February 07 BMFA club affiliation No 0340 FLY SAFE - Fly Again Next gathering at St Andrews Rugby Club, March 12 2007 I do hope you have all paid your BMFA insurance due Jan 1st As you are all aware the club does have an ongoing concern about noise, so please do your utmost to quieten your models, and keep out of the no fly zone.  To remind you that is (when standing on the patch) to the right of the gate clockwise to 90 degrees of the patch. Update on the flying field situation from Mike: We are applying for a Certificate of Lawfulness to fly models from Fennis Fields Farm. Meanwhile we still use the existing area, but with great care not to disturb the neighbours. That means only quieter models for the time being. When and if the certificate is granted, we plan to locate nearer the farmhouse. Mike. Now some more on electric.  If you are getting the feeling I am trying to convert you all - you could not be further from the truth.  I love all the paraphernalia, frustrations and power that come with internal combustion, but the mind should not be closed to different ideas.  Electric is so impulsive.  So easy to grab a model, battery pack and transmitter and relieve the days tensions with a quick flight.  The smaller models can be kept in the car for instant gratification of the craving to fly. I am sure you all know how to treat NiCa batteries, but LiPo are a different species altogether.  Get it wrong and you could end up injured so here are a few snippets I have gathered. My question is why are LiPo packs so cryptically numbered? "We use the designation 10C etc to mean how much a cell or pack can discharge in amps. C always equals the capacity of a cell or pack. An example. Lets use a PQ31003S pack rated for 12C. In this case C=3100mah. The number before the "C" is the multiplier. So 12 x 3100 = 37200mah. To get amps we simply divide by 1000. 37200/1000 = 37.2 amps. 1000mah = 1amp. So for the above pack (PQ31003S) rated @ 12c we now know the max discharge rating is 37.2 amps. Another example: a 20C 1800mah 3S pack. What is its max rating? 20 x 1800 = 36000. 36000mah = 36000/1000 = 36amps. So the 1800 3s pack @ 20c has a max rating of 36amps. So when ever you see a C rating take the number before the letter "C" and multiply the packs capacity by it. That is it. To get amps from your new number simply divide it by 1000mah." BALANCING BASICS The new breed of chargers and balancers almost eliminates the cell-balancing issue in LiPo. The chargers are connected to a separate parallel plug on the pack, and they charge every cell to exactly 3.7 volts (4.2 volts) each. This type of charger prevents any cell from becoming out of balance during the charging cycle. Although this is not as important as it is in larger packs, cell balancing does prolong the life of smaller packs, too. Many chargers have a probe that monitors the pack's temperature when it's being charged. If its temperature exceeds its preset maximum temperature, the charge cycle will stop. This is a handy safety feature that tells you when something is wrong and worth investigating. A rise in temperature rising may be the result of an incorrect charging setting (current or voltage), or it may be that one cell or the pack itself has had it. LiPo balancers also keep packs at peak performance and help to extend their lives by balancing their cells. There are two types of balancers: in-line and passive. The in-line balancers are placed between the series charger and the battery packs. The balancer is connected to the parallel connector and distributes the current from the charger so that every cell is given exactly 3.7 volts. Passive balancers are also connected to a pack's parallel connector, but it measures the voltage from every cell and discharges the higher cells slowly until the cells are balanced. Avoid operating the pack at the maximum allowable discharge rate such as “Sustained” or “Burst.” This discharges the battery fast and leads to higher running temperatures that shorten the life of the pack. Set the cut-off voltage on the ESC to at least 3 volts, and try not to run the pack below that voltage. Nothing will destroy a pack or throw the cells out of balance faster than going below its minimum voltage. In most cases, this is caused by repeatedly restarting the ESC after the first cut-off. Keep in mind that pack temperature rises dramatically as its reserve gets lower. • Always monitor a pack when it's on the charger. • Never charge a pack while it is still in your model. • Always charge a pack in a fireproof place or in a fire proof container. • Always store LiPo packs in a safe place