11-Dec-18 - 04:08 PM

Thermal Circle Text - Thermal Circle 10

Written by Hayden Daley - 13 September, 2007.
Welcome to this edition of the soaring circle, in this edition we will take a detailed look at practicing launches of competition sailplanes using a technique shown to me by ex Aussie team member Tim Mellor to gain the best possible launch height. I will also be giving an explanation of flight trimming; as well as explaining the need to cover as much area as possible when searching for those elusive thermals, using the best lift/drag speed of the model and the lomcevak logger to assist in the set up of the model.

Competitions can be won or lost with launch technique, a higher launch than your competition will allow you to cover more distance is search of lift and have a longer flight time than the other competitors, even if a thermal is not encountered. In 1995 when monthly competitions began at the Doncaster Aeromodellers Club, I was watching ex Australian F3b team member Tim Mellor practice launching, and he was using one of the first molded competitition models that I had seen; and he used a technique that I had not seen before. What occured was when Tim launched he would fly out to the left of launch corridor, and when at around three quarter launch height would turn right, allowing a side on view of the ping, (a ping is when the model is dived downwards to use the stored energy in the winch line to gain more height) and he would then go to reflex and ping crosswind. This technique gave an excellent indication as to whether different set ups of the launch mode on the radio where making any difference to the ping and was also a good way to practice the control movements on the radio required for a good and succesful launch ping; with the most optimized rotation for the highest launch. During the competition Tim Mellors launches were easily out launching the other competitors by around twenty percent or so. I am not sure whether the life of the winch line was shortened by much using this technique; but the Airstrike winch company make a winch turnaround that can swivel and allow for this style of sideways launch. The turnaround is made of aluminum it has an intergrated carry handle, the turnaround sides are an enclosed pulley to prevent lines getting tangled. It uses permaglide bearings for low friction on winch lines to allow a long life for the line and good low drag launches. This turnaround will help protect those valuable winch lines when using this technique to practice launch set ups. When I used this technique to set up competition models, and it has while since I have flown competitions, this technique definitely helped to set up models to launch higher and helped in getting the most optimized rotation at the top of the launch for higher launches.

Not everyone that flys thermal flights is interested in flying competitions, so the need for expensive European competition models is not required to enjoy flying long thermal flights with older style wooden models or older competition models. The need for competition regulated equipment like competition winches is not necessary to enjoy thermal flying with these older style models. One of the most enjoyable way of flying standard either kit built, or older model sailplanes when not competing, and to get long flights is to use long length tow lines. The longest winch line that I have launched models on was 400 meters to the turnaround, an 800 meter long winch line. This provided massive launches and long flights which were highly enjoyable at the time. In the end, these weekends of using long winch lines reached the point where we could no longer fit any more line on the winch when packing up; the winch drum was full by the time the line had been wound in. With these big launches when a thermal was encountered it was often necessary to use crow braking to descend, models got very high, very quickly. Neither myself or other friends lost models due to them being lost out of sight using these launches however their was plenty of close calls. Please keep this in mind when using this style of launching.

When practicing for competitions winch lines become an expensive commodity and a way to get around this problem is to use a double bungee, with a light length line. The double bungee when used on molded models provides a superb way of flying lots of flight’s with very little cost in the way of winch lines. You can match the average competition launch provided with a winch, with the launch height of a double bungee all you have to do is alter the bungee’s line length until it matches your winch launch and you will have a fantastic way of getting lots of flights on the one winch line. Another way of launching is to use a “Hand Tow”. I have seen this style of launch plenty of times at competitions; however I have never owned the equipment required to Hand Tow model sailplanes. The equipment required for this style of launch is a hand tow reel and line. The reel used on the hand tow need’s to be geared to wind in the line without tangles as it descends to the ground; similar to the way winches are wound to the turnaround at the end of a launch. Gearing the reel prevents line tangles after launch. The legal length of a hand tow in the Australian open thermal rules is 175 metres, so this need to be taken into consideration when making Hand Tow reels. Unfortunately I cannot provide the information on how to make a hand tow reel, I have never owned or constructed this launching equipment, but in the right conditions a hand tow can give very competitive launches. And considering the cost of a new winch, this style of launch is not a bad way to begin competing in competitions, it is still a legal way to launch in the Australian Open Thermal rules.

When the thermal flight times required for international F3B events were 7 minutes and the Australian open thermal rules required a thermal flight of 8 minutes it was possible to gain these flight times consistently with good launch technique and the times required very little thermal activity, if any to gain these times. This turned the competitions into landing events, with pretty much every round being won or lost by the distance of the model to the landing spot. Their was a lot of controversy over the changes and I am not sure of the exact date, but the competion flight times were changed to ten minutes thermal flight times; and with the competition known as F3J using a 150 metre hand tow, requiring a ten minute flight, the competition scene changed dramatically. What occurerd was that the need to search for thermals was required in all thermal events; and that attaining the ten minute times where basically impossible without the assistance of a thermal.

