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Gear uplock piston

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tigeryak18t

Joined: 26 Sep 2009
Posts: 233
Location: PARIS FRANCE

Posted: Sun Oct 04, 2009 1:23 pm Post subject: Gear uplock piston

Hello to all,



just to attract your attention on a small problem I had two times on two different planes about the small uplock cylinder locking and unlocking the gears.

The gear is locked in the up position by a small hook . When we select the gear down position air flows thru the normal circuit to the small uplock cylinder that pushes and release the hook. Air goes in the same time into the main cylinder to push the gear down and extend it.

  Those last time I had the problem on my Yak18T and on my friend 's Yak52 just this last week. This small cylinders stopped working locking the gear in the retracted position. On my plane, I discovered the problem fortunately when my plane was jacked and I was making retractation test (my red retracted light did not want to come on and this was the symptom of the normal operation piston blocked on the emergency piston. The actuator of the light was no more depressed) and without possible anticipation my left gear refuses to go down. The hook did not release the gear. The uplock cylinder was blocked.

  The same happened to my friend last week on his 52. He landed with the emergency system and all was fine.

What happened was that those little uplock cylinder are made of two piston moving one on the other and the movement was completely corroded so it was no more moving on normal operation but only in emergency. Inside the cylinder I found a lot of corrosion and even old  grease blocking the cylinder. I had to unmount completely  the cylinders, use a hammer to separate the two parts of the piston paper sand the corroded parts clean completely the interior and apply some Teflon grease.

 I was really surprised how much it was corroded and it seems to me important to attract your attention on this problem. These little cylinders are very easy to unmont. It takes about one hour to unmont it clean it and remount it.

 

Regarding how annoying it is to land with the gear retracted.....I think it is worth checking these uplock cylinders.



If anyone want I can post pictures of the unmonting process.



And if anyone can explain me how difficult it is or how easy it is to make the same for the main gear cylinders I will be happy. I think that now I will try to check all the cylinders.

 

Hope that will help 

-- 

Didier BLOUZARD

didier.blouzard(at)gmail.com (didier.blouzard(at)gmail.com)

0624243672

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_________________
Didier Tiger YAK18T
Member of Commemorative Air Force
French Wing

dsavarese0812(at)bellsout
Guest

Posted: Sun Oct 04, 2009 2:45 pm Post subject: Gear uplock piston

Didier,

 This is not an unusual problem with Yak's (50's, 52, Yak  18T's) with uplock actuators.  In fact, it happens more frequently than one  might think.  The problem is poor maintenance of the pneumatic system in  years past.  As you have already found out, when you disassemble the uplock  actuator you will very likely find rust and corrosion inside.  Very likely  one or more of the C-clips will be rusted or maybe even totally  disintegrated.  It is highly recommended that at every annual inspection at  least one uplock actuator be removed, disassembled and inspected.  Whatever  you find in the small uplock actuator is representative of what you will find in  all the other actuators (undercarriage and flap).  So if you have an uplock  actuator that is not functioning and you find corrosion and rust internally in  the actuator, you can almost count on finding the same thing in your  undercarriage and flap actuators.  Additionally the air start valve is  probably full of junk/gunk as well.  

  

 If the metal parts except the C-clips are in good shape, you  can overhaul the uplock actuators.  I would strongly recommend you do this  before you end up with an in-flight problem with the undercarriage not coming  down.  And believe me, it WILL happen if you don't take care of it  now.  Do not use grease when reassembling.  Use only a light weight  oil.  Grease may block the small holes in the shaft between the main and  emergency sections. (The steel part that inserts into the brass part).   You can pressure test the uplock actuator with shop pressure from a  standard shop compressor.  I would recommend you do this on both the main  and emergency sides before reinstalling in the airplane.

  

 Removing the undercarriage actuators is pretty straight  forward.  Of course you will need to jack the airplane.  First remove  the end of the actuator from the drag link that moves the undercarriage up and  down.  Then remove the bolt and nut at the top of the actuator.  I  would recommend you take the actuators to person who is familiar with  disassembling and reassembling the actuator because it can be difficult getting  the end caps off.  Then when reassembling it is easy to damage the new  seals.  

