Flying in wave

At long last we have had our phase 1 exam results. From what I have heard so far, everyone in the class has passed which is great news, though I won't know for sure until Monday. I was very pleased with my own results, which were actually better than both the school finals and my expectations. Onward to phase 2...

I have two fun flying-related tales to tell you about today — my first experience gliding in wave and my familiarisation flight to Milan a few weeks ago. First the gliding.

This is how the average power pilot sees wave - hazardous!

What is wave?

Mountain wave is an atmospheric phenomenon caused basically by wind blowing across a large ridge or chain of mountains. Obviously enough, the hills force the air to rise as they pass over, and if it is stable it sinks again on the leeward side.

Less obvious is that in the right conditions this rise and fall can continue and intensify downwind of the mountains. The effect can reach up many times the height of the hills themselves. Technically the air is in resonance, which is to say it is bouncing up and down a bit like a spring.

Wave can be a good or bad thing, depending on your perspective. When we have studied mountain wave in ground school, it is presented as a dangerous "avoid at all costs" hazard that can cause damaging turbulence, difficulties in controlling the plane and even make it difficult or impossible to climb away. True enough, it can.

This is how the average glider pilot sees wave - miraculous!

But wave also means lots of rising air, and when that happens, glider pilots are never far away. Yes, believe it or not us crazy glider pilot in our tiny, floppy, engine-less planes actively seek out and fly in mountain wave conditions.

Incredible heights can be achieved this way, and impossible distances covered by the skilful pilot. The UK height record in wave is an amazing 38600' set at the Deeside Gliding Club in Aboyne, Aberdeenshire. This is the same sort of height as your passenger jet cruises. 

In the Andes, the record is a mind boggling 50,671' (see the Perlan Project) and distances over 2000km have been covered in a single flight. They are now aiming for 90,000' in the world's first pressurised glider!

So let's give it a try...

I finally got to try wave flying myself last week, at Aboyne. I was incredibly lucky with the weather, which was mild and sunny with a gentle north-westerly wind blowing. From the forecast, it looked like the wind was too gentle for much wave to form. But as we slowly got all the planes out of the hanger and inspected, got our briefings from the instructors and were ready to fly, a few weak lenticular clouds were starting to appear towards the north.

A lenticular cloud is a distinctively smooth, allegedly lentil-shaped cloud that is associated with the rising parts of mountain waves (see image above). They are strange in that they remain stationary in the sky despite the wind whistling through them — the cloud forms on the windward side and vanishes on the leeward.

I was, frankly, a bit nervous. I hadn't flown since October and there I was poised at the end of an laughably narrow runway about to deliberately aerotow up through potentially violent turbulence. Well, nothing ventured nothing gained!

The tow was certainly lively and both us and the tug plane were bounced around a fair bit, but it was no worse than a strong thermal day back home and I coped fine. Meanwhile, my instructor Mike in the back used his 50 years of gliding experience to direct the tug pilot to where he thought the lift would be.

Suddenly we hit the 'rotor' — and real turbulence. As we were both the sky it took all my concentration (and all of the control deflection) to keep rough station behind the madly bobbing tug plane. At the same time, I was supposed to be watching the vario (vertical speed indicator) to see when our usual climb rate of 4-6 knots rose to 8-10, indicating upward wave. And this was in gentle winds!

Just as suddenly the air went silky smooth and quiet, leaving just the vario beeping madly away to itself. I released the tow rope at 3300' and there we were, gently and serenely climbing at about 2 knots as if by magic.

Lenticular clouds lying in a wave pattern over the Grampians. As a 'flat-lands' glider pilot, I don't
often get to look down on clouds!

I spent some time exploring the air to find the best lift and getting my bearings. Gradually I developed a pattern of S-turns that kept us in the lift, flying dead slow in the eerie quiet between turns. Before long we were over 8000' — smashing my previous PB of 6400' — and with incredible views of the Grampians and Lochnagar.

Gradually we became aware of another, independent wave system building above us, and tried to transition into it but didn't quite manage it. We explored up the Dee valley to Ballater too, but the wave formations were starting to break up and weaken. We heard on the radio that Mike had more customers and we had been flying for and hour and a half — which had flown by — and it was time to head back.

Lochnagar peeking out of the wave clouds

With 4000' to spare over the airfield, I persuaded Mike to let me use some of the height to do the upper air exercises that form part of every glider pilot's annual checks. I practised stalling straight and level, accelerated stalls and stalling out of a turn followed by some full spins and recoveries.

Spinning is another area where power pilots must think we are mad — to a power pilot a spin is a dangerous manoeuvre to be avoided at all costs. To a glider pilot, who spends a lot of time flying slowly in tight circles, an accidental spin is a real possibility and should therefore be practised regularly. They are also fun, in a strange kind of way. Yes, spinning round rapidly with the nose pointing straight down is very frightening, at first (this is what it looks like). But knowing the recovery technique and knowing that it really works is very satisfying.

Down to earth

Every flight ends (one hopes) with a landing, and with a bit of prompting from Mike I executed a scruffy but effective circuit in the unfamiliar landscape and lined up with the long but ludicrously narrow south runway. My instructions were to land deep and roll right to the other end and — whatever happens — stay on the black stuff as the surrounding grass was very rough.

I am accustomed to a 150m wide grass strip, so to me this silly little 4.5m ribbon of tarmac looked impossibly tiny. Fortunately there was only a little crosswind and I found it wasn't difficult after all. I rolled as far as I could, ending up a few metres short of the target line. Apparently the fine for this is one dram per foot to the club chairman, but as I was a visitor they let me off!

About to touch down on the titchy runway

Well that was quite a day, and I think quite enough for one blog. My front-seat ride to Milan will have to wait until next time.

A big thank you to Mike and everyone at Aboyne for their time and making me feel so welcome. I will be back.