubes) too costly. Albert Caquot made hudge effort to accelerate its production but it still needed at least 50 % more work hours than contemporaries.

On the other side, LN 161 achieved all requirements by 1936 and was better than 1938 D.520 with less powerfull engine. Its successor in late 1938 acheived 545 km/h with the same 12Y 31 860 HP engine! (source: magazine "Avions" # 235 Jul. Aug. 2020; even if it was wrong and the engine was the same as D.520 (12Y 45 920 HP), CAO 200 was far better) LN 161 was designed to be modular and easy to produce (probably even more than D.520).

As Loire-Nieuport had better knowledge and industrial equipment, the LN 161 would have been delivered in production at least six months and probably one year before MS 406, giving all time to equip and train all existing Groupes de Chasse before the outbrake of the war.

There was room to put refloctor gun sight internally as it was done later.

French was in contact with British to implement early watch based on radars. A first room was operationnal in Reims but far less efficient than English one. With the same procedures, one could assume that, under event pressure, it would have quickly improved.

I will read carefully you document "TACTICAL EFFECTIVENESS OF THE FRENCH AIR FORCE DURING THE WAR IN THE WEST" before giveng feedback.