  

 Finally, seriously consider overhauling all of the  undercarriage actuators and the flap actuator.  Better to be safe than  sorry.

 Dennis 

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cjpilot710(at)aol.com
Guest

Posted: Sun Oct 04, 2009 3:13 pm Post subject: Gear uplock piston

Guys,

  

 I know these up locks are standard on every Yak and CJ-6 EXCEPT mine.   When I bought my airplane 15 years ago, they were not installed on the  airplane.  Somewhere I remember seeing a pneumatic system drawing without  them.  I've heard of one other aircraft that didn't have them either.   I now have well over 1,800 hours on my airplane with out them.  I  personally think you can get along without them.

  

 Difference?  I merely fly around with my gear handle UP, instead going  to OFF.  If I put the gear handle to OFF (not down), the air merely bleeds  out of the system though the gear handle, and my gear will drop out.  The  same will happen if I happened to lose all my main system air.  One time at  a near by airshow, I sheared the pins in the compressor.  Of course the  system pressure started slowly dropping.  It got pretty (30 atoms) low  before I noticed it.  I turned off my main air valve.  At about 20 to  25 atoms the gear starts to fall.  On the down wind (with zero pressure on  the gage) I put the gear handle from the full UP to the DOWN position.  I  noted that all the "Idiot" sticks were showing the gear nearly down at this  point.  At this point I opened the main valve, and heard a satisfying  normal "clunk" and 3 green lights.   I still had 30 atoms in my system  for brakes (min is 10 atoms BTW) and still had my emergency bottle in  reserve.  

  

 Now I know the book says to put the gear handle OFF after the gear is  retracted.  AND that before extending the gear, one must go from OFF to UP  before going to down.  This keeps the gear from slamming down.  My  point is that it does not matter if you leave the gear UP.  Nothing is  going to happen to the system.  There will always be pressure on the up  side of the actuator and that is all.  This doesn't do any harm  to seals.  Seals are worn out by movement of the piston in the actuators,  not by the air pressure.  

  

 Other folks have said that it is easier on the compressor.  I say it  makes no difference.  The compressor will be putting out the same cubic  whatever's with each stroke .  The regulator will dump the excess pressure  when it exceeds the spring's compression set.  It would do this with or  without the gear being OFF or UP.  BTW if you think by having a over board  dump valve install (some Yak 18Ts) is easier on the compressor, I find that  debatable.  The compressor will still chugging right along with the engine  however - - - - the engine will not be drained of the hp required for the  compressor working to build up that pressure.  Hence it would burn a little  less fuel (does anyone know how much?).

  

 At one point I considered putting up locks back on my CJ.  Then I  considered the operational differences and that they may in themselves be a  failure point.  KISS

  

 Do I recommend taking them off your airplane?  No.  But for ME -  I am fine without them.

  

 So why do the engineers say "Put the gear handle OFF".  I don't  know.  I do know that engineers and the FAA use to say "To remove smoke  from the 707 cockpit, open up the sextant valve and if it gets worse, open  cockpit windows." (Words to that effect in the emergency check list)  Turns  out, that was 100% wrong and 3 friends of mine died at BOS doing what they  were told.

  

 Not that having a gear handle UP or OFF will be as quite as earth  shattering as that, but just the best extreme example I could think of.

  

 BTW (different note) On the B-24 (PW 1830-65 with 14 cylinders) we only  pull though 9 blades. On the B-17 (Wright 1820 with 9 cylinders) we  pull 9 blades.  On the B-25 its a two man (old men) job to pull the 14  cylinder Wright though 9 blades.   I pull my M-14 though 5.

  

  

 Jim "Pappy" Goolsby

  

  

  In a message dated 10/4/2009 5:23:53 P.M. Eastern Daylight Time,  didier.blouzard(at)gmail.com writes:

  	  Quote: 	
		  Hello to    all,



just to attract your attention on a small problem I had two times    on two different planes about the small uplock cylinder locking and unlocking    the gears.

