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Gladys International 21C

The Almost Quarterly Journal of The Sheffield

Society of Aeromodellers Issue115: 2016 ( hopefully)

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Disclaimer: All views expressed in articles are the authors own. Articles are pub-

lished in good faith however the editor and club committee accept no liability for

any errors or omissions. Readers are responsible for independently checking the

accuracy of any information given.

Editorial……………………………………………...3

Wind Up 2: Andy Timmons……………………..….4-7

Over-Hot and Over There: Ed……………………...8-11

A Day With ‘Just Jane’:Phil Barrett………………12-15

Watch The Skies: Ed………………………………..15

Wrong About The Wrights:James Ford………......16-17

The Indoor Duration Nationals: Neil Stewart…….18-22

A Short Guide To Batteries: Andy Timmons……..23-27

Back On The Slope: Ed……………………………..27

Endpiece: Ed………………………………………...28

Contents

Acknowledgements: Thanks to all contributors. Thanks to David Tayler for

editing ‘ A Short Guide…’ and to Tim Scowcroft for the diagrams. All photos by

Neil Carver except:12-15( Phil Barrett) p 2 and 17 ( Anon) , 18-22( Pete Dolby).

Ideas for Gladys? Contact the Editor at [email protected]

Is It a bird… or a plane? See Page16

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Editorial If all has gone to plan you are reading this before Xmas. If not then; sorry

but as you know you just can’t get the staff. Anyway, presuming it is

before Xmas then, Seasons Greetings! Being a miserable so and so I had

no plans to do an Xmas edition but a certain James Ford was adamant that

the cover of the 2001 winter Gladys should be reused so my hand was

forced. For those of you who weren’t around in 2001 the cartoon was by

Phil Lockwood ( also a former Gladys editor). The original caption reads:

“...the tradition of decorating the Callow Bank Slopes at Christmas has a

long history and the picture illustrates an exciting moment sometime in

the early 1900s when the Tripplethwaite Twins saved the local populace

from a great disappointment when it was realised that the giant SSA

Xmas tree was devoid of the Angel on the top.( the result of an unusual

cock-up by the Committee of the day) Fortunately the Twins were at hand

with ‘Elsie’, their steam driven, hot air dirigible-crane to manoeuvre the

missing decoration into place.”

Although Elsie has long retired, Phil continues to be very productive as

an artist and his stunning paintings, cartoons and other creations can be

viewed ( and bought) at: http://www.phil-lockwood.com.Well worth a

visit.

Elsewhere in this edition, electricity is the order of the day and Andy

accentuates the positive, hopefully with no crossed wires. We also see

Phil get a lift in a Lanc., while Pete and Neil fly at Flixton and I ‘hit the

Hiller’. We also have , courtesy of Brian, footage of a genuine U.F.O. No;

it isn’t April1; watch it and wonder. Finally: ‘The Truth’ may be still

‘Out There’ but not when it comes to early flight. In this issue James

tackles the myth that is the Wright Brothers and restores the

Tripplethwaite Twins to the throne of aviation history. About time too.

Whatever you do with sprouts do it safely.

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Wind Up 2 (What a LaRK) ! A.Timmons

In the last edition of Gladys, we looked at rewinding a star wound

outrunner motor. Now it's the turn (geddit?) of LRK, DLRK or delta

windings. There are other winding schemes around and the combinations

of numbers of poles and magnets is myriad. It's not possible to cover

every eventuality in two short articles, but in my experience of RC plane

motors, these two schemes will fix most you'll encounter.

LR and K are the initials of the three guys who came up with the winding

in 2001. They were called Lucas, Retzbach and Küfuss. With an LRK

winding, you only wind the wire around half the number of poles on the

stator.

DLRK (Distributed LRK) follows the same winding idea, but you wind

all the stator's poles. Delta refers to both LRK and DLRK as it describes

the final shape of the wires if you opened the windings up. They form a

triangle - Greek letter delta.

It sounds as though describing how to wind the LRK would be the

simplest place to start, but in reality, I have never found a RC plane motor

wound like that. So I'm going to jump straight in with the DLRK. If you

want to have a go with LRK, a quick search on the internet will provide a

diagram to work from.

