radiopicture
Joined: 23 Jun 2008
Posts: 263
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 Posted: Thu Jul 22, 2010 11:55 pm Post subject: Hydraulic lock |
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Periodically, I read these hydraulic lock disaster reports, and of
course, I appreciate any information that would prevent me from a
similar fate.
I have limited experience compared with most of the folks on Yak-list.
I have owned two Yak-52s and some exposure to a couple of other M-14P
engined planes. Both of my planes came to me with very low time, so
maybe lower cylinder leak-by was not such a problem. Having said this,
a few questions and observations...
In my first plane, the previous owner turned the prop backwards and
bent a link rod for his troubles. He cautioned me, so I never do that.
Francois mentioned stopping if you feel any resistance. Of course,
there's resistance when the pistons approach TDC. The bottom cylinders
are always going to have a bit of oil, unless you just removed the
spark plugs. So, what we're talking about is judgement in terms of
what's not wise to try to compress. I always grasp the blades around
one-third of the way out from the hub.
I worry about all of these modifications and the fact that they add
failure modes. Of course, it's great if the oil pump's internal check
valve works. In the end, I use the Russian methods. If the plane has
been sitting at all (like more then 15 minutes), I pull it through. I
have hoses that are attached to AN fittings that are threaded into the
intake plugs. They are routed to an exit aft of the cowling right
below the coarse fuel filter. There are AN plugs in the hoses on that
end. I just leave the plugs out in between flights. I put them back in
after I'm done pulling through, including when (and if) I prime in
between blade pulls (Winter). This way, the excess fuel runs out of
the intake drains instead of creating their own fluid lock (not that I
prime all that much).
Hopefully, this is enough to keep me out of trouble.
On Jul 21, 2010, at 3:43 PM, Francois Davel wrote:
| Quote: |
<fdavel(at)senninger.com>
Well as an update I would like post the following.
Due to a lot of support from friends and a very good engineer we
managed to replace the bent rod, on #5
Below is what would consider a safe procedure, any comments? or
additions?
I have been thinking a lot about the that fateful day and how the
lock occurred what could have been done to prevent it and what would
I do differently?
We here is what I have come to think of good procedure, to prevent
this happening to myself again, and happening to one of you.
Never pull the prop on the end, always pull the prop half way along
the blade, this gives you less leverage and so limits the problem of
bending a rod with the prop. Which I believe is possible.
Always stop when ANY resistance is felt. Do not try and “squeeze”
through the oil. It is quite possible to “squeeze” the oil past the
rings and so get through a small lock.....but it HUGELY dangerous.
With the leverage you have in your hand through the prop you could
easily damage the connecting rod.
NEVER TRUN THE PROP BACKWARDS!!!!!! This is arguably the most
dangerous thing to do, since it could allow the oil to go up into
the intake manifold, ready to be sucked into the cylinder and cause
damage.
So as soon as there is any resistance felt stop turning the prop,
and open the two bottom cylinders,and allow time for the oil to
drain, do NOT rush. Once the oil has stopped draining then you MUST
screw the plugs back in!!! Then pull another full set of blades, I
usually pull 16 blades. And if there any resistance, then you need
to stop and remove the plugs again. Allow time for the oil to
drain.....do NOT RUSH.
As soon as you can pull your blades and there is no resistance then
you are ready to fly.
There are options, like and oil shut off valve that allows you to
shut the oil off after you have stopped the engine, and this valve
has a switch that will cut the ignition circuit so you cannot start
the engine with out the oil valve being open. Part of the kit is a
oil pump to pump the engine empty. The danger here is the mounting
of the oil valve could damage the oil tank.
It does not take a lot of oil to cause a lock, I have not worked it
out but I would guess that 100 ml will be enough. What ever the
accurate figure is, it is not a lot.
--------
Round Engines RULE!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=305804#305804
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