These ten minute long flights were, and still are a challenge to fly consistently. What is required is a good launch and to then go thermal hunting using the best lift/ drag speed of the model to hunt those elusive thermals. The best lift/drag speed is the speed that the model covers the most distance possible, essentially the most efficient speed for the model to travel as far as possible in search of lift. When I interviewed world champion David Hobby he mentioned that he flys 45 degrees crosswind when he begins to search for lift. This is so that the "sight picture" of the models makes the spotting of thermals easier. It is harder to tell if your model is in lift when it is above you or not to far in front of the launch point. The easiest way to tell if your model is in lift is when a well trimmed, well set up model, increases in speed without input from the pilot. Sighting these increases in speed is easiest when the model is viewed from side on, so it makes thermals easier to find using the "sight picture" technique.

The best way to find the optimum lift drag / speed lift drag speed of a competition models is to start timing flights in the early morning when their is little thermal activity, comparing different speeds and flying a "figure 8" pattern and counting the amount of "figure 8" patterns that occur during the flights. Eventually you will get used too what the best and most efficient speed of the model is. The same goes when using ballast in windier conditions to return to the landing spot from further downwind the best, most efficient speed of the model will be slightly higher but can still be practiced using the figure eight technique. Another way of finding the best lift / drag is to use the Lomcevak Logger which is a miniature pressure sensitive height logger available from Model Flight; and fly the speeds using the logger to compare until the best speed is found. This logger is an invaluable tool and will provide extremely useful information on model set ups and how the model performs in different conditions, it can be a great advantage when used properly..

It is important that your competition model is trimmed well to give you the best opportunity to do well. Trimming can be a time consuming job but it will give you an advantage over the competition when done properly. The first thing to set up when trimming is the center of gravity. The center of gravity is the point on the wing where the model balances un-aided, and the optimum center of gravity is different for every model but around thirty percent of the wing chord is a good place to start. The way to check your center of gravity is to use the "dive test", the involves launching putting the model into about a thirty degree dive and adjusting the weight in the front of the model until the model maintains a constant speed. With a correct center of gravity the model will hold a consistent speed and mark lift properly. However even the best made molded models from the best manufactures can have problems with the angle of incidence being slightly incorrect making the dive test almost useless because the angle of the tail compared to the wing is incorrect. The inaccuracy in the incidence angle makes proper trimming impossible. A pair of incidence meters, one on the tail and the other on the wing can solve a lot of trimming problems and using small amounts of tape to get the incidence right will solve a lot of dramas with trimming models. Because of these problems that can occur with incidence settings I am a big fan of "all moving" tailplanes as used on the Pike Superior, Crossfire and Icon as their will never be any incidence problems. The tail is one piece and impossible to have incorrect incidence angle.

One of the most difficult things to master when learning how to fly thermal flights is the speed to circle downwind when lift is encountered. When circling in a thermal the need to match the speed of the circling model becomes crucial to stay in the thermal. The only real way to learn these speeds is to fly in different weather conditions; until you get used to the downwind circling speed required to stay in thermals with different wind speeds. This is particularly difficult when a thermal is encountered at a low altitude, but becomes easier as the model gets higher; as most thermals grow in size as the height increases. Watching other pilots fly their rounds will help to learn these speeds; as you can see the technique in action.

I was on the internet recently and while researching found this technique of practicing spot landings. What is required is for a helper to stand back from the landing spot a decent length and too hand launch the model towards the spot from different lengths away from the spot. This technique has to be the best way to get those spot landings accurate, and to get lots of practice landings done. Their is a new model just released in Australia made by Jaro Muller, that I believe will be a very successful light air competition model; the models name is Espada-Rxl. I has a wingspan of 3.7 meters, a length of 1.615 meters. The F3J version has a weight of only 1950g. The wing section used on the models wing is the HN 785JM and it has wing area of 70.1 dm2. This model has an all moving tailplane, a good looking wing plan form and should be a fine performer. The models is available from the Airstrike winch company who are now a Jaro Muller dealer and the internet site name for this supplier is Airstrike.com.au. This models planform looks magnificenrt and should be an excellent competitor to the F3J model the Sharon.

I have spoken of this web site before and I has been a while since the site has been mentioned, this web site is an excellent way of acquring well priced competition models. The name of this website is the Aussie RC Trading Page and it can be found at www.rctradingpage.com.au. This web site is the best way to get good priced second hand, often fully built models with radio gear installed for excellent prices and as new competition models are released their is usually a big influx of compition models for sale.Please check this website out as it makes flying in competitons affordable.

In this edition I have tried to provide useful information that will be useful for competiton pilots. I have thoroughly enjoyed writing the soaring circle and can be found at soaring@newlitho.com.au. Please email any topics you would like to see covered and feel free to email questions in regards to soaring releated matters.



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