WINDSOCK

NEWSLETTER OF THE READING & DISTRICT MODEL AIRCRAFT CLUB

October 2006

Musings from the Model Shed

As You will all have read in the last eddition of Windsock, Tony announced his intention to stand down as news letter editor. I am sure you will all join with me in thanking him for a splendid job.

In the mean time I have offered to stand in as acting editor, pending the election of officers at next months AGM. I am happy to continue the role as editor if you should want me to, or if you fancy a go, make sure you come along and put your name forward.

For those of you that don’t know me, I joined the club in Jan 2004 and under the excelent tutalage of David Gray passed my A test last August. I must admit that I don’t fly at our Reading site very often now as I moved to Chalgrove near Oxford and have a site closer to home. I can get to my local site much easier and this allows me more flying time.

This is your news letter, so you will have to let me know what you want – or better still put pen to paper / fingers to keyboard and write something yourself. As I am also the clubs web master, that goes for the web site too. If you have something modeling related to sell or would like to publish a wanted ad , give me a call, e-mail or write (details at the end) and get your item adertised free of charge.

I am not sure where this year has gone, summer flying at Dreadnought has finished for another season, the leaves are turning and like many of you my thoughts are turning to winter projects. In truth, I have a few on the go already that I really want to get fininshed and ready for the spring. I will write something of a review on them when their finished.

It has been a good year for flying, although there were a few days I remember when it was simply too hot to go out, but I certainly had many very pleasant evenings trying to master my trusty WOT 4 or searching for thermals with a glider.

See you all at the AGM – don’t forget remember remember the 5^th of December!

Paul Joslyn, 8 Fairfax Road, Chalgrove, Oxon, OX44 7RS.

01865 400603, 07771 963200 paul.joslyn@xerox.com

Beale Park Float Plane Flyin

October 15^th 2006

The day dawned bright and calm, despite the weather forecasters best efforts of predicting strong winds and overcast skies, it remained a lovely autumnal day, although the wind did pick up a little at times.

Beale Park, for those who have never visited it, is an idyllic setting. Add to that the fact that autumn has arrived and the trees are beginning to transform to myriad of oranges, reds and gold's makes it very beautiful place indeed to spend a day.

Despite attending 3 previous float plane fly-in's, this was to be the first I planned to fly at, and in true modellers style, the date had crept up on me. The last week has been a desperate panic to get the floats finished, covered and an undercarriage fabricated!

Having attended Bob Roper's very informative talk at a club evening a couple of years ago and taken copious notes at least I felt like I knew how and where the floats should fit. For those that were not able to attend the talk I have summarised below.

· The top of the floats should be parallel to the aircrafts datum line - in the case of my WOT 4 this is approximately the top of the rear fuselage

· The 'Step' should sit approx 13mm (1/2” in old money) behind the C of G of the aircraft

· Prop circumference should be about 50mm (2”) above the floats

· Re-balance the model once the floats are fitted to ensure the C of G remains correct

· Don't set the floats too close together as it makes the plane liable to topple over - 300mm (12”) is about right (for a 40' size plane)

The float foam cores, purchased at a very reasonable price from Bob, were then skinned with 1/64^th ply and covered in Solar Tex, with a final couple of coats of fuel proofer to seal the joints and keep the dirt out. The undercarriage was fabricated from 1/8^th rod, joints bound with wire and soldered. A quick test float on the pond and all seemed OK - the fish didn’t seem to mind.

Bob kindly gave the model the once over and a floatation test revealed that all looked good. Following normal pre-flight once over, range checks and engine tweaks, as I had changed fuel, all appeared good to go. Settling my nerves for a moment, I realised I had run out excuses not to “commit aviation”.

So, engine running on song it was off to the water, final control checks, aerial up, clear the engines throat, check wind direction and off she goes. Keep it straight with rudder, gradually open the throttle, speed building. By now on land she would rotate, ease back on the elevator, still streaking across the lake and running out of space, pull back a bit harder and she's airborne leaping off the water as she overcomes the suction!

Grateful for the extra power of a 53' engine, bank left to avoid the rapidly approaching trees and continue to climb out. Apart from needing a little more throttle than normal to cope with the extra drag of the floats, the plane's handling was pretty much unchanged.

After several calming circuits, I decided I had better try and land it. The wind was mainly blowing from the 2 o'clock position, which meant an approach from the left. For those that have not been to Beale Park, the lake is roughly oval with a small kind of inlet to your left that makes a nice approach run. However just at about the 10 o'clock position is a huge Oak tree on the corner of that inlet that has, in the past, claimed more than a few models.

Now you have to fly round the tree giving you two options, fly behind it and hope that model tracks straight until it comes back into sight - not a very wise or safe option, or fly higher to keep the model in sight, leaving you a lot of excess height to bleed off before touch down - now many of the guys flying seemed to cope with this in their stride and my first landing was in fact pretty good, touching down nicely without doing an impression of a skimming stone. Unfortunately landing 2 and 3 weren't quite so good, and in truth a little too fast.

Taxing the model back on water is also an interesting challenge. I did not have a waterborne rudder on mine, relying on the airborne rudder only. The problem is that with the wind picking up a little occasionally the model keeps wanting to ‘weather cock’ into wind all the time, I did however find the torque reaction of the engine useful at times to steer it. This coupled with the rudder I managed to get it back into the bank in roughly the right place.

