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Chasing RPM.


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Do you guys have any suggestiions on how to keep things smooth. I find that I am constantly chasing the RPM during my takeoff and climbout, I keep it in the green, but I tend to work the collective alot. Any secrets to success on this...I fly the 300 btw. My instructor says to keep a constant setting (hover power) and not mess with collective but I don't feel like I have enought power to make a good climb out... Not saying this is bad advice, it just doesn't feel right since i always want too pull max power for take-off. Any suggestions would be helpful...

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Do you guys have any suggestiions on how to keep things smooth. I find that I am constantly chasing the RPM during my takeoff and climbout, I keep it in the green, but I tend to work the collective alot. Any secrets to success on this...I fly the 300 btw. My instructor says to keep a constant setting (hover power) and not mess with collective but I don't feel like I have enought power to make a good climb out... Not saying this is bad advice, it just doesn't feel right since i always want too pull max power for take-off. Any suggestions would be helpful...

 

Your instructor is right, hover power is takeoff power. You should'nt need to move the collective at all during a normal takeoff. If you do move the collective, you certainly shouldn't be pulling up. Tighten the throttle friction a little more than you normally do, and don't pull more power for the takeoff. Think about the relationship between the throttle and collective position. If you pull up, what happens to RPM if you don't adjust the throttle? What happens when you lower it? If you understand what happens when you move the controls you can anticipate the change of RPM, and make the correct adjustments without waiting for the RPM to change.

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Have your instructor point out several times exactly when you transition through ETL. The first four or five flights, at least, the instructor should have made a point to tell you when you transitioned through ETL. If you pick up the 300 into a three foot hover, nose it over ever so slightly, and let it start gradually building airspeed, all the sudden you will transition through ETL and with NO additional power, the helicopter will start climbing. You should never have to pull in any power unless you are making a max-performance take-off, either from a confined area, or just for practice.

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I liked the comment that someone said to tighten the friction. I fly a 300c model and most of the time it sits right at 3100 rpm where I set it after fine tuning it after getting it into a hover. Rarely do I have to adjust it, but if you get to higher altitudes (Especially above 3500'ft) or doing max performance take offs then you will be on the throttle more tweaking it here and there.

 

If the friction doesn't help, maybe the correlator needs some adjustment. Once in a while I have to tweak with the throttle if by myself and running with less than 20-25 gallons of fuel on board.

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I have to slightly disagree here on take off technique. What seems to be assumed is a no wind hover, which is very rare. If you are operating with a 10-15 knot headwind, you will need to increase collective to get a decent roc on take off. What is the point of not pulling pitch on takeoff? Rotor decay in the event of engine failure? I can see some merit to that, but why not get to speed or altitude quicker? Rotor decay is more pronounced in a R22. I think several technique should be introduced and are appropriate, and of course demonstrate various failures on take off. If not touching the collective is used to demonstrate aerodynamic forces or limited power, great, but it isn't something that is appropriate in all helicopters and hopefully you're not going to fly 300's the rest of your life. In the meantime, a thorough understanding of the correlator should help:

 

How a correlator works

 

Knowing what to expect plays a huge role in RRPM control. Good luck.

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If not touching the collective is used to demonstrate aerodynamic forces or limited power, great, but it isn't something that is appropriate in all helicopters and hopefully you're not going to fly 300's the rest of your life.

 

Very true, it may not be appropriate in all helicopters, but he isn't flying all the other helicopters, he is flying a 300. When I teach students normal takeoffs, I start with one technique, and once they are proficient with that technique I introduce other techniques for a normal takeoff. I don't throw all 4 techniques that I know at a new student at once, only one at a time. Further, just because he might fly an S76 or MI-24 one day doesn't mean he should be expected to take off like an S76 or MI-24 when he is still trying to LEARN how to fly in a Schweizer. One step at a time. First learn to fly, THEN learn to fly other aircraft. Not the other way around.

Edited by PhotoFlyer
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I have to slightly disagree here on take off technique. What seems to be assumed is a no wind hover, which is very rare. If you are operating with a 10-15 knot headwind, you will need to increase collective to get a decent roc on take off. What is the point of not pulling pitch on takeoff? Rotor decay in the event of engine failure?

[.

 

A grizzly old filight instructor, read: 26 year old chick, once told me that the most common time for a power failure was during a power change on takeoff, especially in the 22. I dont let my students pull more than hover power on takeoff unless they are settling through before ETL. If they pull an armpit full of power doing a normal takoff they have to dip the disk way below the horizon to maintain the Reccomended Takeoff Profile from the H/V diagram. This overpitching while at such a low altitude has its obvious drawbacks and is a bad habit for student and private pilots to get into. Once they're through the H/V takeoff profile I let them pull power (1"-2") to establish a better rate of climb. Teaching deliberate, smooth and controlled accelerations for takeoffs in my opinion is of the most benifit to the student.

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A grizzly old filight instructor, read: 26 year old chick, once told me that the most common time for a power failure was during a power change on takeoff

The same is often said by fixed wingers -- that failures are most likely to happen with a power change. Trouble is, I've never seen anybody produce a shred of evidence that it's true for either fixed wing or rotorcraft.

