Photo flights and tail rotors

February 21, 2011 by Tim McAdams

The unique ability of a helicopter to slow down and hover out-of-ground-effect makes it an ideal platform for taking pictures or video. To safely perform these types of flights requires a complete understanding of the issues involved with maneuvering a helicopter at slow speeds. One of these areas is understanding the limitations of different helicopter’s tail rotors.

Older model Bell 206B Jetrangers have a smaller tail rotor with a symmetrical designed airfoil that makes it more susceptible to what’s referred to as Loss of Tail Rotor Effectiveness (LTE). According to FAA Advisory Circular AC90-95, any maneuver which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where LTE or an unanticipated right yaw may occur. It also advises of greater susceptibility for LTE in right turns and states the phenomena may occur in varying degrees in all single main-rotor helicopters at airspeeds less than 30 KIAS. 

Another light helicopter that is very popular for photo flights is the Robinson R44. Frank Robinson is a tail rotor expert and designed the R44’s tail rotor to be highly efficient using an asymmetrical airfoil. The R44’s tail rotor is strong and although a lot less likely to encounter LTE pilots still need to exercise caution especially at high gross weights and high density altitudes.

Robinson Helicopter issued the following Safety Notice (SN-34) in March 1999, titled “Photo Flights – Very High Risk.” It describes the problems encountered when the pilot slows the helicopter below 30 KIAS and then attempts to maneuver the helicopter.

“The helicopter can rapidly lose transitional lift and begin to settle,” it states. “An inexperienced pilot may raise the collective to stop the descent. This can reduce rpm, thereby reducing power available and causing an even greater descent rate and further loss of rpm. Because tail rotor thrust is proportional to the square of rpm, if the rpm drops below 80 percent nearly half of the tail rotor thrust is lost and the helicopter will rotate nose over. Suddenly, the decreasing rpm also causes the main rotor to stall and the helicopter falls rapidly while continuing to rotate.” The safety notice recommends photo flights only be conducted by well-trained, experienced pilots.

12 Responses to “Photo flights and tail rotors”

  1. pdxpilot Says:

    Good stuff – never hurts to be reminded of this stuff – I shoot video while I fly – but once the camera is set I don’t touch it.

  2. Ehud Gavron Says:

    I’ve used a headset-holder mounted camera to videotape some flights (http://www.youtube.com/watch?v=CRQ9TikRlEk) and I also have a camera that fits on my head, so where I look it records. These don’t present any challenges — I ignore them and fly.

    I’ve had CFIs tell lots of stories about “The photographer that wanted X.” X is usually something entirely unsafe but sounds cool. “Hover at 50 ft above those train tracks.” “Get me right up to the power lines so I can shoot them with the mountains as the background”, etc.

    The key isn’t to be a high-time experience pilot, but to be decisive enough to say NO and refuse to do a flight outside of parameters with which you’re comfortable. If the requested location, altitude, heading, and airspeed aren’t what you know in your guy is appropriate… tell the photog you can’t do it.

    My 2¢.

    E

  3. Mike Borkhuis Says:

    Another consideration is things flying out open doorways when you’re doing a photo flight with the doors off. Could either camage or get caught in the tail rotor.

  4. G Beck Says:

    Always a good topic to be reminded of, not only with respect to photo flights but any HOGE situation. I was flying nearby a crop-spraying helicopter just this week who was reminded in a hard way. The machine is a total loss but thankfully no injuries. He made a low-speed turn at about a 30 foot altitude into a 15 knot tailwind at high weight, experienced LTE, reacted with a hard left pedal input which stole his power and RPM and resulted into settling between a row of trees that proceeded to chew his helo to pieces. All happened very fast and was a stark reminder to all of us nearby. Thanks for the topic.

  5. Obelix Says:

    I think this article is very pertinent. It is really not too difficult to get into LTE during an OGE hover especially when nearing power limits and/or with a tailwind or crosswind. Also, where LTE is, low rotor rpm is often not far behind. I do a lot of photo flying and I have never experienced full-on LTE but I have felt it coming on on a few occasions and avoided it by picking up some forward airspeed.
    I think the most important thing is to be aware of it’s looming danger whenever in a low airspeed situation and have a plan of recovery. It’s really not difficult to recover from if you recognize it early and leave yourself the space and altitude to do so.

    On a side note: I have so often heard that R22′s and R44′s have such exceptional tail rotor authority. I think this is a bit of a myth to be honest, I really don’t find either model to have that great TR authority. If anything the R22 is quite good, the R44 I would almost say lacks some authority. I think that the industry had become accustomed to the quite bad B206 TR authority when Robinsons came around and hence they seemed great by comparison. But if you really want to experience excellent TR authority try flying an AS350.. it will redefine your concept of TR performance. It is almost too powerful.

  6. Alex Kovnat Says:

    The matter of LTE in helicopters utilizing the usual one main rotor and one tail rotor configuration, is of interest because if you look at Mac McClellan’s latest blog on the EAA website (www.eaa.org), a group of helicopter enthusiasts have been discussing the merits and de-merits of Kamov helicopters. The Kamovs utilize counter-rotating coaxial rotors and therefore, don’t need a tail rotor. One wonders if Kamov helos might be better for missions where you have to hover or fly slowly (relative to the ground, that is) while making short-radius turns so as to keep a television news camera pointed at whatever is of interest.

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