Turbo Prop derate..

[ranklein]

Hello,

Is there a de-rate or an assumed temperature take offs for a turbo prop airplane, just like the jet engine planes?

Thanks!

[Daysleeper]

On the Allison 501 there is a reduced temperature (Turbine Inlet Temp) take off technique.

If my memory is right its 932 C TIT as opposed to 971 C TIT.

Not always a reduced thrust as on cold days you get more horsepower at 932C than you would on a hot day at 971 TIT.

[Cyclone733]

Yep, the Q400 for example has MTOP for hot and high conditions, NTOP (approximately 91% of rated power) and can then be set at one of 5 reduced power settings for take off down to a minimum figure of 81%.

Hope that helps

[ranklein]

Sure helps.
Anyone knows if the ATR has an assumed temp TO thrust?

Thanks again guys!

[The Flying Cokeman]

No ATR does not have that.

[Alpine Flyer]

On the Dash 8-100/300 you can manually select a lower take-off torque using an assumed temperature on the runway tables. The Q300 was to have had an indication of maximum torque allowable for different phases of flight including a FLX setting but apparently deHavilland never certified this or got it to work so it was always disabled and totally removed from later airplanes.

[ranklein]

Interesting.It seems that the turbo prop manufucturers and operators are less concerned when it comes to the ability to protect the engines and maintain them in a better shape by doing the derate take offs.
In the jet engines I guess it's a much highlighted issue.

[Cyclone733]

I've got the feeling it's more down to the engine power. An older model would have perhaps 18-1900 SHP per engine and a more modern aircraft like the Q400 has just over of 5000 SHP per engine. The other reason could be that turbo props are often used because of their better short field performance so quite often you'd want normal take off power.

[ray cosmic]

The Fokker 50 had the FLX selector, so you could set an assumed temperature. Isn't the thing with TP that both the engine and prop are able to operate on optimum RPMs. Therefore less wear than on Jets (?).

[yrvld]

Hello

The Saab 2000 has Flex which does the same as on a jet. The value (in power units) to be set is taken from assumed temp tables.
The Saab 340 does not have dedicated Flex or assumed temp setting but you can take off setting a lower torque (the unit for power on the 340). To find how low, you consult assumed temp tables, providing your operator has them.

[ranklein]

Thanks again you all!!

[galahad]

Normal takeoff for ATR, each engine will give 2475 SHP (90% TQ),
and will increase to 2750 SHP (100% TQ) in case of OEI.

kind regards,

[Alpine Flyer]

All Dash 8s also use less than 100% torque for normal take-offs with automatic 10% uptrim triggered by the autofeather system. In case of reduced power it doesn't go to max TO power but to 10% more than whatever it was reduced to. (Something to do with Vmc I suppose.)

(And at least for the Dash 8-100 there is a "no uptrim" option which allows to use 100% torque for airports requiring maximum performance without the uptrim overboosting the engine. Never seen it in, just read about it.)

[jumpdrive]

in the newer series of ATR's>>>>>>>>>the 500's series
take power is controlled automatically by the EEC (electronicEngineControl)
taking into acc. OAT, through the ADC (airdatacomputer), & other input data
previous model's like the 300'& 320's , dont have this, they have ECU
power for take off had to setted manually ( no notch detent )
this components (of many more that are part of eng. control)
will send all info & data to the computer's
& this will give you the actual power setting
in the 500's is auto, you'll go to a NOTCH detent
and eng power for takeoff will set up automatically
always to 90% of torque not more, its fixed
& of course, the higher the OAT & Altitude, the lower the take off rating
but its always atomatic, you just need to pre-check it before takeoff
and confirm it on roll, tahts it
going back to the begining , what it doesnt have
is an ON demmand derrated T/O powersetting
regardless of bleed's ON or OFF

hope it help's, im not a book worm,
so maybe i missed a few items on the systems, but in general its like that
very simple the logic

[The Flying Cokeman]

Jumpdrive,

Even on the older 72-200 with PEC you had the eec and the "notch" for the power levers, so it's not only for the -500 series.

About the 90% excactly does not really happen in real life ,I have seen anything from 100% to 112% on the -500 series during take off - especially the 42-500 had a tendency to go up to 112%.