Tag Archives: Allison 250-C18

16 February 1967

Wilfried von Englehardt tests the Bölkow-Entwicklungen KG Bo-105 V-2, D-HECA in an out-of-ground effect hover, with engine cowlings removed, 16 February 1967. (Eurocopter)
Wilfried von Engelhardt tests the prototype Bölkow-Entwicklungen KG Bo-105 V-2, D-HECA, in an out-of-ground effect hover with engine cowlings removed, 16 February 1967. (Airbus Helicopters Deutschland GmbH)
Wilfried von Englehardt (Académie de l’Air et de l’Espace)
Wilfried von Engelhardt (Académie de l’Air et de l’Espace)

16 February 1967: At Ottobrun, Germany, test pilot Wilfried von Engelhardt made the first flight of the Bölkow-Entwicklungen KG Bo-105 prototype V-2, D-HECA, a twin-engine, rigid rotor helicopter. Baron von Engelhardt took off at 5:04 p.m. The flight lasted 20 minutes. D-HECA was the second prototype. The first one was destroyed by ground resonance during pre-flight testing.

Messerschmitt AG merged with Bölkow-Entwicklungen KG in June 1968, becoming  Messerschmitt-Bölkow. The following year, the new company merged with Blohm & Voss to become Messerschmitt-Bölkow-Blohm KG, or MBB. The Bo-105 A entered production in 1970. A number of civil and military variants followed.

The Bo-105 is a 5-place light helicopter powered by two turboshaft engines. It has a four-bladed rigid (or hingeless) main rotor. This gives it a high degree of maneuverability, and it is capable of performing aerobatic maneuvers. The two-bladed tail rotor is mounted high on a pylon and gives exceptional ground clearance for a helicopter of this size. There are two “clam shell” doors located at the rear of the cabin section, giving access to a large flat floor. The helicopter has been widely used by military, law enforcement and as an air ambulance.

Messerschmitt-Bölkow-Blohm Bo-105 V-2, D-HECA. (Eurocopter)
Bölkow-Entwicklungen KG prototype Bo-105 V-2, D-HECA, during flight testing. (Airbus Helicopters Deutschland GmbH )

The Bo-105 is 11,86 meters (38 feet, 10.9 inches ) long with rotors turning. The fuselage is 8,81 meters (28 feet, 10.9 inches) long, with a maximum width of 1,58 meters (5 feet, 2.2 inches). The helicopter’s overall height is 3.00 meters (9 feet, 10 inches). The helicopter has an empty weight of approximately 1,276 kilograms (2,813 pounds), depending on installed equipment, and maximum takeoff weight of 2,100–2,500 kilograms (5,512 pounds), depending on variant.

The diameter of the main rotor is 9,84 meters (32 feet, 3.4 inches). The main rotor follows the American practice of turning counter-clockwise as seen from above. (The advancing blade is on the right.) It operates at 416–433 r.p.m. (361–467 r.p.m. in autorotation). The tail rotor diameter is 1,90 meters (6 feet, 2.8 inches). It turns clockwise as seen from the helicopter’s left side. (The advancing blade is below the axis of rotation.)

Three-view illustration of the Messerschmitt-Bölkow-Blohm Bo-105 LS (lengthened cabin section). (Nordic Helicopters)

The prototype was powered by two Allison 250-C18 turboshaft engines, with increasingly more powerful 250-C20, -C20B and C-28C engines being added through the production run. The Allison 250-C18 is a 2-spool, reverse-flow, gas turbine engine with a 6-stage axial-flow, 1-stage centrifugal-flow, compressor section, and a 4-stage axial-flow turbine (2-stage gas producer, and 2-stage power turbine). The 250-C18 is rated at 317 shaft horsepower at 51,600 r.p.m., N1 (6,000 r.p.m. N2).

The helicopter’s cruise speed is 127 miles per hour (204 kilometers per hour) and maximum speed (VNE) is 135 knots (155 miles per hour/250 kilometers per hour) at Sea Level. The service ceiling is 17,000 feet (5,180 meters). The Bo-105 C has a maximum fuel capacity of 580.0 liters (153.22 U.S. gallons), of which 570.0 liters (150.58 U.S. gallons) are usable. The range is 691 miles (1,112 kilometers.

The original Type Certificate for the Bölkow Bo-105 A was issued 13 October 1970. Since then, the Bo-105 series has been produced in Germany, Canada, Spain, Indonesia and the Philippines. More than 1,500 were built.

Wilfried von Englehart tests the Bölkow-Entwicklungen KG Bo-105 V-2, D-HECA, at Ottobrun, Germany, 16 February 1967. (Eurocopter)
Wilfried von Engelhardt tests the Bölkow-Entwicklungen KG Bo-105 V-2, D-HECA, at Ottobrun, Germany, 16 February 1967. (Airbus Helicopters Deutschland GmbH)
Charles (“Chuck”) Aaron demonstrates the aerobatic capability of the Messerschmitt-Bölkow-Blohm Bo-105 CBS-4, N154EH. (Red Bull)
Baron von Engelhardt’s parents

Wilhelm Friedrich Franz Eugen Baron von Engelhardt was born at Schloss Liebenberg, north of Berlin, Germany, 11 September 1928. He was the son of the Rudolf Robert Baron von Engelhardt and Ingeborg Maria Alexandrine Mathilde Baroness Engelhardt (Gräfin zu Eulenburg), and the grandson of Friedrich-Wend Fürst zu Eulenburg-Hertefeld, Count of Sandels.

