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Scheibe SF25 Falke
Slingsby T.61 Falke


sf25c-falke
SF-25C Falke

 

 

Following the successful development of the SF-24 Motorspatz powered glider from the L-Spatz-55 and L-Spatz-III single-seater sailplanes, it was a logical step to produce a two-seater motor glider based on the Bergfalke III. This emerged as the SF-25 Motorfalke which, in its original A-model form, had a cantilever high-set wooden wing with Schempp-Hirth air brakes similar to that of the Bergfalke III but, unlike the sailplane, was a side-by-side rather than a tandem two-seater. The two-place self-launching SF-25 Falke features spoilers, a steerable tail wheel and wing outrigger wheel for taxiing. The engine is mounted forward of the cockpit in conventional tractor style.
 
Powerplant was a 28hp Hirth-built Solo 'flat four' air-cooled two-stroke engine in an installation very similar to the SF-24B Motorspatz, and with a fuel tank of 5.5 Imp gallons capacity. The fuselage aft of the cockpit was very similar to the Bergfalke III’s, being the traditional Scheibe fabric-covered welded steel tube structure, and the wooden tail unit and fixed monowheel landing gear were also similar to the Bergfalke's. The two pilots have dual controls as standard and the Motorfalke went into production, a total of 25 having been built by early 1966. First flying in 1963, although it had certain flaws, 50-odd were produced over the next few years.

 

Later versions of the SF-25, now known simply as the Falke (or Falcon), had low-set two-piece cantilever wooden wings developed from the Motorfalke's with air brakes in the upper surfaces and slight forward sweep.

 
The 1967 SF-25B's span was now 50ft 2.5in and aspect ratio 13.4, compared with the Motorfalke's 54ft 5.5in span and aspect ratio of 16. A more powerful engine was fitted, the forward fuselage underside fairing for the fixed monowheel with brake was revised in shape and outrigger stabilising wheels were fitted under each wing, so that the SF-25B was almost a different aeroplane to the Motorfalke, although just as suitable for basic and advanced training. Its powerplant was a 45hp Stamo MS 1500-1 modified Volkswagen 'flat four' engine which also incorporated some Porsche parts; this was started on the ground or in the air by a pull-cable starter in the cabin, with an electrical starter available as an optional extra and the fuel capacity was 8.5 Imp gallons. Scheibe lowered to wing to the bottom of the fuselage, incorporated supporting wheels under the wings to allow for independent takeoffs. Another optional extra for the SF-25B is a tow-hitch for winch-launching. The tail unit is of wooden construction and there is a steerable tailwheel; dual controls are standard. The maximum all-up weight was also increased to 555kg. Nearly 400 B-Falkes were built before the C-version was released in the early 70s.
 
About 200 SF-25Bs had been built by Scheibe, about 10 more by Aeronautica Umbra Sppp in Italy, plus 35 by Vickers-Slingsby, who are producing a modified verison of the B as the T61E Venture T Mk 2 for the Air Training Corps. The SF-25 Motorfalke was licence built from 1970 by Slingsby Sailplanes Ltd in UK as Type 61 Falke. Slingsby developed a composite sparred model for the Royal Air Force, which acquired 40 Slingsby T. 61 E Venture T. Mk. 2’s for its air cadet program.

 

Scheibe-25-03
Scheibe SF-25B Motorfalke
 
The SF-25C-S is a further improved variant of the SF-25B with an optional Hoffman feathering propeller, adjustable engine cowl flap and slightly modified fuselage, and 20 of this version had been built by January 1980. Power was a 45 kW/ 60 hp Limbach SL 1700EA modified Volkswagen 'flat four' engine driving a two-blade propeller; an electric starter is fitted and the single fuselage fuel tank has a capacity of 9.9 Imp gallons, or 12.1 Imp gallons optionally. Further optional features include an additional exhaust outlet and a slower-turning propeller, these reducing the noise level to less than 60 dB. Optional wing folding was also available, reducing the span to 31ft 2in for easier hangar storage.
 
The Falke '76 was an improved model and featured a number of design improvements, including a domed cockpit canopy, an enlarged fin and smaller rudder with greater sweepback, a coating of laminated glassfibre for the forward section of the fuselage, some engine and exhaust modifications and an alternative twin-wheel main landing gear with wheel spats, which was offered as an option to customers. The non-retractable monowheel is normally unsprung, but a rubbersprung monowheel was also offered as optional.
 
The C-Falke '80 production version became the SF-25K K-Falke '80 with fully-folding wings. Later versions of the SF-25C had an 80hp Limbach L2000 'flat four' engine (the SF25C-2000 model), an electric starter and some other minor changes.
 
