Grob 102 Astir CS tailwheel

[Bud Shaw]

 

Our club owns '76 Grob 102 ASTIR CS. The tailwheel came off during a routine landing. The rubber was essentially rotten where it attached to the glider. We needed a new one and bought it from W&W. I was advised by a long-time 102 owner to use 3M 3000 High Strength Wetaher seal adhesive to reattach the wheel. I have now done so three times. I thoroughly cleaned the surfaces, and removed the adhesive solvent with the recommended solvent remover. Each time, the rubber surface of the wheel separated entirely from the glue that was tightly adherent to the glider. In other words, the rubber surface of the top of the wheel assembly was absolutely free of any glue each time the wheel came off. None of the events themselves were other than routine landings. One time, an attempt to use a tow bar on the glider dolly pulled the tailwheel off.

Recently, I learned from a person at Wings and Wheels that 3M 5200 Marine adhesive is what they use and I have a tube ready to use to try yet again. But yesterday, a friend of mine who has no personal experience or specific knowledge in the matter did some research for me and asked what I thought about using 3M Scotch-Weld. Its description suggest it might be a more appropriate glue to use as it is made to stick rubber to various materials, including plastics.

What experience have you all had reattaching the tailwheel?

[George Haeh]

Weldbond has worked for me on tail skids including a G-103. It's water soluble, easy to work with and has a ridiculously long shelf life. 

Clamping is required for many glues. Elevate the tail and let the weight of the glider provide the clamping force for at least overnight. 

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  George Haeh

  403-370-9033

  gh...@fastmail.fm

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[Mark Mocho]

I have reattached numerous rubber tailwheel "blivets" (my term) to gliders with varying results. From quick-n-dirty emergency repairs to full-on time-consuming procedures with the fuselage upside down and proper tools, adhesives and patience. The best results always involve proper preparation of both surfaces by sanding off all remaining adhesive so that the two surfaces "mate" with no gaps. I generally sand each surface to about 320 grit, making sure that the faces of each part are as flat and uniform as possible. Tape the edges of the mating surfaces with painter's tape to keep drips and blobs from adding to the mess. Next, I wipe the surfaces with acetone and let them dry for at least an hour, with a paper towel over each surface to keep contaminants off. Then, using 3M Yellow Weatherstrip Adhesive #3090, I spread a layer of the "Gorilla Snot" (again, my term- borrowed from the drag racers I used to hang out with) on BOTH surfaces, working it in with a plastic putty spreader. Smooth off any excess that looks like a blob, leaving a uniform, thin coat. It is best to wait about 10 minutes, so the solvents have a chance to evaporate. Now comes the big chance to screw up. Put the rubber tailwheel blivet accurately into position. You only get one chance at this. If you stick it down off center, crooked or in any way misaligned, you now have a major project to get it off. (It might be easier to invent a time machine so you can go back about ten minutes to try again.) Finally, put some strips of Gorilla Tape over a few places and stick them down while pulling tension on the rubber blivet to hold it down and prevent it from lifting if the surfaces don't exactly match along the glue joint. Let it cure at least overnight, and then clean off the protective tape, scrape off any miscellaneous drips the tape missed and use a strip of good quality wing tape (Bowlus Maxi-tape) to mask the glue joint. Good Luck!

(BTW- I recently used some Permatex #81731 Weatherstrip Adhesive on a rubber/aluminum bond, and it seems to be equivalent to the 3M #3090.)

[Mark Mocho]

George suggested using the tail weight to provide clamping force. I disagree, as the rubber tailwheel "blivet" only gets pressure applied from the point of contact of the actual tailwheel. This imparts a force that tries to bend the flexible rubber blivet. If you do this. make sure that the ends of the blivet are securely held against the fuselage with multiple strips of Gorilla Tape applied under tension.

[Bud Shaw]

Thanks for all of your replies.  I have been absolutely meticulous in removing all glue and in using 3M’s stuff for removing solvents that I used.  Note that not one teeny-tiny bit of glue remained attached to the flat top of the rubber blivet when the wheel became detached the last two times.  I also assumed that the pressure from the glider tail resting on the wheel on the ground would not apply pressure evenly 
over the length of the blivet-tail interface so I used tie-down straps up and over the top of the vertical stab to apply pressure in several directions that I am sure created good pressure in as even a manner as feasible over the full surface.  And each time, I applied the goo evenly with a putty knife, working it into the bubble holes in the rubber part.  I also allowed the glue to become tacky as instructed on the 3M 3000 directions before squeeezing the parts together.

In other words, I don’t think the problem was the technique.  I think the 3M sealant I have used will not adhere to the rubber on the new tailwheel “blivet.” I’m hoping someone can recommend an adhesive that is known to work reliably in this application.

[Mark Mocho]

Well, in that case, I got nothin'.

Although I remember the late Tim Mara recommending 3M VHB tape. (VHB = "Very High Bond)

[Moshe Braner]

Last year we had the blivet come off one glider and we re-attached it temporarily with small bits of "Alien Tape" to sit in the trailer for winter storage.  In the spring re-glued with a glue our mechanic recommended - but removing the blivet held by the alien goo was very difficult!

