PT6 question

[A&PMECH]

Hi all, first post, well second after that screwed up first one.

My PT6 experience comes from working on Piaggio's, so some of the numbers I talk about might not apply to you King Air guys as I've never flown one or worked on one. However, it should all make sense.
When you start a PT6 in feather you put a lot of strain on the starter generator and can run the risk of burning it up, or draining that battery if starting without a GPU. If the engine is started in ground idle, at approximately 47% Ng the GCU will disengage the starter. If you start in feather the chances of actually reaching that 47% are pretty remote, if not impossible.
Secondly, the oil tank is integral to the accessory gearbox. With no oil traveling to the prop hub you create an unnecessary amount of high pressure build up in the accessory gearbox. That in itself, is another reason why it's not a good idea to sit around in feather for long periods of time.
Hope this helps

 

[satpak77]

Hi all, first post, well second after that screwed up first one.

My PT6 experience comes from working on Piaggio's, so some of the numbers I talk about might not apply to you King Air guys as I've never flown one or worked on one. However, it should all make sense.
When you start a PT6 in feather you put a lot of strain on the starter generator and can run the risk of burning it up, or draining that battery if starting without a GPU. If the engine is started in ground idle, at approximately 47% Ng the GCU will disengage the starter. If you start in feather the chances of actually reaching that 47% are pretty remote, if not impossible.
Secondly, the oil tank is integral to the accessory gearbox. With no oil traveling to the prop hub you create an unnecessary amount of high pressure build up in the accessory gearbox. That in itself, is another reason why it's not a good idea to sit around in feather for long periods of time.
Hope this helps

You know, I have never heard of this. Not saying its not true, but with approx 4000 hours in the B-350, and ten years of FlightSafety recurrents at Wichita, etc, I have never heard of this.

When you start the engine, it IS in feather, even if the prop control is full forward per the checklist. It will come out of feather when the engine spools up and comes online, but you are long off the starter switch (and BATT) by then.

Does that make sense? Irrespective of the actual position of the prop control in the cockpit (feather position or full forward), when you climb into a King Air (PT-6 anyway) and start it, the prop is always feathered, period.

So "starting it in feather will hurt XXXX" does not make any sense to me.

High Oil pressure in accessory gearbox? I have not heard of this.

Anyone care to chime in...

 

[rettofly]

My PT6 experience comes from working on Piaggio's, so some of the numbers I talk about might not apply to you King Air guys as I've never flown one or worked on one. However, it should all make sense.
When you start a PT6 in feather you put a lot of strain on the starter generator and can run the risk of burning it up, or draining that battery if starting without a GPU. If the engine is started in ground idle, at approximately 47% Ng the GCU will disengage the starter. If you start in feather the chances of actually reaching that 47% are pretty remote, if not impossible.
Secondly, the oil tank is integral to the accessory gearbox. With no oil traveling to the prop hub you create an unnecessary amount of high pressure build up in the accessory gearbox. That in itself, is another reason why it's not a good idea to sit around in feather for long periods of time.
Hope this helps

SOP in Piaggio is to go right through the FX detent to ground idle when starting. If you need to feather one during taxi with a tailwind to save wear and tear, that's OK, but Beta is Betta, especially on sub-zero days. Keeping them feathered while parked does add to heat buildup.

 

[A&PMECH]

On the P-180 the prop is always in feather on start up as well. However, the King Air has independent fuel control levers. In the Piaggio the fuel control unit and the prop levers are rigged as a single unit condition lever, thereyby eliminating the need for independent fuel levers. When starting a P-180, as said by rettofly, you bypass feather into ground idle. That simultaneously introduces fuel to the combustion chamber, opens the prop governor, and brings the prop to a lower pitch. Fuel scheduling between feather and ground idle is identical (meaning there is no increase or decrease in fuel flow for ground idle and feather), it would start normally in a combustion sense regardless of condition lever position. However, the GCU still wouldn't disengage the starter with the same consistency it would with a normal start. There just wouldn't be enough Ng to do it, if it did make it you would be pressing hard against the 30 second duty cycle limit on the starter. You can manually disengage the starter, but chances are you won't get the engine running to self sustaining speed and will be left with a hung start. With the prop just out there paddling away at feather you're greatly increasing the time it will take to get the engine going. You need the spool up to sustain the start the majority of the time.

Now as far as the high pressure I was mentioning. This was something told to me by a very experienced PT6 mechanic who worked 1900s before he worked P-180s. That was not something I personally have seen, but it made sense to me and that's why I mentioned it. Basically prolonged periods at feather, or starting in feather can result in spikes in oil pressure due to the large quantities of oil in the accessory gear drive that is not traveling throughout the system. However, it's not something I will see on the Piaggio because it's hard on the propellers to have them in feather for to long (excessive heat).

The topic starter asked about how it would harm the compressor section and I don't see any reason why the compressor would be affected. I can see ITT spikes due to the free turbine rotating at a lesser speeds than the power turbine, which can cause poor exhaust scavenging. I have never seen that personally though.

 

[Nolife]

Thx for the responses.

It seems that starting with props forward then feathering after start while waiting for avionics and clearance might be the way to go provided to wait time isn’t too long.

I’m looking for a way to reduce noise and stress on the parking brake while getting ready to taxi.

 

[partypilot1]

You can start a PT6 with the prop levers full forward or in feather. I personally would keep an eye on temps because of airflow over the engine and exhaust are reduced. Watch for possible heat buildup around cabin

 

[satpak77]

Thx for the responses.

It seems that starting with props forward then feathering after start while waiting for avionics and clearance might be the way to go provided to wait time isn’t too long.

I’m looking for a way to reduce noise and stress on the parking brake while getting ready to taxi.

King Air ?

 

[Nolife]

Yes King Air.

 

[satpak77]

Yes King Air.

Some ideas, which I practice, to save the 3 hour (joke but...) time on ramp to run the Beech lawyer-designed checklists (it calls for FLAPS-UP like four times.....)

This is a modified order to the Flightsafety checklist but all items are covered.

1. Get clearance and ATIS via Ground Comm. Tell clearance delivery you will be "ready for taxi in 15 minutes". Set your altimeters now.

2. Get V-speeds before pax show up. You have temp off the OAT gage or off ATIS. You should have rough idea on weight of everybody and fuel, cargo.

3. Engine Start: Start the engines, flip avionics and EFIS on, and while that is coming up, do the engine checks, governor checks, etc. Auto-Feather checks also. Knock out the pressurization checks. Some airports you can't do engine runups on the ramp, so you need to exercise your discretion on this.

4. Avionics and EFIS should be online now, knock out quick AP and Yaw damp checks. Get your VOR's, FMS done. Copilot can also do this on the taxi-out, just don't be #1 for takeoff and have your FMS bungled. I personally don't fly out on the SID/etc via FMS NAV, I use old-school VOR radials until the climb-out, and if everything looks cool, I bring the FMS NAV up. I know Generation-Y doesn't do it that way but it is how I do it. I don't fly with an Ipod either....

Anyway, some ideas for you

 

[Nolife]

Good advice. I have an approved realistic checklist but the problem is the ramp is too congested and small to do run-up items and the FMS and EFIS takes at least 5 minutes to start; goofy Chelton system.

Beech's checklist reads more like an instruction manual, takes way too long to accomplish, and it has too many redundant items. Their "Before Landing Check" takes so long that after you put the wheels down and finish reading it you're pulling up to the gate.