 

Anytime we do a max performance t/o or a vertical ascent because of obstacles, we're increasing power from that required to maintain a hover. It would be interesting to sift through the NTSB database and see how many engine failures happen under these circumstances. I'll bet there's very, very few.

 

Having said that, it does seem to me that in a normal t/o profile that it would be easier on the engine, transmission, etc., to not pull additional pitch. But it strikes me that that's a wear and tear issue, not a safety issue.

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The same is often said by fixed wingers -- that failures are most likely to happen with a power change. Trouble is, I've never seen anybody produce a shred of evidence that it's true for either fixed wing or rotorcraft.

 

I don't have any evidence to support what I am about to say, so take it as you will. I have never had an engine failure (for any reason) in a helicopter, but I have had quite a few in various street vehicles. The majority of the time (3 out of 5) when my engine quit, it was with an increase in power. I've had it happen exiting corners on my motorcycle, climbing hills in an ATV, and while accelerating onto the highway in my car. The other two engine failures were because I ran out of fuel on a motorcycle. They also came with a power change, but I was slowing down off the highway, not adding power.

 

In my experience engines do fail during an increase to a higher power setting. I can't imagine the piston engine in my helicopter would act any differently. I know they are different engines, but they all operate on the same principles and should fail in a similar manner, under similar conditions. I don't know if my experience really supports what I've said, but it's enough for me.

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Very true, it may not be appropriate in all helicopters, but he isn't flying all the other helicopters, he is flying a 300. When I teach students normal takeoffs, I start with one technique, and once they are proficient with that technique I introduce other techniques for a normal takeoff. I don't throw all 4 techniques that I know at a new student at once, only one at a time. Further, just because he might fly an S76 or MI-24 one day doesn't mean he should be expected to take off like an S76 or MI-24 when he is still trying to LEARN how to fly in a Schweizer. One step at a time. First learn to fly, THEN learn to fly other aircraft. Not the other way around.

 

 

Where does it say not touching the collective is appropriate in S300's? Where is it written that hover power is take off power? If you have a headwind, which you will in almost all instances, simply maintaining that power may not give you the safest take of profile. I'm not advocating yanking the guts out of it, but if a little tug is needed to make up for the loss of the ground cushion, or simply as a boost to increase the roc I wouldn't make it a rule not to use the power available, just to make a point. The point I was making is that not touching the power seems to be handed down as gospel for some reason, possibly a carry over from C models (or 214's but I doubt it), but different conditions dictate different techniques. Having experienced a few engine failures in helicopters and been witness to even more, I have not seen any that occurred during power changes, and in every case a bit more altitude and airspeed was defiantly an asset. Having practiced a lot of simulated engine failures on take off, in a 300 amongst others, the increase in pitch never had a significant effect on on rotor decay (save for the R22 and like you said, he isn't flying one), but the additional altitude gained gave more leeway in the recovery. I agree one step at a time. Maybe you have a very good reason for not touching the collective. I just think that maybe it's an idea that has been passed down from one CFI to another and isn't the best idea in a lot of cases. I have seen plenty of pilots that make it a focal point on all take offs even at later stages of their careers and can be a habit that is hard to break. Like you said, there are lots of take off techniques, and you say you teach 4 of them. I believe the original poster is up for a check ride soon, and I'm sure they are ready to learn more that a cushion creep take off as it might be easier to try some thing other than a fixed power take off.

 

From the rotorcraft flying handbook:

 

Start the helicopter moving by smoothly and slowly easing

the cyclic forward (position 2). As the helicopter

starts to move forward, increase the collective, as necessary,

to prevent the helicopter from sinking and adjust

the throttle to maintain r.p.m.

 

and:

 

COMMON ERRORS

1. Failing to use sufficient collective pitch to prevent

loss of altitude prior to attaining translational

lift.

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I remember being taught not to increase the collective by my primary instructor. I can only assume it was because he was a Vietnam pilot and they seemed to be very big on power management for takeoff. This was reiterated to me as a min. power takeoff technique (i.e. being MGW with just enough power to hover in a high/hot condition) by my Standardization Instructor Pilot, who had just returned from the High Altitude Aviation Training Site (HAATS) the Army National Guard runs in Colorado, prior to our first tour in Iraq.

 

A VMC takeoff by the Aircrew Training Manual, however, states similar to what the RFH says:

VMC takeoff from a hover. Select reference points to maintain ground track. Apply forward cyclic to accelerate the aircraft while maintaining altitude with the collective. Perform the rest of the maneuver the same as a takeoff from the ground.
I still feel guilty when my spider sense tells me to pull in some collective to keep from hitting the ground.
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As a student you should be introduced to all different scenarios, but one at a time.

The problem with helicopters, and pretty much all other commercial vehicles, is that the more power you have available, the more "crap" your boss makes you load up. So all in all your power reserve will be limited in most situations.

I think it's a good habit to learn early on to be conservative on the power, and then once you master that part, you can move on to the other techniques. In my opinion it also makes the students smoother on the controls.

 

Think I heard once that the main reason for engine failures is not power changes, but temperature changes. I guess a power change could be a contributing factor to a temperature change.......

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