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CJ6 pneumatic system emergency operation

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greshell(at)bigpond.net.a
Guest

Posted: Sun Aug 06, 2006 2:04 am Post subject: CJ6 pneumatic system emergency operation

A couple of questions for all you CJ-6 gurus out0 there.

  

 1.    The text in the manual0 states that the gear selector must be in neutral and the emergency cock0 opened to lower the undercarriage via the emergency method. The actual0 procedure, however, has the emergency cock opened before the landing gear lever0 is set to neutral (or checked in neutral as would generally be the case). Can0 anyone shed any light on the order of these actions and the subsequent0 implications of doing them in reverse?  

  

 2.    If the emergency air0 valve is opened with the main air valve still open, will emergency pressure0 flow to the main reservoir regardless of gear lever position? (ie will being in0 neutral stop this happenning?)

  

 Please excuse my rudimentary0 knowledge of the system, trying to get a better0 understanding. 

  

 Thanks in advance

 Greg Choma

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dsavarese(at)elmore.rr.co
Guest

Posted: Sun Aug 06, 2006 6:12 am Post subject: CJ6 pneumatic system emergency operation

Greg,

 The purpose of putting the gear selector in neutral is to0 discharge all pressure in the landing gear actuators.  When the air is0 depleted from the actuator there is no backpressure and therefore no shock0 absorption.  To explain further, when you move the gear handle from UP to0 DOWN or DOWN to UP you hear air discharging through the gear handle while at the0 same time air from the main air tank is pressurizing the opposite side of the0 actuator.  ie: if your moving the gear handle from DOWN to UP, the DOWN0 side of the actuator is depressurizing while the UP side of the actuator is0 pressurizing.  The discharging air escapes through the gear handle. 0 This process allows the gear to move smoothly.

  

 When you move the gear selector to neutral you discharge the0 pressure in the actuators.  Then when you open the emergency air valve, the0 pressure applied to the DOWN side of the actuator causes the gear to literally0 slam into the DOWN position.  Believe me, it will definitely get your0 attention.

  

 By leaving the gear selector in the UP position and then0 opening the emergency air valve followed by moving the gear selector to NEUTRAL,0 the pressure on the UP side of the actuator is discharging while the emergency0 system air is pressurizing the DOWN side of the actuator.  This action0 prevents the gear from slamming into the down position.  Be sure to turn of0 your main air supply before opening the emergency air valve.  By turning0 off the main air supply you no longer have air pressure from the main tank being0 applied to the DOWN side shuttle valve on each actuator.

  

 Dennis

  

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wlannon(at)cablerocket.co
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Posted: Sun Aug 06, 2006 9:30 am Post subject: CJ6 pneumatic system emergency operation

A few points to supplement Dennis's excellent0 description of system operation.

  

 You should have an emergency gear down placard0 listing the following action:

  

 1. Close main air valve

 2. Gear selector neutral

 3. Open emergency air valve

 4. Gear selector down.

 5. Engage safety latch

  

 Dennis has explained the reasons for actions 10 & 2 and the attention getting result of action 3.

 Actions 4 & 5 are not essential to the actual0 process since the gear is down and locked before you can even think of step 4 -0 emergency air goes directly to the down side of the actuators bypassing the0 selector valve. Steps 4 & 5 are for obvious good housekeeping0 reasons.

  

 Under no circumstances should you attempt to0 retract the gear after an emergency down selection. An attempt to do that may,0 if air pressure is available, leave you with one or more unlocked0 gear.

  

 Once back in the hangar, preferably on0 jacks, you need to depressurize the down side prior to further gear  operation. 

  

 Walt

  

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Scorch

Joined: 08 Aug 2006
Posts: 2
Location: Brisvegas

Posted: Wed Aug 09, 2006 2:29 am Post subject: Re: CJ6 pneumatic system emergency operation

Thanks Walt and Dennis for your replies. You have increased my understanding greatly.



The second part of my question was poorly written. 

What I would really like to know is if the gear is already down, and you need emergency brake pressure in a hurry (like rolling down the runway with no brakes), is it an option just to open the emergency valve with the main valve still open, or will the pressure be lost?



Thanks again

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dsavarese(at)elmore.rr.co
Guest

Posted: Wed Aug 09, 2006 4:21 am Post subject: CJ6 pneumatic system emergency operation

Many, many years ago I was told the emergency system on my Yak 52 was only 

to extend the landing gear.  That was before I really understood the system. 

Then I thought about it and said to myself, "Self, wouldn't it dumb to 

design a pneumatic system to extend the gear in an emergency but not be able 

to stop the airplane once it was landed.  Especially one that also had 

pneumatic brakes!"  So I tested the emergency system on the ground and 

applied the brakes.  They really do work with the emergency system air.



To answer your question directly, yes it is permissible to do that.  After 

you stop, turn off the emergency air valve.  Then bleed off the pressure 

from the emergency side in order for the landing gear actuators to operate 

properly on the main air system again.

Dennis



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