Stupid question: what does a collective do?

[warmachine79]

Hey guys, the last time I was flying a chopper was in Comanche 3 back in 199x somewhere. You increased throttle and if you wanted to go forward, you push the stick down, if you want to stop or go backwards, you pull the stick back. After buying the AH64, I learnt choppers are not that easy as after failing flying the AH64 like I flew the Comanche, I noticed there is an another stick: "The collective" (I am not kidding you, I noticed only now that helos have such a thing). 

 

How does the collective work and do you have a suggestion where to Map on X56 HOTAS? The rotor power I have on the thrust, the other controls are "like in a plance". I occassionally tried around with the collective and managed to move around a little bit, still, I did not do anything "on purpose". So - what does the collective to - it is only one axis, correct? 

[razo+r]

I suggest you to map the Rotor RPM / Power levers to a button or to the left throttle of your HOTAS while binding the collective to the other throttle of your HOTAS.

 

How does a collective work? You pull the collective up, your rotors make more lift and up you go. Drop it and you will also drop.

If you want to go forward, increase collective and pitch the nose down a bit. If you want to slow down, pitch up and drop the collective a bit.

You can also have a look at the manual or wiki or the internet in general to learn more about helicopter controls.

Edited June 13, 2022 by razo+r

[Recluse]

Decided to quote WIKIPEDIA instead of my interpretation which would no doubt be flagged by people who actually KNOW something 

 

Cyclic

 

 

The cyclic control, commonly called the cyclic stick or just cyclic, is similar in appearance on most helicopters to a control stick from a conventional aircraft. The cyclic stick commonly rises up from beneath the front of each pilot's seat. The Robinson R22 has a "teetering" cyclic design connected to a central column located between the two seats. Helicopters with fly-by-wire systems allow a cyclic-style controller to be mounted to the side of the pilot seat.

The cyclic is used to control the main rotor in order to change the helicopter's direction of movement. In a hover, the cyclic controls the movement of the helicopter forward, back, and laterally. During forward flight, the cyclic control inputs cause flight path changes similar to fixed-wing aircraft flight; left or right inputs cause the helicopter to roll into a turn in the desired direction, and forward and back inputs change the pitch attitude of the helicopter resulting in altitude changes (climbing or descending flight).

The control is called the cyclic because it changes the mechanical pitch angle or feathering angle of each main rotor blade independently, depending on its position in the cycle. The pitch is changed so that each blade will have the same angle of incidence as it passes the same point in the cycle, changing the lift generated by the blade at that point and causing each blade to change its angle of incidence, that is, to rotate slightly along its long axis, in sequence as it passes the same point. If that point is dead ahead, the blade pitch increases briefly in that direction. Thus, If the pilot pushes the cyclic forward, the rotor disk tilts forward, and the helicopter is drawn straight ahead. If the pilot pushes the cyclic to the right, the rotor disk tilts to the right.

Any rotor system has a delay between the point in rotation where the controls introduce a change in pitch and the point where the desired change in the rotor blade's flight occurs. This difference is caused by phase lag, often confused with gyroscopic precession. A rotor is an oscillatory system that obeys the laws that govern vibration—which, depending on the rotor system, may resemble the behaviour of a gyroscope.

Collective

The collective pitch control, or collective lever, is normally located on the left side of the pilot's seat with an adjustable friction control to prevent inadvertent movement. The collective changes the pitch angle of all the main rotor blades collectively (i.e., all at the same time) and is independent of their position in the rotational cycle. Therefore, if a collective input is made, all the blades change equally, and as a result, the helicopter increases or decreases its total lift derived from the rotor. In level flight this would cause a climb or descent, while with the helicopter pitched forward an increase in total lift would produce an acceleration together with a given amount of ascent.

The collective pitch control in a Boeing CH-47 Chinook is called a thrust control, but serves the same purpose, except that it controls two rotor systems, applying differential collective pitch.^[3]

Edited June 13, 2022 by Recluse

[warmachine79]

2 hours ago, razo+r said:

I suggest you to map the Rotor RPM / Power levers to a button or to the left throttle of your HOTAS while binding the collective to the other throttle of your HOTAS.

 

How does a collective work? You pull the collective up, your rotors make more lift and up you go. Drop it and you will also drop.

If you want to go forward, increase collective and pitch the nose down a bit. If you want to slow down, pitch up and drop the collective a bit.

You can also have a look at the manual or wiki or the internet in general to learn more about helicopter controls.

 

Yeah, I looked at Wiki, but I wanted to know, how I use them and what distincts them from a throttle. I thought the throttle makes "more lift" and if I leave the main stick where it is, the RPM from the rotors applied via the throttle brings me upwards, and if I tilt the stick forward, it moves the ROM from the rotors applied via the throttle bring me forwards. I was not aware that a helo needs another "enitity" to make a helo work like helos work (and still cannot comprehend why ). 

