auto rotation recovery 300CBI

[joker]

Just to follow a theme that Randy brought up;

 

I think the aft cyclic that we are talking about is more in order to maintain an autorotation attitude, rather than any sort of RPM recovery.

 

*Of course this depends on the nature of the emergency - but for a 'performance' checkride straight-in or 180 auto' type of situation, the RPM should recover naturally, so long as you are within performance limits (weight / DA) and quick / cooridinated in your collective and throttle manipulation.

 

As mentioned, the 60kt attitdue is about right for these helicopters. It just so happens that the 70kt cruise attitude, is very similar to the 60kt autorotation attitude, which also happens to be similar to level. So aft cyclic must be applied to acheive this attitude. If you are slower than 60kts, then let the nose drop naturally (don't try to keep 40kt attitude). Use aft cyclic to hold the autorotation attitude as you get to it. If you are above this 60kts then of course, then apply aft cyclic to hold the nose up at the autorotation attitude as you lower the collective.

 

 

The problem with rote learning 'Down / Right / Aft' for all autos, is situations when the airspeed is already low and / or close to HV curve.

 

Also consideration must be given to the fact that any recovery of RPM by cyclic flare, unless properly managed will result in simply the same low RPM when you level, but this time with lower airspeed. A worse situation. (Forward cyclic again lowers the RPM).

 

So for these practice autorotations, I would prefer to set my autorotation-attitude, and let the aircraft work as it has been tested to do. Save the 'cyclic-flare-to-recover-RPM' menatality for the most dire of situations! e.g. Late to enter autorotation with low RPM.

 

Just a thought.

 

Joker

 

Footnote: What I say here may not be dissimilar to what others have said or meant. I wrote this because I don't want this thread to leave beginners thinking that they must use a cyclic flare 'every time' to recover RPM. This could lead to dangerous habits, and in the least lead to students chasing RPM with collective. Auto's are all about attitude. The aircraft is maintained and tested and the best autorotation speed is found printed in the RFM. Acheiving this speed is your best chance of getting RPM back - IN MOST SITUATIONS. For training - once you have mastered this, then you are ready to move onto other techniques, and critical RPM recovery techniques such as cyclic flaring, and using the cyclic to control RPM.

Edited May 21, 2007 by joker

[coanda]

read cyclic and collective, there are some good auto tip's as well as a fairly clear explanation on proper energy management. chpt. 8, 18, and 30.

[brushfire21]

I think the aft cyclic that we are talking about is more in order to maintain an autorotation attitude, rather than any sort of RPM recovery.

 

 

I am no expert here when it comes to auto's or flying, but read a few things from Joker that made my air stand on end. Depending on what aircraft your in, aft cyclic will need to be used depending on speed. Which Joker mentions in his thread. Please correct me here, but during an auto, aren't you wanting to increase the effiency of the rotor blades when the air is reversed and it comes from below you to help maintain RRPM? If you keep constant forward cyclic during an auto at low forward velocity, I bet the RRPM will drop considerably? At least that has been my experiance when learning and performing auto's.

 

Randy said it best here from page 1, and I think it sums up what joker was saying I think:

 

"The general thought that you will always add a "gentle bit of aft cyclic" is not always correct. In most single engine helicopters, a ballpark airspeed of 60 knots in autorotation will work. With this in mind, if you are above 60 knots, a bit of aft cyclic is beneficial. If at or below 60 knots, especially at the apex of H/V, aft cyclic should be avoided as a gentle but deliberate cyclic movement to attain proper airspeed pitch attitude is paramount."

 

I read into what Randy said, as use cyclic as needed to maintain airspeed/attitude/RRPM etc. If I read it wrong then help me understand then. When I was learning auto's, both cyclic and collective was used to maintain attitude, speed and RRPM. The instructions were, fly the aircraft and do what it takes to get it down using whatever controls needed. Typically it was lower collective, aft cyclic of some sort, and pedal input.

 

It will take some research, but there has been some reported incidents/accidents where the pilot pushed on the cyclic only to have the rotors eventually stop and supposedly reverse while in the air trying to get the blades to go faster for more RRPM. Becuase of this, I am wary of saying not to use aft cyclic. Use the all the controls at your disposal to fly the aircraft and not to get tunnel vision.

[apiaguy]

Dude, you need help

 

[Goldy]

Dude, you need help

 

 

 

Thats it..I'm sticking to Robbies....auto's are a piece of cake in them

[500E]

Attitude, Speed, and watch the RRPM, Just keep in the GREEN, watch even closer if 180 this will increase RRPM, you only need a small lift and then release to keep them in the green.

