Flying the Grumman Mallard G-73T (turbine conversion)

[raphael]

Hello everybody,

I'd like to fly the wonderful Turbine Mallard by Milton Shupe for the Bluegrass Airlines BCAR Rally starting soon. I did a few test flights but still don't know exactly how to handle the PT6 engines : the checklist and reference information included with the aircraft are not very clear to me and I couldn't find anything interesting on the web. Being a piston aircraft pilot, I don't know much about turboprops and would appreciate to fly it... "by the numbers".

Here is what I gathered from the aircraft's documents :

Take-off
- full power (100%) --> max 5 min.
- props full forward (100%) --> max 5 min.

Climb
- power 90%
- props rpm 95%

Cruise
- power "Set % TRQ as REDQ" ????? --> should give 190 KIAS at 6000 ft
- props rpm 90% --> should give 190 KIAS at 6000 ft

Economy cruise
- power 65% and rpm 65% --> with this setting, speed is rapidly decreasing to about 129 KIAS at 7000 ft
- EGT is 694 °C at 7000 ft
- fuel flow is 192 PPH at 7000 ft

Descent
- power "as required"

Approach
- power "as required"
- props full forward (100%)
- best glide speed ????

Landing
- Vref ???

Now, I also don't understand the difference between my throttle joystick (Saitek Throttle Quadrant) and the gauge indication :
- to get 65% engine torque (gauge), I must set my throttle control (joystick) at 44% ; or to get 90%, I must set 64% on my joystick
- to get 65% prop rpm (gauge), I must set my propeller control (joystick) at 29%

Condition levers : do they have to remain at 100% during all phases of flight, and taxi ?

That's it. Anybody wanting to share some knowledge on these issues ?

Thanks a lot in advance and a big thank you again to Milton Shupe for this great aircraft.

Raphael (LSGG)

 

[Tom Clayton]

In the Sim, Ground Idle is best on the ground (duh) to avoid having to ride the brakes. I usually take the active, set the brakes, knock the condition levers to the top, bring the power up, then release the brakes. If I have a longer runway (like a commercial airport), then I can do all that without having to set the brakes.

 

[raphael]

Thank you Tom for this info about the condition levers. The "Low idle" position is only visible in a very unusual position in the VC. As it is not comfortable to adjust the view each time I start the engines, I noted that the "Low idle" position roughly corresponds with the 25% position of the condition/mixture lever on my joystick. I'll move it to 100% just before take-off.

Regarding the cruise settings, I tested the plane and recorded the following values (at 7000 ft and +2°C OAT) :

Torque (%)	RPM (%)	Fuel flow (PPH)	EGT (°C)	KIAS
95	90	378	742 !!!	176
90	90	355	734	174
85	90	338	729	172
80	90	317	723	170
75	90	301	717	169
70	90	282	711	167
65	90	263	701	156
65	65	192	694	129

Last row is "Economy cruise", following the original "Mallard_ref.htm" file. I might use the 75% torque setting for the Rally - need to fly fast to save time in a busy period...

I also found a technical document about PT6A-34 engines mentioning not to exceed a maximum EGT temperature of 740 °C, and will respect this limitation.

All this will do for now but if anybody knows more it will always be welcome.

 

[Motormouse]

My rw PT6 experience is mainly with the large block 45/67 variants, with a little time on the small block 34;
generally speaking the torque applied to prop is a measure of how much power we are extracting from the engine, 100% being maximum; to get most efficiency from engine we need to run it at lowest EGT (gas temp) possible that maintains the torque we require for the airspeed it is desired to fly at.

We would normally take off with fuel cond lever High (as Tom says LOW is for ground handling only) , 100% prop rpm , then advance throttles to set the torque required to achieve take-off and V2 climb +10 knots from the performance charts for conditions of the day, factoring aeroplane weight and runway length etc.

You have to remember that most aeroplane performance charts are written for what is called ISA (International Standard Atmosphere) ; and variations to ISA have to be factored in, such as ambient temp. air pressure for the day etc.

ttfn

Pete

 

[raphael]

Thank you Pete,

I save your message and will follow your recommendations. Without the appropriate performance charts, flying the Mallard will be a bit instinctive though. Never mind : it won't cost anything even if I kill the engines...

Cheers,
Raphael