Sassy.....
 

Large Helicopters large thing!

Small Helicopters all thing!!

I had a trip in a Chinook sim some years ago - thanks JJ and John - and had a bit of a play.

Spot turns with no cyclic input turned about the centre of the aircraft. Spot turns with right or left cyclic turned about the rear or front of the aircraft - but I can't for the life of me remember which cyclic went with which end.

But as a low time pilot (then 70 hours and a PPL on R22s) it didn't take too long to get comfortable enough to sling loads and fly formation . . . but the AFCS is really good !

Who is shooting that machine gun?
 

This is slightly off track but.....

My very first ride in a helicopter was in a Piaseki HRP-1 the original flying banana. The engine was in the rear of the passenger compartment completely exposed (a mechanics’ dream) along with the fuel bladder. I was sitting near the combining gearbox when the pilot put the helicopter into autorotation and the helicopter did not have a freewheeling unit. Instead it had a spring-loaded jaw clutch which sounded like a machine gun going off. It scared the hell out of us that were not familiar with the HRP-1.

:E :E

The CH-46 and CH-47 families have had a very interesting history of AFCS' (whatever Boeing wanted to call them, they eventually are all an Automatic system of some sort).
The latest version is probably one of the finest systems I've ever seen. Simple (relatively) to understand, does a nice job, and makes both the aircraft quite docile.
The CH-46 is the worse of the two with the AFCS off, and is probably due to the aerodynamic shape of the rear fin. I can't speak for earlier models of the CH-47, but the C and D are not bad with everything turned off.
The BV 234 is probably pretty close to the CH-47D, with differences in the electrics and flight instruments.
And the way to turn about the nose is simple to do, but difficult to describe - basically pedal against the cyclic. Turn about the tail is pedal with cyclic.
Empty? They are sports cars.

I seem to rememebr that when lifting to the hover and the weight comes off ( the microswitches associated with) the rear wheels, the longitudinal cyclic control re-datums itself through subtle length changes, via screw jacks, of the control runs. And AFCS Off, the stick gradient is reversed translating to and from the hover. (Now that's inviting the purists to put me right!!)
But that said, an R22 pilot should still have little difficulty hovering a Chinook.

Bloody Bonza!, where do I sign up to have a shot?.
:} ;)

Any US Army recruiting office;)

wizard of oz:
Doesn't the Australian Army operate Chinooks too?

Australian Army Chinooks
 

Shawn,

They sure do.

Cheers,

BM

http://homepage.mac.com/helipilot/PPRuNe/chinook2.JPG

Stealth Chinook:suspect:

Stealth Hook? Looks like a Semi-trailer that sat too long in a gang neighborhood and got "Tagged"!:ok:

To me looks like a chinook used in a secret british SAS operation...
Irak? Afganistan? :E
cool.

Back in 1985 the Spanish Army bought some new models from Boeing, since all "D" production line was going to the US Army they sold the Boeing Vertol 414, which was the civil version half way between the Super C and D.
Those 414 had the L-712 engines on them, FRB's and RPM's indicators in %'s, although oil cooling system and AGB's were the same as in C models.
The other day I was invited to go to my former Chinook batallion brand new Delta simulator. The cockpit and instruments all looked quite alike a C model. Although I haven't seen the BV 234 I would think that they would be closer to the BV 414 than to a D model.
Just my 2 cents.
Buen Vuelo

Chinook Amphibians
 

I was watching the programme "Combat Helicopters" on Channel 5 last night and was amazed to see a US Chinook landing on the sea to pick up a RIB. The initial splash was quite big and, when they showed a shot from inside, the crew were ankle deep in water as they pulled the boat inboard. In fact, they seemed to rely on the backwash to bring the boat inside.

Is this a procedure used and trained for regularly by any Chinook operators?

When you think how that amount of water can capsize a ferry, the control and stability problems for a helicopter must be quite interesting.

I think you will find that the "amphibious" footage was of an RAF Chinook.

