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Vintage RC Helicopters - Kavan JetRanger
Kavan JetRanger (1973) Kavan approached FW Biesterfeld in 1971 with a view to developing and marketing his radi0o helicopter model though Biesterfeld had a near functioning model Huey it was decided to provide a contrast to the Schlüter Cobra by kitting the most well know civilian helicopter, the Bell JetRanger The prototype was displayed late in 1972 and subsequently marketed in 1973 being the first (commercially produced) model helicopter with collective pitch control. The model was very near scale and was of very high quality materials.
Initially the Kavan JetRanger had collective pitch but with only 'Bell' control i.e. flybar with weights and NOT paddles with this type of control providing a high level of stability for hovering and the model was not unduly disturbed by gusts etc. Though control was faster than the Hiller only types the inherent stability of the Bell system meant that when a control input was given the Bell bar moved in opposition to the main rotor as it had a lower centrifugal mass. This opposite movement had the effect of reducing the actual cyclic throw at the main blades. Unfortunately it could only cope with limited flight conditions and a number of test flyers lost control during high banked turns with not having enough control authority (and probably positive pitch) to recover in time; especially if at a low altitude. Another unusual feature was that the top housing carried all the controls for the rotor head and was held in place by six screws which made removal for maintenance an extremely simple and quick procedure. The engine unit was also a 'bolt in' pod and so maintenance on this area was quickly accessible after the top cover was removed. Production models incorporated paddles instead of weights which provided a measure of opposition to the defection on the Bell bar with cyclic input thus giving larger 'effective' control throws. Whilst improving control over the original format it did not provide the full answer.
Full technical description is given along with a comprehensive overview of all aspects of the build including techniques; so much so that it well compliments the supplied building instructions. Interesting 'hands on' setting up technique; I have done that myself in the past but anything goes wrong and well; you certainly have a 'tiger by the tail'.................... 1973 saw the Kavan JetRanger win a lot of major contents however, when you consider the competition was fixed pitch helicopters or own designs then it was to be expected.
To provide a more effective control system the head assembly was later modified to include a flybar with Hiller control thus giving the combined Bell-Hiller mixing that was to become the 'norm'. Cyclic control was now much improved though the standard configuration still resulted in a reasonably 'tame' set up; given that it was collective pitch and gyro's were not generally available, it was probably for the best otherwise tail control would have been nigh on impossible.
The first 'Hiller' modified versions introduced in 1973 did not use any form of 'washout' and so the paddles rotated when collective was adjusted; for efficiency they were set at 0-0 pitch either in the hover, or at circuit pitch setting depending on preference. Later that same year a 'washout' version was introduced making this version head adjustable for more aggressive behaviour and the JetRanger in this configuration was aerobatic. Initially though this washout unit was supplied as an addition and not provided with the basic kit; why, who knows, perhaps marketing ploy as the upgrade kit was provided free as long as the registration card was sent in......... Kit improvements - Jan 1974 article on a number of modifications made to the kit in light of operating experience.
Whilst other have claimed to have looped helicopters before this time the JetRanger was the first to perform a true round loop. This manoeuvre could only be done with the facility to alter the main rotor blade pitch as zero, or negative pitch is required at the 'top' in order to prevent the manoeuvre from ending up as a figure '9'. This was first demonstrated before an estimated crowd number of 25,000 early in 1974 by Mike Bosch. During 1974 the JetRanger was also displayed carrying out a 'roll' which again required zero or negative pitch at the inverted stage in order to keep it reasonably straight and not lose height.
1974 advert featuring an article on the further development of the JetRanger using an very expensive test method; not normally done today never mind at the start of the hobby and shows how seriously Franz Kavan took the subject. The 'history' page is useful though you have to take the initial statement 'with a pinch of salt'. It only took two years to produce the JetRanger though Biesterfeld had been working on his 'Huey' a few years before that and so this could be included in the 'total' development timescale. JetRanger Manual - This is version 2 which incorporates many lessons learnt from the early models. JetRanger Build Guide pictorial
Various constructional views of the version 2 Bell/Hiller model. JetRanger Manual Addendum - Various collection of items covering the JetRanger which supplements the Manual.
Kavan JetRanger Flybarless (1979)
Following on from this in 1979 the JetRanger was available as a rigid rotor (flybarless) model which only goes to show as even 30 years later (prior to the FBL electronic 'revolution') they were considered difficult to fly.
Notes for the first picture below indicate the year as 1976 for the JetRanger flybarless; flybar carrier has been removed and a fixed block fitted in order to attach the original mixer arms so as to retain the collective movement, home design perhaps but must have been one of the first FBL as the official version did not come out until much later.
Last pictures shows what can happen when a JetRanger tips over.... As the top cover was very substantial due to locating the servo's and linkages etc as a unit, in a mishap it stays intact and just rips up the fuselage beneath it. Top of Page (VRHC - Vintage Radio controlled HeliCopters) |
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