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1. 10:03 AM - Re: [Non-DoD Source] Re: YAK 52 - Procedure for emergency gear down (Walter Lannon)
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| Subject: | Re: YAK 52 - Procedure for emergency gear |
down
Hi Mark;
Agreed, it is a complicated question. Am I correct in assuming the shuttle
valves you refer to are the "Emergency" valves? They are indeed a shuttle
type valve but are designed to default (via spring pressure) to the "normal"
position in the event of a zero pressure situation as you describe in your
example.
In that example it would seem that, if the handle was left in the up
position, an immediate unsafe gear situation would result. Retraction may
be prevented by trapped air in the down side but down locks would be
disengaged. No such problem with the selector in the down position.
All the best;
Walt
-----Original Message-----
From: Bitterlich, Mark G CIV NAVAIR, WD
Sent: Monday, September 25, 2017 10:51 AM
Subject: RE: [Non-DoD Source] Re: Yak-List: YAK 52 - Procedure for emergency
gear down
<mark.bitterlich@navy.mil>
Yes can be a reason not to move it to the down position Walt. Give me a
second. First I'd like to add one more tidbit that is not mentioned in
any of the POH's. I managed to figure this one out while ferrying a YAK-50
from East to West coast about 15 years ago.
Dennis mentioned that when both gear levers are in the middle, all air is
relieved downstream of the landing gear actuator. "Vented" is a better word
to use here. But what this also does is to isolate the whole landing
gear pneumatic system from the main air tank, and the compressor and lines.
Why is this important to know? Because let's say you have an internal
actuator leak downstream of the gear actuator levers? Landing gear selected
up, or landing gear selected down, there will be air leaking and it can be
so drastic as to drain the main bottle completely. If you isolate the
landing gear with both (or one in the case of the YAK-50) landing gear
handles in the middle position, you give time for the main bottle to fill up
again completely. In the case of the YAK-50, you actually can fill BOTH
main AND emergency bottles up this way. Both bottles are plumbed to the
compressor on the 50, unlike on the 52 where only the main bottle is filled
from engine compressor!
air.
In any case, you can let the pressure fill back up and then try to make a
second attempt to lower the gear normally. You can do this as many times as
you want, if you feel this is the right thing to do.
In the case of the emergency system, once you open that valve, you cause
shuttle valves to change position on each landing gear. Two on the 50,
three on the 52. That shuttle valve has two positions, emergency or main
air supply. Anyone who has tested the emergency system knows that you must
drain all the emergency air out of the lines, and then select DOWN on the
landing gear actuator lever in order to cause the shuttle valves to move
back to the position where MAIN AIR will be used to lower the gear.
If you lower the gear using the proper emergency procedure (with both gear
handles neutral) air on both sides of each gear actuator is vented, so when
air is applied via the emergency valve, there is no air pressure on the
opposite side of the actuator at all, that would in any way impede full and
rapid movement of the actuator and thus the landing gear. Once the gear is
down, it is procedure to keep air applied on the down side of each actuator,
which is what is happening at this point, unless there is some gross leak.
If you now move a landing gear handle DOWN, you will supply MAIN AIR
(assuming you have any) to the shuttle valve on each actuator. So now you
have two air supplies fighting each other to set the position of the shuttle
valve, which I submit no one intended.
Let me give you a real world YAK-50 example. Chevron seal in one actuator
fails. Gear is selected down. Gear does not come down and lock. Main air
drains to near zero. Gear handle is put in middle position and emergency
air valve is opened. Main gear locks down, but emergency air bottle drains
to zero. In the meantime main air bottle fills back up. Landing is made
with main bottle full with brakes being normal. If the brake handle had
been selected down, it's hard to prove what might have happened, but if the
shuttle valve changed positions, then the main bottle would have started
draining.
So it's a complicated question, that requires full understanding of how this
system is plumbed and it differs between a YAK-50 and a 52 but understanding
what air goes where and why, along with a complete understanding of those
shuttle valves is important for all of us to grasp.
Mark
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Walter Lannon
Sent: Sunday, September 24, 2017 1:32 PM
Subject: [Non-DoD Source] Re: Yak-List: YAK 52 - Procedure for emergency
gear down
Hi Dennis;
Is there some provision in the Yak 52 POH that prohibits movement of the
gear selector to down after an emergency down operation?
Of course every licensed and qualified CJ and Yak pilot thoroughly
understands that the emergency gear down operation completely by-passes the
gear selectors and directs emerg. air directly to the down side of the
actuators. They know this due to their enormous diligence in understanding
their aircraft!
Moving the temporarily inoperable gear selector to the down postition is
called good housekeeping, probably because that is were it supposed to
be during landing.
Cheers;
Walt
From: A. Dennis Savarese <mailto:dsavarese0812@bellsouth.net>
Sent: Sunday, September 24, 2017 9:49 AM
Subject: Re: Yak-List: YAK 52 - Procedure for emergency gear down
No, you do not move the gear selector after you place it in neutral. The
emergency air system is designed to extend the gear without the movement of
the front gear selector. The emergency system is totally independent of the
main air system and the gear selectors.
After you have extended the gear with the emergency system, th time to move
the front gear selector back to the DOWN position is after you have parked
the airplane and shut the engine down.
Dennis
________________________________
From: Jean-Philippe Martel <marty.jpm@gmail.com>
Sent: Sunday, September 24, 2017 8:43 AM
Subject: Re: Yak-List: YAK 52 - Procedure for emergency gear down
Indeed I don't doubt I already saw what you described.
Back to the procedure in flight, the selectors on neutral position +
activation of the emergency valve are enough to provoke the emergency gear
down? Or does one have to pull down the front selector as well?
Le 24 sept. 2017 13:06, "A. Dennis Savarese" <dsavarese0812@bellsouth.net> a
crit :
FYI - Flaps do not work from the emergency air system. If you doubt this to
be true, then test it the next time you have the airplane on jacks doing a
gear retraction/extension test when doing the emergency gear extension test.
With the rear gear selector in the neutral position and the main air valve
closed, once you place the front gear selector in neutral, all the residual
air pressure in the system forward of the main air valve, is depleted. Then
open the emergency air valve to extend the gear. Now attempt to put the
flaps down.
Dennis
________________________________
From: Nigel Willson <nigel.willson@yakdisplay.com>
Sent: Sunday, September 24, 2017 6:52 AM
Subject: Re: Yak-List: YAK 52 - Procedure for emergency gear down
Both gear selectors to neutral. Open emergency air valve. Do not use flaps
since this will use emergency air that could be used for braking.
Regards,
Nigel Willson
Flying Instructor & Examiner |
Airsh3901238792082250297yiv2214189677MsoNormal">http://yakdisplay
<http://yakdisplay/> . com Tel. 07809 116676
Sent from my Samsung Galaxy S7 - powered by Three
-------- Original message --------
From: Jean-Philippe Martel <marty.jpm@gmail.com>
Subject: Yak-List: YAK 52 - Procedure for emergency gear down
Hi!
Could any YAK 52 driver kindly remind me the official emergency procedure to
gear down in case of full pressure loss in the normal circuit, please?
Thank you in advance!
Marty
France
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