 November 06
BMFA club affiliation No 0340
FLY SAFE – Fly Again
Next gathering at St Andrews Rugby Club November 6th - Monday
And the next December 4th No meeting Jan 07
I do hope you have all paid your subs to Mike by now, if not please do so we are still the cheapest in the area, with well cut grass.
FLY Safe, fly again and enjoy – make the most of the weather while it lasts!
The clocks are about to do their hour trick so the autumn/winter is upon us. Don’t be too disheartened we still do get good flying days even if they are short.
For this issue I must give a huge thanks to Wayne Giles for the electric words of wisdom below. It is the forerunner to the next issue where I will be giving some thought to Noise.
ELECTRIC FLIGHT CONVERSIONS
By Wayne Giles October 2006
Until about two years ago, I had been a lifelong builder of glow powered models and had always considered electric power as a very poor alternative, such models being desperately under powered or flying house bricks. As most of my models are sports aerobatic, (Acrowot or similar) I never got round to trying to convert to electric flight. The fact that I was a retired electronic engineer, always made me feel somewhat guilty about it, so I bought an IFO to fly round my garden which was fun but struggled for performance with a 7 cell NiCad setup feeding a standard 280 brushed motor.
Replacing the 280 motor with a 280BB improved the situation and changing the supplied Sanyo 600AE cells for Sanyo 500AR ones made the IFO a reasonable performer and demonstrated two principles of electric flight performance; firstly use an adequate motor to start with and secondly make sure you use the batteries which are capable of delivering the current you need to produce the required performance.
This success encouraged me onto other more ‘normal’ electric models and to look at converting IC models to electric power. During this period, brushless motors appeared on the scene followed very shortly by Lithium polymer batteries, the combination of which has transformed electric flight from an underpowered poor relation to a very realistic alternative to IC powered models. We all know about the advantages of no noise, no oily ‘goo’ and guaranteed starting (and in-flight restarting) that electric power has over IC power, but many modellers need convincing that the power/weight ratio of electric models can challenge that of IC models. The answer to that is: “Yes – now it can”
Although I am a convert, it does not mean to say that I believe electric models are better in all respects; IC models still have that indefinable something, be it the smell of a diesel, or just the mechanical noise and slight unpredictability of a glow or diesel engine. As an engineer, I can still see the attraction of a purely mechanical power plant and how the total reliability of an electric motor set up can be less attractive. Never mind – we now have the danger of lithium batteries catching fire and motors starting unexpectedly to make up for the loss of unreliable starting and carburetion and fuel feed problems!
I believe that many modellers are put off electric models because they feel that they “Just don’t know where to start”. It is a basic fact that you do need to have some understanding of electricity basics to be able to specify motors and batteries. There is an alternative of asking a knowledgeable dealer, about what to buy, but you need to be sure that he is knowledgeable and reasonably honest – after all you are asking him what he should sell to you!
If you want to work it out yourself, you can do so with only a little basic knowledge and some trial and error. The basic knowledge needed of electricity is very simple; so don’t be put off by electrical terms.
Voltage, measured in volts. Think of it as electrical pressure, like the pressure in water measured in feet of head.
Current, measured in amps. Using the water analogy it is the equivalent of water flow, in litres/minute (or gallons/minute if you are as old as me)
If you have a battery, (tank of water) feeding a motor (waterwheel) then the power of the motor depends on the voltage (water head) and the current (rate of water flow). The power is equal to the volts x amps = watts (water head in feet x water flow in gallons/minute). One horsepower is 33,000 ft.lbs per minute, which could be a flow of 330 gallons per minute from a head of 10 ft. as 1 gallon of water weighs 10lb. The direct electrical equivalent is 746 watts, which could be 100amps at 7.46V.
If you have followed that it should all now be clear - if not, don’t despair, you can still work out what power system you need for an aircraft, using fairly simple rules. Remember that the voltage is a function of the battery and the current depends on the voltage applied and the motor load it is feeding, which in turn depends on the load (ie propeller) on the motor.
A very good basic rule of thumb in deciding how much power you need is to take the total weight of the model (in pounds) and multiply it by 50watts for a trainer type model or by 100watts for an aerobatic model. You can now start to look for a suitable motor/battery combination to deliver the required power. A very simple shortcut is to look up the performance details of motors on the Internet. Forward-looking manufacturers publish such data, which is a great help and cuts out a lot of blind experimentation. Good published data will suggest propellers, batteries and motors to produce specified powers.