To start, take the motor apart and get rid of the old wires, remembering to

count the number of turns per pole (and, as mentioned in the last issue of

Gladys, if the wires are glued in, give up. It's not worth the heartache).

Measure the diameter of the old strand and, if there is more than one

strand per wire, calculate the thickness of the new wire using the

technique I described last issue.

Describing the process of winding a DLRK motor gets really confusing

because it's so easy to turn the stator around or upside down while you are

winding it, so what was clockwise becomes anti-clockwise and where

wires start and end gets mixed up. It took me several attempts before I

managed to get one right and after that my success rating was no better

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than 30% for quite a while. However, I eventually worked out a way of

thinking about it that works for me and here it is. First, sequentially

number the poles on their ends. All the DLRK windings I've worked on

seem to have 12 poles, so that's what I'll describe.

Always keep the bottom of the stator facing upwards.( See diagram over)

Leaving about a four inch tail, pass the enamelled wire down between

poles 1 and 2.

Wind 1 anticlockwise then 2 clockwise.

Then pass the wire between 6 and 7.

Wind 7 clockwise and 8 anticlockwise.

Pull off about eight inches of wire, fold it in half and twist it together at

the stator to keep the winding of pole 8 secure.

Pass the enamelled wire down between poles 9 and 10.




Pull off about eight inches of wire, fold it in half and twist it together at

the stator to keep the winding of pole 4 secure.

Pass the enamelled wire down between poles 5 and 6.



Example:

If each wire has six strands and each strand is .015mm in

diameter, then the wire has a total cross sectional area of 6 x

pi x ((0.015)/2)2

Which is 6 x 3.142 x 0.0005625

Which is about 0.0011mm2

Working that backwards, the radius of the single replacement

wire is calculated by:

r2 = 0.0011/pi

Which is 0.018mm. So the diameter is twice that, ie

0.036mm

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Twist together the wires at poles 1 and 12.

Twist all three pairs together at the stator end to keep them together and

stop them unwinding. Trim them to the same length. Cover each pair

with heat shrink, then using a soldering iron and cored solder, burn the

enamel off the ends of the wires to make sure you get a good connection.

Solder each wire pair into the plug that will connect it to the ESC.

Remember to cover the soldered ends of the plugs with heat shrink so

they don't short out against each other and cause you to start all over

again. Reassemble the bell, washers (if any) and circlip.

If you have a multimeter, check the resistance between the three plugs. It

should be very small and the same between each pair. Then check the

resistance between one of the plugs and a bare metal part of the stator. It

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should be open circuit ie, infinite resistance. If this final test shows a

resistance, then the motor might run, but it won't run well and will get

very hot, very quickly. Unwind it, find the bare edge of the stator that is

scraping the enamel off the wire and cover it in superglue. Let it harden

and then rewind.

And that's it. Ok, this is much trickier than replacing a star winding, but

with practice it does get easier. My success rate is almost 100% now.

Often there's a base plate at the bottom of the stator that makes it difficult

to pass the new wire around the poles. If that's what faces you, do your

best. Remember the motor was broken anyway, so what have you got to

lose?

PS: Thank you to all those members who kindly donated knackered

motors for me to test these instructions on.

… and to fill the gap

here is a portrait of

the author as glider

pilot, with bells on. Ed

A quick tip for if your motor does have a base plate on the stator that

is getting in the way.

Heat the stator on an electric cooker hob or with a blowlamp to sof-

ten the glue / expand the stator.

Using two large flat bladed screwdrivers at opposite sides between

the stator and the base plate, twist the stator and base plate apart.

This sometimes works. Often it just makes a twisted mess of the

base plate, so don't try unless you can't rewind it otherwise.

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Over-Hot and Over There; Again. Ed

You may remember a couple of issues ago describing a journey through a

searingly hot California with the intention of visiting 3 aircraft museums

in a day. I described one Well , here are the last two.

Several air-conditioned hours of driving brought us to Oakland Aviation

Museum over the Bay from San Francisco. Turning into the parking lot

we were confronted by an unusually placed British airframe, nothing less

than a Short Solent. This Solent was used in Raiders of the Lost Ark and

if you are there when the interior is open: a “copy of Life Magazine marks the seat where Harrison Ford’s Indiana Jones character sat in the movie”. Wow.

