Turboprop Tips

[TopperHarley]

Hi !

I have recently started flying a PT6A powered machine after thousands of hours flying pistons.

I have been looking for a reference book that can fill me up with info on the finer points of operating turboprops. Any suggestions ?? (Ive tried Advanced Aircraft Systems, and Turbine pilots flight manual - neitehr really spend much time on turboprops).

Some specific questions that pop to mind are:

1. Derated Vs Flat rated - What does it really mean ?? Whats the operational difference to me ?

2. Starting problems - Hot, hung starts etc. Is batterty power the only issue ??

3. Why am I told to turn the genny on the operating engine off when starting the other ??

4. Should I be worried about autofeather failing in an engine failure after TKOF scenario ?

5. The acft is certified under SFAR41 - what do I need to know about this ?? It is considered a small aircraft in my country (under 5700kg) - DOes SFAR41 have any significance ?

6. Best ways to detect water in the fuel ?? ******ed if I can tell if theres water after a fuel drain. Is water as big a problem in JET fuel ?

7. What is the relationship between torque and Np ? Why does a change in Np effect torque ?

8. Flight idle/Beta/ground range - What are they all about ?

Any other hints/tips or things i should be aware of ?? Common problems (if any) with PT6A 's??

Many thanks !

[Sheep Guts]

Is this a wind up?

If not what the hell are you doing flying one without knowing some of these pointers allready.

1. Derated ensures longer engine and HSI life., compared to flat rated.

2.Hot or Hung Starts usually stem from 1 of 4 things
a. Battery Flat or low
b. GPU or Battery Cart flat or incorrect operation{ie. cuts out after engaging the starter}.
c. Starter Generator just about shot ie. Brushes warn beyond Limits
d. Any connection in the system thats lose or arcing.

Now you notice that most indeed nearly all PT6s have Starter limitations which are generally 25 seconds on 1 minute off, 25 seconds on 1 minute off, 25 seconds on 30-60 minutes off. This depends on your POH and type.

Also the start sequence in your POH usually has a minmum limitation of 12% N1or NG or GG. This is only a limitation and should never be attempted. My rule of thumb on this is if I dont get 16% N1 I wont introduce fuel. Anything above is OK but watch the temps carefully. If you add fuel below this and the engine is allready hot youll get a breach of a start limit TEMP, or at least a reportable temp to an engineer. Your POH will specify this.

3.If you leave it on you will draw a large mount of current through the brushes in the opposing Starter/Generator. Causing execessive wear and eventual failure. When you leats expect it.
Some Types approve what thye call Cross Generator or Generator assist starts. Which are usually for emergencies only. Also alot of smaller Types alow it B90 King Air and some Early Cheyenes I believe. BUT GENERALLY DONT DO A CROSS GEN OR ASSIST START EVER.


4. No Just ensure you identify and confirm the apropriate Propellor Lever and move it to the Feather position manually ASAP , after getting control of the Aircraft. Some Aircraft will have different speeds for Auto Feather/ nil Auto Feather operations beware of this.

5.SFAR41 dont know this will research it

6.Well the best way is to let it settle over night. Water is easily suspended in Jet A1 compared to Avgas. That is to say more "Hydroscopic" I believe the correct term is. Then drain using a standard strainer.

7. Same way Prop RPM effects MAP in a RECIP REALLY

8. Get out your POH and get someone to give you a ground school Cause I havent enough time here.

Ofcourse this depends on what Type or - dash version of the PT6 you operate and Aircraft .

Regards
'Sheep

[cjam]

Topper, one of the issues with water in the fuel is that microbes, little bugs called cladosporium resinae , can use the oxygen in the water in conjunction with the carbon in the jet-a to live happy little lives in the fuel system procreating willy-nilly resulting in a sludge that can, in time, block filters etc. If there is no water, then there's no clad resinae.
If the water is not held in suspension it will sit at the bottom and is easy to see,most of the time it is in suspension and the only real way to check properly is with a water test kit though.
That is all for now....you can take a fifteen minute break.