MOTORS
The options are brushed or brushless, (the latter split into inrunners and outrunners) geared or direct drive. The only advantage of brushed motors is cost; they are less efficient, heavier for a given power and fairly short lived, as they tend to be hard pushed in model applications. I would therefore advise the use of brushless motors and to avoid the complication and cost of a gearbox, the extra torque of an outrunner motor is a good choice. Geared brushless motors are generally only used in specialist competition models.
BATTERIES
A few years ago, NiCad’s were the only option, but NiMh packs increased the available power/weight ratio by over 50%. Now lithium polymer packs have doubled the NiMh figures. Coupling this with the capability of brushless outrunners to deliver efficiencies of over 80% and you can now see why electric flight has been transformed.
I have carried out comparison battery testing of the best NiMh cells and the latest lithium polymer 20C rated packs, which demonstrate and confirm the above figures. Combining these results with the specification of the latest outrunner motors show that the combination shows a power/weight ratio of 1.7Hp/Kg, which competes easily with IC power. Electrical systems have the advantage that they can swing large propellers slowly, which is much more efficient than a high revving small propeller.
An IC engine may be able to produce a higher power/weight ratio but it is not possible to use the power without a gearbox.
ELECTRIC CONVERSION EXAMPLE
To demonstrate how to work out the motor/prop/battery combination for a typical aircraft I will go through the calculations for a conversion I am carrying out at present. This is to convert a Glens Models 58” span Extra 330 from its intended power plant of a 46 2-Stroke to an electric outrunner motor.
We can go through a logical sequence: -
(1) Looking at the model specifications, we can see that the quoted weight with a 46 IC 2 Stroke is 5.375lb; equal to 2.440Kg. We must initially assume that we shall finish up with an aircraft of the same weight. This means that we need to aim at an input power of 5.375 x 100W = 537Watts
(2) The average weight of a 46 motor with silencer is 500g and we should also allow for a half full 8oz tank of fuel at 100g. This means that we have saved about 600g by removing these, leaving an airframe weight of 1.84Kg
(3) We now need to find a motor/ESC/Battery combination that will ideally meet the power and weight requirements. Looking on the Model Motors website, we can see that the AXI 4120-14 outrunner can cope with about 350watts to 700watts, depending on battery and propeller fitted. The various combinations of batteries and props. show that 14 x 1700mAh NiCad cells and a 13 x 8 prop. produce figures of 14.6V, 37.9A and 551 watts input. We can use this as a starting point and look for an equivalent lithium battery.
(4) I would suggest that only the latest 20C lithium packs be used (more on that later) and we are looking for a pack that will deliver 38A at a voltage of about 14.6V. If we now look on the Flightpower website and look at the specifications for the 3300mAh and 3700mAh packs, then you can see that a 4-cell 3700mAh pack will maintain 13.8V at 37A which is 10C for the 3700mAh cells. This is a bit less than our target, but is ok to start with; we can always increase the power by loading the motor with a slightly larger propeller, so that it takes a bit more current.
(5) If we now add the weight of the motor+ESC+Battery to the airframe weight, we have 1.84Kg+0.32Kg+0.038Kg+0.38Kg. This gives a new total weight of 2.578Kg, or 5.68lb. Ideally we need 568Watts and the setup will probably give around 480 – 520Watts, but it is a good starting point.
(6) When the system is up and running measure the power with a ‘Wattmeter’, ‘Medusa’ or similar device. (Cost £30 - £45). If the power is too low, use a slightly larger prop. – A small change can make a big difference to current and power.
(7) Checking likely duration; we are discharging the battery at about 37A equivalent to 10C for a 3700mAh battery so that the pack should last approximately 0.1hrs, or 6 minutes at full throttle. Assuming we fly at an average throttle opening of 2/3 throttle we can expect a flight time of about 9 minutes. At my age I find my concentration is failing well before this time! (I find that very hard to believe, editor)
The above system can be used for working out the power setup for any aircraft. The steps are the same; estimate the overall weight, work out the required power, find a suitable motor/ESC/battery/prop combination, recheck the weight and power requirements with this actual power pack, go round the loop again if you are way out and then go and fly it. You should be able to make minor adjustments with prop changes and larger adjustments by adding or subtracting a cell on the battery pack.
BATTERY CHOICE
The suggested cells on the Model Motors website are SubC NiCad’s and only 1700mAh. Even using the latest and best 3700mAh NiMh cells, the pack would weigh about 900g instead of 380g for a lithium pack. Lithium saves well over a pound in weight – more than 20% of the aircraft weight! A quick calculation shows that if we went the NiCad way we would need to add two more cells and finish up with a model 25% heavier and needing over 700Watts.
