Monday, February 25, 2008

Nav1 and plenty of venturis at Wondai

Last Sunday I went out on a navigation exercise with Lee to Wondai (YWND) via Kumbia and came back to Redcliffe via Kilcoy. Redcliffe Aero Club members will recognize Nav1 of the PPL training.

All the navigation was done by dead reckoning. We left Redcliffe at about 11AM and tracked to the north-west, passing the townships of Hazeldean on Lake Somerset, Blackbutt, the Tarong power station and Kumbia. The flight was very enjoyable, with scattered clouds at about 4000 feet, a headwind between 10 and 15 knots and hazy conditions. We did a few corrections for drift using the 1-in-60 method as well as a ground speed check which gave us a figure of 100 knots.

At Kumbia we turned to the north-east and soon had Kingaroy under our right wing. We made a call on the Kingaroy CTAF frequency to let everyone know we were in the area. The Gordonbrook reservoir appeared under our left wing, then the township of Tingoora. Just a few minutes later it was time to start our descent to Wondai and think about how to join the circuit.

There was only one other aircraft in the CTAF, a Texan. I joined crosswind for runway 18 and performed my first landing on a grass strip. The grass was about a foot high, which definitely qualifies for "long grass" on the performance charts! The surface of the strip was uneven, and I had to keep the control column pulled all the way back to prevent damage to the nose wheel and propeller. We shut down, ate our packed lunch in front of the terminal building of this peaceful little airfield and enjoyed the serenity.

I took a few minutes to walk around camera in hand. Wondai is home to the Barambah District Aero Club, which was officially opened by none else than infamous former Queensland Premier Joh Bjelke-Petersen.

Around the corner from the clubhouse, I noticed two airplanes in open hangars.

The first one is a small taildragger with rego VH-MSP. The VH Register tells us that it is an Auster J5, first imported into Australia in 1951. Searching the Web, I discovered the work of Ed Coates, who has been collecting pictures of aircrafts for the last sixty years. His amazing Web site has two older pictures of VH-MSP taken in 1964 and 1990. It further identified the type as an Auster J5 Adventurer.

The type was first manufactured in England in 1947 by Auster Aircraft, a British light aircraft manufacturer which ceased production in 1968. Quite a few of these planes made their way to Australia. There are some beautiful pictures taken at the Auster Rally 2007 in Wentworth in south-western New South Wales. The next edition will take place later this year at Goolwa in South Australia.

The aircraft has a surprisingly narrow engine compartment, about twice as tall as wide, with 4 prominent exhaust pipes on the underside. This looks a lot better than the ugly exhaust manifold that can be seen on these pictures of another Auster J5.

The vacuum system is driven by two venturis, one on each side. The venturi on the port side is rather small and looks similar to the venturis found on Tiger Moths, or at least is similar to the picture of a venturi used on a Tiger Moth and featured in Bob Tait's CPL Aerodynamics. the venturi on the other side is similar in size and shape to the venturis of older Cessna 172s, such as VH-DCO stationed at Redcliffe.

I could only open the door a crack to take the picture below. I would not have wanted to enter the cockpit further anyway because of the scary flying insects inside, some of them about two inches long. According to the placard on the instrument panel, the plane was (or still is?) used for glider towing. Wondai is a pretty popular place for gliders and has a winch launch system.

The J5 type was originally designed as a 4-seater, however the placard clearly says “No Passengers” and “Pilot Max Weight 100kg”. Although the aircraft is fitted with dual controls, these were probably only used for training with no glider in tow. Pilots are rarely the jockey type, and the likelihood of finding an instructor and a student with a combined weight under 100kg can be safely considered as statistically insignificant.

The instrument panel is rather antiquated. It has rocker switches for the two magnetos instead of the rotary switch found on modern aircrafts. The Airspeed Indicator shows a stall speed of about 56 knots clean and 30 knots with flaps down. In addition to the altimeter and magnetic compass, one can find oil temperature and pressure gauges, as well as a massive turn coordinator in the middle and a tachometer on the side. A Vertical Speed Indicator (VSI) was added later and sits on top of the dashboard. Only the left stick has a Push-To-Talk button. I couldn’t see any radio inside though.

