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by Omri Talmon


The main wheels of many aircraft in our fleet are equipped with wheel covers (Piper part no.  24918-00) secured with three AN526-8R4 screws and lock washers.  These screws are inserted into three threaded holes in the aluminum wheel hubs.  This arrangement is far from being ideal as aluminum is not a perfect metal for repeated removal and installation of these screws for  checking tire pressure, and the cleaning, inspection, and lubrication of wheel bearings.  Further, these screws should be well tightened, and here is why:

Upon touchdown during landing, the wheels accelerate from zero speed to about 70 MPH in no time.  Look at the screws on the right wheel:  In addition to the clockwise rotation around the wheel axis they also have a clockwise rotation component around their own axis. Since, like every object, they have inertia, there is a counter clockwise reaction which tends to loosen the screws.  If these are not properly tightened one or more will be loosened after a few landings and pull out of the wheel.  There is a risk, then, that the wheel cover will be caught by the airstream in flight.  It can be bent and the landing gear partially jammed.

On one hand, then, it is important to use reasonable torque to tighten the screws.  On the other hand, the aluminum threads are not very happy with high torque values and, in addition, have a tendency to either grip or strip out.

I faced this dilema following my first emergency gear extension some 24 years ago.  It became necessary because the right wheel cover lost one screw. The cover bent, jammed the landing gear, and caused the circuit breaker to pop.  My solution was to install HeliCoil inserts on the two wheels. Since then; no problem.  The screws can be tightened and are easy to extract.  No gripping or binding.

This modification was documented with just a logbook entry.  I have no idea as to the legal requirements, so interested parties should find out from qualified sources what should be done.  Your individual results may vary.

Some HeliCoil literature is shown below:


Helicoil Wire Thread Inserts

HeliCoil Inserts provide positive means for protecting and strengthening all tapped threads.  They are mirror-smooth, reinforced internal threads of cold rolled 18-8 stainless steel, or other space age material, with hardness far in excess of the usual tapped materials.

The outstanding engineering features of HeliCoil Inserts, long recognized by the leading aircraft, industrial and military equipment manufacturers, have established their widespread use in these fields.  The many company standards and defense specifications for HeliCoil Inserts also prove their wide acceptance. 

 Helicoil Free Running Inserts

Helicoil Free Running Inserts

HeliCoil Inserts are manufactured from High Tensile Stainless Steel Wire which has been formed into a diamond section of exacting standards.  When installed the HeliCoil provides a precision female thread of high surface finish and strength.

Installation of the HeliCoil is achieved by means of the Driving Tang, which is removed after assembly.  To permit the removal of the Tang a Notch is cut into the section to provide a shear point. The design of the notch allows for bolt entry from EITHER END of the HeliCoil.


Omri Talmon, born in 1936, lives in Tel Aviv, Israel. He holds degrees in engineering, business administration and accounting. Presently a consultant, he worked for many years as an executive for several hi-tech companies.  Omri is a private pilot with both Israeli and U.S. certificates.  His ratings include SEL, MEL, Instrument, Glider, and CFI (glider).  Since 1974 he owns and flies a 1966 PA-30-B, registration 4X-CAO.


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