Control Cable Brackets

I've single handedly kept FedEx in business these last few months.  Every turn I take, I end up having to order some random piece of hardware or a part that I didn't know I needed.  It's sure slowed progress down.  I know I still have a few custom fuel hoses to order, but I think I'm coming close to having all of the other random stuff sorted out so I can finally finish up the FWF work soon.

I don't have a picture to show for it, but I did finally put new studs in for the backup alternator.  I did a lot of measuring and determined that the length I needed for studs was slightly different than the studs B&C specs for the alternator extension.  They assume a 3/4" stud penetration into the case, but the studs on my Titan only go in 1/2" (they can't go in further otherwise they'd hit the accessory gears).  That 1/4" difference meant I didn't need the $150 studs!  It took a while, but I finally found a shop in Florida who had the shorter Lycoming studs.  The good news is these are much more common and were only $18 a piece!  I received those last week and got them put in.  At first I was concerned because they went in so easy, but the Lycoming manual specifies that they only need to go in with a minimum torque of 15 in/lbs, which isn't much!  I have not put the alternator in yet.  Once I do it's going to get much tighter and harder to work on the throttle/mixture cables, so I'm going to leave the alternator out until I'm done with everything else.

Last time I got the firewall holes for the throttle and mixture cable started but wasn't able to finish them without a bigger unibit.  Amazon to the rescue!  I opened up the holes with my new unibit and mounted the eyeball passthroughs.  I say that like it was easy, but it took an entire day - just incredibly awkward location, as well as the pain of drilling through not only the stainless firewall but also the stainless sheet that overlays the insulation on the forward side.  Because of the insulation, the screws that came with the passthroughs were too short, so once again I had to order a tiny packet of very specific sized screws.  Thankfully, for most stuff like this I can just use hardware I can order on Amazon.  These screws aren't structural and just have to pinch the eyeball in the mount to set the angle. I took the opportunity and swapped out the phillips screws for allen head instead (the head is on the firewall side).  I figured that would be far easier to deal with than trying to get a screwdriver in there down the road.

For  now I just left the passthroughs loose.  I'll tighten them up once I've solidified the cable length and routing.  One additional passthrough I am still going to have to deal with at some point is the oil cooler shutter cable.  I'm just going to go with the Van's standard for that though.  It's a simple push/pull cable, and the Van's approach is to just drill a small hole in the firewall, slip a grommet in it to protect the cable, then fill around it with fire barrier sealant.

The next step for the cables is a monster - figuring out how to mount the rigid portion (that stays stationary and allows the retraction of the inner cable) to the mount bracket of the throttle body.  I knew that the standard cable bracket from Van's wouldn't work with my engine, so I had already purchased the bracket setup made by the company that makes the throttle body.  Even this isn't a slam dunk though.  It's really just a base to build off of.

The cables I got from McFarlane are a little bit different in measurement than the standard Van's cables.  The length between the portion of the cable that is attached at the bracket to the end is a couple of inches longer than the Van's cables.  That just means that the attachment needs to be pushed further aft in order to get the same throw.  I could have gotten the same short length as Van's by custom order from McFarlane, but that of course came with an incredible price increase.  Since they had a standard cable with an overall length (48") that was close enough to what I needed, I decided to save the money and just modify the bracket vs get a custom made cable.  Because of the new style nose gear that Van's uses now, the bracket has to be modified regardless to allow the cables to wind around the engine mount.  The company hasn't changed the design of the bracket to accommodate the new engine mount with the elastomer nose gear.

I think I installed and removed the bracket and throttle body a good 20-30 times while figuring out how to design a solution.  Here's what I ended up with:

On the throttle side, the slotted bracket (seen to the right - looks like a lego in the picture) that captures the cable had to go aft and in in order to hold the cable in the right position to clear the engine mount.  I initially thought it needed to come in about 3/8" from the main bracket body, so I made a sandwich of aluminum to essentially extend the body of the bracket aft and bump it in the 3/8".  In the end, the 3/8" was more than necessary, so got rid of the second layer.

