Hi Nigel,
A great reply. I read all your responses at least 10 times to absorb what you describe. I am still a learner compared with you , Rob and others in Oz. The thing that has pushed me into working on VH-GNW and WVW really has been the experience with both the repair and flying of our Dimona ZK-GCB. I recall you mentioned some years ago comparing the Dimona with a Grob 109 You are right … the little Dimona has exceeded my expectations by 100%. Not bad considering the design is now 40 years old. Relating to fuel … A couple of Mths ago a very good friend asked me to ferry his Fisher Tiger Moth (About a 0.8 scale) from one airfield to another … about 15 min flying time. The engine is a Walter Micron Mk3 (85 hp) We topped up the tank with fuel from a plastic container (Mogas) Well, I set off and all was good (or seemed OK) though the RPM was a little lower than I expected. Leaving the circuit and heading South, everything turned to custard. Smoke, vibration and no power … Shit!! So a controlled descent into the Auckland gliding club strip which was fortunately strategically placed. A nice little hole in the rear piston. We have it back together and was able to continue the ferry flight (but was a mission to repair and another story) The thing here is the fuel we put in had been stored in a plastic container for a longish period of time. So had gone off big time. Low octane causing bad preignition. So beware of storing your fuel in plastic containers. The 500 hr inspection relates to all the fuel lines forward of the firewall if I have read the MM correctly We don’t have a technical engineering panel here in NZ so all work has to comply with the factory MM or a major repair factory approved. (though I am sure any GFA engineering decision would be accepted over here) . fortunately I do have associates who have had many years composite aircraft experience so am fortunate there. We are still discussing the repair to GNW . Our current thinking is to utilize the fittings from WVW. We are currently cracking all the joins of the centre section of WVW internal panels so will see your repair. We have the detailed drawings of that area which show the Rovings and how far they extend into the structure. With GNW, someone (suspect the Thais) have cut(100mm * 80mm approx.) holes into the outside skin in front and behind the rod end holes on both sides. .. cutting through rovings laid on the skin. The holes were covered with aluminium plates attached by rivnuts drilled into rovings … really quite ugly. I am sure that was not done in Australia. I will keep in contact with you Nigel regarding the repair to GNW as we progress. Best regards Ian W. From: [email protected] On Behalf Of Nigel Baker Sent: Friday, 8 November 2019 2:30 a.m. To: [email protected] Subject: RE: [DOG mailing list] H36 top speed I thought I had addressed your concerns in my mail. Dealing with the fuel hoses etc. should be easy. The manual gives a life of 5 years for the fuel hoses in the H36. Anyone in OZ paying attention to the GFA engineering panel advice would have used 1 of 2 types of hoses preferred and both of which are OK for avgas and low lead alcohol. If using hose supply from either Diamond or Limbach then the fuel is appropriately approved for the fuel types. The electric fuel pump also has a life. The previous pump and the replacement both are ok for said fuel types as I understand. The old mechanical fuel pump rubber parts were OK for said fuel types. The new replacement pump as the original type is out of production surprise surprise and the new Italian replacement is also OK. The Carb diaphragm and parts were and still are OK with these fuel types. So assuming the manual has been followed then all the relative items should have been dealt with but it should all be easily checked from the aircraft maintenance log and in my case most certainly so. It is all clearly listed in my log book otherwise I wouldn’t know where I was from one year to the next. I am not suggesting digressing from the certification of the aircraft at all. If all that is correct then my only remaining concern is those like my aircraft that still have the original FRP tank and not the alloy replacement as per the SB. So until 3000 hours in accordance with the SB I will happily check the tank each annual for degradation but so far so good. I warned about dud fuel and the likelihood of detonation in my post. This subject has been dealt with multiple times on the DOG list and I would hope all members are across that problem. The H36 is a pretty quiet aircraft and it amazes me how anyone can miss the sound when it is all wrong. But then again Rob and I a couple of years ago had the pleasure of inspecting the cylinders and heads from an L2400 fitted to a Typhoon which had a history of being flown outside the top CHT range. The detonation had destroyed the heads and pistons. The CHT got so high the barrel tops softened resulting in them swelling out under combustion pressure to the extent that the cylinders and heads could not be separated. We put the cause down to excessive CHT due to the history we knew. Strangely when asking the pilots about the pinging sound resulted in blank looks. Maybe they were not aware of the symptoms and sound. In any event we have covered fuel quality at length in the past on this mailing list. As I pointed out the rules we operate under here down under are very different and local requirements and governess must be followed. I have attached some pics of the holes cut for the rod end bearing replacement. These were cut with the aid of drawings from diamond. The large ones to the side of the control stick I reinforced with a cast ring made of glass roving’s on the underside of the seat panel. It was not required by the drawings but seemed like a good move. The