The elephant in the aeroplane

In Light Sport Aircraft (LSAs) and Recreational Aviation (RA) – indeed in all flying machines – weight is a key factor. In fact it could be said that weight is THE factor when it comes to light aircraft design – strong (meaning heavy) enough to do the job, yet light enough to carry a reasonable load within the legal regulations of its category. Of all categories, LSAs and RAs have probably the most stringent weight limits applied to them.

Yet in almost all LSA/RA flight reviews I read, there is little or no mention of usable load, empty weights or maximum gross weights. How come nobody discusses this key topic – the elephant in the room? The aircraft may look and fly great but if the usable load is so limited that carrying a couple of typically sized people and a reasonable amount of fuel will take you outside the legal limit for the aircraft – what use is it?

At the recent Avalon Airshow, I wandered around looking at a wide selection of LSA and RA offerings. Many of them were kind enough to display data including empty and maximum weights alongside the aircraft.

All the aircraft I looked at posted a maximum gross weight of 600 kgs or, in a couple of cases, 550kgs and 544kgs. There was a seaplane with a maximum of 650kgs.

The declared empty weights varied between 312kgs and 530kgs although one of them went to the trouble of blanking out the empty weight for some reason. Excluding the anonymous empty weight and the 530kgs machine, the average empty weight of all the LSA/RA aircraft I photographed worked out at a whisker over 360kgs.

One well-known LSA showed – for what appeared to be identical models – empty weights of 360kgs and 390kgs. What, I wondered, could make such a large difference? there appeared to be no parachute rescue system in either, so I (at least) was puzzled.

So let’s have a look at usable loads. Taking a maximum gross of 600kgs, minus the average 360kgs empty weight, leaves you with 240 kgs for fuel, people and baggage. Typical pilots these days tend to weigh in at around 95+ kgs, passengers anything from 60 -100kgs+ – a total for people from around 165-195kgs. Some would say I’m being optimistic! I have certainly seen two big 100kgs+ people get out of an LSA on many occasions. But let’s stick to an average of 180kgs total for people. That legally leaves about 60kgs for fuel and bags. Fuel weighs around 0.72kgs per litre, so without bags you have about 80 litres of fuel. As an absolute minimum, you probably need to allow at least 5kgs for ‘bags’ – remember, tie-down kit, maps, aircraft cover, removable navigation/GPS equipment, headsets, cameras, clothing etc all count as ‘bags’.

Worst case scenario: your aircraft empty weighs 390kgs – see above. You weigh around 100kgs with your boots, headset and clothes on, your passenger the same. You’ve got a 2kgs tie-down kit in the back and your trusty portable GPS on board, plus your passenger’s camera kit. It all adds up to well over 590kgs – leaving less than 10 kgs for fuel, or around 13-14 litres….any more and you’re flying illegally in a 600kgs maximum gross aircraft.

So, what can you do with the elephant? Setting aside the regulations for the class, which lay down maximum empty weight limits based on engine power and number of seats, what implications does this have for buyers and, in particular, flying schools, who want to stay within legal load limits?

First, make sure, before you buy, what is the actual empty weight and thus the usable load. Beware of statements like ‘from 295kgs’ as this weight is often an absolute factory minimum, with no oil, or battery, or bigger ‘standard’ wheels/tyres, wheel spats, radio, antenna, even (in one case I know of) seat cushions and flight instruments. Don’t accept assurances that the factory already weighed your aircraft so you don’t need to – I know of a number of occasions where a repaired aircraft had to be re-weighed and came in much heavier than before repair – in one case somehow gaining over 40kgs (yes, really!) compared with the original factory weight sheet.

Get a written guarantee of the empty weight of the aircraft you’re buying or ask for the aircraft to be weighed just before you take delivery, it’s worth the money – and remember, the manufacturer wants to sell you an aircraft and won’t be the one copping it when you get ramp-checked, or the insurance company refuses to pay out because the plane was flying over the legal weight limit. Or your flying school is audited with a random weight check.

