Spinner
Yesterday (7 January, 2018), flying my IBIS GS700 Magic, ZK-PLC, I headed out from Rangiora (NZRT) to Okarito in southern Westland (it is tiny but does come up on Google Maps) to have a cup of coffee (in their tiny cafe) with the packed lunch that Bonita makes me. I flew via Lake Coleridge and on up to the head of the Rakaia River, making about 10,500' (on oxygen) and was abeam Mt Whitcombe, right on the spine of the island, when, suddenly, at 5500 rpm, a significant vibration started.
I throttled down and found there were rev ranges where it got worse, but at 4400rpm it was hardly noticeable. At that power setting, in the rarer air I could just about maintain altitude, however I was almost down to the official stalling speed (but since I put on the vortex generators I now have a generous margin of safety). At that height my radio call to regional Control should have got through but there was no reply. I put out an open call for anyone receiving this? I get one reply and announced my position, the problem and that I was heading for Mesopotamia station strip, in the Rangitata valley, down in the foothills.
When I got there I was still at, and holding, 7000' (in the denser air, probably) so I put out a call that the problem hadn't worsened and I was now diverting to Rangitata Island (NZRI) where there was likely to be help and advice. I called 'coming straight in' (bugger the circuit) and with Russell Brodie's help found that the fibreglass nose cone of the spinner had a split in the gel coat (but the fibres were still intact). When we took it off the inside was coated with black (aluminium powder) as it had been rubbing on the prop hub. I postulate the the back plate of the spinner has been flexing. Anyhow, though there was some vibration without the nose cone, it was constant throughout the rev range, so likely to be a residual imbalance rather than something else having come loose.
The field got a call from S&R, who had been passed my calls, and I rang them and advised them of my safe arrival - obviously they were as relieved as I; they had been phoning the high country stations along my route asking for them to keep an eye out in case I had to put down precipitously. Nice. I had NOT called PAN PAN, nor MAYDAY, remembering the trouble it had caused last time, for this time I was fairly convinced that with care I could carry on. If the worst had happened and the nose cone shattered but not completely detached, I could have faced really severe vibration, (and put out a MAYDAY) but having found a 'safe' speed I hadn't thought that likely (given that at the time I had no idea what, if anything, had come loose).
So, having identified the likely cause of the problem, and without the nose cone, I took off from NZRI and flew safely home.
Rule No. 1: Don't panic.
Copyright © 2018 Peter Leon Collins
v2, 30/07/2019