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  1. #161
    Co-Pilot BobH's Avatar
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    Sean,

    Thank you very much for the advice. I was worried about what to use, so I've been reading up on the whole covering process, and I agree that non-tautening dopes are the way to go.

    Unfortunately for me, the details of what was used to cover the aircraft, along with all the other documentation, were lost during a house move by a previous owner. I've contacted the original builder, but he can't remember the details other than that he got the fabric and the silver paint from a bloke at his local gliding club. So I'm a bit in the dark regarding what was used. However, I've got some bits of the fabric that I've removed in order to gain access to the inside of the fuselage, and I can see from the bits that I've got, that the colour closest to the base fabric is silver. There's no hint of either pink or green, which I guess must mean that he didn't use any dope, but painted the silver UV undercoat straight onto the fabric. That's backed up by the fact that I can peel the silver paint away from the fabric without it breaking. So the paint hasn't sunk into the fabric, but simply stayed on top as a separate layer.

    Another thing is that there's no hint of a top coat either, so it would seem that he painted it in the silver undercoat and left it at that, probably as a way of saving weight. There are small patches where the silver has been over painted with more silver, but that's probably Halfords silver spray paint I would guess.

    It's worth remembering that I'm not recovering the whole aircraft, but simply covering two small panels at the tail end of the fuselage, under the tail feathers where the area won't get much in the way of UV light anyway. I'll be gluing the panels in place with the poly-tak glue I got with the fabric, and after that I'll see if I can get a small amount of the silver UV paint, but if not then I'll spray it with Halfords silver spray paint in order to match what's already there, and I'll be cutting out two bang panels as well (one each side), so that I'll have easy access to the area in the future.


  2. #162
    Co-Pilot BobH's Avatar
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    Hello again,

    Just an update on the tail spring saga.

    Do you remember I said the nut came off the bolt that holds the front of the tail spring in place, and that because the nut disappeared the spring came loose and moved round to one side? Well, it seems that the nut didn't come loose and fall off, it snapped off! Take a look at the photo below and you'll be able to see that the bolt snapped just after the start of the threaded section.

    IMG_20190911_163758.jpg

    I didn't actually notice when I retrieved the bolt from inside the tail section of the fuselage that the threaded part was missing as it was covered in dirty grease. It was only today when I went to measure the bolt so that I could replace it with a slightly longer one that has a drilled thread, that I found the damage. Needless to say I've now ordered new bolts from LAS, and they'll probably arrive before I next go up to the airfield, so I'll be able to do a trial fitment with the new bolt and see exactly how much thread sticks out from the bottom of the spring.

    I must say that this makes me even more inclined to add in a third bolt between the current two, so that if the front one snaps again the spring won't be able to swing off to one side as it did last time.

    I did read somewhere in one of the Minimax newsletters John Hamer used to send out, that there was a third bolt modification, but I couldn't find any details of it anywhere. I'm now wondering if anyone else has had the same kind of experience as me, and had the spring coming loose and moving off to one side? It was most unnerving having the plane trying to turn left while I was applying full right rudder during the landing roll, and it's not an experience I'd like to repeat. So if by fitting a third bolt I can prevent that from happening again then I think I will. The added weight of an AN3-16 bolt and nut is negligible, but the peace of mind it will give me is worth the weight of half a dozen extra bolts if it keeps the tail wheel and spring in line.

    Oh, by the way, in the picture above the bolt is lying on one of the panels of fabric I cut out from the fuselage tail section. I've examined it closely to see if there's any sign of any form of primer or undercoat between the silver paint and the fabric, but I can't find any evidence of any. So I can only conclude that the original builder just painted the silver paint straight on to the fabric without any prior preparation. If so then it's remarkable that none of it has peeled off, but it's all still there (at the moment!) and for a single coat looks quite good.


  3. #163
    Trainee Pilot tomshep's Avatar
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    I wouldn't bother drilling a further hole. It weakens the wood, weakens the spring and adds weight at the tail. I see no benefit as there are thousands of Maxes flying without.


