300C Correlator performance

[IgorS]

I have been flying an older (1970s vintage) 300C for the past 30 or so hours of my PPL training.

 

I think that the throttle correlator on this machine works poorly compared to some newer 300Cs that I have flown. Unfortunately, I flew the newer aircraft very early in my training, and for only a few hours, so I may just have a case of selective memory.

 

I have to roll off the throttle during pickup to prevent an overspeed. I've been taught that the correlator "starts working" at around 18 inches MP. Last week, with full dual tanks, I was able to pull 20 inches before the helicopter got light. I put the needle in the middle of the green, pulled enough to lift off, and still had to roll off.

 

Max performance take-offs are even more difficult, since I am required by the PTS to put the needle on the top end of the green before I lift off. I have to roll off about 1/4 turn as I pull to stay in the green.

 

On descents, I have to roll off as I decrease the collective, just like an uncorrelated throttle. If I get busy during an approach -- traffic, or a crosswind -- I'll get out of the green.

 

This is driving me nuts. I'd rather have no correlator than this schizo thing. I tell myself that what doesn't kill you makes you stronger. My instructor tells me not to blame the helicopter for my technique issues.

 

Am I crazy, or do the correlators actually work on more recent versions of the 300C?

[fulldownauto]

I've been renting a 2003 CBi for a few months now, and while I obviously can't speak for a new 300C, the CBi's correlator works fairly well. However it seems pretty hard to tell when it's working, I only really notice it on pickups and I do have to roll off a little when at the top of the green moving through light on the skids. Though I certainly don't have to roll 1/4th of the travel, more like one or two notches on the throttle.

 

Even with the correlator I'm rolling constantly throughout the flight to maintain proper RPM, I don't ever lower the collective a significant amount without one eye or one ear on the RPM and I almost always have to roll off. But then again these are smallish inputs, I haven't flown without the correlator, so perhaps it takes care of the large adjustments while I fine tune the RPM where I want it. But all the anticipation and throttle/collective technique still apply, it's become second nature. Though I can imagine it'd be quite difficult if I had to make large imputs at every change.

 

I had a passenger take a video of a pickup to the hover a while ago, from almost light on the skids to liftoff, I only had to make a couple of small throttle adjustments to keep it near the top of the green.

 

Hover

 

Best Regards,

 

James

[IgorS]

That's very helpful. I think maybe my instructors were helping me a bit early on, but now I'm on my own and noticing these little quirks.

 

I only have to roll off a large amount when I make the big pull for the max performance take-off. Otherwise, it's just like you say, small adjustments.

 

It seems wierd. How is rolling off the throttle (on pickup) to compensate for the correlator an improvement over rolling on throttle to compensate for engine load? It's pilot workload either way.

 

No wonder Schweizer offers an optional governor.

[ascott20]

300s are all about situational awareness.  As you get more experienced with a variety of flight conditions, you'll start to know when to add some throttle or roll it off when coming to a hover.  I did all of my civilian training in a 300CB and CBi... I know how you feel.  Just try to anticipate a little bit just prior to each maneuver... it works every time.  I did a little flying in a R22 this year for a SFAR 73 sign-off, and flying with the governor off in that a/c can be a little interesting.  Even with the governor though, I would still take the 300 over the R22 anyday.  Good luck with your training!!!

[fulldownauto]

As you know, the correlator simply correlates a given collective position with a gross throttle position. Not very exact, but it'll do a large part of the rolling itself. I feel like I'm following close to the correlator, for example, when smoothly entering autorotation. While lowering the collective, the correlator is rolling off while I'm making several small corrections from keeping it going high on the way down. Without a correlator, you've got to roll constantly, but with the correlator it's more a matter of making small corrections less frequently, reducing the relative scan time and thus a workload reduction.

 

But with and without the correlator this should become second nature. Anticipation is key, but what makes anticipation easier is doing things more slowly, make a slow steady pull for a max performance takeoff, there will be more time to scan inside and make RPM corrections. If you're already nice and steady, have you tried a different method or correlation? Listening to the RPM in the 300 is pretty easy, and while not a substitute for the gauge, you'll find when you practice rolling by sound, you'll have to look at the gauge less, and it's also easier to make corrections when you're busy, because you'll notice the RPM change subconsciously while doing other tasks, instead of having to look at the gauge before knowing your RPM is getting high/low.