In the next hangar I found VH-DID, a 1963 Cessna 172D, with two identical venturis, one on each side. The D model was the first one to feature the so-called Omni-Vision rear window which improved visibility but also increased drag.

There was virtually no wind when we started up again, so we decided to take-off on runway 36, which saved us having to taxi all the way back to the threshold of runway 18 over bumps, holes and grass. We took off, kept climbing on downwind and left the circuit overhead to the south-east in the direction of Kilcoy. The tip of Lake Barambah was about the only good navigation fix on that leg. Lee recognized Mt Monsildale, but I wouldn't have found it on my own. We found Kilcoy where we expected it, at the top end of Lake Somerset, then crossed the ranges and started our descent towards Redcliffe, leaving plenty of space between ourselves and the overlying Class C airspace.

Approaching Caboolture I made a radio call to say that we were 10 miles west and tracking for Redcliffe, only to realise that I had made the call on Brisbane Radar frequency... Oops. The call was promptly re-issued, this time on the correct frequency. We made our inbound call for Redcliffe just as we crossed the power lines west of the Bruce Highway. Lee asked if I was really sure I was 10 miles inbound. I said yes, then he pointed at the GPS that he had configured to display the distance to YRED. It showed 9.7 miles, not too bad :-)

As I was at 1500 feet overflying the live side of the circuit at Redcliffe I could see VH-MSJ right below me turning base for 07 at 1000ft. We continued to the dead side, descended to circuit height and joined crosswind for 07. The wind was straight down the runway, a very unusual occurence at Redcliffe. I landed on 07, parked between then hangars and shut down. Lee went back in and I took a few minutes to clean up the plane, write down the figures and repack my stuff.

Before leaving in the morning I had followed Lee's advice to put the flight notification acknowledgment printout at the front of the airplane folder, with a big SARTIME written across it. This was a smart move since otherwise I would have forgotten to cancel SARTIME. I called CENSAR over the phone, gave our callsign VH-RAQ, place of arrival and nominated SARTIME, and the person at the other end of the ligne confirmed the cancellation.

In the short debrief Lee explained to me how to use the DG to establish the airplane on track when leaving an airfield without overflying. He remarked on a few other things, such as the fact that I had started my fuel log using departure time and not the time of engine start-up, and that I did not properly monitor oil pressure on start-up. Appart from that he was happy with mu flying, and nav1 was therefore called a success.

Next step is my GFPT test next Friday. Back to the 152, I'd better make sure I go over the aircraft speeds and procedures again. The forecasted weather is showers of rain with lots of clouds and a near-direct crosswind of about 20 knots... Let's see if the test happens. I really hope it will, otherwise I will have to postpone it for at least several weeks, which would prevent me from going solo on navigation exercises, which would seriously delay the advancement of my PPL training. But I guess I shouldn't complain about the rain.

Wednesday, February 6, 2008

The Redcliffe Automatic Weather Station

Because of the bad weather we’ve been having in South-East Queensland for the major part of the last two months, I got into the habit of checking the latest weather observations reported by the Automatic Weather Station (AWS) at Redcliffe before going flying. In the US, an AWS is known as an AWOS (Automated Weather Observing System).

On a number of occasion the weather observations showed south-easterly winds at 20 or 25 knots, i.e. almost direct crosswinds for our 07/25 runway, way in excess of the 15 knots crosswind limitation for the C152. However, when I arrived at the club, the windsock would usually show a wind somewhere between 10 and 15 knots.

This was all good news obviously since it made the difference between flying and not flying. However, this prompted me to try to find out how the weather measurements were made at Redcliffe, and why there was such a discrepancy in wind speed.

