Arado Ar 80

L'Ar 80 sur Wikipedia en langue française :


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L'Arado Ar 80 est un avion de chasse expérimental allemand de l'[Vous devez être inscrit et connecté pour voir ce lien].


Les premiers [Vous devez être inscrit et connecté pour voir ce lien] n’étaient pas encore sortis d’usine lorsqu’en février 1934 le [Vous devez être inscrit et connecté pour voir ce lien] émit un nouveau cahier des charges pour un chasseur devant atteindre les 450 km/h ; aucun moteur de plus de 700 ch n’étant disponible en [Vous devez être inscrit et connecté pour voir ce lien], l’accent fut mis sur l’aérodynamique et le gain de poids.

Parmi les quatre constructeurs consultés le plus handicapé était [Vous devez être inscrit et connecté pour voir ce lien], à qui il était curieusement notifié de réaliser un appareil à train d’atterrissage fixe, les trains d’atterrissage escamotables n’étant pas considérés comme fiables.

Mais cette décision, qui condamnait d’avance le prototype Arado, ne fut pas seule à l’origine de l’échec de l’ingénieur Walter Blume face aux [Vous devez être inscrit et connecté pour voir ce lien] de [Vous devez être inscrit et connecté pour voir ce lien],[Vous devez être inscrit et connecté pour voir ce lien] et même [Vous devez être inscrit et connecté pour voir ce lien].

L’appareil était en effet réalisé en tubes d’acier soudés avec revêtement en aluminium riveté, une technique qui augmentait de près de 16% le poids de la cellule.

Elégant monoplan à aile basse en W très aplati, le prototype Ar 80 V1 (D-IRLI) fut expérimenté en octobre 1935 à Travemünde avec un moteur [Vous devez être inscrit et connecté pour voir ce lien] Kestrel V developpant 812 ch au décollage et 695 ch en régime continu, aucun
Jumo 210, moteur prévu à l’origine, n’étant disponible.

Le prototype fut, comble de malchance, perdu sur accident.

Le moteur Kestrel fut cependant récupéré et monté sur un second prototype, Ar 80 V2 (D-ILOH), jusqu’à pouvoir enfin disposer d’un moteur Jumo 210Ca développant à peine 695 ch au décollage.

En 1937 apparut l’Ar 80 V3 (D-IPBN), machine profondément modifiée avec une aile à dièdre simple pour gagner du poids.

Curieusement devenu biplace, ce chasseur atteignait tout de même 410 km/h.

La [Vous devez être inscrit et connecté pour voir ce lien] avait alors abandonné depuis longtemps ce programme, mais Arado persista avec deux autres prototypes qui permirent au constructeur d’effectuer des essais divers :

L’Ar 80 V4 reçut un moteur Jumo 210Ga à injection et fut équipé d’un poste de pilotage fermé, et l’Ar 80 V5 fut le premier chasseur allemand à recevoir un canon MG FF de 20 mm tirant à travers le moyeu de l’hélice.

Après essais à Rechlin et au centre d’armement de Tarnewitz, il fut affecté à la défense de l’usine [Vous devez être inscrit et connecté pour voir ce lien] à Warnemünde.

Notons enfin que Walter Blume proposa en vain au [Vous devez être inscrit et connecté pour voir ce lien] une version à train escamotable et Jumo 210Ea.

Références

• W. Green & G. Swanborough, Le grand livre des chasseurs. Cliv Paris (1997). [Vous devez être inscrit et connecté pour voir ce lien]
  
• J.R. Smith et Antony L. Kay, German Aircraft of the Second World War. Putnam, London (1972). ISBN
  0-85177-836-4.
  

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[Vous devez être inscrit et connecté pour voir ce lien]

The Arado Ar 80 was a pre-[Vous devez être inscrit et connecté pour voir ce lien], designed by [Vous devez être inscrit et connecté pour voir ce lien] to compete for the [Vous devez être inscrit et connecté pour voir ce lien]'s first major fighter contract.

The Ar 80 was uninspiring in terms of performance and also suffered a number of failures.

The contest was eventually won by the [Vous devez être inscrit et connecté pour voir ce lien], and the Ar 80 [Vous devez être inscrit et connecté pour voir ce lien] ended their days as test aircraft.


Design and development


With the [Vous devez être inscrit et connecté pour voir ce lien] rise to power in February 1933, a plan was put into place to dramatically expand the Luftwaffe.

The new and highly-political[Vous devez être inscrit et connecté pour voir ce lien] (RLM) demanded that the large industrial firms cooperate, keeping construction as secret as possible.

