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  1. #141
    Co-Pilot BobH's Avatar
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    Hello again,

    Did some more work on the 'max last week and this. I mended the tail end of the fuselage, where the block of wood the tail spring bolts to had come loose. I re-glued it with lots of T88 then clamped it and left it for a couple of days to harden and cure. I was then left with a large hole in the fabric on the right hand side of the tail, and a smaller cut in the fabric on the left. As an interim measure I've fixed a thin plywood panel on the right, and some duct tape on the left. In the photos below you can see the temporary cover on the right side of the fuselage, but in the photo of the left side you can see where I cut the fabric, and before I covered it with duct tape.

    Attachment 15127Attachment 15128

    My eventual aim is to remove both the plywood panel and the duct tape, and re-cover the tail end of the fuselage with new fabric, but until I can decide on a fabric to use the temp covers will have to do.

    While I was at it I took some photos of the teleflex mounting brackets. If you remember, I drilled fresh mounting bolt holes in each bracket in order to allow me to adjust the ailerons a little better, and also to add some reflex. Here are photos of each of the mounting brackets in their new positions, with the teleflexes now adjusted to get the reflex for each aileron.

    Attachment 15129

    This is the right one, and you can see that since altering the position of the bracket, the adjuster nuts are now in the middle of the long thread on the outside of the teleflex cable end. This is with the stick now centred and 3/4" reflex on the right aileron.

    Attachment 15130

    This is the left one, and you can see that even after the bracket has been moved along by 10mm, the adjuster is right at the end of its thread when the stick is centred and there's 1" of reflex in the aileron.

    I've done it like this so that if I find the plane rolls to the left when I've got the stick centred, I'll remove reflex from the left hand aileron until it flies straight.
    Last edited by BobH; 02-08-19 at 09:58 AM.


  2. #142
    Co-Pilot BobH's Avatar
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    Continuing from the previous post,

    Having done all that, I then started speculating on where I could fit an extra tank to help balance the plane, and give it greater range in the process. I took one of the 20 ltr wing tanks with me so that I could try putting it behind the seat to see if it would fit. Here are some photos of the tank in different positions, first sideways, then front to back, to see how well it would sit.

    rear tank sideways.jpg

    As you can see, it sits across quite neatly behind the roll over bar, but would require a lot of work to fair it in properly. So then I tried it front to back, to see if that would be better.

    rear tank front to back.jpg

    As you can see, it sits nicely behind the roll over bar, and now it's considerably narrower, so it would be much easier to fair it in to match the turtledeck. What turtledeck you may ask? Surely the plane has a sliding canopy with built in short turtledeck, as shown in this photo of the plane with the wings off.

    Right side 1.jpg

    Ah yes, but when I bought the plane it came with an open cockpit and a small(ish) turtledeck mounted behind it, as you can see in this photo.

    ad left side.jpg

    So I pondered on how well the tank would fit if I refitted the small turtledeck, but mounted it further back, and then faired in the section around the tank. Here's a photo of how it would all go together.

    rear tank and turtledeck right.jpg

    In the photo you can see that I rested the small turtledeck on the fuselage behind the tank, then put a 4 ft long metal ruler on the turtledeck to see how well it all lined up. As you can see if you click on the photo to expand it, there's an almost straight line from the angle of the turtledeck top to the top of the roll over bar. So if that area was faired in, the whole thing would look as if it was meant to be there.

    Here it is from a slightly different angle, and as you can see, it all fits together quite well.

    rear tank and turtledeck right 2.jpg

    In case you think this will upset the balance of the plane, just remember that it's already at the front end of its CG range when only the front 20 ltr tank is filled. However, I've set up the underbelly tank to be a collector. So any and all other tanks I fit will empty into it, and from the underbelly tank the fuel then goes to the filter, and the pump(s), (electric first, then vacuum).

    Here's a collection of screen dumps of a W&B calculator I downloaded from the LAA website, with the headings altered to match my plane, and with the weights filled in to show you how fitting a 20 ltr tank behind the seat balances the plane up much better than it currently is.

    W&B calculations with just front tank.jpg

    Notice that in the first screen dump above I set the max gross weight at 525 lbs. At this weight I can only put 18 ltrs of fuel in the front tank to stay within the CG limits. If I fill it with 20 ltrs then the CG moves to 13.4", which is ahead of the 13.5" limit.

    Now if I reset the max gross weight to 590 lbs, I can see all the calculations working as they should, and I'll be able to see the way the CG moves with the extra fuel that the underbelly tank gives. So first of all, here's the calculations with an empty belly tank (which can never arise as the front tank empties into it). But for arguments sake we'll add in just the empty tank first, and notice I've had to change the front CG limit to 13" in order to show exactly where the loaded CG would be in this hypothetical situation.

    W&B with front tank full belly tank empty.jpg

    As you can see it's still outside of the 13.5" limit, being 13.4" when loaded in this configuration. In this next screen you'll see what happens if the belly tank is full as well as the front tank.

    W&B with front and belly tanks full.jpg

    This makes it worse, and is the situation I find myself in at present. In order to maximise range I fill the plane with as much fuel as it can carry, which in theory is 31.4 ltrs. In this configuration, the loaded CG moves to 13.3", which is well outside the 13.5" limit. However, if I now add a 20 ltr rear tank and fill it, the situation changes drastically for the better, as you can see in this next screen.