[Recluse]

The Throttle affects the SPEED of rotation of the blades. (Though rotor RPM is affected by TORQUE (the resistance on the spinning blades)) The Collective affects the Angle of Attack (pitch) of the rotor blades.  In the Apache, you set the THROTTLE to FLY and leave it there. I am sure that in other, less sophisticated helos you ALSO have to manipulate the throttle to maintain Rotor RPM when countered by resistance and torque)  Lift is generated by the pitch of the rotor blades. Think of the rotor blades as WINGS (hence the term ROTARY WING aircraft) that generate lift by spinning vs. being propelled through the air by a propeller or jet engine on a "FIXED WING" aircraft.

Also, I have to opine that

Comanche 3 was NOT a good simulation of  helicopter flight, though, possibly the RAH-66 was designed to fly differently from a standard Helo via computer wizardry.  All I know is when I went from Janes Longbow/EECH  and any other attempt at a realistic helicopter simulation  to try Comanche, I was perplexed by the flight model where the collective/throttle was more like an elevator control that went up and down. Forget everything you learned from Comanche 3.

Edited June 13, 2022 by Recluse

[corbu1]

Hello warmachine79,

if you are interested how helicopters aerodynamics work in principle, I‘ll recommend the following link.
 

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook

It provides an overview what is needed to lift off a helicopter, which control elements are needed and how they work.

 

[Floyd1212]

24 minutes ago, warmachine79 said:

I thought the throttle makes "more lift" and if I leave the main stick where it is, the RPM from the rotors applied via the throttle brings me upwards

As others have said, the throttle position is set to Fly and is then left alone, and the on-board management system attempts to keep the speed of the rotors constant.  Then adding more collective produces more lift.

 

 

[OLD CROW]

3 hours ago, warmachine79 said:

How does the collective work and do you have a suggestion where to Map on X56 HOTAS? The rotor power I have on the thrust, the other controls are "like in a plance". I occassionally tried around with the collective and managed to move around a little bit, still, I did not do anything "on purpose". So - what does the collective to - it is only one axis, correct? 

Collective lever Pull up/ push down changes the AOA (angle of attack) of your collective (ALL) rotor Blades(chopper's wings) throughout a complete rotor spin. That all blades AOA change means more/ less lift. On the other hand we have the cyclic where the lever/stick only changes the AOA of the blades in the exact point of the cycle you are pushing/pulling the stick (like the ailerons in an aircraft for the rolling). 100% sure you can find out other better tech explanations, but you need to understand what they move and the reasson for that move.

[warmachine79]

1 hour ago, Floyd1212 said:

As others have said, the throttle position is set to Fly and is then left alone, and the on-board management system attempts to keep the speed of the rotors constant.  Then adding more collective produces more lift.

 

 

Ah! That is important to know, so I do not constantly manage throttle power and collective position, but rather but the throttle power somewhere ("just fly dude") and the actual steering of the helo is what the collective does. So it is purposeful to put the collective on the HOTAS and have the throttle power on some easily accessible, but not necessarily as-accurate-as-the-HOTAS-throttle-axis. 

[cow_art]

34 minutes ago, warmachine79 said:

Ah! That is important to know, so I do not constantly manage throttle power and collective position, but rather but the throttle power somewhere ("just fly dude") and the actual steering of the helo is what the collective does. So it is purposeful to put the collective on the HOTAS and have the throttle power on some easily accessible, but not necessarily as-accurate-as-the-HOTAS-throttle-axis. 

Yea exactly. With all DCS helos you can easily have the throttle on keys (or even drag the throttle with the mouse) and be just fine. Usually you only set the throttle once (during startup) then you never touch it again. At least that's what I have been doing for the last few years and I never felt like I was missing anything.

[Dragon1-1]

2 hours ago, Recluse said:

I am sure that in other, less sophisticated helos you ALSO have to manipulate the throttle to maintain Rotor RPM when countered by resistance and torque

This was the case on WWII-vintage R-4 helicopter, and was part of what made it fiendishly difficult to fly, even more so than a normal helicopter. Not sure if Germans put governors on their helos (since the technology existed and was in use on German props), but either way, it quickly became standard even on the simplest designs.