  4. #164
    Co-Pilot BobH's Avatar
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    tomshep,

    Without wishing to disagree with what you've said, nevertheless the thousands of Minimaxes flying with only two bolts are mainly the equivalent of the 91, that have no lower tensioning wires for the tail feathers. So there's less stress on the front bolt, particularly on the bit where the thread starts, which is right where the tensioning wires join together using a flat plate, as you can see in the photo below.

    IMG_20190801_165309.jpg

    Your 'max never had that extra plate outside the fuselage right at the junction of the shank and the bolt thread, or the stresses it places on the front bolt, so the likelihood of the front bolt snapping on your plane was minimal. However, on the 88's the likelihood is vastly increased, as I've found to my cost. So I think I'll drill an extra 3/16" hole midway between the front and rear holes on mine and fit an extra bolt. I might also fit some form of safety holding bracket as well, so that even if the bolt does snap again, the plate holding the tensioning wires can't just float around in the breeze and let the horizontal stabiliser flap about. Don't forget that the 88 only has three bolts holding the tail feathers, not the four bolts the 91's have, so without the tensioning wires, the horizontal stabiliser can twist around much more easily than on the 91's.

    Not only that, but as I said in an earlier post, I read in one of the Minimax newsletters that there was a modification to fit a third bolt. This wouldn't have come about unless others had encountered a problem similar to mine in the past. Obviously someone else already has, and the modification was created to overcome it. However, I've been unable to find any details about the mod, although John Riley did tell me once that he'd seen the document detailing what it was, but had mislaid it. So perhaps I should quiz John Riley again and see if he can find the details this time, before I go making any changes to mine?


  5. #165
    Co-Pilot Sean Dougan's Avatar
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    I see what you mean about the fabric there. That's a shame, unless non-tinted nitrate was used.
    For reference, here's a piece of Poly-Fiber. You can see the pink base layer quite clearly.
    Polyfabric.jpg

    If you were covering the whole aircraft, that's make things easy as you just choose whichever process you're happiest with and go with it. There's also now the Stewart system which is water-based, so no having to deal with that evil vicious Methyl Ethyl Ketone.
    Repairing existing covering is where you need to be sure what's there as you're supposedly meant to use like for like.

    Supposedly. However someone may have, after their tail wheel snapped off and went through the Poly-Fiber covered rudder, patch repaired the damage using Randolph materials with Butyrate dope on top. It actually worked really well.

    Aluminium UV coating being used as the final coat is fine. Many do that to keep weight down.


    Just a thought about that bolt there. Was it long enough? There shouldn't be any lateral loads, such as that cable plate, bearing on the threads. The plain shank should come through every part being held together with washers packing the nut as required.
    We got a mechanical contrivance getting in the way of a good time, and the worst kind of mechanical contrivance - a German Engineered mechanical contrivance.


  6. #166
    Co-Pilot BobH's Avatar
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    Sean,

    Unfortunately the only plans now available don't show the tail with the wire bracing all round. Instead they show the tail with the four mounting bolts and the two bracing struts between the top of the tailplane and the fin. So the bolt length may be too short, but there's no way of knowing. If you look at the picture in my post #164 you can see that the thread is poking through the nyloc nut by about a full thread's width, but the shank may be too short, and I think you're right in suspecting that. I do too, and I think that as the only bolt length shown in the plans nowadays is an AN3-20, that that was what a previous owner fitted. However, I've ordered up an AN3-21 and and AN3-22, so that I can test to see if the shank will protrude through the bottom plate, the spring, and the bracing wire connecting plate before the thread starts. Whichever one does is the one I'll fit, and if necessary pack up any gaps with washers.

    Regarding the covering material and chemicals to use with them. It occurred to me that using the poly-tak will glue the fabric to any existing fabric around the edges of the patch, especially if I try to clean off as much of the original chemical coverings, paint, etc, as possible first, but the rest of the patch could be sealed and painted with anything at all, and doesn't need to match whatever was on the original, because the two chemical coverings won't actually come in contact with each other.