The gear is locked in the up position by a small hook . When we    select the gear down position air flows thru the normal circuit to the small    uplock cylinder that pushes and release the hook. Air goes in the same time    into the main cylinder to push the gear down and extend it.

Those last time    I had the problem on my Yak18T and on my friend 's Yak52 just this last week.    This small cylinders stopped working locking the gear in the retracted    position. On my plane, I discovered the problem fortunately when my plane was    jacked and I was making retractation test (my red retracted light did not want    to come on and this was the symptom of the normal operation piston blocked on    the emergency piston. The actuator of the light was no more depressed) and    without possible anticipation my left gear refuses to go down. The hook did    not release the gear. The uplock cylinder was blocked.

The same happened to    my friend last week on his 52. He landed with the emergency system and all was    fine.

What happened was that those little uplock cylinder are made of two    piston moving one on the other and the movement was completely corroded so it    was no more moving on normal operation but only in emergency. Inside the    cylinder I found a lot of corrosion and even old  grease blocking the    cylinder. I had to unmount completely  the cylinders, use a hammer to    separate the two parts of the piston paper sand the corroded parts clean    completely the interior and apply some Teflon grease.

I was really    surprised how much it was corroded and it seems to me important to attract    your attention on this problem. These little cylinders are very easy to    unmont. It takes about one hour to unmont it clean it and remount    it.



Regarding how annoying it is to land with the gear retracted....I    think it is worth checking these uplock cylinders.



If anyone want I can    post pictures of the unmonting process.



And if anyone can explain me    how difficult it is or how easy it is to make the same for the main gear    cylinders I will be happy. I think that now I will try to check all the    cylinders.



Hope that will help

-- 

Didier    BLOUZARD

didier.blouzard(at)gmail.com (didier.blouzard(at)gmail.com)

0624243672

	




  [quote][b]

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tigeryak18t

Joined: 26 Sep 2009
Posts: 233
Location: PARIS FRANCE

Posted: Mon Oct 05, 2009 1:46 am Post subject: Gear uplock piston

Thanks to all for your kind comments,

  

 merci beaucoup !!!!!

  

 Dennis, I will follow your recommandations and probably have a thorough inspection of all actuators done by a DASSAULT specialist. He has all the specific tools and knowledge.

 Just to moderate, on my plane the left uplock was rusted but the right one was in a good state.

  

 For the liquid to put in the pneumatic system TERMIKAS seems to recommand to mix 50% ethanol and 50% glycerin (found in any good drugstore) and to inject this mixture into the pneumatic system as you say.

 

Regarding the relevance or not of these uplock ...... I question myself. My hungarian operator has been trained by russian engineers and when he was aware that I followed the manual regarding the gear handle in neutral position he told me that this was not the recommandation and I have to keep the gear handle on retracted or extended all the time.

  The only problem is (or might be!!!) the compressor always in charge.

  

 Thanks very much Dennis,

  

 thanks to all

  

 Didier

  

  

 

 

 2009/10/5 A. Dennis Savarese <dsavarese0812(at)bellsouth.net (dsavarese0812(at)bellsouth.net)>

 [quote]  Didier,

 This is not an unusual problem with Yak's (50's, 52, Yak 18T's) with uplock actuators.  In fact, it happens more frequently than one might think.  The problem is poor maintenance of the pneumatic system in years past.  As you have already found out, when you disassemble the uplock actuator you will very likely find rust and corrosion inside.  Very likely one or more of the C-clips will be rusted or maybe even totally disintegrated.  It is highly recommended that at every annual inspection at least one uplock actuator be removed, disassembled and inspected.  Whatever you find in the small uplock actuator is representative of what you will find in all the other actuators (undercarriage and flap).  So if you have an uplock actuator that is not functioning and you find corrosion and rust internally in the actuator, you can almost count on finding the same thing in your undercarriage and flap actuators.  Additionally the air start valve is probably full of junk/gunk as well.  