The Oakland museum is a fairly modest affair but among the post-war

airframes was one known to many of us, an Aeronca Champ; in this case

a 1946 Model AC which had nothing to do with Raiders of The Lost Ark.

The restoration of the Champ failed to include selotape anywhere on the

wings which gave the machine a slightly unreal ‘ factory new’ feel.

Shame.

A brief hop over the bay delivered us to a Mecca of rotary delights and

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t h e

most affluent of our ports of

call. The Hiller Aviation

Museum is pretty much

immaculate and a blast. There

are of course all manner of

Hiller experimental helicopters

and a fantastic flight simulator

of a Hiller Flying Platform.

This unlikely machine was

powered by contra –rotating

ducted fans and incredibly, was

dynamically stable in flight

It was flown by a soldier/ pilot

who stood on the platform and

wiggled his hips in a

provocative fashion to guide the

craft. Well almost anyway. The

designer Charles Zimmerman theorized a person's natural balancing

reflexes would suffice in controlling a small flying machine just like

riding a bicycle or balancing a surfboard. He coined the term "kinesthetic

I have no idea how they flew this in a hall that small

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control," to describe this and blow me down it worked. Oddly enough, of

the 6 that were built, 4 have vanished. A sign in the museum asks that if;

…”you have information regarding the disposition or physical location of other

Hiller platforms please contact the museum.”. Can I ask club members to

check their lofts and sheds please .Anyway you can stand on a replica

hooked up to a computer and fly it by leaning slightly to steer and move

forward or backward. It is great fun to try. Watching someone else do it is

like seeing an aeronautical version of Strictly Come Dancing fuelled by

illegal pharmaceuticals.

Another favourite of mine was this 1946 Republic RC3 Seabee amphibian

which I was told was used by Mr Hiller on weekend fishing trips. More

than 1,000 were produced; to the horror of the local trout population

Then there was the Avitor Hermes Jr.; argued by some to be the first

unmanned powered aeroplane in the world. Well ok a replica of it. It was

designed by one Frank Marriott; an Englishman. Marriott had worked

with Stringfellow in the UK, was passionate about the idea of powered

flight and is claimed by some to be the first to use the term ’aeroplane’ in

the way we use it today. He is also rumoured to have influenced the

design of the Tripplethwaite Twins’ airship ; ‘Elsie’ and was said to be a

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‘reet good bloke’, especially after he had consumed his daily ration of 5

pints of Steel City Stout. The unavailability of this medicinal product in

San Francisco is said to have led to his demise.

The Avitor Hermes Jr. flew in California in 1869;“...before the Wright

Brothers learnt to walk”. This 28ft long airship had a 1 horsepower steam

engine and 18 ft wings making it a ’composite ’ aircraft; part balloon and

part powered glider. Now accepting virtually every account of early flight

is contested to the point of madness, here is a description of that flight

from Scientific American no less :

“The morning was beautiful and still… the conditions were favorable to

success. In six minutes steam was got up - the rudder set to give a slight

curve to the course of the vessel - and the valves opened. With the first

turn of the propellers she rose slowly into the air, gradually increasing her

speed until the rate of five miles per hour was attained. The position of the

rudder caused her to describe a great circle. Lines had been fastened to

both bow and stern, which held by two men, who followed her track, had

sufficient ado to keep up with her at a dog trot."

The Avitor was in fact a prototype model of a design that was to

demonstrate the potential for an airship service between New York and

California. Alas they finished the trans continental railroad first. Oddly

enough the journalist who wrote about the model’s construction was none

other than Mark Twain. Now there was a man a man who really could

spin a yarn…...

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Introduction

As some members will be aware `Just Jane` is an Avro Lancaster Mk VII,

owned by the Lincolnshire Aviation Heritage Centre at East Kirby airfield

in Lincolnshire. The Lancaster was built in April 1945, and intended to

form part of the Tiger Force to attack Japan once the war in Europe was

over. The war in the Far East finished before the Tiger Force was

assembled, so the aircraft was surplus to requirements and sold off to the

French Government. The mid upper turret was removed, and it was then

used for maritime reconnaissance until being again declared surplus.

