Engine Controls
July 1994
Note, this article was prompted by the untimely death of Wes and Millie Gardner, when the throttle linkage in their aircraft malfunctioned.
We have talked about this subject several times over the years yet many builders continue to do less than their best work in this area. Pay close attention, Guys: Your ability to control your engine is second only to your ability to control your airplane. You do your very best work on the pitch, roll and yaw control system and you should do the same for the throttle and mixture controls. Before you do your first flight, and at regular intervals thereafter, get someone to help you check that the throttle and mixture controls do, indeed, move the appropriate range to the full throttle/full rich positions and also to the idle/cut-off positions without the use of any helper springs. If you cannot get the throttle and mixture controls to work satisfactorily without springs, consider going to push/pull cables.
I realize this is a hassle, but not nearly as much of a hassle as losing control of your engine at a critical time. I installed a push/pull throttle cable when I installed an Ellison throttle body almost 1200 hours ago. (This is a mandatory requirement when you install an Ellison and not a bad idea for any carburetor). carefully measured to determine the exact length required, then ordered a custom-made aircraft push/pull cable from Aircraft Spruce. I removed the throttle lever from the Brock throttle quadrant and scribed around it onto a piece of 1/16" thick 2024-T3 aluminum, adding about 2-1/2 inches to the bottom of the throttle lever. This was band sawed out and de-burred.
A small rod end, screwed and jam-nutted to the push/pull cable end, bolts to this lower end of the new throttle lever. The outer cable is secured to a bracket mounted on the inside of the left arm rest (I used a "u" bolt located in the grove machined in the end of the outer cable). At the engine end, the outer cable fits perfectly into a bracket mounted on the Ellison throttle body (provided by Ellison) and the cable end has an aircraft-type ball and socket. The "ball" bolts onto the throttle lever and the "socket" it screws onto, and is jam-nutted to, the cable end. The "socket" fits onto the "ball" and is held securely in place by a threaded insert that can be tightened onto the ball and is safetied with a cotter pin. Exactly the same system can be used for the mixture control.
There are many acceptable ways to obtain reliable engine controls. Just be certain in your own mind that what you have installed is fully functional and safetied so that it cannot possibly come undone or separate in some way. Have other builders or an A&P look at your work, the more pairs of eyes that check your system, the less likely you are to have a failure and a failure in this area is not acceptable and will almost certainly result in, at least, a forced landing. Never forget that!