Firebirds Model Club News

Thank you to Geoff our safety officer for the following safety notices.

Just a couple of reminders this month.

1) FPV, Quads and aerial photography: Firstly, and most importantly, if you fly FPV it is MANDATORY that you enlist the help of another to act as watchman. Apart from being a legal requirement it makes good sense.

There are no specific club rules about where to fly quads, but please bear in mind a) that something small buzzing around relatively close in can be very distracting to other pilots and b) If others are in the air, hovering is not allowed over the strip unless all other pilots are ok about it. Ask first. If you wish to hover in order to get footage of models flying please do it at some distance and well away from the take-off, landing and flightpath of the other models. Bear in mind too that there are national regulations in place in respect or aerial photography. Please make sure you are aware of them. (I’m sure John Hoddinott will be able to point you in the right direction if you ask him nicely). There is some fantastic footage around taken from these machines and they are great fun, so we really don’t want to discourage or restrict their use unless absolutely necessary. Just be sensible, and try not to get in the way of fixed wing flyers.

2) The second reminder is that whatever you put in the air, it is your responsibility to ensure that it is airworthy. This is particularly pertinent with the ready built models that most of us fly nowadays. First thing I always check is the engine mount and wing fixing plates. Do they look up to the job? A bit of re-enforcing with epoxy or fibre glass is often appropriate. While we are at it, what about the servo mounts? Are these properly fixed? In 50 flights time the fuselage around the engine and in the tank bay will often become fuel soaked, so give it all a coat of proofer before you start assembly. How about the undercarriage mounting? It is much easier (and lighter!) to add some subtle re-enforcing now, before it breaks! If the control surfaces are already hinged, give them a good tug, and re-glue the hinges if necessary. If the canopy or cowl/battery hatch is removable, are you happy that the method of retaining them is ok? Again, much easier to do something about it now. Lastly, have a good look at the control horns, clevises and push rods; if in any doubt, change them. Things are a lot better now, but it has been known for Chinese manufacturers to alter the original plastic specification if they can find something cheaper!

That’s about it. If you take care at the building stage, the model will last a lot longer, be safer AND stay in one piece. Happy Flying!

Many thanks to Geoff our resident safety officer for supplying the following article.
Well finally the good weather seems to be here for a bit, and with it hopefully somewhat more of us at the strip, so this month just a few reminders.

1 FAILSAFES Please remember that setting the failsafe on your radio (if it has this facility & most now do) is not only advisable, it is a legal requirement. If you switch off your transmitter the minimum requirement is that the throttle goes to low. Check this at the beginning of each session. Not having this facility enabled can affect your insurance in the event of an accident. The situation with helis is a bit vague – check the BMFA website for guidance.

2 BATTERIES I find that after a year, the performance of NiMH cells drops off considerably. The first sign is that they appear to be charged quicker than normal (If you are using a fast charger). A lot of chargers are capable of cycling the battery and then giving a readout of capacity. If you can do this you will probably be shocked at how bad some batteries that are a few years old have become! Don’t risk it – change the flight pack!

Most electric set-ups include a BEC (Battery Eliminator Circuit) so the Receiver and Servos all work off the LiPo powering the motor. If that fails completely you are really stuffed as you won’t have any control at all! Anything larger than a foamy park flyer really ought to have a separate flight pack for the Receiver and servos so if the worst ever happened you’ll still be able to land under control. Fitting a separate battery means you need to cut the red wire from the speed controller; if you are not sure about this, ask someone!

3 NO FLY AREAS I recently had a rather embarrassing crash due to dis-orientation. In mitigation all I can say is that it was an autogyro, so a bit of a strange shape, but nevertheless I really should have been more careful! Now what surprised me was that I thought it came down relatively close in the next field over by the Scouts, but I was a bit horrified to find it no more than 25 metres from the boundary, and I guess 100 metres from their actual field! The moral is, distances can be deceptive in the air! Keep well clear of the Scouts’ field.

When running an IC engine or electric motor much above tick-over we know it’s prudent to stand behind the prop in case something ‘lets go’. If you’re anything like me, then you will observe this simple precaution most of the time but just occasionally you’ll stay in front of your own or someone else’s model while you/they rev the nuts off it. Should it all go wrong, then the engine might not be the only thing to lose its nuts.

