Firebirds Model Club News

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!

I have had this model for over a year but have only just got around to flying the maiden. A combination of last year’s incessant bad weather, electronic glitches and my own nervousness following one or two ‘eventful’ maidens on other models had been putting me off. As it turned out, the maiden was a complete non-event after a few clicks of trim she was flying beautifully and instantly became my new favourite plane.

The model itself is an ARTF produced by Flight-Model and sold by Staufenbeil in Germany, who made my decision to purchase easy by offering free shipping to the UK. The airframe components are nicely constructed in a traditional combination of lite ply, balsa and Oracover film. The design is intended for electric power only and has it been constructed correspondingly light with a wing loading of around 21 oz per sq ft.

The basic particulars are:
Wingspan: 222cm (87 inches)
Wing area: 70dm2 (7.5 sq ft)
Length: 143cm (56 inches)
Flying weight: 4.5kg (159 oz)

The build was straight forward, the only real complication being finding space in the house big enough to assemble it! My usual building room is only 6 inches wider than the model’s wingspan meaning that if was impossible to get the wings on over the wing tube so final stages of the build were done in the spare bedroom.

Propulsion is provided by a 6s LiPo and an Eflite Power 60 turning a 16×8 prop, giving around 5kg of thrust and 1000 watts of power at full throttle. I fitted high torque digital metal gear full size servos (TowerPro). Receiver power comes from the ESC’s in built BEC (Castle Creations 100 Amp). To provide some redundancy to the receiver power, I have fitted a Scorpion Backup Guard. This is a neat little device that monitors the receiver voltage and incorporates it’s own battery which will kick in in the event of failure of the main supply, hopefully preventing any chance of losing control.

The model’s flying characteristics are very docile making this a relaxing and enjoyable model to fly. The light wing loading and ample power combine to make the take off easy, full throttle will see the model airborne after a few feet so throttle moderation is required for a more scale-like take off!

As is typical of these high wing types, rudder is needed in the turns to stop the tail from dropping. This could be mixed in on the radio but I prefer to add rudder manually. The relatively large control surfaces mean there is plenty of authority and mild aerobatics are certainly within the model’s capabilities. Flight times of over 15 minutes are possible on a 5000mAh battery so there is plenty of time in the air to practice these manoeuvres, or just stooge around doing nice scale like passes. Landings are again helped by the low wing loading and the model can be slowed right up for a gentle touch down.

The Taylorcraft is a lovely looking plane, the lines of which are captured well by this model. The larger size of the model certainly gives it presence both on the ground and in the air. Electric models of this size are still relatively uncommon and I have received a few surprised comments from people expecting to find one of those noisy IC engines under the cowl!

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!

VQ do a range of 60″ ish span warbirds that retail for about £100 each. The fit, finish and overall quality is reasonable but not great, par for the coarse given the price I guess. Build was straightforward. Scale wise it is very much a stand-off plane, in fact, stand-way-off. It’s at its best in the air.

I fitted standard Futaba 3003 servos and set the throws indicated by the manual. This gives a nice slow roll and smooth manoeuvres. She’s had plenty of hard landings and luckily for me, the airframe has proven to be quite tough. I have flown this most of the good weekends over the 3½ years that I owned it and I can tell you that it is an excellent flier. I have also flown the ME 109 from the same VQ range, which is also a great flier. The FW 190 comes in at 3Kg. I seem to remember the ME109 was about 2.7Kg on similar wing area.

The pilot figure is a bit special, having been expertly painted by Firebirds own artist John H. Who really is an expert in this field having painted many battalions of war game figures. John gave a club talk on this subject a while ago and many useful tips were given. John painted this figure and donated it for the club’s Christmas raffle, which I was lucky enough to win.

I decided to fit a used OS 70-FS, purchased from the HMFA Great Southern Auction (I think it was £70). Before I fitted the motor, it was bench run (down at the club) and I had quite a problem with fuel feed and breather pipes. Lots of people helped me out (Dave, Roger & Russell among others) and we eventually blanked off the pipe that ran from the crank case to the exhaust. This cured all running problems so she was fitted to the FW190 and it has run nicely ever since. The 70 sized four stroke is an ideal match for this plane giving plenty of power.

During one flight at Beaulieu the fuel tank bung fell out, partially soaking the tank bay area with fuel. Upon inspection, the bung opening was so rough that the bung did not fit properly. This was simply fixed with an aftermarket tank.

When I bought the plane, I also bought the optional VQ retracts to go with it. Mechanically, given the price, these worked very well. The only problem being that the wheels were a little too far aft of the wing LE and the plane kept nosing over (on take-off and landing). A lot of landings required that the U/C wire be straightened slightly to avoid binding on the next flight.

After a few months, I bit the bullet and decided to swap the VQ mechanical retracts for some HobbyKing (£7) servoless retracts plus the Oleos from HK too. They don’t just drop in, I had to do a bit of butchery on the mounting to make them fit. I also took the opportunity to mount them with the leg angled forward to stop the annoying nose-overs on landing.

Having now had quite a few landings on these, I can vouch for them as being a good cheap U/C on a plane this size. I have so far collapsed two of them by turning too sharply (at speed) on landing. The sideways force on the leg being pushed inwards breaks something (plastic gears I guess) and then you need a new one. The Oleos are sprung with no damping, so some landings look like Zebadee is in control.

Summary
Pros:
• An excellent flyer for not a lot of money that has weathered well after a lot of use and abuse.
• Solidly built but not overly heavy. The fully sheeted fuselage has withstood some very heavy landings including at least one belly landing.
Cons:
• VQ seem to use an unusual covering material (vinyl I think) that pulls apart the seams in the hot sun. This slackens the covering and you then cannot shrink it tight again
• Some of the hardware was a bit suspect e.g. the fuel tank bung that fell out.
• No spares available – e.g. My broken spinner cannot be replaced.