Hi Dico,

I realize that my input avoids a direct answer to your question, but the cowl attachment problem you are having trouble with is one that I see often.  From my perspective, the solution goes in a different direction than trying to decide which attaching screws to use.  I wonder why the kit builders and just about everyone have not simply planned for easier and better systems that are readily available to overcome the difficulties you are pointing out. 

The first photo is my cowl installed without engine – (I recently pulled the engine for overhaul. )  You won’t see any screws of the type you are complaining about – Phillips, Camlock, Robertson, Torque or otherwise in that photo of the cowl.   Close inspection will reveal a total of three 10/32 countersunk hex head screws silver soldered onto the end of .080” wires.  One each are at the outboard lip of the air intake scoops and one is just in front of the copilot side windscreen where a pin tracks across the rear aft edge of the upper cowl.

The second photo demonstrates where there were ten screws securing the cowl to the framework around the nose gear.  Last week I took the time to replace all those screws with two more Carbinges, one on each side so that there are NO fastening screws anywhere on the cowl anymore.  Now there are a total of five visible countersunk hex head screws in the entire cowl and that is all.

The third photo is an application I don’t think I’ve shared on the LML previously.  It shows how I use short pieces of Carbinge to secure the small tabs of the cowl behind the Prop spinner.  The wires are custom formed and bent so that they follow the inside of the cowl and snap  into an attachment point made out of a graphite tab.  They are installed and removed using the intake scoop for access and are very simple to operate by the  Braille  method.

I did not know if replacing existing screws or other attachments would be a big job, but I found that replacing those on the bottom of the cowl last week was a very straightforward and rewarding process.  I can recommend to anyone that having a conventional system already in place does not in any way inhibit this improvement.  In fact it takes most of the hard work  out because the geometry is already taken care of and for much of the process, the existing attachments can be used as temporary retainers while you fit and bond in the replacement Carbinge materials.

Understand that I have a vested interest since I own Leading Edge Composites, the company that builds Carbinge and has patent pending rights on the technology.

We call the attachment system using Carbinge “Zippin” because the system acts much like a zipper. 

Good luck with your cowl.

Best regards,
John Barrett

www.carbinge.com

Hi All,

I'm wondering why we don't use Robertson screws (http://joneakes.com/jons-fixit-database/418-History-of-the-Robertson-Screw)  on our airplanes... namely on the cowls and other areas that are removed often.   Having taken my cowling off and on about 15 times in the last couple months, the Phillips screws get chewed up pretty good.  The Robby screws would be infinitely better I would think -- certainly cosmetically they would look better after many de-cowlings.

Is the main reason because the Robertson screws are Canadian and the Phillips are US and the airplanes are US?  Or is there a technical (or other) reason we don't use them?

-Dico