The present Safety Code has an error in Section 9.6 which should state…Propeller tips should be painted or colored in a visible and contrasting manner so as to increase the visibility of the propeller tip arc. While the old safety code was being scanned into the computer the word 'should' was inadvertently changed to 'shall' which generated a couple of phone calls from a pilot that didn't want to paint the propeller tip of a warbird because that would be contradictory to scale. The current Safety Code will also be updated in the near future.

Flexing in any part of the linkage between a servo and it's control, and even the engine, can spell disaster and the destruction of an airplane.

One primary concern is to keep all pushrods as straight as possible. A pushrod with a bend is the weak point in the link. The bend gives the pushrod a natural place to flex. Keeping the rod straight will force the pushrod to find a weak spot to flex.

Most pushrods are also braced about every six to eight inches. This bracing doesn't have to be very bulky. It only has to support the side to side pressure of the pushrod under a pushing force. I usually make my bracing from 1/8 inch balsa. Either a wide piece of balsa with holes (slightly larger than the pushrods) drilled in it at the proper locations, or balsa strips about 5/16 inch wide (one on top and bottom of the pushrods and small strips on either side of the pushrods) glued to either the fuselage sides or cross braces. Remember that it only has to withstand the side to side pressure which is not very great. This is especially true for flexible pushrods such as the nyrod. The threaded rod used in our giant sized airplanes should be a 4-40 thread size (2-56 thread is OK for engines and smoke etc.) as a standard minimum. Most of these wires are only semi-hard and can be bent fairly easily. I know a few pilots that buy a little harder and thicker stock and cut their own threads. You would be surprised how much stiffer their pushrods are.

Clevises are usually attached to the ends of the pushrods. Nylon clevises are generally not strong enough for giant scale. Steel clevises are made of very hard and brittle spring steel. Do not over bend them while opening them up as this will weaken and even break them. There should be a nut on the back side of the clevis to lock the clevis to the thread. There is a lot of slop in a clevis that does not have a lock nut behind it. This is a good place to use Locktite to help insure vibration doesn't loosen the nut. Clevises also need a keeper to keep them from springing open from the great loads that are possible. Most common is a 3/16 inch piece of fuel tubing fitted over the closed clevis. Silicon tubing is not recommended because it breaks easily. Some clevises come with a spring that wraps around the clevis while others come with a tiny clip that attached to the pin that runs through the horn. These keepers also work fine. Other types of connectors such as a z-bend in the wire, ez lock or quick lock connectors have their place in the hobby. It is for you to decide which method works for you. Control horns come in many shapes and sizes. A person could get lost trying to decide which one to use.

All I can suggest here is to use a horn that is designed for giant sized airplanes or rated heavy duty. You can now purchase servo arms and wheels that are especially designed to giant sized airplanes. They cost more that the servo arms that come with the radio systems but are well worth the investment. They are much stiffer that the standard servo arms and provide little or no flexing. I highly recommend them. Cable systems (pull-pull) are more difficult to install. Full sized airplanes have them, but they have the advantage of a steel frame for support. Pulleys are also used to route the cables.

Hooking up the cables directly to the servo arm is not the proper method of a pull-pull system. The servo arms flex too much and you don't want to put too much pressure on the servo arm shaft. Therefore a tiller bar is generally used. All the servo does is move the tiller bar, which in turn moves the control surface. The complexity of this system is a main reason that fiberglass or aluminum pushrods have become the norm. I use a pull-pull system on my rudder, but use two pushrods instead of cables from the servo to the rudder. Actually both sides are push-pull, to be more accurate.

Hopefully these ideas will help explain these systems as well as generate thought to a safer flying airplane.