Disc SF 25

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Disc SF 25 falcon
SF 25 C 2000
Type: Touring motor sailer
Design country:

Germany Federal RepublicFederal Republic of Germany BR Germany

Manufacturer:

Scheibe-Flugzeugbau GmbH / Scheibe Aircraft GmbH

First flight:

May 1963

Production time:

1963 -

Number of pieces:

> 1500 (including licensed buildings)

The Scheibe SF 25 Falke is a two-seater, mixed construction motor glider , which was developed and manufactured by Scheibe-Flugzeugbau GmbH from 1963 . It became one of the most built motor gliders in the world. The main reasons for this success were the "side-by-side" seating arrangement, which simplified the training, the simple and robust composite construction as well as the good-natured flight characteristics. Another member of the Falken family is the SF 28 "Tandem Falcon" developed from the Bergfalken IV , in which the seating arrangement has been changed in favor of better aerodynamics. The pilots sit one behind the other, which allows for a slimmer fuselage.

history

Right from the start, the Falcon was designed as an aircraft that was easy to fly and maintain in order to offer glider clubs an inexpensive alternative for training and winter flight operations. The composite construction method was ideal, as most clubs at that time were familiar with it through self-construction and maintenance of the existing glider fleet and had the necessary tools at their disposal. When developing the Falken, Egon Scheibe was able to fall back on experience with motorized variants of his Mü 13 and the single-seat motor glider SF 24 "Motorspatz" . The first flight of the A-Falcon took place in 1963. The design as a shoulder-wing aircraft was not convincing because the maneuverability in the air and maneuverability on the ground left a lot to be desired. In addition, the A-falcon required a helper to hold the wing during takeoff. Many A-Falcons were therefore modified on the landing gear to enable a start without an assistant. These deficiencies have been remedied with the SF 25 B. From 1967 the B-Falke was developed as a low-wing aircraft and in 1968 received type certification from the Federal Aviation Office . 373 copies of the B version were built and detailed improvements such as a folding wing mechanism for space-saving storage, simplified entry, variable pitch propellers and more powerful engines were made in the SF 25 C. With the later built-in engines, the falcon became an inexpensive tow plane. The journalist Wolf Heckmann , who flew with the SF 25 C D-KOEO from Germany to Australia in around 230 hours, provided special evidence of the efficiency and robustness of the aircraft construction .

construction

When constructing the falcon, Egon Scheibe took a pragmatic approach; so as few parts as possible should be redesigned. Therefore, the wings of the Bergfalke II and the horizontal stabilizer of the sparrow were taken over unchanged . The horizontal stabilizer is still used unchanged in the currently produced SF 25 C. The fuselage consists of a covered tubular steel frame, while the wings are made of plywood and are also covered. The chassis originally consisted of a central main wheel with a drum brake. The SF 25 B added small support wheels under the wings and a steerable tail wheel that improved maneuverability on the ground. Later the C-Falke was also available with a bipod or nose wheel landing gear. The entry requires a certain sportiness, as the high side wall has to be climbed first. The plexiglass hood opens to the front and is then held in position by a strap. Since 2005 there has been a new hood design in which the hood, which is no longer divided, is lifted at the front to open and then swiveled backwards. The falcons have only moderately effective airbrakes on the top of the wing. Due to the large cross-section of the fuselage, however, steep approaches by side gliding are also possible. The drum brake of the main landing gear is activated by pulling the airbrake lever as far as it will go.

Versions

SF 25 A

SF 25 A at Anspach airfield 1973: shoulder-wing aircraft with support wheels on the fuselage
SF25a in Erlangen

The SF 25 A was designed as a shoulder- wing aircraft. The chassis consists of a main wheel and a tail wheel, several machines also had support wheels attached to the fuselage and main wheel. The “A-Falke” was given a grinding bow at the wing tips, which some holders also provided with small wheels.