[DmitriKozlowsky]

Collective is a helicopter control that changes angle of pitch of all rotor blades of main rotor at same time , at same rate, to same angle.  In other words collectively. Cyclic changes pitch angle of each rotor blade individually , or in a cycle. Collective is used to control vertical velocity of a helicopter in hover and low speed forward flight. At higher speeds above 16-20 knots, collective is used to control vertical velocity of helicopter without changing the attitude of the helicopter (roll, pitch, yaw), and maintain positive G loading in rotor,  that control with cyclic would cause. Positive +.2 or higher G loading on disk is critical for flight safety. Near zero or negative G, as caused by aggressive cyclic forward, can cause blades to flap excessively, risking a mechanical collision with rotor mast or with fuselage.   Throttle grip on smaller and older helicopters is part of the collective. In modern turbine powered helicopters, and some piston powered helicopters, the throttle (amount of fuel fed to the engine) is controlled by engine governor, to keep main rotor RPM at constant rate. So as collective is pushed down or pulled up by pilot, the amount of power required to maintain rotor RPM changes, and that is the function of governor. In that sense some view collective as throttle, but that is erroneous view. The governed throttle is reacting to collective movement, to maintain rotor RPM, not controlled by collective. In helicopters without governor, the pilot controls throttle via twist grip installed on collective, to maintain required rotor RPM.

[Despayre]

They assimilate; resistance is futile.

 

Wait, wrong sim...

[Leg2ion]

'How does a collective work' - such an innocent question and bound to elicit a few multi faceted responses!

So, (and as eluded to in a few responses to above) a Collective control is a pilot input lever that will 'collectively' increase/decrease pitch on all blades at the same time.  Unfortunately - things are not that simplistic, so whilst the desire may be to increase pitch (initially) uniformly across all blades - this cannot happen due to advancing and retreating blade speeds coupled with aircraft forward speed. In essence - in forward flight advancing blades - so those going forward into the airflow - need less pitch (which equates to less lift) due to increased airflow (advancing speed plus fwd aircraft speed) across the aerofoil section of the blade, whilst those retreating - so heading backwards away from fwd speed airflow need more pitch (equating to more lift) due to decreased airflow (retreating blade speed minus fwd aircraft speed). Overall effect is to keep relative lift across the rotor disc equal to prevent dissymmetry of lift.  This is governed by basic flight control rigging where everything is pinned in position and angles set by adjusting the control rods (simplistic explanation)!

In terms of 'power' - in the good ole days a lot of levers had a twist grip throttle, so was down to pilot skill to 'roll on' power to the engines to sustain power to maintain rotor speed - so the engines were manually governed. If you can picture a case whereby the blade pitch increases when the collective was raised to, say, transition into a hover from initial start-up, so in terms of airflow across the disc the blades will slow down, so the engines need to provide more power to maintain or increase rotor speed to counter the slow down effect. 

Then things got a little bit more advanced, whereby the throttle (independent of the collective) would be set (to fly), and the engines were fitted with a governor which would detect engine slow down (which meant rotor slow down) so would open a valve in the fuel management unit to increase fuel flow to increase speed and counter the slow down. Minor pilot input was required. 

Nowadays there are electronic control units fitted, and the system is basically automated - the idea being to take the workload off the pilot (who has better things to be doing on a battlefield). So these units govern the engine power output into the rotors transmission to maintain rotor speed - and are fed by a myriad of variables (from the airframe sensors and the engines), and in addition have 'anticipators' - another unit that will detect collective movement and anticipate a power demand (or reduction) and tailor the fuel flow to suit. 

Then you need to factor in the yaw and cyclic inputs and how the interlinks interact ...

 

[Scott-S6]

On 6/13/2022 at 3:40 PM, warmachine79 said:

Ah! That is important to know, so I do not constantly manage throttle power and collective position, but rather but the throttle power somewhere ("just fly dude") and the actual steering of the helo is what the collective does. So it is purposeful to put the collective on the HOTAS and have the throttle power on some easily accessible, but not necessarily as-accurate-as-the-HOTAS-throttle-axis. 

Have a look at page 52 of the manual. This explains what the throttles (power levers) do. It's very simple on the apache - when the engine management system is working you have three positions: off, idle, fly. Pretty self explanatory. You can also take manual control of the engines ("lock out") but that's not for normal operation.

[Hammer1-1]

To make it easy, just think of it as the collective simply changes the blade angle from fine pitch to coarse pitch.

[Sinclair_76]

tl/dr

The lift vector is perpendicular to the rotor disc and in a stationary hover equal and opposite to gravity. 

Collective decreases or increases the vector and cyclic changes the direction of that vector.

In practice there's a lot of external variables but in essence it is that simple.

