Hi All,
I guess this is a rather tricky subject so I will be as circumspect as possible. Our H36 has been out of the air now for 6 mths because of a serious and potentially dangerous propellor problem (along with 2 other HO-V62 props.) The issue relates to cracking of the ferrells (those bands of metal at the base of each blade which the counter weights are clamped on to). We have had 2 types of cracking . one which was a hairline crack extending horizontally around the Ferrell (quite difficult to see) and the other which was very obvious from the top to bottom of the Ferrell. Both not visible with the counterweights fitted. Of the 3 cracked prop ferrells, (2 * Grob 109's and our H36) all aircraft have been hangered Obviously I am far from happy. The support from Hoffmann has not been anywhere as one would expect. The impression I have is that they seem to be not willing to support these small props into the future. An example is their unwillingness to provide the only Australian (and New Zealand) service company (For the HO-V62 prop) with any approved Technical data despite the fact that they sent one of their engineers to Germany for a technical training course. This really is a very bad state of affairs. There could be a few reasons why the ferrells are cracking Possible a manufacturing problem relating to the Ferrell material (aluminium .. what composition etc) or insufficient epoxy infusion of the wood material at the root end making it more susceptible to humidity and hence expansion Or faulty maintenance. So right now I am in the process of attempting to get some sort of approval to install a 2 blade electric controlled Airmaster prop (which uses Sensnich composite blades) A real plus is they are constant speed so would really enhance the Dimona's total operation . nice because of thinner, more efficient blade design and adjustable preset prop positions including feather. Their operation is the same as a standard CSU operation except there are 3 preset RPM setpoints as well as totally adjustable like a normal oil pressure type CSU. And quite simple to install. In New Zealand, maintenance of gliders and repairs are carried out by NZG approved engineers but anything outside of that follows the standard GA rules. Currently I have * Ordered a set of blades (Ordered by Airmaster to Sensnich) right hand rotation 62 inch total prop diameter 2 blades. * Discussed the idea with Diamond Canada who have suggested to seriously look at an NZ STC to do this. I am OK to carry out the engineering work / documentation and if approved could be available for other H36 owners * Discussed with Nigel Baker (Limbach Australia) who also has had similar issues with the Hoffmann HO-V62 props and was supportive of the idea There is a lot of info on youtube about the technical aspects of the airmaster props. Being a NZ company of course has its advantage for us. MT also produce a prop (TSO'd) the problem is both the cost, delivery delay and down here in NZ, freight costs are a real killer. So that's where I am at. I would like to hear opinions from other H36 owners if possible. Best regards Ian Williams Drury New Zealand Engineer for .. ZK-GCB ZK-GPH ZK-GNW ZK-GOC