The above is the advantage of the latest lithium cells, the downside is cost and, as we all know by now, the potential danger if mishandled.
Costs are coming down and will continue to do so because of demand, but we will have to continue to be careful with lithium batteries and not abuse them. We have been spoiled over the years, as both NiCad’s and NiMh cells will withstand horrendous abuse without complaint. If you wish to go half way, you might consider lithium ion cells which are available in metal cases and are unlikely to ignite. These are about midway between NiMh and lithium polymer in terms of power/weight ratio, and will probably be available cheaply in the near future. They are being developed for use in portable power tools so large quantity production is likely with resultant low prices.
Assuming you are using lithium polymer, you will no doubt be aware of the special charger necessary and the dangers of charging in cars etc.
There is another characteristic of lithium batteries which is not so widely known and which is not advertised by suppliers and that is their life dependence on discharge rate. If you cane them by taking too much current, their working life is dramatically shortened in terms of charge/discharge cycles before they lose capacity. It is for this reason that I would suggest the use of 20C rated cells and only operate them at 10C rates.
Keep your eye on Bob Smith’s “Technology” column in Quiet and Electric Flight magazine; he is intending to test this aspect of lithium batteries and quantify the problem, so that the best battery brands will be clear. At present some suppliers make 15C and 20C claims for lithium packs that cannot cope with these discharge rates. Operating such packs at high discharge rates results in a working life of literally only a few tens of cycles.
USEFUL WEBSITES (No connection with any of them!)
Model Motors (AXI) www.modelmotors.cz
Flightpower www.flightpower.co.uk
Jeti (Speed controllers) www.jetimodel.cz/eng/hlavnien.htm
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 November 03
At The Field
By the time you read this, the preparation of our new strip in the adjacent field should be well underway. Arrangements have been made for rolling and mowing on Friday 31st October. Hopefully the morning crew will move the electric fence at the same time, although I have no first hand information; all this has come second hand from a club member. Presumably the padlock, to which we all have a key, will also move on the same day.
Access after the 31st will be via the gate next to the canal bridge, which is just a few hundred yards further along the lane from our current access.
Parking will be well inside the field. As you enter the field turn left, not forgetting to close the gate behind you, and follow the hedgerow around the corner of the field. Hopefully someone will have thought to put up a sign in the area where we're supposed to park. If not, parking should be just before the hedgerow ends. Please try not to spin your wheels or do anything else that will cut up the turf. We must take every care not to upset the farmer.
As for flying, try and avoid over flying the house that is situated along the lane a little way from the gate. Also do try and keep away from the farm. Make every effort not to upset our neighbours.
We could now have problems with noise due to the close proximity of these various dwellings. So, if your model is noisy please don't fly it until you've done something about it. Try and fly a smaller pattern instead of blasting around all over the neighbouring countryside. Little things like this will all help.
Let's hope we can soon match the superb finish of our old patch and continue to enjoy what is possibly the best strip in the country.
Many thanks to all those who took the trouble to tramp around the new field and so decide the location of the new strip.
 Glow Plugs
Do you get a big rev' drop at idle or full bore when you disconnect your glow plug driver? Experiencing unexplained engine cuts even though the model has performed perfectly before? If so, then there's a fair chance you need to change your glow plug.
To cause ignition of the methanol fuel we use in our engines a catalytic reaction between the platinum plug element and the methanol fuel, combined with just the right amount of compression, is required. So it's pretty easy to see that if the platinum element contained in the glow plug has deteriorated that we may begin to experience symptoms such as poor idle, lack of rapid throttle response and unexplained engine cuts in flight.
Commonly found problems with the plug element are:
Deformed plug element:
Usually the result of too high a compression ratio or very lean running or both. Also operating at very high revs, as in pylon racing or ducted fan use. Tuned pipe users should be especially aware of this. Head shims are usually available and should be fitted to reduce compression and cure the problem. Too high a compression ratio or too hot a plug can sometimes be diagnosed by “knock”, which makes itself apparent in flight as a severe rattling sound from the engine. Try a cooler plug before resorting to head shims. Overheating of the element with the use of a battery with too high a voltage will also deform the element - not so common now that most use the 1×2 volt Ni-Starter.
