Pedal/collective to slow the rotors

[Frenchrotorhead]

Hello to all,
Disclaimer : I'm a PPL, so only little experience, and I wouldn't try what I'm about to describe, merely wondering if it is ever used to save time/reduce the risks for the immediate environment (people, animals) of a spinning rotor.

Is it feasible/wrong/stupid/bad to add pedal input after shutdown (as much as terrain will allow without spinning the machine around) to slow the rotors faster ?

Moreover, is it feasible/wrong/stupid/bad to gradually add collective for the same purpose ?

Thanks for your replies, again, I'm a PPL, never in a hurry when flying, and don't envisage to use these techniques, so feel free to say its ridiculously stupid :=

[tony 1969]

collective is a no no,
I have no problem with left pedal (in a 300 becasuse there's no brake:ugh:)

[mikelimapapa]

Never heard of dynamic rollover being an issue, but raising the collective at low rpm can cause excessive flapping which can damage the rotorhead and cause M/R to contact the tailboom.

[OvertHawk]

Collective is a no-no (my main concern would be flapping / and sailing)

Pedal can be fine (and quite effective), depending on what the flight manual says.

Always read the flight manual and speak to an experience pilot on type

OH

[John R81]

Collective - no

Pedal - I would be v. careful. Living in N Europe, very easy to get into a routine which - in icy conditions - you may apply without thought and end up frightening yourself / others (or worse).

I would not go there. Particularly as a low-hour pilot.

[waragee]

I stand to be corrected but if memory serves me right I thought the Bell 47 manual stated that some collective pitch could be applied once the RRPM had dropped below a certain figure. (Perhaps a third)
I also think the H269C could have been approved to apply left pedal once the RRPM had dropped below a certain figure to assist with RRPM slowdown.

[before landing check list]

I have parked several times on top of a cliff. The blades would be just over the edge. The wind would keep the blades turning. So I did add some collective to get them to stop. It was a UH1H and it worked HOWEVER I can see flapping would be a consideration. I see no problem being gentle, left peddle and pay attention to the operators manual.

Jerry

[before landing check list]

Collective - no

Pedal - I would be v. careful. Living in N Europe, very easy to get into a routine which - in icy conditions - you may apply without thought and end up frightening yourself / others (or worse).

I would not go there. Particularly as a low-hour pilot.

If you are talking about the helicopters yawing on the ground (Or on the water with floats etc) with application of the collective then I would say I do not think so. The engine (I am assuming here) is off therefore there is no torque. That being said if you were using a rotor brake the helicopter will tend to turn in the direction of blade rotation upon brake application.

[before landing check list]

Good question by the Frenchrotorhead.

[before landing check list]

I need to do some research on the dynamic rollover thing.....

[Frenchrotorhead]

The main reason I see adding a little collective as being a bad idea is the risk of ground resonance (rigid multi bladed rotors), excessive flapping (hinged two bladed rotors) and blade sailing in both.

But then again, isn't it the case (pitch with RRPM going down) at the end of a full, engine off auto ?

[John R81]

BLCL

Try it on an icy pad. No engine to supply torque, use pedal to apply counter-torque, round you go!

On an icy pad there is almost zero fricional resistance to any input force.

[FH1100 Pilot]

Like so many things in helicopter aviation (e.g. hot refueling, getting out with the engine running, scud-running), using the collective and/or pedals to slow the rotor after shutdown should be accompanied by the caveat: DON'T BE AN IDIOT! USE SOME COMMON SENSE!

The Bell 47 indeed once allowed for up to 1/3 of the collective travel to be used for slowing the rotor. Even if a 47 had a rotor brake, it would barely stop a Schwinn bicycle much less a set of high-inertia metal blades. Once the 206 was invented (and with it a better rotor brake) that procedure disappeared from the flight manual.

Then later on Bell got all antsy about people using left pedal to slow the rotors, because the tail rotor could bang against the flap stops. But banging against the flap stops can happen even when shutting down in strong crosswinds and stuff. So the wise, old 206 pilot trims the pedals to minimize this during shutdown. Sometimes it takes left pedal; sometimes it takes right. You have to find that "sweet spot."

