Castellated nuts……how tight?

It was early in the Phase One flight testing of a Lancair Legacy, when I discovered a problem which was caused by having castellated* nuts tightened too far.

The problem was not immediately evident, as all high speed taxy testing, and in fact the first flight, had been uneventful.

It was during the takeoff run of my second flight that the aeroplane was wanting to duck off the left side of the runway.

With full right rudder, and a touch off right brake, the takeoff was continued.


Supplement 1

The Legacy does need a lot of right rudder on takeoff, and on this second takeoff, I had held my feet on the brakes as I brought the power up initially.

Supplement 2

This image shows the many castellated nuts attaching brake master cylinders and rudder pedals.

This particular Legacy was fitted with the newer style of rudder pedals that hang from above, instead of being floor mounted. The owner of this Legacy had elected not to fit the floor panel into the LHS in order to give extra room to stretch out under the pedals.

What that means is that your heels are not resting on the floor whilst applying brakes, and this makes it difficult to feel the release of the brakes through the movement of the rudder pedal.

What I found was that the left brake master cylinder was not being released (or released very slowly) as you took your toes off the brakes. Once several of these castle nuts were backed off a little and lubed, the aircraft brake system was ops normal.

*A castellated nut, also called a castle nut or slotted nut, is a nut with slots (notches) cut into one end.

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