Rough or lumpy element:
This is a build up of engine by-products that become attached to the element and which will severely restrict its catalytic action. Discard the plug if you observe this. It can often be found in an engine that is fairly new as we have microscopic pieces of metal flying around the combustion chamber from the running in process.
Old age:
The element looks dull and powdery. This is sometimes accompanied by surface cracking which, for some reason, is more often found in plugs from four stroke engines.
Experimentation with plugs is often worthwhile in engines that have less than perfect carburetion. As an example, the big Super Tigres all suffered from an overly rich midrange. The accepted (partial) cure in all circles is the use of the very hot O.S. “F” type four stroke plug. The problem is resolved on new Super Tigre engines produced in China.
So, never neglect this vital element (groan!) on which the smooth running of our engines depend!
NASA Tests Laser Powered `Plane
 A remote-controlled plane powered from the ground by a laser beam has been tested by the US space agency (NASA). Laser-powered planes could be used for surveillance. In what is thought to be an aviation first, the development could lead to the creation of aircraft that do not need to carry onboard fuel.
The flight of the small model plane was conducted in a hanger at NASA's Marshall Space Flight Center in Alabama. "It really is a groundbreaking development for aviation," said Robert Burdine, laser project manager for the test.
 The 300-gram (11-ounce) plane, with a 1.5-metre (five foot) wingspan, was launched from a platform. The laser tracked the aircraft in flight, directing its energy beam at specially designed photovoltaic cells carried on the fuselage to power the plane's propeller. "The craft could keep flying as long as the energy source, in this case the laser beam, is uninterrupted," said Mr Burdine. "This is the first time that we know of that a plane has been powered only by the energy of laser light." As the plane does not need to take on fuel or batteries, it would have more room for scientific instruments or communications equipment. Scientists think it could eventually be used for surveillance and to provide communication links. "A telecommunications company could put transponders on an airplane and fly it over a city," said David Bushman, project manager for beamed power at Dryden Flight Research Center in California. "The aircraft could be used for everything from relaying cell phone calls to cable TV or Internet connections."
Nasa reportedly sees great potential in using laser power for developing new planes. "We think this is a step in the right direction," said Mr Bushman
New Newsletter Editor Required
Anyone who wants to take over the newsletter should contact Mike ASAP.
I shall finish after I have produced the December issue, my 19th, so whoever takes over has plenty of time to get geared up and ready for action. My thanks to those of you who made my task a little easier by contributing material. Jez.
Quote:
In the early days they said I was trying to make a statement, but I was just trying to make a living.
Captain Bonnie Tiburzi, American Airlines, first woman hired by a major airline. G :-)
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 November 02
At the Field
Not a lot to report this month. The strip is in superb condition, but of course the rain has now arrived and that great big heat gun in the sky has switched itself on to “low” for a while so we'll be paddling around in mud all too soon. The car parking area is already quite soggy so do take care not to spin your wheels when parking.
Q
Friday the 18th was a “Bad Day at Black Rock”.
First Derek Reeve had a radio problem or interference and blew up his Gangster in spectacular fashion quite close to the cars. I managed to let my model slip from my grasp as I was putting it down and snapped off the elevator horn. Then, incredibly, Flymo Jeffs also had some kind of radio trouble and after making a few hair raising swoops and dives blew up in the adjacent field. Norman Wilkinson had total radio failure as he was running up his engine before take off, and Derek Kent was having engine problems that finally put paid to his session, but only after his engine had sucked in his kneeling pad with a very loud “SMACK” that made everyone jump! If it weren't for bad luck we'd have had no luck at all!
Q
Haven't heard of any exciting winter projects other than those covered last month, although there's a rumour that Wayne Giles intends building a twin boom pusher camera ship. He'll be able to use it to photograph the construction of the new airport as our field disappears under the end of its runway!
If you're building anything do let me know, especially if you think it'll be of interest to others.
I'm busy with another single rotor DC autogyro which is a conversion of a .25 powered low wing sport model fuselage that I've had knocking about for years; it should be flying in a few weeks (provided I've got my sums right!). After that I have a Gee Bee Sportster Model Z plan to while away the winter evenings with and, like everyone else I suppose, a whole raft of projects that are just never going to be built!
Naked Ordeal for
Hijacked Couple
As you probably know our field is on Cathiron Lane. The following report (from The Observer) may just put you off staying late at the field…
A courting couple's car was hijacked and driven around the streets of Coventry for an hour while the partially dressed couple sat stunned in the back seat.
