I categorically don't use battery carts. Must be engine driven, or be AC line powered. I have very reasonable service from those, never had one fail yet, though I watch for it.

A good test for me is to not turn on my batteries, and just motor the starter ("crank" in TPE331 parlance). If the GPU alone cranks the engine well, then I got a good one and can do the real start sequence.

TPE331 owners know a lot about what makes a good GPU. They are probably harder to start than most jets. I use a lot of GPUs on the road.


Given the batteries are also enabled during a GPU start, how could the start be hotter than no GPU? If the GPU goes offline, then finish on battery you would have used otherwise (but now helped at least initially by the GPU, plus charged from it a bit).


If you just came from hours at FL410 and did a really fast turn, the battery could be quite cold. In cruise service, it isn't providing any energy or really charging, so little to no internal heat generation. The oil will be warm which will reduce the start load, though.

Mike C.

This one seems to be one that will not carry our load without the voltage dropping to 27v. (not us, stock photo)

Not in a 525 Model. Battery is in the tail aft of the baggage compartment. The outflow valves exhaust into the tail and keep it warm. That area never gets very cold.

A GPU that drops only to 27V when I engage a starter is a REALLY GOOD ONE!

27V on your start bus means 28V or more at the GPU itself, there is loss in the cables.

Mike C.

Excellent design.

Mike C.

When I turn on avionics and blowers. not the starter...

Most of the GPUs have adjustable voltage. I have seen some set as low as 26v, others higher than 28. Most aircraft systems have over voltage protection and won't allow the GPU to connect. I adjust the GPU as high as possible without going over 28v.

I can always tell how good the GPU is by watching my battery voltage during the start. Normal voltage sag goes down to 19v without a GPU. A good GPU will keep it above 23v; not so good, somewhere between 19-23. But I'm like Mike, as long as your systems are designed to keep the batteries online during the start and you have good batteries; even a bad GPU should only help your start out.

Good or bad, it's preferable to start the PC12 NGs with a GPU for a few reasons; if one is available, I won't hesitate to use it. The large PT6 takes some amps to turn.

- a GPU gives a much cooler start when doing a quick turn and you have to motor the starter to bring ITT down.
- Apex avionics take a while to boot; drawing precious power from your batteries. Also on a power cart, you can have everything loaded and pre-taxi checks done to the point of pressing the start button and you are ready to taxi.
- you can run the AC or heater to keep the cockpit comfortable.

I wish the PC12 had a small APU. I don't know much about APU technology concerning weight/cost to power output but there would be a weight swap for eliminating one of the batteries (NGs have 2) and I'd be willing to give up some useful load for one.

agree....

Not the JetGo....At least it is not accessible to the line folks.

But as you said, it can't hurt....and I can get the cockpit checks and flight planning done.

Jeff

When I used to skydive, the 'GPU' was wooden cart with a couple of truck batteries. It was only used once or twice a day.

Or if several people are flying it, then uses odd or even days to determine which is first.

Is that fairly common? I see a lot of batteries in that area.

Is that fairly common? I see a lot of batteries in that area.

Saw a Mustang parked at 2W5 today and had a chance to walk up and get a good look. Are all straight-wing citations that close to the ground? Those flap hinges can't have more than 18in clearance. Great looking little plane.

The Mustang is actually not a straight wing, it is very slightly swept back. This is of no aerodynamic consequence, but yet there it is.

The modern design is to not have the wing spar penetrate the fuselage cross section. So the wing is under the fuselage. In the Mustang, this leads to the wing being very close to the ground. The same thing was done with the 525 (CJ to CJ4) series.

The older style, 500/550/560, has the spar going through the cabin cross section. This results in a somewhat higher wing, but not overly so. It can lead to lack of dropped floor where the spar has to cross through the cabin, however. I think taking the spar out of the cabin and not disrupting the fuselage hoop stress during pressurization are the primary factors for the new style.

I kind of like the look of the older style, seems more clean to me than the wing sort of slid underneath.

Mike C.

The Mustang has a 12 degree sweep on the leading edge. It helps with cruise speed and helps buffer turbulence. Regarding wing height, landing gear length determines wing height, regardless of how the wing is mounted to the fuselage.