Arado Flugzeugwerke, under the direction of Erich Serno and Felix Wagenführ, largely stopped being an designer of aircraft and increasingly became a production facility for other companies.

However, the company had just completed the [Vous devez être inscrit et connecté pour voir ce lien] fighter.

Several orders were placed for the Ar 65, and a follow-on [Vous devez être inscrit et connecté pour voir ce lien] model.

This made Arado one of the few companies with actual fighter design experience, and they were considered
for future developments

During 1933, the Technisches Amt, the technical department of the RLM, concluded a series of research projects into the future of air combat.

One of these was Rüstungsflugzeug IV for an all-metal [Vous devez être inscrit et connecté pour voir ce lien] single-seat [Vous devez être inscrit et connecté pour voir ce lien], replacing the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] then in service.

The plane needed to have a top speed of 400 km/h (250 mph) at 6,000 m (19,590 ft) which it could maintain for 20 minutes, while staying in the air for a total of 90 minutes. It was to be powered by the new [Vous devez être inscrit et connecté pour voir ce lien] engine.

It also needed to be armed with at least three [Vous devez être inscrit et connecté pour voir ce lien] with 1,000 rounds each, or one 20 mm[Vous devez être inscrit et connecté pour voir ce lien] with 200 rounds.

The plane needed to keep [Vous devez être inscrit et connecté pour voir ce lien] below 100 kg/m², which is a way of defining its ability to turn and climb.

The priorities for the plane were level speed, [Vous devez être inscrit et connecté pour voir ce lien], and maneuverability, in that order. [Vous devez être inscrit et connecté pour voir ce lien] sent out a letter in October 1933 asking for a "high speed courier aircraft" in order to start the work, and in May 1934, the actual R-IV request was sent out and made official.

In addition to Heinkel and Arado, [Vous devez être inscrit et connecté pour voir ce lien], and [Vous devez être inscrit et connecté pour voir ce lien] competed. They had to deliver three
prototypes for head-to-head testing in late 1934.

Although Blume was officially the director of design at Arado, it was Rethel who did most of the early work on the design. Rethel was well aware of the advantages and disadvantages of the [Vous devez être inscrit et connecté pour voir ce lien] technique, but the company had never built such a design and was thus at a distinct disadvantage in relation to Heinkel who had used it on their [Vous devez être inscrit et connecté pour voir ce lien] Blitz design from 1932.

However he felt that he could not only design a successful monocoque aircraft, but in fact make one that was both lighter and easier to build than the techniques being used at other companies.

His solution was to use two sets of skinning plates formed in long strips running front to back along the plane.

The first set of plates was formed roughly into the shape of a C, which a small flange at the open ends of the C where they could be easily riveted to the hoop bulkheads.

Using this system he was able to eliminate one more piece of internal structure, the stringers that would normally run between the bulkheads.

He used a second set of sheets that were flat, so they could easily bend front-to-back.

They were cut into teardrop shapes, which exactly fit into the gaps between the main [Vous devez être inscrit et connecté pour voir ce lien].

Not only did this system allow for the "perfect" aerodynamic shape, but in theory it was also lighter and easier to build.

The system looked so hopeful that other parts of the aircraft's design were allowed to be heavier and less risky as the weight savings in the [Vous devez être inscrit et connecté pour voir ce lien] should compensate.

The rest of the plane was conventional.

The forward fuselage and inner wings were formed up from steel tubing with removable [Vous devez être inscrit et connecté pour voir ce lien] sheeting over it, the outer wings were aluminium formers and skinned with aluminium on top and fabric on the bottom.

Like the Heinkel designs, the wing included a reverse-gull bend to shorten the [Vous devez être inscrit et connecté pour voir ce lien] legs, but unlike the Heinkel it was almost straight on the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] instead of the more complex [Vous devez être inscrit et connecté pour voir ce lien] planform favoured by the Günter brothers.

In order to avoid cutting the outer wing formers with outward retracting gear, Rether decided to have the landing gear retract directly to the rear.

To lie flat, the wheel would have to be rotated through 90° as it retracted.

To do this, he put the main oleo strut inside a larger tube that was mounted to the pivot point on the lower leading
edge of the box-[Vous devez être inscrit et connecté pour voir ce lien].

As the gear retracted a small arm would pull on a lever mounted to the oleo, turning the leg inside the larger tube.

Prototypes and testing


The design, now known as the Ar 80, was completed without the aid of Rethel; he left the company in 1934 to join BFW leaving Blume in charge of the project.

The plane was designed to mount the Jumo 210 engine, driving a wooden two-blade fixed-pitch propeller.