[Sheep Guts]

Cjam spot on chap. Forgot that. Also there is treatment for this stuff its called BIOBOR. You add it to your tank after filling. Its suppose to eliminate the bug.


Regards Sheepster

P.S. TIME FOR LUNCH, I here theres a good Wendys down the road.

[john_tullamarine]

I don't fly PT6 but have had some peripheral involvement with them so the following has more of an engineering than pilot slant.

1. Flat rating. Normal engine characteristic is for output to increase as OAT decreases at constant altitude. On many engines the mechanicals become the limiting factor (typically gearboxes, combustor pressures, or whatever) and the machine output has to be restricted at OAT below that at which the mechanical limitation becomes critical. Alternatively, the OEM may chose to limit the engine to a lower than maximum output for a variety of reasons. In this lower OAT region, the engine is said to be flat rated as the power or thrust output is limited to provide the relevant maximum which the mechanicals can tolerate or the OEM choses to adopt.

Operationally this means that the RTOW fall off with increasing OAT for a given runway is modest until the engine is no longer flat rated and then falls off much more rapidly with increasing OAT.

Derated certification. If an engine is capable of a certain output with whatever level of progressive deterioration in service, then it is reasonable to presume that the mechanicals and the hot end will last longer (ie cheaper maintenance) if we hold the output below the maximum. There are two ways to approach this

(a) flexible thrust settings (normally used on jets) where the engine is operated in a manner which uses a lower than maximum thrust output .. but the limitations are based on the certificated maximum thrust capability. For US rules, the maximum reduction is 25 percent.

(b) derate thrust where the engine is limited by the electronics or mechanical settings to be able to produce no more than a specific percentage of the maximum capability. This has significance cost implications and may have some performance advantages in certain circumstances. Many of the modern jet engines are certificated to several thrust rating levels, selectable by the flightcrew via FMS or similar wizardry.

Derate and flex can be used in conjunction. This may well result in considerably lower thrust output than the 25 percent flex limit for the maximum thrust certification.

2. Cranking power probably is the most significant factor. Others include wind (especially if from astern).

3. Cranking loads during turbine start are very high .. typically something in excess of 1000 amps. The generator is not much use for these sorts of current drain figures. The secret is to use ground power for starts to save the ship's battery

4 Failure of autofeather is very serious on a direct turboprop (typically the older engines) as the windmilling prop has to drive a whole bunch of turbomachinery through the gearbox. Much less of a problem on a free turbine but still of interest.

5 SFAR41, now defunct but still relevant to older SFAR41 aircraft, upped the ante of FAR23 a bit towards FAR25 to facilitate the development of early commuter aircraft. There is a useful FAA memo on the subject which you might like to read (http://www1.faa.gov/certification/aircraft/TypeDesignChangesSFAR41Airplanes.pdf).

6 Two significant problems with Avtur is that the fuel's colour often masks water and water may stay in suspension for considerable time. As a result it is usual to employ chemical means to detect the presence of water and there are several processes in common use.

7 I will dig out some charts for a couple of dash variants and come back with some numbers ..

8 Better for rated pilots to address this one for the particular engine.

[Sheep Guts]

There are not many common problems with the PT6. The early models had problems with low TBOs and HSI intervals. But as the engine has eveloved over the years the Modern Machines are much better. Having TBOS of around 3500 Normally with exensions upto 5000 hrs for FAR 135 and 121 ops ( Charter and RPT), THE ENGINE HAS A GREAT RECORD! But dont belive its bullet proof cause it aint. I have around 2000 hrs on PT6 powered Aircraft without a problem,( except a machine I wa sscheduled to fly had a compressor failure on the ground after start ). Another mate of mine had one go in the Air, but hed had 3000 hrs on PT6s at that time. Both these failures were incidentally on PT6-20 Engines which have had problems in the past with low TBOS and single stage nozzles which give high Start temps. The later versions and had dual stage nozzles which gave a staggered start temp much better.