Indeed so.

At least some of the footage (that showing a Chinook with plimsoll lines on the outside) was of an aircraft from Boscombe. Venue was Lyn Brenig.

I think the interior footage of the surfing crewman was of the BD trial, too.

I have seen several pictures of Chinooks landing on lakes (but have nowhere to host them so can't post them), including one of a RIB coming into the back, looks quite impressive taking off with all the water gushing out.

I believe all the pictures I have seen have been on lakes, not the sea, ie fresh, not salt, water. I seem to remember that salt water can be very damaging to aircraft, but fresh water isn't so bad, am I wrong? (it has been known to happen)

That would be bloody impressive - a MIB maybe, perhaps 2 of them, but not a RIB!!

HPT

Any one got any pictures to post of Chinnooks landing on water??

Silly question time: I take it Chinooks can't float on water without a certain amount of collective input, would I be right in assuming this?? If so how do you keep a large helo on the water rather than upside down/under the water!?! :confused:

HPT,

Not quite sure what the MIB you refer to is, but it is quite feasable that a RIB (rigid inflatable boat) could enter a the rear of a chinook

The boat on the Boscombe footage is indeed a RIB, it enters the Wokka at a fair rate, about 5kt. Better carried inside than underslung , as a surprised motorist found when one was dumped (Oscillating badly) from a Wokka near the A303 some years ago.

Then there was Smokey's (IIRC?) attempt to undersling the Ark Royal on Ex Purple Helmet in 1987...:)

The MIB is a Medium Inflatable Boat, flat bottomedwith no hard bits. The RIB is rigid bottomed as you describe and either 21 or 28 ft long.

The RIB, due to hull shape, could not get into the Chinook fully and was not claered to do so in the UK. Of course they may have driven up to the ramp and transferred pax, but don't see the benefit of that.

Gainsy - I have never seen a RIB in the back of one, perhaps this precedes my experiences. The Boscombe pictures I have access to do not show a RIB, its a MIB.

PPF - The Chinook will float quite happily at collective gound detent position which is positive pitch giving about 20 torque. By the way, this exactly the collective position that is used during ground operations following landing.

The procedure itself is quite straight forward and the speed is controlled by collective and water depth by cyclic - its best to give the crewman a good six inches in my experience :O . The Chinook has a power down ramp facility, i.e, one that doesn't freefall under gravity, so you can for the buoyant ramp into the water.

HPT

HPT,
OK, 'twas the boffin at Boscombe said it was a RIB. To me it was just a speed boaty thing. V impressive technique though. They released the film to the Beeb but the d'head producer ditched it (and some v. low level parachute trials) in favour of some Bona mates doing press ups.:zzz:

Chinook taking a bath:


http://www.boeing.com/companyoffices...dvd-110-05.jpg

Water landings on the Delaware River next to the Boeing Philadelphia factory.
The Chinook is watertight and fully capable of landing on water for special operations and similar missions. The Chinook remains afloat even with the rotors not turning, and a special kit facilitates water operations.

http://www.boeing.com/companyoffices...dvd-110-05.htm

(Look at gallery for more)

OK, I just looked at the pictures again, it was a MIB (never heard that term before), as it didn't look like any of the RIBS I've dived from, none of which would have fitted.

Apologies for the mistake, but my boat knowledge is a bit limited (that's why I work in aviation).

The pic I've got from the inside of the boat coming in quite good, the loadie is seeing how high up the inside he can climb.

If any wants a look or can host then, PM/Email me.

http://www.chinook-helicopter.com/hi..._The_Water.jpg

Pasted from www.chinook-helicopter.com where they reckon a CH47 can float for 30 mins without engine power.
http://www.army-technology.com/proje.../chinook14.jpg

Multi-Rotor question
 

An argument came up in the pub yesterday between me and a mate which raised a question concerning helicopters which hopefully someone here can answer.