It found its way back to the UK, and served as the gate guardian at RAF

Scampton for several years before being bought by Fred and Harold

Panton in memory of their brother Christopher. He was the Flight

Engineer in a Handley Page Halifax, shot down and killed by a night

fighter on an attack on Nuremberg in March 1944.The Lancaster was

relocated to the old RAF station of East Kirkby, and following a detailed

inspection it was brought back to a condition that allows it to give taxy

rides to the public.

The long term objective is to return it to flight, although this will require

several million pounds to fund a total strip down and reassembly in order

to achieve a Certificate of Airworthiness from the CAA.

Our Visit

Recognising I would be 65 this year, Anne decided that something special

had to be organised. She booked me on the VIP experience, which also

allowed her to tour the aircraft although not take part in the taxy runs.

We were asked to present ourselves around 9am, and I was allocated to

one of the two groups of 12 people to ride in the aircraft. The normal

practice is for one taxy session in the morning, then the second one just

after lunch. Both groups were given a briefing at 9.30 which lasted for

A Day With Just Jane:Phil Barrett

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about 30 minutes. This covered the events of the day, an outline of the

bomber offensive against Germany, and the history of `Just Jane

As I had been given a morning slot, I could then join the aircraft and try

all the various positions from the rear gunner’s turret to the cockpit. The

immediate impression on climbing into the fuselage is how cramped it

was. We had a guide with us all the time we were in the plane, explaining

how the crew operated and their various roles on a mission

To access the rear turret you had to shuffle over the tailplane main spar,

then turn round to fit in the turret. The tail gunner had the most isolated

and coldest position on the aircraft, and all were volunteers! His parachute

was stowed in the rear fuselage, so to escape he had to traverse the turret,

climb over the spar, find his parachute then jump. Trying to do that in a

plane corkscrewing or on fire does not bear thinking about.

The cockpit was fascinating. The pilot was alone in the cockpit, with an

excellent view both forwards and to the sides. I was able to move the

control yoke and rudder pedals, and was amazed how easy they were to

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move given the long mechanical linkages back to the control surfaces.

Again access to the front fuselage was difficult due to having to climb

over the wing main spar. Whilst the mid mounted wing made possible the

huge uninterrupted bomb bay below, it certainly created problems for

internal movement.

The Taxy Trip

The twelve of us had agreed where we would be located for the ride, and I

chose the mid upper turret as I thought the view would be the best, and so

it proved.

The pilot started each of the engines in turn, and we taxied out to the grass

runway. Ultimately we were positioned at the end of the field, which

allowed the engines to be run up to full power for a simulated take off.

The sensation of gathering speed was tremendous, but of course

ultimately the throttles were cut and the brakes applied. We then returned

to the hard standing, and once again the Merlins were run up to full power

for a brief time in order to clear the plugs. In total the taxy trip lasted

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around 20 minutes, and every one memorable!

The Rest of the Museum

We then had the opportunity to tour the site, The control tower has a

really interesting series of tableaux showing what it would have looked

like when a raid was on. The main hanger had some good displays,

particularly of bits of wreckage recovered from crash sites in

Lincolnshire. The combined shop and restaurant again had some excellent

photographs and exhibits, and we were treated to a really good lunchtime

meal as part of the VIP package.

The gift shop was well worth a browse, with some relevant books and

DVDs. We really enjoyed the whole experience. Most of the staff were

relatives of the founders of the museum, and they really cared about their

visitors. There is an excellent website for the Lincolnshire Aviation

Heritage Centre, and it gives dates for when the taxy events will take

place. Spectators simply paying the museum entry fee get an excellent

view of the aircraft as it starts up, taxies out and returns.

Well worth a visit, and Anne enjoyed it too!

Anyone who is a member of this club can tell tales of strange things in the

sky. Most of these very rapidly become strange things on the ground in

bits. Brian Clamp however has gone and captured a genuine U.F.O. on

film. He was pointing a video camera at the supermoon and on playback

was amazed to see he had actually shot an airliner flying across the moon.