The snag is that props don’t come off that often, which is really a good thing I suppose, but it can make you a bit blasé about taking precautions. I have recently had two incidents where the prop, complete with spinner, came off and hurtled away at great speed from the rest of the model.

On the first occasion, I was testing a Saito 115 four stroke engine and had already had the prop on and off a couple of times. I guess I had not done the locking nut up tightly enough and the whole lot flew off at near full power. It flew forward in a nice straight line and struck the ground about 6 metres away. It then careened into a trellis and a fence, coming to rest nine metres away (a nicely rounded 3 fence panels).

On the second occasion (Easter Sunday), a failed E-clip meant that the rotor housing and shaft of the electric motor I was testing, joined forces with the prop and spinner for their brief and wild excursion. The rear wheel of Matt’s Landover put an end to their travel ambitions. I guess they travelled about 4-6 metres.
Both motors were swinging 15” props, which are certainly capable of inflicting deep and nasty cuts.

Another reason not to stay in front is that there is also a possibility that the whole aircraft might escape its restraint. Of course I’m just reinforcing what we have all been taught, understand and practice pretty well really. I just think it’s good to have the occasional refresher.

PS: I replaced the E-clip and made a collet that screwed into a flat I ground into the shaft. That should hold the bleeder on.

Once again we have a LiPo battery charging horror story that did result in a fire and very nearly a significant one.

It all started when the blue and silver charger near the centre of the picture was being used to charge the Turnigy Orange TX directly in front of the charger. OK, I hear you saying “what Orange TX?” Well, it’s that rectangular mess that is actually just the PCB and a few miscellaneous components that weren’t completely annihilated by the fire.

Further towards the front of the bench and to the right we have a few more lipos that were either pre, post or actually on charge. They were also destroyed and of course added fuel/heat to the fire.

The circular item near the front left is the remains of a Lander EDF unit. Only the aluminium part remains, all the plastic bits melted/burned away.

Near the top right a blue upright aerosol type can is visible. This is a can of gas for a blow torch. Shelving units immediately to the left (not in the above picture) also house a can of blow torch gas. Add to that a garage full of foam models, various glues, solvents and paint products and it’s a wonder he didn’t end up with a Fukushima style accident.

Fortunately, the fire did burn itself out. The MDF worktop seems to have inhibited rather than added fuel to the fire. There must have been some serious heat so I was impressed that it didn’t burn.
Directly above the charging Orange TX was a brand new Spektrum DX 9. This suffered some heat damage (partially melted handle) and a fair amount of smoke damage but is still quite usable.

Pete is unsure of exactly what transpired but he’s guessing that the Orange TX batteries may have been very low before they went on charge (having been using them quite a bit that day). It was an old battery and it is possible that the TX was left switched on before charging commenced.

As with my own fire/explosion experience a few months back, this event reinforces the fact that LiPos really don’t like being discharged below a certain threshold and get angry if they are.

The insurance company inspected the damage and did pay a reasonable sum to compensate for the damage to the garage and the model gear within.

Builders were organised and work commenced on a new garage interior. As it happens the builders didn’t seem to be qualified to deal with anything more complex than a hammer. They actually managed to add to the damage by smashing a glass door panel. After some bungled plasterboard work, Pete decided to do the repairs himself. The insurance ended up paying a little extra for that.

All the garage work has now been completed and includes a new, more fire resistant charging area. The opportunity for a Spring Clean wasn’t missed too, so a lot of rubbish went off to the landfill.

Pete has added new Orange and Spektrum DX8 TXs to his fleet.

Pete said that his main lesson learned was to not leave LiPos unattended during charge. We’ve all done it but it’s a bad habit that the manufacturers themselves advise against.

Many thanks to Geoff our Safety officer for the following article.

A little story from about 35 years ago this month (I know, I know, I’m slowly turning into a sad old git).

In the early days of electric flight I was lucky (if that’s the word) to assist in some small way with evaluating the very first commercial electric r/c model to come onto the market. Our local model shop in Portsmouth was run by Ray and Audrey Brown. Now Ray was a brilliant and highly skilled modeller; some of you may remember his highly successful “Chevron”, kitted by Model Flight Accessories. Through his connection with MFA he was given a pre-production kit to check out. It was a cute little high wing model called the Hummingbird and amazingly it was electric! It featured a Mabuchi 540 brushed motor, 8 cell NiCad pack, and a servo operated on/off switch for motor control!

