Questions about replacing ski bottoms

[jgerard]

I spend the last hour reading everything I could find on SC.org about ski's

I have a set of Fed 2000A's I am going to clean up and use on my cub here in Central/Eastern Wa this winter. The bottoms have 1/4" plastic with an alum skeg on them now. I would like to put new UHMW on and would like to extend them out past the edge a bit.


I was wondering how thick and wide I should make the new skeg using UHMW.

Is there a certain amount you can extend the width with out needing approval?

What is the consensus on 3/16" vs' 1/4" thick.



Jason

[behindpropellers]

I spend the last hour reading everything I could find on SC.org about ski's

I have a set of Fed 2000A's I am going to clean up and use on my cub here in Central/Eastern Wa this winter. The bottoms have 1/4" plastic with an alum skeg on them now. I would like to put new UHMW on and would like to extend them out past the edge a bit.


I was wondering how thick and wide I should make the new skeg using UHMW.

Is there a certain amount you can extend the width with out needing approval?

What is the consensus on 3/16" vs' 1/4" thick.



Jason

I'm replacing mine also. Plan on going with 3/16 and extending them 1.5". I plan on taking them to a shop I know with a press brake and having them put a 45on the edges 1" in before I mount them.

Tim

[irishfield]

1/4 is toooo thick.. 3/16's will last a life time and 1/8" is easier to work with, brake up the edges for your overhang and heat/form if needed.

As for approvals... don't think a set of Federals ever came out of the factory with UHMW on them.. so don't think I'd be askin!

[SteveE]

Jason,, i read all the old posts too, I just replaced my AERO 2000's with 1/4" UMHW based on the recommendation of a few on this site, plus the fact we dont get a lot of snow and have a lot of rocks. I called AERO and they offer that size replacement too, but I just bought the stuff at a plastic supply in Tulsa. Anyway, I went a full 2" wider all around and turned them into AERO 3000's, well, the same size anyway. The curvature of the bottoms helped the UMHW curve up anyway, so I didnt need to bend it..... it was 5 lbs per ski heavier than what I had.. Flip the coin if I would go 3/16 or 1/4 again.. The 1/4 will be stiffer on the outer edges that stick out past the ski, good thing. These will probably last me forever. I am no ski expert by any means,, but thats what I did. I left my metal skeg on, its 1" wide by about 3'long. If it gets stuck, I'll just kick it good.

[irishfield]

Just an FYI... when you store the skis in the summer, put them in the dark somewhere or at least out of any direct sunlight/shop light. Not sure on the newer UHMW.. but the older stuff in white isn't/wasn't UV stable and it will deteriate and crack/dry out when left in the sun. Might as well get as many years as you can out of the stuff.

[Dave Calkins]

3/16" does the job, and is 25 percent lighter than 1/4"!! Store them out of the sun, as Wayne/Irish said.

I use 3/8"UHMW for replacing metal skegs. Works great!

UHMW springs back quite a way when bent, but forms nicely if the springback is taken into account. Edges that are kicked up give the skis some resistance to side-slide on off-camber LZ's or when turning fast. This resistance is a very good thing. Skiplanes are damaged due to side slip/sliding turns every season!

Aero3000's with the UHMW 2.5 inches wider per side is common here in SouthCentral Ak for Cubs, and works well, even on Cesnna 180's at gross weight.

Check your 43.13 for what percentage wider you can go.

PS, some of the "V" bottom skis (Federals) cannot be helped for deep snow performance. I was told that in the ultimate deep, cold, light fluff powder snow, a "V" bottom ski seems to just plow itself a trough and bury, never stopping until bottom is found or the wings are resting on the snow. The indivivdual who mentioned this has the credentials and experience to corroborate this statement, and says he's seen a stock flat bottom ski sit on top of the fluff, right next to a buried airplane with a V bottom ski. FYI

PPS, make sure the pedestal/tunnel rivets and tunnel/deck rivets are all tight. They get loose!!

[mike mcs repair]

you can also heat form the stuff, for your angles..... and around fun shapes like round tail skis...

practice on scraps first of course....

I don't remember if we did 3/16 or 1/4 mostly, see bunch of both in scrap pile here...
think I once used 1/8" and it was wimpy and wavy pain..... would not try again, and not for extending edges...

[cubdriver2]

Federal skis all look the same but there are left and right skis, It's hard to tell and a lot of ski guys don't know the difference. If you put them on a level table and view from the front you will notice that the pedestal is not perpendicular to the ski bottom. The pedestal should lean away from the airplane so that when installed the outside edge is higher then the inside edge. Had an old timer here that had flown skis all his life and we had a ski flyin and another old timer walks up and is admiring his plane and say's " nice Pa11 but your skis are on backwards " and showed us why. I even saw one with 2 lefts or 2 rights but forget which way it was. My point is just because the guy you bought them from had the cable/bungee tabs pointing to one side doesn't mean they are on correct. The early Fed SC1 and SC2 skis has a rectangular pedestal that is perpendicular to the bottom but the axel bushing welded into the pedestal is at an angle to get the outside edge higher.

