CH-47 Question

[Steve]

Are the basic flight controlls the same in a CH-47 as they are in a conventional helicopter (Like a blackhawk, etc) or is it a completely different setup?

 

[Ollie]

Well, yes and no. The controls are set up in the same manner as in conventional single rotor aircraft - you have a cyclic, pedals, and the collective is called a "thrust control." They have pretty much the same effect on the aircraft as on single rotor aircraft, but the way the controls interface with the rotor systems is very different.

 

[USMCmech]

I spent a lot of time on CH-46s, the Chinoks little brother.


The flight controlls are the same in the cockpit, Cyclic, Collective, Yaw pedals.

However the systems that actually move the rotorhead work a little different. There is much less "tilt" available in the rotor head than a conventional helo. This is because the two head can work opposite each other to change direction. To pitch foward, the foward head drops collective, and the aft head rasises collective, but this is all done by the pilot pushing the cyclic foward.

On the CH-46, the ground stearing is done by tilting the forward head right or left. The CH-47 is actually a taildrager, and the same thing is done by the aft head.

 

[Ollie]

I spent a lot of time on CH-46s, the Chinoks little brother.


The flight controlls are the same in the cockpit, Cyclic, Collective, Yaw pedals.

However the systems that actually move the rotorhead work a little different. There is much less "tilt" available in the rotor head than a conventional helo. This is because the two head can work opposite each other to change direction. To pitch foward, the foward head drops collective, and the aft head rasises collective, but this is all done by the pilot pushing the cyclic foward.

On the CH-46, the ground stearing is done by tilting the forward head right or left. The CH-47 is actually a taildrager, and the same thing is done by the aft head.

In the 47, the pilot's inputs don't directly do anything to the rotor heads. They send signals to flight control computers that apply the inputs via a series of hydraulic actuators as they see fit to give the pilot what they think he wants. There is no direct control linkage between any of the flight controls and either of the rotor heads. Also, there is no way for the pilot to control the aircraft without hydraulic pressure.

Pitch fore and aft is based on differential collective pitch, lateral inputs cause both discs to tilt in the direction of the input while pedal inputs cause the forward disc to tilt in the direction of input and the aft disc to tilt opposite. Using a combination of pedal and lateral cyclic, the pilot can make the aircraft pivot about the forward or aft rotor head.

I guess the 47 could be called a taildragger, but it has 4 wheels. Steering is controlled by a power steering control in the cockpit. The pilot has a spring loaded knob on the console between the pilots' seats that he uses to steer left and right. The rotor heads have nothing to do with steering. The parts that acually move to steer the aircraft are hydraulic power steering actuators mounted on the aft landing gear.

 

[mudkow60]

But to "dumb it down", for a pilot flying a twin rotor is like flying a tail rotor, correct? Just that folks comming from twin to tail don't always realize the inherent limitations in a tr aircraft.

 

[Ollie]

Flying a tandem rotor is like flying a tail rotor in that you can perform, at the least, the same maneuvers.

All the 47 drivers I know of learned to fly in single rotor helicopters, so everybody knows the limitations of the conventional design. I could still give you the explaination of LTE, loss of t/r thrust, loss of components, etc. if I really needed to.

 

[USMCmech]

In the 47, the pilot's inputs don't directly do anything to the rotor heads. They send signals to flight control computers that apply the inputs via a series of hydraulic actuators as they see fit to give the pilot what they think he wants. There is no direct control linkage between any of the flight controls and either of the rotor heads. Also, there is no way for the pilot to control the aircraft without hydraulic pressure.

Pitch fore and aft is based on differential collective pitch, lateral inputs cause both discs to tilt in the direction of the input while pedal inputs cause the forward disc to tilt in the direction of input and the aft disc to tilt opposite. Using a combination of pedal and lateral cyclic, the pilot can make the aircraft pivot about the forward or aft rotor head.

I guess the 47 could be called a taildragger, but it has 4 wheels. Steering is controlled by a power steering control in the cockpit. The pilot has a spring loaded knob on the console between the pilots' seats that he uses to steer left and right. The rotor heads have nothing to do with steering. The parts that acually move to steer the aircraft are hydraulic power steering actuators mounted on the aft landing gear.

I stand corrected.

I didn't realize that there the CH-47 was so much more complex than the Phrog (ch-46).


On the Phrog the nose wheel is free swiveling, all ground direction changes are done by the foward head.

The CH-46 has hydraulic flight controls, but there is no computer at all. Just lots of push rods, cables, bellcranks, and accuators.

 

[CH47Driver]

Not Quite Right...

I know I'm being the typical Type A here but I had to post a minor correction to Ollie's post. He said...

Originally Posted by Ollie
In the 47, the pilot's inputs don't directly do anything to the rotor heads. They send signals to flight control computers that apply the inputs via a series of hydraulic actuators as they see fit to give the pilot what they think he wants. There is no direct control linkage between any of the flight controls and either of the rotor heads. Also, there is no way for the pilot to control the aircraft without hydraulic pressure.



This isn't entirely correct. What Ollie said gives the impression that the Chinook is fly-by-wire. The flight controls are linked to the rotor heads in the same way that the controls of a jumbo jet are linked to the control surfaces, via hydraulics. He's absolutely correct that without hydraulics, you cannot move the controls. (I've seen many a kid try while sitting in the cockpit at airshows). The AFCS (Advanced Flight Control System) computers work in conjuction with the pilot's inputs and serve to stabilize the aircraft in flight as well as provide other functions such as heading hold, airspeed hold, ect. This is evidenced by the fact that you can lock out the computer's inputs and fly the aircraft with the AFCS off (it often isn't pretty but it can be done).

I know I'm geeking out a little but had to put in my two cents...