Reply-To: Sky2high@aol.com
Reply-To: lancair.list@olsusa.com
From: "Scott Krueger" <sky2high@hotmail.com>
To: lancair.list@olsusa.com
Cc: Sky2high@aol.com, MarkM@Lancair.com
Bcc: 
Subject: Lancair LNC2 and Legacy Hydraulic System Problems
Date: Thu, 24 May 2001 17:57:12 -0500
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Message-ID: <F111Qq5pneeFUtLch9w000003d2@hotmail.com>

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Lancair 235/320/360 and future Legacy hydraulic system considerations:

These Lancair landing gear electro hydraulic systems use the same components 
and have the same problems.

1.	Failure to pull the relay circuit breaker in conjunction with pulling the 
motor circuit breaker during electrical system testing or flight may cause 
the gear relay to be selected with no panel indication because the light is 
driven thru the motor breaker.  The gear relay (up or down) energized for a 
long period of time may result in failure of the relay or failure to 
de-select the relay during later normal operations.

Solution:  Cascade the relay circuit breaker off the motor circuit breaker.  
Pulling the motor circuit breaker then deactivates the relay circuit.

2.	20 or 22 gauge wire is used to power the motor-in-operation indicator 
light and, if shorted, can cause a fire because the indicator is driven off 
the motor relay 50-amp circuit.

Solution:  Use diodes to isolate each relay “indicator” circuit and an 
inline fuse to match the indicator-light wire size.

3.	Pressure drop causes pump to cycle on for a short time.  This can occur 
with the gear up or down or in both cases.  It becomes most troublesome when 
these cycles are less than 20 seconds apart.  Under certain circumstances 
(night, all lights on and flap transition) the cycle may cause a sufficient 
voltage drop on an essential bus to cause a re-cycle of some instrumentation 
(Rocky Mountain Micro-encoder, Vision Micro engine instrumentation).

Solution:  There are many, including installing a switch to de-activate the 
pump circuit.  In this case the circuit is re-activated by the pilot every 
15 minutes or so.    Many people believe there are internal leaks in the 
cylinders, dump valve or mis-built pump.  I believe the solution centers on 
the pressure switches, but, since I am seeking assistance, let me set up the 
work I have gone thru and the solution I think is right –

For at least 2 years, I have had the pump re-cycle during gear up.  Recently 
that cycle was repeated every 10 seconds.  Also recently, the pump began 
frequent recycling whilst the gear was down.  This began to seriously worry 
me.  So, since I would have to open lines to isolate the problem and, since 
I have been flying for 5 years, I decided to rebuild instead.  First, I 
rebuilt all six actuators (cylinders).  No change. I then got a new dump 
valve from Lancair (old valve was circa 1989, the same as fuel shut off, 3/8 
inch flow and made in Italy – New valve is Thai, Ľ inch flow and 3/16 inch 
shorter) and I went thru much work to change it over.  No Change.  Next, I 
decided to install a newer pump, the same as the one used in the Legacy.  I 
decided not to send my old one back to Oildyne because of its age.  Of 
course, I did not want to change my hard lines, so I had to tap the center 
of the pump to receive my old small metal reservoir and drill and tap the 
cast body for the filler port.  Better results since the pump did not cycle 
during gear down, but continued to do so on gear up.  Here are the 
repeatable results of further tests with the plane on jacks, gear raised and 
master switch off:

16 hours elapsed time - Main gear doors down 2 inches.
38 hours elapsed time – Main gear doors down 4 inches, nose gear door down 1 
inch.
3 days elapsed time – Main gear doors down 6 inches, nose gear door down 3 
inches.

Each time, the master was turned on and the pump ran for a momentary blip to 
return to the trip pressure.  Since I have had trouble with the 2nd 
generation VEP hi-pressure switch related to cold temperature (not shutting 
the pump off, required pulling the pump breaker) and continual tweaking of 
the pressure setting, I bought a third generation switch from Lancair and 
after some imaginative plumbing, replaced the old.  Note, even though all 
flare ends were carefully done, very little tube flare was left on the old 
plumbing – the hi pressure must have been slowly pulling the tube out.  The 
new switch was marked for 1000 psi and if that was accurate, it was not 
enough pressure to retract the nose gear or, more specifically, to unlock 
the link against the gas spring pressure.  This is an important point to 
remember for later.  After adjusting the pressure switch quite a bit to a 
much higher pressure, I went flying.  Otherwise, no change - Remember that 
the gear up was still re-cycling every 30 seconds or so.  However, now I 
have about 1 second of radio static before the “pump on” indicator lights up 
for the momentary pump run to satisfy the pressure switch.  Try that on a 
1200 mile cross country and you become quite cross. I believe the switch 
contacts are slowly brought together rather than snapped.

Putting all this together, much less hydraulic pressure is required to hold 
the gear up than is required to get it up, especially, to break the nose 
gear over center lock against the gas spring.  It is clear that the gear 
does not “leak down” very much with reduced pressure.  The pressure switch 
acts at a specific pressure and if the pressure changes just a wee bit, the 
pump is activated.  This is wrong.  Either the pressure switch must have a 
reasonable dead band or a 2-pressure, 2-switch pressure switch with 
associated logic circuitry must be utilized.  I have found such switches on 
the Internet but I don’t have the expertise to select an appropriate one.  
Some are very fancy $300 switches with digital pressure readout at the 
switch or others that don’t quite fit our environment.  I refuse to put the 
current deficient system in my Legacy, So:

Any hydraulic or electrical engineers out there that can help me find 
appropriate switches would be greatly appreciated.

Thanks,

Scott Krueger
LNC2 N92EX
Legacy kit #2
Direct reply to Sky2high@aol.com


PS Others with similar experience?


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