My local friend Rich shared a good story about the time his ski bungee decided it couldn't hold the tip up anymore, and things got a little scary.

https://backcountrypilot.org/features/category/live-to-tell/the-out-of-control-surface-a-loose-ski-mishap

I sent this story to another friend, who said something similar had happened to him. Here's his reply, for the betterment of our ski flyers:

I pulled nose-up hard and fed in power…changed the angle of incidence and popped the ski back in place. Then no flaps and nose high at slower flight…kept AOI higher—that kept the ski in place and I went direct to my mechanic's airport. Then I got an inclinometer and measured the wing incidence compared to ski incidence. We made the ski 0.5 degrees higher angle than the wing (discovered after install it was .5 degrees less than then wing…thus the aerodynamic cause of the event)

Good bungees help, but it’s more the aerodynamic force and inertia in turbulence and changes in force that bungees are supporting. And they can’t overcome an incorrect angle, even if new.

One of the essential things to verify on a ski plane is the length of the forward limit cables. As this story notes, IF those cables are too long, and a ski goes over because of a weak bungee or just air pressure, the airplane may become uncontrollable.

Kudos to the author for having the presence of mind and the skill to save this aircraft in that situation. He did precisely the only thing that could have saved his life in that case.

Somewhere in the 1990s, many of us realized that the newer aircraft grade bungee material had a much shorter life than the bungees of old. This is about when springs started becoming popular to replace those forward bungees. I had the (almost new) bungees on a Super Cub on straight skis "relax" in minus 30 degree temps. I was able to fly the plane home with the ski tips more nose down than ideal, but safe, because the forward limit cables were the proper length. And, yes, these were cold weather bungees. In any case, I became a fan of springs, as opposed to bungees.

I've seen a few ski planes with a lot of slack in the forward limit cables with the plane on the ground. Consider what those skis will do if the bungee or spring broke.....

Thanks to Rich for sharing his story.

MTV is spot on here.
Ski rigging has serious safety implications and although springs are better than bungee's (shock cord), they are not approved on all installations resulting in a lot of bungee's still in service. I use Atlee Dodge gold and silver springs on my straight ski's, they are the answer in my opinion. I ran bungee's on our J-3 in Alaska, my solution was to put the tail on a sawhorse when on skis to reduce the bungee tension. Unless flying every day, I would relax the bungees by some "creative" method. Regardless, the forward and rear check cables require precise rigging, treat them as if your life depends on them, because it does.

TR

I checked last year for approved springs on my 185’s fluidyne installation and was told by Atlee Dodge that no such approvals exist. Anyone aware of any approvals for same?

Boreal1 wrote:I checked last year for approved springs on my 185’s fluidyne installation and was told by Atlee Dodge that no such approvals exist. Anyone aware of any approvals for same?

Our maintenance folks in Alaska viewed the springs as an "equal or better" substitute for bungees. They were generally willing to sign that off as a minor.......till the FAA caught on to this and said no. The Fairbanks FSDO, however, would field approve springs substituted for bungees.

I'd see if you can get a field approval from your FSDO, or another if possible, or a DAR if the feds won't approve it.

Boreal1 wrote:I checked last year for approved springs on my 185’s fluidyne installation and was told by Atlee Dodge that no such approvals exist. Anyone aware of any approvals for same?

I easily obtained a FA from the FAI FSDO for Atlee gold springs in lieu of bungees on my Airglas 3000's, HOWEVER, as wheel replacement skis, the geometry and resulting tension on the spring changes only due the maximum angle as allowed by the forward and aft check cable limits. With the hydraulic ski, the ski moves forward and aft with a change in elevation as well. The very first question that should be answered is what the length difference is (if any) between the ski up and down positions. I have a set of Federal AWB 4820's that I desired to replace the main bungees with springs. After a talk with Justin at Atlee Dodge (very helpful by the way), I decided there is not enough meat on that bone in relation to the time spent getting them approved so I continue to run bungees on these per the Federal drawing. As I suggested in a previous post, if not flying for a few days, I disconnect the bungees to relax them thus extending their service life in my opinion.

If one could find an existing FA of same, there is a better chance of approval utilizing springs on the hydraulic ski. Without such, my opinion is the return on investment (even if it is time only) does not warrant the reward.

TR