Flew the Coupe! – Part 12C – Belt yourself in, this could get rough!

One of the things Woodstock lacked was shoulder harnesses.  Since the plane was apart I know this was a great opportunity to add in a new belt system.  Several of my friends have added great shoulder harness systems to their planes.  Surely adding belts to an Ercoupe should be simple.  No, it turns out not so much.  There are some options but the original Ercoupe was not designed to include mounting points for shoulder harnesses.  After a lot of using the google I found there were two possibilities.  One solution was to use the design and paperwork other coupe owners had provided to the coupe community via the owners club.  This solution looked great.  It added some brackets to the rear fuselage tail cone bulkheads.  The use some steal threaded rod to tie the structures together and finish the end of the rod to attach an inertia reel shoulder harness system.  I liked a lot about this solution.  It also allowed the use of a “Y” harness that held both shoulders.  This I believe to be a lot better than the single cross over shoulder belt we have in most cars.  I was sent some pictures by a few folks that had this belt system.  It looked good but the down side was:

  • I would have to collect all the parts
  • I would have to fabricate a number of brackets
  • I believe riveting would be required
  • I’d have more work to create the paperwork for the FAA
  • The  cost of the recommended belts alone was nearly $700

Here is what that system looks like:

thumbnail_Shoulder Harness Attachment


There was another system some folks had used that consisted of some other fabricated brackets that involved riveting a major new doubler to the skins internal to the tail cone.  This system would require a lot of riveting that would all be visible from outside of the airplane.  Since I am very proud of Woodstocks unblemished polished skins I did not want to a lot of drilling and riveting through them!

Here is what that system looks like:


So what other options where there?  Well a company called Alpha aviation offers a kit with everything you need!  They were very friendly when I called them up to ask about it and that seemed like the quick path to shoulder harness safety and nirvana!  Regular readers of my blog will already be able to detect the I am clearly showing the signs of early onset airplane ownership dementia!   NOTHING with an airplane is quick except for the reduction of your bank balance!

So I ordered the Alpha kit.  What I go was some pre-cut and bent aluminum to fabricate some brackets.  New belts.  A bunch of fasteners.  Instructions and the paperwork to file with the FAA to make this an approved field modification. Excellent!  How hard could this be!  This blog entry will be sharing the experience and the results.  So I spent a number of evenings studying the instructions and the parts.  I made an immediate decision.  The kit included rivets for part of the installation of the bracket into the plane.  I don’t rivet or do I own any of the tools to do that.  Also that looked like a two person job.  I’ve got friends that have built metal airplanes and I have watched them rivet things together.  You can learn to do it for sure, but I wasn’t interested at thus point to add that skill to my talents.  Also I believe to do it right you need a good compressed air source and a rivet gun.  That wasn’t practical.  I looked at alternatives.  I could consider a blind or pulled rivet.  Those are regularly used in aircraft construction.  They aren’t particularly attractive.   Wait, what about screws and locking nuts?  So I went to research the relative strength of fasteners to see what would be the result of that substitution.  A little research showed there could be concerns related to shear as the threads of a bolt make them more subject to failures in shear.  Hmm.  Well I would going to be using 6/32 stainless steel screws and in fact the brackets were already going to be constructed using that very same bolt.  Examination of the calculations for the force the system is designed to withstand showed the fuselage skins and bulkeads would fail far earlier than the fasteners.  Screws it is!  In fact the Ercoupe has lots of 6/32 screws in its assembly.  Here is a picture of some of those fasteners on my Ercoupe:


So two things about that picture.  That is NOT corrosion.  That is old polish and grime around the screws.  Also those are the original flat screws.  They are EVIL.  They have a very narrow slot that normal screw drivers do not seem to fit.  I have replaced all of these with new Phillips head screws!  Much nicer to work with. 🙂

Step one of the installation is to fabricate the brackets.  You are given two preformed pieces per side.  You must drill them out to then bolt them together.  One of the pieces is a re-enforcement and the other serves as the actual harness attachment point,  I decided to ask a friend to let me use his workshop.  He had a drill press I thought would make this go easier.  It did help although you could do this step with a hand drill and a good vice.  Extra care should be taken when drilling the holes in the bracket to be used to attach the bracket to the skin as the hole spacing will be visible from outside of the plane.  Note to future self, when you crack time travel, go back and make yourself pay more attention to drilling those holes!

