My SQ2 Mods

Shovels...ahh getting old when experience tells us to drill some holes in them so water can drain away when shoveling wet overflow on lakes from under stuck planes on skis. Had a C-185 on AWB 3600's submarine one ski under a foot of snow and a layer of ice above a foot of water and the main lake ice cover. Chopped and dug a trench until I could drive it up on the lake's shore and turn it around. Shovel had holes and an axe was handy. The two idiots onboard had forgot the snowshoes in the truck but bunny boots full of water saved the day.

Gary

Edit: We shoveled the wet snow away and cut trench in the thin upper ice layer as noted as the left ski and tail ski were stuck in it. Then moved the plane slowly in steps until near the shore it got thinner water. We filled the trench with snow and drove the plane back up on top to the shore. Shoveled bare spots on the dry shore, dropped the wheels, and turned the plane. Pumped the skis down and left for coffee and pizza. I had drug the lake three times hard before landing (three wide tracks next to each other) but no overflow showed until we slowed down.

Beringer Wheels & Brakes. Finally got around to installing them. 4+ lbs weight savings on each side and significantly better braking. And I finally have myself a parking brake.

New TK1 Gear (6x3) and shocks

Looks nice Phil. What type of fitting attaches the lower shock strut to the landing gear? Fixed threaded end or flexible Heim joint? Any safety cables planned? If you grab the front of the skis while elevated can you twist the gear?

Gart

I like seeing that gear. I'm curious about the three bolts and the extra bolt holes in the axle assembly. I see one attaches to the shock assembly, but what do the other two do, allow the axle to be adjusted width-wise?

Barnstormer said:

New TK1 Gear (6x3) and shocks

Click to expand...

kind of wimpy in the twist area of any modern gear at the bottom.... must be built based off of original gear blue prints, instead of looking at modern gear/lessons learned/multitudes of planes bent from gear failures.... prop strikes are expensive, so are wings......

Gary, fixed. I haven't used safety cables in the past with 700 hours on the first version of these and thousands of off-airport landings, but I have very little time on skis and know little about the loads they create. I actually have been wondering if instead of safety cables I could use Amsteel- no stretch and super strong- and very light.

RVBottomonly, the axle is separate from the landing gear, so not strength loss from being welded to the gear. The axle slips into a collar and the bolts retain it. Brilliant.

Phil as you have seen tires flex and skis don't. Different loads on the gear is obvious.

For CAR 3 aircraft like Cubs:

.§ 3.257 Supplementary conditions for
skiplanes. The airplane shall be assumed resting
on the ground with one main ski frozen in the
snow and the other main ski and the tail ski free
to slide. A limit side force equal to P/3 shall be
applied at the most convenient point near the tail
assembly, where P is the static ground reaction
on the tail ski. For this condition the factor of
safety shall be assumed equal to 1.0.

For Part 23.505

135. What is the typical method for determining the load factor for a ski installation?
a. A ski installation should use a load factor determined by either of the following two
methods:
(1) Perform drop tests, with skis installed, on a surface simulating frozen hard- packed snow or ice; or
(2) Use a conservative formula (see SPECIFICATION—Aircraft skis, National Aircraft Standards Committee, NAS 808, paragraph 5.1(a)).
b. Ski installation factors should include consideration for fittings, tubes, axles, nuts, bolts, etc., which attach the skis to the fuselage. Ski-gear loads normally run about 115 percent to 125 percent of wheel-gear loads. Also see 23.737, Skis.

23.485 Side load conditions (like tires I assume)
(Amendment 23-45)
131. Is there any policy available on this section as of January 1, 2007? No.

For Experimentals you're on Mars. Enjoy the view.

Gary

Barnstormer said:

Gary, fixed. I haven't used safety cables in the past with 700 hours on the first version of these and thousands of off-airport landings, but I have very little time on skis and know little about the loads they create. I actually have been wondering if instead of safety cables I could use Amsteel- no stretch and super strong- and very light.
.

Click to expand...

There was some discussion earlier on synthetic safety cables.
these were made out of 3/8” Dyneema and performed very well when shock loaded.

Edit: 1/4” Dyneema below photos.

Thanks Oliver and Gary.

Here is what I got from Tony: "I doubt you could twist the gear leg enough to create an issue at the clevis. Interesting idea though. I’ll have my guys do some computer modeling and engineering on the subject and see what the calculator says. Generally rod ends suck. We only use them when there’s no other option. The threaded clevis we use is 4140 chromoly then heat treated to 50 rc and nickel Teflon coated. It’ll bend almost 90 degrees before breaking."