It was hopelessly under powered, and Ray managed a couple of flights just about staggering around the patch. A couple of days later in the shop, Ray, now a bit disillusioned, handed the whole thing over to me to see if I could do anything with it as MFA were hoping for some feedback. A quick check of the battery pack showed that one cell was a bit down so we replaced it ready to try again.

It’s interesting to reflect at this point that in these early days of commercial electric flight the real danger was perceived to be the unvented NiCad cells. If the battery heated up too much, either through discharging too far (no automatic cut out in those days) or by overcharging, there was nowhere for the expanding electrolyte to go, so the batteries exploded! I witnessed this a few years later, and it happened after the flight with the model just sitting on the ground doing nothing. Very impressive, and very little left! Fortunately it was about 20 ft away from anyone.

Anyway, back to the Hummingbird. With a fully charged pack and ready to leave for the field I decided a quick check was in order. Now for some reason I took it into my head that the best place to do this was on the bed. . . . . . . .

Now a nice soft bed is not really the best place to stand a transmitter up on. Before I had a chance to grab it, it had toppled forward, ever so slightly moving the throttle stick, but just enough to operate the motor ON switch in the model.

It was at this point that the really big difference between IC and electric became violently obvious! Ever wondered what they put in all the little pockets of a Duvet? (I’m sure we used to call them “continental quilts”?) I found out very quickly because the room was soon full of it!

Fortunately, and I’m not sure how, I didn’t get injured grabbing anything and managed to stop the motor, but the damage to the bed was extensive. Every time I power up an electric model I remember this little incident, and so far it has stopped me doing anything stupid!

So what are the lessons? According to the latest BMFA figures an increasing number of personal injuries are now related to electric power systems. I’m convinced that none of these would happen if a few simple rules are adhered to.

Firstly, at home on the bench.

1. Modern speed controllers are designed to be more or less idiot proof, but they can go wrong! If you are setting up a model NEVER do it with the prop fitted. The most common scenario is to have the throttle reversed. If you’ve done this, even if you realise what has happened it is very difficult to convince yourself that the throttle needs to go the wrong way to stop the motor! No prop = no damage. Don’t run the motor with the prop fitted in the workshop unless you have plenty of clear uncluttered space. Better still, take it out in the garden.

Secondly, at the field.

1. Even if the transmitter throttle is in the wrong position modern speed controllers should not start the motor until the throttle has been cycled to arm the system, but apparently this can go wrong, so ALWAYS have it in mind that the prop might start spinning the instant you connect the battery. Hold the model securely and get behind it when you connect the battery. If the model has retracts make sure the transmitter switch is in the correct position!

2. The design of some battery compartments is such that the battery has to be fitted from the front, through the propeller arc, often with the model on its back. By far the safest way here is to fit a shorting plug such that the final connection is only made with the plane upright, but if this is not practical it’s often possible to wedge the prop firmly on the ground; If it does try to start the worst will probably be a burned out speed controller, although arguably it will already be damaged to allow this to have happened, so you’ll not have lost anything!

3. Once the model is ready for flight it is potentially capable of injury. Assume it could start on its own and treat it accordingly. If you use a transmitter tray be particularly careful when putting the straps over your head – it is SO easy to knock the throttle stick up. . . .

4. After flight, the FIRST thing to do when the model is clear of the strip is to disconnect the battery. NEVER leave a “live” model in the pits unattended.
Having hopefully taken all that in, you might be wondering what became of the little Hummingbird? Well, it survived with nothing more than a broken prop and although by today’s standards its flight envelope might best be described as “barely adequate” it did fly quite well and went into full production.

When the battery pack failed again after about thirty flights I gave up and fitted an Enya .09 and it was eventually retired fuel soaked about five years later. I can’t help thinking that if they had sold it as IC from the start it might have done better, but that would have been boring!

Take a look at this melted Nimh battery from a Spektrum DX8 transmitter.

This one belongs to Terry. Paul A. is also familiar with this situation because he had one melt too. In fact his battery looked worse than this.

Having looked around on the internet, it’s a common problem.
The cause? Overcharging. It turns out that the DX8 charging circuitry has no means to shut off the charge current as the battery reaches capacity and starts to heat up.
Overheating is not normally a problem at the low charge currents (typically about 100-200mA) used by the little wall plug chargers. The reason being that the battery can easily dissipate the heat as it is charging.
That is until you factor in the shrink wrapped battery pack, surrounded by foam packing that is inside a plastic box. Then heat dissipation becomes much more difficult.