[Bud Shaw]

Now we’re talkin’!  I bought a handful of that tape from W&W on their recommendation, but I’ve hesitated to try it.  It seems like a really good option if it works - eliminates much of that fussiness associated with gooey stuff.  Did you consider leaving it taped on?  Or do you think it would have worked long term.  The blurb about it uses the word “permanent”. I thought about adding strips horizontally along the seam on both sides after taping the horizontal interface together. 

Thoughts??

[Charles Mampe]

Is it not adhering, or is it ripping a layer off and leaving it glued to the fuselage?

My usual issue is not prepping well enough, or, old glue. I usually use plain old Weldwood contact cement available almost everywhere.

[Michael Opitz]

Just remember that the tail skid is the first line of defense from breaking a tail boom in a ground loop situation.  Gliders 

are designed to absorb energy and break in a sequence of easy - going to harder - repairs once a certain amount of energy

has been imparted to the airframe.  The sequence goes something like this: 

1) break tail skid off - tail skitters sideways over the ground with no damage - just glue skid back on

2) tail skid digs in and tail boom breaks, or the energy to dissipate is so great that the tail boom breaks anyway

3) tail boom breaks along with the fuselage at the trailing edge of the wing as well

4) tail boom and forward rear fuselage break and now there are 45 degree cracks in the wings starting at the wing root trailing edge

and radiating outward toward the wingtips.  

5) obviously, more catastrophic results happen if there is even more energy to dissipate 

The German glider engineering term for these points is: "Sollbruchstelle" - place where it is designed to break.

So, the more "permanent" you make the bond with the tailskid, the more risk you take in having a broken tail boom to repair in

the event of a ground loop.  That's your call on the risk that you are willing to manage.

Mike Opitz

RO

[Charles Longley]

I’ve always used 3M VHB tape with very good results! It’s relatively easy to pull the tail wheel off with my ASW-20 using it. 

[Cliff Hilty]

I'm pretty sure I used 5200 on my ventus tail wheel that had been cut out so that only about a 1/3 of it was actually touching the surface of the glider. It worked well except it needs humidity to set up after 2 days in AZ with less than 20% it was still moving around but after wetting some rags and covering it whole assembly it set over night and you would have to cut off the rubber to get it off.

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[Cliff Hilty]

I turned my fuselage upside down in a big and used flat strap tiedowns around the vertical stab to put pressure on it. It worked flawlessly for the next 6 or 7 years till I sold the airplane! 

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[Joe Gieseke]

Do it and see how it works out.

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[Cliff Hilty]

Bud, I thought I wrote it but don't see it I used 3m 5200 and it worked great. The problem with the VHB tape is it doesn't get into all the little divots and in my case I had a metal plate with bolts sticking out where I had installed a tail tank so very little of the tail wheel had a smooth surface for bonding.

Cliff

[christopher behm]

3m5200 comes in original and fast cure. Make sure you get the fast cure. 

Original can take up to 7 days to cure, but will cure even underwater and is waterproof. 

Said the boat captain of 41 years. 

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From: rasp...@googlegroups.com <rasp...@googlegroups.com> on behalf of Charles Longley <kuzi...@gmail.com>
Sent: Thursday, September 26, 2024 11:24:59 AM
To: RAS_Prime <rasp...@googlegroups.com>
Subject: [RAS_Prime] Re: Grob 102 Astir CS tailwheel

 

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[Greg Arnold]

Cut a thin piece of plywood in the shape of the top of the tailwheel assembly, attach it to the tailwheel with screws, and then glue the plywood to the fuselage.

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[Mark Mocho]

Only problem with this "solution" is that, since the tailwheel rubber "blivet" is designed as a "weak link" that will break away from the fuselage and (hopefully) save the tail boom from damage in the case of a ground loop, the screws through the plywood may hinder the "breakaway" and transmit the forces to the tail boom. Or, if the screws tear loose, the rubber blivet gets destroyed. I would rather reglue an undamaged blivet as opposed to repairing a tail boom or buying another rubber tailwheel blivet.

I've been flying with a tailwheel blivet on my Pegasus for 20+ years, and only had one break away during an aborted launch when I went in the weeds. But I've reglued at least 10 for other pilots. Only had one failure, but it was because it was an emergency "quick 'n dirty" repair for a contest pilot and we didn't have time to adequately prepare the mating surfaces. Plus, the 3M adhesive was several years old and kind of gummy when it came out of the tube. As with everything involved in aviation repairs, proper preparation prevents piss poor performance.

[Brian Roach]

My club has a baby grob, and I've reattached those darn glue-on tailwheels more times than I can remember.  My conclusion is that it's possible to attach them in ways that are club resistant, but forget about club-proof.  All of the previous advice about 'clean and flat' is good.  Personally I've had decent luck with ordinary weldwood contact cement and also very wide double sticky tessa tape. Sometimes you still end up with random gaps at the edge, when/if that happens I fill the gap with any plausible strong adhesive that can fill a gap.

As soon as you think you got it licked, some random idiot is guaranteed to yank the tail sideways during ground handling .... if the tailwheel doesn't get removed on the spot, the attachment probably got badly weakened and the tailwheel will mysteriously fall off at a later time.

Good luck!

Brian