The mysterious Loire 250 fighter (revised the September 15, 2019 *)

The Loire 250 was the second fighter of the 1934 contest to fly in 1935. Today, she remains unknown by most people.

She has done a real perfecting of her flying qualities, and, despite some remnant aerodynamic oddities, she demonstrated really good performances.

Amazingly, she was "forgotten" by the CEMA under the pretext of the nationalizations affecting quite all the French aeronautic industry.

A rather light fighter 

Long of 7.81 m (0.32 m  shorter than the Morane-Saulnier 406), this little fighter weighted 1,700 kg empty and 2,150 à 2,191 kg at take-off with armament (source: L'Aéronautique, November 1936).

The wingspan was 10.80 m and the total wing area was 16.40 m². A front view of the fighter displayed a dihedral layout which already looked like those of the tiny Jodel D9 French sport plane (1948) and,15 years later, the heavy US Navy fighter-bomber McD-D F4 Phantom II. 

Smooth connecting surfaces were fitted to the leading edge of the wings.

The wing loading was 131 kg/m², announcing a good maneuverability.

Personal document of the author -  Front view of the Loire 250 -

The Loire 250 look rather different than most of the bulky contemporary fighters engined by radial air-cooled power plants (e.g. the Polikarpov I 16, the Seversky P 35). 

She belonged to a new and rather slim generation which culminated with the FW 190, the Nakajima Ki 84 Hayate and the Hawker Fury of 1945.

This French fighter used a Hispano-Suiza 14 Ha engine delivering 980 hp.

Initially, the 2 blades fixed pitch wooden air-screw was 2.75 m in diameter.

The fuel tank contained only 330 liters (as discussed below).

The French aeronautical weekly Les Ailes of September 19, 1935 announced the next factory outing of the new Loire fighter: "At LOIRE-NIEUPORT. - One proceeds to the last assemblies  of the new single seat fighter Loire. 

This aircraft is an all-metal low-wing monoplane, fitted with a radial air-cooled Hispano engine, of 1,000 hp. 

The monocoque fuselage is of a great fineness and the streamlining of this fighter is very nice. 

The first flight is expected to be done with Sadi-Lecointe at the controls."

Personal document of the author - From L'Aéronautique, 1936 -
The glassed canopy was a bit too long but announced the one of the Mitsubishi A6 M2

The maiden flight occurred the September 27, 1935, and was reported as follow by les Ailes of the October 03, 1935: "At LOIRE-NIEUPORT.— The new fighter had done her first flights. 

At first, Sadi-Lecointe flew short strait lines, then he have flown long enough. A little after, Nadot had also flown her. 

The impression after these first tests is excellent.

Other flight tests will follow actively under the direction of engineer Asselot, designer of the Loire aircrafts."

This good general impression, while her contender Morane 405 was flying since more than a full month, indicated the Loire was seen too as a good contender for the contest.

The October 10, 1935, the same weekly confirmed the pilots Sadi-Lecointe and Nadot continued to fly with "Some modifications of the aircraft controls have been made on the Loire 250."

The following week, "the Loire fighter - Hispano 14-Ha engine - have done short perfecting flight tests."

The initial look of the Loire 250 fighter likely before the first flight:
The air-screw is a wooden 2 blades fixed pitch one and the landing gear is a fixed one.

The October 24, alone Pierre Nadot tested the fighter.

The November 21, 1935, Les Ailes told us about the Loire fighter: "This fighter fly almost daily with Nadot at the controls."

For the first time after 2 months of flight testing, it appears that something leaves to be desired:  May be the Hispano-Suiza 14-Ha engine was not perfectly reliable or not sufficiently powerful.

Nevertheless, the November 28, 1935, Les Ailes came back on the subject: "The Loire fighter, type 250, Hispano 14-Ha engined, is continuing successfully her perfecting flight tests; This new kind of engine appears to give any satisfaction to the pilots."

The December 12, 1935, "Surtel and Nadot flew the Loire 250. The fighter will be modified, the engine is disassembled."

From December 20, 1935 to January 5, 1936, despite a very bad weather, Les Ailes of the January 9, 1936, wrote about a lot of work about the two prototypes of fighters manufactured by Loire-Nieuport. "Nadot had flown numerous tests with the fighter Loire 250."

The January 10, 1936, despite “a forceful storm” (which involved the territories of Great Britain, France, Belgium and Germany, killing 16 British people and 2 German ones), the Loire 250 displayed a full demonstration of all the aerobatic maneuvers, like do also her 2 contenders, the Morane 405 and the Nieuport 161. 

