Attaching lines to bellcranks

[bill bischoff]

Here is some info on how I will be connecting the lines on my new profile Crusader. I will be attaching the lines directly to the bellcrank. I do this primarily to eliminate the chance of line connectors getting fouled, plus it eliminates a bit of drag.

The line ends are constructed in the usual manner. The eyelets I used are Brodak BH321 large thimbles (eyelets). They match perfectly with the DuBro #135 4-40 blind nuts which serve as the line attachment buttons. The other key ingredient is 4-40x1/4" button head cap screws. I used Associated RC car hardware, # ASC6288. Button head screws were chosen for their low head profile to eliminate interference.

First, drill and tap the leadout holes in the bellcrank 4-40. Then, install the screws. Be sure to use Loctite. Next, thread a blind nut onto a long 4-40 bolt (to use as a handle). screw a regular 4-40 hex nut down on top of the blind nut, and "jam nut" them together so they don't move. With a Dremel and cutoff wheel, file the round flange of the blind nut down to match the hex nut. The idea is to create a blind nut with a hex flange that can be tightened with a 1/4" nut driver. Repeat two more times. The lines should be free swiveling when the blind nuts are tightened down over them. If necessary, lightly sand the thickness of the eyelets, or enlarge the holes slightly. I did not find this to be necessary. Color code everything with a dab of paint and you should be done.

My intent is to remove the lines after the day's flying. I am not concerned about the nuts coming loose. If you are worried, a drop of 5 minute epoxy on the threads during assembly should get you through the day. For a more permanent installation, use Loctite.

My apologies to Eric Conley if I stole his idea. I know he does something like this, but I don't remember the exact details.

[Wayne J. Buran]

Nice Job bill. Thanks for the detail pics.
Wayne

[john e. holliday]

Another fine job by Bill.   I now have it all printed off for use.  Now I just need to get out and practice.

[Bob Reeves]

You sure did a nice job of grinding a hex head on those blind nuts. 

[eric david conley]

     Hi Bill, you certainly don't owe me any apologies. Actually I owe you many thanks for what I have learned form you over the years that I have flown carrier. As has been the case for me I have gotten almost all of my ideas from you and this is just one of many that I use. As far as the few things that I have dreamed up and started to use in some of my carrier planes I soon found out that you had already done much of them and either discarded them or improved them well beyond where I was at. I think that one of the biggest reason I use so much of your ideas is that you were so good about printing the things that you were doing in carrier in the NCS news letter. Plus you have a gift of explaining thing very clearly in just a few words.
     I did change one thing with the BC and that was to use 2/56 bolts and blind nuts to attach the flying lines. I felt that they were plenty strong (as compared to the control lines) and they didn't take up quite as much room. Eric

[Wayne J. Buran]

Bill, what did your pushrod set up look like on this application.
Thanks
Wayne

[bill bischoff]

Go to the "What are you building for 2012..." thread, reply #57, picture #2. It's some detail shots of my Hellcat. I am using a Dubro 4-40 ball link on a 4-40 threaded pushrod. I use the standard duty ball link, but if you don't trust it they also make a beefier heavy duty version. I use a solder clevis at the elevator, since the ball link gives me the necessary adjustment capability. Plus, I have seen the solder-on threaded couplers fail at the end of the threads, so I try to avoid those. The ball link allows full swiveling, unlike a clevis or a Z-bend.

I tap the bellcrank for the screw that holds the ball link, just as I do for the line buttons. Once the screw is installed with Loctite, you can take the lock nut off to adjust the ball link without having to hold the head of the screw. I use a button head screw for this, just like I do for the line buttons, to avoid clearance/ interference problems.

Try it out. It works great for me!

[Wayne J. Buran]

I thought that was so but I wanted to make sure. I assume you did that for clearance as that is the problem I ran into when I started duplicating your set up for the lines. So all three lines come out equal and what line length do you shoot for. Thanks for the help Bill.
Wayne

[bill bischoff]

Since I don't use leadouts, the throttle line will be several inches longer than the elevation lines. When I tie the lines, I shoot for a handle to fuselage length of 60' 1". I usually make lines for each airplane, and make them on the airplane. I make up the airplane ends at home, then make the other end at the field. I make the up line first, and this establishes the overall length. Then I make the down line, which establishes the neutral position of the handle and elevator. The throttle line is last, and requires a bit of fiddling and trial and error to get full bellcrank movement. Definitely a two person job. When making the end, I start a few wraps of copper wire to hold everything in place, but I can make minor adjustments to the length by pulling the line through the wraps one way or the other. Once it's right, I'll finish the wraps. Most of the time I can be accurate enough that I can use the same size line clips on all three lines.

One thing that I have found to be extremely helpful is to pre-stretch the wire before making up the lines. Due to the way stranded lines are made, there is a bit of elongation when they first have a load applied. This is enough to mess up your precise line lengths. I initially cut my wire to about 62', and with a helper, give each piece a good tug before making up the ends. The bit of extra length gives something to wrap around a rod or screwdriver handle for pulling.

[Wayne J. Buran]

Bill,
Thanks
Wayne