small hole at the bottom of the front seat panel section was to be able to get an in hex drive into the SHCS that holds the rear rod end in place. The hole in the floor in front of the seat section is the front rod end mounting. It is better to start further forward and work backward toward the seat to avoid inadvertently damaging the roving’s. The seat assembly and Centre console form part of the fuselage structure. Especially over the tunnel for the undercarriage bow where there are complex being moments. Thus repair is really only practically achieved from the outside not inside. It is not a difficult repair but it is complex and done in stages. VH WVW had this repair done to it after a really really really heavy ground strike/heavy landing incident. The steel tube that spans between the front and rear rod ends was replaced and laced back into place with roving’s as original and then the rest of the structure laid up from there working outwards. Like I said things are different here so no need for a factory approved repair scheme. In fact some years ago Alexander Sleicher released an SB that clearly stated that any fiber repair could be carried out following the repair principles defined in the Maint Manual “including propellers” as long as the person is approved for the task in the country of operation. That is me and quite a few others who have the training and experience to do the damage and repair assessment as well as being able to carry out said repair which usually includes jigs, molds. Vacuuming etc. not simple stuff. Cheers. Nige. From: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > On Behalf Of Michael Stockhill Sent: Thursday, November 7, 2019 10:22 PM To: [email protected] <mailto:[email protected]> Subject: Re: [DOG mailing list] H36 top speed My concern regarding use of alcohol blend fuel is this: While the current manufactured Limbach and Rotax may be certified for use of such fuels, is there any assurance that soft parts such as hoses and seals used and still existing in older aircraft and engines fabricated before these fuels existed can tolerate alcohol without degradation? In addition, in a previous life I investigated a Beech Bonanza accident where the owner was using auto fuel, notwithstanding the fact that its Continental engine was not one qualified for a supplemental type certificate (STC). Removing one spark plug and seeing the piston's bead blasted appearance was all that was necessary. He had gotten away with his charade for quite a while, until he onloaded some fuel that was of lower octane than advertised. Sourcing auto fuel lends a bit of trepidation to its use in airplanes. M On Thu, Nov 7, 2019, 12:10 AM Nigel Baker <[email protected] <mailto:[email protected]> > wrote: Hi Jarek Ian and all. I have experienced this pitch problem once before on an IS 28 M2 (worst aircraft I have ever flown) and while I knew the answer I didn’t tell the owner as I considered him a loose cannon on maintenance. He wrote the aircraft off during landing which was pretty predictable given what I had noted in his flying and thus I was never asked to fix his problem. I have been looking for the appropriate data which I have somewhere but can’t put my hands on for the dimension of the pitch change step on the pitch setting nut’ I have found data for the 2 pitch angles between climb and cruise but not the step dimension. The nut I refer to is the round nut which is fitted to the central pitch drive shaft which is positioned beneath the alloy channel with the nylock nut on top to secure it all. That nut has a step in it that the slide plate engages with the nut when de pitched in flight for pitch change. To understand it you need to remove the spinner and action the blades by twisting at the root to move pitch position then move the slide out from Centre and release the blades to lock back on the nut. That is the cruise position. A small twist of the blade allows the slide to return under its spring force towards Centre and on releasing the blades it is locked in climb pitch. Centrifugal force is what courses the slide to move out from Centre hence the need to change to cruise at around 2200 and climb near idle. I hope you have grasped my explanation but toying with it the best way to work out how the function works. The nut sets the climb pitch position so yes 3000 static is good. Bring the RPM back to cruise pitch change RPM and do the change then open the throttle again. If you get a static drop of 200 to 250RPM then the prop is fine. If it is greater and the RPM Is less than 2600-2700 RPM then I suspect the wrong nut was installed at your recent factory service. To check this using the angle data which is listed in the prop manual requires accurate angle measurement so best done by a competent propeller ground engineer. I am not near my aircraft which is over 200ks from me. However if Ian Williams or someone else is in a position they could give us a reference to check to. To do so remove the spinner and set the prop in the cruise position. Now using feeler gauges the distance between the climb position step and the pitch select slide. This propeller is used on many aircraft types and thus settings for fine pitch and cruise vary a lot. The change in amount of pitch is controlled by the length of the step in the nut. The Longeazy is a good example. The RPM change from climb the cruise is significant. Slippery in cruise hence the big pitch change. The ASK14 has a Hirth 4 cylinder 2 stroke engine and a 2 position Hoffman prop. Same assembly but without the slide. I know a couple of this type have had the nut replaced and the slide assembly added so it has 3 positions like ours. I also know someone who has made his own nut with 2 steps so he has 4 pitch positions. I am not suggesting any of this is