Arado Ar 80
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The Arado Ar 80 was a pre-World War II fighter aircraft design by Arado Flugzeugwerke, designed to compete for the Luftwaffe's first fighter contract. The Ar 80 was both uninspiring in terms of performance and also suffered a number of failures. The contest was eventually won by the Messerschmitt Bf 109 for good reason, and he Ar 80 prototypes ended their days as test aircraft.
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Background
In 1931 Albatros Flugzeugwerke, the famous WWI aircraft manufacturer, declared bankruptcy after trying to stay solvent during the depression and following German hyperinflationary period. Worried about the loss of one of the few long-term design teams, the Reichswehr stepped in and broke the company up into parts. Much of the company was merged with Focke-Wulf under the leadership of Kurt Tank, while several of the designers and technical managers were sent to Arado.
Arado Handels-Gessellschaft, as it was then known, was forced to take Walter Blume as their new chief designer, replacing long-time lead Walter Rethel. Blume was a former WWI pilot with 28 kills and winner of the Pour le Mérite, although his design credentials were not quite as impressive. Although the company directors were upset with being forced to take on Blume (and other associates) they also realized that he was well liked within the Reichswehr and that his placement made future contracts much more likely.
At about this point in time Heinrich Lübbe, the current owner, felt that he was about to lose control of the company. In November 1932 he withdrew a large amount of capital. In fact this guaranteed he would lose control of the company, as the Reichswehr became highly suspicious of the company and ordered an audit.
With the Nazi rise to power in February 1933, a plan was put into place to dramatically increase the size of the Luftwaffe, first to 225 fighters by April 1934, and then to 450 a year later. The new and highly-political Reichsluftfahrtministerium (RLM) demanded that the large industrial firms play along with the plans, keeping construction as secret as possible.
Arado was still considered to be somewhat suspect, and the RLM effectively ordered the company to re-form. On March 4th they became Arado Flugzeuwerke, under the direction of Erich Serno and Felix Wagenführ. This marks the point when Arado stopped being its own company and increasingly became a production facility for other companies.
At the time, however, the company had just completed the Ar 65 biplane fighter under the direction of Walter Rethel. The plane was the best of the conteporary designs and several orders were placed for the Ar 65, and a follow-on Ar 68 model. This made Arado one of the few companies with actual fighter design experience, and they were naturally consulted for future efforts.
Contest History
(this section is boilerplate included in all articles on the 1935 contest)
During 1933 the Technisches Amt (the technical department of the RLM, or T-Amt) concluded a series of research projects into the future of air combat. The result of the studies were four broad outlines for future aircraft:
- Rüstungsflugzeug I for a multi-place medium bomber
- Rüstungsflugzeug II for a tactical bomber
- Rüstungsflugzeug III for a two-place heavy fighter
- Rüstungsflugzeug IV for a single-place fighter
The Rüstungsflugzeug IV was intended to be an all-metal monoplane single seat fighter aircraft, or interceptor actually, replacing the Arado Ar 64 and Heinkel He 60 biplanes then in service. While it was intended the R-IV aircraft would beat all others then flying, the requirements were nevertheless not terribly hard to meet.
The plane needed to have a top speed of 400 km/h at 6000 m (250 mph at 19,500 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 Junkers Jumo 210 engine. It also needed to be armed with at least three machine guns with 1000 rounds each, or one 20 mm cannon with 200 rounds. One other interesting specification was that the plane needed to keep wing loading below 100kg/m², which is a way of defining the plane's ability to turn and climb. The priorities for the plane were level speed, climb speed, and then maneuverability (in that order).
In fact the R-IV specifications were not really thought up inside the T-Amt at all. In early 1933 both Heinkel and Arado had sent in privately-funded designs for a monoplane fighter, and the T-Amt simply collected the best features from both and sent them back out again. Hermann Göring 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, the R-IV specifications were sent to Focke-Wulf. Each were asked to deliver three prototypes to be delivered for head-to-head testing in later 1934. A few months later Bayerische Flugzeugwerk (Bavarian Aircraft Manufacturers, or BFW) started flying their Bf 108 design that was built to the original "sports aircraft" request. The 108 was an advanced design, and on its strengths the R-IV tender was oftered to them as well.