Glenn

[Tim]

How do you experts attach the 3/16, or 1/4 inch to the bottom of aero skis, rivets or counter sunk screws with nuts on top.
Another question, on one of my skis the bottom is bent up under the tunnel, so now the skeg is even with the bottom of the ski, I know driver abuse.
Is it time for a new aluminum bottom?

[SteveE]

Tim, either way. I used stainless #10 machine screws w stainless lock nuts. 100 degree countersunk heads so they will work w the micro countersink drill tool. Took some time to drill out the old rivets. But for your skis, I would use gorilla glue.

I thought my bottoms were bad till I took off the old plastic, they looked good as new. You might find out the same thing.

[mike mcs repair]

How do you experts attach the 3/16, or 1/4 inch to the bottom of aero skis, rivets or counter sunk screws with nuts on top.
Another question, on one of my skis the bottom is bent up under the tunnel, so now the skeg is even with the bottom of the ski, I know driver abuse.
Is it time for a new aluminum bottom?

ski still strong? taller skeg....

I use regular AN countersunk screws & countersunk washers and nuts, not stainless.... and the usually painting the ski after new bottoms installed....

riveted one set (the 1/8" bottoms), to save weight, not worth it....

[aktango58]

Jason,

Does that mean that you do not want me to send this set????

[jgerard]

Ok... So I drilled off the plastic bottom and skeg to see how much repair work was needed. This ski has a patch on the front and a few cracks in the bottom where the pedestal rivets on. One of the cracks has opened back up. Someone had tried to fill in the concave bottom surface with bondo and fiberglass to make a smooth surface for the 1/8" plastic that was riveted on.

What do you ski experts say? I can grind out the cracked weld and re-weld that area. What about the welded on patch on the nose of the ski? The flange just below the pedestal where the center tunnel rivets to the bottom skin is bent more than I think it should be. Both skis show the flange area under the pedestal to be bent much more than the rest of the rivet seam.

I need to take the bottom off the other ski to see what it looks like but from the out side that ski is in better condition.

Should I try to take the kinks out the bottom skin along the sides?

Should I try to fill in the concave areas on the bottom of the ski before putting UHMW on?

Or should I just have George send me his serviceable set of Fed 2000's from Juneau?



Jason




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[aktango58]

Does you want to ski fly this month, or in April??????


Bet you though you got a good deal, didn't you

Next time, take Eatons Good set!

I can truck freight them to Seattle for about $35.... but will be gone until next week, so puts them there in about 12 days.

[WindOnHisNose]

Jason, we have just replaced the bottoms of my Federal 2200 skis with 1/4" UHMW, and it did add 10 lbs per ski, if I recall correctly. As Steve mentioned, we, too, used stainless steel screws that were countersunk, with locknuts. I know that rivets would be less in weight, but I want to be able to replace the bottoms easily, should they crack.

The UHMW is really easy to work with. We extended the bottoms about an inch all the way around, but did not bend up the edges. Jason Erickson at Wipaire suggested that it really doesn't need to be bent up for this small increase in size, but that if you are doing much more than 2" you should bend the outboard edge of the ski.

Darrel Starr will be posting more photos of the skis...see the other thread on "Rerigging Federal Skis". We are going to put the finishing touches on the skis tomorrow, mount and rig them Saturday morning. They look terrific.

Regarding the increase in weight, I am not too concerned about this when I compare the relatively mild increase in the weight of the skis as compared to amphib floats!

Randy

[AK-HUNT]

Jason,
I like 3/16 with 2" extra, bent 30-45'. Would not use 1/4. I riveted on the last couple sets of aero 3000s with 6 softs. I think I like them better than screws. You will do a hell of alot of flying b4 u replace a bottom unless u r doin it wrong.
Skeg of uhmw for sure. If u are on much glare ice have a bolt head sticking down for drag. (inside row of screws on landes or atlee. 2nd to last skeg bolt on aero)
All that is opinions and probably wrong. But working on several planes here. Like Dave said, the aero 3000 with big bottoms is first rate for deep pow.

Those skis look about ready for the scrap pile btw.

[Dave Calkins]

Sorry about those skis Jason. Bummer!

these ones were riveted on with #6's. Super Clean set of skis. They were new from Aero...went straight to BigLake powdercoaters (AeroSKi's aren't known for their stock paint lasting a full season), then got 3/16 plastic.