Amazingly, the February 2^th, 1936, Les Ailes published a complete article on the Loire 250. 

Some of the published data were inaccurate, as the empty weight (1,500 kg) and the weight at take-off (2,000 kg).

The dimensions were good but the performances were theoretical:

• The top speed was 485 kph;

• The climbing time to 5,000 m will be inferior to 5 minutes.

One may read another climb time later, likely related to an increase of the take-off weight.

The weekly Les Ailes told us about the Loire fighter the March 12, 1936. 
After a brief stay in factory, the test flights were resumed: "The Loire 250 his now fitted with her definitive Hispano 14-Ha engine, which had no reduction gear box. The pilot Nadot flew several flights with this fighter."

The Avril 2, 1936, the reporter of Les Ailes wrote: "Always numerous flight tests with the two recent fighters, Loire 250 and Nieuport 161, respectively by Nadot and by Lefèvre.

The perfecting of these two aircrafts is rather complete, both will soon enter the CEMA.
They will be formidable contenders for the Morane 405."

Such a commentary demonstrated the Morane 405 appeared no more as the favorite of the French fighter contest for competent and independent spotters.

Two weeks later, Les Ailes insisted again about numerous perfecting flights done by Nadot with the Loire 250.

The following week, we learned the Loire 250 was testing a variable pitch air-screw.

During May 1936, the reporters became silent about the fighter prototypes, one of the sad consequences of the huge Front Populaire strikes.

The June 18, 1936, Les Ailes told us : "Numerous tests flights of Lefèvre [...] with the new Loire 250 fighter which have got a variable pitch Hamilton air-screw." 

The July 30, we can read: "The Loire 250, with a Hispano 14-Ha engine, received modifications for some of her fairings." 

The August 6, Les Ailes wrote: "Lefèbvre carried out tests with the new Loire fighter, Hispano 14-Ha engine fitted with the new variable pitch air-screw; The enter to CEMA would be occur soon." 

The September 3^th, 1936, les Ailes reported the Loire 250 continued to fly, but Surtel succeeded to Lefèbvre at her controls (Lefèbvre was more associated to the Nieuport 161 fighter).

Original document of the author, from L’Aéronautique 1936 - The Loire 250 in her last configuration. The cockpit canopy was too long, the engine cowling was too large, the streamlining of the engine cowling was inexistant and the exhaust pipes were not well designed: That "costed" circa 50 kph!

The November 5^th, the fighter was at the ultimate finishing stage in the factory.

At the Paris Air Show, in November 1936, the Loire fighter was exposed on her stand.

The British weekly Flight of the November 19, 1936, dedicated to the Paris Air Show, reported, after some laudatory words about the tiny Mureaux 190 fighter:

"Two larger, heavier and higher powered machines in the 300 mph category are the Loire-Nieuport 250 and the Morane-Saulnier 405.

(…)

The Loire is fitted with one of the new Hispano-Suiza 14 Ha two-row fourteen-cylinders radial of 980 hp and is a low-wing cantilever monoplane with a wing of peculiar formation.

The center section is proportionately wider than usual and is given no dihedral, this being reserved for the outer panels.

The undercarriage retracts in an inward sense into the wing which carries trailing-edge flaps designed to keep the landing speed down to 62 mph in spite of the wing loading of over 30 lb/sq.ft. [sic!].

The fuselage behind the big Hispano radial is of circular section as far back as the pilot's cockpit thence developing an oval section.

The cockpit enclosure is of more than usual interest because its tail fairing is quite transparent to improve the field of view.

Full night-flying gear is specified, together with two-way wireless, two canons mounted in the wings and two machine guns.

A three-bladed Hispano-Suiza air-screw is fitted, being a Hamilton type built under license in France. 
In round figures the maximum speed is given as 300 mph and the time of climb to 13,120 ft as five minutes."  

Original document of the author - The Loire 250 at the Paris Air Show, hiding the already obsolete Loire 46 fighter, which just entered service

The November 22, 1937, Les Ailes commented as follow the présentation of this aircraft: 
"The look of the Loire 250 fighter is striking for any spotter. 
She is one typical example of the aerodynamic improvements obtained through the research on the interactions between the diverse parts of the aircraft.

The connecting surfaces between these parts were thoroughly designed and, if the one between the trailing edge of the wings and the fuselage (= Karman) meets our requirements, we were particularly interested by the sophisticated “fore Karman”, connecting the NACA engine cowling to the wings to make the landing speed slower.

This new feature has been proved experimentally in the wind-tunnel at slow speed, and, after, by about twenty hours of flight testing.

The Loire-Nieuport 250 is a single-seat fighter which fulfill the 1934 program of the French “Armée de l'Air”. 