If you've flown a Hughes 500 you know that there's a spring that pulls the left pedal forward as the rotor slows. Sort of an "automatic" rotor brake.

In my non-rotor brake-equipped Bell 206B, I sometimes use a bit of collective and pedal to slow the blades, depending on how badly I have to pee. I said a "bit" of collective. The forces are certainly no stronger than those imparted by a hovering auto (or powered flight in the case of the t/r), and I'm careful to not let either of the rotors get flapping too wildly. I do not just yank full-up on the collective and jab full left pedal in and then exit the a/c in a big hurry no matter how urgently I have to do the aforementioned deed.

Use the brain God gave you, and don't be an idiot. Apply a bit of common sense and be smart about these things. If we all did that, perhaps we wouldn't have flight manuals that are as thick as the Manhattan Yellow Pages, with all sorts of admonishments to the stupidest among us.

[Lonewolf_50]

I remember learning to fly helicopters in Jet Ranger (206). There were cautions against using the T/R and collective to slow down the rotor when we shut down after a sortie at Whiting Field. (Can't recall if it was in the NATOPS or the squadron SOP, been nearly thirty years).

Of course, my instructor nearly always, when he was doing the shut down, added a bit of rudder and a bit of a colective ... but woe unto the student who did that. :cool:

FH1100: agree with most of your post.

[Fun Police]

the flight manual for the machine you are operating should describe the limitations regarding this. as a CPL or PPL, any pilot should be familiar with what they say and act accordingly as i can not imagine the manufacturers putting limitations in there for sh!ts and giggles ;)
fp

[SuperF]

We often use pedal / collective to slow the blades, however generally only in a wind as the damn things won't stop themselves (no rotor brakes). If you do it gently you will actually reduce the beating that they get by leaving everything centered... 206 and 204's, and only start playing with when less than about 30% or so, no slippery surfaces, so not much chance of going round.

A worse habit I have seen, is standing outside the machine, leaning in and shutting it off.:eek: with that quick whack of the throttle, if you do it the wrong way you are in for some fun.... Have even seen guys lean over the left seat, on right hand drive, and whack it off. Surely an opportunity to get it wrong. Before you go off about getting out of a helicopter with blades turning, let's forget that as it is well covered, and outside Europe seems to be a well accepted practise, main reason it goes wrong is when they leave it at flight idle! :ugh:

[Pilot DAR]

If you've flown a Hughes 500 you know that there's a spring that pulls the left pedal forward as the rotor slows. Sort of an "automatic" rotor brake.

MD 500 and 269/300 are similar in this regard. I have been taught that it is poor form in these machines to allow the pedals to sit hard over in either direction for any length of time. As the tail rotor blades are retained by blade straps, which are slightly streched at their edges during full deflection, full defection is to me kept to a minimum.

I have seen many techniques demonstrated after touchdown. I have always been most comfortable with the "attend the controls, and hold them in their sweet spot, until it stops" approach myself.

[army_av8r]

Im not a huge fan of adding a lot of pedal while shutting down only because your putting stress on the tail boom and attachment bolts(yaw thrust being applied at the end of the boom but skids not allowing the turn) i just dont imagine that being too good for the mounting bolts... and with the wrong crosswind/pedal input your can actually make the T/R blades "auto-rotate". if the manual allows for either then its obviously ok, but i prefer gentle application of collective and watching the tip path to avoid stop contacts. in general these techniques wont save much time, but with a strong wind and a weak battery, shutting down on a pinnacle... you gotta do whats needed to get them stopped and get the electricity offline. no jump starts on mountains. just follow the Manual and be smart!

[tony 1969]

perhaps I should have added left pedal after engine has stopped so in the 300 the main rotors speed will be down around the 150 rpm mark, cant see this putting much stress on anything, ( I could be wrong I frequently am:\)

[lelebebbel]

Im not a huge fan of adding a lot of pedal while shutting down only because your putting stress on the tail boom and attachment bolts(yaw thrust being applied at the end of the boom but skids not allowing the turn) i just dont imagine that being too good for the mounting bolts

I always thought that this is exactly what the tailboom was designed for? What do you do if you want to climb - just let the machine yaw right, because left pedal would put too much stress on the tailboom?