Wilhelm von Engelhardt had an early interest in aviation.  His stepfather, Generalmajor Carl-August von Schoenebeck, a World War I ace, commanded the Luftwaffe flight test agency at Flugplatz Rechlin-Lärz, Rechlin, Germany. Von Englehardt was able to meet a number of well known German pilots, some of whom were guests at the family home. At the age of 16, he began flight training in gliders.

With the approach of the Soviet Red Army, von Engelhardt and his family fled to Austria. (General Shoenebeck was held as a prisoner of war until 1948.) He trained in hotel management in Salzburg. Following his release from Allied custody, General Schoenebeck formed Luftfahrt-Technik, a distributor for several aircraft manufacturers, including Hiller Helicopters.

With the assistance of General Schoenebeck, in the early 1950s von Engelhardt went to Paris, France, to train as a helicopter mechanic. He next became a helicopter pilot, then flight instructor, in 1958. He flew the Hiller 12, the Bell 47, and the gas turbine-powered Sud-Ouest Djinn. Von Engelhardt flew the SNCASE SE.3130 Alouette II in Papua New Guinea, 1961–1962, then returned to France where he trained as a test pilot at École du personnel navigant d’essais et de réception (EPNER) at Istres.

Von Engelhardt was recommended as test pilot for the Bölkow-Entwicklungen KG Bo-46, by the helicopter’s rotor system designer, Hans Derschmidt. The Bo-46 was an experimental high-speed helicopter. Von Engelhardt made the first liftoff of the prototype aircraft 14 February 1964.

Bölkow-Entwicklungen Bo-46 V-1, D-9514, with the Derschmidt rotor system. (Johan Visschedijk Collection, No. 6705/1000aircraftphotos.com)

Wilhelm von Engelhardt served as Bölkow’s chief test pilot, from 1962 to 1973. He then became the company’s sales director and director of customer service training.

With the Soviet occupation of eastern Germany, the village where Baron von Engelhardt was born was seized. It later came under the jurisdiction of the German Democratic Republic. Following the reunification of East and West Germany, the government of the Federal Republic of Germany held control of Schloss Liebenberg.

Schloss Liebenberg is now a hotel. (Michelin)

In 1996, without informing the local population, the Federal Office for Special Tasks Related to Unification, government’s privatization agency, placed the entire village, including the castle, the 13th century church, all the homes, farm buildings and stable, for sale. The asking price was so high that it was impossible for the villagers to come up with enough money to buy their home town. There was considerable outcry from the villagers, who said that they felt as if they, too, had been put on sale.

Baron von Engelhardt, who was living in a rented coach house on the estate that his family had owned for more than 300 years, gained international recognition for his attempts to negotiate a reasonable outcome.

With his wife, Evamaria, he edited and published Brücke über den Strom, (“Bridge over the Stream”), the letters of his cousin, Sigwart Botho Philipp August zu Eulenburg, Count of Eulenburg, a musical composer who was killed during World War I.

Wilhelm Friedrich Franz Eugen Baron von Engelhardt died 24 January 2015, at the age of 86 years.

Wilfried Baron von Englehardt 1928-2015)
Wilhelm Friedrich Franz Eugen Baron von Engelhardt (11 September 1928–24 January 2015)

© 2019, Bryan R. Swopes

10 January 1966

The prototype Bell Model 206A JetRanger, serial number 1, civil registration N8560F, hovering out of ground effect. (Bell Helicopter Company)
The prototype Bell Model 206A JetRanger, serial number 1, civil registration N8560F, hovering out of ground effect. (Bell Helicopter Company)

10 January 1966: The prototype Bell Model 206A JetRanger serial number 1, N8560F, made its first flight at at the Bell Helicopter Company plant at Hurst, Texas. This aircraft would be in production for almost 45 years. The final JetRanger to be built, Bell 206B-3 serial number 4690, was delivered in December 2010 and production came to an end.

During early production of the Model 206A, cabin sections were built by Beechcraft and Agusta then shipped to Bell at Fort Worth. (The vertical seam just to the rear of the fuel cap distinguished the two.) Oil pressure and temperature gauges for the engine and transmission, the loadmeter and fuel quantity indicator were provided by Cessna.

The  Bell JetRanger is a 5-place, single-engine light civil helicopter based on the Bell Helicopter’s unsuccessful OH-4 entrant for the U.S. Army’s Light Observation Helicopter (LOH, or “loach”) contract. It is flown by a single pilot in the right front seat. Dual flight controls can be installed for a second pilot. The helicopter was certified for VFR flight, but could be modified for instrument flight.

