Wednesday, July 29, 2009

Stalls theory and revision flying

After having lessons cancelled because of sickness and weather, today I was back for my next lesson.

Today's mission was to be stalls. We went through the theory during the briefing but when we went out to fly the visibility was too poor to actually do stalls.

First we went through what a stall actually is. Contrary to what most people think, stalls in aeroplanes do not have anything to do with the engine (unlike in a car). Stalls occur when the wing's angle of attack goes beyond the critical point.

The angle of attack is the angle between the chord line of the wing (an imaginary line running through the wing from the leading edge to the trailing edge) and the airflow.

The angle is the Angle of Attack (AofA)

When the wing goes beyond the critical angle of attack (16 degrees usually) it experiences a reduction in lift. It is possible to stall at any airspeed or attitude - it is possible to stall whether flying straight and level, climbing, descending etc. The wing does not 'lose lift' (which would imply that there was no lift at all and the plane would just plummet to the ground), it experiences a 'reduction in lift' which means that it will descend.

Relationship between Lift and Angle of Attack (AofA)
- the top of the red curve is where the stall occurs.

It is generally not possible to stall unless the pilot actually forces the plane to stall. It is not possible to be simply flying along and then stall, the pilot must do something to force the stall (such as raise the nose attitude). It is considered bad airmanship to go into an unintentional stall.

Before entering the stall, there are a number of checks to go through.
  • H - Height
  • A - Airframe
  • S - Security
  • E - Engine
  • L - Location
  • L - Lookout
Height refers to the height of the plane above ground level. The stall must be recovered from by 3000ft AGL so it is generally advised to be around 4000ft AGL before entering the stall. Airframe means checking that the landing gear is raised (if applicable) and the flaps are in the desired position. Security means checking that all hatches and harnesses are secure (basically doors and seatbelts) and there are no loose items that might fly around the cockpit during the stall. Engine means checking for normal engine operation. Location means checking that you are away from any towns and anything to crash into (other aircraft, mountains etc). Lookout means to make an inspection before performing the stall (generally do a 360 degree turn) to check that the area around (both to the sides, above and below) are clear.

Location is important with stalls as you can't perform stalls over towns or built up areas. This is because, as Jeremy put it, 'when people see a plane stopped in the air with no engine noise, they tend to crack the shits and call the police'.

In order to force the plane to stall, the power needs to be reduced to idle (around 900-1000rpm) and the nose needs to be raised beyond the critical AofA.

Symptoms of an approaching stall include:
  • decreasing airspeed and noise level
  • controls less firm and less effective
  • pre-stall warning (noise)
  • shuddering airframe
  • relatively high nose-up attitude
During the stall the nose will drop by itself and the aircraft will descend.

To recover from the stall, the angle of attack is reduced by moving the control column to the neutral position as the nose drops. Then, as the airspeed increases, raise the nose slowly and simultaneously apply power. Raise the nose until it is back in the climbing position, as this will allow us to recover the height we lost during the stall.

I also got around to apologising for my vagueness regarding things like the handing over/taking over procedure. By the sounds of it though, I'm not the only one! Anyway, it's all sorted now, I know what I'm meant to be doing and why!

After the briefing we popped outside to see if the sky was clearing up (it was pretty cloudy). It did seem to be slowly clearing so we decided to wait 10 minutes and see what it was like then. To fill in the time, we started to fill in my logbook.
The logbooks are pretty easy to fill in, you just need to put in dates, the type and rego of the plane, the PIC (instructor's name), what we practiced and the time.
Example Logbook page (not mine, clearly)

While Jeremy was printing my training records, Neroli (the wife of the guy who owns Lilydale) came over and started talking to me. She sends out an email to all the female pilots and wanted my email address (which was fine). Then she asked me "So are you going to live in Australia permanently?" I was like "Yes. I was born here, really!" (I get this so much, apparantly my accent sounds fairly British). Jeremy was pretty amused by the whole thing.

Logbook complete, I was sent out to preflight Jab 4929. I've found out that some bright spark has removed the pull ring on the 4929 that allows the rudder pedals to be moved forward - unfortunately today I was back to stretching to reach the pedals.
I started the preflight and realised that the fuel drain tester had somehow disappeared so I had to pop back inside and find one. Then when I got back outside and was preflighting, these two guys came over and started doing stuff with the plane (checking the wheel I think) - I'm assuming they were maintenance guys. Luckily, they said it was all alright to fly! I went through the rest of the preflight and I'm getting loads more confident at it. When Jeremy came out I got around to asking the few questions I've been meaning to ask for a while. The first was about checking the brakes - to tell if the brakes are getting too worn, the brake pads will be scratched and clearly used looking (they weren't). The second was whether or not I'm meant to dip the fuel tanks during the preflight - apparantly I'm not since there isn't a dipstick. I'm quite pleased about that as, since the fuel tank lids are on the tops of the wings, I'm not sure I'm tall enough to be able to do it!

We jumped into the plane, went through the checks and I started it. I learnt from my experience last lesson and this time I checked my headset was plugged in before I put it on (luckily, since it wasn't). I taxiied us to the runway and Jeremy took control for the take off.

When we got to the training area the visibility was clearly not good enough to go up to 4000ft to do stalls, so we decided to do a shorter revision lesson. We did a mixture of climbing, descending and turns (all types). Although it was disappointing that we couldn't do stalls, it was good to have a refresher on all of this. We only flew for about 30mins today since the visibility was poor and when we started to head back to the airfield the wind was clearly coming up, it was getting a bit bouncy.

Jeremy took control for the landing. There was a slight crosswind so during the approach the nose of the plane was pointing slightly to the side. I taxiied us back, did the last checks and we jumped out.

I've booked lessons for this Saturday and for Wednesday 12th August. Jeremy is going on holiday in the week between and, although I could have flown with a different instructor, after my experience with Murray I figured it was easier to just wait. Hopefully the weather on Saturday will be good enough for us to do stalls.

I've been looking into buying my own headset. I was going to wait until Christmas (to try and get at least part paid for by my parents as a present!) but I'm not sure I'm going to wait that long. To put it nicely, the school ones aren't fantastic, so it would be nice to have my own. Headsets range in price from $200 (school ones) to $1,500 (like Jeremy's Bose). However when I do buy one I'm not going to choose one based on price, but based on comfort, because it is a long-term purchase that will (hopefully) last me for years. I'm going to ask next lesson if Jeremy has any recommendations and I'll try and find a shop with a good range where I can try them on. There are so many different options around, it's going to be a difficult choice!

Random things I learnt today:
  • You can't move the rudder pedals in 4929 (gah)
  • Jeremy likes Freddo Frogs
  • People apparantly think I'm foreign