[loggerman]

If you pull the collective on a 300 during shut down the corrallation will increase the revs of the engine defeating the object !

[waragee]

loggerman you are guilty of engaging the keyboard before thinking about your reply, a mistake which I am guilty of too often.

In the scenario discussed here we are shutting down and at the point of introducing collective to aid in reducing RRPM the engine is closed down and will not be a factor.

I was told that using collective is no good in a 300 as it lifts the blades off the droop stops thus enabling a potential boom strike.

[Soave_Pilot]

I'm not a huge fan of adding a lot of pedal while shutting down only because your putting stress on the tail boom and attachment bolts(yaw thrust being applied at the end of the boom but skids not allowing the turn) i just dont imagine that being too good for the mounting bolts


I always thought that this is exactly what the tailboom was designed for? What do you do if you want to climb - just let the machine yaw right, because left pedal would put too much stress on the tailboom?

I don't agree with you lelebell but I agree with Army av8r, too much left pedal overtime would put stress on tailboom attachments, think as flying with the aircraft out of trim... not just counter torquing the main rotor as you would climbing.

[Hell Man]

Have made use of 'collective braking' in 204s, 205s and 206/Ls throughout my entire career and have had the collective at around 80% pitch just moments after shut down.

Never troubled myself with t/r application (too little benefit) but collective braking can reduce the wind-down time when necessary.

If you leave the lever up too long you will definately start slamming the stops and if that is left unchecked you can unseat the entire transmission. However, long before this ever occurs you can feel it approaching and its simply matter of smartly lowering the collective.

That's what I've done but - I'm not recommending it for others and increasingly new ships have rotorbrakes making this practice unnecessary.

[army_av8r]

i suppose i should also add that my feelings about the added stress on the tailboom are just that... they are my gut feelings. it may not cause any more stress than what is seen in normal flight, i just personally dont feel comfortable applying those inputs on the pedals. i feel i can control the main rotor much more safely. in the end, these techniques are really only used when i need the rotor stopped quickly or when the wind makes them want to spin forever. im generally not in enough hurry to bother with these techniques.

[kev_laline]

If you're on your own in an R44 and try raising the collective whilst the blades are turning you're at serious risk of dynamic rollover, even if the rotor RPM is well below normal operating range.

Is the risk of a dynamic rollover less likely if you have others with you in an R44 when you raise the collective after shutting down? Please enlighten us.:ugh:

The main reason I see adding a little collective as being a bad idea is the risk of ground resonance

If you're going to get into ground resonance, it will have already happened a long time before you shut down.

[Shawn Coyle]

The tail boom is stressed to take a lot more load than could be applied to a tail rotor at idle and below. There is absolutely no chance of doing damage to the bolts or any other structure.
There may be other reasons for not wanting to use tail rotor pitch to slow the rotors, but none would be caused by loads on the tail boom attachment bolts.

It's also impossible to get into dynamic rollover with the rotor blades unpowered and decelerating from idle RPM - you can't generate enough rolling moment or thrust to tilt the helicopter over.
You might have a problem with blade flapping, but not with dynamic rollover.

Same thing with ground resonance - first of all, you can't get ground resonance in a two bladed rotor (if that's what you're flying). And in any other multi-bladed head, with no power going to the rotor blades the rotor blades will find their own place in lead-lag. If one lead-lag damper was going bad, it would have gone bad when there was a large difference in drag between advancing and retreating side wouldn't it?
Raising the collective would increase the drag on all the blades at the same time, and if you were going to get ground resonance, the collective position wouldn't make any difference.

Where do these last two old wives tales come from???

[gentleben]

thanks for clarifying Shawn, there sure are some weird ideas out there, was thinking the same but couldn't put it so eloquently!

[kev_laline]

They were referred to in posts 2 & 12.

