September 2012 Archives

Resumed Work on Cowl

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I haven't touched the plane in a month, but I have a really good reason...honest!  First, I've been really busy at work, but what's really killed all of my free time is that we bought a new plane!  We've finally outgrown the Cessna Cardinal that has been our family plane for a number of years now.  Even though the kids are still small, we're basically right at gross weight with full fuel and baggage.  It's also pretty slow and has pretty anemic climb which is important around here.  I'd been thinking about building an RV-10 after I finish the 7, but the ride in my buddy's A36 Bonanza changed my mind.  I ended up buying a 1/4 share of a 2001 turbo-normalized A36 Bonanza with really low time in fantastic shape.  The search itself took quite a lot of time, but I've also been taking the Advanced Pilot Seminars course to learn to fly it lean-of-peak as well as the BPPP course to learn about how to fly the aircraft.  I've also been reading books and articles in preparation for the transition training that starts next week.

Anyway, a month is way too long, so I decided to use the long weekend to get restarted.  I prepped the lower side hinges and riveted them to the cowl with some West Systems G/Flex epoxy which will stay more flexible than their 105 epoxy.



I used some AN426A rivets to avoid crushing the fiberglass.  This is very slightly recessed from the side of the fuselage, but that's perfect because I'm going to add a layer of lightweight cloth over these rivets and then a coat of dry micro so that it can be sanded perfectly flush with the fuselage.



I also made a really rough cut in the side of the cowl to insert the hinge pins that attach the sides of the cowl together.



Here's a wider shot to show where these pins stick through.



I riveted the side hinges on the upper cowl this afternoon.  Like all of the hinges that are riveted to the cowl, these are additionally secured with epoxy.



Here's the other side of that rough cut in the side.  The oval mark is the approximate outline of the covers that will secure (and hide) the end of the hinge pin.  All of that part of the cowl will be cut away, so it didn't matter that this was such a gross cut.



Here is one of the hinge pin covers.  These are made by Aerosport Products and they're really nicely machined.  They come with a set of blanks that are slightly oversized to use when modifying the cowl to provide clearance for paint.  These will look great when everything is completed.



I spent an hour or so tonight prepping the firewall hinge on the upper cowl.  Because of the tight curvature of the cowl in this area, the hinge eyelets bind together.  This wasn't a problem when fitting the hinge initially, but it has to be corrected before the hinge is riveted to the cowl.  I filed bevels in each eyelet in the region of the hinge with the tight curvature.



Here you can see that the bevels provide clearance between the eyelets.  I only did this to the forward half of the hinge, and only in the last foot or so on each end.



Up until now, I've been using some 0.120" aluminum hinge pins to keep the hinge halves aligned during the cowl fitting process, but these have to be replaced with stainless steel to provide the necessary strength when flying.  Van's recommends using 0.090" stainless steel pins to make it easier to insert them because of the tight curvature, but other builders have complained that this makes for a sloppy fit and that you can make the 0.120" stainless steel pins work if you bend them right.  I cut some hinge pin stock to length and spent 30 minutes or so getting the curvature right so that it essentially follows the curvature of the firewall without any force on it.  I then sharpened the end of the pin so that is won't get hung up on the edges of any eyelets.  After putting the bends in the ends of the pins as shown here, it was pretty easy to slide them in and out.  I need to fabricate a little clip on the firewall to retain them and keep them from sliding out in flight, but that should be pretty straight forward.



Diagnosing Servo Wiring Issue

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Since upgrading to SkyView 4.0, the SkyView system can't see my pitch servo.  4.0 added support for the secondary bus, and a number of people have seen errors after upgrading due to wiring errors.  Although I wasn't seeing any alerts about wiring errors, members of the Dynon forums suggested I double check the wiring anyway.  I spent a couple of hours tonight checking continuity between all the wires and verifying the servos had a good power and ground connection.  All my wiring looks good, so I'm not sure what the problem is yet.
I spent a little more time tonight trying to diagnose the servo issue without any luck.  I put that aside and decided to to fabricate a clip to keep the upper cowl to firewall hinge pins from sliding out.  It's just a simple piece of 1/16" angle with one leg cut down and some notches filed in each end.



The hinge pins need a few bends to make them run parallel to the firewall and to provide a handle to use to pop these pins in and out of the retaining clip.



Riveted Top Cowl Hinge

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Now that the upper cowl hinge pin retaining clip is finished, I can go ahead and rivet the hinge to the cowl.  I mixed up some epoxy and flox and riveted the hinge on.  It ends up taking way more time to clean up all the excess epoxy after doing this than the actual riveting.  Any excess epoxy in between the eyelets will prevent the two hinge halves from nesting together, so it's important to get it all out before the epoxy cures or I'll have to grind it out later.



I've been mulling over how to retain the hinge pin for the vertical hinges that hold the lower cowl to the firewall.  I wanted something that is very secure, but easy to remove without tools.  After sdome fiddling around, I stumbled on a solution that I really like.  I mounted a K2000-06 nutplate part way down the hinge with a couple of AD rivets (I used AD instead of A for the extra strength).  I then bent the hinge pin so that there is a depression where the spring normally sits.  The spring doesn't look like it's stretched much, but this is a very stiff spring and requires a fairly good pull to get over the end of the hinge pin.  I ran an AN507 screw into the nutplate backward and just tighten it down against the hinge (there isn't a hole there because I didn't want the screw to show on the outside of the cowl).

I'm super happy with this.  It's very light, easy to install and remove, but can't possibly vibrate loose.  And if the spring ever breaks, it will be easy to replace.



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This page is an archive of entries from September 2012 listed from newest to oldest.

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