Sunday, May 3, 2009

Look mum, no wheels!

After getting checked out in the Archer I decided to go for the next aircraft up in the Piper family, the Piper Arrow. This way, I would have access to the entire fleet of single-engine aircraft at the Schofields Aero Club.

This was a little bit more involved than a check flight though, since the Arrow has a design feature for which I was not yet endorsed: a retractable undercarriage. Undercarriage being a fancy name for a landing gear.

I had already obtained an endorsement for aircraft with a variable-pitch propeller (the so-called Constant Speed Unit endorsement) propeller last year on the Cessna 182, so I was already familiar with this aspect of the Arrow. The only thing to keep in mind really is "rev up and throttle back" to avoid overboosting the engine, and the manifold pressure and RPM settings for climb and cruise, 23-23 and 25-25 in the Arrow.

Each of the two main wheels retracts by rotating 90 degrees towards the fuselage into the wheel well situated inside each wing. When retracted, the main wheels are parallel to the wing. The nosewheel retracts by rotating aft. The pre-flight inspection includes checking the wheel wells for any obstruction such as birds nest and the like.

Each wheel has its own hydraulic actuator. On the photo below, the silver arm of the actuator can be seen. It is extended when the gear is down. The pressure is provided by a reversible electric pump: it pumps fluid into the actuator to make the gear go down, out of the actuator to make it go up. Once the gear is in position, either up or down, the pump stops and a shuttle valve isolates the actuator lines from the rest of the circuit. This keeps the fluid lines under pressure without having to keep the pump on, which comes in handy for emergency gear extensions. More on that later.

The main wheel doors are linked to the wheel leg. A microswitch somewhere reports if the door is closed, and activates the "gear unsafe" warning if it is not. Which I understand is utterly unreliable in the Arrow. The pipe on the right-hand side of the wheel is simply the hydraulic line to the main wheel brakes, which is a completely separate hydraulics circuit from that of the landing gear actuators. Hydraulic pressure for the brakes is simply provided by a master cylinder connected to the top of the rudder pedals, the so-called toe brakes.

On the main left wheel is a "squat switch", a microswitch that opens the electric circuit of the electric pump when the gear is extended and on the ground. This way, the gear cannot be retracted when on the ground. Of course we didn't try it. Call that lack of faith, but we were only one faulty switch or faulty wire away from a very, very embarrassing wheels-up what? Parking?

The plan was to go to the training area to get me used to the feel of the aircraft, operate the landing gear and perform the emergency gear extension procedure. We taxied and I called ready for 28R at the holding point, to which the controller answered that they do not have a runway 28 at Bankstown, so I re-issued my ready call with 29R this time.

Take-off didn't feel too different from the Archer. When I first flew the Cessna 182 I remember being surprised by difference in power with the 172SP, not so much going from the Archer to the Arrow. I guess a fairer comparison would be between the Archer and the Cherokee Six. Passing 400 feet I touch the brakes to stop the wheels from spinning, pull the gear lever over the detent and up, and a few seconds later the three green lights go off, and we climb a lot better.

Once in the training area Olivia pulls the circuit breaker for the landing gear pump and I went through the checklist for the emergency gear extension. This involves first checking that it is not the light bulbs for the three greens that are the problem. The bulbs are designed to be pulled out of their sockets and swapped very easily, which I find is very neat.

Then we slowed down the airplane and I pressed the emergency landing gear button. What it does is release the pressure from the gear actuator lines. The actuator no longer maintains the gear up, which then falls under its own weight into the down position. Same story for the nose wheel, except that gravity is not enough to lock the nosewheel down because of the relative wind. A spring is therefore used for moving the nosewheel fully into the extended position.

When the gear free falls into place it locks with a sound not very different to that heard on airliners when the gear goes down. Which feels good. Once the gear is down I do a normal retraction. We do one practice engine failure which takes me onto final for a ploughed field. Olivia asks me to keep a tight circuit since we're not very far from Camden CTR. We go around and go back to Bankstown via the 2RN. The day is quite misty and it's early morning, so we're greeted by the sight of the 2RN radio mast sticking out of the mist. Thank God there's a strobe on that entry point, otherwise I wouldn't have found it.

We join the circuit behind a Cherokee for a few touch-and-goes. The Cherokee is slower than us and at some point we have to request an extended upwind leg for adding a bit of space between us and him. In-between the CSU and the landing gear that's a lot of things to keep in mind when in the circuit. Feels like going back to GFPT days when a circuit in the 152 felt overwhelming.

Olivia insists that I do not rush the downwind checks and wait for the gear indicator lights to come up and not skip to the next item on the check list while the gear is coming down, which usually takes about 7 seconds. Pitch is only put to full fine on final, otherwise it is left where it is from downwind onwards, power adjustments are made with throttle. On final we check Red-Green-Blue for mixture to full rich, gear down and propeller pitch to full fine.

After three circuits we make a full stop and taxi back. Olivia recommends I work on memorising the cockpit actions and checks to be conducted while in the circuit for next time. Today was in Arrow III VH-SFJ, next time will be in Arrow IV VH-LSG. The big difference between the two is that the model IV has a T-Tail, which Olivia assures me is not terribly different from the regular tail assembly, except it's a lot heavier in the flare.

So what I do for the next hour is to sit in LSG, get used to where everything is and take picture of the panel so that I can later prepare flows patterns at home, an idea I found reading Sam's blog.


Anonymous said...

Good Story. Shame NRF is no longer available though.

Julien said...

Thanks! Indeed, VH-NRF crashed a couple of weeks ago, no fatalities.