    Whatever I do use will be on the outside of the patch, and won't come in contact with whatever is beneath the glue. Furthermore, around the edges I can always just use a spray can of either silver or aluminium paint to sort of match to the colour of the rest of the plane, and this won't create a bridge for the two coverings (say Poly-fiber and Randolph) to reach and interact against each other.


  7. #167
    Co-Pilot BobH's Avatar
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    Went up to the airfield today and took the clamps off to see how well it had all glued together. Apart from finding the indentations of the plastic feet on the clamps cast into some of the glue on the bottom plate, all was well.

    IMG_20190912_155615.jpgIMG_20190912_155718.jpg

    So then I started stripping the fabric back so that I can put the fresh fabric on.

    IMG_20190912_165553.jpgIMG_20190912_165624.jpg

    I did a trial fitment of the spring, but found that the rear hole in the spring has worn a bit, so the bolt is a loose fit in it. There are two ways I can overcome this.

    One is to drill the hole out and fit a AN4 bolt instead of the AN3 used currently.

    The other is to put the spring onto something solid with a convex surface, then get a big hammer, also with a convex surface, and centre the spring on the rear mounting hole, then give it a bit of a wack with the hammer. That should squeeze the hole in a bit, and I might have to redrill the hole out to 3/16" for the original bolt to fit.

    Decisions, decisions!

    I'm still going to add a middle hole between the current two holes and this should help to keep the spring aligned even if the rear hole is slightly loose around its current bolt, but the temptation is to drill it out to 1/4" and fit a larger bolt into a newly round and on-size hole. I know this would add a certain amount of weight, but I need to add weight at the back anyway, as the plane is currently very nose heavy, so I'm not worried about an extra 50 - 100 grams or so.

    Oh, I started disconnecting the engine this evening, and tomorrow all being well I'll use the block and tackle to lift it out of the engine compartment so that I can see about fitting the M5 starter. I'll take lots of photos of what I get up to so that you can see how I progress with the project.


  8. #168
    Co-Pilot Sean Dougan's Avatar
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    Doubt you'd add much weight from sizing up the fasteners.
    AN3-20 is about 10g, AN4-20 about 16g.

    Could probably do the front one as well to make it a bit more robust. 3/16 toothpicks do strike me as a bit under-specced for a rear spring.
    We got a mechanical contrivance getting in the way of a good time, and the worst kind of mechanical contrivance - a German Engineered mechanical contrivance.


  9. #169
    Co-Pilot BobH's Avatar
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    Sean,

    In the end I did nothing. I didn't drill the hole out, or try bashing the spring to peen the edges and reduce the hole size. I've done a trial fitment with the three bolts and it looks like this.

    IMG_20190913_183238.jpg

    I've also added a small L shaped bit of galvanised steel as a form of support strap across the bottom of the fuselage to stop the wood from being compressed by the spring moving up against it. You can see it in this next picture.

    IMG_20190913_183314.jpg

    I glued it on with some epoxy, and once it's been fabric'd over and painted it won't notice as a separate item.

    You probably can't see it very well in the photos, but I've changed all the nuts over from being nyloc type to being castellated, and I've bought drilled thread bolts to replace the originals. So once fitted in place, the castellated nuts and split pins will stop any from coming loose, not that they did anyway, but you never know.

    Next up is to start covering it all with fabric, then shrinking the fabric (but not too much) after which it'll get a couple of coats of primer, then a top coat or two of silver, to match what's already there.

    However, that wasn't all I got up to today at the airfield. I also took the engine off and fitted the M5 starter.

    Here's a picture of the M5 kit I received last week.

    As was removed from box.jpg

    and here's some pictures of what I did with it.

    IMG_20190913_154509.jpgIMG_20190913_170108.jpgIMG_20190913_174359.jpg

    And here's a photo of what I managed to do to myself in the process.