Next, work out your true weight and that of your passenger/co-pilot – including boots/shoes and clothing. Add that to the real aircraft empty weight to work out how much fuel and baggage you can carry. Can you still carry full fuel as well as people and bags? If not how much are you prepared to compromise? Personally, I have a 2-3 hour bladder, so I don’t often need full (fuel) tanks. But what about that 2-hour flight to a place with no fuel, plus the journey home?

Even if you and your passenger are quite light, remember that when you come to sell the aeroplane, the customer might be a flying school, or a lot heavier than you, potentially limiting your sales options.

There’s another one I hear a lot: ‘the plane’s safe to 750kgs gross, so you don’t need to worry’. But you DO. Safe it may be, legal it’s not…remember ramp checks and insurance companies?

Last but not least is the issue of centre of gravity (CofG). The CofG limits are calculated to fit in with the maximum gross weight of the aircraft – how many owners/pilots of LSA/RA aeroplanes actually calculate the CofG before taking their (maybe slightly heavier) friend for a quick morning flight? Tanks full? Feels a bit slow to lift off? Or maybe too quick, with a rearward CofG? No problem, the plane will fly OK…until it doesn’t. Read some accident reports about exceeding CofG limits.

Some people might feel I’m being a bit picky – after all, how often do you get ramp checked? Or insurance companies weigh the aircraft before paying out? Actually, surprisingly often. But the laws of physics can’t be denied; if you frequently fly at or over the aircraft weight limit, it will wear out much quicker. Safety margins are compromised and the flying characteristics will become more and more like a heavier GA-type aircraft. The cruise will be slower, the stall will be higher and you stand much more chance of bending the landing gear if you come down a bit heavy.

Ignorance of the true empty weight of your aeroplane is no defence. Don’t ignore the elephant! You have been warned!

Testing an Airmaster constant speed propeller on the Foxbat

For the last 45 flying hours, we have been evaluating an Airmaster electric constant speed propeller on our Aeroprakt A22LS Foxbat demonstrator and comparing it with the standard on-ground adjustable 3-blade KievProp.

For those of you not familiar with the New Zealand manufactured Airmaster prop, it is a superbly made and easy to use piece of kit. This particular example was retro-fitted after the aircraft arrived in Australia and installation was straightforward. It is a Rotax mandatory requirement that a manifold pressure gauge is fitted with a constant speed propeller, so this was included too.

After discussion with Airmaster, the prop was fitted with three WWR70Z Whirlwind blades, with an overall diameter of 1775mm (about 70″).

Operation of the prop pitch is via a control unit on the instrument panel (it fits into a standard 2.25″ hole), which connects electrically with a motor inside the prop hub, which changes the pitch of the blades. The control unit has a rotating knob with four settings: ‘Take-off’, ‘Climb’, ‘Cruise’ and ‘Hold’. For the Rotax 912ULS engine, these settings correspond to full power RPM values of 5800, 5500 and 5000 respectively. The ‘Hold’ position keeps the RPM to whatever setting you choose, so long as the pitch angle can accommodate. There’s also a small up/down switch for ‘Auto’ and ‘Manual’ operation. Finally there’s a separate spring loaded pitch toggle ‘coarse/fine’ switch which enables you to change the pitch manually. [The evaluation propeller did not have the ‘Feather’ setting on the rotary switch as shown in the photo – this is intended for use on motor gliders. However, the propeller can still be feathered by holding down the lower switch for 5 seconds. There is also a controller with a reverse setting, aimed at seaplanes.]

In normal use the system is very simple to operate – when you’re lined up on the runway, ensure you’ve set the switch to ‘Auto’ and dialled up ‘Take-off’ and apply full power. The engine revs to its 5800 redline and the aircraft takes off like a scalded cat! At about 200 feet above ground, still on full power, rotate the dial to ‘Climb’ and the RPM drops back to 5500, the maximum continuous RPM for the 912ULS. Finally, when you are ready, dial in ‘Cruise’ and throttle back as needed. At altitudes below about 2500 feet we tended to adjust the ‘Cruise’ throttle to give about 25-26 inches of manifold pressure at 5000 RPM.

As an additional piece of information, we checked the static thrust of the Airmaster propeller at full throttle and 5800 RPM, using a calibrated strain gauge, and compared it with the standard KievProp at the same static full throttle RPM.

