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!
