Flying a twin rotor

[Karl]

I've been reading that book on Vietnam. It's got me wondering how are Twin rotors like Chinooks or flying bananas flown/controlled?

Thanks

Karl

[copter doctor]

I haven't flown one, worked in the back ( Flight Engineer ), but it is basically like other helicopters. The Chinook has a cyclic and pedals but they call the " collective " the thrust lever. Since there are counter-rotating rotors, the pedals are used for hover turns mostly and not used as often as a main rotor-tailrotor set up. To do a pedal turn one disc tilts one way and the other the oppisite way. I know there are some tandem pilots on here that could share more information. Hope that helps some.

[Karl]

Thanks. That's more than I knew before.

[Inferno]

Fore and aft cyclic inputs actually increase or decrease collective pitch of the fore or aft rotors.

[palmfish]

I've been reading that book on Vietnam. It's got me wondering how are Twin rotors like Chinooks or flying bananas flown/controlled?

Thanks

Karl

 

It's actually a "tandem rotor."

 

Thanks to very complex flight control systems (mechanical mixing linkages, hydraulic servos, Longitudinal Cyclic Trim Actuators (with Landing Gear Proximity Switch), and Advanced Flight Control System, the Chinook flies pretty much like any other helicopter. It is remarkably nimble and easy to control.

 

The biggest difference is not adjusting the pedals when changing power (thrust) or during slope landings.

[Karl]

I knew that but spaced on the name.

Are they still called tandem if it's set up like a Kaman Kmax?

 

Kmax

 

Thanks

Karl

[Wally]

"Tandem" implies fore and aft.

[rick1128]

I knew that but spaced on the name.

Are they still called tandem if it's set up like a Kaman Kmax?

 

Kmax

 

Thanks

Karl

 

 

The K-Max and the Husky use a system called the Flettner system. The rotors are driven off of one gear box.

 

If I remember correctly, the Chinook's rotors are intermeshed and the transmissions are connected together and to both engines. So the rotor blades miss each other and you are able to operate single engine.

[palmfish]

The K-Max and the Husky use a system called the Flettner system. The rotors are driven off of one gear box.

 

If I remember correctly, the Chinook's rotors are intermeshed and the transmissions are connected together and to both engines. So the rotor blades miss each other and you are able to operate single engine.

 

The Chinook has 5 transmissions. Each engine drives a gearbox that outputs to the main transmission. The main transmission can be driven by either or both engines. The main transmission is then connected to the foreward and aft transmissions via driveshafts, and this is how the timing of the main rotors is maintained. It's also one of the most vulnerable parts of the aircraft. The main driveshaft is a thin-walled, hollow aluminum tube that runs along the top of the helicopter under a thin cowling.

[FLHooker]

I like this thread...

 

The pedals are also not called "anti torque pedals", they are directional pedals, because we don't anti nothing with them! No tailrotor limitation!

 

Rick, you are right, the rotors on a chinook are synchronized, each blade is 120* out from each other, the only way they can touch is if the synchronizing driveshaft, which runs (like palmfish said) from the combining transmission to the forward transmission fails.

 

Overall, like others have stated... the Chinook flies just like other helo's, the inputs are the same, etc... just don't need to touch the pedals.

[palmfish]

Phew! I was hoping a real Chinook pilot would come to the rescue before I had to dust the cob webs off my old manuals!

[Guest pokey]

I have always been interested in the tandem rotor's control system. The swashplates don't tilt fore/aft at all? only sideways & up & down? I built a R/C 47 back in the 80's, but never flew it----i was debating on the forward flight configuration & decided on tilting the swashplates along with a differntial collective for trim. I dont know if it was right OR would have worked. A friend of mine had aquired a HUP retreiver a few years back & we were discussing ever him flying it,,,,, seems he found an old pilot who flew them for sperry ( the autopilot people) & the old bird said & i quote "the auto pilot worked fine on the ground, but? turn it on in flight & its suicide" They say that tandem rotors will tend to fly "sideways" w/ out the autopilot turned on ( the newer autopilots that actually work). The rear rotor is looking for "clean air" ( doesnt like flying in the fwd rotor's wash). That was the reason for the Retreiver's large vert tail fins.

 

Any comments from 47 pilots?

[Guest pokey]

OMG OMG OMG this is my friend, i guess he did get it flying...... RIP John

 

http://www.pacificflyer.com/2009/12/three-...age-helo-crash/

[FLHooker]

Pokey, No, the swashplates do move fore/aft. At around 70 kias, the LCT's (Longitudinal Cyclic Trim) program the rotorheads (tilt forward) to keep the fuselage level. When we come up to a hover, the LCT's retract, but on the ground they program to 9* on the FWD head, and 4* on the AFT head for ground taxi. However, we do not have cyclic feathering at a hover.

 

As for the "flying sideways" he is right, with the AFCS off, the helo wants to fly sideways, and just as you stated, the aft rotor wants to find clean air. It equates to us actually having to dance on the pedals in flight. You can get it trim'd up and only use small inputs on the pedals when you are straight and level, but it's game on in a turn. Turns it into an overpowered TH-67 at a hover The nose will also swing left when you are taking off from the ground too, requiring right pedal. It's a blast!

 

 

CHAD

[Guest pokey]

Thanx Chad, i get it ( not as often as i like tho) no seriously,, but? i dont understand this part

 

 

 

However, we do not have cyclic feathering at a hover.

 

It's a blast!

 

 

CHAD

 

and i bet its a blast ! ( you mean w/ the AFCS off? ) even with it on i bet !

 

AFCS=? AutoFlightControlSystem ?