Hi Ian, You have had more than your fair share of problems! Some comments.... - All the Dimonas with the old style ailerons that I have worked on have a noticeable upwards (negative) deflection. Does your's? Do you think this could be a factor? - Regarding prop cracks....I think all props should be dynamically balanced and I think not doing so causes significant long term problems.
Cheers Rob Rob Thompson 0429 493 828 On Tue, Oct 31, 2023 at 3:49 PM Ian WIlliams <[email protected]> wrote: > Hi All, > > I thought you all may be interested in the following > > > > 1. We have finally got our replacement prop from Hoffmann (10 mths) > and was rather expensive so when I was told a forklift fork had gone thru > the box in transit my reaction was rather predictable. Fortunately it was > not damaged > 2. Before this happened, I had contact with Airmaster props here in > New Zealand. They could produce a really nice little constant speed prop > (electrically operated) which would be a real plus for the L2000 Dimona”s. > However I got a call from the head honcho of NZ CAA airworthiness who > totally rejected the idea. (being a type certified aircraft) Hence the > Hoffmann prop. However now the Limbach engines no longer have EASA > approval, that may change the H36 type certificate to enable “special > Category” or even “experimental” so if there is anybody interested in > installing an Electric Airmaster prop that will fit on an L2000 Limbach > (correct rotation) let me know as I have organised 2 blades (Made by > Sensnich). > 3. I think the cracked ferrells of the props has been caused by > excessive temperature and humidity levels in our uninsulated, shingle floor > and wet hangar over a long period of time. So I am thinking of a controlled > heated insulated blanket over the prop and engine. Raychem Autotrace > heating cable seems a good suggestion or a slightly modified electric > blanket. > 4. Currently I have almost finished an annual inspection on H36 S/No > 3667 ZK-GPH It has been a real mission. I found a turnbuckle fork end > of one of the thrust cables under the engine was broken .. and had been so > for a long time so was held only by lock wire. Quite strong lock wire I > reckon > 5. I have ferried it around NZ for subsequent owners and the aileron > control was unacceptably stiff, to a point of “sticking” when operated. > Making it a really unpleasant little rocket to fly. > > This H36 was not a Thai one, but was imported to NZ from Italy (tho German > registered D-KEBA) in 2010. However it does have the early “aileron push > rod in compression when both ailerons are forced upwards. This was a > design problem which was corrected with later serial No’s which had the > rods in a tension mode. The aileron bell crank for the older Dimona’s is > fabricated from tube while the later (tension) bellcranks are made up of > flat plate and there is only 3 bearing sets in the wings as opposed to 5. > > > > Now for the jucy bit .. > > We made a detailed inspection of each of the 10 bearing sets (5 per wing) > with a small camera and found some of the bearing sets (3 ball bearings > pointing inwards on a 3 piece metal “holder”) mounted on wooden mounts > ie the control rod passed thru the bearing sets and through a hole in the > mount. We found that some bearing sets were not installed dead centre of > the mounting bracket hole The over all clearance being about 1 to 2 mm. > > The upward load on the ailerons of the H36 when doing say 90 Kts is REALLY > high. And I think is underestimated. Hence the compressive load into the > pushrods is also VERY high forcing the rod to bend like a snake. Putting a > high lateral load to each bearing set. > > So with misaligned bearing sets some of the bearings were not touching the > rod hence “rubbing” on the wooden bearing set mounts. So that is why the > ailerons were really stiff in flight but seemed OK on the ground > > > > To repair was a mission. We didn’t want to put holes in the wing so > designed a cutter system which we made from a short length of brass > turned it down to 18mm, put an 8mm thread in one end, rounded off the other > end and drilled a hole thru the thing used a 6mm drill cut off and a > cutting edge ground so it protruded from the brass”slug” about 3 -4 mm. > we then used an old push rod with the “slug” on one end and a battery drill > at the other and with great care, removed the mounting bracket material as > close as possible to the metal bearing fittings. > > > > So it still needs a test flight but problem solved. I think Hoffmann has > issues because prior to changing the push rod configuration, there were > about 5 different variations of bearing sets in the wings. > > > > If any of you want to see some pictures of the procedure let me know. > > > > Our Dimona (ex Thai) bearing sets had a solid nylon outer including the > outer ball race, so we had no choice than to make big holes and replace > them. As they all were seized Another Ex Thai (currently being restored) > didn’t have ball type bearings, just Teflon (or nylon rings) S/no 3667 > fortunately had proper bearings (ie with a metal outside ball race) and a > nylon “tyre” against the push rod. > > > > So I thought you all may be interested. I am astounded that the aircraft > has been flying for over 40 years like this and would be interested in your > comments > > > > Best regards > > > > Ian Williams > > Drury > > Auckland > > New Zealand >