Having an integral metal structure and taking advantage of the cantilever low-wing layout, she had balanced control surfaces thoroughly designed to avoid all kinds of hazards associated to great speed.

Following the altitudes, this fighter top speeds are:
                   395 kph [at sea level], 
                   480 kph (at 4,500 m) and 
                   450 kph at the service ceiling of 10,000 m.”

The last mention of the Loire 250 fighter by Les Ailes was published May 6, 1937:

"The LOIRE-250 was to begin her official trials when her manufacturer was nationalized.

This prototype, using a Hispano-Suiza 14-Ha engine delivering 980 hp, was exhibited at the last Paris Air Show.

She is flying since eighteen months and her perfecting is fully completed.

…

She is now in a hangar of the Villacoublay airbase, ready to demonstrate the controlled flight performances in order to obtain useful data on the value of the Loire 250, as want the designers of this fighter.

The Loire-250 was designed for the French program of the single-seat fighters of 1934 and, soon, we will got the prototypes for the program of 1936. 

Fitted with very similar engines, but beneficiaries of new aerodynamic assets, one expect they will easily exceed the wall of 500 kph."

What a beautiful example of diplomatic synthesis!

The French Aeronautic Press in 1937 experienced a very different life than the previous year: Her liberty was no more sacred facing the CGT unionists and the political orders. 

Pierre Cot and his favorites were deciding everything. A frontal opposition would be very dangerous, as quite always in the 1937 Europe. 

Highlighting the Loire 250 was really perfected, the columnist informed us this fighter was actually perfectly stable. 

Telling us the Loire designers were asking controlled performances, he inform us that this fighter outperformed the Morane 405 (as also the MS 406, this last designation being applied for an identical aircraft using an identical engine).

The Loire 250 outperformed the Bloch 150 too, which has just first flown in May 1937 with very poor performances.

None of the MB 150, 151 and 152 reached really better performances than the Loire fighter before 1940. The Bloch 15x were perfected only at the final part of the MB 152 series, and with the MB 155.

The performances

They were published by L'Aéronautique, for the Paris Air show of November 1936:

• 395 kph at sea level,

• 435 kph at 2,500 m, altitude reached in 3 minutes

• 480 kph at 4,500 m,      "          "             5' 30"

• 470 kph at 6,000 m,      "          "             7' 40"

• 450 kph at 8,000 m,      "          "           12 minutes

The landing speed was 100 km/h.

These values appeared very close to those of her Nieuport 161 stablemate.

The same data were given by other sources but L'Aéronautique was alone to suggest they resulted from a mathematical correction taking into account the expected power of the 14 Ha engine (which was not given but may be ranging from 1050 to 1120 hp).

Simple reverse calculations allows us to obtain measured top speed of the Loire 250: From c460 kph to c475 kph at 4,500 m. 

Such top speeds appear, today, as rather slow. But one may remind:

• The Brewster Buffalo XF2 A-1 did not exceed 447 kph during the Navy early trials in 1938 (a complete work was done to obtain good performances).

• The Grumman XF4F-2 was limited to 468 kph at the same time. 

• With regard to the Bloch MB 150 M, she was then flying at only 434 kph, like the Morane 405 of 1936 (in Louis Bonte, Histoire des Essais en Vol, Docavia # 3). The Bloch was intensively perfected, not the Morane before the very late (5 years) MS 410, in April 1940...

This suggestion of a recalculation seems not clear at all. 

As she was, the Loire 250 fighter was not a dirty plane, aerodynamically speaking: 

• Her wings displayed not the excess of relative thickness seen in the Hawker Henley (or in the Hurricane Mk I). 

• The fuselage appeared rather streamlined so a top speed of 485 kph at 4,500 m was likely.

Nevertheless, if we remember the political situation of the 1936 France, one understand it was difficult for the Air Minister Pierre Cot to order the Morane-Saulnier 405 / 406 - with, actually, a real top speed of 435 kph - when a radial engined fighter was able to fly at 485 kph.

Moreover, these performances were obtained by the Loire 250 in an aerodynamic configuration still suffering from a non-optimal aerodynamic configuration:

• The NACA cowling was very basic, worse than the one of Bloch MB 151 (of 1939) and MB 152 using the huge one meter in diameter cooling air intake.

• The exhaust pipes were not facing backward.

• And many other parasitic drag generators.

These shortcomings reduced the top speed from at least 40 to 50 kph.

{Parenthesis: The Hispano-Suiza 14 Ha or AA was the origin of some controversies:

 I – This engine appeared in Les Ailes of January 18, 1934, as a 900 hp engine in the first perfecting stage. 

