Philip Whiteman on preserving the aircraft – and your own neck – during the winter months
As they say, in Britain it rains in summer and in the winter it just rains harder. While this often feels all too true, winter can also be a lot colder so comes with a host of additional hazards to flying like ice, mist and fog.
It pays to be prepared. While we all dress for the season, it is easy to forget there are some parts of the aircraft that need to be protected from the chill. Those who fly Rotax-engined aircraft will be familiar with the need to blank off more of the radiator to prevent over-cooling, and even primitive old machines like the J3 Cub have a cooling restrictor (in the form of a blanking plate) that should be fitted in winter to allow the oil to reach and maintain correct operating temperature.
One thing to note is that, according to aviation fuel and lubricant manufacturer Shell: ‘Typically, many naturally aspirated engines are running at oil temperatures that are too low. This can cause excess moisture in the crankcase, which can lead to rust or corrosion on critical engine parts… In most cases, a cruising oil temperature of 180-200°F (82-93°C) is preferred. Oil temperatures below 170°F (77°C) usually do not allow for the proper boiling off of water, which leads to rust.’
Multigrade oils are suitable for year-round operation. If you are still using monograde engine oils, you should change to a lower-viscosity oil for the winter. In fact, it’s a good idea anyway to change the oil, be it multi- or monograde, at the end of the flying season, rather than leave old oil ? which will be partly degraded and contaminated with corrosive combustion products ? in the engine.
It is best not just to run, but to fly your aircraft during the winter ? ground running doesn’t get enough heat into the oil to drive out all the moisture. There are lubricating oil additives like CamGuard that are claimed to offer enhanced protection against corrosion, not least of Lycoming camshafts, which sit above the crankshaft. If you are not planning to fly, consider filling the engine with an inhibitor like AeroShell Fluid 2F, a combination of W100 engine oil and additives specially designed to protect against rust and corrosion and to minimise the effects of humidity.
Returning to personal comfort, it is a good idea to check the cabin heater/demister is working properly before you really need to use it in earnest. Sometimes it may be better simply not to use the thing at all. Many light aircraft use exhaust heat exchangers that may leak, allowing carbon monoxide into the cabin. As my Cub’s heater is notorious for being barely capable of warming an area the size of a dime on the sole of each of the front-seat occupant’s feet it is permanently wired off. I’d rather shiver than risk being gassed!
One final airframe consideration ? control cable tensions may need to be adjusted. If they were over-tensioned in the summer, they may have become too taut in the winter.
Be weather aware
‘Continued flight into bad weather is the number one killer in UK general aviation,’ warns the CAA. In winter, it makes sense to be flying in improving weather ? flying after the ground mist has cleared and not so late in the day that it is building up as you fly.
Airframe icing is another potential winter hazard. ‘The most likely temperature range for airframe icing is from 0 to -10°C,’ says the CAA. ‘It rarely occurs at –20°C or colder… Pay attention to any icing warnings. Note the freezing level, it can be surprisingly low even in spring and autumn. You may need to descend below it to melt an ice build-up, but beware of high ground. Remember that altimeters over-read in very low air temperatures, by as much as several hundred feet. You can be lower than you think.’
As it does rain more heavily and aeroplanes are generally left sitting around, often out in the open, for longer periods, winter is when risk of water contamination in fuel tanks is high. Before moving the aircraft do make a point of draining fluid from all the water drains.
The presence of even a very thin layer of frost, ice or snow on an aeroplane can have a far greater effect on lift than you might imagine. The CAA cites tests that have shown that a coating with the thickness and surface roughness of medium or coarse sandpaper reduces lift by as much as thirty per cent and increases drag by forty. ‘Even a small area can significantly affect the airflow, particularly on a laminar flow wing.’
The need to clear all frost, ice or snow before flying is obvious, and this can be done with de-icing fluid or brushes – or simply by positioning the aircraft in the sun and waiting for the stuff to melt. Beware of water collecting in spinners or inside control surfaces and then freezing, which can produce serious out-of-balance forces or even flutter.
After a period of winter operation wheel spats can end up packed full of mud or slush. One friend of mine actually had his Cessna’s nose spat split asunder by the mud that had built up while operating from a very wet farm strip. The CAA reports that on one occasion 41kg of mud was removed from the three spats of a four-seat tourer.
Increased takeoff and longer landing runs
Wet snow, slush or mud can seriously lengthen the takeoff run or prevent takeoff altogether. In winter, it makes sense to walk the runway at any private airstrip or unfamiliar airfield. And it’s not just a case of whether you can taxy and takeoff, but whether it is wise to be doing so. Even if you have suitable balloon tyres, your tailwheel may be cutting deep grooves in the turf, spoiling the pitch for other users. If it is especially muddy, great clumps of the stuff can be thrown up onto the wings and even through the propeller (don’t ask how I know this).
In the air, carburettor icing is one of the worst enemies. CAA SafetySense Leaflet 14 Piston Engine Icing spells out the hazard in full, but in the absence of dewpoint information, you can assume high humidity and a raised likelihood of carb icing when:
• the ground is wet (even with dew);
• you are flying in precipitation or fog; or
• just below cloud base.
If you encounter airframe icing or, worse still, freezing rain you must descend into warmer air. ‘If you see ice forming anywhere on the aircraft, act promptly to get out of the conditions,’ warns the CAA. ‘Don’t wait until the aircraft is loaded with ice. If freezing rain is encountered in flight near the ground it is best to land as soon as possible.
‘Even a thin coat of ice on the aircraft justifies a twenty per cent increase in approach speed. Remember that ground temperatures fall quickly during the late afternoon on an exposed airfield and by dusk ice may be forming on any wet runways.’
If you are seeking definitive and authoritative advice on winter operations, Pilot recommends CAA SafetySense leaflet No3 Winter Flying, available as a free download. Other useful sources for advice on engine operation, lubricating oils and additives are Shell and CamGuard.
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