Oliver said:

There was some discussion earlier on synthetic safety cables.
these were made out of 3/8” Dyneema and performed very well when shock loaded.

Edit: 1/4” Dyneema below photos.
View attachment 41627
View attachment 41626

Click to expand...

Oliver,

What size is the rope in the photos? 3/8 or 1/4?

When I splice nylon or poly rope, I use a fid and bring the tail in and out, on opposite sides of the main line. The tail is inside for 2 inches and then outside for an inch. I repeat this twice and leave the tail inside. The tail never seems to "creep" out when going from slack to taught 10,000 times. Maybe overkill, but we lost a skiff on the way to Seattle that just had an internal splice. One morning I looked out on wheelwatch and there was only a rope back there. The sharpie mark on the rope, added for cut measurement, was still there. The splice had crept open. I see the black thread sticking out. Is that a "stop" ?

With the splice out in 90 mph, turbulent air, and never held firm by strong tension, I wonder if it might loosen up?

Thank you for the post and the 2, excellent photos.

Jonny

Jonny,

Rope is 1/4”
You can “lock” the splice as you described, not sure if it compromises the overall strength of the splice. Might be tough to do if there’s hardware attached to the other end of the line, though I’ve heard it’s possible.
Other options are to whip it, or lock it with a few stitches. (black thread in previous photo)
you are correct though, it will defiantly work itself loose otherwise.

I’ve been thinking to do some more experimenting when I get some time.
Thinking to do some back to back pull tests substituting 1/8” 4130 against 3/16” stainless currently being used as attach points.

Oliver said:

Jonny,

Rope is 1/4”
You can “lock” the splice as you described, not sure if it compromises the overall strength of the splice. Might be tough to do if there’s hardware attached to the other end of the line, though I’ve heard it’s possible.
Other options are to whip it, or lock it with a few stitches. (black thread in previous photo)
you are correct though, it will defiantly work itself loose otherwise.

I’ve been thinking to do some more experimenting when I get some time.
Thinking to do some back to back pull tests substituting 1/8” 4130 against 3/16” stainless currently being used as attach points.

Click to expand...

Oliver,

Do you have a strain gauge ? It would be extremely interesting to get some "data" on the results. On my tabs, so that I can go as light as possible, I use the thinnest size that has shown to work in the past and then run a TIG bead around the holes, on the flat topside. If you look at your picture of the tabs that broke, they don't stretch/brake in the middle; where the meat is, it's out on the thin edge, by the hole. Some 70,000 psi TIG rod has always -- seemed, to help that out. Retempering a small tab is easy. Having a thicker edge for the bolt or cable thimble to ride on, also --seems, like a good idea. It would be great read some thoughts from some Engineers.

Thanks again for the great photos !

Jonny

Let me know if you get spooled up for a test. I would contribute some $ to that.

Jonnyo said:

If you look at your picture of the tabs that broke, they don't stretch/brake in the middle; where the meat is, it's out on the thin edge, by the hole.

Click to expand...

That break appears to have elongated the hole which stretched the metal at the end thus the tearing action. Have you thought of doubling up on the hole with a washer just welding around the half of the circumference towards the end of the strap?

Unfortunately I don’t have a strain gauge,
i, rather archaicy, pulled on hardware to the point of failure.
metal was the weakest link. The amount of force applied may have well exceeded what’s necessary to save a plane with gear failure.

cunclusion so far is that Dyneema exceeded expectations and can be ruled out as the weak point.
if there’s more interest in proceeding, maybe start a new thread and bounce some ideas around.
Thanks
doug

Barnstormer said:

Gary, fixed. I haven't used safety cables in the past with 700 hours on the first version of these and thousands of off-airport landings,

Click to expand...

any pictures of what failed, just says “ gear collapsed” in the AIN report today

did you have safety cables installed??

If so, did they help?

skywagon8a said:

That break appears to have elongated the hole which stretched the metal at the end thus the tearing action. Have you thought of doubling up on the hole with a washer just welding around the half of the circumference towards the end of the strap?

Click to expand...

ended up going with 1/8” 4130, made the tabs a little wider to provide more meat on either side of drilled holes.
pulled on it to the point of cord failure with no evedince of distorting the metal.
About 50 hrs on Dyneema cord so far. No evidence of fraying or I’ll effect from elements or wind buffeting.