Cowling Fixings
Posted: Wed May 18, 2022 1:31 am
by 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
Re: Cowling Fixings
Posted: Wed May 18, 2022 5:51 pm
by 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
Re: Cowling Fixings
Posted: Wed May 18, 2022 5:53 pm
by 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
Re: Cowling Fixings
Posted: Thu May 19, 2022 7:50 am
by 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.
Re: Cowling Fixings
Posted: Thu May 19, 2022 9:37 am
by 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.
Re: Cowling Fixings
Posted: Fri May 20, 2022 6:08 am
by Skippydiesel
DCASonex wrote: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?
Re: Cowling Fixings
Posted: Fri May 20, 2022 7:54 am
by 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.
Re: Cowling Fixings
Posted: Fri May 20, 2022 10:17 am
by 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.
Re: Cowling Fixings
Posted: Fri May 20, 2022 12:31 pm
by Bryan Cotton
Check out this thread:
viewtopic.php?f=21&t=6624&p=50248&hilit=Skybolt#p50248
Re: Cowling Fixings
Posted: Fri May 20, 2022 7:10 pm
by Skippydiesel
DCASonex wrote: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 toolThe 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?
Re: Cowling Fixings
Posted: Fri May 20, 2022 7:11 pm
by Skippydiesel
Bryan Cotton wrote:Check out this thread:
http://www.sonexbuilders.net/viewtopic. … olt#p50248
Bryan you are a mine of information. Very helpful, thanks!
Re: Cowling Fixings
Posted: Sat May 21, 2022 12:11 pm
by DCASonex
Still have the tools, but they are so simple you could make your own much cheaper and faster than post to Oz.
David A.
Re: Cowling Fixings
Posted: Tue May 24, 2022 7:07 am
by Skippydiesel
DCASonex wrote:Still have the tools, but they are so simple you could make your own much cheaper and faster than post to Oz.
David A.
Thanks David.
Re: Cowling Fixings
Posted: Tue May 24, 2022 7:22 am
by Skippydiesel
I have now written to Skybolt twice , seeking advise/information and have yet to have a reply.
In frustration, I am contemplating just purchasing their Cloc 2000 kit system SK28S3-SET1 OR ZG28S3-SET2.
Both cover, the same, a very wide grip length, essential for the irregularity of home built fiberglass cowling.
As far as I can work out the difference between the two systems is in the Adjustable Receptacle - one being Stainless Steel (probably heavier) with 3/32" rivets, the other “Skytanium” (probably lighter) with 1/8" rivets.
What I need now is;
-
A recommended spacing so that I can order the correct number of units.
-
To understand the merits of the Stainless Steel Adjustable Receptacle SK28S3-SET1 with 3/32 " rivets compared with the “Skytanium” Adjustable Receptacle ZG28S3-SET2 with 1/8" rivets.
All help suggestions welcome.
Re: Cowling Fixings
Posted: Tue May 24, 2022 9:09 am
by GraemeSmith
OPINION follows.
On a different aircraft - I found the adjustable receptacles to be fiddly to setup, hard to keep setup and subject to wear and failure dues to vibration inherent in 4 banger engines with 2 bladed props. At 450 hours they were junk and I went back to fixed receptacles.
Cheaper and easier to keep setup up - fixed receptables and then a small collection of different length fasteners till I found the setup that worked. Then retaining rings to keep the correct length fasteners in the correct holes. Also as previously mentioned - the fasteners need to sit in washers to protect the fiberglass from wear.
I’m not sure what spacing formula might exist. My Legacy Sonex has a total of 6 spaced across the top back edge of the cowl halves. Three per side. A good soft layer of vibration tape under the cowl and on the flange to stop fretting and give a little “spring” when fastening down.
You might also just walk around the tie downs with a tape measure and see what others have. I’m guesstimating from memory that Cessna uses 4" centers
Re: Cowling Fixings
Posted: Tue May 24, 2022 5:37 pm
by Murray Parr
skybolt.jpeg (128.35 KiB) Viewed 2157 times
cowl3.jpeg (157.2 KiB) Viewed 2157 times
cowl2.jpeg (90.01 KiB) Viewed 2157 times
cowl1.jpeg (111.43 KiB) Viewed 2157 times
I went with the RV kits through Skybolt because they are more economical to purchase and Skybolt said the smaller series weren’t strong enough for a sonex. They should also wear the cowl out less due to the grommet system they use. I used the spacing on the Sonex plans at the horizontal split because I already had the Dzus fasteners installed (which were increadibly difficult to use) and I just enlarged those holes. If I were to do it again I would have moved the forward holes back just enough to avoid the curve. The 2 fasteners near the prop are also challenging so I went with winged fasteners there to free up a hand while installing them. The rear fasteners were originally spaced as per plans but I added 3 more for strength, could have added another but my oil inspection door was in the way for that.
