Lorn wrote: <= ;<None of the above solutions would have stopped me from having a gear u= p landing. =E2=80=A6=E2=80=A6.
Wolfgang's pressure switch closer would h= ave saved my bacon.>>

= Lorn,

= I would be careful with that conclusion.

= The failure to extend, or more accurately, the failure= to fully extend, on the 320/360 gear is one mode that hasn=E2=80=99t reall= y been discussed in any great detail on the LML. It is certainly at least as important of the hydraulic= lock that has seen a lot of attention.

= When retracted, the landing gear stores a lot of poten= tial energy. Gravity, and in= the case of the Outback Gear, aerodynamics, are trying to pull the gear ou= t of the wells. This stored = energy becomes very significant during the extension cycle.

When =E2=80=98gear = down=E2=80=99 is selected, the pump pushes the spool against the up-side po= ppet to open the =E2=80=98up=E2=80=99 circuit. This unlocks the high side circuit and allows the gear t= o start down. Initially the = gear isn=E2=80=99t driven down by the pump. Instead it is pulled down by gravity. The initial volume flow rate generated by falling= gear is more than the return side of the pump can absorb. This in-rush and backing up of fluid generat= es a pressure spike that impinges on the face of spool. If high enough, it will begin to push the spool= back and start to close off the poppet valve. As this occurs, back= pressure is transmitted though the high-side circuit, through the cylinder= s, all the way back to the low side circuit and corresponding pressure swit= ch. If the pressure spike cl= imbs to the low side pressure switch setting, the pump will shut down. This is a very fast and dynamic = event. Several key factors c= ome into play: The pressure = generated by the inrush of fluid from the descending gear decays very quick= ly; The pump is transfer flu= id at a near constant rate; = The pressure spike takes a finite time to propagate; And finally the pump has inertia. Even if the pressure spike momen= tarily reaches the low side pressure switch setting and power is cut to the= pump, the spool down of the motor combined with the rapidly decreasing pus= h from the gear can enable the spike to drop back below the pressure switch= setting. This can be heard = as a hesitation in the pump shortly after gear down is selected. It can also be observed when monitorin= g system pressure during the event. = If the spike is long enough in duration, the pump can be shut down = completely with the system remaining in a stable condition. In that case:

1= . = ; Both high and low s= ides will be pressurized at a value higher than the low side pressure switc= h (550 psi in a nominal case)

= 2. &nbs= p; The spool will be = centered

= 3. &nbs= p; The gear down pres= sure switch is open (pressure just above set-point)=

4.= = The gear up pressure= switch is closed (pressure = between high and low set points)

<= FONT face=3DCalibri>In this state, the gear can still be retracted, but not= further extended. The syste= m is in a state where it thinks it is fully extended. This condition will unfortunately not be correcte= d with Wolfgang=E2=80=99s module.

<= ?xml:namespace prefix =3D o ns =3D "urn:schemas-microsoft-com:office:office= " />

So how does one res= olve the issue long tem?&nbs= p; The solution is actually quite simple; Increase the pressure sett= ing of the low side pressure switch. = ; As the pressure switch setting is increased, the pressure spike ha= s less influence and the duration of the pump interruption decreases. Once the setting is higher than t= he pressure spike, there is no longer any interruption in pump operation an= d the gear always extends normally.

<= o:p>

<= FONT face=3DCalibri>Chris Zavatson

<= FONT face=3DCalibri>N91CZ

<= FONT face=3DCalibri>360std

<= FONT face=3DCalibri>www.N91CZ.net

From:= Lorn H Olsen <lorn@dynacomm.us>
To: lml@lancaironline.net
Sent: Monday, February 20, 2012 4:58 AM
= Subject: [LML] Re: 320/360 Hyd= raulic Pressure Switch

Angier,

If you are flying= and the gear doesn't come down, opening the dump valve for a fraction of a= second and then closing it, fixes the problem.

On a climb out your = switch would work but the problem only occurs when there is at least a 50= =C2=B0F temperature raise. Why not just land and open a fitting? To see if you are= going to have a problem on the ground, just open and then close the dump v= alve. The pump should run. If it doesn't, you will have to open a fitting t= o relieve the pressure. You could also install pressure gauges and just loo= k at them.

The pressure gauges are probably the 1st extra item that = should be installed.

The problem with all of the above solutions is = that they can require a pilot's time at the worst possible moment.

N= one of the above solutions would have stopped me from having a gear up land= ing. At the OM, on an IFR approach, I put the gear lever down. It was very = turbulent. I was busy keeping the dirty side down. At 500' I was crabbed 45= =C2=B0. The wind was 6kts on the ground. I just didn't notice that both swi= tches were open.

Wolfgang's pressure switch closer would have saved = my bacon.

Lorn

> From: "Greenbacks, UnLtd." <N4ZQ@= VERIZON.NET>
> Date: February 17, 2012 1:07:36 PM EST
> =
> Seems to me the simplest and least expensive option would be to in= stall a momentary on switch in the cockpit to override and close the open p= ressure switches.
>
> Just my 2 cents.
>
> Angier= Ames
> N3ZQ

--
Lorn H. 'Feathers' Olsen, MAA, ASMEL, A= SES, Comm, Inst
DynaComm, Corp., 248-345-0500, mailto:lorn@dynacomm.us<= BR>LNC2, FB90/92, O-320-D1F, 1,800 hrs, N31161, Y47, SE Michigan

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