Control Cables

The control cables are a basic function of any engine really.  With a constant speed prop I have essentially three cables similar to whats depicted in the plans; throttle, prop, mixture.  What varies on my set up is the routing, mounting and lengths.  The main culprits are my tunnel mounted throttle quadrant, forward facing fuel servo and the air conditioning system. Each of these changes the cable lengths and in the case of the mixture the mounting bracket.

For the cables I went with California Push-Pull based on a number of referrals.  Here are some basic things I learned about control cables.  The point where the cable is hard mounted to a structure is called the 'bulkhead'.  Then there is the 'throw' which is the distance the threaded ends will move.  In my case and most other builders I picked a 2.25" throw.  Meaning the two working ends will essentially shift back and forth that much once connected to whatever you're connecting it to.  That throw will give you another measurement between the bulkhead and the swivel support tube to include the threaded end at mid-travel.... All clear??  Wasn't for me even after reviewing the measuring guide.

Some items I had to mentally digest was that whatever your cabin side bulkhead to mid-travel threaded end measurement was should be somewhat similar on the working side. So on a 2.25" throw cable you couldn't have the cabin side be 6" and the throttle side be 10".  Unless maybe if you start threading extensions on at one end.  Also not every item has the same move distance on the working end.  For me the throttle matched my lever movement, but prop and mixture were about half. From a working perspective pushing full forward on all three levers results in full throttle, full props and full rich on the mixture.  If I pulled everything back the throttle comes all the way back but the prop and mixture level stop just over halfway but they're at their limits.

Full Throttle, Props, Mixture

All Back

The last item deals with the measurements, after all my conversations with David at Push-Pull I thought the measurement for length was bulkhead to bulkhead, but it's from threaded tip to threaded tip.  I spend A LOT of time doing the measurements, double and triple checking so I was surprised that my cables were about 10" too short when trying to install them. Realizing the mistake I talked to David and ordered a new set.  The good news is I talked to my buddy Mike who's building an RV-10 and he's going to be able to use them, but they'll have to be shortened first.  My final 'new' cable lengths are-

176-vtt-2.25 93"

176-vtt-2.25 72"

176-vtt-2.25 74"

With my new cables they were able to be installed and were spot on for length. It takes some tweaking but I was able to get the new ones installed and routed fairly easy.  Given these are thicker diameter than stock Vans ones I had to do some drilling out on my pass-throughs, brackets and used bigger adel clips.

Speaking of brackets I did have to make a new bracket to mount the Mixture cable.  The stock would have had it something like 14" back and adding a bunch of threaded extensions doesn't sound like a good idea.  I had previously worked up a bracket that mounted on the bottom of the sump but that really didn't work out.  This bracket made the bulkhead within 2" of the rod end, which was an issue after learning the above.  I decided to wait until I got my new cables and then retroactively work through a bracket. Now if you're really good at steel work then you should try and do something like Larry did on his fantastic build shown here.  He came up with a steel bracket that replaces the stock bracket that mounts on the bottom of the sump and ends up moving throttle and mixture to a single side.  Given I had an issue with even understanding how these cables work I decided to utilize the stock bracket and fabricate something just for the mixture.

I ended up not fabricating anything but rather re-purposing an already powder coated steel hinge.  It's original intent was to be installed in the wing, which I had done, however replaced it with the servo bracket so had it just laying around. I went through several ideas but decided to just keep it as simple as possible and make some bigger holes in it and hang it off one of the elbow screws off the bottom of the sump. Hard to really see it in the picture but I had to slightly bend it to accommodate an upward angle.  The back of the piece also prevents any serious movement as well.  Maybe I'll do some safety wire just in case.

Here are several other pictures showing the Prop and Throttle runs and how I have them aligned.  Because of the AC the prop run has to go over the engine and with the forward mounted fuel servo had to reclock the throttle a bit.  All seems to work out though.

Last picture might be a hard to see, but the lines follow a fairly solid path to the per plans firewall breaks.  Like with all these firewall penetrations I used some 3M fire barrier to fill in the gaps.