Hello Ski Plane Pilots,
I have a six inch crack in the plastic bottoms on my Aeroski 2800s. The plastic is 3/16 white Lexan, and is a real job to fabricate and replace. Anyway I was wondering if anyone had had any luck with heat or chemical welding of ski bottoms? Any advise would be greatly appreciated.

Thanks,

James

ski bottoms are made out of uhmw not lexan. Lexan is much too brittle and would shatter on the first landing. They are not that much of a chore to replace, and once that UHMW gets old enough to start cracking, you just need to replace it. Unless of course you hit something real nasty and broke it.

UHMW = Polyethylene (like a milk jug or cutting board, milky/translucent in appearance)
Lexan, Plexiglass = Polycarbonate (like windscreens, clear in appearance)

You might try doing a base weld with a soldering iron and a stick of ptex from a ski shop as filler.

I ran over a sharp rock with my R2800s and put a dandy gash in it a couple years ago. Here in Maine we have guys who fabricate plastic tanks for the fishing and lobster industry. I took my whole ski to him in the summer, and he ground out the crack and filled it back in with plastic weld. The color even matched. Its been 3 yrs and still looks like new. Charged me 60 bucks. These guys are real craftsmen, and make a lot of different stuff out of sheets of plastic. I can try to find his name if you are interested. Where are you located?

Jim

As Akavid says, once the UHMW gets aged enough that it CRACKS, it will crack again, and again. It's done for.

Fresh UHMW will stand up to a gouge by a rock, etc. and yes you can fill it. But, when it starts to crack, it's done--pull it off and install new UHMW.

And, I strongly suggest using 1/4 inch UHMW for the new. This stuff will last many years before it starts to crack, but once it starts cracking.....

And, a crack can lead to a sag in the material, and if it's in the wrong spot, it can act like a huge SCOOP. Takeoff may not be possible.

Replace it--it's a little time consuming, but it's not that difficult. And, the difference between new and old UHMW is dramatic.

MTV

I ran over a sharp rock with my R2800s and put a dandy gash in it a couple years ago. Here in Maine we have guys who fabricate plastic tanks for the fishing and lobster industry. I took my whole ski to him in the summer, and he ground out the crack and filled it back in with plastic weld. The color even matched. Its been 3 yrs and still looks like new. Charged me 60 bucks. These guys are real craftsmen, and make a lot of different stuff out of sheets of plastic. I can try to find his name if you are interested. Where are you located?

Jim

Thanks Jim,
I have a guy locally that makes plastic tanks for crop-dusters that might be able to help me out too. Changing out the plastic, drilling then countersinking all the holes takes a lot of time. I was just looking for an easier way since the plastic is new.

James

3/16's thick?? My Datum skis for my 740 lb empty Rans S-7 uses 1/4"... I would just buy new, thicker, material and fix it that way, maybe for good. Unless it is a huge certification hassle? Still, seems like thicker would be better, and maybe why it cracked already.

You could also just land on perfectly smooth snow in ideal conditions, but that wouldn't be any fun!

Yes, the thinner stuff "bags" out, and that leads to cracking. I would not use less than 1/4 inch thick UHMW on skis.

MTV

The last time I redid my bottoms I used what they call "reprocessed" UHMW. Its black with little specks in it. As I understand, they regrind all the scraps from the manufacture process and recast it. It seems to be a lot more UV stable than the white. The white is food grade plastic and is not UV stable, and as MTV noted it will eventually degrade and crack then its done for. The black reprocessed is about 2/3 the cost of the white food grade in all thicknesses. We have also used blue, which is a lot more abrasive resistant than either white or black, but at twice the cost. If you can buy a whole sheet it saves a lot $$. We use a ton of the stuff in conveyors and truck bodies and get it in 5 x 10 sheets. If you know a contractor who runs trailer dumps most of them are lined with 1/4 Tivar or uhmw, and the bottoms of the trailer are worn out long before the sides. You can get some pieces for cheap if they are not beat to pieces over time. 2 places in Maine sell the stuff and ship it any size, Haines Manufacturing in Presque Isle 207-762-1411, and Lane Supply in Brewer 800-432-7667 both good guys.

Jim

The white is UV unstable? Damn, I used something called "PolyMax", described in my FarmTek catalog as : "white high density polyethylene (HDPE)", 1/8" thick, to slick up the top of my rusty steel truck bed ramp from my hangar slab down to my runway. I pop riveted it with wide flange pop rivets. Soon as the snow goes I will be lifting it off what passes for my front lawn, using my crane, and stashing it behind an outbuilding until next winter. I was agonizing over leaving it in the sun all summer..... I may buy some cheap 7/16 OSB just to keep the sun off.