But that wasn’t all. Just before the airliner flies from right to left ( about

15 seconds into the film) a mysterious thingy (or a pair of thingies) tracks

upwards past the bottom edge of the moon. I don’t think it was John

Penton as he doesn’t fly at night, but see for yourself at:

https://www.youtube.com/watch?v=xeNSU8VIPTY&feature=youtu.be

Watch The Skies: Ed

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Wrong about the Wrights: James Ford

History insists that the Wright brothers were the first to achieve the

controlled sustained flight of a powered heavier than air aircraft on

December the 17th 1903.However powerful evidence has recently

emerged showing otherwise. Documents unearthed from the SSA

historical archive show that in fact it was Sheffield’s own Tripplethwaite

Twins who were the first to achieve this milestone in aviation history.

Frank and Albert Tripplethwaite were pioneers in both steam and aviation

and born into a long line of innovative industrialists. Their father, Fred

made the family’s fortune with his now famous Tripplethwaite Steam

Powered Toilet Brush and the royalties from this secured the twin’s future

allowing them the freedom to become Victorian gentleman inventors. The

twins set up a small workshop in Heeley. The building is long demolished

and now a B&M Bargain Store but a keen historian may find a small

plaque near the entrance which commemorates the site’s significance.

The Tripplethwaites were not renowned for their philanthropy but their

reputation as ‘tight-fisted’ can be refuted by a sworn statement from a

barman who witnessed Albert buy a round following the first known

meeting of the SSA in March 1888.At least 3 people were in attendance.

The club proved to be only one outlet for their prolific imagination. They

are credited with the invention of the first steam powered wheelchair as

well the unique steam powered nasal hair clippers and the first practical

steam bicycle which, in 1875 astonished onlookers by achieving 62mph

down the Dronfield bypass. The airship Elsie (see front cover) which was

commercially successful, almost fulfilled their passion for aviation but

since 1890 they had also been experimenting with gliders based on the

designs of Otto Lilienthal. By 1893 they had mastered controlled descent.

It is not known when they decided to attach rockets to the glider but the

archives contain a receipt in March 1893 for 20 line carrying marine

rescue rockets. What is undisputed however are the events of November 3

in that year when Albert Tripplethwaite took his place in the history

books.

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It was cold and windy the day when Albert dragged the glider to the top

of Higger Tor. In attendance were 3 SSA members, 2 gamekeepers and a

small dog named Jess. Professor Phileas Barrettson, one of the SSA

observers picks up the story:

“Albert braced the glider into the wind while Frank lit the fuses. The

glider shot off and to our horror plummeted earthward. Mercifully it then

hurtled upward like a scalded cat. It was terrifying to witness this poor

man propelled into the heavens trailing smoke and fire. His screams were

testament to the foolishness of this endeavour. At the extinguishment of

the rockets he was barely visible but descended slowly, with evident

control. He came to rest at the far side of Burbage valley and there we

found him. He was unharmed although a little scorched. He shook with

both fear and laughter and all he would say was; ‘Most peculiar’.”

One of the gamekeepers, Donald Trumpton was equally shaken and is on

record as saying;” This gentleman has both courage and lunacy in equal

measure. Should he attempt this again I shall be forced to summon a

constable to protect him from his folly.” To commemorate this historic

event the committee had the landing spot enclosed with railings. They can

be seen from the road just before Burbage bridge. The glider survived

largely intact and remains on display in the Hunters Bar Aviation

Museum ( closed Tuesdays).

Stop Press; 2 poor images dated 1893 have also just come to light. One

clearly shows Albert's flight path while the other seems to show

Trumpton, the gamekeeper looking on to the landing spot. He looks

remarkably like Terry. Ed.

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The Indoor Duration Nationals: Neil Stewart

The indoor duration Nationals took place from the 16th to 18th September,

2016. Peter Dolby and myself represented the Northern Area BMFA as

the only entrants from the north, unless you count Dave Whitehouse from

the Clayton Green flyers who attended on one day and flew in one class.

The contest is held in the Brabazon hangar at Filton, Bristol, once the

home of the Bristol Aircraft Company. More recently the hangar was used

to assemble and service Concorde and they still have one on display on

the old runway. The site itself is now owned by the Airbus corporation

and understandably security is tight. The Bristol aircraft museum is

housed in the next hangar to where we flew. You need to pre-enter any

flying events and can’t just turn up as security won’t let you in if you

aren’t on the list.