The couple's ordeal started in Brinklow's Cathiron Lane at around 11pm last Thursday (Oct' 10th) The pair, both in a state of undress, were in the back seat of a parked Citreon BX when another car pulled into the car park. Two men then came up to the car and asked for a cigarette.
When the window was wound down both men jumped into the front seats and sped off with the shocked couple still in the back.
The car was driven around Coventry until 12.20 am, when the hijackers let the woman out of the car in Aldermans Green Road.
Minutes later, her 28 year old partner was assaulted, stripped naked and dumped in Farren Road.
ARTF?
Watch out if you intend buying an A.R.T.F. in preparation for next season. Internet RC message boards are full of people posting messages of airframe failures due to poor construction.
Here follow a couple of typical examples:
.....the first flight of my Flair Giles 120 after doing the stall test, loop, roll etc it was decided to do a few low passes. When directly in front of me and at about 4 feet from the ground it started to roll right so left aileron was applied to correct this but when level it just sank quickly and bounced on the strip followed by a short glide and then landing. The damage to the model appeared minimal (broken undercarriage etc) but a close inspection showed the right wing panel to have partially snapped where the brace finished......The top and bottom spars are made from 1/4 balsa which to me seems inappropriate for such a model....
and:
…..there have been a couple of structural failures at our field. The first 3D (Weston 3D Hype) was powered with a Saito 80, this one lost its tail plane (the fuselage failed at the rear leaving big chunks of balsa top and bottom both sides of the tail). The second fractured the balance on one side of the elevator (joints) this one was powered by a Moki 51. Neither model had been flown beyond the limits you would normally expect of this type of model. Weston's comments on the first were that it had been overstressed with the Saito 80, now I considered this model to be underpowered and had made the decision to power mine with a 91 FS. The second model fortunately survived but I am now thinking along the lines of selling mine rather than risk my new engine and radio.....
So if you buy one of these dubious machines thoroughly check key points such as wing joiners, dihedral braces, tail attachment etc. It's one thing to have an undercarriage collapse on landing but imagine the possible consequences of a wing or tail failure in flight, especially with a large model.
Ho hum... Caveat Emptor.
Any Use?
Do you use cocktail sticks to secure your control surface hinges? Have trouble cutting tiny bits of film to cover them over once they're fitted? Then buy yourself a paper punch from one of the big supermarkets for around £3. With this you can punch out hundreds of perfectly round film patches. There's even a container that collects them for you so you can keep plenty of spares for future repairs.
Q
If you've ever had a flutter problem that despite perfect control runs and hinging won't stop, you might try this.
Cut off the trailing edge of the control surface so that it's square and not rounded as is usual.
It appears to work but don't ask me why. I'm sure I read somewhere that the X-15 rocket research `plane suffered with rudder flutter and this was the cure for that too. After this modification the trailing edge was a foot thick!
I see Concorde loses a chunk of rudder now and again; maybe they should try it on that too…
FMS
More links for Flying Model Simulator stuff:
http://www.rc-sim.de/
for aeroplanes, helicopters and sceneries. Hope you can read German!
Also visit:
for leads to connect your transmitter to your computer.
Or contact:
Another source of leads is:
If you're really into it and want to modify the .par files for increasing control throws etc take a look at:
There are also lots of aircraft, FAQ's and a manual in English. The best FMS site I've come across.
November Meeting
The November 5th club meeting will take place at the St. Andrews Rugby Club, Ash Lawn Road, Rugby, as usual.
Our speaker will be Graham Clarke, late of Model Craft model shop in Coventry.
Graham will give a talk on pylon racing past and present and will have pylon racers old a new on display. He's been involved in pylon for many years and has produced many successful designs and even kitted them. An associate of Graham will also display a gas turbine jet model. It should be an excellent evening.
Up and Coming
For the December 3rd meeting we have Tony Hooper as our speaker who will bring his 1/3 scale Avro Tutor for our inspection. Tony is also a full size aviator and apparently owns three aircraft.
No meeting in January
February 4th is the Concours d'Elegance with a special class for ARTF models, and prizes for the winners.
Q
After the numerous complaints that were received about the lack of speakers it seems ironic that we still can't get more members to attend club meetings.
Thanks to the efforts of Charles Aitkenhead we are getting good, interesting speakers, so please rally round and attend if at all possible. Thanks.
Quote:
In our dreams we are able to fly . . . and that is a remembering of how we were meant to be.
- Madeleine L'Engle, 'Walking on Water: Reflections on Faith and Art.' G :-)
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