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HawkerPilot2015
Joined: 10 Jan 2006
Posts: 503
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 Posted: Wed Aug 01, 2007 4:12 pm Post subject: Airplanes that talk to you.... |
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I have got some decent time in various types of airplanes from jets to props. Some have avionics that tell you when something is wrong or about to go wrong. Some airplanes have different ways of talking to you. The Yak is pretty good at talking to you and telling you there is an issue.
I recently had some air issues that were tracked down to a small seal leak in a gear actuator. So, off comes both acuators for overhaul. Well, that small seal leak probably kept me from having a catastrophic gear actuator failure which would have prevent the gear from going down if they were up and locked. The end cap on the right acuator was cracked and near failure. Had the small leak not happened first, the cap probably would have gone! I certainly did not like to find out that I had a bad cap but it sure beats landing gear up or worse..one down and the other up! Two new caps are being machined and will be made better and stronger than the old ones. (By the way, there was JB weld on the acutator that failed. I am pretty sure that the Russians do not use JB Weld....two people have owned the airplane since it was brought to the US..but just one operator)
While dealing with the acutator issue, I took a look at little shimmy that had just started in the tailwheel. I had just replaced the tire and figured that would cure the problem. It needed to be changed. No joy on the shimmy fix. Uhmmmm?? A week or so later, I find a new problem, the airplane was moved with the TW lock engaged damaging the TW fork. Damn....not again (a shop busted it last time) Out comes the fork for a repair and I figured now was as good a time to put the new TW shock cap that TJ and Mike Hanshew made the -50 community last year. The reason a new was made was that one -50 owners failed and could have ended worse than it did. So doing what Americans do best, two guys in AZ adapted and overcame and helped keep these birds flying. Well, good thing I had that little shimmy, I pulled the shock out and the bearing that was back there fell out in my hand! I am not sure how many landings she had left in her but I would guess not many before that bearing would have failed and caused me to lose control of the ass end of the airplane. That shimmy was the whisper before a scream!
I have come to respect the things this airplane tells me. I am guessing it has saved me more than once. Listen to your airplane...it speaks in a language evry pilot should understand.
For you -50 folks, the folks in AZ are doing some good things with the airplane. Get a hold of them and do yourself a favor. Have some parts on the shelf for your next annual!
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jan.mevis(at)informavia.b
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| Posted: Wed Aug 01, 2007 11:37 pm Post subject: Airplanes that talk to you.... |
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Very interesting, Tim.
Indeed, I also listen very closely. Sometimes you also have to watch.
Yesterday I had an experienced friend fly my plane. So I could see it fly. I
was rather amazed to see that the right gear leg all of a sudden VIBRATED
when he pulled the gear in at takeoff. Afterwards I asked him if he noticed
anything special but he did not. I'm going to put my 50 on Yaks to check the
whole gear.
Does anyone have any idea what may have caused this vibration ? It was very
strange : the right leg moving in, and after having turned about 10 degrees,
it oscillated rapidly fore-after, but only for a second, and then it moved
further in and locked without a problem. I could not see whether the same
problem happened at the landing.
Jan Mevis
RA2005K
YK50
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dsavarese(at)elmore.rr.co
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| Posted: Thu Aug 02, 2007 4:08 am Post subject: Airplanes that talk to you.... |
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Jan,
My first guess would be the actuator. Second guess would be the bushings in
the gear leg binding. I think when you put it on jacks and do a retract
test you'll find the problem. You may have to disconnect the actuator arm
from the gear leg and do another retract test to isolate the problem.
Something in the mechanism is most likely binding.
Dennis
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viperdoc(at)mindspring.co
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| Posted: Thu Aug 02, 2007 5:32 am Post subject: Airplanes that talk to you.... |
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Jan,
You need to look at all your gear attachment points. From the actuator
attachment bolt in the wing to the push rod attachment on the strut. Also
look at the 4 bolts that anchor the strut to the wing (doubt that is the
culprit though). But it will confirm the structural integrity of the gear
and gear box.
Suspect it has more to do with the actuator movement not completely seating
as it withdraws the strut. Something causing a transient binding as it
approaches completion of the retraction.
Have you noticed an scuffing on the sides of the gear as well?
You said this was a fore - aft vibration? Not a rotational (side to side)
vibration. Rotational would be more like the bushings in the scissors
wearing.
Jacks and a retraction test is a good idea. That should help to isolate it.