The information is not easy to find, but if you go to the page for a monthly weather report for Redcliffe, you will find this mention:

This Automatic Weather Station (AWS) is located in Talobilla Park, and sources its wind measurements from an anemometer on Redcliffe jetty.

I went to have a look today and found both the AWS and the anemometer. Apologies for the photos being a tad on the dark side, but today was really one of those days. Redcliffe received 60 mm of rains in about three hours. When I walked into the club I could see Tony and Lee hurriedly pulling planes inside the hangar before the thunderstorm hit. That was the first hint that no flying would happen. Then I looked at the weather radar with Mal and lost all hope of flying today, so we spent half an hour booking lessons for the next weeks and discussing the planning of the rest of the training, and my options for the CPL.

Back to the AWS. The anemometer is actually difficult to miss, it sits on top of a tall metal pole right at the end of the Redcliffe Jetty. The height of the pole is about 10 meters, in line with Bureau Specification 2013 on "the siting and exposure of meteorological instruments and observing facilities" which reads:

[...] ideally anemometers should be exposed over level terrain at a standard height of 10 metres above the mean ground level at locations completely free of all obstructions to the air flow.

Both wind speed and wind direction are measured here. Interestingly, there is another wind direction sensor (wind vane) on a shorter pole just a couple of meters away. On top of the pole also sits a UHF antenna similar to a rooftop TV antenna.

Finding the AWS at Talobilla Park was a bit harder. It is actually located inside a fenced enclosure on top of a hill at the back of a baseball pitch and is hidden from view by a curtain of trees.

A side effect of my search for the Redcliffe AWS was to discover the existence of the Redcliffe Leagues Padres Baseball Club. I didn't even know baseball was played in Australia. Around here we prefer to play that variant of baseball that involves a flat bat and week-long games known as cricket. The Padres' newsletter claims they are “the biggest and some would say best baseball club in Queensland”. Unfortunately I do not know how many baseball clubs there are in Queensland so I can't really put this statement into perspective.

Back to our meteorology topic. The AWS itself is your regular little white hut one meter above ground. It measures temperature, dew point temperature, atmospheric pressure, relative humidity and rainfall. I couldn't see any rain gauge though. Maybe there's an opening at the top of the box to let rain in, or maybe rain is measured somewhere else.

There is a pole nearby with two antennas similar to the one at the Redcliffe Jetty. One of the two antennas points in the direction of the jetty, most likely for a point-to-point radio link to transmit wind measurements to the AWS. The other antenna points in a different direction and is probably used for sending the measurement to the Bureau. It seems odd though that the BOM implemented their own wireless communication network while they could simply hook up the AWS to the cell phone network or a land line.

With all this information in mind, the position of the anemometer on the Redcliffe jetty may explain why the reported wind is stronger there than at the aerodrome. The anemometer is about 3 nautical miles to the east-south-east of the aerodrome. When the wind blows from the East or the South-East, it hits the anemometer first, travels over the ground and finally hits the windsock at the aerodrome. As the wind blows over populated area, it is slowed down by friction and by tumbling over buildings, houses, trees and a few small hills.

According to Bob Tait’s CPL Meteorology, surface wind speed drops by one-third over water and two-thirds over land in comparison with the speed of the gradient wind at altitude. This implies that surface wind over land is half of surface wind over water. I do not know if the distance of three miles from the jetty to the aerodrome is sufficient to slow the wind down to what can be called surface wind speed, but the order of magnitude seems about right: when the wind is blowing at 25 knots at the jetty, we get less than 15 knots at the aerodrome, which makes crosswind landings possible yet challenging.

Saturday, February 2, 2008

My very own headset: a David Clark H10-60

As mentioned in my previous post, I finally decided to buy myself a headset. I decided on a David Clark H10-60. I bought it online from SkyGeek in the US and got it shipped to Australia, which saved me about $150 compared to the cheapest Australian pilot shop. To put things in perspective, that’s one hour of solo flying in the C152!