Attitude is real important this should stabalise RRPM & speed if correct.

[Petter]

Petter: the correlator is a very simple mechanism attached to the collective and throttle cable that merely pulls more on the throttle cable as the collective is lifted. Ask your mechanic to show you sometime between the seats... is is very easy, but much more difficult to explain the correlation. With less load on the blades the engine does not need as much throttle/power to maintain rpm. When you pitch the main blades and put a load on the rotor system it would tend to drag the rpm down but the correlator increases the throttle setting as you lift on the collective...... clear as mud??

 

I alaway undersatood the correlator apiaguy, just not why it's responsible for increasing your rpm so much on pickup, but thats clear now, thanks

 

On the aft cyclic issue.. What if you are cut in climb? you allready have your 60kt attitude (and airspeed), but you have a corse pitch setting so you'll loose more rpm. If the rpm decays too quick you'll need aft cyclic.

60 kt at any altidude above 7 feet is out of the HV diagram, but still I wouldn't like to be cut at 100 feet during climb out.. I know I'm being a bit dificult and that this isn't normally done during training, but it's an interesting thread. Anyone have any experience with low speed autos?

[flyby_heli]

On the aft cyclic issue.. What if you are cut in climb? you allready have your 60kt attitude (and airspeed), but you have a corse pitch setting so you'll loose more rpm. If the rpm decays too quick you'll need aft cyclic.

60 kt at any altidude above 7 feet is out of the HV diagram, but still I wouldn't like to be cut at 100 feet during climb out.. I know I'm being a bit dificult and that this isn't normally done during training, but it's an interesting thread. Anyone have any experience with low speed autos?

If your engine quits on takeoff the same rules apply. I always show my commercial students take-off engine failures from about 250-300 feet AGL on climbout. Your reaction needs to be a little quicker, but everything else is the same...keep a 60 knot attitude and RRPM in the green.

What do you mean by low speed autos? Vertical? 20 knots? below 60 knots?

All of these can be done, and this is another thing I demonstrate to my commercial students. The important things are to keep the RRPM in the green, use gentle attitude changes and remember to start increasing your airspeed at a safe altitude (so, at least more than 450' AGL) that way you stay outside the HV diagram, and get your airspeed up before the flare so you have enough energy to arrest your descent rate, slow your airspeed and if neccesary build up RPM in the flare. If you are working on your commercial, ask your instructor (or at Bristow ask your stage check pilot) to demonstrate this for you, I'm sure they are willing to!

 

Lykke til!

Edited May 24, 2007 by flyby_heli

[joker]

All,

 

It seems I must be more careful with what I say on this subject. So here's a disclaimer to start with:

 

Your instructor is the best person to give you advice. Everything you read here is opinion, and doesn't represent the best way of doing things. Discuss options with your instructor and NEVER try anything new without agreement first.

 

Now that's out the way, let's continue.

 

Brushfire21, I must admit I was a little confused by your post. What was it that 'made your 'air stand on end'. My advice or the advice from others?

 

Let me try to be clear.

 

In my posts, I was trying to differentiate between the kind of 'aft cyclic' application that we see in say, 'Low RPM' drills'. That would be definite (and aggressive) manipulation of the cyclic with intention of driving up decaying RRPM - in other words...a flare!

 

During a well initiated autorotation (as in a private checkride) there shouldn't be any need for this kind of 'flare'. RRPM should restore naturally.

 

Now, depending on speed and aircraft, weight and weather, it is most likely that you will need 'aft cyclic' in order to maintain / establish the correct autorotation attitude. This would be the same aft cyclic whether you had power on or off.

 

My post was trying to simply differentiate between these two. Earlier posts in this thread did not seem to clarify what and why aft cyclic was applied. I have seen students who use way too much aft cyclic. From the entry to the termination, they are behind the aircraft and chasing the RPM with cyclic and collective. This is what we should try to avoid.

 

Use aft cyclic to establish correct attitude - if necessary a flare can restore a decaying RPM, but be careful with this.

 

I hope that clears up my own posts a little. I'd be interested to hear what others have to say.

 

Joker

 

Note: In my last two posts, I have deliberately not mentioned 'forward' cyclic. However, read into my posts carefully, particularly when I mention 'establishing autorotation attitude' from lower airspeeds.

Edited May 24, 2007 by joker

[Petter]

Takk skal du ha flyby_heli!

 

I'm doing my instrument rating, I'll be working on the commercial in a month or so. I've tried the zero airspeed autorotation, hehe, have to admit it was an interesting feeling the first time.

Edited May 27, 2007 by Petter