Arado Ar 80
Encyclopedia
The Arado Ar 80 was a pre-World War II
fighter aircraft
, designed by Arado Flugzeugwerke
to compete for the Luftwaffe
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 Messerschmitt Bf 109
, and the Ar 80 prototype
s ended their days as test aircraft.
(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 a designer of aircraft and increasingly became a production facility for other companies.
However, the company had just completed the Ar 65
biplane
fighter. 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 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 monoplane
single-seat fighter aircraft
, replacing the Ar 64
and Heinkel He 60 biplane
s 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 Junkers Jumo 210
engine. It also needed to be armed with at least three machine gun
s with 1,000 rounds each, or one 20 mm cannon
with 200 rounds. The plane needed to keep wing loading
below 100 kg/m², which is a way of defining its ability to turn and climb. The priorities for the plane were level speed, rate of climb
, and maneuverability, in that order. 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, Focke-Wulf
, and Bayerische Flugzeugwerk
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 monocoque 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 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 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 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 as the weight savings in the fuselage
should compensate.
The rest of the plane was conventional. The forward fuselage and inner wings were formed up from steel tubing with removable aluminium
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 landing gear
legs, but unlike the Heinkel it was almost straight on the leading
and trailing edge
s instead of the more complex elliptical
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-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.
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 Ar 67
design. The engine had less than optimal supercharging
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 hangar
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 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-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 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 constant speed propeller
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.
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 canopy. 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.
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 aileron
s along with the flaps. Testing continued for some time in this form, resulting in the "Arado traveling aileron" and "Arado landing flap".
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
, designed by Arado Flugzeugwerke
Arado Flugzeugwerke
Arado Flugzeugwerke was a German aircraft manufacturer, originally established as the Warnemünde factory of the Flugzeugbau Friedrichshafen firm, that produced military hydroplanes during the First World War.-History:...
to compete for the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
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 Messerschmitt Bf 109
Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...
, and the Ar 80 prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
s ended their days as test aircraft.
Design and development
With the Nazi rise to power in February 1933, a plan was put into place to dramatically expand the Luftwaffe. The new and highly-political ReichsluftfahrtministeriumReich Air Ministry
thumb|300px|The Ministry of Aviation, December 1938The Ministry of Aviation was a government department during the period of Nazi Germany...
(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 a designer of aircraft and increasingly became a production facility for other companies.
However, the company had just completed the Ar 65
Arado Ar 65
-See also:-References:* Green, William, and Gordon Swanborough, The Complete Book of Fighters...
biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
fighter. 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 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 monoplane
Monoplane
A monoplane is a fixed-wing aircraft with one main set of wing surfaces, in contrast to a biplane or triplane. Since the late 1930s it has been the most common form for a fixed wing aircraft.-Types of monoplane:...
single-seat fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
, replacing the Ar 64
Arado Ar 64
|-See also:-References:* Green, William, and Gordon Swanborough, The Complete Book of Fighters ...
and Heinkel He 60 biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
s 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 Junkers Jumo 210
Junkers Jumo 210
The Jumo 210 was Junkers Motoren's first production inverted V12 gasoline aircraft engine, produced just before the start of World War II. Depending on version it produced between 610 and 700 PS and can be considered a counterpart of the Rolls-Royce Kestrel in many ways...
engine. It also needed to be armed with at least three machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....
s with 1,000 rounds each, or one 20 mm cannon
Autocannon
An autocannon or automatic cannon is a rapid-fire projectile weapon firing a shell as opposed to the bullet fired by a machine gun. Autocannons often have a larger caliber than a machine gun . Usually, autocannons are smaller than a field gun or other artillery, and are mechanically loaded for a...
with 200 rounds. The plane needed to keep wing loading
Wing loading
In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly,...
below 100 kg/m², which is a way of defining its ability to turn and climb. The priorities for the plane were level speed, rate of climb
Rate of climb
In aeronautics, the rate of climb is an aircraft's vertical speed - the rate of change in altitude. In most ICAO member countries , this is usually expressed in feet per minute and can be abbreviated as ft/min. Elsewhere, it is commonly expressed in metres per second, abbreviated as m/s...
, and maneuverability, in that order. Hermann Göring
Hermann Göring
Hermann Wilhelm Göring, was a German politician, military leader, and a leading member of the Nazi Party. He was a veteran of World War I as an ace fighter pilot, and a recipient of the coveted Pour le Mérite, also known as "The Blue Max"...
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, Focke-Wulf
Focke-Wulf
Focke-Wulf Flugzeugbau AG was a German manufacturer of civil and military aircraft before and during World War II. Many of the company's successful fighter aircraft designs were slight modifications of the Focke-Wulf Fw 190.-History:...
, and Bayerische Flugzeugwerk
Messerschmitt
Messerschmitt AG was a famous German aircraft manufacturing corporation named for its chief designer, Willy Messerschmitt, and known primarily for its World War II fighter aircraft, notably the Bf 109 and Me 262...
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 monocoque 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 He 70
Heinkel He 70
The Heinkel He 70 was a German mail plane and fast passenger aircraft of the 1930s, that also saw use in auxiliary bomber and reconnaissance roles. It had a relatively brief commercial career before it was replaced by types which could carry more passengers...
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 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 as the weight savings in the fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
should compensate.
The rest of the plane was conventional. The forward fuselage and inner wings were formed up from steel tubing with removable aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
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 landing gear
Undercarriage
The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...
legs, but unlike the Heinkel it was almost straight on the leading
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
and trailing edge
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
s instead of the more complex elliptical
Elliptical wing
An elliptical wing is a wing planform shape that minimizes induced drag. Elliptical taper shortens the chord near the wingtips in such a way that all parts of the wing experience equivalent downwash, and lift at the wing tips is essentially zero, improving aerodynamic efficiency due to a greater...
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-spar
Spar (aviation)
In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles to the fuselage. The spar carries flight loads and the weight of the wings whilst on the ground...
. 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
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...
of roughly the same era.
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
Rolls-Royce Kestrel
|-See also:-Bibliography:* Erfurth, Helmut. Junkers Ju 87 . Bonn, Germany: Bernard & Graefe Verlag, 2004. ISBN 1-85780-186-5....
VI engine for use on their Ar 67
Arado Ar 67
|-See also:-References:* Green, William, and Gordon Swanborough, The Complete Book of Fighters...
design. The engine had less than optimal supercharging
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
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 hangar
Hangar
A hangar is a closed structure to hold aircraft or spacecraft in protective storage. Most hangars are built of metal, but other materials such as wood and concrete are also sometimes used...
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 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-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 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 constant speed propeller
Constant speed propeller
A constant speed propeller is a type of propeller that can change its blade pitch to take better advantage of the power supplied by an engine in much the same way that a transmission in a car takes better advantage of its power source...
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.
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
Rechlin-Lärz Airfield
Rechlin-Lärz Airfield is an airfield in the village of Rechlin, Mecklenburg-Western Pomerania, Germany, which is certified for aviation equipment up to 14 tons weight...
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 canopy. 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.
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 aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s along with the flaps. Testing continued for some time in this form, resulting in the "Arado traveling aileron" and "Arado landing flap".