The industrial design firm of Charles Wilfred Butler

“. . . was responsible for the complete redesign of the Bell OH-4A prototype army helicopter (1961) into the Bell Jet Ranger (1965). He and his designers restyled the machine inside and out in the manner of automotive design, creating in the process one of the world’s most successful and beautiful helicopters.”

Encyclopedia Britannica.

The JetRanger is 38 feet, 9.5 inches (11.824 meters) long, overall. On standard skid landing gear the overall height is 9 feet, 4 inches (2.845 meters). The Bell 206A has an empty weight of approximately 1,700 pounds (771 kilograms), depending on installed equipment. The maximum gross weight is 3,200 pounds (1,451.5 kilograms). With an external load suspended from the cargo hook, the maximum gross weight is increased to 3,350 pounds (1,519.5 kilograms).

The two-bladed main rotor is semi-rigid and under-slung, a common feature of Bell’s main rotor design. It has a diameter of 33 feet, 4.0 inches (10.160 meters) and turns counter-clockwise (seen from above) at 394 r.p.m. (100% NR). (The advancing blade is on the helicopter’s right side.) The rotor blade has a chord of 1 foot, 1.0 inches (0.330 meter) and 10° negative twist. The airfoil is symmetrical. The cyclic and collective pitch controls are hydraulically-boosted.

The first Bell 206B JetRanger (Bell Helicopter Co.)
The first Bell 206A JetRanger, N8560F. (Bell Helicopter Co.)

The two-bladed tail rotor assembly is also semi-rigid and is positioned on the left side of the tail boom in a pusher configuration. It turns at 2,550 r.p.m., clockwise, as seen from the helicopter’s left. (The advancing blade is below the axis of rotation.) The tail rotor diameter is 5 feet, 6.0 inches (1.676 meters).

The turboshaft engine is mounted above the roof of the fuselage, to the rear of the main transmission. Output shafts lead forward to the transmission and aft to the tail rotor 90° gear box. The transmission and rotor mast are mounted tilting slightly forward and to the left. This assists in the helicopter’s lift off to a hover, helps to offset its translating tendency, and keeps the passenger cabin in a near-level attitude during cruise flight.

A vertical fin is attached at the aft end of the tail boom. The fin is offset 4° to the right to unload the tail rotor in cruise flight. Fixed horizontal stabilizers with an inverted asymmetric airfoil are attached to the tail boom. In cruise flight, these provide a downward force that keeps the passenger cabin in a near-level attitude.

The 206A was powered by an Allison 250-C18 turboshaft engine (T63-A-700) which produced a maximum of 317 shaft horsepower at 104% N1, 53,164 r.pm. The improved Model 206B JetRanger and 206B-2 JetRanger II used a 370 horsepower 250–C20 engine, and the Model 206B-3 JetRanger III had 250-C20B, -C20J or -C20R engines installed, rated at 420 shaft horsepower at 105% N1, (53,519 r.p.m.). Many 206As were upgraded to 206Bs and they are sometimes referred to as a “206A/B.” The Allison 250-C20B has a 7-stage compressor section with 6-stage axial-flow stages, and 1 centrifugal-flow stage. The 4-stage axial-flow turbine has a 2-stage gas producer (N1) and 2-stage power turbine (N2). These were very light weight engines, ranging from just 141 to 173 pounds (64.0 to 78.5 kilograms).

The helicopter’s main transmission is limited to a maximum input of 317 shaft horsepower (100% Torque, 5-minute limit). The engine’s accessory gear unit reduces the output shaft speed to 6,016 r.p.m. N2, which is further reduced by the transmission’s planetary gears, and the tail rotor 90° gear box.

The JetRanger has a maximum speed, VNE, of 150 miles per hour (241 kilometers per hour) up to 3,000 feet (914 meters). Its best rate of climb, VY, is at 60 miles per hour (97 kilometers per hour) and best speed in autorotation (minimum rate of descent and maximum distance) is at 80 miles per hour (129 kilometers per hour), resulting in a glide ratio of about 4:1. The service ceiling is 13,500 feet (4,145 meters) with the helicopter’s gross weight above 3,000 pounds (1,361 kilograms), and 20,000 feet (6,096 meters) when below 3,000 pounds. The helicopter has a maximum range of 430 miles (692 kilometers).

After being used as a factory demonstrator and development aircraft, N8560F was retired from flight status and used as a maintenance ground training device at Bell’s training school at Hurst.

Note: The Model 206A-1 was adopted by the U.S. Army as the OH-58A Kiowa. Though very similar in appearance to the Model 206A and 206B, the OH-58A differs significantly. Few of the parts are interchangeable between the types.

Three view drawing of the Bell Model 206A/B JetRanger with dimensions. (Bell Helicopter TEXTRON)
Three view drawing of the Bell Model 206A/B JetRanger with dimensions. (Bell Helicopter TEXTRON)

© 2018, Bryan R. Swopes