REFLECTOR:Nose gear sag and brake problem.

Dave Black reflector@tvbf.org
Sat, 04 Oct 2003 04:25:45 -0400


Mel,

> the nose gear is not
> retracting enough to close the doors.  The sag is about 1/2 "
> and the gear can be pulled up easily by hand.  

Is this the point at which the gear contacts the sequence valve? 
If you pull it up by hand while the pump is running, do the doors close?

If you've installed the valve per plans, a great deal of force (by the gear)
is required in order to activate the valve. So much so that in most
installations the nose gear will stop retracting at the point where it touches
the sequence valve. It stays hanging out until the mains have fully retracted.
Then, as the pressure builds up very high, the nose gear will retract and the
doors will slam. Is this how yours normally works?

> I haven't changed anything since I last retracted the gear.  Brendan
> suggested that the pressure switch may be cutting off too soon.  

It does seem to be a pressure switch issue. A great deal of pressure is
required to activate that sequence valve, and apparently your pump is shutting
off before reaching that high a pressure. I can't explain why the adjustments
don't work. This may be part of your problem, for surely with ENOUGH pressure,
the nose gear would retract. I seem to recall that my pressure switches were
originally wired backwards. 

The other possibility is the sequence valve itself. Make certain the valve
operates smoothly. Maybe it needs lubrication. It's a finicky little bugger.
Make certain the button that activates it is still installed and adjusted
correctly. 

Experimentation has shown that the best location for the sequence valve is 1"
to 2" from a gear pivot point. This way the valve gets all the leverage it
needs in order to activate smoothly. The farther the sequence valve is from a
gear pivot point, the more hydraulic pressure is required to activate the
valve. And the greater the tendency of the doors to slam when it does
activate. If the sequence valve is located 1" to 2" from a gear pivot point,
the gear will retract fully and the doors will close smoothly BEFORE the mains
retract. 

> Does anyone have a suggestion?  I had planned to fly
> to Copper State, now Xmas is in doubt.

I suggest that while not proper, a partially extended nose gear is not a
safety-of-flight issue. Thus it's not sufficient reason to cancel a flight.
But I also believe you'll have this problem solved within the next day or two. 

Dave Black
Shortwing RG