The foam packing is in there because Spektrum also sell a larger battery for this TX, which is a 4000mah LiPo not a 2000mah Nimh. When installing the LiPo, the foam has to be discarded to make way for this larger battery. The foam simply stops the smaller pack from rattling around in the TX.

So basically, the message is, if you are doing a long charge on one of these, watch out for this problem. Check the voltage of the pack (say by turning on the TX every hour or so) to see when it’s nearing completion. I would be extremely wary of leaving this on charge overnight in the house while you’re sleeping.

At £30-£35 the Spektrum branded LiPo replacement battery is expensive.
(example: http://www.sussex-model-centre.co.uk/shopexd.asp?id=33559)

An alternative to the Spektrum branded version of the LiPo is HobbyKing’s one, at just about £12. Here’s the link:
http://www.hobbyking.com/hobbyking/store/__37361__Turnigy_4000mAh_Spektrum_DX8_Intelligent_Transmitter_Pack_UK_Warehouse_.html?strSearch=dx8

I’ve been using the Spektrum LiPo for over a year now. I highly recommend it because it only needs charging every two or three months and doesn’t seem to suffer from the heating problem. The irony here is that LiPos are normally the scary batteries. Nimh batteries have always seemed tame.

I have a home-grown safety incident to report. Just as I was getting used to handling lithium polymer batteries, I became complacent and one bit back.

The battery in question was a 2 cell (7.4v) 4000mah LiPo. One of a pair that I use in my Twinstar.

I charged these both up on the 21st June so they would be ready to use on the following weekend. I charged them at a fairly low current so they took ages, I was in no rush.

When the charger beeped to let me know that the second one was charged, I thought I’d finish watching the telly before unplugging it. Consequently I forgot and left the thing plugged into the charger for the next 24 hours.

When I noticed this the following day, I thought “damn! I bet that has discharged the pack by some percentage”. Without checking the pack, I set the charge program off again to top the pack up.

The only mistake I didn’t make was leaving the charge process unattended. After about 30 minutes of charging, I heard a small crack followed by a fizz sound. Guessing that this could be the battery (I also thought it might be something I had cooking), I had a close look and could see that the pack had swelled up.

I immediately unplugged it and took it outside (carrying it be the lead). I then prepared a bowl of salt water to provide an environment to safely discharge the pack. I dropped the pack in and went back into the house.

About a minute later there was a very bright flash and a moderately loud bang. I ran outside to find that the battery had clearly exploded and jumped out of the bowl of water.

Some kind of black deposit mixed with water was sprayed everywhere. The battery continued to burn for about 5-10 minutes.

My guess now is that the battery must have completely discharged when left plugged in for 24 hours. This would have left the pack in a state where it couldn’t be recovered. I guess that the combination of the battery’s condition and whatever the charger tried to do to inject a charge, resulted in this catastrophic failure. I will be a lot more cautious the next time I suspect that a pack might be discharged by mistake.

The picture above was taken less than a minute after the explosion and about two minutes after it was inside my house. You’ll notice the black charred deposit on the stones either side of the pack. This was where the pack flared intensely for a few seconds after it landed on the stones. The explosion was when the pack was inside the bowl. Imagine that flaring on the carpet.

I count myself fortunate that it didn’t explode in my house or while I was carrying it outside. I hope that you can also learn from my experience and exercise appropriate caution with these packs.

Wind? What Wind!
I suppose we have to put it down to Global Warming, but it strikes me that more often than not these days the wind is blowing directly across the strip. Whatever happened to those prevailing south westerly winds we used to get?

This is a bit of a bummer, but it’s all good for left thumb practice! So what’s the secret? Well, of course, there isn’t one – just a bit of thought and some common sense.

Take off
If you are flying a relatively small and lightly loaded model the safest and best way is to take off across the strip directly into wind, but what if the wind is directly onto your back? A bit of a compromise will be necessary here if we are to avoid flying close to other pilots after take-off. There are two things we can do to help. One is to make sure when flying we are all standing relatively close together at the “pits” end of the pilots strip. This will leave as much clear space as possible for take-off. The other thing, if you are the pilot, is to be very aware of what is likely to happen during and immediately after take-off. On the ground, and certainly until flying speed is reached the model will want to weathercock into the wind – a particular problem with a high wing tail dragger. Will this alter the course towards other pilots? If so you might like to think about where the take-off run should start. If the model has any dihedral and takes off even slightly out of wind, it will be particularly prone to being rolled as the wind gets under the wing, so be prepared!

