| Wet Gliders and Big Ears |
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About this article 31 Dec 2015
In a recent committee meeting the dangers of wet wings and big ears were discussed with some members not realising the factors/risks involved. Unfortunately I seemed to know too much and as Safety Officer it was suggested I should write something about this for the club. So here goes ...all you should know about wet gliders and big ears. For a short version, just read the summary at the end. I should add that I am lucky enough to be able to ask advice from the Ozone test team, who have all been instructors. Russ helped a lot, if it had just been me, you might have just got the summary!
The advice is simple – don’t! Gliders just don’t like water. They don’t even like to get wet on the ground as water action can help separate the coatings from the fabric, this is why you should ensure that you don’t pack away a damp glider for a long period of time, but more importantly for your safety you should avoid flying your glider when wet. Rain obviously gets a wing very wet, but flying in cloud can do it too. A bit of cloud flying may cause a bit of dampness, and is not usually a problem, but if the water starts streaming down your risers then it is probably time to try and get out of the cloud. And getting wet so high up would usually mean that your glider will be well dry before you get back near the ground. So why is a wet glider not good to fly? The first thing to realise is that designers don’t design wings to fly in rain – and therefore wings are not tested or even flown wet during development. A wet glider is heavier – a heavier wing will behave differently in manoeuvres. The wing may actually have water collected inside the cells, so the trailing edge actually collects the water. Cloth sticks together more easily when wet. It seems like modern wings are more susceptible to go parachutal when wet, this is probably because (I can’t say for sure) of their increased efficiency, and thus higher angle of attack at trim speed than the wings of old. So, first and foremost pilots MUST avoid flying in the rain …basic piloting judgement is more important than specific, skilled piloting ability in such circumstances. If a pilot is caught out and they can see a high likelihood of getting wet, then they should land immediately, preferably in an area that is not raining, even if it is not near their car. If the glider becomes wet, damp even, then they must not use big ears, or b-line stalls. They should keep speed (hands up) at all times, fly away from the hill and spiral to lose height, actually steep 360’s in sink maybe better than hard spiralling because I would be worried about a steep climb out if the exit was poorly managed. Only use this method if you have plenty of height and as ever do not do this near the ground. Go into this carefully to ensure that your wing does behave properly in a steep 360. In straight flight, if necessary, use a small amount of speed bar or at least have the foot on the bar, ready to apply speed if they feel the wing starting to go parachutal. If the wing does go parachutal then use no brake input (release wraps if you have them), wait for the wing to stabilise above the head (approx 2-3secs after initial drop back) and then apply speed bar, full speed if necessary to make the wing fly again. When making approach keep speed bar applied and gently use rear risers to make approach. Training, training, training. If pilots know parachutal and full stall then they will be better prepared if the event occurs. Regular SIV training will help reduce the chance of loss of control. If a fast descent is not needed, and you are high up then just fly with as minimal input as necessary and keep your speed up. Check out the behaviour of your wing – it is always hard to really tell how wet your wing is, but if you are sopping wet then you know your wing is sopping wet. Weight shift turns are probably better than using your brakes. If needed then use small control inputs. With plenty of height and if you know your mistake of getting wet in rain won’t be repeated then you may have enough height to dry your wing and carry on flying. Otherwise, gently fly it to the ground and try and choose a place where little input will be needed until you are about to set down. If you are low down when you get wet then just fly it in to land as gently as possible – landing by your car is not important (but obviously don’t fly into it either).
Big ears is taught as a descent technique, and some people use it as they think it adds stability in turbulent air. Big ears to get down because you fear being blown over the back will often add to your woes as your increase your drag and go slower so get blown over the back faster. I can honestly say I cannot remember the last time I used big ears. If you need to use it to get down then you have messed up in your judgement. I always go by the thought that a designer made a wing to fly well; they did not design it to fly well in big ears. If you need to get down faster then use a spiral – keep that wing flying properly. The big ears for added stability thing is old school, very old school and in my opinion very poor advice. It did have some validity in the old days when nobody knew what they were doing and gliders were very prone to collapse. Big ears increases wing loading therefore reducing the chances of collapse, but using big ears to keep the wing open in rough air is like sticking your head in the sand, you forego pitch and pressure control, and nothing replaces active flying when it comes to keeping a wing open in turbulent air. Pulling big ears in such circumstances would be good advice if it was your grandma in the air on her first flight, but for a qualified pilot it is poor advice and a poor mantra for them to follow. Active flying is the key. Big ears adds drag, and drag slows the airspeed and increases the angle of attack. This increases the chance of stall.
Are a couple of characters best avoided! Wet gliders can be susceptible to parachutal stalls, Big ears increase the chance of a stall – put the two together and I don’t think much more needs to be said. Wet cloth can stick together, so the aerofoil shape is lost. This may also make it more difficult to get big ears out – as well as any extra weight caused by the possibility of water collecting in the tips if you really got wet. Big ears puts the cloth together and so can cause stickiness in getting the ears out. Bigger pumps may be needed to get the ears out, if your wing is already close to a stall because of the increased angle attack caused by the drag from the ears and from the glider being wet, then a big pump could easily stall the wing.
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