 

 

 

 

[TrevorMcNeill]

On 6/13/2022 at 8:38 AM, OLD CROW said:

Collective lever Pull up/ push down changes the AOA (angle of attack) of your collective (ALL) rotor Blades(chopper's wings) throughout a complete rotor spin. That all blades AOA change means more/ less lift. On the other hand we have the cyclic where the lever/stick only changes the AOA of the blades in the exact point of the cycle you are pushing/pulling the stick (like the ailerons in an aircraft for the rolling). 100% sure you can find out other better tech explanations, but you need to understand what they move and the reasson for that move.

Fun fact, if you push forward cyclic its actually changing the pitch of the blades at 3 and 9 o'clock positions, they do this because of gyroscopic precession. Effects of a force placed on a rotordisk won't take effect until 90° later in the direction of the rotational plane. 

[TrevorMcNeill]

On 6/14/2022 at 2:40 PM, Leg2ion said:

'How does a collective work' - such an innocent question and bound to elicit a few multi faceted responses!

So, (and as eluded to in a few responses to above) a Collective control is a pilot input lever that will 'collectively' increase/decrease pitch on all blades at the same time.  Unfortunately - things are not that simplistic, so whilst the desire may be to increase pitch (initially) uniformly across all blades - this cannot happen due to advancing and retreating blade speeds coupled with aircraft forward speed. In essence - in forward flight advancing blades - so those going forward into the airflow - need less pitch (which equates to less lift) due to increased airflow (advancing speed plus fwd aircraft speed) across the aerofoil section of the blade, whilst those retreating - so heading backwards away from fwd speed airflow need more pitch (equating to more lift) due to decreased airflow (retreating blade speed minus fwd aircraft speed). Overall effect is to keep relative lift across the rotor disc equal to prevent dissymmetry of lift.  This is governed by basic flight control rigging where everything is pinned in position and angles set by adjusting the control rods (simplistic explanation)!

In terms of 'power' - in the good ole days a lot of levers had a twist grip throttle, so was down to pilot skill to 'roll on' power to the engines to sustain power to maintain rotor speed - so the engines were manually governed. If you can picture a case whereby the blade pitch increases when the collective was raised to, say, transition into a hover from initial start-up, so in terms of airflow across the disc the blades will slow down, so the engines need to provide more power to maintain or increase rotor speed to counter the slow down effect. 

Then things got a little bit more advanced, whereby the throttle (independent of the collective) would be set (to fly), and the engines were fitted with a governor which would detect engine slow down (which meant rotor slow down) so would open a valve in the fuel management unit to increase fuel flow to increase speed and counter the slow down. Minor pilot input was required. 

Nowadays there are electronic control units fitted, and the system is basically automated - the idea being to take the workload off the pilot (who has better things to be doing on a battlefield). So these units govern the engine power output into the rotors transmission to maintain rotor speed - and are fed by a myriad of variables (from the airframe sensors and the engines), and in addition have 'anticipators' - another unit that will detect collective movement and anticipate a power demand (or reduction) and tailor the fuel flow to suit. 

Then you need to factor in the yaw and cyclic inputs and how the interlinks interact ...

 

Aren't helicopters so fun?! All I want to do is go from a hover to forward flight. okay, Simple! Just a bit of forward cyclic....Wait now im descending, okay ill raise collective! Wait now im starting to spin guess ill use left pedal now

[dburne]

5 hours ago, TrevorMcNeill said:

Aren't helicopters so fun?! All I want to do is go from a hover to forward flight. okay, Simple! Just a bit of forward cyclic....Wait now im descending, okay ill raise collective! Wait now im starting to spin guess ill use left pedal now

Been there, done that, have the T-shirt. Especially when transitioning from forward flight to hover.

[Hammer1-1]

9 hours ago, TrevorMcNeill said:

Aren't helicopters so fun?! All I want to do is go from a hover to forward flight. okay, Simple! Just a bit of forward cyclic....Wait now im descending, okay ill raise collective! Wait now im starting to spin guess ill use left pedal now

only amateurs fly forward.

[5ephir0th]

You should know that on helicopters the rotors  (main and tail) runs at a fixed rpm (you can increase or decrease it but you usually runs constant on the flight time) so the collective change the pitch of the main rotor blades: if you increase the collective you incrase the pitch of the main rotor blades, generating more lift so you go up, and if you decrease it then the reverse happens.

Tail rotor works the same, with pedals you change the pitch of the tail rotor blades.

The moderns helicopters have a thing called governor that change the engine power to mantain constant the rotor rpm

Edited June 26, 2022 by 5ephir0th

[pii]

On 6/25/2022 at 1:15 AM, TrevorMcNeill said:

Aren't helicopters so fun?! All I want to do is go from a hover to forward flight. okay, Simple! Just a bit of forward cyclic....Wait now im descending, okay ill raise collective! Wait now im starting to spin guess ill use left pedal now

Sounds like you need to anticipate what is about to happen.