So, what did we find?

At 5800 RPM on full throttle, the Airmaster developed around 200-205 kilograms of static thrust, compared with about 195-200 kilos from the KievProp. When you take into account that the Airmaster prop is about 12.5 kilos heavier than the KievProp, at these RPMs and power settings, the props were in effect generating about the same thrust per kilo of aircraft weight.

In comparison with the KievProp, the Airmaster gave similar take-off distances and climb rates, although the KievProp had a slight edge above 200 feet, as it remained at 5800 RPM compared with the Airmaster 5500 ‘Climb’ setting. Rotax allows a maximum of 5 minutes running at 5800 RPM, so if you’re in a hurry, you can leave the prop/engine running at this speed. For both the Airmaster and KievProp, 5 minutes at 5800 RPM will get you well over 5000 feet above your take-off point!

When joining the circuit for landing, we reduced power and changed the prop setting in stages – ‘Cruise’ around the middle of downwind, ‘Climb’ at the start of base and ‘Take-off’ somewhere down final approach, so that full power was available in the event of a go-around. The Airmaster gave a noticeable ‘airbrake’ effect when moved to fully fine pitch, increasing the descent angle. Similarly, in the event of an engine out glide, it would be a good idea to set the prop full coarse (or even feather it) with the manual setting, to reduce drag from the stopped or windmilling prop.

The main differences come out at the ‘Cruise’ setting of 5000 RPM. At this setting the Airmaster gave a steady 95+ knots True Air Speed (TAS) – we are lucky enough to have a Dynon D10A on our panel, which shows TAS. The fixed (on-ground adjustable) KievProp set to give 5800 RPM on take-off could only manage around 80+ knots in the cruise at 5000 RPM. However, when set to the factory recommended pitch (giving about 5100 RPM on take-off) the KievProp will at least match the Airmaster cruise speed at 5000 RPM, although take-off and climb will not be quite as spectacular.

And there you have it in a nutshell – the Airmaster will give you great take-off performance and a good cruise speed in the same flight. The standard fixed-pitch KievProp you can achieve fantastic take-off performance or a good cruise speed, but not both in the same flight. However, the ‘factory’ setting will at least match (and maybe even exceed) the cruise speed of the Airmaster, albeit with a small dent in the take-off distance and climb out rate.

Whether the Airmaster is worth losing around 12.5 kilos of load capacity and a cost of around A$13500 (about US$9750) including GSTax, installation and manifold gauge, is a question only each individual owner can answer.

Glider towing with the A22LS Foxbat

Sunday 17 March 2017 dawned clear and a relatively cool 20 celsius at Tyabb Airport. My friend Mike Rudd and I were flying that morning up to Benalla, north of Melbourne, to submit our A22LS Foxbat demonstrator to the Gliding Club of Victoria to test-tow a couple of gliders.

The flight from Tyabb to Benalla was uneventful except for a thick smoke haze up to about 6000 feet due to the smouldering remains of some large bushfires in the area and an almost total lack of wind. About an hour and 20 minutes after take-off, were touching down at Benalla. Gliders were already in the air, albeit in much smaller numbers than the last time we visited, just over 3 years ago.

I flew a short acclimatisation flight with Rob Pugh, the tow pilot for the day (I am not licensed to tow); he made one of the smoothest landings I have experienced in someone who had never flown the type before. Very reassuring for the remainder of the morning! Rob then did a couple of circuits on his own to check out the Foxbat handling without my 85 kilos of ballast in the passenger seat – anyway, towing is only permitted with one person on board.

The first glider – a single seat SZD51 Junior with gliding instructor Steve Hobby on board – was hooked up and, with GoPros activated on the Foxbat, Rob applied full power and took off. Temperature on the ground was about 30 Celsius (about 85-86 Fahrenheit), giving a density altitude at ground level of well over 2500 feet. There was almost no wind at all. Tow time to 2000 feet AGL (2500 feet on the QNH, about 5750 density altitude) was almost exactly 6 minutes and Rob was back on the ground just over 3 minutes later.