Hispano-Suiza wanted a new and more powerful engine partly using the technology of the Wright radial air-cooled 9 cylinders.

The first tests were reported by Les Ailes of the February 1^st, 1934: The 14 Ha engine delivered 960 hp at 1750 rpm. It was said also to be 1.20 m in diameter. 

II – As far as I know, the first flight test of the 14 Ha was in September 1935, with the Loire 250. 

Initially, it used only of 100 octane fuel, identical to the one used by the Air-France company. 

As no comment was done, it appears logically this engine experienced no insurmountable problem. 

The performances being promising, not surprisingly, the Loire fighter had flown dozens of flight hours from 1935 to 1936.

III – The story of this engine became completely different in 1937 with Jacques Lecarme, an engineer- test pilot, and his friend Louis Bonte, when a lot of problems occurred with the bomber Lioré-Olivier 45.

The first flights of the LéO 45 have been found excellent, with the same Hispano-Suiza 14 Ha engines, especially the flying qualities were seen as flawless. 

For these test flights, this bomber was devoid of any fairing for the legs of the landing gear.

Unfortunately, later, right after the assembly of the landing gear fairings, the LéO 45 became vicious during the take-off: The new fairing were masking the two rudders during the first part of the run. 
But this important issue was aggravated by the very forward position where the landing gear was positioned: The bomber got out of hand... 

This problem could have been fixed by replacing the classical landing gear by a tricycle one...  

Thereby, the flight testing must take more time to fix this purely aerodynamic but unexpected issue.

It never rains but it pours, during a calibration test at low altitude – the engines running full out while they were using the 87 grade of octane – the crankshafts of the two engines broken simultaneously at Saclay (10 km of Paris).

Fortunately for the crews, as also for the bomber, due to the flat landscape of the Saclay plateau, the external temperature rather cold and the exceptional skill of the test pilot (Doumerc), no other issue occurred.

The HS 14 Ha have not supported to run so fast for a so long duration with a so "bad" fuel.

Quite identical mishaps were experienced by Rolls-Royce at the very beginning of the Merlin engine (which was fixed by a lot of work) and, after, by the Peregrine engine which was discontinued, downing the excellent Whirlwind twin-engined fighter.

If Lecarme (in Louis Bonte, Histoire des essais en vol, Docavia #3) acknowledged that, “somehow miraculously”, no issue was following after fitting generous oil radiators, he attributed only to the Hispano engine the excessive delay of perfecting the LéO 45.

So, the French Air Ministry directed Lioré & Olivier to stop any further aerodynamic investigation on the take-off stability and to proceed directly to the mass production of the LéO 451 using only Gnome & Rhône 14 N engines.

That order had lethal consequences…

IV – From the other hand, the Koolhoven FK 58 fighter prototype, using the radial air-cooled Hispano 14 Ha - renamed 14 AA - took off for her maiden flight mi-Juillet 1938, and was able to exceed 500 kph.

This engine was a new variant, more powerful (1080 hp) with an important increase of the cooling surfaces and using Sarrazin dampers.

The French government ordered several dozens of FK 58 fighters but imposed the GR 14 N engines. These new FK 58 was 30 kph slower than the prototype and have got no victory... 

V - The Latécoère company designed the Laté 570, a B4 bomber, which was conceived to use of the new Gnome & Rhône 18 L delivering 1350 hp.

The first flight of this excellent bomber was delayed for almost 2 years by the enticement of workers by CGT unionists who wanted to punish Mr. Latécoère to have not accepted the nationalization of his plant!

Only the Hispano-Suiza 14 AA engines, with their actual bad reputation, were available.

Amazingly, these rejected engines ran very well.

The Laté 570 was exceptionally easy to fly, able of very tight maneuvers, achieving 470 kph à 5,000 m. This powerful bomber was able to deliver 2,000 kg of bombes, a bomb load 700 kg heavier than the one of the LéO 451.}

  

The Loire 250: A bad fighter?

Absolutely not.

Amazingly, the Loire 250 was never accepted by the CEMA which preferred, later, the Bloch 150 M (alias MB 151) or le Curtiss H 75, which had lower performances until 1939.

The Loire air-screw was 2.75 m in diameter. In 1939, the Bloch 152 used an air-screw of 2.90 m in diameter. 

That was the consequence of the bad idea of using an engine devoid of reduction gear box (such a conception forbade any full out dive...). 

Also, a too little air-screw reduce the speed capabilities of an aircraft…

In the literature, we have read the deciders of the Loire-Nieuport company preferred clearly the Nieuport 161 fighter to the Loire 250 one.