With a “normal” weight model with no dihedral i.e. a Wot 4 or larger, you can get to grips with a crosswind properly, and it’s great fun trying to perfect the technique. Be aware though, that during the run it will still want to weathercock and may bring the take-off path directly towards you and the other pilots. Think about it before you start, and definitely don’t just whack the throttle open – take it gently! Start the run slowly. If it’s a trike undercart there should be no problem, but with a tail dragger you will need a fair bit of “up” to keep the tail wheel on the ground so you can steer. As the speed builds up, gradually open the throttle and let the tail rise. You’ll normally be used to having to add a bit of right rudder at this point, but in a cross wind it might have to be left. Think this through before you start. Once off the ground, let the speed build up before you climb away. At this point you’ve got two choices: You can let the model climb away keeping it on track with the ailerons and letting it appear to be crabbing, or you can hold a bit of rudder on (stick pushed in the “down wind” direction), correcting with a bit of aileron. The first method is normal of course, but for an added challenge try the second and see if you can make the effect of the wind seem to disappear! – A bit silly maybe, but quite impressive.

Landing
This is a bit trickier to do neatly. If the wind is coming from behind you, there is not only the danger of drifting into the far fence, but also of swinging after touchdown. The last thing you need is to land short and then career towards the flight line, so plan to land half way along the strip. This way if it swings after landing there will hopefully be no one in the way!

If the wind is in your face, the plane will want to drift over your head. Nip this in the bud and don’t be afraid to go round again. If the plane gets on the wrong side of you things will go pear shaped very quickly! Again, aim to land a bit further down the strip than normal.

As with take-off, there are two ways of approaching things. Whichever way you choose to do it, the aim is to land with no sideways drift as the wheels touch. This is vital with a large model where it is possible to do serious damage to the undercarriage if you get it wrong. (Yes, I’ve done it!)

The first (and normal passenger aircraft way) is to approach without any rudder, just steering the right course, and letting the model come towards you in an apparent side slip. (It’s not really side-slipping, but this is what it will look like from the ground). Just before touchdown straighten the model with the rudder, correcting with ailerons as necessary. Don’t over flare and keep the speed a little higher than normal. If you get it right the wheels will not scuff and you’ll have cracked it! The problem with this method is that at the last minute you really have a lot to think about all at the same time, but if you get it right it can be very satisfying.

I tend to cheat, and use method two, as it’s not quite so critical at the last moment. As you approach, add a bit of rudder away from the wind direction. Hold this on all the way down and fly the model on ailerons in the normal way. You’ll need to correct the track with a bit of aileron in the opposite direction to the rudder – ie the controls crossed. (yes, it is actually side-slipping now, but this time it won’t appear to be!) Again, keep the speed a little higher than normal. If you get it right the wheel nearest to the wind direction should touch down first.

So there we have it. Next time there is a nasty cross wind, don’t leave the model in the car, treat it as an opportunity to practise something a bit different!

Ever had that heart stopping moment when you take your eyes off your model for a quick glance at something else, only to find that (for what seems like an eternity) you’ve lost it? I bet you have!

The reason is that when looking up into a clear sky our eyes tend naturally to focus at infinity until there is something to see – ask any full size pilot. It may only be for a second or so, but if the model is travelling at say, 50 mph it certainly ain’t gonna be where you last saw it!

Many newer radios now offer telemetry with the information being sent back to the transmitter display, (I’m sure you can see where this is leading!) so the temptation is there to take you eye off the model to look at the screen. I think the golden rule has to be “don’t be tempted under any circumstances!” Either have someone else with you to read it, or better still, if you are lucky enough to have a built in audio feature, use it via an earphone. (Not the speaker please; we don’t want the flight-line full of chattering transmitters do we?)

This, of course, applies equally to FPV. There are proper guidelines set out in your BMFA handbook for operating this type of model, stipulating that there must be a “watcher” on a buddy box at all times to take over control if necessary.

The somewhat grey area here is the small foamy with a built in camera, and screen integrated into the transmitter. As far as I am aware a buddy box is not an option with these, so if you have one of them, at least make sure you have someone with you when you fly!