Development history
Although Blume was officially the director of design, it was Rethel who did most of the early work on the design. Rethel was well aware of the advantages and disadvantages of the monocoque technique, but the company had never built such a design and was thus at a distinct disadvantage in relation to Heinkel who had been using it on their He 70 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 rivetted 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.
If you imagine long parallel sheets rivetted to a cigar-shaped surface, you'll see that the space between them gets smaller and smaller as you approach the tip. To fill out this gap 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 stringers.
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, the weight savings in the fuselage should more than make up for it.
The rest of the plane was rather conventional. The forward fuselage and inner wings were formed up from steel tubing with removable aluminum sheeting over it, the outer wings were aluminum formers and skinned with aluminum on top and fabric on the bottom. Like the Heinkel designs the wing included a reverse-gull bend to shorten the landing gear legs, but unlike the Heinkel it was almost straight on the leading and trailing edges instead of the more complex eliptical 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 degrees 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-spar. As the gear retracted a small arm would pull on a lever mounted to the oleo, turning the leg inside the larger tube.
In general terms the resulting design was very similar to the Hawker Hurricane of roughly the same era. Both planes would be considered "interim" designs by everyone involved. With the power of the Rolls-Royce Merlin the Hurricane would go on the be a valuable design for the early part of the war, but with the indifferent German engines, the Ar 80 would prove less lucky.
Prototypes
The design, now known as the Ar 80, was completed without the aid of Rethel. In 1934 he left the company to join BFW. This left Blume in charge of the project.
The plane was designed to mount the Jumo 210 engine, driving a wooden two-blade fixed-pitch prop. 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 525hp Rolls Royce Kestrel VI engine for use on their Ar 67 design. The engine had less than optimal supercharging which led to poor performance for the Ar 67, but it would at least have the plane in the air while they waited for the Jumos to arrive.
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.
But 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 hanger 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.
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 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-spatted and faired set of gear similar to those used on their various biplane designs. Several months were lost in the conversion.
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 3,593 lb empty. Fully loaded the plane was 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 255 mph.
In early 1936 the Jumos finally arrived. The 210 had even less takeoff power than the Kestrel, but its altitude performance was comparable. Although the speed did increase with this engine at higher altitudes, low-level performance and climb both dropped. Arado argued that the fitting of a constant-speed prop would boost both, with the speed climbing to 264 mph, but this was not attemped before the plane was sent off to the contest.
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 the 8th of February, 1936, and later moved to meet the rest of the planes at Rechlin 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.
Additional prototypes
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 410km/h. 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 a canopy. The plane was first used for testing a 20mm 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, including the Bf 109 the Ar had lost to in the contest.
In 1938 the V3 was rebuilt once again, this time to test a new Fowler Flap design Arado was intending to use on their Ar 198 and Ar 240. Testing showed that the flap was so effective that the lift distribution along the wing changed radically, so a further modification was added to "droop" the ailerons along with the flaps. Testing continued for some time in this form, resulting in the "Arado travelling aileron" and "Arado landing flap".
Conclusions
The Ar 80 seems to be a victim of its own success. It was Arado's own design that led to the limited goals of the R-IV fighter contest, but that also meant it was the oldest of the designs entered. Given the pace of aircraft development in the early 1930s the last plane to be designed was almost certainly going to be the best, and that's exactly what happened when the Bf 109 won.
Combining Arado's lack of experience in monocoque construction, and Blume's failure to fix the gear retraction system, it seems reasonable to suggest that the plane never had a chance. Given this and the fact that the Ar 80 was built in only three examples, it's not surprising it remains little-known.
References
- Arado, History of an Aircraft Company, Jörg Armin Kranzhoff, Schiffer Publishing, 1997
- Warplanes of the Third Reich, William Green, Galahad Books, 1990
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