Low Rotor RPM Warning System, Illustrated

A video to go with an earlier blog post.

I’ve written at least twice in this blog about the low rotor RPM warning system on Robinson helicopter:

I thought it might be good to illustrate what it looks and sounds like on video. You can find the video at the bottom of this post.

Before you watch the video, please read this explanation. The video is not narrated; I wanted the helicopter sound to be heard. If you don’t read this, you won’t know what’s going on or why.

  1. At first the helicopter is at cool-down RPM (around 65%). I’d just come in from a flight and was getting ready to shut down when I decided to use my Flip camera to make the video.
  2. I wind up the RPM by twisting the throttle. Watch the tachometer in the upper right corner. Needles are matched for engine (E) and rotor (R) RPM.
  3. When RPM gets to about 80%, the R44’s electronic governor takes over and brings it up to 100-102% engine RPM (the green arc).
  4. I simulate a low rotor RPM situation to test the system. (The system is required to function for flight so I test before every flight.) This requires me to raise the collective about an inch and then slowly roll off the throttle to reduce RPM. You can hear the engine pitch change and see the needles start to droop.
  5. At 97% RPM, the warning system engages with an audible horn and a light. A pilot who misses this would have to be blind and deaf (and thus, would not be good as a pilot).
  6. In the test, I push the collective down to shut the horn off and let the governor roll the throttle back up. If the horn came on in flight, you’d use the low rotor RPM recovery procedure, as discussed in “Reacting to Low Rotor RPM,” to regain RPM before it dropped to the point where it was not recoverable and became catastrophic.

Here’s the video:

The system looks and works slightly differently on different helicopter models. But the basic operation and test is the same.

5 thoughts on “Low Rotor RPM Warning System, Illustrated

  1. Maria,

    One thing I’d like to point out (I’ve pointed it out to Robinson who ignored me much to my annoyance). The newer noise canceling headsets can do a pretty good job of canceling out the R22/R44 low RPM warning horn. I have a pair of Zulu (which I love). With the noise canceling on and soft music playing, the horn is totally non-audible (which is why I seldom play music when I’m flying). If you are looking away from the light you can easily miss the low RPM warning system. Of course, you should notice the difference in the 1P vibration of the helicopter, but low time people probably wouldn’t notice this. Robinson really should run the audible warning into the audio panel as well, but they don’t seem interested in doing that. Perhaps after an accident…

  2. @Paul Cantrell
    Wow. If you can’t hear the low rotor RPM warning horn, then you probably can’t hear the engine, either. I wear Bose headsets and have no trouble hearing the horn (with or without music on). I also once heard the engine “skip a beat” — which nearly caused my heart to do the same. I would never wear headsets that blocked out vital engine sounds or the sound of warning horns.

    Maybe your warning horn volume is somehow misadjusted? You might want to look into that.

  3. Nope, ’cause it’s true in the half dozen Robbies I fly. Probably the Zulu are just more effective in that particular frequency than the Bose. Unfortunately they don’t work as well in a turbine helicopter so I usually end up using my old David Clarks in the Bell (and give up the convenience of the Bluetooth connected cell phone). On the ground of course. I would never use the cell phone in flight ;-)

  4. @Paul Cantrell
    Can you still hear the engine noise? Seriously: I wouldn’t want to wear anything that blocked out the sound of the engine. If you’d ever heard it hiccup as I have, you’d know why. That’s a sound I hope I never hear again.

  5. I agree that the warning horn should be going to the audio panel with its own volume control. After years of abusing my hearing, I’ve started wearing ear plugs with my helmet , and can’t hear much outside noise.

What do you think?