that's well out of the reach of children. • Never allow LiPo packs to overheat. • Always ensure that LiPos have adequate air space around them. • Never over-charge a pack. • Always charge LiPo packs at 1C. • Never charge a pack that looks swollen or puffy. Breaking news As a response to the noise complaints published last November, and further development of the marina we are taking steps to relocate our normal takeoff & landing area closer to the farm buildings. So far, we have moved the fence posts to roughly mark out the intended area and have conducted flight tests. We have also purchased a second-hand tractor mower at about half the price of the mowing contract to give us a cost saving and more flexibility. At the club meeting Monday the 6th Feb., when there were 9 members present including Chairman, Secretary and Deputy Safety officer, the following was agreed: 1. Relocation will be completed by 1st March. At which time the gate lock will be changed and future access will be from Little Lawford Lane to Mr. Merris' Farm (no key required). 2 Parking will be on hard standing near to farm buildings. Cars will display an access permit (being designed). These permits will only be given to paid up members with proof of insurance. 3. There will be an Extra-ordinary Meeting at the St. Andrews Rugby Club on the 2nd Monday of March (March 12th) when procedures may be clarified and permits handed out. (That is, no meeting on Monday 5th March because the Rugby Club has a committee meeting then) 4. Between now and the 1st of March, we shall conduct our site risk assessment and prepare appropriate club flying rules. These will be held in laminated form at the site, and published to all members. This is a sign of the times. We have been flying at the Fennis Fields Farm now for at least 20 years, with a happy relationship with Mr. Merris and his father before him. We have applied to the Rugby Borough Council for a Certificate of Lawfulness to fly from the farm in order that we may continue to do so. However, we must abide by noise and safety regulations (refer to the BMFA handbook) and these will be strictly enforced. Mike Pearson FLY Safe, fly again and enjoy Stu

February 03 Center of Gravity: An Idiots Guide It's all very well designing and building the model of your dreams but if you have no way of working out the C.G. you're going to be taking an awful risk with the "third of chord" method on that all important first flight. It may be fine on the average sport type model that usually has a long tail moment arm and generous tail area, but on a scale model it could quite easily result in disaster.    Here's a method for finding a safe Center of Gravity position for those critical first flights.    There's a bit of working out to do but nothing serious. So get those calculators out and get started. First, here's the formula for quick reference. All measurements in INCHES.    For tailless aircraft and deltas the C.G. is simply the Average Chord divided by 6.    The first thing to find is the Average Chord of your wing. For a constant chord wing it's just the chord. But for a tapered or swept wing it's a bit more difficult. They say a picture is worth a thousand words so take a look at Figure1: Figure 1 Simple enough. For biplanes, triplanes etc, the Average Chord is measured from the Leading Edge of the leading wing to the Trailing Edge of the trailing wing. View the two wings in planform as one, and if there's taper or sweep apply the method in Figure1. Figure 2 In Figure 2 the red line denotes how we must view the two wings as one for the purposes of the Average Chord measurement. For the Wing Area part of the calculation you must add together the combined areas of all wings.    For elliptical wings divide the Wing Area by the Wing Span to give the Average Chord.    Second is Wing Area. Simply multiply the Wing Span by the Average Chord.   For Tail Area do exactly the same as you did for Wing Area.    Last is the Tail Moment Arm. To get this figure measure the distance between a quarter of the Average Chord of the wing to a quarter of the Average Chord of the tail. See Figure 3. Work out the average chord and area for your tailplane in exactly the same way as the wing. Figure 3 Now we have all the relevant information it's time to apply the formula. I'll use make believe values that apply to that lovely little aircraft above. :-) Span = 60 inches. Average Chord = 10 inches. Wing Area = 600 sq inches. Tail Area = 108 sq inches. Tail Moment Arm = 25 inches. 