I’m often asked why the cost to fly in a helicopter is so high.  The answer is simple… maintenance.  Nearly every part on a helicopter has a life limit.  When the designated number of flight hours or calendar months is reached, the part gets overhauled or replaced.  Divide the cost of replacing each part by the number of flight hours allowed to get an hourly maintenance cost.  Add that up for all the parts and you get a total cost per hour for helicopter maintenance.  I’m simplifying a bit, but you get the idea.  Many operators have gone out of business because they didn’t put money aside every flight hour for scheduled maintenance.  Faced with a fat bill from the mechanic, they simply go under.

Loyal readers will remember that in our last blog post we flew N280MM down to All Terrain Aircraft in Pendleton, OR for a TT strap retrofit.  About four days into the project, I got the call from my mechanic that we all dread.  While putting the rotor head back together he felt a little “slop”.  Nothing dangerous, but definitely enough to make a good, vibration free, blade track nearly impossible.  Now we get to see some of the costs of unscheduled maintenance.

Enstrom In Maintenance Shop

Slop in the rotor head = $$$

The only way to figure out what’s causing the slop is to start taking things apart.  I got a call later telling me there were worn dog leg bearings and some wear on the lower swashplate.

The video to the left will help you understand what the swashplate does.  It takes all the control inputs from the pilot and translates them into changes in rotor blade pitch angle.   Overhauled swashplate:  $3000.00.

Dogleg bearings are relatively cheap, only $50 x 3.  Trouble is it takes about 5 hours of labor to get to them and then replace.  Shop labor is $100 per hour so add another $650.00 to the bill.

Time to track the rotor blades

Getting rotor blades tracked to a state I call “butter smooth” is one part science and two parts magic.  Anyone can learn the technical part of tracking rotor blades.  The magic part requires at least a level 50 rotor blade mage, some pixie dust, and likely some sort of animal sacrifice.  I’ve never inquired about the latter since I fear the truth.

With the Enstrom 280FX, there are three stages to the tracking process.  First you want to get rid of any stick shake, then minimize vibration in hover and forward flight.

The picture to the right shows the cyclic with a vibration sensor.  A second sensor mounted near the main rotor mast measures the rotor rpm.  Vibration is measured at a particular rpm by the Vibrex 2000 (second picture on the right).  It provides a vibration level in incidents per second (ips) and a clock angle.  Lower ips means a smoother ride.  The clock angle tells you which rotor blade should be adjusted to lower the ips.   Adjustments to pitch links on each rotor blade change the track.

Pilot and mechanic measure ips and clock angle then adjust pitch links in an effort to reduce the level of vibration… rinse and repeat.  Once the stick shake is within limits, the process repeats for blade track in hover and forward flight.

According to my mechanic (level 80 rotor blade mage) this was done in the past by raising a stick with chalk on it up in to the rotor blades while they were turning.  The mechanic would then look at the marks on the blades after they stopped to figure out which blades to adjust.  Yikes!

The blades won’t track?

After several hours of tracking, we finally realized there was another issue with the rotor head.  We’d track the blades to the “butter smooth” state, go fly for a bit, and come back to the ramp with lots of vibration and stick shake.  The blades were not staying in track.

Conversations with a local Enstrom whisperer and the factory tech reps led us to believe that the main rotor dampers were worn.  There’s a picture of a main rotor damper to the left.

When each blade is turning, it also moves forward (lead) and backward (lag) relative to the other blades.  There is a hinge at the inner edge of the blade that allows this motion.  In order to keep the blade from swinging wildly back and forth, the engineers developed a blade damper.  The damper is a hydraulic piston that offers resistance to the blade and keeps it from moving too much.

When the dampers begin to wear, the blades move too much and the rotor system won’t stay in track.  New dampers:  $4500.00

The cost of helicopter maintenance

What was supposed to be a 4-5 day process of upgrading the rotor head to TT straps became a nearly three week process.  The final tally?

TT Strap Upgrade:  $20,000

Lower Swashplate:  $3,000

Dogleg Bearings:  $150

Main Rotor Dampers:  $4,500

Labor:  ~$4,000

Total:  $31,650

Remember, this was all unscheduled maintenance and in addition to the scheduled maintenance we budget for.  At the end of the day safety is what matters most.  If the helicopter needs something, it gets it.  Hopefully this will soften the blow when the next scheduled maintenance interval arrives in 50 hours or so.

I cannot speak highly enough about David Styer at All Terrain Aircraft in Pendleton, OR and the Enstrom factory tech reps.  Some of this expense was fortunately covered under warranty by the factory.  It’s great to know that Enstrom stands behind their products and takes care of the customer!

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