For the selection process, I first proceeded by elimination. Since I expect this headset to last me for many years, there was no point skimping on quality. This took care of some of the cheaper brands such as Altronics and Flightcom.

On the other hand, the price of some of the top-of-the-range General Aviation headsets is so incredibly high that it borders on the ridiculous. I’m sure they are all fantastic pieces of technology, especially headsets such as the Bose-X. If I ever end up with a career in aviation I think I’ll go for one of these. But not now.

I also looked at recent expensive headsets such as the Lightspeed Zulu. The ad calls it “the world’s quietest ANR headset”. It may be true, but with a price tag well over $1000 it’ll be some time before I have one in my flight bag. It’s a pity, because it has some very nice features, such as the possibility of plugging in any mobile phone with a “hand-free” feature. This may come in very handy in flight for obtaining weather reports and forecasts, checking availability of fuel or simply letting people know everything’s OK (or not, depending).

To make a long story short, I decided in the end to go for a David Clark headset. The brand has a good reputation and good worldwide service, and all the people I asked around me were very positive about this company’s products. I also found a lot of good feedback about them on pprune. Going through their list of products, I narrowed down my choice to two models, the H20-10 and the H10-60.

In the end I decided on the H10-60. I didn’t like the look of the H20-10, especially the abundance of green plastic and the squarish shape of the ear cups. From the technical description both headsets sounded comparable. My only concern was weight. The H10-60 is nearly a hundred grams heavier than the H20-10, which can make a big difference on a long flight. I couldn't find any decent comparison of General Aviation headsets online that would go beyond listing the characteristics given by the manufacturer. I could find some useful anecdotal information here and there, but that's about as useful as the Internet was in the selection process.

After considering all these different trade-offs, I decided to go for the H10-60. Now that the selection was over, the next challenge was to find where to buy it from.

I had a look at the Web sites of all the Australian pilot shops I could find. I looked at SkySupply, Airsupport, Concept Aviation, AeroShop, the Downunder Pilot Shop, Skylines, Ozpilot and SkyShop. SkySupply clearly came ahead of the pack with a price tag of $490. The other two shops that offered the model were Airsupport at $630 and the Downunder Pilot Shop at $650.

Since most headsets are manufactured in the US, why not try to order directly from there? The US are a larger market than Australia, and with lower taxes, so American pilot stores such as Sportys and SkyGeek may have a better deal. SkyGeek turned out to be the cheapest, with a price tag of US$ 314. The headset carrying bag was an extra US$ 16, and the shipping cost was only about US$ 20 with the Fedex Economy option.

I ordered from SkyGeek and I received the headset and its carrying bag one week later. All was in perfect condition, and the grand total was US$ 352. In Australian dollars I was charged exactly $409. Quite a good deal in the end, I saved about $150. It sounds to me as if the Australian pilot shops took advantage of the fall of the US dollar vs. the Aussie dollar but didn’t exactly pass on the savings to their customers. I mean, why charge $48 in Australia for the exact same headset bag sold at the equivalent of $17 in the US? That’s nearly three times the price.

The David Clark carrying bag is very good, must better than the ones usually given away for free with cheaper headsets. It is made of very sturdy fabric and has three pockets, including one zipped one. In the zipped pocket I have space for my pilot license, ASIC card, wallet, car keys, mobile phone, etc. The other two pockets are great for holding a couple of pens, the local VTC and a few sheets of paper or cereal bars if need be. That’s the only bag I take when I go on local flights.

The headset itself is amazing. The gel ear seals work really well, even with sunglasses on. The headband is easy to adjust and doesn’t move. The mike stays perfectly in place. The volume controls on top of each earcup are easy to find. And you can’t even feel the weight of the headset on the top of your head. OK, I’ve only used the headset for about one hour at a time so far, so we’ll see how it behaves on longer flights. But I'm pretty confident I'll keep on calling it my very own awesome headset for many years.