• Troy Newman's Elevator Setup
  
  
• Engines used @ 2001 F3A WC
  
  
• Futaba new FF9
  
  
• Various YS 140 Engine Mounts
  
  
• YS 140 DZ
  

• Introduction
• Cable, Pull-Pull Analysis
• MK BellCrank Analysis
• Alternative Method - Troy's favoured approach
• Initial Setup
• Servo and Elevator Connections
• Servo Choices - JR

Troy Newman is a regular contributor to the NSRCA Publication, K-Factor, and placed tenth at the 2002 US F3A Nationals.

The following information is provided as a "How to" Article, nothing more. I am presenting it as a result of requests by other modelers to see the method. The author assumes no responsibility for any failures of the method show. I have used this method now for a long time and no failures. The installation and the attention to details are critical in the trouble free operation of this setup. In essence we are dealing with glue joints, and builder manufactured components. Its up to the builder to take every precaution he feels needed and assumes all risk of the operation. Read these instructions entirely before you dive into building this thing. There are some options given later in the directions that may fit your needs better and your choices early on will restrict you options later. I give the method I use. You can adapt this to anything you like.

In my opinion the absolute best elevator control assembly is designed to be light, strong, and allow the least amount of differential between the elevator halves. The following setup is not my design, but I have adapted a couple of different methods of mounting to insure that the best solution for me. I have done this same setup on 4 planes and just finished it on a 5th. Since 1999 I have been running this setup in F3A aircraft with hundreds of flight a year and zero failures and zero maintenance.

In comparison to this I have a couple other systems to address and why I don’t use them. I will only deal with single servo applications because I like a single servo. Any of these setups including the MK Bellcrank can be driven with 2 servos. Two servos give a weight penalty not only in the servos but the extension wire. You would be surprised at how much a 1 meter extension weighs. There is also the issue of matching the servo travels. This has become almost a non-issue with today’s digital servos. I know several top flyers using the JR 3421 digitals one on each elevator. These are great and provide a good solid connection. Since they are digital the centering and the holding power make them perfect in the dual application. I found I liked a single servo better!

Cables, Pull-Pull
First of all many people like cables it’s a pull-pull setup and its very light. Another big advantage to cables is the fact that it is infinitely adjustable. You are not limited by the 1 turn of a 2-56 thread in adjustment. If done properly the connection is solid and feel is great. The next plus for cables is the fact that you can tune all 4 travels of the elevator exactly the same throw at the end points. This can be done easily using the length of the control horns and comes out dead on.
I have not used the Kevlar type cable setups. I choose 30-40lb test nylon coated steel fishing line from the fishing shop. It comes in 30ft rolls for about $2 and the little crimpers are about the same $2 a pack. You can do many many planes with this $4 purchase. Now for a Cable type system to be effective in a model you have to make sure that the line is absolutely a straight line from servo to the control horn. This means exits in the fuse must no touch the cable and be totally free of any friction. Anything touching the cable will cause it to fray and fail. You also have control horns on top and bottom of the surface. This is pretty easy since most people choose a 6-32 bolt as the control horn. So you just leave it run through and attach top and bottom.

Cables have many good sides, but here are my downsides. It doesn’t look as clean and as neat. Function before form this is OK. Also you have to make absolutely sure the cable is no riding on anything inside the fuse like the fuse exits. This will cause the cable to fail early in its life. I have had some cable failures not many and not recently but they have failed. The key here I think is using eyelets rather than rigging couplers. The eyelets allow the cable to loop around the connection rather than kink. The kink will cause a failure. So in this case it is again not as clean and neat a setup. The tension of the cables is critical. If too tight it will “pop” into place and cause grief with your servo trying to center and also causes side loads on the servo shaft.. While too slack of a cable will cause a mushy feel. I have found that as the cable ages with the loads we apply they will stretch slightly and become loose. So another drawback is the fact that you have to keep checking them and make sure the tension stays constant.

I know how we measure cable tension in the mechanical engineering world, one way is to deflect it (push in the middle) and measure the distance it deflects. But what is a good number? The other problem is that the cable could be stretching under loads. Since there is a cable going to each of the elevators top and bottom you are stuck with 4 different cables with possible different lengths all be them small differences. You also have 4 sets of connections that are not done exactly the same in the same spots. This can affect the stretch and you can get different tensions on all 4 cables. So you can get differential in theory based on the material and the methods used to secure the cables. I want those elevators going up together no matter if I have huge loads on them or not.

This says I will bank the cables and look for better ways. I want the best solution and cables may be it for me but lets look further. Not only that, but the cleaner looks are important to me. I always have trouble getting the exit hole right on the cables, and this becomes critical. A sure fire way to make it right is to have the hole oversized. This affects the looks. Personal Preference!

MK bellcrank method
The MK bellcrank is a wonderful little device. Ball bearing sockets make the transfer of forces friction free. It works well. But you have to abide by some rules. You must use a stiff pushrod to serve the middle. I recommend CF pushrod like sold by Central Hobbies with the titanium ends. These get used for the pushrod devices both serving the middle of the MK and as the outputs to the Elevators. I choose the 5/32” rod for the output rods and the 3/16” for the input rod. This works very well. Another thing is support the input pushrod or have a very short run at it. Otherwise the loads could cause this to bend and the solid connection will not be there under large loads. At least in theory the two sides will deflect the same amount as the rod in the middle bends slightly so you should be good to go. Then you have lots of connectors.

Some guys have converted the Mk to cables pull-pull inside the fuse and pushrods outside to the elevators. This is in my opinion not the best of solutions because you have no way to watch those cables to look for wear and you are getting the same tension issues as before. Next is the device is made of plastic, however strong that maybe it does flex a little. So when using your ball links and stuff don’t use the standoffs this will make the connection have a moment arm larger and will cause the arms to flex even more. It would be a great little thing if it was aluminum but the price would be higher. Also you need to use ball bearing connectors everywhere. This insures free flow of all the connections and eliminates the friction in the system. You need a total of 6 connectors, which means using the top of the line MK stuff with the ball bearings for the best setup you have about $8 per connector for a total of $48 in connectors. Add in the price of the CF pushrods with all the titanium ends. Say it is another $25-30. Remember there are 3 separate pushrods you have to setup. This combined with the $30 for the Bellcrank itself means you have a $100 elevator setup.

Now some people choose the Fiberglass DB pushrods. They are black and some guys are convinced they are CF and they are less expensive than the Central Hobbies CF ones baby. Well I have used them in the past and the ones I have had including the black ones are not CF rather they are black colored fiberglass arrow shafts. They also weigh more than the Central Hobby stuff and not nearly as rigid. So I use them on 60 sized sport stuff. The $100 setup is a bit pricey but will work superbly if installed right. You will never feel the elevators getting differential even though when you flex them with you hands you can make differential. I guess our flight loads are lower than my greasy palms. This entire $100 setup also has a weight to it. I don’t mind weight because it’s needed for strength but have to watch for excessive weight gains. I weighed all the MK stuff including the support plates in the fuse the screws to install it and all the pushrods made up with the connectors. The weight was 4ozs this seems high to me. Now I used the MK device for a couple of years and felt it was the way to go. I had nothing better at the time so it was the best solution. But its weight was a killer and so was the price tag. So I banked it for another option.

Troy's Preferred Elevator Setup