The handling of the four-cylinder two-stroke boxer engine " Hirth F10", which was often installed at the time and originally designed for operation on snowmobiles, required a high degree of technical understanding, as it required a considerably different operation compared to the four-stroke engines used in general aviation . The starting procedure also required a certain sportiness on the part of the pilot using a manual pull starter in the narrow cabin. If the gasoline-air mixture was set too lean during flight operations, this inevitably led to burned-out piston heads and melted spark plugs within a few minutes, which, in connection with the unfamiliar starting process, unjustifiably earned the engine the reputation of unreliability. The noise development was also quite annoying even by the standards of the time: volume and frequency earned the A-falcon the nickname “ lawn mower ”. As an alternative, the were Hercules - Wankel engine W2000 from the motorcycle and later the Rotax 447 used.

In flight operations, the falcon's soaring performance was the focus. That is why there was also a clutch for the winch start. Even if the A-falcon is not one of the most maneuverable aircraft, distance flights of 300 km and pure gliding times of over 5 hours were recorded. These are favored by the approx. 75 kg lower empty weight compared to the successor versions and the good slow flight characteristics of the A-Falcon, which enable better use of even weaker updrafts. The very stable and good-natured flight characteristics in connection with the rather sluggish response of the rudder gave the A-Falcon the nickname " motor cow ".

56 copies were made.

Technical specifications

Parameter Data
crew 1
Passengers 1
length 7.58 m
span 16.6 m
height 1.90 m
Wing area 17.5 m²
Glide ratio 20 at 85 km / h
Slightest sinking 0.9 m / s at 75 km / h
Empty mass 285 kg
Takeoff mass 485 kg
Wing loading 27 kg / m²
Minimum speed 60 km / h
Maneuver speed 140 km / h
Top speed 180 km / h
Engines 1 × Solo 560 A2C to 26 HP or Hirth F10 A2C

SF 25 B

SF 25 B at Klagenfurt Airport

The SF 25 B "B-Falke" has been revised in numerous points compared to the A version: in addition to the changed wing design, a fundamental revision of the landing gear was carried out. In addition to the central main wheel with drum brake, the B-Falke received small support wheels under the wings and a steerable tail wheel to improve maneuverability on the ground. The change to the VW-based Stamo engines brought the reliability required for safe continuous operation. This enabled the development towards a touring motor glider to be completed, while the A-Falke had more of the character of a self-launching glider. This made the falcon interesting as an inexpensive training machine outside of gliding operations. In Great Britain, a total of 76 B-Falcons in different variants were built under license by Slingsby Aviation as T 61 with different engines. Forty-five of the T 61E and F Venture T Mk2 versions of the Rollason RS MK2 engine (1.6 l, 48 hp) were used for the training of the British Air Cadets . Some B-Falcons were built under license by the companies Sportavia-Pützer ( Dahlemer Binz ) and Aeronautica Umbra (Italy). In the early B-Falcons, the engine was started from the cockpit using a reversing starter . Electric starters were later used. The installation of the starter and the necessary lead-acid battery reduced the possible payload, however, since the maximum take-off weight of 555 kg remained the same. The Stamo engine, which is no longer available today, has been replaced by a 54 hp Sauer 1800 engine or a 60 hp Limbach 1700 engine in many B-Falcons .

Technical specifications

Parameter Data
crew 1
Passengers 1
length 7.50 m
span 15.30 m
Wing area 17.50 m²
Wing extension 13.4
Wing profile Mü
Glide ratio 22nd
Slightest sinking 0.95 m / s at 70 km / h
Preparation mass 360 kg
Max. Takeoff mass 555 kg
Wing loading 31.71 kg / m²
Minimum speed 60 km / h
Top speed 190 km / h
Service ceiling approx. 5000 m
Engines 33 kW (45 PS) Stamo MS 1500/1 or 1500/2

SF 25 C

SF 25 C on landing

The SF 25 C "C-Falke" is the most widespread variant of the Falken family and is still being built today. The original C-Falke has the 60 hp Limbach SL-1700-EA engine and was also produced under license by Sportavia-Pützer on the Dahlemer Binz. The later SF 25 C 2000 received the 80 hp Limbach L 2000 EA. In the mid-1970s, the shape of the fuselage was slightly changed to today's "humpback hood", at the same time the control sticks, which had previously been mounted centrally on a rocker, were replaced by parallel sticks and the ailerons were mass balanced. A deep hood cutout, initially available as an option, made entry easier and is standard on the hood that is currently being built. The engine with the Rotax 912A or 912S , which has an output of 59 kW (80 PS) or 73 kW (100 PS), is currently available . Since the beginning of 2009, the 85 kW (115 PS) Rotax 914F has been offered in the SF 25C together with a take-off weight increased to 690 kg. With the Rotax engines, the Falke has sufficient power reserves for cost-effective towing of gliders, with the Rotax 914F towing loads of up to 800 kg are permitted.

