Real Helo Collective function..

[Cezar11]

Was wondering if any real helo jockeys out there could answer this...

 

in a real helo... does the collective stay put at any point on it's travel or does it always want to bottom out? I know there are collective brakes on some, but was wondering if the brakes are more of a "won't let it move" kind of brake or if their sole purpose was to keep it where you want because without the brake on, it would bottom out on its own?

 

I would think that since you have to take your hands off the collective during flight to flip switches and other stuff, you wouldn't want it moving on it's own..

[nemises]

I'm not a real helo pilot, but I have seen several discusions on here about it.

 

In the real KA50, the collective stay's where it is, and the pilot has to hold in the Collective Brake to be able to move the collective handle itself. Once he releases the collective brake, the collective stays in place with friction.

 

As for other helo's ? ..hmm I've only ever flown in a Robinson once (introductory lesson type thing) , and for the life of me I cannot remember whether the Collective wanted to fall on it's own or not..I expect not though...I rather expect there to be some resistance at least that holds it in place...as you say, if you needed to scratch your noe, you wouldnt want to suddenly bottom out the collective.

[EtherealN]

A somewhat similar question that has struck me: since both the collective and the cyclic control the same thing - the angle of attack of the blades - just in a collective or cyclic manner respectively, does a high collective setting reduce the relative travel you get through the cyclic?

 

The closest thing I have on hand to look it up is an RC helo I have, but that thing isn't entirely representative of real helicopters (it can hover while upside down ffs!)...

[tutmeister]

I've flown a few types of helicopter, amongst which the Apache D. Some types will drop straight to the floor, but newer ones default to center at about cruise torque. Most have a screw-like ring around it that you twist to increase friction, thus you can control how floppy or how stiff the collective is, or set it fast completely. Having it set fast is obviously not recommended, as in most emergencies you're going to want to lower the collective immediately.

 

But anyway, so when you're in cruise configuration and want to check a map, or flick a switch, you can, with friction on. The apache D can do most things hands-on the collective, with a cursor control allowing you to manipulate the MFDs from your thumb on the collective.

[BRraptor]

A somewhat similar question that has struck me: since both the collective and the cyclic control the same thing - the angle of attack of the blades - just in a collective or cyclic manner respectively, does a high collective setting reduce the relative travel you get through the cyclic?

 

They certainly not control the same thing.

 

Collective = blades angle of attack

Cyclic = swash plate inclination

 

You can see in F2 camera, helo stopped on the ground, move both and see the difference.

[geogob]

Technically, the collective also controls the swashplate, but instead of tilting it, it moves it up and down uniformly (although I'm not quite sure how it would work with a dual rotor. I think it's not that different as the two rotors probably work with differential input).

[Frederf]

The cyclic controls bank and pitch by dissimilar blade AoA along the rotor disk. The collective controls lift by uniform changes in blade AoA all over the rotor disk. That is pretty similar.

 

It does beg the question if there's a max AoA that a blade can achieve, perhaps certain collective/cycling input combinations are beyond the maximum AoA limit where those collective or cyclic inputs would be within the limit if the other input (cyclic or collective, respecitvely) was putting less demand on the rotors.

[Jack57]

Whether the collective will fall, rise or stay put when left unattended without any friction devices depends on the loading on the blades, including such things as the trim tabs which are set by the LAME's and not dynamically by the pilot.

 

It is not uncommon for pilots to vacate an idling helicopter - used to do so myself when hot-refueling - and there are instances of helicopters becoming airborne when the pilot forgot the friction lock on the collective. It is probably more common however for the collective to want to fall under its own weight.

[hannibal]

when i saw photos of the puma and blackhawk, it seems like it can stay where it is when you let go...i make this determination from all the cockpit photos i have seen...because some people have left the collectives both up and down as the helicopters are parked in the hangar or before flight.

[Draco]

In the R-44 it'll drop slowly. I'm not a fan of using collective friction becasue in the event of engine failure we have 1.1 seconds to enter the auto before the rotor rpm decays below critical limits and the blades fold up.

[VS461]

Hey all,

Mi-8/17/24s' collective stays where you've left it. They have hydraulic released collective brakes. But you can tighten or loosen this before take-off preparing for a landing with the emergency hydraulics (only main hyd actuates the brake release). So if you loosen it too many, it drops slowly. Strange thing on long enroutes: why we are slowing down and/or descending???:D

 

On other helos: I've just tried a certified Robinson R-22 simulator, the collective remained in the preset position, I think.

 

As Frederf said, both cyclic and collective actuate the rotor blades by the same rods. I don't read about high collective restrictions of the cyclic about my Hind but highest collective angles are present in two situations: take-off/hover/land and high-speed level flying. Neither require high-angle cyclic activity. And if, for example, at a hi-speed flight you start to maneuver the Hind with the cyclic so intensively, you will exceed the G-limitations and you can cause stall on the blades. So the angle addition is not a practical problem. And, of course, the helo's fuselage follows the rotors by the swivels/elastomers: we don't need (relative) high blade AoA change for a 45° of bank.

 

We :joystick: maneuver the Mi-24 at cruising speed or below: that means about 2/3 of the maximum collective angle (before the maneuvers:D). An other issue: at this speed and collective we have enough power remaining for the maneuvers.

 

The things I've written above is caused by the Hind's limitations, but I think this stands for other helos as well. Think on fast jets: dogfights are not performed at Mach 2.5.

 

Cheers!

Edited January 23, 2009 by VS461
accuracy

[Frederf]

So you're saying that cyclic + collective authority are theoretically coupled and can limit each other but in practice it never really comes up?

[AlphaOneSix]

I've done at least my fair share of flight control rigging on various American, European, and Russian helicopters, and in every case, the cyclic has full movement regardless of the position of the collective. In other words, with flat collective, if you can pitch the swashplate forward 4.5 degrees, then at full collective, you can still pitch the swashplate forward 4.5 degrees.

 

Of course, as mentioned by VS461, there is really never a reason to do such a thing in flight, I've just done it many times on the ground.

[VS461]

So you're saying that cyclic + collective authority are theoretically coupled and can limit each other but in practice it never really comes up?

Yes and agree with AlphaOneSix. Cyclic and collective actuate the same blade control rods through the plate. So I can say that they can limit each other theoretically. But now, after a few words about it, I think our Russian friends did their homework well :), so this blocking would appear well beyond the operational (rod length, booster buffer etc.) settings. Maybe I can ask for a try during the next ground-powered hydraulic test (and ask someone from the hangar guys. At least a smart idea:D). During a flight, it really does not a factor.

Cheers!