The contest is held over three days and you are allowed six timed

competition flights in each class you have entered, with the best two times

to count toward the final classification. We had entered eight different

classes, so that’s a lot of flights to do. What we normally do is to time

each other’s flights (you are not allowed to time your own). So it goes

like this: You agree who is to fly and whoever it is lubes their motor and

The Brabazon hanger is huge, and home to a small herd of flying reindeer

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puts it on the torque meter and starts to wind to full turns, then backs off

(back winds) to the launch torque (which has been established with

practice flights). He says he is ready and then timing can commence as

soon as he launches. Timing ceases when the model lands. The timer

records the score on the time sheet and the flyer takes the sheet to the

results compiler. Saying that some of these flights can take ten minutes,

and winding the same, then you have to put your score card in, it is

unlikely that you can do more than a couple of contest flights in an hour.

Well that’s enough explanation, how did we go on? On the Friday we

both started to fly pennyplane (3.1 gram 18 inch duration model) Having

not had any practice in high ceiling venues, and seeing the ceiling height

at Brabazon is 60 odd feet we struggled to get up to height. We

eventually managed to get a suitable trim (rubber/prop/turns/torque) that

took us there, and we both managed an official timed flight of around

nine minutes each. However that was the morning gone and it was the

lunch break , during which there was a hand launched glider competition

so we got out our gymminie crickets (a lightweight version of the BMFA

kit) in readiness for the afternoon session.

I didn’t have the same difficulty getting the times with these, in fact I did

6.53 with a practice flight, but I didn’t have it timed. If I had I’d have

The Brabazon in its heyday

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easily won the class, but I managed a couple of 6 minute plus flights, and

I was happy with that. Pete managed to lose one of his crickets in the

rafters, but still recorded a total of 11 minutes 30 seconds with his reserve.

As we were leading the competition at the time we didn’t put any more

flights in, that was probably a mistake, but we had other classes to fly.

On Saturday we thought we had better fly another class, so we chose no-

cal (profile 16 inch semi-scale). Being scale models these don’t fly for

very long, with any flight over four minutes good indeed. We were both

flying Fike E models. Pete had a new one, but I only had last year’s

model, and it wasn’t new then. I managed a total of 6.15 and Pete 5.30. It

was clear that others were doing longer flights, which we thought was

down to propeller design. This is something we will work on for the

future.

We thought we’d better get some better times in pennyplane as the air

seemed quite good with warm sunshine outside, but the day soon turned

into a disaster.

Pete put more torque on his motor and was soon flying above the girders

in the roof space, It looked like a 10 minute flight if he could get away

with it. Unfortunately he couldn’t and his model lodged in the overhead

crane tack. We tried to get it down with the helium balloon, but only

Up, up…. and into the girders.

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retrieved the tailplane. I wound for an official flight but was down in

about eight minutes, which was no good at all. I re-measured the motor

and found I had used an undersized one. I changed it and I had a practice

flight and but recorded 7.31 so I rewound with more torque to try to get a

better time.

Well, my plane was soon flying just below the girders, but just as I

thought it was cruising and wouldn’t get any higher, it did. I think there

was a layer of warm air in the roof. My model flew round between the

girders and just as I thought I’d get away with it, my model stuck in the

same place as Pete’s. I was flying my best model but luckily had a reserve

which was nearly as good. I put in a safe flight with it but only 8.31,

which was not good enough as I was looking for over nine minutes.

Pete went up again with his second model but that went too high and he

lost that too. We decided to do something else and I practiced with my

legal eagle (a small cabin duration model) Then it was time to finish. A

frustrating day for both of us. In the evening we had the traditional contest

banquet at a local pub, and we both felt much better after that.

Neil times a model; unaware of a surprise visitor.

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Sunday -“As I walk through life I hear times winged chariot drawing

near” (Andrew Marvell – Metaphysical Poet). You may not think that

metaphysics and aeromodelling have much in common but the fact was

that we were running out of time. The contest ended early at 3.30pm and

we hadn’t flown in a number of classes we had entered. We both quickly

put in a pennyplane time and luckily we both still had a model. Pete did

9.15, and I did 9.09. I then flew legal eagle, just putting in two mediocre

flights. We then had a go at ministick (7” lightweight) with two flights

each, just to get a place.

