Printable View
My airplane has a two piece fiberglass cowl. The lower sections bolts to the fuselage and the top section bolts to the bottom section with non-captive screws that screw into nutplates attached to the inside of the lower cowl. There are four screws on each side, so a total of 8 screws hold the top cowl on.
i don't really like the non-captive screws and it is not unusual to lose one in flight.
I'm interested in your opinions on what to replace them with such as dzus or camloc or something else.
I will suggest that 4 screws on each side sounds like too few. How far apart are they?
The nutplates should not allow the screws to vibrate loose. They are not doing their job. Are they metal nut plates or is the locking a fiber insert? Should be metal.
As an example, my Pitts has 6 screws that hold the top cowling to a flange on the firewall and then 6 more fasters on each side just for the sheet metal top cowl. There are 6 screws holding the front of the top cowl to the nose bowl, and 8 screws holding the top of the nose bowl to the bottom.
As I think about your 8 screws, I will suggest that they are coming loose because the threads are loaded up too much combined with the vibration and hear of the engine. You likely need more fasteners to hold the top cowling on.
Best of luck,
Wes
N78PS
But it's a certificated airplane...it must be right....:rollseyes:
Yeah, ah, I wasn't wild about four per side, but that be the way she came from the factory in '77.
This is probably the textbook example of where a Minor Alteration would make the airplane safer. But before I choose a solution, I'd like to tap the collective wisdom and get the pro and con of dzus, camloc and other captive fasteners.
Well AC43.13 is pretty conservative but I offered the number of fasteners on my ship to illustrate the difference in numbers, and lay the groundwork for my assertion that using only 8 total fasteners puts more load on each one and makes them prone to unscrew and fly away.
I will offer the perspective on 1/4 turn fasteners that they can only be removed using hand tools (electric screw drivers work really well removing screws...), are bulkier and heavier, they do have parts break like clips depending on the type, require special tools for installation, and when you try to align the top cowl to put it back on, they stick out and try to scratch the paint of stuff that they drag across. My observation is that they work best on access doors that have a hinge on the other side. With airplanes like Cessna's that have 1/4 turn fasteners to secure the cowling, you still sort of need 2 people to hold the cowling about where it needs to go and then wiggle and pop the 1/4 turn fasteners into their sockets as you try to not drop the cowling on the floor.
So for large curved, hard to juggle, fully removable, panels I personally do not think that the 1/4 turn fasteners buy you any more convenience and reduction of effort. That said, for large flat panels, where you can use a shoulder or hip, even simple gravity, to set the panel in place while you turn the fasteners, 1/4 turn fasteners can make removal and replacement easy.
So as with many airplane question, the answer is "it depends".
Best of luck,
Wes
N78PS-that-has-hinged-cowling-cheeks-with-quarter-turn-fasteners
I would respectfully disagree about not using 1/4 turn fasteners. I have Camlocs in one plane that has a 2 pc glass cowl. 3 camlocs on each side to hold the lower cowl to the airframe and lots along the sides to hold the upper cowl to the lower cowl, and 7 across the back of the upper cowl to fasten it to the airframe. I've not lost a camloc in 17 years and 1000+ hrs flying this plane now, and depending on how they are captured (there are two ways to capture them) they can fully retract so don't stick out to get caught when installing/removing the cowl.
Another plane I built using Southco fasteners in a metal cowl (SuperCub Clone). I intended to use Camlocs as my experience with Camlocs has been pretty good. However, I had a few Southco Fasteners so decided to go with them. In that particular application, I like them better than the Camlocs. With Southco fasteners, I recomment using the plastic cupped washers under the head of the fasteners to keep from abraiding the paint/glass/metal.
I have had planes with Dzus fasterns as well. While they appear to be incredibly simple, I didn't care for them as they seemed to be more difficult to get to latch.
I have also had a plane with piano hinges as cowl fasteners. I didn't care for them in that application as I always had to fight the hinge back in as the aluminum cowl sides were always springing out against he hinge while I was trying to install the hinge pin, but if everything is lined up correctly without loading the hinge, they can be made to work reasonably well and do make for a very clean cowl parting line.
-CubBuilder
A friend of mine changed his Cessna cowl Southco fasteners to nutplates and screws. The feds tagged him with a condition notice (8620-1) - unapproved mod. Had it not been something as common as a Cessna, they would have never noticed. I put in Camlocks with an STC and everyone was happy again. For a cowling, it's hard to beat camlocks. One of the best "quick" fasteners ever invented.Quote:
Originally Posted by TedK
I will agree with the 1st poster above: more screws are needed and the nut plates need to be metal & in good condition. My previous & current planes have both been fiberglass with top & bottom cowlpieces. 6 & 7 screws per side (respectively). Those metal nutplates are tapered threads, and will not let a screw loosen if they are in good condition.
Hard to believe the feds will violate you for adding a few more fasteners to the cowl, but stranger things happen......
I had a similar issue with my brand "C" airplane. The forward part of the cowling uses tinnerman nuts (NAS395) and sheet metal screws. The engine vibration would case the sheet metal screws to vibrate loose and occasionally a screw would fall out.
The simplest, fastest, easist way to solve the problem is to change the tinnerman nuts / sheet metal screws for clip nuts and MS machine screws. Specifically floating, locking clip nuts that are aircraft quality. I've not lost a screw is over 20 years using this method.
http://www.clipnuts.com/general_uses_clips.html