Message-ID: <37FF4944.881E8633@regandesigns.com>
Date: Sat, 09 Oct 1999 06:55:17 -0700
From: Brent Regan <brent@regandesigns.com>
To: Lancair List <lancair.list@olsusa.com>
Subject: Re: Hydraulic Flap Cylinder Throw LNC4
Mime-Version: 1.0

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Dave is right that the flap hydraulic cylinder should be rigged to allow the
piston to bottom at both ends of it's stroke. The Fowler bracket and flap
pushrods should not provide the end of stroke limits.

In order for the two flaps and hydraulic cylinder to be coordinated, they
must be rigged properly. In a bellcrank system, the stroke ratio between the
driver and driven pushrods is not always 1:1 (assuming equal length arms).
This ratio can be adjusted by lengthening one pushrod while shortening the
other, effectively changing the position and cord length of the swept arc of
the bellcrank. All 5 bellcranks must be adjusted together to achieve
symmetrical and complete deployment of the flaps without binding the system
at the ends of stroke.

This is not an easy process as there are an infinite number of ways to set
them incorrectly and only one right way. It took me a day and a half, not
including several breaks to let my blood pressure settle back into the
green. The problem I had was getting enough flap deployment so if the
factory had supplied a shorter cylinder, my airplane would have been more
difficult to rig.

My advice is to make a chart of the system, measure and record the initial
lengths, make a change and record the results. This way you can see trends
and follow them. I am unaware of any universal method for adjusting the flap
system as every one is slightly different due to building variances.  If all
else fails (your as built dimensions are outside the limits of adjustment),
then machine a spacer (fat washer) for inside the shaft end of the cylinder.

It is apparent from David's post that his flaps are not symmetrically rigged
as only one pushrod on the left side bent indicating that it was the first
to reach it's limit by enough of a margin to allow it to bend. It has been a
while since I reviewed my manuals, but there isn't a caution about proper
flap rigging, there should be.

The aileron system has a similar rigging requirement. I found that having
two digital inclinometers (one on each aileron) was very helpful in getting
them set properly.

Curiously, rigging an aircraft requires a similar mindset to setting up the
suspension in a race car. If you don't have a buddy that is familiar with AC
rigging then a race car mechanic would be my second choice.

Regards
Brent Regan


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