Engine cowlings screws => Camlocs

[Gilbert DRIEUX]

I plan to replace ALL screws, top and bottom, with camlocs.
Is taht a good plan ?
(despite the cost...).

Regards

[Dan Patch]

A number of years ago there was some discussion about using camlocks in this application.  I seem to recall that one problem that was encountered was that of interference at the spar flange since the cowl has to slide rather than lift off.  The solution was to mount the cowl outside the flange rather than under it (as called out in the plans), and it was said that this made cowl removal a lot easier, regardless of the attach method.  Personally, I don't care much for the 'outside the flange' mounting idea because the cowl is more vulnerable to detaching by tearing through the screws/camlocks in tension from differential pressure loads acting on the cowl.  

As an alternative, I would check out the 'hinge pin' attach method so nicely executed by Bill James (see the Feb. POM Article).  Could be a lot cheaper than camlocks, and nothing beats this approach for speed on/off and for all-around slickness.  Could take a while to build?  Whatever you decide to do, however, be sure that it is up to the job!  Having the cowl go through the prop is bound to be undesirable; and this isn't just a theoretical problem as we have had a few do just that.  If in doubt, multiply the square inches inside the cowl times a conservative WAG at the pressure differential in psi (use Waiter's P vs. speed table, an agressive descent speed, and assume the load is concentrated on a couple of fasteners).  Wow, that's a lot of force!!

(Re)build and fly safe!

[Joe Person]

Gilbert,

If you do opt for total "outside" flange mounting, a configuration that worked well for me was to have a 1-inch tall BID stiffener that is perpendicular to the inside surface of the cowl, all along the forward edge of the cowl, about 1.5 inches aft of the forward edge.  The internal mounting flange attached to the fuselage/centersection forms a vertical flange face as well, so that the two vertical faces contact each other.  Both vertical flanges stiffen the cowl/fuselage attach area, so as to keep any vertical distortion between fasteners from happening.  It has worked well.  The cowl flange also makes up the additional plies of BID along the forward edge (to allow sufficient material thickness for proper countersinking in the cowl itself).  As is typical, this BID is laid up +/- 45 degrees.  One has to make forms inside the cowl to make the stifffeners.  I simply used 1/8th inch balsa wood tacked in place with automotive body filler (i.e. Bondo), with duct tape on the mating face of the balsa for release.

To get the vertical portion of the attaching flanges on the fuselage, the cowling mating surfaces are duct-taped, and the cowling is jigged to the fuselage with wood strips & Bondo.

To keep the edges of the cowling straight while adding the stiffeners, straight pieces of wood were bondoed spanwise along the edges that mate to the centersection.

I use ordinary 100 degree screws to attach my cowling.  Bill James' cowling installation is certainly much more elegant, however.

Bon chance,