We turned to 35cm (a 1 gram duration model) Pete broke his and

couldn’t repair it in time. I damaged my best prop, repaired it, did three

official flights with the best two totalling 20 minutes and with my last

flight just minutes before the competition ended.

We then had the champagne flyoff (last one down) for the ministick

models to finish at 3.30pm.Unfortunately Pete’s fin fell off as he wound. I

managed a flight but my model didn’t climb like it should making several

low passes and just missing the other flyers. I later discovered that the

Teflon thrust washer was missing from the propshaft but I wasn’t too

bothered as I don’t like champagne!

At the end of the day we didn’t do too badly. Pete was 3rd in pennyplane

with 18.18 and I was 4th with a second less. I was 2nd in gyminnie with

12.17 and Pete 3rd with 11.30, Pete was 2nd in ministick with 10.14, and I

was 4th with 9.38. We were 5th and 6th in no-cal. I was 5th in legal eagle,

and 2nd in 35cm with 20 minutes.

So Pete got two bronze certificates and a silver and I got two silver. You

get points for each completion depending on the number of entries (e.g. if

there are 10 participants the first gets 10 the second 9 and so on) and they

are totalled up at the end. Just to show that effort pays off I was 2nd

overall, and Pete 7th out of 26.

That’s all for now, but remember free flight flying continues at Bradfield

all through the winter !

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Many people find electricity hard to understand as you can't see it, and

unless you stick your finger in a mains socket (don't - I didn't tell you to)

you can't feel it. However water provides a useful, reasonably close,

analogy. Electric current – measured in amps (I), corresponds to flow; and

voltage measured in volts (V) corresponds to pressure. Battery capacity is

volume measured in milli Amp hours (mAh).

So let's apply this to batteries. The voltage of a battery depends upon its

chemistry and state of charge. Dry cells are about 1.5 V when new. They

run down and then have to be thrown away. Nickel cadmium cells are

between 1.4 V and 1.2 V. Lithium polymer (lipos) are rated at 3.7 V,

although fully charged they top out at 4.2 V (any higher and you will ruin

them) and when they are discharged, just over 3 V (any lower and your

ruin them again – hence the fancy chargers and battery monitors that keep

the voltage between these two limits).

Using our water analogy, imagine the battery is a bucket whose five

gallon capacity is full of water. A big hole in the bottom allows the water

to drain out quickly, a small hole allows it to drain out more slowly. With

a waterwheel in the flow you get a lot more power with a big hole in the

bucket, but for a short period of time: the small hole gives less power but

for longer. However you still end up with a five gallon puddle on the

floor. (FIG 1)

A perfect battery

would have a

constant voltage at

i t s t e rm i n a l s

irrespective of the

load applied, but

nothing in this

world is perfect

(except, perhaps

s t i c k y t o f f e e

pudding). So a real

A Short Guide to Batteries: A. Timmons

24

battery can be represented by a perfect battery connected to a resistance.

This resistance is caused by the way the battery is constructed and tends

to be lower for bigger batteries. It also increases as the battery ages. This

occurs if the battery is stored fully charged or overheated and, especially

with lipos, over discharged. The manufacturers of more expensive

batteries will quote this resistance measured in milliohms (mOhms) but it

is more usual just to quote a C rating.(FIG2)

C is the capacity of the battery in mAh, for example an 800mAh battery

will supply 800mA for one hour, or 80mA for 10 hours. The C rating

tells you the multiple of its capacity that the battery can safely deliver, so

a 800 mAh battery with a rating of 20 C can safely deliver 20×800 or

16A. However the higher the current the shorter the time it can deliver it

for. In this case it can deliver 16A for three minutes (hours times 60

minutes divided by the current drawn: 1×60÷20). Usually C ratings are

shown as a range something like 20 – 30 C or 65 – 120 C. The lower

value is the maximum current that the battery can safely constantly

deliver, the upper value is the absolute maximum current the battery can

supply in occasional short bursts for example during take-off or in a

vertical climb.