Independently of the disk, the Loravia company in France offered the modification of the SF 25C and D as a glider tug equipped with the 64 kW (87 hp) Limbach L-2400 at the end of the 1990s. This variant was approved in France in 1997 and named SFL-25R.

The design is essentially the same as the predecessor type SF 25 B. The chassis is available in three versions:

  • Central wheel version (central nose wheel, tail wheel and support wheels under the wings, can also be equipped with a center of gravity coupling for winch launch)
  • 2-leg version (two main landing gears in front of the center of gravity + tail wheel (no support wheels))
  • 3-leg version (two main landing gears behind the center of gravity and a nose wheel)

The flight manual of the SF 25 C specifies a narrowest pitch circle diameter of 15 m for the bipod version and 5 m for the nose wheel version.

Technical specifications

SF 25 C "Rotax-Falke" with nose wheel landing gear
Parameter value
crew 1
Passengers 1
length 7.6 m
span 15.3 m
Wing area 18.2 m²
Wing extension 13.8
Wing profile Mü
Glide ratio 23-24
Slightest sinking 1.1 m / s
Empty mass approx. 438 kg (from 2009: 455–475 kg)
Takeoff mass approx. 650 kg (from 2009: 690 kg with Rotax 914F engine)
Wing loading 33.5 kg / m²
Minimum speed 60 km / h
Service ceiling 4300 m

Motor variants

Only the Rotax versions are currently in production; Factory information 2010 for 690 kg.

Parameter Limbach L 2000 EA Rotax 912A Rotax 912S Rotax 914F2 adjustment prop.
Cruising speed 150 km / h 170 km / h 180 km / h 200 km / h
Rate of climb 3.2 m / s 4.0 m / s 5.0 m / s 6.4 m / s
Take-off run approx. 140 m approx. 110 m approx. 100 m approx. 95 m
Range (55 l tank) approx. 700 km approx. 600 km approx. 900 km (80 l tank)
Flight duration 4-5 h 4.5 h 4 h 4-6 h
Fuel supply 55/80 l 80 l
Travel consumption approx. 11.5 l / h approx. 13 l / h

SF 25 D

SF 25 D of the LSC Babenhausen in the summer of 1986

After the new, more powerful engine in the C-Falken had proven itself, the pilots of the significantly less powerful B-Falken asked for the more powerful 1700 cm³ Limbach engine (L 1700 E0) with 44 kW (60 PS) can also be used. A conversion option was therefore developed at the company Scheibe. In order to accommodate the heavier engine, the hull had to be structurally reinforced. In return, the wings were shortened to a span of 14.68 m and the maximum take-off weight increased to 580 kg. Due to the necessary changes to the airframe and structure, these conversions were only carried out in the factory; B-falcons converted in this way were then referred to as SF 25 D or “D-falcon” for short.

SF 25 E

The SF 25 E “Super-Falke” has a wingspan of 18 m and a 64 hp Limbach engine. The increased wingspan and the use of a three-position propeller (take-off, cruise and sail position) increased the glide ratio from 22 to 28. For space-saving hangaring, the outer wings of many specimens can be folded onto the inner wings, the separation point with single-lever operation was similar to that of the the RF-5B "Sperber" executed.

SF 25 K

This variant has a 49 hp engine and star wheel steering .

The special feature was the foldable wings, which took up much less hall space when hangaring.

See also

literature

  • Gerd Zipper: Falkenhorst. The history of the disk planes . Weishaupt, 1999, ISBN 3-7059-0059-5 .

Web links

Commons : Disk SF 25  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Overview of the operating manuals. In: scheibe-aircraft.de. Retrieved August 8, 2015 .
  2. ↑ Test: SF 25E Superfalke. Flug Revue 11/1975, p. 28ff.