BV, in the late `50s Westland built the Belvedere,tandem rotor helo,twin engine,originally for the RN,who decided they didn`t want it ,so it ended up in the RAF.The engines ,however were mounted vertically,one behind the cockpit,the other down at the aft end.The rotors were conventional 4bladed metal,with power controls ,but both rotors/g`boxes were joined be a `syncho-shaft,.The difference between this system and the Chinook is that each engine effectively powered each rotor,but the synchro-shaft kept the two power units balanced.If you had an engine failure,either engine could drive the lot,so only in that case was the s-s taking full torque..Also the aircraft did not have such a blade` overlap` as the Chinny,and had more height difference between front and rear rotors..There were a couple of s-s failures,but aircraft landed cautiously,as the rotor RPM could be balanced on the twin throttles..
There were 3 main problems for flying the Bevelgear,;getting in,climbing a 6ft ladder,starting the engine behind the cockpit ,cartridge -Avpin-light-up,and getting out in a hurry if the Avpin starter blew up...!!
By the time it left service in the late 60`s,most of it`s tech. problems had been sorted,but it did great work in the Far East,was able to lift home 3 Whirlwinds home that I had scattered around Borneo( one was a tail-rotor and gearbox departure) ,all returned to service later...
As an aside I did get a trip in a JagT-Bird with Ron Burrows,laden with `dumb test.bombs`,took 99.95 % of B-Ds runway to get airborne(over 1minute rolling),and the noting control deflections ,G,yaw reponse,for an hour.....I was a bit of a `sucker` for those trips...and didn`t puke....