Thanks for another common sense input Shawn. :ok:

[fadecdegraded]

Personal experience weather it be good or bad it was experience non the less.
206 L and B full left pedal to slow the blades no prob.....but tried to pull a bit of collective once to slow the the blades in a jet box holy sheit will never do that again, main rotors went bizzuek, its not a good thing.

Seen military pilots pull FULL collective in 205s to slow rotors not pretty but they did it every shut down, was PNG defence force but.:D

[DoinTime]

Explain that to a Mechanic that was killed in Orlando:=

He was ground running a 300 to warm up the engine oil (yes they did it with the rotors engaged, at flying RPM (don't ask me why, I guess they wanted to reduce the risk of shaft overspeed [when rotors are not engaged], or maybe just wanted it to warm up quicker) The practice has since been stopped.

He applied collective to slow the rotors, just after engine shut down. The helicopter got into ground resonance (I will not go into the details of what happened next) He was killed, may he rest in peace. There were a bunch of un-willing witnesses, as it was right in front of the hanger.

As you can imagine the rotors would of been at a high RPM for this to have happen. Just be careful.

My question, what's is the rush??? OK in windy conditions I can understand some assistance in stopping the rotors. But otherwise, you can not wait the extra couple of minutes??:ugh:

DT

[Shawn Coyle]

simondh:
You can't generate enough lift with the rotor at idle and no engine powering it to get the helicopter light on the skids, let alone roll it over. Most machines stop producing any useful lift at about 65% rotor RPM, even with the engine powering the blades around.

[SuperF]

I'm with shawn on this one. after full down auto in UH1, you have enough inertia in MR blades to just get off the ground do a 360ish turn and sit back down again, you are going down as you are turning so better be good at it. Once blades get down below about 80-90% maybe more or less, not really looking inside, you aren't going pretty much anywhere, and that is in a light utility UH1. no way in hell a 44 will do much, except smack a tailboom if you are silly about, once engine has been wound off and rpm started to decay.

Also if you park your 44 just right, shut the engine off, no rotor brake, about 15-20 kts, blades will free wheel all day, now what do you do? Good for all those lowtime pilots in the UK, as they log flight time until the blades stop turning.....

What a lot of us here have probably not said, as it was assumed, is shut down, wait for rpm to decay, 60 sec or so, then when about 50% pull collective. As previously said, we only tend to do it in the wind to slow the damn things down, otherwise they do it fine themselves.

[helisphere]

I think it prudent to add that any pilot using these techniques should consider the type of rotor system on the particular aircraft they are flying. For example a standard semi-rigid rotor like most of the Bells aren't going to give you any problem with a collective raise until the rpm gets fairly low and there is the possibility of hitting the teeter stops too hard but, as another already pointed out, you can see that one coming and once the rotor is slowed way down you don't gain much braking from collective anyway.

Though I have never personally seen or heard of damage from this I would think one should be a little more careful in a Robinson or most articulated rotor systems simply because these aircraft have droop stops that actually support the weight of the blade when there is no lift or CF, unlike a true semi-rigid rotor. And these droop stops are very short coupled to a very long blade with lots of leverage. So the blade is capable of generating fairly high forces on these droop stops if allowed to jump up and pound the stops. But again, this can be seen relatively easy by the pilot and avoided.

[before landing check list]

John, in relation to the icy pads I believe you are referring to the friction of the transmission. That is where the nose of the helicopter tries to follow the direction of the disk. Just like the bottom of an auto with the engine actually failed as opposed to idle. You will see it there also. There is no torque per se.

[Arm out the window]

fadecdegraded, I agree about not doing it in a 206 (pulling collective after shutdown to slow the blades), or at least being very cautious about it, as the transmission mounts (spring and cup type) can really get some nasty-sounding and feeling bounce going - I had to do it to stop the blades once when parked in a hillside pad with a very strong updraft, and it wasn't much fun.

The 205, on the other hand, with the 5-mount transmission, is a much better prospect, and I've certainly used collective many times to slow the blades after shutdown in those. I think the worst you can do in that case is make the blade grip reservoirs leak if you have them.

Comes down to the type you fly, naturally enough, and I certainly wouldn't rule it out as something never to be done if the need was there.