The SF-25C received its type certification in September 1972 and by January 1980 a total of 295 of this version had been built by Scheibe, plus another 50 built under licence by Sportavia in Germany, who also built 80 SF-25Bs.
 
The SF-25-2000 has an 59 kW/ 80 bhp Limbach L 2000 EA, and is offered with a conventional powered aircraft two wheel landing gear instead of a single sailplane type main wheel.
 
 Sch-SF25-01
 
In the mid-70s, the C-Falke received another design overhaul with a more bubble-shaped hatch, a suspension system for the main wheel, and a more streamlined tail. From the 80s, conventional landing gear with a steerable tail wheel, and even tricycle landing gear were offered. The aircooled VW-based Limbach and Sauer motors were eventually dropped in favour of the watercooled Rotax, with 80, 100 and 115hp variants being certified. Max all up weight has kept climbing steadily, from 580kg to 650 and finally up to 690kg in the latest versions. The SF25-C in all its variants is by far the most common Motorfalke model. In its Turbo-Rotax form it is used mainly as a glider tow rig. The powerful Rotax motors allow safe towing of even heavy modern 2-seater gliders with a max all up weight of 800-850kg, representing a true alternative to thirstier, traditional tow planes.
 
The D-model is essentially a factory-converted B-Falke with a more powerful 60hp Limbach engine, which necessitated strengthening the fuselage and slightly shortening the wings (to 14.7 instead of 15.3m). This came about when the then-new C-Falke was released and many owners of the older, underpowered Bs wanted to upgrade. In practice it is hard to detect much difference between a D and C-Falke in cruise or glide. All up weight was increased to 580kg, which means the useful load tends to be better on the D than many other Falkes.
 
The SF-25E Super-Falke is basically an SF-25C-S with a wing increased in span to 18m (59ft 0.75in); the fuselage aft of the wing has a wider section than that of the C-S to improve airflow at the wing root, and the fairing for the non-retractable monowheel, which is now rubber-sprung as standard, is now larger. Production aircraft also have a tailwheel, Schempp-Hirth air brakes in the wing upper surfaces and a cabin heater fitted as standard. The same 48 kW/ 65hp Limbach SL 1700EA engine as in the SF-25C is fitted, driving a two-blade feathering propeller, which substantially increased the glide (around 28 as opposed to 22), there is a 12 volt battery and alernator for electrical engine starting, and the engine cowl flap is adjustable. Wing folding of the outer panels is optional, as on the SF-25C-S, and the same outrigger stabilising wheels are fitted under each wing. The wingtips can be folded inwards, thereby reducing the wingspan to 10m to facilitate hangerage, similar to a Fournier RF5B. The Super-Falke made its first flight in June 1974, and the type took first place in the advanced two-seater class at the First International Motor Glider Competiton; a total of 52 Super-Falkes had been delivered by January 1980. The type is structurally the same as the SF-25C-S, and has the same side-by-side seating with dual controls; like the SF-25C, optional folding wings were available for easier hangar stowage.

The SF25-K is a version with foldable wings - in this case with wings that fold back completely to dramatically reduce the required hangar space. The “K” stands for “Klappfluegel” – "folding wings". Very few of this variant were produced, as the folding mechanism was complicated and added a fair amount of weight. 
 
Sch-SF25E-02
Scheibe SF25E Super-Falke

 

Falkes were built under license by equivalents of the SF-25B and -25C with a Rollason-Volkswagen 36 kW/ 48 bhp 1,600 engine, without and with electric system respectively.

 

sf-25-2

 

Postwar production by Umbra concentrated on licence manufacture of the Scheibe SF-25B Motorfalke motor glider for the Italian and North African markets.

 

Slingsby Sailplanes began production under licence of the Scheibe SF-25B Falke two-seat motor glider as the T61, construction of the first Slingsby-built example beginning in April 1970; a total of 35 were built. The T61 and T61A have the 45hp Stamo MS1500-1 engine with manual starter as fitted to the SF-25B, whereas the T61C has the Stamo MS1500-2 with electric starter. With Slingsby's long record of supplying gliders for the needs of the Air Training Corps, it was not surprising that the possibilities of a motor glider such as the T61 for ATC training should be considered, especially its time-saving potential in being able to dispense with winch launches and retrieving vehicles, and its ability to continue flying in weather when unpowered sailplanes were grounded. A prototype Slingsby-built T61 serialled XW983 was evaluated as the Venture T Mk 1, and this led to an order for 15 of a special version, the Venture T Mk 2, by the Ministry of Defence (Air) for Air Training Corps use.
 
