Try My Pics Laurie. Attached. Nige.
From: Laurie Hoffman via dog Sent: Sunday, May 24, 2015 4:24 PM To: [email protected] Subject: Re: [DOG mailing list] Engine mount for Limbach Hi All, Not being an engineer (I've always seen myself of more of an artisan and lover!), you'll need to take my following comments with some caution. I have never flown the Mk2 so unable to give a comparison on aileron circuitry from the piloting perspective. We do have a set of Mk2 wings for sale as an aside. Since we first started flying GYT, the thing that struck me from the beginning was the extra resistance in the side to side movement of the stick compared with conventional glass aircraft. My understanding is that this is a function of the installed spring tension and can be varied by changing the spring tension. I also thought that ours was that way as an assist to long distance, higher speed touring. Correct me if I am wrong Rob. The aircraft is very stable in this configuration. Never noticed any snatching Macca or oscillation/feedback of or from the ailerons as mentioned by Michael, under the full range of flying conditions. Despite the resistance YT is a delight to thermal and was doing some hands off soaring today incidentally, made possible I assume via the extra friction. Another assumption was that the even upward ailerons deflection at higher speeds (around 20mm as Ian W. mentioned) is a rigging adjustment designed to improve performance along the lines of reflex flap settings on sailplanes. I would be quite concerned about any H36 needing full or close to full forward trim and it may well be at least partly associated with the snazzy new paint job Michael as its hard to believe that the Dimona could have been in service for very long previously with that characteristic. It wasn't reweighed after the paint job? Re the thrust line inclination, I assumed this was for improved prop clearance. There is a noticeable difference in tail height in three point between the fixed tail wheels and the suspension tail wheel assemblies installed which impacts on the thrust line so some variation there. The resulting unusual low nose attitude even when climbing is a huge boon to visibility ahead when otherwise the nose would be obscuring much of the sky, especially during descent. I have wondered if this was also an intended consequence of the engine mounting. I often get things wrong so pleased to be corrected on any of the above. PS Where are those bloody cutout pics Macca? PSS Don't be too upset Rob and Nige as being an engineer doesn't necessarily exclude you from being artisans and lovers also. Regards Laurie Hoffman -------------------------------------------------------------------------------- From: Ian Mc Phee <[email protected]> To: DOG LIST <[email protected]> Sent: Saturday, 23 May 2015, 22:50 Subject: RE: [DOG mailing list] Engine mount for Limbach What Ian says is true I believe. I do know the later version is nicer to fly. Earlier version wanted to snatch the control. Ian Mc Phee 0428847642 On 22/05/2015 1:03 PM, "Ian Williams" <[email protected]> wrote: Hi Michael, Thanks for your reply. I still think NZ is not too bad, though not so much of it. I thought a quick response was necessary based on my thoughts about your friends aileron issue. However I will also try and get you up to speed with the aileron changes. I am the engineer for 2 Dimona’s and 2 Grob 109’s here in NZ. One Dimona (ZK-GCB) is ex Thai Air Force which I have “restored” over a 5 year period. During that time I have had a lot of help and good advice from Nigel Baker Ian McPhee Laurie Hoffman, Rob Thompson and John Callaghan … all fine upstanding Australians. If I have made any errors in this discussion I am sure it will be corrected. The difference between the systems is that if you consider there is a load pushing both ailerons up, the aileron push rods are in compression (old system) and in tension (the later system). The old system uses 5 bearing sets in each wing and the new one only 3. They can be clearly checked which is which because the outer aileron bell crank of the old system is made from tube steel while the later one is made from flat steel. I have some photos I can send to you showing the difference. As I indicated, the ailerons on GCB lift about 20mm or so at 100Kts. If you attempt to duplicate that on the ground manually, the load you have to put into the aileron to lift 20mm is VERY high. That indicates the up load in flight is also very high. So it is a logical improvement to change the aileron push rod to a tension mode). Even with the 5 bearings, there is still enough up force from the ailerons to bend the aileron push rod between bearings. (where the 20mm lift comes from). Nigel indicated It is not a practical idea to modify the aileron circuit of the older Dimona’s. On GCB I also found all 10 (3 bearing) bearing sets inside the wing were seized. Because the ball bearings used at the time had their entire outer ballrace made from nylon. Maybe OK short term but as you may know, nylon does tend to absorb water and slightly expands…. Hence seizing all the bearings. They are not easy to replace as 5 large holes need to be made under the wing and their associated repair schemes, however can be done. Diamond supplied the new bearing sets which were a complete steel bearing but with a nylon “tire” in the outer edge. A much better system and the same as used on the Diamond DA 40 elevator rod. Re your friends Dimona, An issue like that would set off a big alarm. There could be a few issues. Some Dimona’s didn’t have any push rod bearings at all .. just bushes so if there was any radial play that could cause a problem. Also the bearing sets were mounted in plywood brackets butt glued to the inside skin … not really that strong. I am thinking that maybe one or more of these wooden brackets has come off. Also based on my above comments regarding the high flight loads put back thru the aileron circuit in flight, maybe you should make a closer inspection (try using a USB enderscope). Also note that the older aileron push rod has a joint about 5 feet or so into the wing from the root rib. This can make things a bit confusing as well. I will put together some photos for you .. .also will show the holes we made to replace the old bearings and also of the new and old bearing sets. Is there anything else you would like a picture of. Best regards Ian WIlliams From: [email protected] [mailto:[email protected]] On Behalf Of Michael Stockhill Sent: Friday, 22 May 2015 12:59 