Now, I see in the catalog they also sell black PolyMax, described as "High-molecular weight-polyethelyne (HMWPE). The black costs more. They make no claims as to which is better for UV, just a general claim for both types "superior UV properties". Even the thin white stuff cost me 300 bucks, plus freight, so I didn't spring for the black. At least the white stuff is working great for the time being, the skis slid on it like ice!

Friend here & I are about to replace the UHMV on the bottom of our skis.

I'm wondering about the installation method(s) and what to watch out for.
First thing... are pop rivets OK? That's what's on my skis now, & seem to be just fine. (Oh, & I'm not certified)
What order should I install the rivets...one side first, alternate sides proceeding down the length... or?
Any issues with keeping the plastic "tight" so it won't bulge?
What else ??

I have access to a long-handled hand riveter, and/or an air squeezer. Advantage: solid rivets?

Nimpo,

I have three set of skis from different manufacturers and all share one trait. The retention of the applied UHMW is accomplished by putting fasteners through retainer strips of thin stainless steel that then holds the UHMW. The fastener heads don't contact the plastic directly. For what it's worth all my skis have flat bottoms so the fastener heads will make contact with the snow and ice. My fasteners are countersink head machine screws with nylock washers, at least on the skis I have photos of and can review from the computer. I've built snowgo sleds with UHMW bottoms using pop rivets and the rivets have become damaged when they snag on things including hard ice. My solution there was to use a spade bit and relieve the area where the rivet goes so the head sits flush with the UHMW surface. In you don't use retainer strips you'll need big heads on the rivets and I don't recall seeing any high quality structural rivets with wide flanges, just hardware store rivets. Getting the heads flush is important with those. I need to go dig out my FliLites today so I can snap some pics of the different solutions on my own skis if that helps. Let me know.

""I can snap some pics of the different solutions on my own skis if that helps. Let me know.""

I get the picture, thanks for the heads up, ya ol' SB.
My current plastic bottoms are pop riveted with pretty wide "heads" and show no damage. I have a crack starting on one ski. They are 3/16" but we're going with 1/4". I did (briefly) consider counersinking 'em a tad but there's 188 rivets in each ski. I don't land on anything but lakes, hidden surprises in meadows scare me.

Here's one of my Airglas 3000s. Countersunk machine screws through the metal strips and countersunk machine screws w/ countersunk finish washers at the tips. Variations of the theme include extending the UHMH beyond the ski edges to increase ski area. Another is to use UHMW instead of the SS strips. What you see works fine for my needs.

Nimpo,

I wouldn't use pop rivets unless you know of some that are countersunk. I've used flush rivets or countersunk machine screws. Either way works fine, and you can countersink the machine screw or rivet heads directly into the plastic just fine. No NEED to apply additional metal strips....

I don't like any metal strips on the ski bottoms, because those metal strips will frost up while parked. That may or may not be a problem, but I've seen them frosted up bad enough the airplane wouldn't move under it's own power, even though the plastic bottoms were clear.

Instead of metal "wear strips" which those are "officially" I replace them with a strip of slightly thicker UHMW, attached the same way as the bottoms are.

As to the sequence, you need to have the UHMW cut to fit (though I know some guys who attach the plastic, then use a router to trim it) the ski bottoms. Then, just like working with sheet metal, use cleco fasteners to secure the plastic in place, while you attach. It should be well secured around the perimeter and in the center of the ski, where the wear strip is. So, you should have the plastic attached with a number of clecos, then attach a flush rivet or machine screw in one spot, then one across from it, then one on one end, then the other end, and keep working your way around the ski. And, don't forget the center wear strip.

If you prefer wear strips on the ski edges, as shown in Stewart's photo, I'd use UHMW strips, and fasten directly through them, obviously with slightly longer fasteners.

None of this is particularly difficult, just a little time consuming.

As Stewart mentioned, some folks extend the UHMW out from the edges of the skis by an inch or two to provide slightly more bottom area. I've never heard of anyone in "officialdom" being concerned with this or with using UHMW for the wear strips on the ski bottoms.

MTV

More pictures. My FliLites and Fluidynes both utilize metal runners and primarily employ countersunk solid rivets. The Fluidyne center runner is affixed with machine screws since the top side is inaccessible under the ski tunnel. Both sets of skis use bucked rivets in the metal runners and directly in the UHMW where applicable. The machine screws visible in the FliLites are there to capture cable tabs on the top of the skis. All three sets of my skis use 1/8" plastic.





