1
Gladys International 21C
The Almost Quarterly Journal of The Sheffield
Society of Aeromodellers Issue115: 2016 ( hopefully)
2
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
3
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.
4
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
5
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.
Wind 9 anticlockwise then 10 clockwise.
Then pass the wire between 2 and 3.
Wind 3 clockwise and 4 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 4 secure.
Pass the enamelled wire down between poles 5 and 6.
Wind 5 anticlockwise then 6 clockwise.
Then pass the wire between 10 and 11.
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
6
Wind 11 clockwise and 12 anticlockwise.
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
7
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.
8
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
9
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
10
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
11
‘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…...
12
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
13
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
14
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
15
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
16
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.
17
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.
18
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
19
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
20
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.
21
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.
22
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 !
23
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