The first production T Mk 2, serialled XZ550, made its first flight on 2 July 1977 and deliveries began that autumn. A total of 19 T61F Venture T Mk 2s had been completed by the beginning of 1980. The T Mk2 differs from previous Slingsby- and Scheibe-built SF-25Bs in having a special glassfibre spar encased in plywood and many other glassfibre components are employed. Use of this material in the spars and elsewhere both reduces the empty weight and increases the maximum permissible take-off weight, and hence payload. New glassfibre seats are also featured of improved comfort and designed to reduce the hazard of loose articles slipping under the seat into the control area. The powerplant is a 45hp Rollason Ardem 'flat four' of 1,600cc driving a two-blade fixed-pitch propeller; this is a version of the Volkswagen car engine modified by Rollason Aircraft and Engines Ltd of Shoreham, Sussex, and has single ignition and an electric starter.
 
The T61G Falke is a civil development of the Venture T Mk 2, with a 60hp Limbach SL 1700EA 'flat four' engine driving a Hoffman two-blade fixed-pitch propeller (a variable-pitch one can be fitted if desired).
 
The Scheibe SF25 Motorfalke was probably the first practical touring motorglider. It is certainly one of the most built types (around 1500 in total).
 
Scheibe Flugzeugbau GMBH, the original manufacturer, eventually closed its doors in 2006, partly because of the lack of a successor for Egon Scheibe, but probably also due to the increasingly difficult trading conditions after the boom of Ultralight/Microlight aircraft that have taken over a large portion of the market for fun, relatively cheap, and easy to fly recreational aircraft - and arguably also the unwillingness of the company to embrace modern glass-fibre construction techniques, preferring to stick to the traditional mixed construction style (fabric-covered wooden wings and steel tube fuselage). The Motorfalke design was subsequently taken over by the newly formed Scheibe Aircraft GMBH based in Heubach (Germany), which has certified the Turbo-Rotax powered version with the glider towing market in mind. 
 
Sch-SF25-02
 

SF25B
Engine: 35 kW/ 45 bhp Stamo
Wing span: 15.53m / 50.3ft
Wing area: 14.47sq.m / 188sq.ft
Aspect ratio: 13.4
Empty Weight: 335kg / 740lb
Payload: 195kg / 430lb
Gross Weight: 530kg / 1170lb
Wing Load: 36.63kg/sq.m / 6.1lb/sq.ft
Airfoil: Mu
Seats: 2
No. Built: 300
L/DMax: 22 @ 80 kph / 43 kt / 50 mph
MinSink: 1.00 m/s / 3.3 fps / 1.96 kt
Structure:steel-tube/ fabric fuselage, wood/ fabric wings and tail

SF-25C / C-S Falke '76
Span: 50 ft 0.25 in
Length: 24 ft 9.25 in
Height: 6 ft 0.75 in
Wing area: 195.9 sqft
Aspect ratio: 13.8
Empty weight: 826 lb
Max weight: 1,345 lb
Max speed: 112 mph (power on)
Max cruising speed: 99 mph
Min sinking speed: 3.28 ft/sec at 43.5 mph
Best glide ratio: 23:1
Take-off run: 590 ft
Range with max fuel: 466 miles

 

SF25C-S

SF25-2000

Engine: 59 kW/ 80 bhp Limbach L 2000 EA
Seats: tandem two-seat

Scheibe SF25E Super-Falke
Engine: 48 kW/ 64 bhp Limbach
Span: 18m / 59 ft 0.75 in
Length: 24 ft 11.75 in
Height: 6 ft 0.75 in
Wing area: 187.3 sqft
Aspect ratio: 17.8
Empty weight: 904 lb
Max weight: 1,389 lb
Max speed: 112 mph
Max cruising speed: 99 mph
Cruise: 93 mph
ROC: 450 fpm
Min sinking speed: 2.79 ft/sec at 47 mph
Best glide ratio: 29: 1 at 53 mph
Take-off run: 490-655 ft
Endurance: 4 hours

 

Venture TMk 2
Span: 50 ft 0.25 in
Length: 24 ft 9.25 in
Height: 6 ft 0.75 in
Wing area: 195.9 sqft
Aspect ratio: 13.8
Empty weight: 827 lb
Max weight: 1,350 lb
Max level speed: 92 mph
Min sinking speed: 3.28 ft/sec
Best glide ratio: 22:1
Take-off run: 650 ft
Range: 248 miles

 

Rotax-Falke
Seats: tandem two-seat

 

 


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