Just a minor correction, the Lynx still holds the record for speed...

Why would you use either dual (Chinook) rotors, or intermeshing vs concentric, contra-rotating systems like the KA-50?

The limiting factor for forward speed in a "normal" rotor system is the retreating blade stall.

The blade tips on my Bell 47 rotate at almost exactly 200mph. If I am going forward at 100 mph, the right (forward moving) blade tip "sees" a 300 mph airflow over it while the left (rear moving) blade tip sees a 100 mph airflow. If you go forward fast enough at some point the outer parts of the blade going "backwards" has no airflow over it and stalls. In a dual rotor system like the Chinook the blades rotates in the opposite directions so each rotor would have a retreating blade on opposite sides of the helicopter limiting (balancing?) its effects.

Hello all. Long time lurker, first time poster.
I've been a Chinook Flight Engineer for going on 24 years, and closing on 5000 flight hours. Lots of correct answers here. Yes, 5 transmissions. One forward, one aft, one combining, and two engine transmissions. 11 driveshafts connect it all together. Dual fully articulated rotor heads, with three fiberglass rotor blades rotor blades apiece. The blades weigh around 350 lbs. each. Twin T55-GA-714 engines produce around 3750 SHP continuous with up to 4500 SHP in contingency power. Max gross weight of the -47G is 54,000lbs, but I will tell you it won't get anywhere near 200 kts without a significant tailwind. I have seen 205-210 GS at altitude heading east in the winter. Normal cruise is around 110-120 knots, and there is a gauge in the cockpit to measure rotor system stress that must be satisfied depending on gross weight and altitude.

The tandem rotor design gives a very generous center of gravity for both internal and external loads, and is a very stable platform. With the Digital Advanced Flight Control System (DAFCS) it is laughably easy to fly. The configuration is a bit different then conventional helicopters in that the pitch attitude is controlled by differential collective pitch, meaning if you pull back on the stick, the forward head increases collective more than the aft head causing the nose to rise, and vice versa for forward stick. Roll is simple, and yaw is controlled by the rotor systems tilting opposite directions. Interestingly enough, the Chinook can yaw around the center fuselage, the forward or aft head by simply cross controlling the aircraft.

Thanks for starting this thread so I finally have something to contribute!

V/r,

Brad

Brad...Welcome to BT!!! Thanks for joining in the conversation

Thanks for that Brad. I'm familiar with the mast moment indicator on some hingeless rotor systems, is the "gauge in the cockpit" you refer to on the CH-47 similar? A mast strain measurement?

So...what's the ratio of maintenance hours/flight hours on a Chinook?

Ed,

There are strain gauges mounted to a fixed link on both the forward and aft swashplates. It's basically a wire that changes resistance as it's compressed or stretched, based on the stress to that fixed link, and that signal is measured and processed by a box and sent to either a gauge in the cockpit or displayed on an MFD. Green is good, yellow is meh, and red is bad, so do something to get it back into the green!

V/r,

Brad

So...what's the ratio of maintenance hours/flight hours on a Chinook?

Glenn,

Great question and one I don't know the answer to off the top of my head. There are many metrics and tools to define it. Our computerized logbook system could probably spit that number out, but I'm not sure as to it's authenticity.

I can tell you that it generally takes me and another experienced flight engineer about an hour and change to complete a Preventative Maintenance Daily (PMD) inspection. We do that prior to the pilots showing up to preflight, which is just another set of eyes looking at everything. My PMD is more in-depth than the preflight. On completion of the flight, I do a post flight which basically consists of a quick visual check on the major components, filter buttons, and fluid levels.

V/r,

Brad

The CH47 Chinook has a feature not present in other stuff I’ve been on-the hell hole.
The opening is enormous when you’re trying to get around without chicken strap on. The opening is tiny when you’re getting sucked back into the ship.

If you want to go fast, just tilt your rotors.

V-22 top speed is 270 Kts @ Sea Level.