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| Issue 37 (July 2009) |
Words: Jim Innes |
The joy of flying is certainly one of the main reasons to be in this hobby. Getting that heli built and up in the air is an awesome experience. Many of us who have been flying for a while know far too well about the "almost out of fuel" phenomenon. The joy of flight is sometimes so great that we forget that our models run on finite amounts of fuel or electrons. Knowing how long your heli can fly with the fuel or batteries you have is simple to calculate and can be a lifesaver for your model.
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TIMERS, TIMERS, TIMERS
One of the first things a new heli guy with an electric model needs to learn is how to set up the flight timer in their radio. This is different for each brand of radio but is easy to find and setup. On a JR or Spektrum radio, you simply go to the Timers menu and enable the timer. You can then choose if you want a stopwatch timer or a countdown. In our case you want a countdown function.
Sometimes a timer must be turned on and off via a switch on the radio. On some models you can program the timer to turn on and off with the throttle stick or other radio function. The important thing is that you know how to set up your timer and then use it every flight. If you have a radio without a timer, you can buy a cheap wristwatch that has timer functionality.
BASIC FLIGHT TIME CALCULATION
The process you follow for calculating your flight time depends on whether you are flying a nitro or electric heli. Since the methods are a bit different we will discuss them separately.
NITRO HELICOPTERS
Your first reaction to the idea of having a timer for a nitro bird is probably "Why would I?" There are actually a few good reasons to run a timer on a nitro bird. For one , in this day and age many pilots have a mix of electric and nitro birds in their fleet. Since their electric birds need timers, it makes sense to use a timer for all their helis so that they get into the practice of using it every flight. Second, I know many pilots that have had to end a flight with an emergency auto because they lost track of time and suddenly found themselves with an out-of-fuel helicopter. And third, there are helicopters that have the fuel tank in a hard to see part of the helicopter. A scale model is a good example of this issue.
Nitro helis are the easier of the two to figure out flight times. Just fly until you run out of fuel, make a dramatic save, and check the elapsed time. All kidding aside, before you begin figuring out how long your heli can fly on a tank of fuel you need to break the motor in and get it properly tuned. Once the heli is flying to your liking, you can simply fly your regular routine while running the stopwatch timer on your radio. When the heli is about out of fuel, land and check the time. Set your countdown timer to a time a little below what the stopwatch recorded (giving a small safety margin) and you are good to go. If you make setup or head speed changes later on you may need to record your flight time again.
ELECTRIC HELICOPTERS
The common recommendation with LiPo batteries is to run 80% of the capacity or less out of them during each flight. This means that if you have a 5000 mAh battery, you would want to take out a max of 4000 mAh (80% of 5000) during a flight. This is why it's important that you use a charger that displays the capacity put into a battery during a charge. It makes it easy to see how much juice is being used during each flight. If you are using an on-board wattmeter you can check to see how much capacity was drawn from the pack during a flight immediately after you land.
It is crucial to use a timer with electric models in order to take care of the battery packs and avoid a possible LiPo failure. Always keep the above mentioned 80% rule in mind. It is recommended that you fly 5 or so flights to break in a new battery pack, keeping the flight time to 3 minutes or less. After these break in flights are done, set your timer to 3 minutes and fly your standard routine.  
Charge the battery and see what was taken out of it during your 3-minute flight. You can divide the mAh that was put back into the pack by 3 to get an estimate on how much energy your heli uses per minute of flight. Adjust your timer for the next flight accordingly and fly again. Ideally, you want your timer set so that you are taking almost exactly 80% of the pack capacity without going over. Figuring out your flight time is as simple as taking the 80% capacity figure from your pack and dividing it by the mAh per minute we found above. What you end up with is the approximate amount of minutes you should be flying that heli and battery combo. Just as on a nitro bird, any change in setup or head speed later on requires that you adjust your flight time accordingly. 
What Kind Of Flight Time To Expect From Your Heli
One of the details often omitted from a manufacturer's brochure is the average flight time a customer should expect with a specific heli. One reason for this is because there are so many flying styles and setups that each model can be setup for crazy short flights or long, docile ones. What type of electronics you run, how fast the head is spinning, and how your bird is set up can have a drastic effect on your specific flight duration. With that being said, I have found that there is a pretty reliable average for most heli types:
MOST ELECTRIC MODELS: You can expect most electric models running current generation LiPo batteries to get anywhere between 3.5 and 8 minutes per flight. Four to five minutes seems to be the norm on an electric heli.
NITRO BIRDS: Most nitro helis are designed with a fuel tank big enough to get at least 8 minute of flight time. Some of the models with bigger tanks and efficient engines running moderate head speeds can get upwards of 15 minutes a flight. I have noticed that 10 minutes seems to be the average for a nitro bird.
CONCLUSION
Using a flight timer can not only save you from having to save a suddenly unpowered helicopter, but it will also help you keep your batteries in tip-top shape. I have seen new batteries that were over-discharged puff up and become useless within a handful of flights. Well-maintained battery packs can easily deliver 200+ flights during their lifespan. Take good care of your heli by ensuring that there is always fuel left in the tank and electrons to spare in the batteries by keeping track of how long it is in the air during each flight. Remember, it is easier to land and refuel or strap in a new pack then it is to pick up a crash scene or dispose of a beaten-up battery. Have fun and see ya at the field!
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