    IMG_20190913_174351.jpg

    That hurt a bit, and it happened because I had to cut away part of the fan cowling and also part of the M5 plastic cover for it all to fit together. You can see in this photo how I had to cut away both the fan cowl and the M5 cover.

    IMG_20190913_174417.jpg

    I was using a model knife to do the paring of the plastic, and somehow I managed to pare into the side of my index finger. There was quite a bit of blood, and I realised I didn't have any first aid stuff with me, so I wrapped my finger in some paper towel and held it on with a pair of cable ties. Worked well too!!

    I've brought the engine home for the weekend and I want to change the mounting bolts that hold it to its wooden mounting plate. You can see them in this picture.

    Engine mounting bolts.jpg

    Whoever fitted them didn't take into account the depth of the allen type head on the bolts, and they've been hammering the bottom of the engine compartment every since I've owned the plane. I did wonder why it seemed to vibrate so much, well now I know. See this picture to see what I mean.

    Engine bay.jpg

    You can clearly see the four indentations from the bolt heads. So I want to replace them with either studs as per the original, but they may not be long enough, or I'll have to get hold of four M10 x 45mm hex head bolts with a 1.5 thread, which is much more coarse than a standard M10 x 45 bolt thread. I'll have a look on Ebay to see what I can find.

    Once I've done that I'll see about refitting the engine, but due to the extra width with the M5 fitted, I'll have to cut out part of the right hand engine bay wall to allow for the starter motor. Nigel Ramsay has already sent me photos of what someone else had to do to their engine bay, and I fully expect to have to do the same.

    Then it's just a case of wiring it all in and testing it out to make sure it all works.

    Not much then! At the rate I'm going I should be finished by October.... 2021!!

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  11. #170
    Co-Pilot BobH's Avatar
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    Right,

    Where to start? This morning my new hex headed M10 x 45mm coarse threaded bolts arrived. These are what holds the engine to the wooden mounting plate that is then attached to the airframe with Barry mounts. So I fitted the new bolts and made sure to lock them in with Loctite 648. These hex headed bolts are not so high as the previously fitted allen bolts that managed to hit the bottom of the engine bay, but with the new hex headed bolts fitted there's actually a gap, so finally the vibration from the engine should now be tamed.

    IMG_20190917_105348.jpg

    Unfortunately, when I managed to fit the engine in the bay I didn't take any photos of the gap. I'll try to get some pics tomorrow when I go up to the airfield again, to finish off wiring up the engine and starter, and then panel in the tail end of the fuselage.

    But I digress. To return to the story of what I did today! I made up a bracket to support the starter motor, but found that once it was on, I couldn't put the engine mounting bolt in, so I had to take it off, then fit the mounting bolt, then refit the bracket. You can see what I mean in these photos.

    IMG_20190917_105152.jpgIMG_20190917_105221.jpg

    However, having one engine mounting bolt sticking out of the bottom of the mounting plate made things a bit more difficult later on when I got round to actually fitting the engine in the bay.

    With the new bolts in place, and the motor support bracket in place it was time to take the whole caboodle up to the airfield and see about fitting the engine into the plane. That was easier said than done, due to the extra width on the side under the exhaust manifold. I had to cut away lots of wood in the side wall of the engine bay, and also cut back the horizontal gusset on the exhaust side in order to get the motor to drop in. You can see the gusset after I cut it away in this picture of the engine bay with the engine now fitted.

    IMG_20190917_184936.jpg

    And in this one you can see the hole I made in the side wall of the engine bay to allow for the front end of the starter motor.

    IMG_20190917_184910.jpg

    Anyway, the engine's now in place, and bolted up all nice and tight, and it is a bit tight as well. I knew there wasn't much room at the back of the engine, but I didn't realise quite how little till I fitted it in with the M5 on the back. See how close it is in these pictures.

    IMG_20190917_191612.jpgIMG_20190917_191637.jpg
    Last edited by BobH; 17-09-19 at 21:57 PM.


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