How Not to Install Radio Controls in a Model Aircraft

Recently a member at my club purchased or traded for a plane from another flyer.  He then presented me with the model and asked me to make it flight-worthy.

My thoughts at the time were that the plane in question should be considered a total and disposed of.  Nevertheless I decided to bring it to my shop and look it over to see if it were salvageable.

What is not shown here is that the wing feels like a box of bricks.  I have no idea what is under the covering, but whatever it is there is a lot of it.  The fuselage is shaped like a banana and there are several degrees (at least 5°) of left thrust.

The aircraft has patches all over it.  The horizontal stabilizer and fin are both crooked.  The fin cants over about 8°.

The next time I met up with the man who owns the model I asked him if he really wanted to pay me to do the work necessary to make the plane airworthy.  In my mind that meant an entirely new fuselage which I would have charged him more to build than he could buy another ARF of the same type.  He declined and the model was returned to him.

Flight-Worthy Aircraft

I have belonged to several clubs.  Some had strict safety rules that were enforced whether or not the flyers liked them.  For example, one club I belonged to required a Safety Officer to inspect new or repaired aircraft from nose to tail.  He had the authority to ground any aircraft for any reason.  If a flyer did not like it he could bring it up before a board of review.  One rule I remember was that all flat hinges had to be pinned.

This may seem a little anal-retentive, but I liked it because obviously unsafe airplanes were not allowed to fly.  Additionally, many mistakes were caught that may have been the demise of the model.  In those cases the builder probably appreciated the scrutiny his plane was subjected to.

Other clubs I have belonged to utilize the honor system.  This simply means that it is up to the pilot to exercise his own judgment to determine if a plane is flight-worthy or not.  Unfortunately, I have seen some really unsafe aircraft take to the skies.

In a period of less than a month I saw several wings fold, wings part company with the aircraft and planes take off with the ailerons reversed.  Given the choice, I would rather have the fascist Safety officer.

Dead On Arrival

The following image shows the radio installation in this model.  Again, this is how my fellow club member received the model.  This was not his handiwork.

The first thing I notice is the use of EZ connectors on the primary control surfaces.  This is an extremely poor practice because EZ connectors often fail in two different ways.  The set screw can come loose or the connector itself can part company with the servo arm.

EZ connectors are inherently sloppy and cause twisting loads on servo arms because of the amount they are offset.  EZ Connectors are fine for no or low-load items such as throttle, but I do not even use them there.  In fact, I do not use them at all.  In any case never use these kinds of connectors on any flight surface.

Use a Z-bend, quick connector (uses an L-bend), clevises (solder or threaded) or captured ball links (helicopter style) instead.

Information about Pushrods and Linkages

The second thing that is apparent is that the servo mounts are not in the same plane.  The middle rail is lower than the other two rails by about 3/8" which means the servos are not mounted properly and the servo arms do not rotate in a plane parallel to the pushrods.

If you look closely you can see that the mounting tab of the left-most servo is actually being bent down under the force of the mounting screws.  It is more difficult to see the other tabs, but they are all like that.

Lastly, notice the servo mounting screws.  Some of the rubber grommets have been over-compressed and have completely lost their vibration absorption capability.  I did not pull the servos out but I suspect that the eyelets were not installed in some of the grommets.

It truly disturbs me that anyone would think this is an acceptable installation.  Unfortunately I see things like this far too often.  If you do your radio installation before you build the fuselage you can avoid misalignment problems and have a simpler, more reliable and cleaner installation.

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Copyright © 2003 Paul K. Johnson