These are on Ron T.'s very nice exp. SmithCub ("Skydozer")

[jgerard]

I didn't buy them, they were sitting in the back one of the hangars on the field here. I was told I could use them but will probably just return them to their hiding spot

Jason

[jgerard]

George,

I sent you a PM with shipping info - Thanks!!!!

Jason

[SteveE]

Here are a couple pics of Aero 2000's that are now 2" wider.

[aktango58]

Steve,

all you need is snow!!!

(and all I need is a plane)

suks for both!

Jason, check pms

[SteveE]

Not predicting much snow this year,,

[Litecub]

Jason;
I have done both 1/8" and 3/16" when replacing the bottoms on 4 sets of Federals now. I would not use 1/8"again as it is wavy and not holding up well where the rock have gouged back when I had a long tow to the lake on dolly wheels. Replacing the aluminum bottoms I used 1/8" 2024 T3 and have broke the edges up 1 1/2" on the sides on the first couple but have found it easier to keep the metal bottoms flat and extend the 3/16" plastic as much as 2"which is easier to form upwards depending how big of a foot print U want. Somewhere around 18" wide has been the best on my Cubs and Glastar. Riveting with soft counter sunk rivets is light, clean and quick with the pnumatic squeeze to hold on the bottoms and side skegs. 3/16" bolts with the heads on the bottom, 6" back of the axle on each side skeg will give enough drag on ice to help stop. I have pictures posted on the site that show the skis, dolly wheels and tow bar. Enough for now my two fingers are worn out -I go fly to check the traps. B

[aktango58]

Imagine moving stuff from two hangers 100 miles... packing into a trailer, pulling it out and putting it into storage as you organize...

And as we unpacked this load, (second to last), I finally got to the box I thought I had seen my 1.25-1.5 axle adapters in...

And you know what, found them in 30 seconds...

All will be well Jason, just tell me how many parts you want... skis, landing gear, cabane vee, extenders for cabane vee to fit 3" gear (did you order those?), bushwheels...

Will send out when I get to Juneau, just get a picture of your bird is some cool spots!

[cubflier]

Any reason to not use black uhmw on ski bottoms?

Jerry

[Tim]

Any reason to not use black uhmw on ski bottoms?

Jerry

No, I have black UHMW on the bottom of my skis and see no problem. Reason I went with black, it was free

[zenpilot]

Any reason to not use black uhmw on ski bottoms?

Jerry

Everything dark colored near my airplane parking melts out a lot faster this time of year. I have to pile extra snow underneath it while it's parked, to extend my ski-flying season a couple weeks. I figured the white UHMW would keep the snow around just that much longer, but I suppose it's the difference of a week or two at the end of the season. And, free is free!!!

[mike mcs repair]

Any reason to not use black uhmw on ski bottoms?

Jerry

wouldn't you be thawing and refreezing more??? from sun when still bellow freezing?

[8GCBC]

Do you think "Cub Yellow" is in the "too dark" category for skis vs. white? The majority of my ski tops are "Cub Yellow", bottoms are white.

Colors accelerate endothermic heating. To what extent?

[Matt 7GCBC]

I have run the Aeroski R2800s for several years and thought I'd show the recent recover job.
Had a flat tire when landing 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. Talking to Aeroski, 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.
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

Getting the plane back to the hangar
ImageUploadedByTapatalk1363498198.973820.jpg
Starting point
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Bottoms look good
ImageUploadedByTapatalk1363497792.895030.jpg
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
ImageUploadedByTapatalk1363497840.485263.jpg
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.
ImageUploadedByTapatalk1363497867.340122.jpg
Speedy countersinker and rivet bucker!
ImageUploadedByTapatalk1363498050.892626.jpg




Marking the wheel cut outs which can be quite a bit smaller than original.

[Matt 7GCBC]

I bought a box of the wide flange rivets from Grainger. The heads are 5/8" and the pre crimp grip length is .675". A one pound box was $26. These are the rivets used on the skegs and the bumpers where the swing arm rests on the tunnel. I was going to replace the black bumpers with some thick tire pieces. Wondering of anyone has other thoughts?

[8GCBC]

I like the aft handles on the skis. Good for tight turns, when only manual turning will work. Manual turns using the "arm" of the tail only is hard on the gear, axles, and skis, if the snow is powder. Thx for the pictures, nice.

[Ursa Major]

Very nice job Matt. Are there any issues with leaving the rear tunnel area covered, rather than open as original? I understand and appreciate the increased floatation, but I wonder about the ability to raise and lower the skis around the tire. Tire clearance with packed snow, maybe leaving the ski jammed in position? I like what you did, and have seen similar apps in Alaska, just wondering, as I'm contemplating doing the same.