See you tommorow

Regards
Sheep

P.S. Your home work tonight. Go and get that POH and read about the PT6. Define for me the BETA Range and Reverse range of your props in degress and the specified limits on N1 for these operations and temp limits too?

[604guy]

Topper,

Just have a few seconds here so won’t go into a lot of depth for answers. First off, I ASSUME that you are going to receive some formal training…RIGHT?

Hot starts – Keep in mind that about ¾ of the air going through your engine is for cooling purposes, only the remaining ¼ is used for combustion. The amount of air being drawn through the engine is dependent on the speed of the engine (revolutions of the gas generator). The slower the engine the less air is being drawn in. The non-variable is of course the amount of fuel being introduced at engine start. So if your engine is not turning fast enough when you introduce the fuel you can have a hot start. Reasons can include low battery/inadequate GPU voltage. (Neither of which should happen because the pilot is supposed to check that before attempting a start). Mechanical problems with the starter/generator etc can also be a cause but it is the pilot that decides whether to introduce the fuel or not.

Xgen starts – dependent on the aircraft type. Some applications call for xgen start as normal procedure but this of course would be fully covered in your formal training.

Water in jet fuel – in addition to previous comments remember that water goes into suspension very readily with jet fuel. Attempting to drain fuel after the aircraft has been towed etc is a waste of time. The time to do this is after the a/c has been motionless for several hours.

[flyer75]

First day on PPRUNE...
I have read about the poor guy who had the mind to ask technical questions about the engines hes using to defy his own gravity...scary...

On the other hand I spent 4 to 5 years flying metro3s and be1900 single pilot for a freight operation in South Dakota,USA and the only thing i needed to know was to fly an ils,ndbs whats that again?avoid cbs as much as i could in KANSAS and make sure no red light even thought of lighting up during start...

A part from that what else does one need to know...checklist and memory items/flows are there for you...they are your friends,,eventhough checklists can get old and dirty after a few freight dogs used them to scratch the ice off the leading edges and props.

Sure enough I decided that the red eye life was getting strainious so decided to convert my FAA ATPL o the glorious JAA ATPL.
Needed ground school so here i went to OXFORD..where they filled my poor freight dog head with technical information during eight months..first pass in all subjects..i must be technically fit and somehow clever..did help a bit to pass my IR/type rating with the CAA.lEARNING THE 737 MANUAL IN A 10 DAYS COURSE IS A BIT TRICKY BUT HEY THANX OXFORD TO HAVE woken up my memory..i passed..

Well a year later i could barely tell you how to calculate Mach number from TAS or explain how a piston engine works or what a great circle/"RHUM" Line is......

Bottom line....experience is the main factor in learning..if its getting too dark upfront and no ones on the frequency..go back to where you come from....

Just dont burn out your engines trying to learn their limits by experience..a little reading is essential..


Tailwinds,

Flyer 75

[IHL]

TopperHarley:

Cross generator starts on PT6 powered KingAirs can cause the operating engine to exceed ITT limits. Our company procedure was to have the operating engine at High idle (70%) before attempting a start, and monitor the ITT of both engines during the start. Even at hi idle I've noticed a 50 Degree rise in ITT on the operating engine.

NB: you got to be thick skinned to post on Tech Log.:ouch:

[604guy]

IHL
The start checklist for many of the newer Kingairs requires that the operating engine be in high idle before starting the xgen start procedure. I can assure you that it does not cause any ITT problems whatsoever.

[Sheep Guts]

Ok Topper,
Please dont keep us in suspense any longer what Type of Aircraft and PT6A version is fitted? Lets see, it could be one of the following:

1. B200 KingAir-----------PT6A-42/41s
2. B90 King Air------------PT6A-20/21
3. DHC-6-300-------------PT6A-27
4. DHC-6-200-------------PT6A-20
5. EMB110-----------------PT6A-34
6. DHC-7-------------------PT6A-50 BY 4
7. B300 KingAir-----------PT6A-60
8. B350 King Air----------PT6A-60
9. Shorts 360-------------PT6A-67
10.B1900------------------PT6A-67
11.RHIEMS406------------PT6A-112
12.B100 King Air----------PT6A-28
13. CaravanC208---------PT6A-114



Thats all I know. Not sure on Shorts 330, Cheyenes, Y12(CHINESE JOBY), are there any others?


