Gavin Grimmer
It is quite simple in that I’m using Google Earth’s “Elevation Profile” Tool on a
saved measured line and scaling the angle of view to determine what can be seen.
Of course, this means checking across the low lying areas to the point where the
ground rises up again... in this case on the lower side shown of the white shaded
area.
Taking into consideration what Donna Krane saw, apply her report to what D. Peters said... “Heard to the north, came south (towards him) for a bit... and then turned”, but note he said south-west. If it turned south-west then he could not then have seen it as there was a large hill blocking his line of vision, so once again a case of east and west getting mixed up.
If we continue on changing the “west” to the “east – or south-east”, then it starts to make sense. The track from where Donna saw it turn east towards where Jimmy saw it was east.
Also note that he said he could see a red beacon flashing.
Renae Wilkinson also remembered the red, but couldn’t remember if it was flashing or not... after all, it was a long time ago, so she did well.
Note that both of these witnesses commented how they could hear it and yet it was downwind from them – at around 10 kms away (and got closer for D. Peters)! I’ve taken note of planes with the same motor and propeller combinations flying around here and at cruise settings, you’re lucky to hear them at 3 kms away... and that is with no wind.
The majority of the traditional aircraft engines (Lycoming and Continental) run at
maximum rpm setting of 2700 whereas these particular fuel injected Continental motors
fitted to the Cessna 210, 206, and 185 have a maximum rpm of 2850 (for 5 minutes
only) and with the 80 inch 3 bladed propeller fitted, on maximum rpm the propeller
tip speed is close to the speed of sound, hence they produce a lot of noise at that
rpm! It’s not so much the motor that can be heard, but in effect mini sonic booms
come off the propeller tips... at least that is the way I understand it.
The motor
was rated for full power (2850 rpm) for 5 minutes only, yet it was heard for a lot
longer than that from around 10 kilometers away in windy conditions... even when
it was downwind of the observers, and to be that noisy means it was up around the
maximum rpm (or even more).
There was only one plane that I knew of that could make a noise as loud as that,
and that was a Cessna 185 used for parachuting operations with a larger 84 inch propellor,
and it had the same motor as that in VH-MDX.
It could easily be heard in the neighbouring
town – Havelock North 10 1/2 kms away. The owner insisted that because that was what
the Pilots Operating Manual said the motor should be run at for take off (2850 rpm),
so that was what he was going to use... no matter how many people complained...
So judging by this parachuting plane noise, with MDX having a smaller diameter propellor,
to equal the tip speed of this C185 calculates to an engine rpm of 2920 taking into
account the lower air temperature that MDX was flying in... using the calculator
found on: https://pponk.com/props/#1463774934977-1d7f57b4-6b2b
MDX pg 59