Nederlandse Helikopter Industrie (NHI)

The Nederlandse Helikopter Industrie (NHI) was a Dutch helicopter manufacturer. It was founded in 1955 as a commercial successor of the "Stichting voor de Ontwikkeling en Bouw van een Experimenteel Hefschroefvliegtuig" (SOBEH - the Foundation for Development and Manufacturing of an Experimental Helicopter 0. From 1951 on, SOBEH developed and built two helicopters, the H-1 (1954) and H-2 (1955). After having met its goal of developing a helicopter, SOBEH ceased activities. Further development and serial production were granted to the newly formed NHI. This was a joint venture between aircraft manufacturer Aviolanda and truck company Kromhout. NHI quickly came forward with an improved design, called the H-3 Kolibrie (Hummingbird). This helicopter made its first flight in May 1956. The Certificate of Airworthiness, based on U.S. requirements for rotorcraft, was issued in March 1958.

Design

The H-3 was a two seat general purpose helicopter. It has a duraluminium tube superstructure, an open cockpit and an undergear of metal skids. The design is distinctive because it is ramjet powered. Two ramjets, one at the tip of each rotor blade, power the helicoper. The small tail rotor is powered by the motion of the main rotor. The ramjets could run at any given fuel, which gave the helicopter a certain versatility.

The ramjets made a complex engine and gear box unnecessary. Kromhout designed and built the ramjets. Each engine generated 20 kg thrust. The last models had an improved engine, built by Aviolanda, generating 23 kg thrust.

In order to start the ramjets, a small 2 hp auxiliary power unit set the main rotor in motion. At a rotorspeed of 70 rpm, the ramjets were to be ignited.

Variants with ski’s, floating devices and medical evacuation stretchers were developed and tested, but these versions were never produced. A version as crop duster was developed, and in due time, the H-3 was mainly marketed as crop dusting helicopter.

Production

The H-3 was assembled at Aviolanda. Subassembly took place at Aviolanda which built the fuselage and at Kromhout which built the engines. Fokker, a subcontractor to NHI, built the rotorblades. Final assembly took place at the newly opened Rotterdam Airport.

The initial production run counted ten helicopters of which the first three were used for development, testing and airworthiness tests. The second production run of ten helicopters was undertaken by Aviolanda after Kromhout left the joint venture. This second production run was to be equipped with an uprated ramjet. It is unsure whether the improved ramjet was ever produced.

Commercial failure

Although the H-3 was considered to be technical success, it never was a commercial success. Despite its low acquisition price, the project became a failure. Several factors attributed to this failure. In the first place, the Hiller H-23 Raven was provided to the Royal Netherlands Air Force by the United States for free under the Mutual Defense Assistance Pact (MDAP). Second, the two most important designers, Jan M. Drees and Gerard F. Verhage, left NHI. The company never recovered from this knowledge drain. The third reason stems from the radical design. The ramjets at the tips of the rotorblades were too unconventional for the time. Potential buyers did not consider the ramjet to be safe. Fourthly, the extraordinary fuel consumption of the two ramjets made the helicopter uneconomical to operate. Therefore flight time and flight range were quite limited which made the helicopter unattractive for commercial or military use.

Production list

Overall, nine H-3’s were built between 1958 and 1959 by NHI at Rotterdam Airport when Kromhout was still a parent company. After Kromhout left, Aviolanda built another two H-3’s at their Papendrecht plant.

The few production models were mainly exported to Israel, Germany, the UK and the Dutch East Indies. A few models stayed in the Netherlands.

Demise

During its existence, NHI was confronted with parent companies in trouble. Kromhout ceased building trucks in 1958 due to stiff competition from DAF. It kept building engines and finally the company was taken over by Stork. As a result, Kromhout gave up its partnership in 1959. Aviolanda resumed production of the H-3 on its own.

Finally in 1961 production ceased due to a lack of orders. Subsequently, NHI was liquidated by Aviolanda. The failure of NHI was only a contributing factor to the liquidation, as Aviolanda and Fokker were having hard times. Aviolanda depended heavily on licenced production of foreign designs, which made the business uncertain. Fokker was having troubles with the then slow selling F.27 Friendship.

Remains

The remains that are known of, are to be found at the aerospace museum Aviodrome. Aviodrome has one H-2 and one H-3 on display.

pecifications (H-3 Kolibrie)

;General characteristics
* Crew: 1 pilot
* Capacity: 1 passenger
* Length (fuselage): 4.22 m
* Main rotor diameter: 10.00 m
* Tail rotor diameter: 0.84 m
* Height: 2.59 m
* Empty weight: 270 kg
* Takeoff weight: 650 kg
* Fuel capacity: 400 liter
* Powerplant: 2x Kromhout TJ-5 ramjets, 100 hp each

;Performance
* Max. speed: 113 km/h
* Max. cruising speed: 90 km/h
* Range: 70 km (with pilot only)

ee also

*Fairey Rotodyne - a gyrodyne (jet tipped rotor driven at take off and landing only)
*Rotary Rocket - with rocket tipped rotor blades
*Hiller YH-32 Hornet - another helicopter with ramjet powered rotorblades