Skip's Corner

Short Duty Cycles

The Question –

Do short duty cycles have an effect on battery longevity?

The Answer -

I will attempt to explain why ANY aircraft battery is NOT designed to perform satisfactorily with short durations of being recharged between the high rate of current of discharge (capacity) required to make a successful turbine engine starts.

Think of the storage battery as being like a bucket of water. With an open top that is full (charged capacity) that you can dump or spill as much as you want rapidly (loss of capacity) BUT you only have a limited volume of water capacity to refill the empty bucket because of your resupplying water filling pipe or hose, so you cannot replenish the capacity lost that you had quickly dumped for some reasonable time before the bucket is full (capacity) again.

Storage batteries are something like this, they can release high rates of power to crank a turbine engine from its static or stopped condition to the starter/generator that is also not moving and because it takes hundreds of amperes to overcome this stalled condition to get all the rotating components moving (at least ten percent of the capacity is used to motor the engine) to draw the cool air into the compressor section BEFORE the compressed air is introduced to the combustion section where fuel is ignited and the fire and super-heated air impinges on the turbine to provide enough energy to have the turbine drive the compressor so the electric starter motor than can be shut off.

Usually aircraft turbine starting batteries have enough stored energy (capacity) to make three successful starts before their capacity is drained to the point of causing a hot or aborted start

A storage battery in a poor state of charge (SOC) or health (worn out below the minimum airworthiness requirement) will and do cause hot starts the ruin the turbine engine, IF the battery DOES NOT HAVE ENOUGH CAPACITY to keep the starter motor turning the engine , driving the compressor and forcing the hot air back to drive the turbine until the turbine can drive the compressor, then the engine stalls and the hot air and flames are allowed to back-up into the aluminum compressor section causing EXPENSIVE engine overhauls or replacements

My first suggestion would be to modify your 350/355’s with the Canadian Airbus Helicopter STC to install our 28Ah P/N RG-390E in the tail boom.

Second install a spare battery, I believe Airbus Helicopters has a SB for dual batteries, If not AIRLIFT in Norway does.

Third, carry a start stick by STARTPAC .