David Greys prototype based on the 'free flight' contra-rotating helicopter configuration was developed and manufactured in 1972 thus becoming the first US Radio-controlled helicopter kit; the Whirlybird 505.

Du-Bro Timeline

Below is a list of introduction dates for Du-Bro helicopters and 'major' upgrades; I have not included minor kit variations, change of body colours etc.

1972 Whirlybird 505
1973 Hughes 300
1974 Shark
1975 Tristar (Scorpion-Hughes 500D-Enstrom F-28)
1976 Shark (60)

Dub-Ro advert 1976 for 'training' system, note the flybar 'cans'.

Du-Bro also produced a training set with extended landing legs with 'wiffle' ball as they called them which allowed the helicopter to slide in any direction and prevented it from being 'tipped' over.  Additionally, one of the main problems with learning to hover was the control of the tail, especially with collective pitch which did not have the tendency for torque correction that a fixed pitch system displayed.  To counter this an extension to the tail boom was also supplied which had a very large circular auxiliary fin; in a breeze this tended to act as an early 'heading hold' gyro which stopped the helicopter rotating.

By 1977 Dub-Ro just seemed to 'stop' developing their helicopters and let the range die out.  Not certain on the exact cause however, the heli-Baby had become popular and Dub-Ro models in comparison could be considered quite crude.  It would have thus been very expensive to attempt to develop their own machines to compete and as American RC Inc had already beaten them past the post in making a 'copy', financially I suspect the decision was taken to pull out and just produce what they had as long as sales were there.  Hopefully further research may turn up more definite information.