How many of you remove your tail struts at annual to check the bottom mount stubs for corrosion? I found ones on a customer's plane that had the bolts rusted half-way through, and the stubs themselves cracked full-length through the bolt holes.

Anyway, every time I pull the struts (just did mine today), I cringe at how hard I have to pull up on the horizontal tail to get the strut to clear the upper mount stub (yes, this is after pulling all four bolts and sliding the strut all the way down on the bottom stub. Anyone else have this issue? Is there a better way? I know I could remove the horizontal tail planes completely, but I'd rather not have to mess with separating them at the control horn and unhooking the cables, and all that.

Andy

I just got a new set of tail struts from Maule which I'd like to install soon. I'm replacing the two main struts, and planning on also adding the bolt-on extra struts.

I'm curious what folks are using for paint and primer on these. It's been suggested that I powder coat them, but as I expect to have to occasionally retouch them due to mostly off-airport flying, I'm leaning more towards primer and epoxy paint.

Any suggestions on what kind of primer to use for best long-term adhesion and corrosion resistance? I see mixed opinions online on primer types, and on whether one should use an acid etch solution. The new Maule tail struts are stainless steel.

Also, what are folks doing for corrosion treatment on the inside of the tubes? A mechanic friend told me he uses a linseed oil treatment, which is a new concept to me.

If they’re stainless, I’d be tempted to NOT paint or powder coat them. Stainless is very corrosion resistant as-is. I’d just put a nice thick leading edge tape on them to reduce rock damage.

The linseed oil treatment is commonly used on the inside of the wing lift struts, as they are plain steel, but should not be needed on the stainless.

Thanks, Andy. That's an intriguing idea that's growing on me - leaving the stainless unpainted. I have non-stainless components on my boat which see regular ocean spray, and they seem to be fine after years of exposure, with just a couple of applications a year of Corrosion-X, so I'd imagine the stainless should do pretty well.

I assume they came undrilled. Drilling stainless can be a bit of a chore...

By the way, be sure to have a GOOD look at the lower attach stubs for integrity of the plastic or RTV filler material, and corrosion down in the stub itself. Not sure the year of your plane, but this is a significant issue on older planes. I found two cracked right through from corrosion on an annual. No one had caught it on a preflight or previous annual, even though it was cracked through to the outside. Many are badly corroded inside, but look fine on the outside. There is a service bulletin on this.

I assume they came undrilled. Drilling stainless can be a bit of a chore...

I appreciate the heads up, Andy. I'll make sure to look closely at the mounting stubs when I pull the old struts.

The new main replacement struts are unpainted stainless and are predrilled, which should either make my life very easy, or completely miserable, depending on if all the holes end up matching. The bolt-on aux seaplane struts are prepainted (white) and appear to be made of the standard material (chromoly?).

Andy Young wrote:How many of you remove your tail struts at annual to check the bottom mount stubs for corrosion?

Andy

Andy, is it necessary to brace the horizontals with the struts removed??

I plan on pulling mine for annual (mostly because they're rock chipped like crazy) to have them painted/powdercoated. However, now I know I should be looking for corrosion there. Thanks for that tip

The horizontal stabilizers will support their own weight, but I always worry about tripping and falling on them, or forgetting they are unsupported and leaning on them, so as soon as I have the struts off, I put a stool or something under the ends to provide some support.

If the sealant in the lower stubs is cracked, you must dig it all out and address any corrosion in there, and refill with sealant.

Andy Young wrote:

If the sealant in the lower stubs is cracked, you must dig it all out and address any corrosion in there, and refill with sealant.

this is covered by Maule service letter 59:
mauleairinc.com/pdf/serviceletters/service_letter_59.pdf



i recently did a prebuy on a 1983 M6-235 and found the strut lug completely rusted out. held together only by paint. i grounded it right there, after i stuck an ice pick through the rusted lower lug. the previous owner had no idea, and had flown the aircraft in that condition. it is going to get a complete tear down and rebuild now.
even with the aux (dual) strut mod, they both use a common lower attach.

Andy Young wrote:The horizontal stabilizers will support their own weight, but I always worry about tripping and falling on them, or forgetting they are unsupported and leaning on them, so as soon as I have the struts off, I put a stool or something under the ends to provide some support.

If the sealant in the lower stubs is cracked, you must dig it all out and address any corrosion in there, and refill with sealant.

Andy, thanks for the advice!

My turn has come...

While washing the belly today, I saw a hole on the lower RH strut attach point. I am pretty bummed, but please to have found it now. I have found service letter #59 and will now start the repair process. I need to remove the struts and will likely have to get the horizontal stabs off as well. Dreading cutting the fabric open.

First need to order replacements from Maule and will likely go with the dual strut option. I cant find details on the stub portion welded to the longeron. Anybody have a drawing reference number?

Any other suggestions of improvements or upgrades while that portion of the rear fuselage is open?

Keep in mind that the additional strut attaches to the same stub, so no added strength in that respect, though it does stiffen up the forward part of the stabilizer.

As far as other work to do while you’re there, you could consider installing a metal belly, since you have to cut fabric anyway. Big job though, and you don’t need to cut off all that much to do the stub repair.

Here are some photos of the dual tail strut installation on my MX-7-180. I don't have the Maule drawing on my parts DVD.

The weld repair on my tails strut stubs has finally happened. Took a long while to get replacement stubs from Maule to South Africa. Reassembly is now in progress.

Regarding the Service letter 59, the recommended sealant is “silicone rubber”. Is there a particular brand or something else that can be used to seal the stubs? The welder who did the repair even suggested filling the stubs with grease.