Low RRPM during takeoff

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Garthman
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Low RRPM during takeoff

Postby Garthman » Sat May 26 2018, 05:57

Hi everyone i was reading the report below from the ATSB about a low RRPM during takeoff.

https://www.atsb.gov.au/publications/in ... -2018-006/

I would be interested in knowing if this has happened to anyone? and the best recovery if altitude is not on your side?

Thanks
Probbo
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Re: Low RRPM during takeoff

Postby Probbo » Sat May 26 2018, 09:18

Unfortunately it happened to the driver in the desert that day.
#1 Roll the throttle wide open. #2 Reduce collective pitch.
If the ambient conditions and the local surrounds are favourable you may get away.with it
tailrotor
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Re: Low RRPM during takeoff

Postby tailrotor » Sun May 27 2018, 08:16

Basica What Probbo said, each circumstance is different but in my hours spent in robbos the most common and dangerous failures that have happened are magnetos dropping points, values jamming and governors failing. Interesting that the report mentions that the insurance guys went straight to the right mag and checked the gov, but the failed mag could easily have been the left one (which in my experience has much more chance of failing due to oil ingress) and the gov could have simply been flicked off accidentally on takeoff. Anyway I'm sure the report will tell all. If it happens to you the only real thing you can do is hope your in the right profile over something soft and don't be afraid to manually control the throttle and give it some curry to save yourself at the bottom of the glide. No point staying in the engines parameters if you roll the whole aircraft up. Anyway that's just my opinion I'm sure plenty of people will tell you it's wrong :|
kcconnected
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Re: Low RRPM during takeoff

Postby kcconnected » Mon May 28 2018, 00:08

This could also be self induced pilot error. Not saying this is the case but it is possible. New pilot, tight landing zone with lots of obstacles, death grip on the throttle not allowing the gov to do it thing. Had a couple students do this to me over the years.
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Blade
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Re: Low RRPM during takeoff

Postby Blade » Mon May 28 2018, 02:56

It is interesting that a weight and balance figure is not mentioned in the report yet.

The best hope of recovery and order of execution at 30ft and 30kts above a surface you cannot land on is to 1. Lower collective 2. Roll on throttle 3. Cyclic flare. By reducing Collective first the blade drag is reduced allowing tq to increase RPM more effectively. The small cyclic flare adds to the RRPM and reduces some of the effect of lowering the collective. With a speed below 35 kts power required is already high so pitching forward will do less for reducing power required and more for reducing RRPM.
Best advice, use good T/o technique. As per RFM Section 5. Accelerate to 35kts not above 10ft then advance climb to 60kts. Do not use more than 2 inches MAP more than IGE hover, if RPM drops below 101% lower collective.
Probbo
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Re: Low RRPM during takeoff

Postby Probbo » Mon May 28 2018, 03:37

Hi Blade,
Due to the correlation between collective pitch and throttle position on R44 Helicopters, by lowering the collective it directly begins to shut the carby butterfly which will decrease engine power. The throttle linkage path has an over travel spring which allows the geometry of correlation to be overridden. This is why it’s important if encountering a low rpm situation to immediately roll the throttle on closely followed by reducing pitch.
Cheers
Mallard
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Re: Low RRPM during takeoff

Postby Mallard » Mon May 28 2018, 05:19

Probbo wrote:Hi Blade,
Due to the correlation between collective pitch and throttle position on R44 Helicopters, by lowering the collective it directly begins to shut the carby butterfly which will decrease engine power. The throttle linkage path has an over travel spring which allows the geometry of correlation to be overridden. This is why it’s important if encountering a low rpm situation to immediately roll the throttle on closely followed by reducing pitch.
Cheers


Spot on probbo, lowering before rolling on you are going to end up in the bushes in an R44.

Roll it on into the detent and hold it there and then lower. If you have sufficient height wait for the RPM to come and try fly away... if not hold the throttle on the stop and milk collective to cushion landing... use any available power.
Helinaish
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Re: Low RRPM during takeoff

Postby Helinaish » Tue May 29 2018, 01:31

So according to the ATSB report...

• Flight departed 1821 CST
• Low RRPM horn activated at 22.5 inches, and 26 kts
• Airspeed was increasing (Increased Attitude)
• Power was increasing (Increased Blade Pitch)
• Airspeed and Power continued to increase while E&R were decaying.
• No immediate fault can be attributed to the machine

Pilot fatigue...poor decision making? ...

Remedy...self explanatory.
Niko
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Re: Low RRPM during takeoff

Postby Niko » Tue May 29 2018, 02:50

Helinaish wrote:So according to the ATSB report...

• Flight departed 1821 CST
• Low RRPM horn activated at 22.5 inches, and 26 kts
• Airspeed was increasing (Increased Attitude)
• Power was increasing (Increased Blade Pitch)
• Airspeed and Power continued to increase while E&R were decaying.
• No immediate fault can be attributed to the machine

Pilot fatigue...poor decision making? ...

Remedy...self explanatory.


Besides pilot fatigue and decision making, there are other reasons how the LRRPM Warning System can activate at 22.5" and 26kts [@ Elv 1600ft and +38' Temp]. Granted even under those conditions full aircraft rated power output of 225HP[+] is available. The failure can be explained by partial/fully mechanical failure as well. These failures can sometimes not be immediately found - the ATSB report will be released relatively shortly. They will have a better insights into what caused the accident and remedies, which very well can be Pilot Fatigue or Poor Decision making. But until then, we do not know

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