It took about a long hour to get the brackets built to go into the plane.  I spent some time talking over the next step with my friend OIan.  It looked like getting a drill back into position to drill the mounting holes in the airplane was going to be a challenge.  Maybe a 90 degree drill or in this case Olan lent me a flexible drive that could be fit to a normal drill.  So it was off to the hangar to install the brackets!  Wait, I forgot.  The Alpha kit was originally designed to be fitted to an Ercoupe that had the extended baggage compartment and that requires the removal of the stock rear “hat shelf”.    Arg!  How would I route the harnesses?  I would have to cut a pair of holes in my rear shelf.  I called up Alpha and they said that was the correct thing to do but didn’t have any other details.  I spent some time looking my shelf and realized I really didn’t want to cut a piece of the plane that had been put in it back in 1946.  I don’t know why i mattered to meme but I found I’d rather not.  So I called up Univar,  the current owner of the Ercoupe design and they told me they not only had new ones but they were about $70!  A bargain!!  So I got one of those on order right away!

Here are some pictures of the bracket installation:

Note that one of the pictures shows the bolt heads outside the airplane.  You can see the brackets are attached to the major stringer that runs along the fuselage side.  These should be very secure.  I realize I jumped ahead again.  I needed to remove that rear shelf.  I also decided to totally remove the baggage sack and seat rear cushion,  All easy except the shelf.  That is a two person job.  There is an 8/32 screw on each side that needs someone inside the plane with a wrench on the nut and someone outside with a screw driver.  So I had some scheduling set backs to get a time when I could get my friend Olan out to help with that.   But I got it out and got those brackets mounted.  So I attached to shoulder strap to the brackets and sat in the seat to see if I could figure out how the new shelf would need to be trimmed to clear the belts.  Again since I was working alone I tried to snap a picture to get some idea where things needed to be cut.  Here is the fitting the belt picture:


Using the insanely scientific method of “that looks right” I marked the new rear shelf that had arrived and headed to Olan’s to use his saw to cut the panel.  Here is the panel with the cut outs:

So the panel was cut.  A note about the panel.  It came “painted” but poorly.  I stripped it and then added a couple of coats a epoxy grey.  I also bought some rubber channel to use to prevent the harness chaffing om the metal.  So all I needed to do now was put it all back together.  I decided the next step would be to finish installing the new belts.  The end of the shoulder harness was bolted to the bracket with a shouldered bolt and a bushing.  That went together very easily.  So now all I had to do was swap the belts and I’d soon be flying!  Woot!

Wrong!  The original seat belts used a totally different way to attach.  The used a system called a “three bar slider”.  It turns out that in the late 70’s the FAA increased the failure requirements for aircraft seat belts in new airplanes.  They did not mandate retrofitting early planes but the manufacturers soon learned the the majority of the belts they sold would need a different attach system.  So support for belts using the three bar system dried up.  Alpha had taken the easy route and just designed the kit to use a newer belt.  But for me I would need to cut out my old mounts to use the new belts!  Grrrr!  So I called up Alpha and they apologized and immediately sent me the missing hardware (a couple of more bolts and bushings).  In the mean time I called the actual belt manufacturer to see if they offered a belt system I could use that still had the three bar attachment.  Well, they probably did but they weren’t sure.  So no joy there.  In fact they referred me to their dealer “Alpha”!  I would cut out the old pieces.  Well more correctly again my friend Olan to the rescue.  He had an angle cutter he thought would make short work of the job,  I needed to cut out two steel triangles and two large steel plates.  Here is a picture of Olan cutting out the old pieces!  Needless to day I covered a lot of things with a wet towel and had the fire extinguisher out!


Here is the old hardware we cur out:\

IMG_20170610_150932467 (1)

And here is the new hardware Alpha sent out.  Note this is now included in the kit:

Here are the old belts:


and the very nice new belts:

So now the belts could be easily finished.  I needed to slightly ream the hole on the old bracket to accommodate the new bolt and then the other ends of the belts just snapped to the existing center hoop.

So with the whole system in I could refit the rear shelf and replace all the rest of the interior.  But I had shoulder harnesses!  Woodstock was one step closer to flying again!  At this point I owe a thank you to Alpha Aviation and my friend Olan.

In the next blog entry I’ll share the adventure of replacing the baggage sack and wrapping it all up.  Till then fly safe!


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