[mvivion]

I like the aft handles on the skis. Good for tight turns, when only manual turning will work. Manual turns using the "arm" of the tail only is hard on the gear, axles, and skis, if the snow is powder. Thx for the pictures, nice.

Those aren't "handles". They are the actuators to "raise" the tailwheel". I wouldn't advise using them as "handles".

and, Matt, let us know how having the aft center part of the ski covered with UHMW works out for you. I have a feeling that The manufacturers left that area open for a reason.

MTV

[cubdriver2]

Mike if you blow the picture up you'll see that it's just a bridge/truss to support the independent heels and the rear wheel axel, Bolted fast



Glenn

[Matt 7GCBC]

Should note that the wheel opening is where I marked, not just what I started to cut out. I previously sent pics to a couple people of the "finished" project and got replies asking if I was trying to convert them to straight skis and just how many beers had it taken to complete the project!
The hoop on the back is as cubdriver noted, just a raised bridge to keep from having the additional drag in the snow if it was a straight axle. With the back deck covered, the need is eliminated.
With the spring snow, it definitely builds up now on the back deck, but falls away pretty quick in the air, compared to the front of the ski buildup which makes a hard brick. I suppose there would be the potential to freeze up in the wheel well area and prevent ski retraction. I have had other portions of the ski hang up and have found that simply touching the tails to the snow as I fly past a ridge on the way home seems to free things up nicely. Historically this is the event that my passengers seem to recall with the most excitement in their retelling of a fun day ski flying! "And then he says 'we're just going to bounce the skis off this mountain top to unstick them'!"
The main thing I was/am concerned with is the potential for the tail to act more as a shovel as opposed to flotation. I beveled the leading edge of the UHMW behind the tire, where the back deck starts, but obviously this will have minimal benefit to keep the platform floating upward. I thought about putting a doubler on the leading edge to help it bow up and keep it from bowing down and digging. After a couple days use however, the leading edge is bowing up and forming an upward arch on its own.
The 1/8" UHMW cuts relatively easily and if there is a problem, I can simply remove the back deck, even in the field, and start over.
I did talk to one guy who had been willing to be a test pilot and did the mod to one ski and the other was with the open back deck. He said he noticed a bit better flotation, and smaller turning radius with the closed deck on the inside (reckoned the open rear gave more rail effect and harder to turn) but when he did the comparison test, the snow was pretty compacted below and not more than a few feet of fluff on top. Surprisingly there was no yaw or roll effect from the assymetric surface of the skis, but he noted that as with external loads, you wouldn't want to do stall/spin testing like that! :^o

[8GCBC]

Mike if you blow the picture up you'll see that it's just a bridge/truss to support the independent heels and the rear wheel axel, Bolted fast



Glenn

"Rgr that"... Aft handle is (looks) fixed, looks strong in photograph (unconfirmed here ! )...just thinking outloud. I wish my skis had a solid aft handle for really tight turns, when moving tail in very tight conditions, where engine blast no good.

I bumped into a small sapling once and wished I had had a handle to get the aircraft turned and free to start the engine. Opinion. I used the tail for levergage and had to get under the ski to move (and turn), if aircraft was at "gross", probably would of needed shovel etc! Axle took more twist than needed. Opinion.

[Dave Calkins]

Matt, I've done what you have for a Husky guy.

It seems like the real performance increases come from getting the "later" or "Maule" style retract arms that allow the tires to tuck up higher.

Getting the tailwheel mount arch on top of the ski like you have rather than the original mounting scheme where the "axle" was dragging in the snow is also KEY!!

The jury on the "closed tail" performance improvement is still out. A respected cub-driver said his best solution ended up getting rid of the tail wheels (Snow machine skid-idler) and having open tails.

Also, a quasi-closed tail that has a "slot" rather than a fully bridged tail would eliminate the "aft portion, tip up" contour drag from the plastic being tipped up directly behind the wheel. It is a drag.

This ski design has a lot of potential for it's simplicity and light weight if it can be optimized for a broader mission than the original design envisioned.

Keep an eye on any steel parts that are near the aluminum. We have had issues with the dissimilar metals corrosion that only disassembly and epoxy primer would solve. One a/c was dinged due to a failure of the pedestal/tunnel attach rivets as a result of no effort to isolate/insulate the pedestal from the tunnel.....not on these skis....on the staight skis.

[8GCBC]

* Longitudinal flotation = good (smoothing)

* Lateral flotation = bad (draggy)

[Matt 7GCBC]

Yes, skinny nordic skis are great for gliding and going fast. They sure suck in the powder though. Fat skis are so much better in the deep stuff as long as you have slope angle or in the airplanes, HP. The balancing act is as you note, how much power is available to overcome the drag and how much floatation is really needed for our operating conditions, weights, etc.