The basis of the argument was as follows (and this is very basic stuff, so please forgive me). On a normal helicopter there is a single rotor. When this revolves to provide lift it generates torque which will cause the fuselage to revolve in the opposite direction to the rotor. To counteract this a tail rotor is fitted to provide a counter-thrust to the fuselage so it doesn’t spin. However if a helicopter has two contra-rotating rotors the forces between the two balance out so there is no need for a tail rotor to stop the fuselage spinning.

But (and here the argument started) there is still a requirement to turn the fuselage (to face the direction of travel, saves getting a crick in the neck when flying backward). In the standard single-rotor machine this is, I believe, done by varying the thrust from the tail rotor so it provides either too much or too little (which will turn the fuselage). However how is it done on a multi-rotor machine?

I claimed it could be done, at least theoretically, by varying the properties between the rotors (different pitch or, less likely, different speed for the two would produce a torque imbalance which would turn the machine). He insisted that they must have some external thrust, either from a tail rotor or variable ducting for the exhaust (for the turbine powered machines) to turn them (I cited the Chinook as not having a rotor but he insisted it has ducted thrust).

Does anyone know if this is possible (or even has been done) or am I talking through my posterial orifice again? (And there is a pint riding on this).

How to control a Chinook...
 

I believe I am correct when I say that there is definately no "notar" type system on a chinook or a tail rotor. Essentially when pedals are pressed in the cockpit both rotor systems are tilted in opposite directions.

I got this from another website:
"This is accomplished by pedal only inputs. By depressing one pedal over the other, cyclic inputs are put in both systems in opposite directions to pivot about the center of the aircraft. Both rotor systems receive equal cyclic inputs, and the helicopter just spins nicely at its center without the pilot having to move his cyclic control at all. A pivot around the tail is accomplished by heavy cyclic inputs by the pilot, and little or no pedal inputs. This will make the tail stay in one place, and the nose of the aircraft move laterally until it spins about the aft mast."

Needless to say it is a complicated system that requires a lot of linkages, a lot of control tubes, and a pilot who trusts his maintenance crew to make sure it all was put together properly!

Hope you won that pint....

MadsDad, as copterfamily states, there is no sideways thrust in the Chinook other than from the main rotors.

You may like to look at this thread for a more indepth explanation.

PS, the BV234 was/is the civil version of the Chinook.

Ah, but what about Kamovs?
 

When both rotors are on the same shaft, one above the other, applying different cyclic to both would serve only to bend the shaft (or if you're really out of luck, the tips would touch).

Being on the same shaft and generating equal amounts of lift and torque, they normally cancel each other out. When you want to turn on your axis, pressing, say, left pedal reduces the pitch on the anti-clockwise rotor and increases it on the clockwise rotor - result, fuselage turns anti-clockwise, or 'left'.

You win the beer.

Your only mistake was the statement "On a normal helicopter, there is a single rotor."

The single rotor is an abnormality. Future rotorcraft will have lateral symmetry, just like every other vehicle; and animal for that mater.
http://www.unicopter.com/No_Tail_Rotor.gif

With apologies to those who ride around in motorcycle sidecars.
:D

And now, the rest of the story
 

Discount just about everything stated by Fr O'Blivien in the above referenced post.

As previously stated if you push the "rudder" pedals the helicopter will spin about the center of the fuselage. This is differential pitch input in the fact that one rotor has a cyclic input to the left and the other rotor system has a cyclic input to the right. Pressing the opposite pedal will result in the helicopter spinning in the opposite direction. Cyclic input will not cause the blades to hit each other as they are locked in a fixed position relative to each other this is called phasing.

If the pilot moves the cyclic to the left or the right the helicopter will move in the direction of cyclic movement and once again cyclic input will not cause the blades to strike each other due to the fixed phasing. A coordinated pilot can input cyclic movement and at the same time press the pedals and the helicopter can be made to pivot either about the forward mast or the rear mast depending on the coordinated pitch input. A really coordinated pilot can perform a maneuver called walking the dog in which he alternates the pivoting from the front mast to the rear mast and back again.