Sheep

[TopperHarley]

Thanks for the info guys.

For better or for worse, the ground course I did placed a lot of emphasis on rote learning numbers. I have nearly every number in the POH comitted to memory (What temp does the CABIN AIR DUCT O'HEAT anunciator come on at ?) but perhaps it was assumed that I knew the fundamentals.

A very experienced pilot once told me "You dont know what you dont know" - I think I am in that position.

Sheepguts - Its the -112 in the F406

WRT my homework - You wouldnt believe this sir but you see I was looking after a friends dog.... I only went out for five minutes..... !

The power leaver pedestal is marked in three ranges. Flight, Ground Idle, reverse. With a gate between flight and ground idle. Very little reference to Beta in the POH.

One mention in the definitions part of section 1 "BETA MODE - Engine operational mode in which propeller blade pitch is controlled by the cockpit power lever. Ground ops only"

Then later on that "To acomplish reverse pitch, the power levers are retarded beyond idle, over the gate and into the BETA position"

From the limitations section of the POH, prop blade angle at 30" station:
* Feathered = 85.5 degrees
* Low pitch = 18.5 degrees
* Full reverse = -13.5 degrees

and engine limits:
* Idle = 685ITT
* Max reverse = 1382 ft-lbs, 725ITT, 101.6%Ng

Was that what you were after sheepguts ??

Regarding Flat/De rating - A lot of people have told me that this engine is DErated, however the POH says that its flat rated to 500SHP. Ive also heard the phrase "Bulletproof" mentioned in close proximity to "derated" (should I be worried??). Is there a laymans definition of derated that is perhaps confusing me ?

Thanks again for your help people - If youve got any more useful comments please keep them coming - Im keen to find out all the things I dont know !

[hptaccv]

'flight idle' is a few % higher than 'ground idle', basically a different power setting.
'Beta Range' can be translated as reverse, or negative blade pitch. This is controlled by the power lever (although it is basically a blade pitch change) in order to be sure of the engine being in idle before reversing.

I'ts been a while, but i also remember the condition lever having two detents, high and low idle, basically only used for cross-engine starting in hot&high conditions. PT6-61 (cheyenne pa42)

regarding flat- and derated engines:

relative to outside air temperature:

flat rated meaning the engine is rated to a certain power limit, before reaching itt limits for example. On reaching an ambient temperature which leads to egt limitation, this will be the limiting factor, thus leading to less power available.

a de-rated engine on the other hand, is limited to an itt of say 700°c, even though the manufacturer limit might be 750°c. This reduces maximum available power throughout the whole temperature range.

I stand to be corrected! (excuse my stumbling english!)

[redsnail]

Great thread. Never too old to learn stuff.

Sheepy,
Shorts 330 = PT6 45
Shorts 360-100 = PT6 65R
Shorts 360-200 = PT6 65AR
Shorts 360-300 = PT6 67. What letter is after it I don't know.
:D

[F111]

-67R on the Shorts 360-300.

[TopperHarley]

Thanks again for the info guys...... It is really appricated.

Has anyone got any general hints or tips that might make teh transition easier or safer ??

Any checkies that see people do things in turboprops that make you cringe ??

Thanks again

[Crossunder]

Well, let's see...

Your Company will (hopefully) introduce you to their SOP, and you will also receive a technical course prior to flying training. That should clear up any questions you might have.
Apart from that; flying turbo props is the easiest thing in the world, except flying jets. No tricks, no funny business, just fuel on or fuel off.
Never understood what the fuzz is about.