wise or legal but telling you this so the versatility of the unit is understood. If I am correct about my best guess of the problem from previous experience then Hoffman need to fix their mistake and fit the correct nut. If you are having trouble reading and understanding my descriptions then consider how hard it has been for me to write this. I keep reviewing it to make sure it makes sense and is understandable. I have likely failed. Sorry but the best I can manage. The Limbach and Rotax engines are permitted to run on alcohol blends and is becoming the norm in that class of engine. In the Limbach engine the rubber components being the factory fitted hoses on the engine, the Carb and fuel pump diaphragms and seals etc. are rated for alcohol blends. The engine is certified for alcohol blends. Around the world alcohol blends are becoming the norm for mogas. In Australia there are 2 states where the use of alcohol is mandated in mogas so you really can’t avoid it. Peter Limbach told me the reason the Limbach is certified for Avgas as well as 98 unleaded is because of certification requirements and market acceptance rather than by simple choice. He prefers unleaded. Except for lead, avgas is the purist fuel on the market. Mogas specs change with the season keeping your car running smoothly so it is far from pure. Discussing issues I have found on top overhauls, full overhauls and prop strike bulk strips on engines running on avgas (Including the L2400 DFI 100HP liquid cooled engine prop strike) he agreed with my views and said yes that’s why we prefer you run on unleaded. The lead fouls spark plugs yes, but even worse it fouls valves especially the exhaust and cakes thick on the combustion chamber and piston crown. This build up causes run on at shutdown/hot spots for ignition etc. It also fouls the piston ring grooves and can lock the rings as I have seen happen before. I have also experienced exhaust valve failure caused by it leaking due the build of that horrible yellow cake. Having said all that there are some other considerations to be respected. I almost exclusively use unleaded. Some times I am not able when touring and the mogas point in town is a long way from the airfield so I use the on field FBO reluctantly. I am always wary of the fuel octane with mogas. The fuel companies mess with the formulae a lot to meet the 98RON. This results in volatiles that will at times rapidly evaporate out and reduce the RON significantly. So always be aware of the risk of detonation. It may come from the pump already degraded or often degraded while sitting in the tank if the aircraft sits idle for some time. Avgas can also degrade in the tank over time but the time factor is significantly longer and thus not usually a problem. While our engine is rated for alcohol blends you must also consider the suitability of hoses and boost pump used in the airframe for alcohol blends. That is actually easily achieved in our case. The let down is the fuel tank if it is composite rather than alloy. There is a question mark on the resin used in the tank manufacture. I check the tank each year as per the SB and have not ever detected any degradation. However someone in a different country could well have a different result with their local fuel supply. So due diligence is required to meet the requirements of your local aviation authority, tank inspection, and checks on the other fuel carrying items in the airframe for suitability. All issues must be considered carefully. Meanwhile I don’t use avgas and advise others in OZ to do same but our rules are set by our sporting body the GFA not the government body. We are very different and what we can do here often is not possible in other countries. Hope my ramblings are of help. Cheers. Nige. From: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > On Behalf Of Ian Williams Sent: Wednesday, November 6, 2019 7:42 PM To: [email protected] <mailto:[email protected]> Subject: Re: [DOG mailing list] H36 top speed The RPM’s and speeds are what suits us. There are only 2 Dimona’s in New Zealand .. some distance from each other. So it would be good to get data from other Dimona operators. IW Sent from my iPhone On 6/11/2019, at 9:38 PM, Ian Williams <[email protected] <mailto:[email protected]> > wrote: Yes … an L2000 Limbach and an HOV62 prop. What is your static full throttle RPM on the ground ? From: [email protected] <mailto:[email protected]> On Behalf Of Jarek Steliga Sent: Wednesday, 6 November 2019 9:14 p.m. To: Laurie Hoffman via dog <[email protected] <mailto:[email protected]> > Subject: Re: [DOG mailing list] H36 top speed Hello Ian Williams, I am really worried after reading your reply. Are we talking about H36 with Limbach 80PS and Hoffmann HO V62 propeller? If so, what could be the reason for the serious underperformance of my power plant? Regards Jarek On Wed, 6 Nov 2019 at 09:05, Jarek Steliga <[email protected] <mailto:[email protected]> > wrote: Hi Ric, 1600 hrs / 12 atm pretty consistent on all cylinders Regards Jarek On Tue, 5 Nov 2019 at 12:46, Ric Sutton <[email protected] <mailto:[email protected]> > wrote: Hi Jarek how many hours do you have on your engine/ what are the compressions like? From: <mailto:[email protected]> [email protected] [mailto: <mailto:[email protected]> [email protected]] On Behalf Of Jarek Steliga Sent: Monday, 4 November 2019 5:06 AM To: <mailto:[email protected]> [email protected] Subject: [DOG mailing list] H36 top speed Hello, I noticed that at level flight with the prop at cruise angle I can hardly reach the air speed of 150 km/h at RPM 2500 (full throttle). Is this something to worry about? Should not the top speed be around 190 km/h at RPM 3000? With the prop at "start" position the full throttle revs are 3000. Any comments please? Regards Jarek