1) Average Chord divided by 6:   10 divided by 6 = 1.66 2) Tail Area x 3:    108 x 3 = 324 3) 3 x Tail Area x Tail Moment Arm: 324 x 25 = 8100 4) 8 x Wing Area:   600 x 8 = 4800 5) 8100 divided by 4800 = 1.68 6) 1.66 + 1.68 = 3.34 So the Center of Gravity for our model is 3.34 inches from the leading edge when measured along the average chord line. You will notice, of course, that this position is almost exactly one third of the average chord!! Ho hum…. If you've been paying attention you'll have realised that you can pretty much place the CG where you want it by adjusting tail areas and the moment arm. This can be useful on some scale types that have a rearward undercarriage and are prone to nosing over. If you download CG Calc' from our website you can play around with areas and moments to your hearts content. Flight Box Catches Fire During a flying session at a BMFA affiliated club site, the pilot and his helper noticed a flash or arcing inside the flight box. The starter was immediately disconnected and the 12V battery removed. After this it was noticed that the bottom of the plastic flight box was bubbling the cause of which was not immediately apparent. After 15 seconds or so, the pilot and his helper tried to remove the flight box from the pit area and as the pilot's helper bent over to pick it up, the flight box exploded in his face, throwing him some 30 feet and causing burns to his face and scalp which required specialist hospital treatment.    The explosion was caused by the ignition of half a gallon of methanol based fuel which was stored inside the plastic flight box together with the 12V battery and associated circuitry. Unfortunately, the flight box was so badly damaged that inspection did not reveal the detailed cause of the ignition. However, it is highly probable that an electrical fault ignited either spilt fuel, fuel vapour, or probably both causing the plastic flight box to melt and the fuel container to ignite. Unfortunately, methanol burns with a very pale blue flame which is barely discernible in daylight resulting in the pilot and helper being unaware of the seriousness of the situation.    Fortuitously, there was a source of water nearby which was used to cool the burns whilst awaiting medical assistance. A Word from our S.O. I have not had much to say in the last three newsletters, and no one has contacted me with perceived problems, so is all well? If any of you do have safety thoughts then please, lease let me know. Its no good saying in hindsight, `I thought that might happen.'    I hope all of you had a very good Christmas and will have a safe New Year. Just a thought or two, nothing heavy. For those of us insane (or should that be dedicated) enough to be flying during the winter months please bear in mind: Putting your transmitter on damp ground is not such a good idea! Cold conditions puts extra strain on batteries, please be diligent in checking their performance, they hold your tentative link once flying. Watch the sky! The cloudy, gloomy wintry days do not make visibility easy. Some models colour schemes blend very nicely, its no good saying `it was there a second ago.'    For those of you who are snuggled warmly over the building board: Don't forget to exercise your battery packs, not forgetting the transmitter. Take the opportunity to check airframes. Before venturing out after a lay off do double check everything.    Lastly, after a time without flying, although we don't like to admit it, we do get a bit rusty in technique. Give yourself a simple flight plan to get your hand in, don't overtax yourself or the plane. I have to give a very big THANK YOU to Charles for organising some outstanding speakers. Unfortunately the meetings have been very poorly attended!!! By listening to others adventures and exploits we can all learn. We should all wish to learn and be receptive to thoughts and ideas to make us better, hence safer flyers. Keep SAFE, happy flying, happier landings. Stuart. Concours d'Elegance The February 4th club meeting will be the Concours d'Elegance. There will be two classes to compete in:  Own Built and A.R.T.F. Prizes, which could well become valuable antiques in time, will be awarded for both categories. Intriguing is it not? Do come along and have a go. I'll be there with something or other if only to find out just what the prizes are! When I asked my son if he thought I could win he rather unkindly said, “Dad, from what I've seen you could turn up with a roll of Solarfilm and a stick and win!” :-) So prove him wrong and bring your pride and joy along and give us all a good thrashing! See you there! Quote: Flying might not be all plain sailing, but the fun of it is worth the price. Amelia Earhart G :-)