 

Hope that made some sense. Those tips worked for me. I love flying the 300 over the R22. As ascott said, situational awareness is increased when you always know how much power you're pulling/rolling and are able to better feel the flight requirements of the helicopter.

 

James

[flingwing206]

There's a couple of tricks which help with the 300-series corrolator.

 

On a pick-up, start with full-down collective and RPM in the BOTTOM of the green. As you initially raise the collective, the RPM will start rising - well before you get light on the skids, the RPM will be near the top of the green. You will still have to make adjustments, but there won't be as much "roll-off then roll-on", and you won't have to fixate on the tach to prevent an overspeed.

 

Any time you are going to make a power/RPM change, scan the MP & tach, then use the appropriate control first. For example:

 

You note high RPM. Look at the MP. If it is LOWER than you want, raise the collective. If MP is higher than you want, roll off throttle.

 

Low RPM, same idea. If MP is too high (or throttle is already full-open), lower collective. If MP is too low, roll on throttle.

 

If you want to raise MP, check RPM - if it is near/at the top of the green, merely hold pressure against the throttle while raising the collective. If you are coming from a low MP setting (going around, for example), you won't need to add throttle until the MP passes about 23". If RPM is lower to start with, lead with a little throttle - squeeze on throttle until RPM is at the top of the green, then raise collective.

 

Lowering MP is similar - if at a high MP setting, lead with throttle - get the RPM headed slightly down, then lower collective. If MP is below 22", you may not need to touch the throttle, and at lower settings you may need to roll on a touch to maintain RPM.

 

Entering autorotation in the Schweizer smoothly is as simple as leading with a touch of throttle, then lowering the collective in about the tiime it takes to say "autorotate". Remember, the right pedal is connected to the THROTTLE, but the aft cyclic is connected to the COLLECTIVE. If  you chop the throttle, you'll get a lot of yaw but the nose won't drop until you get the collective down.

 

Power recovery is equally simple - while in the last 200' or so of your auto, roll the throttle to 2000 engine RPM. When you raise the collective to recover, the needles will (smoothly) join themselves, and the power will come in nicely until you hit 23" or so at which time you will have to roll on additional throttle. Try this one - it is like magic!

 

Ok enough random thoughts. Hope this helps!

[dangerouslyclosetoavolcano]

fling

 

thanks for the tips there on flying the 300. I have 115 hours R22 and as of today have a whopping 3.3 in the 300CB. I must say Im very impressed with this helo. My instructor was hyping up the whole no governor thing, but I actually found it pretty easy to get used to. Auto's were very interesting! The ship falls like a darn brick! For all the 300 promoters out there, i have to say that I finally get why you prefer it to the R22. Anyway, I wanted to ask you about your autorotation advice. You said to roll on to 2000rpm in the descent, I was taught 1700rpm - is there much difference in end result? I especially like the right then left pedal needed right at the end of the flare! Lastly, I am having problems flying the approach. It feels very fast even though my airspeed was good and therefore I end up overshooting. There was no tailwind!!

[IgorS]

I think Fling was referring to the 300C, which operates at 3100 rpm vs the derated CB, that operates at 2800. That probably explains the difference.

[flingwing206]

Anyway, I wanted to ask you about your autorotation advice. You said to roll on to 2000rpm in the descent, I was taught 1700rpm - is there much difference in end result?

No real difference in how this works between 1700 and 2000 RPM - the key is that you have the correlator activated by bringing the RPM up slightly. It's easier to see 2000 RPM on the tach than 1700, the difference is immaterial. Your school may be thinking about the 1600 RPM engine speed limit with the rotor disengaged. However, if the belts are tensioned (as they are in autorotation), then the lower coupling shaft is not subject to lash (which is what causes damage in a disengaged overspeed).

 

As far as normal approaches go, if you are used to using the "spot on the windscreen" technique to hold an angle, realize that as the helicopter slows, the pitch attitude goes more and more nose-high. If you try to keep the spot in the same place past the first 1/3 - 1/2 of your final, you will either: not slow down, or under-arc your approach. You have to fly the second half of your approach by noting apparent ground speed (perirephal vision and side glances), and maintaining the approach angle independant of the spot on the windscreen (which has to move down as the helicopter goes more nose-high).

 

Hope this helps!