However, this engine was not going to be ready until the contest was supposed to be over, so all of the contestants looked for other engines to fill the hole.

In this case Arado proved to have the advantage, as they had already purchased a 391 kW (525 hp) Rolls-Royce
Kestrel VI engine for use on their [Vous devez être inscrit et connecté pour voir ce lien] design.

The engine had less than optimal [Vous devez être inscrit et connecté pour voir ce lien] which led to poor performance for the Ar 67.

The V1 prototype first took to the air in the spring of 1935, one of the first of the planes in the contest to do so.

However, one of the company test pilots lost control at low altitude only weeks later, and V1 was written off.

The landing gear had already proven to be a real problem in these few short weeks.

It continued to stick half-closed when retracted, although luckily it returned to the down position for landing.

Repeated attempts to find the problem were fruitless, when they put the plane on blocks in the [Vous devez être inscrit et connecté pour voir ce lien] it would always work flawlessly.

Eventually it was found that the air pressure on the front of the strut in flight made the oleo jam in its tube so it couldn't rotate.

Another problem discovered during construction of the V1 was that Rethel's monocoque technique in fact turned out to be much heavier than expected. Some of this was a problem in the actual design; since the sheets ran the length of the plane, they had to be as thick as the thickest point on the entire plane.

More traditional designs could use lighter or heavier gauges in various places.

The main problem, however, was that the design required considerably more rivets than expected, and as a result the plane was overweight.

La mitrailleuse MG 17 :


[Vous devez être inscrit et connecté pour voir cette image]

V2 was rushed to completion but the Jumo was still unavailable.

In order to give the contestants some sort of realistic engine, the RLM had traded Rolls-Royce an He 70 for four
518 kW (695 hp) Kestrel V engines.

Although the V was the same basic engine as the VI, it had much better supercharging and was in fact the most
powerful inline engine of the day.

The various companies competed heavily for access to these engines for their prototypes.

Perhaps some idea of the future outcome can be seen in the fact that BFW received two, Arado and Heinkel one each, and Focke-Wulf none at all.

V2 was completed with the Kestrel by autumn of 1937, and started company testing.

Once again the gear proved to be a problem.

Blume immediately blamed all of the problems on Rethel, after noting that he was always skeptical of the design.

He decided that the performance problems of having fixed gear would be offset by its lighter weight, and the Ar 80 then reverted to using a well-[Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien] set of gear similar to those used on their various biplane designs. Several months were lost in the conversion.

Un RR Kestrel

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The use of the fixed gear didn't save as much weight as expected and the plane was still 16% over the design weight at 1,630 kg (3,590 lb) empty.

Fully loaded the plane was 2,100 kg (4,630 lb) even without armament, which made it underpowered even with the Kestrel V.

Drag was also higher than expected. It's no surprise then that the plane proved to have very disappointing performance, reaching only 410 km/h (255 mph).

In early 1936, the Jumo engines finally arrived.

The 210 had even less takeoff power than the Kestrel, but its altitude performance was comparable.

Speed did increase with this engine at higher altitudes, but low-level speed and climb performance both dropped. Arado argued that the fitting of a [Vous devez être inscrit et connecté pour voir ce lien] would boost both, with the speed climbing to 425 km/h (264 mph), but this was not attempted before the plane was sent off to the contest.

Un Junkers Jumo 210 :

[Vous devez être inscrit et connecté pour voir cette image]

Although the Ar 80 had been one of the first planes to fly, the continued problems with the gear and engine supply meant it was one of the last to arrive for the head-to-head fly-off.

It was delivered to Travëmunde on 8 February 1936, and later moved to meet the rest of the planes at Rechlin-Lärz
Airfield in March.

It was clear all along that the plane had no chance against the Heinkel and BFW designs, a fact that Arado was made officially aware of after only one month.

By this point, V3 was already finished. In order to try to save weight, the design had removed the gull-wing and replaced it with a "flat" one, requiring slightly longer gear legs.

It also mounted the Jumo 210C with the constant-speed propeller, which boosted speed to 410 km/h (255 mph).

By this time, the RLM had already given up on the design, so the plane was not sent for testing and instead hangared at the Arado plant.

In 1937, the V3 was resurrected as a flying testbed for several experiments.

It was fitted with a second seat behind the pilot for an observer, and also added an enclosed [Vous devez être inscrit et connecté pour voir ce lien].

The plane was first used for testing a 20 mm cannon firing through the spinner, making it the first German cannon-armed fighter.

This system, called the "motorkanone", would become a standard feature of most designs.