Retrieve model, Rx off, Tx off and heave a huge sigh of relief at having lost my ‘float plane’ virginity!

Wandering around looking at the other models and talking to some of the pilots, we seem to have a good turn out. I counted 25 models in all, with pilots from as far a field as Farnham. The ubiquitous WOT 4 seemed a popular choice with 6 float-burdened examples on offer. Also two Magnatilla’s, one of which was electric, which flew every bit as well as the other powered by a four stroke, a brace of Puppeteer’s, some sea planes and an assortment of others, electric and IC all made for a very good days flying.

Well done to Joe, as this was also his first time flying off water. Also to Dave B, who with his new camera supplied the superb pictures. I think I speak for all when I say many thanks to Bob, Andrew and all those that helped organise a great day.

Can’t wait until the next one!

PS and a special thanks and congratulations to Dave Gray who turned out to help on his 40^th wedding anniversary – I guess by now Mrs Gray must be used to, what is for most of us, an obsession wit

All Pictures in This issue by Dave Belcher

Flight Power Talk - Report

On Tuesday 17^th October, John Badley and Andy Kirby from Flight Power came to St Barnabus hall and give us a talk about the company and its products.

Flight power is comparatively young for a company, being only 3 years old and came about to fulfil a need for quality Li-Po batteries. At the time of its inception, Li-Po’s were still fairly new and the quality of the products available at the time was variable, one battery would be fine, then next would fail prematurely for no obvious reason and with little come back to the suppliers/manufactures. So Flight Power was born, with the intent to improve quality and supply the modelling community with reliable batteries with predictable performance.

In the early days, the cells were bought in, carefully checked, matched and soldered up into packs all by hand. Today Flight Power have a partnership with the factory in Malaysia that manufactures their cells, so are able to keep a tight control on pack quality. Indeed the early processes for checking and matching cells are still in force today, all be it in an automated form no doubt.

John and Andy went on to impart some of their experience in using, maintaining and getting the best from Li-Po batteries, which I have tried to summarise below.

· Cell voltage is critical to cell life. Cells must not be charged to over 4.2v – this may cause thermal runaway and a fire! Discharging below 3.0v per cell can destroy the cell at worst and at best make it difficult to re-charge as most charges will detect the abnormally low voltage and refuse to charge.

· Set your battery cut off device to 3.1v – 3.2v, this will only shorten your flying time marginally, but will improve cell life

· Cell balancing is not only good practice, to prevent over charging of individual cells, it will also enhance pack performance and life.

· The new Flight Power Balancer has a ‘fuel gauge’ facility, plugging the pack into the balancer allows each cell’s state of charge to be viewed on a bar graph display

· The ‘C’ rating dictates the rate at which you can draw current from the battery. E.g. a 4000mAh pack rated at 20C can supply 20 x 4 = 80amps. However running packs at maximum C rating will shorten their life. Estimated continuous running at max C may result in 20% reduction in pack capacity after as little as 50 cycles. Versus running the same pack at half C capacity (running a 20C pack at 10C) will take 200 cycles to reduce its capacity by 20%.

· Prop the model to give about a C rating of about 50 – 75% of the pack’s max rating e.g. for a 20C pack, choose a prop that gives 10 – 15C at full throttle. This should give 10 – 15minutes of flying time and give good pack life.

· Charge at 1C – again higher charge rates will shorten pack life.

· Li-Po’s unlike NiMh’s or NiCd’s like being discharged a little then re-charged. They do not suffer from any memory effect, nor do they specifically benefit from the occasional full cycle.

· Li-Po’s have a very low self discharge. If you charge your batteries to fly on say a Sunday, but weather stops play, the cells will not have significantly reduced in charge level by the next Sunday.

· To long term store Li-Po’s charge them to about 3.8v per cell – that way if they do loose a little charge, they will still be above the 3.0v per cell minimum.

· After a days flying, it is better to charge your cells and put them away charged, for same reason as above.

· Charging a very cold cell can damage it e.g. its been in the garage and there was a hard frost over night. Warm the pack slightly first.

· When installing the batteries in a model – the ends are vulnerable, so protect if possible and restrain with Velcro strap or similar – running at 10C should not cause the battery to heat up. If running harder allow for cooling air.

· If you need to dispose of a Li-Po – connect a small bulb e.g. 6W car bulb across the pack and COMPLETELY discharge the pack. Then stand in a bucket of salt water over night – the salt water attacks the pack and neutralises the cells.

Charge times / rates

And finally, on the Click here to find a simple chart I worked out to give you the correct times to slow charge NiCd’s and NiMh’s –

NOT TO BE USE WITH Li-Po’s

The top axis shows battery capacity, the left axis shows charger output. This then gives charge time in hours to charge to 120%, which is the recommended charge for slow charging NiMh’s and NiCd’s.

For example, if you have a 1600mAh pack and a charger with an output of 300mA’s the table will give you a charge time of 6.4 hours.

Alternatively, if you have a variable / multiple output charger and you want to charge your batteries in say 8 hours because you forgot to put them on charge and you need to get up early to go flying, 8 hours on a 1600mAh pack requires 240mA charge rate

I hope you have enjoyed my first edition of Windsock and find the table useful, I have it pinned on the wall next to my charger.

Comments, suggestions or articles to:

Paul Joslyn, 8 Fairfax Road, Chalgrove, Oxon, OX44 7RS. 01865 400603 – 07771 963200 or paul.Joslyn@xerox.com