That's very hard to explain, so hopefully this picture makes more sense.  There's nothing pretty about it, but the angles and location of the slotted bracket have to be very specific.  Without making an entirely new main bracket body, I'm left with doing the Frankenstein approach.

This is one of the 30 test fits.  I'll probably need to put an adel clamp on the engine mount where the cable passes by just to ensure it doesn't rub.  It doesn't touch right now, but it's fairly close.  I made sure to set the slotted bracket at a distance that allows me to get full throttle throw with about 1/8"+ of extra room at the control knob.  So the throttle will reach full forward before I bottom out at the panel.

I'll spare the details of the mixture side.  It was the same story of off and on testing to get everything in the right place.  The difference on this side is that the slotted bracket works best in a different orientation.  The throttle and mixture controls at the throttle body are not symmetrical - on the throttle side the cable is on the outside of the main bracket body, but on the mixture side it's on the inside. Putting the slotted bracket in the same orientation as the throttle side would send the cable right into part of the engine mount.  I bolted a piece of aluminum angle onto the main body, which allowed me to get the slotted bracket pushed aft and in and allow it to clear the engine mount by holding the cable from underneath.

Bottom Cowl & Control Cables

Little by little.  That's the name of the game these days.  I've spent the last few weeks working on cars, so not much time left for the plane.  This past week I chipped away at the lower cowl fit.  It's a bit tougher to deal with by myself than the top cowl has been - gravity always seems to win and makes getting it set into place hard.  It's a lot bigger than it looks in pictures!  I got it set against the fuselage and used the same method for trimming as I did the top.  I drew a line 2" aft of the firewall and then transferred that to the cowl.

The instructions say to just do the bottom portion for starters, but stop before going up the sides.  The idea is to make it match up with the bottom firewall first so you can then always get it into a predictable position before cutting the sides.  I trimmed the bottom, but was definitely conservative.  I'm going to have to do the off and on thing a hundred times to get it right, just like the top. Given how hard that is, I'll probably wait until I have some help.

Shifting gears - I finally received a couple of things I've been waiting on for a long time - the extension kit for the backup alternator and the firewall penetration steel grommets for the throttle/mixture cables.  I bought the grommets because the routing I decided to use for the cables makes them take a big turn through the firewall and the grommets help support them (the grommets are basically a split steel ball that clamps around the cable and can hold them in position).  I pulled the forward top skin off the fuselage so I could get at the aft side of the firewall for drilling.  This would have been nice to do eons ago before the engine was even on, but not knowing where everything would end up going, I didn't want to drill a bunch of holes in the wrong places.

You can see the holes I started below the top firewall stiffener.  I am putting the passthroughs in the angled portion of the inset of the firewall.  Drilling through thin stainless steel is always loads of fun!  I got the screw holes drilled, but my unibit isn't large enough for the center hole.  Guess I need another tool!

This is what I have to show for the next 6 hours of work.  Not much!  Figuring out the exact cable routing took a lot of head scratching.  The cables I got are beautifully made (McFarlane), but as is the norm these days, they won't fit without making some modifications.  The routing for the mixture is going to take it right into the vertical exhaust support.  I decided the best plan of attack was to swap the exhaust support to the other side of the cable bracket (the big, gold bracket).  I moved it from the inside to the outside.  In doing so, I had to make a longer steel tube and a longer rubber hose because now the support has to attach to a different sump bolt.  It's not ideal, because it changes the angle of the support so it's less vertical than it was before, but there's not much else I can do.  I think it should still keep the exhaust from moving vertically.  

The cable bracket has to be modified a little, so I pulled it and the throttle body off and did some surgery on it.  I'm sure after another 6 hours I'll have a single bolt in.

I thought I was going to get the alternator put in, but surprise surprise, I ran into an issue with the studs.  I had been told I could use normal 1/4-20 bolts cut off to make studs, so I bought some and went that route.  Nope.  They thread in with finger pressure alone.  Not exactly what they should be doing!  It turns out the standard Lycoming studs are indeed 1/4-20, but the threads on the end that go into the case are a slightly different shape, even though the pitch and diameter are the same.  That slight difference makes them fit much, much tighter. So in the end, I really need the Lycoming studs to get a good fit.  Back to the waiting game!