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Was ist Fluggeschwindigkeit?

By Adam Hunt

 

CFNDec08  CFNDec08 

Spitfire and Hurricane. Photo courtesy Eric Dumigan

For our October meeting we arranged a special guest speaker, Rob Erdos, a National Research Council Test Pilot.

When he isn't doing research test flying for the government, Erdos spends his spare time flying rare aircraft for Vintage Wings of Canada at Gatineau Airport.

Vintage Wings operates an unusual fleet of antique aircraft, with an emphasis on World War Two fighter types. Erdos' duties at the Vintage Wings hangar include flying the British aircraft, including the Spitfire XVI and the Hurricane IV.

If regularly flying these two classic fighters isn't enough, Vintage Wings also provides maintenance expertise to another flying museum, the Russell Aviation Group of Niagara Falls. Not only does the Russell Group have a Spitfire IX and a Hurricane XII, they have a very rare fighter, a Messerschmitt Bf 109E-4.

Because of his familiarity with the British fighters and his background in flight testing, Erdos was invited to do the test flying on the 109, a task he eagerly agreed to.

There are few pilots in the world today who have flown a Spitfire, Hurricane or Bf 109 and perhaps only a handful who have flown all three. Therefore Flight 8 was pleased to have Erdos come and compare them in a presentation he entitled “The Battle of Britain Fighters – a Flight Test Perspective.”

Erdos started his presentation emphasising his perspective is not that of a fighter pilot, but of a professional test pilot - although he is an air show demonstration pilot and regularly flies formation and aerobatics.

He also mentioned the three aircraft he is comparing are not from the same era, as the 109E is really a pre-war aircraft while the Spitfire XVI is a mark from much later in the war. His approach was to contrast the three aircraft in each phase of flight and provide comparisons.

COCKPIT FAMILIARIZATION

Erdos emphasized all three aircraft were from an era before ergonomics had been invented and that the designers of each aircraft installed things where they fit, often without regard for the pilot who had to make it work in the air.

The Spitfire cockpit features an unusual control stick, hinged at the floor for elevator movement but hinged just below the two-handed “spade grip” at the top for aileron movement. This was done because the cockpit is too narrow for a conventional stick arrangement.

Erdos described the various Spitfire instruments and controls as being “thrown in at random.” The aircraft does have some novel features, such as a single lever on the stick for the pneumatic brakes. Once the lever is squeezed the brakes are varied using the rudder pedals. Not only are the brakes pneumatic, but so are the flaps, gun breeches, radiator doors and supercharger gear shifting, all run from a single-engine-driven air compressor. However, the landing gear retraction is run on hydraulics.

Getting onto the wing of the Hurricane is a challenge, as the trailing edge is high, so the designers built in a retractable stirrup to help with the process. The Hurricane features a high canopy railing; when sitting in the aircraft the canopy sill is just below chin height.

Inside the Hurricane cockpit the steel tube and fabric construction is evident. There are no floorboards in this very utilitarian environment and anything dropped, like a pencil, is lost.

The Messerschmitt features semi-reclined seating for “g” tolerance, an advanced feature for its day. The 109 cockpit is tiny, Erdos explained, even for pilots of smaller stature. With the hinged canopy closed the clearances around the head and shoulders are close to nil.

The German aircraft has some unusual cockpit features, such as concentric trim and flap actuation wheels, that actually allow both to be moved together, an idea that works well when extending the manual flaps, which requires simultaneous trimming.

The Russell 109 is authentic in almost every respect, having been actually flown in the Battle of Britain as well as on the Russian Front. It once was the personal aircraft of famed Luftwaffe ace Hans-Joachim Marseille.

The authenticity of this aircraft means that all the instruments are in unfamiliar metric units, such as oil pressure in kg/cm2. Even the airspeed indicator does not indicate airspeed in knots or mph, but instead indicates fluggeschwindigkeit in km/h.

GROUND HANDLING

Erdos reports that all three aircraft are challenging taildraggers on the ground. All are blind ahead to some extent, although the Hurricane less so and all require “S” turns while taxiing.

The British fighters have the unusual lever brakes to make things more complex, while the 109 has conventional toe brakes, perhaps its only virtue on the ground.

Of the three, the Hurricane sits most level and has the best field of view. The Spitfire is nose heavy and can be nosed-over at idle while standing still with the brakes on, if the elevators are not held full back. It is also blind on the ground, due to the long nose and the aircraft is prone to engine overheating.

The German fighter is conversely tail heavy, which at least allows judicious use of the brakes although the long nose also renders it blind on the ground plus the tighter cockpit and the need to have the side-hinged canopy closed to taxi, makes seeing difficult.

TAKE-OFF

Due to the Spitfire's large propeller the aircraft cannot have its tail raised to level on the ground, or the prop will strike the ground. This requires that it be flown off and landed from a three-point attitude. It also means that the visibility is as poor on take-off as when taxiing.

On take-off in the Spitfire, full power must be applied judiciously and the left turning tendencies of the aircraft, caused by an additive combination of engine torque, slipstream effect (P-factor) and asymmetric thrust, must all be overcome.

