Rigging the Flaps page 1

January 23, 2008

As previously mentioned, all control system pulleys require some sort of cable retainer to prevent the cables from slipping off of the pulley, should it become slack.  There is probably no control system on the Bearhawk that is more susceptible to slack in the cable than the Flap system.  This is because it is a one way system (i.e,. the cable only pulls the flaps down, but springs pull the flaps back up).  When you taxi in a strong enough tail wind, the wind can actually overcome the strength of the springs and make your flaps go down, thereby putting slack in the cables.  Without proper pulley retainers, these cables can fall right off the pulley.

The cable retainers have a couple of requirements:
1. They must come close enough to the pulley to prevent the cable from coming off, without actually touching the pulley.  
2. They should be secured to the surrounding structure so they cannot rotate.

Here is my rendition of the cable retainer for the flap pulleys:

The top part sits to within 1/16" of the top of the pulley, so the 1/8" cable cannot slip off.  The long leg with a tab will be used to prevent the guard from rotating.

Here is the pulley and its cable retainer installed in the fuselage:

As you can see, the little tab has been wrapped around the "V" tube at the baggage bulkhead location.  I will install a hose clamp there later to fully secure it to the tube.

Likewise the pulleys up near the rear wing attachment on the fuselage need cable retainers.

Photo courtesy of Bill O'Sullivan

The next item that must be fabricated before we can finish off our flap system cables, is the triangle cable junction piece, where the one cable splits into two cables, just aft of the baggage bulkhead.  The newer plans call for a piece of .125" thick 4130N steel plate for this triangle. This piece and the connecting bolts, will endure some fairly heavy loads so .125" thick is required here.  Here is the set-up with the turnbuckles installed:

The cable shackle at the bottom will connect to the cable coming from the flap handle in the cabin.  The two turnbuckles will attach to the cables coming from each flap control horn.

The first cable was attached at the bottom of the flap handle with a cable shackle. This cable rubs slightly against the shock strut mount only when in the fully retracted position. It clears it as soon as the handle is moved to deploy the flaps. One builder, Pat Fagan, welded on a steel "skid plate" to account for this:

Fagan's #232 Bearhawk - courtesy of Russ Erb's CD

The cable comes off the flap handle and is threaded through to the two gang pulleys on the fuselage bottom.  This cable is threaded through the furthest pulley on the starboard side (passenger side) of the fuselage.

Next a cable was attached to each flap drive horn on the wing root:

Note that the cable is oriented with the cut side of the cable facing downward. This helps prevent interference with the aft wing spar attachment piece.  

These cables were then threaded through the flap system pulleys and fairleads to meet at the cable junction triangle:

Notice in the picture above that the bottom cable has been  installed with a regular crimped Nicopress sleeve.  However, the cables running up to each flap have only been temporarily clamped with hardware store cable clamps, for now.  This will allow us to adjust the length of the cable before making the final connection.

Now the flaps are mounted on each wing and the push rod for each flap is attached between the flap drive and the flap hinge.  The flap retraction springs were also installed at this time  The rod end bearing in the flap pushrod was then adjusted until the flaps were in the full "up" position, with the pushrod "T" resting against the rubber stop, and the flaps aligned with the wing root trailing edge:

Click here to go to Rigging the Flaps page 2