Hope this helps,
Doc
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HawkerPilot2015
Joined: 10 Jan 2006
Posts: 503
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| Posted: Thu Aug 02, 2007 6:38 am Post subject: Re: Airplanes that talk to you.... |
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Be very careful with the retraction test. It is a bit unnerving. I have done it a few times and every time it scares the hell out of me. I do not like airplanes on jacks.
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rvfltd(at)televar.com
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| Posted: Thu Aug 02, 2007 6:39 am Post subject: Airplanes that talk to you.... |
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Jan,
I am pretty sure that most of what you are feeling is the "scrubbing" of
the ram as it moves in the cylinder, but I would agree that you need to
get the aircraft on jacks and give it a through looking at. When I
overhaul actuator clyinders I always check to see if the ram extention
and retraction is smooth and fluid in it's travel. I have seen many
that moved is short jerks, sort of "stutters" in and out. This is
usally caused by one of three things, incificient flow of air (air flow
is restricted and it has to move the ram then build up more pressure,
move the ram again, and so on), 2nd it could be that the wrong 0 rings
were used at overhaul and the ram is too tight in the cly, or 3rd it
might be that who ever is maintaining the aircraft has injected an
excessive amount of tool oil into the system and has washed all the high
pressure grease off the cylinder walls. The latter reason is most
likely if the actuators have been in the aircraft for a time and have
been operating properly up to now. Limited use of air tool oil in the
pneumatic system is a good thing up to a point, but you should not
exceed the spec in the manual.
Always Yakin,
Doug Sapp
Mevis wrote:
[quote]
Very interesting, Tim.
Indeed, I also listen very closely. Sometimes you also have to watch.
Yesterday I had an experienced friend fly my plane. So I could see it fly. I
was rather amazed to see that the right gear leg all of a sudden VIBRATED
when he pulled the gear in at takeoff. Afterwards I asked him if he noticed
anything special but he did not. I'm going to put my 50 on Yaks to check the
whole gear.
Does anyone have any idea what may have caused this vibration ? It was very
strange : the right leg moving in, and after having turned about 10 degrees,
it oscillated rapidly fore-after, but only for a second, and then it moved
further in and locked without a problem. I could not see whether the same
problem happened at the landing.
Jan Mevis
RA2005K
YK50
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rvfltd(at)televar.com
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| Posted: Thu Aug 02, 2007 8:09 am Post subject: Airplanes that talk to you.... |
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Tim and all,
Retraction tests should not be something that you should be afraid of.
You should only be afraid if you are trying to do the test without the
proper equipment. If you are trying to do a retraction test without a
full set of 4 jacks you really SHOULD be scared. The "headed" jack
which supports the engine is a must as is the tail jack. If you don't
have a tail jack you can get by with a stand of some type but the
standard issue tail jack works the best. I know of at least one 50 that
ended up on the floor with both jacks stuck though the wings, a CJ's
tail broke the flimsy sawhorse tail stand and it squatted so hard that
it kinked the tail cone and the broken saw horse bashed a hole in the
bottom of the horizontal stabilizer. The $250.00 cost (each)of the
headed jack and the tail jack is pennies compared to the cost to repair
the damage if it comes off the jacks. Another point to consider is
that the lack of restrictors ($2.00 each) in the proper places
throughout the pneumatic system is another leading cause of jacking
accidents. When the gear slams up there is a huge amount of up force,
plenty to make the aircraft "hop" up just enough. When the gear comes
down they seldom if ever hit the wells at exactly the same time, so you
have a huge outward side load from one side then the other as they slam
down to lock.
I mention the prices above not in an effort to sell parts, but to
demonstrate the foolishness in taking a chance without the proper
equipment. I confess that back in the days before I stocked jacks I
tried to do a retraction test on my 18, and ended up replacing both
leading edge skins, about a $3000.00 job before it was all done. Bitter
memories.
Always Yakin,
Doug
Tim Gagnon wrote:
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HawkerPilot2015
Joined: 10 Jan 2006
Posts: 503
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| Posted: Thu Aug 02, 2007 8:27 am Post subject: Re: Airplanes that talk to you.... |
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Doug,
I used all four jacks you sold to Jay Hodge. I could have put another 100 on the thing and it still would not make me ok with a retraction test on the -50. BUT, I will echo your statement with regards to the jacks. The "headed" jack is worth its weight in titanium. The tail stand is being used as we speak.
Proper maintenance with the proper tool is cheap insurance.
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jan.mevis(at)informavia.b
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| Posted: Thu Aug 02, 2007 12:40 pm Post subject: Airplanes that talk to you.... |
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Thanks all of you for your helpful advise. This list is really great !!!!
I'll keep you informed about the oscillating problem of the main gear.
Jan
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