Fuel consumption rates

[Sir Puma]

The other day I wanted to take the FSX default Beech King Air on a maximum distance trip. According to the notes on the aircraft it should have a ~1760 NM range. So I set up a trip from KPWT to KLWC using the Hi Airways which makes for a ~1360 NM trip. Leaving ~400 NM of play. According to the notes the aircraft has a max service ceiling of 35K but I can never get any aircraft to fly well at the max altitude so I set my flight for 25K.

A thousand miles into the trip I was left with ~150 lbs of fuel and it was giving me the option to auto refuel. I had prop pitch, throttle and condition levers full and fuel flow was ~500 PPH.

When I reduced my throttle to 70% and prop to 80% I can get the fuel flow down to ~400 PPH. With full levers my indicated airspeed is ~180 Kts and with the new settings it drops to a snails pace at ~165 Kts.

I would think that even though the fuel flow drops, the drop in airspeed wouldn't really extend my range. So what gives? If the range is supposed to be 1760 but I can only get 1100 out of it, what am I doing wrong? It would be nice if there was something that would define the best cruising alt is.

Also, wikipedia lists the King Air 350's max cruising speed as 289 Kts at 25K, but I can't even get close to that with my max only at 180.

[JoBee]

First things first, I would not put 100% faith in any numbers that don't come out of the Pilot's Operating Handbook for any given plane.

The numbers in Wikipedia could be wrong, the numbers provided by Microsoft have been wrong before.

As for your specific numbers a 20% reduction in fuel burn only cost you about 9% of IAS, so it does pay to pull back the levers.

Not to mention how much happier your A&P will be.

I wonder if the range is based on covering that distance at cruise settings, without factoring in the added burn required in climb.

I would always recommend you fly by the numbers, which in the KingAir is 1600RPM at cruise and I typically run at 80% N1which nets about 200PPH/engine, if memory serves.

Also remember what you see in the plane is Indicated Airspeed, which will be less than True Airspeed, which is what would be listed in Wiki as max cruise speed.

Check the GPS, it will give you ground speed, which will be closer to True Airspeed (+/- wind).

cheers,
Joe

[Sir Puma]

I'm not sure how you're getting down to 200 PPH. When I set my throttle at 80% (8800 RPM) and my props at 45% (which gets me down to 1560 RPM) my fuel flow is 400 each side. Hopefully it will be enough to get me 1400 miles. I did reduce my props to 40% and throttle to 40% and got 200 PPH, but then I started shedding the airspeed so fast I figured I was going to stall.

I'm running the flight again at 400 PPH and I'll see if I can make my destination.

[Sir Puma]

Well, I did the flight. I ran at 400 PPH for the first half and that kept me at about 180 Kts. The GPS doesn't show actual, at least I couldn't find it, but the HSI looked like it had an airspeed in the upper right corner that showed between 260 and 300 Kts. I powered back to about 60% throttle and that dropped my fuel flow to ~320 PPH and my indicated airspeed down to 170. I made my landing but ran out of fuel just as I reached the end of the runway.  Had to call the fuel truck.  8-)

I think if I trim the throttle to 60% once I reach cruise altitude I should be able to clear the 1400 NM needed for an ILS trip and still have enough fuel to make it to the pumps and parking. (ATC always makes you go a ways around to make an ILS landing.)

[JoBee]

I came in to post these and saw your reply, thought I would post them anyway

Cruising at 25,000ft with no wind. IAS is 147 knots, HSI (coupled to GPS) shows a true airspeed (no wind) of 218 knots. 80% power, 1600 RPM= 240 PPH per engine


90% power (basically full throttle) fuel flow is up to 360+ PPH, 178 IAS, 260 from the GPS


Turned off the anti-ice, IAS up to 194, TAS up to 281 @ 450 PPH


After that shot I climbed up to 32,000. My TAS was reading 288, right on the Wiki's notes of 289.

Just after I leveled off at 32,000 both engines died. Not sure why, unless they were tired of full throttle

Couldn't get them running again until I was down to about 26,000.

