Engine running and blades turning between flights
 

Why do helicopters keep the engines running and blades turning while loading and unloading passengers and bags?

Is the shut down and start procedure too lengthy? Start cycles on engines?
At what time length between flights does it make sense to shut them down? Does it make a difference whether it is a turbine or reciprocal engine?

Just wondering thanks

You've essentially asked and answered your own question. "Is the shut-down and start procedure too lengthy?" Yes, sometimes. "Start cycles on engines?" Definitely, particularly on short sectors. You could also add; Lack of ground-power for re-start, this is important at altitude. Lack of technical support in case of difficulties. etc

"Does it make a difference whether it is a turbine or reciprocal engine?" I've not worked with recip-powered helicopters so can't give a definitive comment, but I would imagine it's pretty much the same. I've seen turbine-powered helicopters sit on the ground for 20 - 30 minutes with their engines running, all in a days work on some operations.

Start up and shutdown are when most of those niggly tech faults turn up. Keeping them running (like London black cabs until it was decided that running diesel engines for 18 hours a day, most of it idling, wasn’t that great for the air quality) cuts those down, most HDFM systems can do a download with rotors running for checking between flights. Also avoids the need for a turnround servicing between flights. In Abz, the main driver though is that many oil companies do not want their passengers on board during start up and/or shutdown.

I heard from a doctor that one of the South African air ambulances (J'berg EC135), was once blades turning for >24hrs continuously attending in the region of 10 patients with rotors running refuels and patient loading/unloadings. The pilot would drop the crew and patient off at A&E, unload rotors running, lift to the hems base next door, unstrap and fuel the aircraft, then hop back in and fly back to the A&E, pick up crew and off to the next patient... :}

Presumably there was a shift swap in there somewhere, why not shut down for that? I'm not sure on the details - does anyone know any more about this? Apparently Eurocopter said it was the first time they'd heard of it happening.

From the mechanical side, the start and shutdown of an engine is the most detrimental to its useful life, especially turbines. The main points are thermal and lubrication issues.
Also most turbines have a max internal temp limit prior to start so if on a short turnaround may have to wait for it to cool before start.
W1

For recip's it's not so much about cycles, but it is very much about the time factor.

Consider the garden variety R44. Even with a warm engine, you figure it's about 3 minutes from activating the starter to full rotor RPM, and on shutdown 2 minutes of cool-down (minimum, unless it's very cold out), 30 seconds of throttle closed spin down to pulling the mixture, 30 seconds before rotor brake can be applied, and call it 30 seconds getting the rotor stopped. About 3.5 minutes for shutdown total. Optimistically, one cycle is going to take about 6 minutes or a tenth of an hour. That is unsupportable for operations like rides at special events, agricultural op's, etc. Time is money! The op's around here like to see at least 6 loads an hour for rides, including loading and unloading. It's a quick trip at $30/seat. It would have to be 3 times that or more if the helicopter shut down each time, and nobody would pay it.

One other factor is winds. The 500 and I'm sure other many other aircraft are sensitive to shutdown in high winds. The main rotor can contact the tailboom as the rotors start to droop.

Some of the places we are working in the mountains doing powerline work where there is 25-40kts of wind 300+ days of year yet light winds down on the plateau where we hangar. On some of the more windy days we will takeoff at 7am work till 7pm and never shut down, usually fly for 6-8 hours and sit for 2-4 (spread out throughout the day) The wind is often the deciding factor on weather to risk shutting down on the mountain at the LZ.

Time is not a factor for us in a billing sense. We bill off of collective hobbs. So the customer doesn't get charged for time on the ground.

- Cycles is a factor (wear on the turbine and starter)
- Risk of problems on restart is a factor. But we always have a mechanic and GPU with us.
- Wind is a factor.
- Turnaround time, e.g. time to get back out there and fulfill a need is a factor. In addition to the 3 minute cool down you risk hotstart with re-starting right away after shutdown.
- Fuel burn is a factor, albeit a minor one.
- Safety is a factor, as far as we would like to shut down at least once a day and have the mechanic give the helicopter good a look-over, most days that happens, but not always. They always give it a look-over several times a day, but sometimes its still running.

With properly trained crews the difference in risk between hot fueling a fueling shut down is negligible.

We don't have passengers to load, but even if we did, I would have no problems loading small groups of trained passengers with an escort.

As for bio breaks, that what frictions are for. with the 500 at ground idle you can pull the collective up to your arm pit and rock the cyclic and it wont fly. the blades aren't going fast enough to generate lift. So its not like some aircraft that you have to worry about a breeze rolling over, e.g. the Kmax.