Tandem Rotor Helicopter

0:00 Intro
0:08 Components
0:44 Engine Input
0:58 Engine Start
1:14 Two Engine Operation
An animation of a twin-engine, tandem rotor, helicopter drive system
This was loosely based on the CH-46 Sea Knight with two turbo shaft engines in front of the aft transmission. The engine output shafts are on the rear of each engine and both input power directly into only the aft transmission. The forward transmission is not directly powered from the engines, but rather from a synchronization shaft the runs the length of the fuselage.
Tandem rotor helicopters require a synchronization shaft which powers the front rotor system directly from the aft transmission. These aircraft can fly with one engine failed. With one engine powering the aft transmission, the forward transmission will also receive power via the synch shaft. A failure of the synchronization shaft is immediately catastrophic because the forward and aft rotor blades will contact each other soon after this failure.
I didn't model the rotor controls, but control of a tandem helicopter is done with collective and lateral cyclic blade pitch. Aircraft pitch control comes from differential collective pitch at each of the rotor heads. Yaw control comes from differential lateral cyclic pitch and roll control from simultaneous lateral cyclic pitch. Longitudinal cyclic commands are used for speed trim (in the CH-46 and CH-47) and not for aircraft pitch control.
I did the modeling in Fusion 360 and rendered this in Blender.

[@isaacbrooks1430]

You should go over differential collective pitch in tandem rotor helicopters!

[@mrabhi100k]

Thanks

[@gabedarrett1301]

How does the synchronization shaft handle the extreme torsion load? Does it have anything to do with those two connectors on the shaft itself?

[@bzig4929]

I'm not really sure I can answer. I've seen them up close and there's nothing special... the sections are just thin walled metal tubes. In some aircraft they are carbon fiber. The connections are flex plates that allow for some small misalignment because the aircraft bends and twists under flight loads.

[@isaacbrooks1430]

Chinook pilot here, the synch shafts move a lot! In all directions under load. I’ve often wondered the same thing but they work like the drive shaft going to a rear differential in any conventional car. They are rather thin walled hollow shafts but they are very finely machined and inspected. It’s still a bit of magic to me but they are proven!

[@erwin.f5426]

How to work coaxial rotor?

[@clutchtucker]

I believe a coaxial rotor would literally just be two rotors connected together, except the top one would be rotating in another direction instead of the bottom to counter torque. They'd pretty much just be stacked on-top of eachother.