Fr O’Blivien made a statement about the tilting of the transmissions when the pilot inputs forward cyclic. This is not the case. Movement of the cyclic either forward or rearward will cause one rotor system to increase collective pitch and the other to decrease collective pitch which causes the helicopter to move in the direction of the decreased collective pitch.

The pilot does not have any input relative to forward or aft cyclic stick movement other than to effect the collective pitch levels of the respective rotor system. When the helicopter reaches a forward speed of around sixty knots forward cyclic pitch is automatically applied to both rotor systems and at this time the pilot can lower his collective stick. When the speed drops below sixty knots the forward cyclic input is removed and most likely the pilot will have to increase collective pitch to a level it takes to fly with decreased weight.

:E :E

RE: Kamov
 

Good evening all!

Correct me if I'm wrong but I always thought that the big russian coaxial twin rotors use their downwash wich acts on the tailboom rudder to turn?

Lu,

Why is it the Chinook has only Pivoting and Swiveling Actuators on the rotor heads....One of each per head...driven by two independent hydraulic systems?

Kamovs
 

Woolf, you suddenly made me wonder if my information was correct. Then I thought about autorotation.

With the airflow up through the rotor (and of course the tail), what happens? If it's the sheets of metal on the tail that are used for yaw control, then the effect of the pedals will be reversed. If it's differential collective, they won't.

I'm imagining that yaw control by the tail fins would be achieved by pivoting them at the top and swinging them in the opposite direction to which you want to spot-turn.

CH-47 hydraulics
 

To: SASless

To the best of my knowledge the swash plates on the CH-47 have two each hydraulic actuators that impart both lateral (cyclic) input as well as collective input. Each swashplate has an extension arm that is about a foot or more in length. Attached to this extension arm is an electrical actuator that retracts to provide forward cyclic when the helicopter reaches approximately sixty knots. When dropping below sixty knots the actuator is commanded to extend returning the respective swashplates to the commanded collective setting.

The control geometry is such the when applying lateral cyclic the swashplate pivots on the extension attach bearing for the electrical actuator. When forward cyclic is imparted by the electrical actuator the swashplate pivots on the bearings on the hydraulic control actuators.

An added side note: The CH-47 is a cargo and troop carrier and at that time (below sixty knots) the rotor systems are operating at high collective settings and at high power settings. When the rotorheads are returned for overhaul many of the high value components are scrapped due to cracking from high stress levels.
This is especially true for the rear rotor.


:E :E

How the systems yaw
 

Oookay, well someone might beat me to this, but…

Tandem rotor system, like the Chinook:

To yaw, one rotor “banks” left while the other banks right, fuselage pivots in middle. I hear (but have no firsthand experience) that a good Chinook pilot can, through finesse with cyclic, collective and pedals induce the big tandem to pivot around the nose or tail.

Coaxial rotor system (contra-rotating rotors stacked on top of each other), like the Kamov:

To yaw, one rotor increases collective pitch while the other decreases collective pitch. The resulting difference in torque about the rotor driveshaft(s) causes the aircraft to pivot about the rotor mast. The vertical tail surface provides stability in forward flight

Synchromesh counter-rotating rotors (side-by side), like the Kaman:

One rotor pitches forward while the other pitches back, dragging the fuselage around a point between the rotor masts (a lateral version of the tandem, I suppose). Again, the vertical stab provides stability in forward flight.

That's as far as I know, anyway.

What Flingwing207 says is essentially correct, with one small exception. The "Synchromesh" description is totally correct for the Side-by-side configuration, and part of the answer for the Intermeshing configuration.

The Intermeshing configuration is sort of a hybrid between the Side-by-side and the Coaxial. Most Intermeshing helicopters use both opposed longitudinal cyclic and differential collective.

http://www.unicopter.com/B318.jpg

£260m Chinooks are grounded turkeys, say MPs
 

eh?