Re: Cowling Fixings
Posted: Tue May 24, 2022 7:39 pm
by Skippydiesel
GraemeSmith wrote:OPINION follows.
On a different aircraft - I found the adjustable receptacles to be fiddly to setup, hard to keep setup and subject to wear and failure dues to vibration inherent in 4 banger engines with 2 bladed props. At 450 hours they were junk and I went back to fixed receptacles.
Cheaper and easier to keep setup up - fixed receptables and then a small collection of different length fasteners till I found the setup that worked. Then retaining rings to keep the correct length fasteners in the correct holes. Also as previously mentioned - the fasteners need to sit in washers to protect the fiberglass from wear.
I’m not sure what spacing formula might exist. My Legacy Sonex has a total of 6 spaced across the top back edge of the cowl halves. Three per side. A good soft layer of vibration tape under the cowl and on the flange to stop fretting and give a little “spring” when fastening down.
You might also just walk around the tie downs with a tape measure and see what others have. I’m guesstimating from memory that Cessna uses 4" centers
Reference; Your experience - Interesting observation regarding Adjustable Receptacles. They seem to be the answer to a home builders dream (fitting to composites structures). It would be informative to hear from others on the service life of these expensive fittings.
I am with you on the "Cheaper and easier " - my first intention was to just use “Truss” type screws with a Nylon washer, into a fixed Receptacle - my son, the designer/builder of the cowling , did not approve wanting something more aeronautical.
As mentioned earlier - My partially built Sonex was supplied with sufficient Skybolt Cloc 4000 Adjustable Receptacle fixings to secure the cowling to the airframe. The 4000 are very large (compared to the 2000 range) and not suitable for the curvature on the sides of the cowling.
Have already purchased something similar to " vibration tape" for the the same reasons you mention.
Spacing formula/recommendations - I assume that aluminium cowlings & certified aircraft are likely to have very different spacings to a home built/experimental. The Vans recommendations are probably “on the money”.
Re: Cowling Fixings
Posted: Wed May 25, 2022 7:39 pm
by Skippydiesel
Sleepless night - decided to go back & investigate Truss head screws, with nylon (or similar) washer, mated to a Floating lock Nutplate.
Plusses;
Very much cheaper
Easier/quicker to install
Assured torque (wrist click)
Available through local supplier/quick delivery
If I want to install Skybolt fixings can always do that later
Negatives;
May take a little longer to remove/install cowling
Will have to carry spare screws & washers in the event of loss/damage
Wont look as “Flash” as the Skybolt offerings
Re: Cowling Fixings
Posted: Thu May 26, 2022 7:19 am
by GraemeSmith
Measured in the tie downs yesterday:
Cessna 150 - Horizontal seam 6" centers. Curved seam to hold to firewall - 10" centers
Cessna 172 - Horizontal seam 5" centers. Curved seam to hold to firewall - 8" centers
Re: Cowling Fixings
Posted: Thu May 26, 2022 5:59 pm
by Skippydiesel
GraemeSmith wrote:Measured in the tie downs yesterday:
Cessna 150 - Horizontal seam 6" centers. Curved seam to hold to firewall - 10" centers
Cessna 172 - Horizontal seam 5" centers. Curved seam to hold to firewall - 8" centers
Thanks Graeme
Not sure how relevant the examples of metal cowlings on certified aircraft is - my gut feeling (truly scientific) is 100mm (4 in) spacings on my fiberglass cowling. Spacing will be adjusted to accommodate , tight curve, internal clearance, etc.
Its important for my aft located coolant radiator, receiving only cowling air, that air leakage is minimised. To this end, fixings will be close, to (hopefully) reduce leakage, due to “bowing” under operational air pressure.
Re: Cowling Fixings
Posted: Thu May 26, 2022 6:10 pm
by racaldwell
Or you can have your son get out the cloth & resin and make an engine cooling plenum. Then little stress on the cowl fasteners.
This one did not take very long to make.
Rick Caldwell
Xenos 0057
CAMIT 3300
Engine Cooling Plenum Sm.jpg (152.81 KiB) Viewed 884 times
Re: Cowling Fixings
Posted: Fri May 27, 2022 2:35 am
by Skippydiesel
racaldwell wrote:Or you can have your son get out the cloth & resin and make an engine cooling plenum. Then little stress on the cowl fasteners.
This one did not take very long to make.
Rick Caldwell
Xenos 0057
CAMIT 3300Engine Cooling Plenum Sm.jpg
Looks great Rick.
Unfortunately wont help my installation. My coolant radiate is located at the bottom of the firewall. It depends on getting a good air flow from within the cowling. As totally experimental & yet to fly, I am assuming that I must try to minimise air leaking out of the cowling. (would post photo’s but have had no luck in that area.)
You can check out the build on https://webuildplanes.com/cliff-jarvis/