But, the Nieuport was involved in a lethal crash (she was not responsible at all, as I explained) and the Loire not experienced problem: One would have expected a more open mind of the test pilots and deciders.

The Loire 250 have flown without accident for 18 month, so she may not be seen as dangerous.

Assuming the minimal hypothesis for her performances, anyway, the Loire fighter of 1936 was 30 kph faster than the Bloch 150 M of 1937.

Moreover, the relatively low wing loading of the Loire 250 (131 kg/m²) provided her a clearly better maneuverability than those of the Bloch 152 (156 kg/m²).

The Loire 250 for the French Navy carriers? Yes, a wasted chance…

In 1936, the French Aéronavale used, on the Béarn aircraft carrier only some Wibault 74 fighter (top speed 230 kph). 

All other major navies used fighters that can fly at least 100 kph faster (like the Royal Navy, with its Gladiator ;-), or worst, when using the Skua or... the Roc!).

In place of choosing the best adaptable fighters among the French more recent prototypes, the French Navy ordered a fighter belonging to the previous generation.

That was the Dewoitine 376 (in fact, it was a product of Lioré & Olivier deciders in order to squeeze the Emile Dewoitine leadership). This already obsolete fighter was said to fly over 405 kph but she never reached the 380 kph of the terrestrial D 371 prototype (source: Les avions Dewoitine, Cuny & Danel, Docavia). 

OK, these fighters were maneuverable and climbed well but the association of a bad air-screw with a not well balanced crankshaft induced numerous (and tremendous) vibrations which themselves induced frequent engine failures and, even, structural destructions...

Simultaneously, a new contest was launched by the French Navy, in 1938, to obtain a fighter for the 2 new aircrafts carriers Joffre and Painlevé. The favorite contender, the Dewoitine 790, issued from the D 520 with a larger wing, was initially scheduled to fly only in the spring of 1941!

A real naval tactician should have chosen, as soon as possible, in 1936, the most appropriate fighter among the existing prototypes of the 1934 French fighter contest.

The Loire 250 was already particularly suitable to be used on board of the Béarn aircraft carrier:

• She was already able to land at 100 kph (62 mph).

• She occupied, on the ground and without folding the wings, the relatively little surface of 84 m², about 80 % of the surface occupied by most of her potential opponent or contenders, allowing a significant fighter covering of the French fleet.

• She had better performances than most of her potential opponents.

• With such a fighter, the Béarn would became a dreadful capital ship, the Loire 250  being able to carry bombs for dive bombing.

• The armament would be constituted by:
• Either 2 HS 404 guns of 20 mm and two 7.5 mm Darne belt-fed machine guns with 600 cartridges each;
• Or four 7.5 mm Darne belt-fed machine guns with 600 cartridges each.

One may argue the fuel tank was very insufficient for a naval aircraft.  

The real fuel consumption, for one hour full out with the 1080 hp variant, was 359 liters, exceeding the fuel tank capacity by 30 liters, theoretically allowing just 55’ of flight.

So, a completely different possibility deserve to be analyzed: Using a significantly lighter and thinner engine even it delivered significantly less power.

This lighter fighter variant would have been interesting, using one of the two tiny 700 hp radial air-cooled engines designed by Gnome & Rhône (14 Mars) or by Hispano-Suiza (14 AB).

The first light engine to be ready was the Hispano 14 AB which weighted 490 kg instead of 647 kg for the HS 14 Ha and its diameter was only 1.01 m.

With this engine at maximum power, the 14 AB powered "light" Loire 250 fighter would have flown during 1 hour and 33 minutes.

The second engine was the Gnome & Rhône 14 Mars weighted 410 kg and had diameter of only 0.95 m. 

At maximum power, the 14 Mars powered "light" Loire 250 would be able to fly 1 hour and 42 minutes.

OK, the loss of power would induce mechanically the loss of 40 to 70 kph (from 415 to 440 kph following the chosen engine).

However, one may rectify these results because these calculations don’t take into account some other data, among them the reduced diameter of these engines, which allows a gain of about 40% of the engine cowling section.

In such a case, one may expect a gain of about 20 kph (from 435 to 460 kph). Such fighters would have been at least as efficient than the Fokker D XXI of the Netherlands Air Force.

Supplementary aerodynamic works should give supplementary gains totaling about 30 kph, (allowing a top speed ranging from 465 kph to 490 kph).

Two years later, the conversion to the 100 octane fuel will increase the power to 800 hp, allowing a new 20 kph step, (allowing a top speed ranging from 485 kph to 510 kph).