The Hurricane, Erdos reports, is much more conventional and less demanding on take-off, although it does suffer from a slow undercarriage retraction speed and a low maximum gear-extended airspeed of just 104 knots, requires a steep climb on take-off until the gear is up and locked.

The 109 suffers from its toed-out, narrow and forward pointing landing gear, which can cause the aircraft to swerve on the ground. Erdos reports that the locking tail-wheel must be locked or the aircraft will crash on take-off every time.

IN-FLIGHT

The Spitfire is well-known for its superb handling qualities, stemming from a control system with no friction and no free-play (slop) at all. The aircraft has control harmony reversed from the norm. Usually aircraft are designed so that the ailerons are lightest, then the elevator and the rudders are heaviest in a ratio of 1:2:4. The Spitfire has a light elevator and heavier roll control. Erdos notes the ailerons get very heavy above 340 knots.

In contrast to the Spitfire's zero-friction controls, the Hurricane's control system uses bushings instead of bearings and the result is high system friction. The aircraft has weak to negative static longitudinal stability, meaning the nose doesn't tend to return to the trimmed attitude, but stays where it is aimed.

It has an unusual yaw-pitch couple as well and is not as fast as the other two fighters. The aircraft does have a fast roll rate, even faster than the Spitfire. In flight, due to the routing of the cooling lines and other utilities, the cockpit gets hot and most flights are flown with the canopy open.

The Messerschmitt design has a fin and rudder that are just too small and so it has poor directional stability, making the pilot work to keep it pointed in the right direction. There is no rudder trim and the elevator controls are heavy at higher speeds.

The ailerons have so much travel they can actually stall in flight, causing a loss of effectiveness and stick vibrations. Unlike the British fighters the 109 has only manual adjustment of the prop pitch via an electric switch requiring the pilot to continuously “beep” the prop rpm in manoeuvring flight.

DOGFIGHTING

Erdos admits he doesn’t have much air combat experience, but says the Spitfire and the Bf 109 are well matched. The Spitfire has a lower wing-loading at 22 lb/sq ft. compared to the 109's much higher 32 lb/sq ft.

The 109 is a small aircraft with a small wing, a low coefficient of drag and it accelerates quickly with the nose down. The Spitfire's elliptical wing is ideal to minimize induced drag and so it retains energy and hence airspeed better than the 109 in a tight turn.

The combination of the Spitfire's lower wing loading and wing planform means it can turn more tightly than the 109. The 109's strengths would have made diving attacks rather than turning combat their preferred engagement.

With its two 7.92 mm machine guns and two MG-FF/M 20 mm wing cannons the 109 had a good firepower advantage over the eight gun .303 armed Spitfires and Hurricanes that it met in the Battle of Britain, although later Spitfires and Hurricanes added 20 mm cannons of their own.

APPROACH AND LANDING

All three fighters are flown in a military overhead break, rather than a conventional square circuit. This is a requirement because of the long noses on these aircraft. Final approach has to be a curving path so the runway can be kept in sight. A straight-in approach, as flown in a typical light aircraft would mean the runway would not be visible at all.

In the overhead break all three aircraft are flown similarly, with about 220 knots airspeed at initial, 130 knots downwind and about 85 knots on the curving base to final turn.

The Spitfire is again blind on landing and must be three-pointed due to the large propeller. Because it is nose heavy, brakes must be avoided to prevent a nose over and prop-strike. Ground time must be kept short to avoid overheating the Merlin engine.

The Hurricane can be landed three-point or “wheeled-on” and lands much better with some power held into the flare. At idle the prop acts as an air brake and pulling power above the ground results in a drop to the ground immediately.

Due to the downwash from the wing and the large flaps the Hurricane's horizontal stabilizer operates in disturbed air at higher angles of attack and a three-point landing requires large elevator movements. Erdos reports that wheel landings are easier.

The 109, with its manual flaps, requires a longer break to allow a longer downwind to extend the flaps by cranking the wheel and trim together. Like the Spitfire, in other than a curving final, the runway disappears for the 109 pilot.

As on takeoff the landing gear geometry makes the aircraft a handful on landing and while taxiing. Also as on takeoff the full-swivelling tailwheel must be locked to avoid a flip into the weeds.

Unlike the Spitfire, because the Messerschmitt is tail heavy, brakes can be used fearlessly when needed, allowing the aircraft to be flown into quite short runways of as little as 1,300 feet.

ASSESSMENT

Erdos notes that each of the three fighters has its strengths and weaknesses and a good fighter pilot would learn to use the strengths of his mount against the weaknesses of his opponent.

Which one does Erdos rate as the best of the three?

Not the 109. Its lack of a prop governor results in a high pilot workload and its poorly designed landing gear and worse ergonomics make it less than ideal.

Not the Hurricane either. Its lack of speed for the horsepower and its handling deficiencies make it a second rate fighter for its day.

That leaves the Spitfire on top, despite its overheating and ground handling problems it is still a better aircraft than the other two.

COPA Flight 8 would like to thank Rob Erdos for his fascinating presentation. The impressions of a modern test pilot on the details of these three famous fighters truly was the next best thing to flying all three yourself, something few of the flight members will have the chance to do.