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Whats Been Bugging Gil?

September 15, 2013

I mentioned in the last post that I had a task that was really bugging me.  Well I finally figured it out this AM and all is right in the world.

Back in the early Spring, on a drizzly and chilly day I attended my local EAA Chapter meeting at the XNA airport.  It was tower tour day.  While there I saw Al and Brenda Smith of Neosho Missouri.  They had driven down and we sat and talked about all things RV.  They built an RV6, the old RV6, the one that wasn’t pre-drilled.  They have more recently built an RV-12 which they flew to Oshkosh this year.  While we talked they found that I was getting started on my fuselage.  I had a bunch of questions which they were good enough to answer.  They also offered up their rotisserie.  I thanked them for the offer but told them I was months away from needing that.

What is this Rotisserie of Which You Speak?

An RV rotisserie is a contraption used to turn an RV over on its longitudinal axis.  Once you mount the RV on the rotisserie you can roll it into any position you want so that you can work on it.  I wondered if I really needed one, though.  When I got close to the time where I was going to roll the canoe I decided that having a rotisserie was really a good idea.  Having to re-position the RV on sawhorses required a logistical effort, and frankly the sawhorses seemed to be straining to hold everything up. They were cheap plastic ones from Lowes.  With a rotisserie just up the road waiting for me I decided to take them up on their offer.

I traded a few emails with Al and arranged to meet them at the hanger Saturday before last.  My son and I piled into the 4-Runner and made the 60-minute drive to Neosho airport.  Their hangar is pretty big.  They rent space to 2 other people.  There are 2 identical Zeniths and a C-182 sharing the hanger with their RV-6 and RV-12.  When we got there Brenda had the front wheel and leg fairings removed and was cleaning them after doing some repairs to the brakes.  They also told me that the RV6 was going to be for sale soon.  Its going to makes someone a nice plane.  It was built about 15 years ago and has been well cared for and used.

Their hangar is what many long time pilot hangars look like.  Memorabilia from places they’ve  flown, the smell of AV gas and oil, Old furniture off to the side to sit and visit on.  There are racks with containers of parts and tools, hardware and electronics. Of course there is order to the bins, but if you aren’t the Smiths then it wont make sense.  Some of the parts are new, some are used.  Some of the used ones are still perfectly serviceable and some are broken, examples to be used for some upcoming project.

The rotisserie had been pulled out and dusted off.  It sat there waiting for me.  Driving up there I wasn’t sure they would fit in the rear of the 4-Runner, looking at them I knew they would fit just fine.  They seemed very simple in design and shouldn’t be any problem getting them to work.

This is where there should be a picture, but I cannot find the one I need.  😦

I loaded them into the rear of the truck and we said our thank yous and goodbyes and headed back to Bentonville.  When I got them home I sized them up and everything seemed pretty clear, at the time.  But I wasn’t paying that close attention, because it would bedevil me going forward.

When the canoe was done and flipped I started to return my attention to the rotisserie because I knew it wouldn’t be much longer before I was going to have to get it mounted.  Thats when I noticed a problem.  The front part of the rotisserie was not complex at all.  Four bolts that go into the same position as the motor mount bolts.  It would be hard to mess that up.  But the rear mount is what really baffled me.

If you look at an RV profile and you draw a straight line from the bottom of the spinner to the tail, you’ll notice that the line come out under the tail.  It doesn’t come through the tail.  The designer of this rotisserie must have gone through some serious trial and error to get it working.  Look at this picture.  The black arrow points to the bolt on the aft mount that rotates.  The steel rectangular tubing attached to it rotates around this bolt.

2013-09-15 14.42.10edit

What bugged me was I could not figure out where to drill holes in that aft bulkhead to accommodate the two bolts a the green arrow so that it would rotate smoothly around the bolt at the black arrow without flipping the whole thing over.   If I drilled them too high then it might tip over going upside down.  If I drilled them too low it could tip it going rightside up.  I also had to worry that any holes I drilled where going to interfere with something coming later.  Would the hole impeach the integrity of the bulkhead?  I just didn’t know the answer to these questions.  I drew diagrams on a white board, I mocked up one solution after another and none of them would work.  I had asked Al about it, but it was 15-years ago when they’d used this and he and Brenda couldn’t remember any detail about it.  One thing I knew for sure.  I wasn’t going to drill anything until i was happy with what was going on.

Arriving at the Solution

I started out with one main idea.  The designer must have wanted the plane to be level while upright.  Why make this assumption, you may ask?  Why not, I’d answer.  I have to start somewhere.  I measured the height of the roatating bearing on the forward and aft parts of the rotisserie and came up with 37″ as the height.  From this point I decided to start with the front mount and work from there, hoping that inspiration would come eventually.

The hardware that came with the front rotisserie needed only slight modification.  One hole was not in a good spot on the bracket so I re-drilled it.

Green arrow is where 37

Green arrow is where 37″ was measured and grey arrow is where I had to redrill the hole.

As you can see there isn’t much to wonder at here.  Bolt the two pieces of angle aluminum to the firewall and bolt it to the frame.  Done.  From here I used my sawhorses to position the rest of the plane level, then I went to the back and started looking at that bulkhead with the rotisserie up against it.  A glimmer of an idea started forming.

Exit for the tail wheel.

Exit for the tail wheel.

This is an older picture, but it shows what I was looking at.  If you open this picture you will see just above the hole where the tail wheel spring goes a single machining hole.  One of the bolts in the rotisserie was lined up with this hole perfectly.  Ah ha…my glimmer of an idea was starting to glow.   One thing that I know about this bulkhead is that it is where the vertical stabilizer will mount on the plane.  Drilling holes just anywhere is a bad idea.  I starting looking for the plans for the VS so I could see if there was any inspiration there.  That is where I found my glowing idea was now burning white hot.  That machining hole, ultimately, will be one of the the holes used to secure the VS to the tail.  Drilling it out to 1/4″ is inevitable.  Of course there is one other hole that needs to be drilled into the bulkhead.  I measured and found that it was going to interfere with nothing.  I also need the hole eventually; I have to pass a wire back to the rudder for one of the running lights.  Viola.  It all came together in my mind and made sense.  Now I was ready to drill.  It mounted just fine and works beautifully.

2013-09-15 14.05.55

This is what it’s all about.  Attacking a problem and muddling through it.  Not giving up until the problem is solved and it all works.  Now I can go to work this week and not be unhappy because I left this task undone.

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