However, these figures should be treated with a large pinch of salt

because many manufacturers overstate the C rating. One of the very

interesting features of telemetry is just how large the voltage drop can be

when demanding high currents from the battery. When the throttle is fully

25

open the low voltage alarm will sound and once the power is reduced to

gentle cruise the voltage recovers very quickly. This voltage drop is due

to the internal resistance of the battery.

Batteries do not push electricity through a circuit, they supply it according

to the demands of the circuit. So imagine you've got a battery, motor and

ESC in a plane. The design of the motor, the size and pitch of the

propeller and the weight of the plane all influence the current the circuit

demands. Ohms law says V=IxR where V is the voltage, I is the current

flowing through the circuit and R is the resistance of the circuit (which

includes the resistance of the motor and the internal resistance of the

battery). The current flowing generates heat, which is why motors can

burn out and batteries might be warm or even hot after a flight. If you

exceed the C rating the battery might overheat, go into thermal runaway

and burst into flames!

The C rating is useful when charging the battery, as to ensure long battery

life it is advisable to charge at 1C. Some batteries allow charging at

higher rates, but this tends to shorten their lifespan. It also increases the

risk of thermal runaway leading to a short intense fire!

Cells in series and parallel

People often refer to these convenient little power packs as batteries, but

strictly speaking, a battery must have more than one cell. Lipos (and

other batteries) are made from standard cells connected together either in

series, parallel or both.

If you take two lipo cells and wire the negative of one cell to the positive

of the other and take the feed from the other two terminals, the capacity

available is that of each cell, but the voltage is the combined voltage. So

with 800mAh cells, you'd have 7.4v available at 800 mA for an hour.

Wired in this way, the cells are said to be 'in series' and as there are two of

them, it is shown on the battery pack as '2S'.

If you take two cells and wire the two positive terminals together and the

two negative terminals together, you still only get 3.7v, but the capacity

available is now the capacities of the two cells added together, so two

800mAh cells connected in this way will produce 1600mAh, or 3.7v at

26

400mA for four hours. Wired this way the cells are said to be 'in parallel'

and as there are two of them, it is shown on the battery pack as '2P'.

(FIG3)

Wiring cells in parallel does not have to be done with cells of equal

capacity: you can wire 100mAh batteries to 3000mAh batteries quite

safely as long as they have the same voltage (ie cell count or S rating),

which is how parallel chargers can charge several batteries at the same

time. For safety the batteries should be of similar age and state of charge,

so there is not a high current flow as one battery tries to charge the other.

The two ways of wiring cells together are not mutually exclusive – with

enough cells, you can do both. The table opposite shows the available

voltage and current for various combinations of 800mAh cells. In practice

few people build battery packs, however if you have, say lots of

2200mAh 3S batteries, then putting two in parallel saves buying higher

capacity batteries and gives increased versatility. This gives a 3S2P

battery with 11.1 volts and 4400mAh, suitable for higher current draw and

larger planes.

In the next edition of Gladys, we'll be tackling quantum physics, gluons,

string theory and why you can't drown in gravitational waves, even if you

can't swim. And no, gluons are not bits of planes attached with Por.

27

On the left we have Geoff captured on one

of his final Callow launches. Geoff has

now left us for the soaring delights of

Exmoor and we wish him well.

Below is another image allegedly from a

glass plate negative found in the SSA

archives. It seems to show the gamekeeper

prostrate in shock as Albert flew off. The

hat however seems different to

the other photograph and the

position of the sun appears to

be wrong. Of course it could

just be Terry lying on the

hallowed Callow peat last

summer; a Chair without a

chair you might say...

Cells

in par-

allel

Cells

in

series

Total

number

of cells

Vol

tage

Capacity in mAh Desig-

nation

1 2 2 7.4 800 2S

1 3 3 11.1 800 3S

1 6 6 22.2 800 6S

2 0 2 3.7 1600 2P

4 0 4 3.7 3200 4P

3 4 12 14.8 2400 3P4S

Back on the Slope; Ed

28

At Dronfield Ron describes the carp he caught in Millhouses

boating pond……..

..and at Lodgemoor Robert fails to get his new $2 portable Imax

Cinema to work.

All the best for the New Year and lets hope , in the

words of Nat King Cole we can beat that jive Jack,

stop our divin’ and: Straighten up and Fly Right!!

Endpiece