I have no argument about the tricks other guys add to skis. With my straight skis I like the metal runners since when I'm on straights I park in the fingers at Lake Hood. Directional control is important in tight spaces. In all cases the metal runners have never caused me any grief except when I tried to taxi across a paved road with inadequate snow cover and another time trying to fly off the strip to land on the lake. Metal strips on pavement or gravel with stop you cold, and mine did. It's very embarrassing to turn 90* off heading while on the gravel strip on skis, and very difficult to get righted!

OK, so it seems unimportant whether I use screws or rivets to attach 'em, but IS important to countersink 'em. Understand. I definitely will replace the metal skegs with the UHMW, I got the frozen/frosted metal skeg T-shirt! I was planning on bending the edges up a bit to help prevent an edge "catching" if I was sliding sideways a bit, but then if the edge doesn't catch, the skeg WILL. Maybe chamfering both a bit would help & still give directional control.
Now planning to wait 'till summer when the skis are off anyway.

By cutting the new bottoms exactly 14" wide (1" overlap) I can get 4 out of a 4X10' sheet if I round the ends (not cut rectangles) so I can increase the angle along the 4' sides. Will lay out the sheet & make a pattern that will work so we won't need that second ($200) sheet for the last ski!

Nice clear/still day today, -10*C, so she's plugged in! Saw 4 moose the other day pawing the snow about 5-600 yds above the tree/brush line. Stuck out like a sore thumb in hte sunshine up there!

Logan,

I wouldn't chamfer the edges of the wear strips (skegs). Don't worry about those hooking in a side load. The thing people are concerned about with turning up the ski edges is to prevent that edge from just flat digging in.

Best thing to do is simply keep the side loads to a minimum.

REmember, part of the role of those wear strips/skegs is to provide directional stability. Grinding them down on one edge will reduce their effectiveness in that role.

MTV

mtv wrote:Best thing to do is simply keep the side loads to a minimum.

OK Mike!

I have run the Aeroski R2800s for several years and thought I'd show the recent recover job.
Had a flat tire when landing on pavement resulting in a need to redo my bottoms. Wish I would have looked at the forum before I started. I used 1/8th inch UHMW material on the bottoms and1/4" for the skegs, because that was what was on there before. I think the 3/16th would have been better and maybe 3/8" skegs. I think 1/4" would be harder to work with and heavier than I need. Talking to Troy at Aeroski (who is ALWAYS amazingly helpful), they use the 6-7AD rivets, so that's what I purchased and finished both skis using a hand squeezer around the edges. Didn't burst any aneurysms or hernias, but probably came close. Those are big AD(hard) rivets. Got hold of some 6-7A (soft) rivets as I was finishing - SO much better/easier for non structural stuff like the ski bottoms. Live and learn. At least I got some good practice and a workout. 6-8 rivets are needed for the places where there is a doubler when using the 1/8" plastic and likely when going to the 3/16" plastic.
Extended the outside edges an inch, but could easily have done 2" with the 3/16. Left the back decks closed in and it has worked well on flights since. Haven't done any deep snow since, but did notice that when manually turning the plane, I didn't have to pull the skis around much, as they were sliding around better. Have now thought of getting rid of the big U bar in the back, but nice to have a place to grab when turning the plane and skis manually. I have always had the rear cross-bar hoop/axle mounted on the tops. Just had to machine out some room for the tunnels so they would lay against the ski top. You lose some clearance on the pavement, but if you're not operating on gravel, it won't matter. They aren't good for gravel ops anyway.
For many years having the kids around the hangar has reduced my ability to get much of anything done, unless they are otherwise occupied destroying something that I have to clean up later. At 6, Miles now was kicking my butt to keep up with the work flow and we got the second ski done in an afternoon. He wasn't around when I did the first ski and it ended up taking several evenings and quite a few adult beverages.
The sheets for the bottoms were $100 a piece and the 1"wide strips for the skegs were $5 each

Plane defrosted and preheated after an overnight at....?

Getting the plane back to the hangar

Starting point

Bottoms look good

Skegs first. The 1/8th was a benefit here as I could see through it when drilling the holes in the bottom sheets to line up with the pre existing holes in the skis

The 1/8th molded nicely to the curve of the ski after left lying on the ski bottom overnight. I didn't do that with the first one and was struggling with it a bit more to avoid bulges or waves in the UHMW.

Clecos weren't working for me, so used vice grips and clamps

Speedy countersinker and rivet bucker!



Marking the wheel cut outs which can be quite a bit smaller than original but realize how much the tires will bulge out with speed and hitting things like pavement grooves. Go too small and you'll be dealing with a flat.