Removing Sting S3 Parachute for Service=Major “Ouch!”

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

Moderator: drseti

User avatar
drdehave
Posts: 356
Joined: Fri Apr 13, 2012 10:45 am
Location: Davis, CA

Removing Sting S3 Parachute for Service=Major “Ouch!”

Postby drdehave » Mon Oct 02, 2017 7:15 pm

If you followed the other recent thread here on SportPilotTalk (viewtopic.php?f=3&t=4865), you know that I recently removed my Galaxy parachute system (GRS) for required maintenance. What I failed to describe in that thread was the significant unanticipated cost that was incurred. Here’s what happened.

We had just deactivated (per instructions) the black powder packet & rocket fuel and placed the rocket trigger (i.e., containing a percussion cap) in a vice, to detonate it with a rubber mallet. The resulting “boom” was way greater than either of us expected!

Then, my mechanic, who is a beefy guy at 240 lbs, headed back to the cockpit to tidy up, before I took to the air for the return home (the GRS is not required equipment in the Sting). As he stepped onto the lower (trailing edge near the root) wing, we heard another loud “pop.” It was a piece of core-board-rib breaking and delaminating from the skin of the lower (underside) wing where the flap control rod passes through a cut-out in the rib.

My mechanic tried to shoulder the blame. But I assured him it wasn’t his fault. He’s been walking around uneventfully on those wings for nearly 10 years now. It appears that this is a known weak spot and all it took was someone at the Sting “person” weight limit (i.e., 240 lbs) stepping in the wrong place. Have you noticed the prominent “NO STEP” placards in that same area (trailing edge, near root) on the latest models of Stings? I think there’s a message worth heeding, there.

However, during the repairs, we also discovered two other likely contributing factors in my particular case: 1) the cut-out area of the core-board, that the flap control rod passes through, had obviously been damaged by that rod during repeated (for annuals and other purposes) removal and installation of the wings (Fellow Sting owners: this is something you should really be very careful about. Have a “spotter” monitor that cut-out the flap rod passes through anytime you are taking off and/or replacing the wings); and 2) the right wing (where the break & de-lamination occurred) appeared to have a faulty lay-up of flox (thick fiberglass paste) in the corner, where the carbon-fiber skin of the wing meets the core-board rib. Most of the injected flox (or more likely, just applied with a wooden stick) had fallen down after application, possibly due to lack of viscosity, rendering it ineffective.

Our repairs focused on laying down some new fiberglass in key areas and injecting copious amounts of viscous flox into the right places, using a large syringe with attached tube. The German epoxy the airplane is built with-–MGS L-285–-was used. For insurance, we fixed not only the damaged right wing, but also the apparently undamaged, but nevertheless weak, left (pilot-side) wing, too. Repairs were accomplished by removing the wings (and then the flaps), placing them on sawhorses, and then working on one side at a time, utilizing gravity to assist with proper flox injection & contact. It was also a great time for deep cleaning and putting a good coat of wax on the undersides of the wings (as opposed to working on them from below, when attached to the airplane).

After removing the 35-lb GRS, I offset the weight loss and retained the original CG (center of gravity) by placing a 20-lb sandbag in the rear of each of the two luggage boxes; alternatively, I could have foregone the sandbags and just adjusted the trim, while still retaining an allowable CG. With the sand bags, once the GRS is returned and reinstalled, I’ll still have my original, near-perfect, trim setting.

I also want to take this opportunity to memorialize for fellow Sting owners (and other USA-sold, European LSAs which utilize the GRS) our (i.e., USA owners) options for required GRS maintenance. There are two GRS dealers in the USA: SportairUSA at Little Rock, Arkansas and SportPilotShop at Torrance, California. If you choose Sportair, you can expect to take your airplane to Little Rock for a minimum of 2 days; however, when you leave, your updated GRS will have been installed. If the trip to Little Rock is not your cup of tea, or is otherwise infeasible, you may want to consider the SportPilotShop option I am using. They provide instructions for removing and disarming the GRS which you then ship to them. They forward it on to the manufacturer in the Czech Republic. It then comes back to you about 6 weeks later, serviced and ready for reinstallation (we'll see--it ain't happened yet). Costs for these two dealer options vary widely and are themselves moving targets, so I won’t give dollar numbers here. Inquire for yourself. Just be aware that if using option B through SportPilotShop, you’ll need a knowledgeable mechanic to accomplish and record GRS removal and reinstallation. And this is a relatively dangerous process.

How dangerous? Well consider this. I was just told by a friend and fellow Sting owner in Germany, that in one European incident when the chute was being serviced, an accidental firing sent the rocket completely through the wall of a house, then a ricochet sent it back and completely through the hull of the Sting, before "going off into nature." I rest my case...

I will report the conclusion of my story when my GRS is returned and safely reinstalled--and I have removed that "in-op" placard from the dash.
027 (1328 x 747).jpg
027 (1328 x 747).jpg (215.24 KiB) Viewed 251 times

041 (1328 x 747).jpg
041 (1328 x 747).jpg (160.21 KiB) Viewed 251 times

049 (1328 x 747).jpg
049 (1328 x 747).jpg (116.92 KiB) Viewed 251 times
Last edited by drdehave on Wed Oct 04, 2017 11:27 am, edited 4 times in total.
Sting Flight (Flying the Sting LSA)
http://www.youtube.com/user/9162069934/featured

User avatar
drdehave
Posts: 356
Joined: Fri Apr 13, 2012 10:45 am
Location: Davis, CA

Re: Removing Sting S3 Parachute for Service=Major “Ouch!”

Postby drdehave » Mon Oct 02, 2017 7:19 pm

Three more pics in this series:
flox 002 (1328 x 747).jpg
flox 002 (1328 x 747).jpg (187.54 KiB) Viewed 249 times

013 (1328 x 747).jpg
013 (1328 x 747).jpg (116.05 KiB) Viewed 249 times

030 (1328 x 747).jpg
030 (1328 x 747).jpg (153.57 KiB) Viewed 249 times
Sting Flight (Flying the Sting LSA)
http://www.youtube.com/user/9162069934/featured

User avatar
drdehave
Posts: 356
Joined: Fri Apr 13, 2012 10:45 am
Location: Davis, CA

Re: Removing Sting S3 Parachute for Service=Major “Ouch!”

Postby drdehave » Mon Oct 02, 2017 7:21 pm

Final three pics in this series:
025 (1328 x 747).jpg
025 (1328 x 747).jpg (244.63 KiB) Viewed 249 times

042 (1328 x 747).jpg
042 (1328 x 747).jpg (221.47 KiB) Viewed 249 times

049B (1328 x 747).jpg
049B (1328 x 747).jpg (248.62 KiB) Viewed 249 times
Sting Flight (Flying the Sting LSA)
http://www.youtube.com/user/9162069934/featured


Return to “Ask The Mechanic”

Who is online

Users browsing this forum: No registered users and 1 guest