Cirrus POHs can be found here.
You have to use Chapter 5 for both POHs and choose a sensible altitude (e.g. 15 000ft) and a certain BHP value (% of ponies available).
As neither airplane is turbocharged and the maximum %BHP the TB20 can run at best economy is 75%, we have to use the highest altitude at which the TB20 can deliver 75%. That is 6500ft.
SR22 got 310BHP, TB20GT 250BHP so 75% (the max one can run with peak mixture) would be 187.5BHP for the TB20 which corresponds to 60% BHP on the Cirrus.
At 6000ft and ISA, the SR22 gives 162KTAS and 14.1GPH (59% BHP), i.e. 11.5 MPG. At 6500ft and ISA, the TB20 gives 157KTAS and 14.0GPH (75% BHP), i.e. 11.2MPG.
The Cirrus is slightly better but I think it can carry more weight. Also the equation will move in favor of the Cirrus as one gets higher but it becomes apples to oranges because the TB20 doesn't have the horse power to compete.
Will any NA engine make 75% at 14000 feet? I have the IO540-C chart here
and you can see the 75% intercept (RH graph) is about 8000ft. I cannot see how any NA engine can possibly differ in this respect - unless something is drastically wrong in the way its fuel metering system scales over air density, which may be the case for carb engines.
The thing I had problems on was working out the useful load, which you suggested ought to be thrown into the comparison.
And I would suggest working out the useful load with full fuel, otherwise it doesn't make much sense.
I have changed it to use 6500ft because of what you say. I always think in turbonormalized engines (like mine 
) where you get 100% BHP at all levels.
And I would suggest working out the useful load with full fuel, otherwise it doesn't make much sense.
I would not do that. Engines have about the same SFC so more fuel will get you there faster or it will get you further. Fuel is part of the useful load and all charts are at MTOW.
May I modestly add that my 1940s airframe design TR182 compares pretty well in that above scenario? 15GPH and 156KTAS but 600kg useful load. It becomes much more efficient at higher altitudes though.
PS: Why on earth does Socata have charts for 4500 and 6500ft, did they expect their customers to only fly VFR?
I've never understood the TB20 POH charts. They show a range of about 1100nm (against the real best of 1300nm) and fuel flows that are correspondingly higher.
The reason for going for FL100+ is because you can fly with a wide open throttle (WOT) and run at ~ 65% power.
Actually FL080 gives you 75% (see my post above) but FL080 gives poor utility value for Eurocontrol routings; I rarely bother to file below FL140 for that reason, though I level off at FL110-120 on nice days.
Furthermore, you get even more economy (maybe a few % more) by going to low RPM, say 2200, which I can't do at FL080 at WOT (the engine sounds too rough). Also the SR22 doesn't have any way to set 2200.
So I think comparing NA performance in the Eurocontrol context, FL120 is a good point. The fact that you (practically) need oxygen to fly useful long distance IFR is just one of the bizzare ways in which European ATC systems (and airspace) have been set up.
May I modestly add that my 1940s airframe design TR182 compares pretty well in that above scenario?
That just shows there is no free lunch in physics, especially at low subsonic airspeeds
The SR22's 81 USG usable fuel
Note, I believe the SR22G3 & G5 increased fuel capacity to 92 USG usable...
Incidentally, now that we're all bragging about our precious parts: Just got a performance data point from my new DA42-VI at the factory: 157 KTAS at FL110, ISA+5; 60% power, 10.2gph of Jet A (both engines). Damn, those diesels are efficient...
157 KTAS at FL110, ISA+5; 60% power, 10.2gph of Jet A (both engines). Damn, those diesels are effective...
That is also very close to the TB20 in MPG except you get a spare engine thrown in
Yes; diesels are very good (when they work).
Unfortunately the UK is now taxing avtur same as avgas, though the tax is declared on a voluntary basis (business and training flights exempted).
In fact I flew in a DA42 a few years ago and its low altitude performance (3000ft) was exactly the same as the TB20: 140kt IAS, 11.5USG/hr). The Cessna 400 was also the same.
I don't see much bragging. What I see is that most planes of a similar shape and size are really very similar.
when they work.
That's why I've got two of them hanging out there!
What I see is that most planes of a similar shape and size are really very similar.
Yep. Laws of physics.
Well, imagine how well a Cirrus would do if it had a retractable gear and it was built with modern composite technology (weight!).
And imagine how expensive a 2013 TB20 would be and why Cessna only restarted the primitive designs but not the more advanced onces. The Cessna 206 (built until today) is a 1960s 210 with fixed gear (the early 210s had a strutted wing). The 182RG and especially 210 could just not be sold at what they would cost today.
The DA42's airframe is extremely poor in my opinion, now with the DA42-VI they are finally getting to what the airplane should have looked like from the beginning. I have to admit, the DA42-VI is very tempting.
IIRC Cirrus decided against retracts because they only lost about 5kts with fixed gear while gaining substantial weight. Same story with the Columbia.
Would a 2013 TB20 be more expensive than a Cirrus if they could sell the same volume?
I think the only reason Cessna didn't restart the advanced designs is because they never sold in sufficient numbers, it's all about volume.
Interesting comparison of efficiency. Now, didn't Pipstrel just claim that they've managed to break the laws of physics? 200kts at 10gph, too good to be true?
IIRC Cirrus decided against retracts because they only lost about 5kts with fixed gear while gaining substantial weight. Same story with the Columbia.
That's what I would tell everybody if I was Cirrus. I don't believe a word of it.
A Cirrus must be considerably cheaper to produce than a TB20 and Socata would have had to invest money to modernize the plane with G1000, new interior, etc. The market was not big enough and Cirrus did a few things right and now owns the complete market.
Beech still builds one or two Bonanzas a year but the price tag is huge and they are bankrupt now. So Cessna did something right, too.
