Hi Michael. The lift of the ailerons in flight and at speed is natural and can’t be rigged out. The reason that it can’t be adjusted/rigged out is because if you compensate for the droop e.g. set them low on the ground by the amount they rise in flight they will bind up before full deflection for take off and landing. In fact they will dramatically reduce the total throw of the control. Been there done that. I tried it on the ground and worked it out real fast. The lower overlap joint of the aileron skins protrudes forward and this clashes with the rear/aileron hinge spar at the max down value. In fact I had to relieve some of that joint on 2 aircraft in order to get it to go into tolerance based on ground values let alone compensated. There is a small amount of adjustment that can be made to the bias at the outer aileron bell crank which may help but not by much.
I have never seen centring springs in the aileron circuit in any other euro glider except for the Dimona and I have worked on many types. The springs were in the original design then disappeared and returned again in the HK36 Super Dimona. I am still bemused by it all. Asking the factory about the H36 did bot result in an explanation or a reason for their existence. Cheers. Nige. From: Michael Stockhill Sent: Saturday, May 23, 2015 9:47 AM To: [email protected] Subject: Re: [DOG mailing list] Engine mount for Limbach Thanks, Nigel, My friend's H-36 has evidently had that characteristic since he purchased it about 15 years ago; he had figured that was just how they fly and hadn't said anything. I had flown it on a few test hops, but never in disturbed air. Last year, there was some turbulence during my hop, and I noted the characteristic. His father was along with me (a PhD in aeronautical engineering) and was as puzzled as me. I'm going to take a serious look at it next week and rerig it in accordance with the manual. Understand that I am blowing smoke at the moment, and am like a blind man trying to describe an elephant, until I really dig into the issue. I'm putting some thought into Ian's observations and wonder if he is allowing for the wing droop at rest when he needs those forces to displace the ailerons, equating that force with flight loads. I'm still working through that. I haven't read them this season, but I recall that the rigging instructions include putting an upload on the wingtips.I might go so far as to put tufts on the wings and ailerons of both his and my birds. As I think back to my early flights in mine, I recall that it seemed to take quite a bit of force to initiate roll and I thought it different from most aircraft I had flown. Now, of course, I am used to it. My hazy recollection of European certification standards is that they have required centering springs in aileron systems at least at some time. We're entering our season now! Happy flights, Michael On Fri, May 22, 2015 at 7:22 AM, Nigel Baker <[email protected]> wrote: Hi Michael. Ian is on the money with his description. If your friends H36 has just started presenting with this then it is of concern. However it is also one of the traits the H36 shows sometimes. Why Wolf put the centring springs in the aileron circuit bemused me until I flew it with the old aileron system. Both systems have a bias in aileron differential that fits within the tolerance listed in the manual. So the old system seems to work to the upper end of differential and the newer to the lower. This is to say that up aileron is greater on the older system than the newer and down is less than the newer system. End result is that depending on adjustments and manufacturing tolerances some of them have a desire to want to roll into a turn. Thus if you fly into a thermal and strike the core on the left the aircraft wants to roll left as the pressure on that aileron is higher and the bias wants to drive it that way. An advantage of this is that the system talks to you and lets you know through the stick which side the lift is better. Helps get around a 100 in 2 hours engine off. Yeh I know that’s slow but then it is comfortable and social. Cheers. Nige. From: Michael Stockhill Sent: Friday, May 22, 2015 2:14 PM To: [email protected] Subject: Re: [DOG mailing list] Engine mount for Limbach Ian, Thanks immensely for your response. On a personal note, I presented a paper at the International Society of Aviation Safety Investigators convention in Auckland in a previous life (as an NTSB Investigator) and toured the North Island, including a day or two in Wellington and also taking the train to Auckland. In a perfect life, I'd summer here and "winter" in NZ! I'll digest your thoughts over the next few days...I'll be inspecting my friend's H-36 next week in Washington (state). It really gives me much to think about. I do understand that the ailerons droop in static configuration and move upward in flight, and I do--of course--have the rigging information. That is a natural characteristic of the wing flexing according to the rigging info and my observations. I don't recall his serial number, so will take that into consideration, based on your comments. Regarding the odd flight characteristic: I haven't encountered such in the past. And I don't understand the reason the A/C is so tail heavy, unless there is some undocumented repair work, although the beautiful $17,000 paint job is obviously heavy. In order to remain within CG, a minimum of 20 pounds needs to be carried in the passenger seat! I flew it about a year ago, and recall that it needed almost all nose down trim for level flight. Regarding my bird, I have several hundred flights and hours in it. Three hours or more soaring if I wish, and highest unpowered flight was over 14000 feet. It taught me soaring. I now also have a PIK 20E that I also enjoy (there sure is a lot of monkey motion to stowing and deploying the engine in flight). If I was pressed to keep one, it might be the H-36 as I enjoy giving rides and the Limbach is certainly more complacent than the screaming Rotax. Cheers, Michael Stockhill On Thu, May 21, 2015 at 8:54 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