I borrowed this pic from the Learning Center and circled in red where the GPS shows ground speed (true airspeed +/- wind).


Hope this helps.

cheers,
Joe

[Strategic Retreat]

Just after I leveled off at 32,000 both engines died. Not sure why, unless they were tired of full throttle

Couldn't get them running again until I was down to about 26,000.

Nothing wrong with that. Real aircraft engines work the same way. If they stall, they cannot being restarted above a critical height that depends on the kind of engine.

As for the rest of your post... why, oh why are you still trying to squeeze blood from turnips? Abandon the default planes and find yourself a good add-on, even freeware.

[Sir Puma]

JoBee, I think you're confusing throttle settings with the engine RPM gauge. When I set my throttles to 80% (as shown by mousing over the throttle levers) my engine RPM is around 90, not 80. I believe that the engine RPM gauge should have a X100 on it's face. If I run my throttle down to about 54% then the engine RPM reads 80. Unless of course it's supposed to be %N1 and they just mislabeled it.

I do tend to run with real world weather on, simply because I like the challenge of running into random weather. I know my wind speeds and directions will be different. I'm not sure how to get the wind displayed like you did.

The GPS has two map displays, heading up and north up. With it set to heading up it displays the GS (Ground Speed) with North up it doesn't. 

I tried your settings  with clear weather and it doesn't give me the fuel rate you have. When I set my props at 1500 and my engine at 80 (54% throttle) my fuel flow is 300. But at least airspeed is sufficient. To get my fuel flow down to 250 I have to cut my throttle down to about 25% (or 75 on the gauge).

[Sir Puma]

As for the rest of your post... why, oh why are you still trying to squeeze blood from turnips? Abandon the default planes and find yourself a good add-on, even freeware.

If someone would produce a Cessna 441 or Piper PA-42 for FSX I would. 

[JoBee]

JoBee, I think you're confusing throttle settings with the engine RPM gauge. When I set my throttles to 80% (as shown by mousing over the throttle levers) my engine RPM is around 90, not 80. I believe that the engine RPM gauge should have a X100 on it's face. If I run my throttle down to about 54% then the engine RPM reads 80. Unless of course it's supposed to be %N1 and they just mislabeled it.

Nope, not confused at all.

I don't pay any attention to the throttle position, only what the gauges say.

Actually the RPM gauge (not the prop RPM, the other one) should have a % on it.

I'm not sure how to get the wind displayed like you did.

If you mean "to get the windspeed displayed on the screen", I did it by pressing Shift+Z.

If you mean "to get a windspeed of 0 knots", this flight was done with the "Clear Weather" theme. By having no wind the GPS ground speed should match my TAS.

[quote]
I tried your settings

[Strategic Retreat]

As for the rest of your post... why, oh why are you still trying to squeeze blood from turnips? Abandon the default planes and find yourself a good add-on, even freeware.

If someone would produce a Cessna 441 or Piper PA-42 for FSX I would.

[BigTruck]

[quote][quote]

Digital Aviation has an awesome Cheyenne, but it's payware, and I believe it's modeled after the PA-31, not the 42.

[Sir Puma]

I understand, yet not having available your favorite planes is NO reason to punish yourselves that harshly. Remaining users of the default planes is masochism... no, it goes BEYOND that, well into the territory of willing crippling self mutilation.

I do wish I had the spare cash to purchase some of those payware planes. But $20-$50 for one aircraft with a couple skins is way too steep for my wallet. Though they are very nice.

I kind of thought that gauge seemed funny with the RPM mark but no x100 mark.

I believe my anti ice was off. I don't use it unless it's needed for icing conditions.

[DaveSims]

As for the rest of your post... why, oh why are you still trying to squeeze blood from turnips? Abandon the default planes and find yourself a good add-on, even freeware.

If someone would produce a Cessna 441 or Piper PA-42 for FSX I would.

[coalpedlar]

Try the Gulfstream(s). Great planes.  I have a new cockpit if you want it, too.

[Sir Puma]

[quote]Try the Gulfstream(s). Great planes.