   

 If the metal parts except the C-clips are in good shape, you can overhaul the uplock actuators.  I would strongly recommend you do this before you end up with an in-flight problem with the undercarriage not coming down.  And believe me, it WILL happen if you don't take care of it now.  Do not use grease when reassembling.  Use only a light weight oil.  Grease may block the small holes in the shaft between the main and emergency sections. (The steel part that inserts into the brass part).  You can pressure test the uplock actuator with shop pressure from a standard shop compressor.  I would recommend you do this on both the main and emergency sides before reinstalling in the airplane.

   

 Removing the undercarriage actuators is pretty straight forward.  Of course you will need to jack the airplane.  First remove the end of the actuator from the drag link that moves the undercarriage up and down.  Then remove the bolt and nut at the top of the actuator.  I would recommend you take the actuators to person who is familiar with disassembling and reassembling the actuator because it can be difficult getting the end caps off.  Then when reassembling it is easy to damage the new seals.  

   

 Finally, seriously consider overhauling all of the undercarriage actuators and the flap actuator.  Better to be safe than sorry.

 Dennis 

 [quote]  ---

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_________________
Didier Tiger YAK18T
Member of Commemorative Air Force
French Wing

dsavarese0812(at)bellsout
Guest

Posted: Mon Oct 05, 2009 4:05 am Post subject: Gear uplock piston

Regarding the compressor always being "in charge" because you  put the undercarriage selector in neutral - it has no effect on the compressor  whatsoever because the compressor is always charging the system when the engine  in running.  Your Hungarian operator is 100% correct.

  

 Another reason I do not subscribe to putting the undercarriage  selector in neutral (with one exception which I will explain shortly) is because  when you put the selector in neutral, the actuators are totally  depressurized.  That is the "woosh" sound you hear when the selector is  moved to neutral.  If you move the selector to the DOWN position for  landing from NEUTRAL, the undercarriage will slam into the down position because  there is no backpressure on the actuator from the UP side.  This is not  good for the undercarriage, or the actuators.  The pressure on the UP side  of the actuator acts as a "shock absorber" when the selector is put in the down  position.

  

 The ONLY way moving the selector to neutral is  acceptable is if BEFORE you move the selector to DOWN you first move  the selector to the position the undercarriage is already in.  In this  case, back to the UP position.  By doing this, you re-pressurize the  actuators and then you can move the selector to the down position.   Unless you get into the habit to do this every time you cycle the undercarriage,  leave the selector in the UP position.

 Dennis  

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mark.bitterlich(at)navy.m
Guest

Posted: Mon Oct 05, 2009 1:16 pm Post subject: Gear uplock piston

Just a note.  The YAK-50 does not use UP LOCK actuators.  Instead, the

uplock is controlled by a spring and movement of the main gear actuator

itself.  



All the corrosion issues are the same as has been reported, but there

are just two main actuators to worry about.  



Mark Bitterlich

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mark.bitterlich(at)navy.m
Guest

Posted: Mon Oct 05, 2009 1:22 pm Post subject: Gear uplock piston

There is one more occasion when it is actually smart to move the

actuator level to neutral and this is if you have a bad bad air leak. 



It is entirely possible to have a leak in your landing gear system where

it only leaks when the landing gear is selected UP or selected DOWN.  



If that happens, you can end up bleeding out your whole air bottle and

not have normal air available for landing.  



I had this happen on a YAK-50 that I was ferrying out to California.  In

that case, the leak only happened with the gear in the DOWN position.

Keep in mind that the landing gear on a YAK-50 does NOT work the same

way as the YAK-52, and in the 50, the down and lock system is fully

mechanical.  If the gear is down and locked, it does not require air

pressure to KEEP it down and locked.  The 52 uses actuator locking balls

I think (Dennis? Anyone?) but the 50 has a stand alone mechanism.  



Anyway, it is possible to lower the gear... Put the handle back to

neutral, then allow the air to pump back up, and actually LAND with the

actuator in neutral.  My leak was so bad, I had to do this, or I would

have had no brakes on landing.  Of course, if you could, the better move

would be to select DOWN right before you landed.  



Point being, putting the landing gear handle in neutral can ISOLATE a

bad leak and allow you to regain full air pressure. 



Mark Bitterlich

  

 



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