    W&B calculations with all tanks full 2.jpg

    So by filling all tanks to capacity, then taking off, the gross weight of the plane is up at just under 590 lbs, and the CG is right in the middle of its range. I could then choose to half empty the rear tank first, or half empty the front tank first, and whichever I do the CG would stay within limits. So if I had to do an emergency landing just after take off, the plane would be much easier to manoeuvre than at present, as currently it is very nose heavy with full tanks.
    Last edited by BobH; 02-08-19 at 10:27 AM.


  3. #143
    Co-Pilot BobH's Avatar
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    Hello,

    I took the 'max up for an hour this evening and managed three landings. The first wasn't too bad, although I did manage to bounce a bit. The second and third landings weren't so good, and at first I thought it was just me being a bit rusty, but then I noticed that the tail end of the plane seemed to be a little lower than usual. Upon close examination I found that the nut on the bolt that acts as a pivot for the tail wheel control arm had come off.

    Tail pivot nut lost 1.jpg

    In the picture above, if you click on it to expand it, you may notice that the lower wires that tension the horizontal stabiliser are hanging loose. That's also because the nut had come off. That one bolt does two jobs on the 88. It is the pivot for the tail wheel control arm, and also the anchor for the lower tensioning wires for the horizontal stabiliser.

    The sad thing is that I knew the nut wasn't tight, but the reason was that if I tightened it up, then it squashed the tail wheel control arm so that it couldn't move. This was despite there being the proper 3/32" thick bushing as per the plans. Being a nyloc type nut I wasn't expecting it to come right off, but somehow it managed it. Mea culpa!! Next time I think I'll get a longer bolt and drill it so that I can use a castellated nut and a nappy pin.

    You can see in this next photo that having only one bolt holding the spring in place isn't a good idea.

    Tail spring loose 1.jpg

    So now I've got to take it all to bits again, but this time when I reassemble it I'll make up a 1/8" bush for the tail wheel control arm, so that even when the bolt is fully tightened, it won't squash the control arm. I'll also see about strengthening the whole area, as I found that the piece of wood I'd only just glued back together with T88 had come apart again. However, I'm not sure that it came unglued. It looks more like the wood has split away just above where I'd glued it. So this time I'll add a couple of alloy brackets to hold the wooden block in place. I might also add a bracket or two to make sure that if the spring ends up only being held by one bolt again, it won't be able to move to one side or the other, which is what it's done in the pic above. I wondered why the plane almost ground looped during the last landing, now I know why!
    Last edited by BobH; 09-08-19 at 09:08 AM.


  4. #144
    Captain Roger Mole's Avatar
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    Morning Bob, a quick question... aren't you a bit worried that wooden bits seem to keep splitting and breaking? It's a serious question and not meant to be a dig or anything.


  5. #145
    Co-Pilot BobH's Avatar
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    Roger,

    I know you're not having a dig. In all seriousness, the simple answer is yes, I am worried. Looking at the plans for the plane, the area should be pretty much solid, but mine isn't. Here's a picture of how the bottom rear of the fuselage is built up, showing the thin upper wooden plate, the thick middle plate, and the thin lower plate.

    Tail section of fuselage.jpg


    What isn't shown in the diagram above is the curved end thin plywood panels attached both sides to help strengthen the tail. These are very good, but do get in the way if the tail needs to be rebuilt. So I shall have something to keep me busy during the next few weeks, but hopefully when it's all done the tail will be a bit stronger than it currently is, and the tail spring won't come loose again.

    I think I'll have to remove the middle block of wood as well as the bottom and top pieces, and replace the bottom piece altogether. I'll also have to make sure that the middle and upper blocks are re-glued solidly, and I may add alloy plates top and bottom, bolted through the longerons, to ensure that nothing can move again.

    Here's another part of a diagram, but this one shows the mountings for the tail spring.

    Tail spring mounting.jpg

    Unfortunately, the plans have changed since my 88 was built, and the original drawings it was built to have been lost. So I can only go by what is shown in the above two diagrams, as being the way forward. However, one thing I won't be doing is changing from the chains and springs connection to the rear wheel, to a single solid rod as shown in the above diagram. This is a terrible idea, and I don't know why they changed the design away from the chains and springs design used on my 88.


  6. #146
    Co-Pilot Antoni's Avatar
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    Bob, I've had three MiniMaxs all with the standard rod steering system. Had the current aircraft for more than 10 years. To be honest the tail-wheel structure on my current one is not brilliant and gets awkwardly bent over time (not the aluminium spring itself). As a result there have been times when the wheel was canted and not even in line with the rudder. (Recently aligned and welded it)

    Never a problem at all. Not even with a few landings onto Sandtoft's single hard runway.

    I noticed on the USA Buzzards site they praise the springs-and-chains approach to the high heavens but I'll stick with Wayne Ison's original simple design.
    "The single biggest problem in communication is the illusion that it has taken place" - G.B.S.


  7. #147
    Co-Pilot BobH's Avatar
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    Antoni,

    As far as I know Wayne Ison's original design was for chains and springs. This was then superseded by the single rod idea.

    The trouble with the single rod is that on a hard runway, as the spring bends, it affects the angle of the tailwheel, so that if you bounce your plane, as the spring bends upwards, the tailwheel turns left. This can unsettle people who don't expect it, and the people on the Buzzards site were quick to notice it.

    Mine has the chains and springs, and I like the fact that a) if the spring bends upwards it makes no difference to the alignment of the tailwheel, and b) there is some give in the system so that I don't feel the wheel trying to kick back against my pedal.


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