Page 21 - March 2015 Volume 9, Number 3

below zero. I have been told that the actual starter tests that Beech conducted aimed for the worst possible set of extenuating circumstances, hot OATs and higher density altitudes. Furthermore, they did not actually start the engine but rather merely motored it with the starter while monitoring Starter/ Generator temperatures.
More than once I have been asked about the typically- sluggish engine starting acceleration experienced on cold days, and the question involves the necessary exceedance of a starter time limit. Namely, starting the stopwatch when the starter switch was activated and stopping the timer when the starter switch was turned off at Low Idle (or above) speed, led to the realization that more than 40 seconds had elapsed. Uh-oh!
Don’t lose any sleep over this one. You see, once the exhaust gases start to flow, the workload of the starter is decreasing in synchronization with the workload of the exhaust gases increasing. At some point – usually in the mid-40 percent N1 range – the engine becomes self-sustaining due to its own gas flow. The starter is no longer expending power at all, but merely going along for the ride. The exact point at which the starter’s heat generation becomes so small as to be immaterial is impossible to locate due to the variety of conditions that may be experienced on a particular start, but it is my strong belief that all concerns about starter time limits are rendered null and void after we see N1 leave its stabilized starter-only speed and continue its acceleration, now being aided by exhaust flow.
MARCH 2015
I have also heard worries along this line: “My mechanic is not being careful enough about the starter time limits. I’ve seen him start the engine, run it up to make a check, shut it down, make an adjustment, and then do the whole thing again and again. I know he’s not letting the 30-minute cooling time go by, even after the third or fourth start!”
Again, no worries. With the engine actually running, now the starter has been turned off and the generator has been switched on. Yes, the generator also develops heat – the more so as load increases – but not as much as the starter. More significantly, now we have enough compressor speed that the cooling fan is doing good work in helping dissipate the thermal energy. If you’re still worried, just ask the mechanic – after making his engine adjustment and before reclosing the cowling – to simply place his hand on the Starter/Generator to gauge its temperature. If he comes back with blisters on his palm – which he won’t! – then have him wait a little longer to let that sucker cool.
A situation in which starter time limits can indeed be exceeded due to maintenance procedures is while doing motoring compressor or turbine washes and/or rinses. Fuel is never introduced so all rotational energy is provided by the starter. A competent mechanic will know this already, but you may want to remind a new helper that he cannot run the starter too long, nor wait too short of a time between uses, when doing this important task.
Finally, what about us, the pilots? When is it most probable
KING AIR MAGAZINE • 19