I found that hinges work great for the sides, both vertical and horizontal.
I used screws across the top, bottom and each side of the spinner. The top because of ease of cowling installation and across the bottom because the hinges kept breaking.
After flying for over 25 years they all still look great and I would do it the same way today.
Since we are discussing the pros and cons, I would like to convert the piano hinge along the aft top of the cowl to SkyBolts. What is the process and how difficult and time consuming is it?
After building a plane with both methods, I think I would use the screws and nutplates on any future builds.
One thing I haven't seen mentioned yet was that the internal hinge pins are not comfortable to remove when the engine and everything inside the cowling is hot. Reaching your arm up inside the oil door on a hot engine can bring on involuntary vocabulary outbursts.
Early in my build, I had an experienced builder tell me that you have to be thinking about maintenance and easy access when you're actually flying this thing. He put quarter-turn fasteners (a.k.a. cam-locks) along the aft edge of the top cowling and hinges that can be accessed externally on the side seams. After you have top off, access to rest is easy. The underside of the bottom cowling aft edge also had quarter-turn fasteners. I did the same and haven't regretted it.
OK so why would a builder spend additional time/ money on a part of the build?
For me it was if I could improve looks, performance or future maintenance.
I looked at what others were doing and came to a couple of conclusions.
I don't like the looks of the Skybolts. I like the clean look of the hinges. I even used hinges on the wing tips.
What is wrong with or what can be improved with the hinge method.
Air leaks - I added a small plate at the top corners of each side to reduce the air leakage through the gap.
Top of cowl movement when pressurized.
Difficulty of getting to, removing and installing hinge pins for the top.
Both of these were solved by installing equal length hinges on the top and cutting a small trapezoidal hole on the top of the cowl. Mounting a bracket to the top firewall with holes for the hinge pins. A small Trapezoidal plate screwed to the bracket to keep the pins in place and hold the cowl down. This also allowed the use of the proper size pin rather than a smaller diameter pin to get around the corners. Easy to remove and no play in the cowl top.
Also used plates with screws along both bottom sides.
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Mark or Phat - would you be able to share a picture of how you access the pins when your top cowling is on, please?
Thanks!
This is a rather underrated comment. I was always so frustrated having to remove these pins when the engine was hot. If I didn't have on gloves and a long sleeve sweatshirt I'd have some nice burns! I'm honestly surprised more people don't complain about this.
On both my 7A and my 10, I used the hinges along the sides of the cowl, but on the my first plane (7A) I used Skybolts around the firewall..... and I didn't really like them.
I didn't like how the Skybolts hung down below the cowl, so that every time you put the top cowl back on, you risked scratching the forward fuselage paint. I also had a few that the retainer clips would not hold in over time.
On my more recent 10 build, I just used #8 screws, tinnerman washers and nutplates. Instead of $500 in Skybolts, I have about $20 in fastener costs. With a powered screw driver, it takes maybe a couple of minutes longer to get the cowl off, but there is nothing hanging down to scratch the paint.
After building a plane with both methods, I think I would use the screws and nutplates on any future builds.
After 3 years my top cowl hinge pins where getting a little “sticky” even though I Boelube them almost every time. I decided to polish them with (below) and after doing this they slid in like buttered. I did get a lot of oxidation off when I did this. Highly recommend.