Joining Thermals

There are four important matters to consider when joining a thermal already occupied by one or more gliders, and every single one must receive your full attention.

1 You must have in sight all of the gliders that are in the thermal
2 All the gliders in the thermal must be able to see you
3 You must plan your method of arrival and entry to the thermal
4 All the gliders in the thermal must understand your plan

#1 Sighting gliders circling is not easy, and a variety of backgrounds and conditions can conspire to make it even more difficult. Gliders are like kangaroos on the road; where there is one, there will be more, and it is the one you don’t see that will do the damage. After you decide that you have them all sighted, then start searching for the one(s) you haven’t seen - don’t get a fixation on the ones already in view. Keep your scan going over the entire width and depth of the thermal, as one aircraft in a particular stage of the turn may be impossible to see at first glance.

You must also keep in mind that there could be gliders close to you heading for the same thermal. Aim to keep your search going all around, especially above as you will usually be slowing down and gaining altitude as you approach the lift area. THIS IS NOT A TIME TO BE LOOKING AT YOUR VARIO – ALL EYES OUTSIDE!

#2 A glider approaching a gaggle at high speed in a straight line will be next to invisible. The frontal area is very small, and we need to increase this and ensure some horizontal movement so that those gliders already established have some chance of seeing us coming. If we are making our own decisions we will want to sample the air as we approach the lift anyway, as it will be best to have an image of the thermal in our own mind. This will lead to some gentle weaving and “feeling” of the air that will make your glider more visible to those ahead. If not, you should attempt to avoid a direct head-on arrival. You should arrive at only a little above thermalling speed, and with consideration of all the established glider’s positions so that they have a good chance to see you.

#3 A good concept of spatial awareness is vital in the arrival phase. While still well back from the thermal you need to have a good idea of where you will arrive in amongst the gaggle, in relation to all the gliders. There will need to be a space for you to fit into (!) and if not, you will start a gentle turn outside that of the gaggle until they have rotated further and you can see room to move in. DON’T PUSH!

Please, do not arrive at the gaggle at full cruising speed and attempt to pull up amongst them – this is extremely dangerous, as you will have considerable vertical velocity to judge as well as your horizontal position. It will also inevitably mean you are out of sight of one or more gliders, and they are out of sight to you at some stage. If you do this a couple of times someone will punch you in the nose, which will be a very good thing…

#4 As above, you must always manoeuvre in a safe and predictable fashion. Try not to surprise the other pilots with any of your antics. As you fly at higher levels of competition, it is likely that you will have gliders flying at lesser separatio, but the pilots generally behave more predictably. If the pilots of the gaggle see you approaching at a sensible speed and behaving as if you are having a good look out the front and working to fit in comfortably, they will be far more receptive and will often open out their turn a little to let you in more easily. Roll into the thermal smoothly and positively, and likewise when leaving keep all the changes of direction predictable.

Keep a good lookout as you leave the climb, especially below as you accelerate. Above all, be careful and courteous.

Open Class Manoeuvrability

Open Class gliders are big, usually 25 metres or more in span, and heavy, often flying somewhere around 800 kg. This means that they have much inertia. They are slow to roll, and take some time to change speed. Their control response is worst at low speed, as when thermalling, and some account of this needs to be taken by other pilots when sharing airspace.

Give these gliders a little more room when you are near them. They will thermal at about the same speed as any heavily ballasted glider, around 55 to 60 knots. Try not to surprise them by doing something unexpected in a thermal, forcing any rapid evasive action. Generally they will not cause you too much trouble; because of their slow and graceful movements you will find their changes of direction quite easy to anticipate, and it is unlikely that they will manoeuvre into a position faster than you can manoeuvre out of it.

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FLIGHT MANAGEMENT AND CIRCUIT PLANING

"The two things that have the greatest potential for killing you in a glider are failing to maintain a good lookout at all times and failing to maintain a safe speed near the ground."

This article is complimentary to a more general one titled "Flight Management Decision Making" which is available in the Safety section of the CGC Web Site. It concentrates on the manner in which you enter the circuit area, with particular reference to the situation at Caboolture.

All pilots will be familiar with the concepts of the active and dead sides of the circuit and the general requirement to stay clear of the active side unless on or joining the downwind leg of the circuit. Likewise all will know that the preferred flight path prior to joining downwind is one which brings the glider into the "funnel" from the dead side of the circuit, or joining crosswind from the dead side. 

However it is an unfortunate fact that many pilots fail to manage their flight such that this is practicable. Some have even been observed using what our RTO (Ops) calls the "salmon" approach. This is like the salmon swimming upstream against the current and running into a large bear. In other words, flying upwind on the downwind leg and then doing a U turn to track downwind! This is not only unsafe; it is contrary to regulations as is turning right into or within a left circuit pattern. 

Please reflect for a moment on your typical actions during the downwind leg - make your radio call, complete the FUST check, assess wind direction and strength, select your landing area and assess the angle to it, check for any obstructions on the field, monitor safe speed near the ground, continually review the angle to landing area and adjust the flight path if necessary. Oh yes, and LOOKOUT for other aircraft and monitor radio calls for evidence of conflicting or converging traffic. During this process the last thing that you want to be confronted with is some idiot flying a reciprocal path at circuit height, or crossing in front of you from the direction that you least expect. SO DON’T DO IT YOURSELF!

NEVER fly upwind on the live side of the circuit! The Visual flight guide 2007 (most power pilots’ bible) recommends being 1 nm out on the downwind leg for power aircraft.  Therefore the “NO GO” area is at least a mile out from the runway if below 2000 ft. Some of the reasons for this are:

1. Power aircraft may descend onto the downwind leg from higher than 1000ft AGL.

2. Power aircraft may climb out on the downwind leg.

3. High power aircraft have a standard circuit height of 1500 ft and over 1 nm lateral displacement on the downwind leg .

4. Allowance must be made for other aircraft not being at exact recommended altitude. 

5. In cabin workload in power aircraft is much higher than gliders and lookout is somewhat impaired on the downwind leg.

So always manage your flight so that flying in a contrary direction near the downwind leg area will not be necessary. Except in an emergency you must plan your flight to join crosswind (preferred), or join the downwind leg from upwind of the joining funnel. In this regard, and particularly on tows to 2,500 ft or less, it is essential that you consider your eventual circuit joining pattern when deciding which direction to fly on release from the tow – yes, that early!  Heading towards the active side of the circuit on release may eventually result in an inability to join safely.

Also you must never assume that, just because you took off on Rwy 06, that Rwy 06 is the only active runway in use on the day. You MUST LISTEN to radio calls by other aircraft in the area and act/respond appropriately.  

Of course there will be times when unexpected sink or lift will mean that your planned circuit entry is no longer an option. In such circumstances there will invariably be more than one option available due to the runway layout at YCAB and a key factor in the decision making process must be avoiding possible conflict with aircraft in the circuit. In such circumstances a radio call should always be made to alert other users of your new intentions. 

Above all - LOOK, LISTEN AND THINK during what is potentially the most dangerous part of every flight and communicate your intentions clearly.

And NEVER put yourself in a situation where you have to “swim against the tide” in order to join circuit.

Brian Wade
CFI

7 September 2007