Cowling Fixings

[Skippydiesel]

Have just got to the stage (hopefully last major hurdle) of considering how I am going to secure home designed and built fiberglass cowling.
The first builder of my Sonex Legacy, has supplied sufficient Skybolt Cloc 4000 Series fasteners to secure the two "halves" of the cowling to the airframe. Non for securing the upper/lower halves together.
The Cloc 4000 series is way over specified for securing the top to bottom and being so large will not conform to the curvature of the cowling - so this system is out, as far as securing the top to the bottom.
Have gone on the Skybolt web site and have perused their catalogue, so am aware of their smaller sized offerings - Cloc 2500, 2600, 2700, 2800.
I dont know what the relative merits of each system is. The only on line advise I found relates to "overlap width" - my overlap is going to be (not done yet) about 15-20 mm with a combined grip thickness of approximately 4-6mm.
Being fiberglass and home made, means that lay up thickness does vary a little, so whatever system I use will need to have "Adjustable Receptacles" so that the Studs all end up being flush with the surface of the cowling. (Preferred studs will have "Phillips" head and be flush fitting).
I am interested in;

Any alternative fixing systems you may recommend ( & why?)
Your thoughts on the most appropriate Skybolt Cloc system

[racaldwell]

I used 8-32 SS Flathead Screws for the top cowl half to fuselage junction. There are three nutplates per side. BTW, I made a three piece cowl from my original vertical split Sonex cowl. I really like being able to take any one section off fairly quickly.

The horizontal top/bottom connection on the sides are with piano hinge inserted from the rear. The side/lower firewall connection is also piano hinge. The bottom seam is #8 screws into my cowl flap structure and piano hinge up to the opening for the oil cooler air inlet. There are three screws above that inlet up to the prop. There are two screws in the front to hold the joints together next to the prop/inlet on each side and one screw on the other side of the inlet on each side.

Why? Because it was cheap, fast and easy to do. Trade off is the extra minutes with a screw gun to deal with the screws.

You could probably find pictures of it on my EAA Builders Log.

Rick Caldwell
Xenos 0057 37 hrs engine 3 hrs gliding

[racaldwell]

I used 8-32 SS Flathead Screws for the top cowl half to fuselage junction. There are three nutplates per side. BTW, I made a three piece cowl from my original vertical split Sonex cowl. I really like being able to take any one section off fairly quickly.

The horizontal top/bottom connection on the sides are with piano hinge inserted from the rear. The side/lower firewall connection is also piano hinge. The bottom seam is #8 screws into my cowl flap structure and piano hinge up to the opening for the oil cooler air inlet. There are three screws above that inlet up to the prop. There are two screws in the front to hold the joints together next to the prop/inlet on each side and one screw on the other side of the inlet on each side.

Why? Because it was cheap, fast and easy to do. Trade off is the extra minutes with a screw gun to deal with the screws.

You could probably find pictures of it on my EAA Builders Log.

Rick Caldwell
Xenos 0057 37 hrs engine 3 hrs gliding

[Skippydiesel]

I was going to go for flat head (Truss) fasteners - relativly cheap/simple/light but my Son, who made the cowling kicked up a fuss and basically emotionally twisted my arm to purchase a1/4 turn system - hence the question about Skybolt Cloc systems.

Would still like to get some informed comment/advise on the smaller Cloc systems.

[DCASonex]

Have the Skybolt fasteners on mine, with the adjustable sockets so as to use one length of stud. Many but not all of my studs are captive and that avoids any mix up. I can remove my cowl with just the tip of the nail file blade on key chain sized Swiss Army knife which makes for more frequent removal which i see as a safety advantage.

David A.

[Skippydiesel]

Have the Skybolt fasteners on mine, with the adjustable sockets so as to use one length of stud. Many but not all of my studs are captive and that avoids any mix up. I can remove my cowl with just the tip of the nail file blade on key chain sized Swiss Army knife which makes for more frequent removal which i see as a safety advantage.

David A.

Hi David - Got a few questions;

Which of the Skybolt systems did you use.
What spacing formula did you apply? AND why?
Did you purchase/borrow/hire any special installation tools? If so which ones.
What rivet size did you go for?
Did you purchase from Skybolt or an agent?
Any other useful information?

[GraemeSmith]

Service Letter from the FAA today about failures of 1/4 turn fasteners leading to losses of inspection panels. Damage or aircraft handling issues resulting.

They are seeking further information and any service difficulty reports to figure what is going on. At this time it seems to be "poor maintenance procedures" without being specific as to why.

--

I use Countersunk Southco fasteners set in 100 degree washers. The washers are glued into the fibre glass on the cowl and are there to take the wear. Otherwise you quickly wear through the fiberglass with fasters alone. The split spring retainer washers on the back are a must if you are going to keep track of which length goes where.

[DCASonex]

Had to dig to find 11 year old receipt for this. Have more info in hangar but stuck home with COVID. All purchased were direct from Skybolt.

17 - # SK213-2 Receptacle 2000 series C
8 - # SK213-2D dimpled
25 - # ZG28S3-2 Skytanium TSO-C148
30 - # SK2600-LWS cloc retaining ring
1 - # SK-T26 cloc fastner tooling
1 - # Template-213 cloc fastner tool

The above being 11 years old, things may have changed a bit, bit this should get you started.

I made my own conversion from stock vertical split cowl to horizontal and used hinges to connect the top to bottom along the straight sides, but if doing it again would just use a couple of more Skybolts, spaced 5" - 6"apart.

As to the FAA failure notice, it was on turboprop planes and I have used my setup for 10 years with zero problems. Even flew once with the pins not installed in the side hinges, and was near VNE on that flight. NOT recommended, but no problem that time. I do have two Skybolts installed on each side of propeller as that looked to be a critical area. Have seen others with just one fastener each side.

Studs can be held with the retaining rings on all areas that are flexible enough to engage or disengage the fasteners by flexing the cowl. but at from corners and next to the prop, I remove them.

David A.

[Bryan Cotton]

Check out this thread:
viewtopic.php?f=21&t=6624&p=50248&hilit=Skybolt#p50248

[Skippydiesel]

Had to dig to find 11 year old receipt for this. Have more info in hangar but stuck home with COVID. All purchased were direct from Skybolt.

17 - # SK213-2 Receptacle 2000 series C
8 - # SK213-2D dimpled
25 - # ZG28S3-2 Skytanium TSO-C148
30 - # SK2600-LWS cloc retaining ring
1 - # SK-T26 cloc fastner tooling
1 - # Template-213 cloc fastner tool

The above being 11 years old, things may have changed a bit, bit this should get you started.

I made my own conversion from stock vertical split cowl to horizontal and used hinges to connect the top to bottom along the straight sides, but if doing it again would just use a couple of more Skybolts, spaced 5" - 6"apart.

As to the FAA failure notice, it was on turboprop planes and I have used my setup for 10 years with zero problems. Even flew once with the pins not installed in the side hinges, and was near VNE on that flight. NOT recommended, but no problem that time. I do have two Skybolts installed on each side of propeller as that looked to be a critical area. Have seen others with just one fastener each side.

Studs can be held with the retaining rings on all areas that are flexible enough to engage or disengage the fasteners by flexing the cowl. but at from corners and next to the prop, I remove them.

David A.

Your a good person David - great information.

Do you still have your;

1 - # SK-T26 cloc fastner tooling ?
1 - # Template-213 cloc fastner tool ?

If so would you consider selling & posting to Australia?