Cowling Fixings

[Skippydiesel]

Check out this thread:
http://www.sonexbuilders.net/viewtopic. ... olt#p50248

Bryan you are a mine of information. Very helpful, thanks!

[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.

[Skippydiesel]

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.

[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;

1. A recommended spacing so that I can order the correct number of units.

2. 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.

[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

[Murray Parr]

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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.

[Skippydiesel]

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".

[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

[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

[Skippydiesel]

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.