a.m. To: [email protected] Subject: Re: [DOG mailing list] Engine mount for Limbach Ian Williams I follow DOG from Montana, one of the prettiest of the Great Satan's 50 states. I own an H-36, SN 3518, and maintain another for a friend. I read your post discussing a modified aileron actuation mechanism. I am not familiar with that, so wonder if you could enlighten me? My friend's H-36 has an odd characteristic--at the onset of any disturbance or turbulence, the ailerons oscillate. I'd call it aileron snatch, but it doesn't quite fit the formal definition for the phenomenon. I'm headed his way in the next couple days to check the rigging; last time I was there, we checked and there is no play in the system. His bird is very tail heavy for some reason, so its CG is very near the aft range. This may or may not be relevant. Best, Michael Stockhill On Thu, May 21, 2015 at 5:14 AM, Ian Mc Phee <[email protected]> wrote: Interseting your observation about the tilt of the engine and may explain something. Ours points up for some unknown reason but is goes so well. We have bing carb and I had to finally fit different jets in each carb to even up temeratures (one 2.05mm and other 1.90mm). Bings only adj is jets. Ian McPhee Ian McPhee On 18 May 2015 at 09:29, Ian Williams <[email protected]> wrote: Hi All, Interesting reading. Nigel … rip into it, I am looking forward to seeing the finished HK36. Regarding the engine mount for the H36, One thing I have noticed, looking at all the pics of Dimona’s available on the internet is the thrust line of the earlier H36’s seems to be different as compared with the later ones … I mean that if the prop is vertical and you are looking at it from the side, the prop angle looks as if it is at the wrong angle ref the fuse … it pointing “up” The later H36’s seem to have a lower “angle “ relative to the fuse. (Havn’t explained it that well but you should understand). Our H36 is an earlier one (S/no 3537) We have 2 alloy spacers on the rear mounts which decrease the angle a bit which I assume is the same for all the ex Thai Dimona’s. Later h36’S seem to have a lower angle. Of interest, we have just done 100hrs in GCB since its first flight in June last year. It is a great little rocket and by far has exceeded our expectations. It has the original aileron control configuration but a new set of bearings in the wings (5 sets per wing) A mission to replace but works well. It is different in that the control forces than the later ones … the stick is quite “firm” around the centre for a small lateral control input but max aileron control load at speed is actually significantly less than a Grob 109 which I am involved with. It does take a little to get used to but is quite OK. With the new bearings there is no “sticking” at all. When cruising at 90 kts or more, the ailerons do lift up about 15mm or more. However both are even. Looking at the wing section and the pressure distribution under the ailerons it is quite clear that the compressive load into the aileron push rods is very high so the modified configuration was a logical one. We have had 2 problems … the first was a fuel blockage where there was some crap in the banjo bolt at the bottom of the fuel tank which was impossible to see (looked like grey cotton wool) .. ie between the finger strainer and the 3 outlet holes of the fitting … not helped by using some CRC rubber for a small sealing job on the tank (learn’t a real lesson there) However all replaced, flushed out and OK. The other issue is at lower RPM and lower airspeed the prop tends to slip into fine pitch. Not a major problem as in cruise mode it is OK. Other interesting things are · I have installed an MGL fuel computer using the original VDO float and a new turbine type flow sensor … a great system as you know exactly how much fuel is available and it also removes the non linearity of the fuel tank contents (5 calibration points) · The engine indicates an oil temp around 65 to 80 degrees C cruising. RHS rear cyl drops to about 120degrees C and the LHS side around 160. I think the variation is caused by a slightly different mixture setting of the carbs. Take off cyl hd temps around 190 (depending on the OAT) · I have installed a 5 V regulator supplying power to a small GPS plus a couple of USB sockets to keep ipads etc charged (note if using USB sockets the 2 * signal pins need a specific bias voltage to enable apple products to accept a charge … tricky people those apple dudes. · I also connected the comm. Radio audio amplifier to double as the Intercom amplifier with a panel switch that turns it on or off. Very simple and works real well. Combined also with a MP3 socket so ad you are cruising along, you can play music from your iphone thru the headsets. A real spin off also is if someone calls you the ringing and audio from the iphone is directed thru the intercom so no problem hearing the person calling. So all good. If any of you happen to come to New Zealand I would love both to see you and can provide some accommodation if required. I think Wolf Hoffman did a great job all those years ago. Best regards Ian Williams ZK-GCB From: [email protected] [mailto:[email protected]] On Behalf Of Ian Mc Phee Sent: Saturday, 16 May 2015 10:53 p.m. To: Laurie Hoffman; DOG LIST Subject: Re: [DOG mailing list] Engine mount for Limbach I will take photos tomorrow but it is a great (brilliant) mod & you must have it in a L2400 to gain access to oil filter. Engine in and out is a piece of cake especially when you remove front engine mounts AND the front Truss (2 bolts). Engine goes in and out with muffler exhaust all attached to engine. So easy. Im On 16/05/2015 7:29 AM, "Laurie Hoffman via dog" <[email protected]> wrote: Hi Ian, Re removable front cowl panel. Did you find the template that you had? Regards Laurie Hoffman ------------------------------------------------------------------------------ From: Ian Mc Phee <[email protected]> To: DOG LIST <[email protected]> Sent: Saturday, 16 May 2015, 7:21 Subject: Re: [DOG mailing list] Engine mount for Limbach They are VW part & will check old box later for number or may have it written up in logbook. Front ones need drilling and cutting. Back is as is ready to use. Do you have the removable panel at front? Great mod. Ian Mc Phee 0428847642 Box 657 Byron Bay NSW 2481 AUSTRALIA Ian m On 16/05/2015 5:27 AM, "Angel Jimenez Martin" <[email protected]> wrote: Hello everyone, Could someone tell me if it has the same engine mounts Limbach flock of Dimona and Dimona Mk 2. Greeting