Next up was a 2-seat Twin Astir glider with just one person on board. This glider is affectionately known as the ‘concrete swan’ – the heaviest 2-seater in the club, so it would be interesting to see how long it took for the trip. In the event, tow time to the same altitude took only 30 seconds longer and Rob was back on the ground again, around 3 minutes after release.

We are making a short video of the test-towing which will be uploaded to our YouTube channel shortly. Meanwhile, Rob had a few candid comments about Foxbat towing. “Of course”, he told us, “with only 100hp available, the Foxbat won’t be competing with our Pawnees [my note: one of which has a liquid cooled Chevrolet V8 engine!]. But the Foxbat performed very well, considering the lack of wind and the high density altitude. The total take-off to landing times of just over 9 minutes worked out much better than the 13-14 minutes we were expecting. I think the high lift wing really helps it outperform many other Rotax engined types when towing”.

Successful glider towing is a complex equation – it’s not just how long it takes to reach altitude, it’s also the total air time on the tug (based on which, the glider pilot/customer pays), fuel costs, maintenance costs and any depreciation costs on the aircraft tug – many club towing aircraft have been written down to zero in value over the years.

However, the overall exercise was to determine how well the A22LS Foxbat performed – and the answer seems to be ‘much better than expected for such a small aircraft’. This feedback, together with excellent reports from other countries using the A22 for glider towing, confirms our belief that the aircraft will handle 75-80% of  typical towing tasks at around a third of the costs.

 

High risk turns

Here’s a great video by legend Wayne Handley, all about the use of rudder in turns. Although written primarily for ag pilots, the lessons he gives are equally applicable to pilots who often fly close to the ground – for example when stock counting or mustering – or even just the rest of us when we make that last turn at 500 feet on to final approach to land.

His explanation of what causes one wing to stall before the other is excellent, as are his instructions for spin avoidance and wing-drop recovery.

Although posted nearly 10 years ago, the lessons in the video are just as important today as they ever were! Great stuff from Wayne Handley and a quarter hour well-spent!

As usual, to view the Vimeo video, click on the picture or here: Smart Turn by Wayne Handley

Dan Johnson tests the A32 Vixxen

Light aviation’s guru blogger Dan Johnson grabbed the opportunity to test fly the newest FAA LSA-approved aircraft, the Aeroprakt A32 Vixxen.

Click the photo above or here to see the article and accompanying video: Dan flies the A32

You can read more – much much more – about all manner of light sport, recreational and ultralight aircraft on Dan’s blog: ByDanJohnson.

Why LSAs crash so much

I have long held a view that Light Sport Aircraft (LSAs) are not, as many people seem to think, just less expensive ‘mini’ GA aircraft.

For a start, they are built to much tighter weight tolerances than typical GA aircraft and thus need careful maintenance to ensure that they remain airworthy. Don’t get me wrong – a correctly maintained LSA can have a life span of many many years – but alas, in Australia, quite a few LSAs are quite legally owner-maintained by people who do not really have the skills, experience or knowledge to do so….but that’s another rant.

More importantly, LSAs have quite different flight handling characteristics from typical GA aircraft. This starts with taxiing, where dyed-in-the-wool GA jocks often describe them as ‘squirrely’, through to take-off performance: what typical school GA trainer will take off in 4-5 seconds after applying power, as many LSAs will? In the cruise, the light wing loading of most LSAs (remember, the regulation requires a stall speed limit of 42 knots ‘clean’) is more susceptible to turbulence – although the great upside of most LSAs is that they are a lot more responsive (to some, ‘fun’) on the controls.

This responsiveness, however, can potentially cause problems when it comes to the approach and landing phase of flight. For a start, approach and landing speeds of most LSAs are around 50 knots or even slower, a speed which feels dangerous to many GA pilots. Come in faster and you’ll likely over-control, and/or float or balloon the aircraft, with potentially disastrous consequences.

To further expand our thinking, Paul Bertorelli of AVweb has made a great little video on the subject of accidents in LSAs, which you can view by clicking on the picture above or here: Why Light Sport Airplanes suffer so many crashes

Most of Paul’s statistics refer to the USA market but all of his comments apply to LSAs the world over. Enjoy the video!