Has anybody taken a decibel reading of the exhaust on that Sparrow
   Hawk ?? Karibian



We did before the conversion to the rotary engine.  We noticed that the
sound ranged from the high 70's to the mid 80's for a person on the
ground.  Obviously there were a couple of up close readings that broke
100!  But it was not as loud in the cockpit.  (we also snagged some
reading from the few Robinson Heli's that  were flying by us...on the
high end they were somewhere around 82db...The sound from the
Sparrowhawk is a higher pitch and a different tone - a bit more annoying)

Interestingly enough we also tried 3 different propellers and noticed a
large difference in the DB readings by changing the prop.  Propellers
tested were the Warp Drive, IVO Magnum and a 2 bladed Prince prop.  The
Prince was MUCH quieter and gave off a more harmonically low tone (as
you know low tones do not carry as far, that is why a Train horn in a
high pitch so that it will carry and WARN!)

We tested different mufflers and found slight noise reductions w/a VERY
expensive muffler designed by Honda, but found no great noise reduction
worth the money.

We also worked a bit on the tail boom upper and lower as there was some
concern that the air off the tips of the props were interfering there
and causing additional noise.  Sure enough.  Groen Brother's Aviation in
an effort to quiet things up also noticed the same interference and in
their second kit version raised the upper tail boom.  In the noise tests
by the manufacturer they blamed the noise on the propeller and are now
doing 3 bladed tests with the Prince Prop that has curved tips. They
also discovered that the tone of the noise was part of the problem and
hope that the prop change will fix that as well.

When we flew the Sparrowhawk with the RotaryAE engine by Rotamax the
tone was a much deeper sound that didn't seem as annoying.

Nate Oldham


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