You are forgetting about flat rating.

Both the TBM and KA350 have basically the same engine core.

The TBM flat rates it to LESS power than the KA 350.

If you power back the KA350 to the SAME power (per engine) as the TBM is doing, then it has the SAME effect on range being low or high. Each KA 350 engine would be burning the SAME fuel as ONE TBM engine.

You are basically trying to say there is some fundamental lesser efficiency of twins but using the fact that Beech didn't flat rate as much to prove it. No dice. What you are seeing is just an artifact of flat rating the two airplanes differently.

The fact Beech lets you USE more of the engine power lower doesn't mean a twin is suffering some exotic new drag unique to it.

Mike C.

You've put your foot slightly on the scale, off by 2.8 GPH. You probably were using ISA -20C numbers.

The numbers for 850 from the POH, ISA, 6300 pounds ("mid weight"), max cruise:

0 ft, 88.8 GPH, 245 KTAS
5 kft, 81.6 GPH, 257 KTAS
10 kft, 76.0 GPH, 270 KTAS
15 kft, 72.8 GPH, 285 KTAS
20 kft, 69.0 GPH, 300 KTAS
25 kft, 66.8 GPH, 318 KTAS
30 kft, 58.0 GPH, 316 KTAS

For recommended cruise:

0 ft, 88.8 GPH, 245 KTAS
5 kft, 81.6 GPH, 257 KTAS
10 kft, 76.0 GPH, 270 KTAS
15 kft, 72.8 GPH, 285 KTAS
20 kft, 69.0 GPH, 300 KTAS
25 kft, 66.5 GPH, 316 KTAS (*)
30 kft, 55.5 GPH, 310 KTAS (*)

(*) only two that changed

Source (so everyone can check):

http://www.tbm850.com/IMG/pdf/PIM850GC.pdf

Now we need a KA 350 POH...

Mike C.

The KA 350 at twice the power (2 engines) of the TBM (1 engine) will go faster than your Acclaim. The KA 350 won't go quite as fast as the TBM. That is true at all altitudes.

There is no special extra drag that twins get down low. The aerodynamic effects are the same and proportionate for both singles and twins.

There is no special extra fuel consumption that engines get when hung on a twin. Same power output is same fuel flow whether the engine is on a single or twin.

Mike C.

The KA 350 at twice the power (2 engines) of the TBM (1 engine) will go faster than your Acclaim. The KA 350 won't go quite as fast as the TBM. That is true at all altitudes.

There is no special extra drag that twins get down low. The aerodynamic effects are the same and proportionate for both singles and twins.

There is no special extra fuel consumption that engines get when hung on a twin. Same power output is same fuel flow whether the engine is on a single or twin.

Mike C.

Oh, I don't think they are that far off at sea level, but let's say 180knots at 45gph, so $1.25 per nm at $5.00 a gallon for 100LL, or $1.36 per nm at $3.80 a gallon for Jet A. Actually not that much of a difference now, is it

Add 30knot headwind and a TBM is actually much cheaper.

Same PER ENGINE fuel flow.

Not total.

That explains the confusion...

Mike C.

Ummm... Anybody got anything on the SF50 we haven't heard before?

Must have missed this post:

A KA350 will fly quite fine on 65 gph at FL250. It's not going to be fast, but it will fly around quite happy at 220-230pph per side.

Yes.

Tim

15k is avoiding winds.

At 17.5 I burn 73GPH
At FL260 I burn 55GPH

So 18 gallons over the course of an hour is no big deal when you hold over 400 gallons of gas. At $4 gallon it's only another $72 per hour.

Not all jets can go to FL450. Smallest that can are CJ2+ and Phenom 300.

But not turbulence and weather sometimes.

15K can be howling and bumpy and 410 is smooth and much less. Then there are days when it is other other way around.

Right now over ATL, 15K is 40 knots, 410 is 150 knots, about the worst place in the US today. Seems like the TP has a serious advantage today. But how much?

For a jet like a CJ2, it is ~150 knots faster at 410 than the PC12 is at 15K. Thus the PC12 is 77 GPH and 210 GS (2.73 nm/gal) and the jet is 120 GPH and 250 GS (2.08 nm/gal). Not as different as one might expect. If fuel alone was the issue, I think I'd rather be in the CJ2 at 410 than the PC12 at 15K. The extra fuel burn would be worth it for 2 engines, faster, and higher. Over a 600 nm cruise segment, the fuel difference is 68 gallons more and 27 minutes less for the CJ2. That's a pretty good trade off for these types of airplanes.

Cabin is larger on PC12, so not apples to apples exactly. TBM would be faster, but smaller cabin.

Winter has a way of making you want to have a faster airplane and more altitude options. Favors a jet.


You are going slower lower, so the cost impact is more than that, the hourly costs of maintenance and engine reserve come into play, for example.

Mike C.

But not turbulence and weather sometimes.

15K can be howling and bumpy and 410 is smooth and much less. Then there are days when it is other other way around.

Right now over ATL, 15K is 40 knots, 410 is 150 knots, about the worst place in the US today. Seems like the TP has a serious advantage today. But how much?

For a jet like a CJ2, it is ~150 knots faster at 410 than the PC12 is at 15K. Thus the PC12 is 77 GPH and 210 GS (2.73 nm/gal) and the jet is 120 GPH and 250 GS (2.08 nm/gal). Not as different as one might expect. If fuel alone was the issue, I think I'd rather be in the CJ2 at 410 than the PC12 at 15K. The extra fuel burn would be worth it for 2 engines, faster, and higher. Over a 600 nm cruise segment, the fuel difference is 68 gallons more and 27 minutes less for the CJ2. That's a pretty good trade off for these types of airplanes.

Cabin is larger on PC12, so not apples to apples exactly. TBM would be faster, but smaller cabin.

Winter has a way of making you want to have a faster airplane and more altitude options. Favors a jet.


You are going slower lower, so the cost impact is more than that, the hourly costs of maintenance and engine reserve come into play, for example.

Mike C.

yes,
but who fly cruise at sea level? Even in an 850 you will never see cruise level over 70 gph.




I'm looking at 850 numbers. 86gph at sea level.

I think the CJ2 would do it, 6 plus bags, PDK to APA, right now.

The winds die off quite a bit after leaving the ATL area, down to about 40 knots by APA.



Mike C.