ATR72/Q400 IDLE Fuel Flow

[CabinMaster]

Does anyone have numbers at hand about the IDLE fuel flow of either model (I guess they are pretty much similar). I am looking for ground idle and flight idle, if something like this applies to a prop.
I have an ATR72 manual and I am wondering about the fuel burned at descent. I know you always need to burn some fuel to keep the engine running (300kg/hr and more for a CFM56), but there are various descent profiles in the manual and I have problems identifying the idle fuel.

Thanks for any info.

[Coffin Corner]

Q400 on the ground in discing is about 180kg per engine.

In the descent at idle at 235kts it's 225kg per engine.
In the descent at idle at 200kts it's 140kg per engine.
In the descent at idle at 275kts I've no idea, I'll look on Monday when I fly next.

Hope this helps.

[CabinMaster]

Thanks, helps a lot.
Considering that Q400 and ATR72 uses similar engine, the ground idle number should be applicable to both aircraft. As the ATR72 has about 3000hp (compared to Q400s 5000hp), I would assume the ATR to have only 60% of that idle fuel flow (probably a bit more as those things cannot be scaled linearly).

[CabinMaster]

And could someone give me the limit airspeed (VMO) of the Q400. The ATR72 has 250 KIAS and M0.55. The A400M to my knowledge 300 KIAS and M0.72.

Thanks.

[Lord Spandex Masher]

The Q400 has a Q limit of 285KIAS and about .58M.

[Tu.114]

Just a little point for accuracy - the Q400 suffers from the installation of the same cockpit windows the previous series have. Those are only certified for birdstrikes up to 246kIAS, so the Vmo will see a linear decrease from 285 to 245kIAS (which is the Vmo for the -300) while descending from FL100 to FL80. Takes a few flights to get used to that.

[Piece of Cake]

The Vmo on the Q400 varies with altitude

Below 8,000ft 245KIAS
at 10,000ft 282KIAS
at 18,000ft 286KIAS
at 20,000ft 275KIAS
at 25,000ft 248KIAS
at 27,000ft 238KIAS

[GusHoneybun]

As stated above, the Vmo is variable dependent on altitude.

From the AOM.
0 - 8000ft : 245KIAS
to 10000ft : 282KIAS
to 18000ft : 286KIAS
to 20000ft : 275KIAS
to 24000ft : 248KIAS

For the best TAS (~365kts), fly somewhere between 18-20000ft. Not very flight efficient through.

[CabinMaster]

Thanks for the info.
Can anyone check his FCOM (apparently a few people here fly the Q400) and give me RPM and propeller diameter of the Q400. The Q400 has a lower diameter than the preceding models?

If anyone is interested what I need all that stuff for: I am trying to make a suitable performance model for a turbo-prop. Biggest issue at the moment is to get propeller efficiency (and useful gas turbine data for partial power operations).
I had to learn that propeller efficiency is a pretty complicated thing. And that is without Mach number effects.

By the way: the ATR72-500 uses a 3.93m propeller rotating at 1200 RPM (=100%), normal cruise setting is 82%. The propeller alone weights 180kg a piece.

[Piece of Cake]

Q400 props are 4.11m in diameter (13ft 6in)
TAKE OFF RPM 1020
CLIMB RPM 900 or 850
CRUISE RPM 850

Sorry I don't know the diameter of the props on the other earlier Dash models.

[Coffin Corner]

Originally Posted by TU.114

so the Vmo will see a linear decrease from 285 to 245kIAS (which is the Vmo for the -300) while descending from FL100 to FL80. Takes a few flights to get used to that.

I wouldn't say it's linear mate, watch what happens at about FL83, the VMO band shoots down quite quickly.

CC

[CabinMaster]

Thanks.
By the way: the ATR72-500 has an effective top speed of 280 KTAS at 18t gross weight. Burns 360kg/(hr & ENG). More efficient at same weight is flying at max altitude, achieving 266 KTAS at the expense of 280 kg/(hr & ENG). What I see from the cruise performance charts is that only below FL100 the aircraft is actually VMO-limited, above that the engine sets the limit. It never actually sees its MMO-limit in cruise flight.
Always interesting to learn the differences between jets and props when it comes to performance.

[Tu.114]

Coffin Corner; thatīs interesting. I have always been under the impression that the Vmo tape moves at a constant speed (with constant V/S of course) in that FL range and the OM-B also claims a linear decrease. But with the many little oddities about this plane, who knows - I will keep an eye on that next time.

[Tu.114]

Cabin Master - in fact, the Q400 is closer to a jet here than other props. Depending on factors like FL, OAT and gross weight, it is very well possible to exceed Vmo during cruise with MCR (Max. Cruise) rating - in winter usually even at FL250 and with a fairly heavy plane. To combat this problem, there are cruise power setting tables that will result in a good margin to Vmo. Ah, the joys of not having an Autothrottle...

[Coffin Corner]

Well I may be wrong mate, but like you say it does catch you out sometimes, I remember it coming down quite quickly, especially noticeable if you haven't got your speed back at 235kts by FL80. I'll check it out on Monday when I fly next, but I was under the impression it moves a little faster. This could be an illusion of course.

CC

[White Knight]

I'm intrigued by the original question.... Who really cares? I flew 42s and 72s and never had the faintest idea what the ff was unless I looked at the gauges (that's why they're there). I do know it can't be much 'cos they didn't exactly carry a lot of fuel in the first place.. Maybe 1400kgs for 42 and 1800kgs for 72...

[Phobos2]

The propeller alone weights 180kg a piece

actually its 30kgs per prop....thus 180kgs in total.

[no-hoper]

ATR 72 has PW 124/127 engines.Q-400 PW 150.Only the first digits are the same...

[CabinMaster]

Originally Posted by no-hoper

ATR 72 has PW 124/127 engines.Q-400 PW 150.Only the first digits are the same...

I assume that basic engine architecture is similar. So the value might be scalable. Anyways, I just need a rough guess to check versus the ATR72 Descent table. I am using SFC-based engine model, which works well in cruise but fails for descent (as zero thrust means zero fuel when using SFC).

[Tu.114]

Cabin Master - the PW150 has major differences from the previous models. Now I do not know the PW124/127 on the ATR but I dare say it is similar to the PW123 series on the DH8-300. The PW150 has a 3 stage axial low pressure compressor instead of the radial NL unit on previous designs. Engine control is via FADEC, not via a mechanical fuel control (although on the 123 it is influenced a bit by a electronic control unit). Also the propeller is fundamentally different both in design and its auxiliary systems. And maybe another point important for Your calculations is the fact that the PW150 on the DH8D is not fully rated (the engine is capable of about 7.000SHP) but derated to 5.000SHP. This is very much noticeable when observing ITT values - unlike the PW123 which is often near its limiting ITTs at startup and from takeoff to the top of descent, the PW150 runs much cooler. So please take extrapolated values from previous engine series with a grain of salt.