I’m “thinking” about a Cirrus (without having ever sat in one, much less driven from the left seat). In reviewing performance characteristics, I’m very curious about an anomaly I can’t find any background on: The SR22T has a longer takeoff distance and lesser climb rate than a non-turbo SR22 (according to the manufacturer’s website). Why???
With identical airframes and MTOW’s., and with nearly identical power ratings (315 vs 310), it makes zero sense to this engineer that takeoff roll for a 315hp turbo is almost 50% longer than for a 310hp non-turbo (1,517’ vs 1,082’) AND rate of climb is (modestly) less at 1,203 FPM vs 1,270 FPM. The fact that the turbo make about 10% more torque than the non-turbo (315hp @ 2,500 vs 310hp @ 2,700) doesn’t help my confusion.
Is it possible the composite prop of the turbo is significantly less efficient than the aluminum prop of the non-turbo? That doesn’t make sense to me either, but it’s the most logical explanation I can come up with.
In a car for example turbos are often used to increase horsepower from base models such as a turbo Porsche having more performance than a NA 911.
In the Cirrus HPs start the same and the turbo robs a bit of power and efficiency at sea level. In a high DA or higher altitude the turbos maintain 315HP and have a substantial advantage.
Historically on a standard day the NA planes beat the turbo to 8-10k, but most days are not standard.
Rerun the numbers for your typical mission. For fun run the numbers on a hot day at Telluride!
You analysis is spot on for standard days at sea level. But, if you add hot and high or cold and icy to the mixture , a turbo FIKI will “quite a few times” outshine NA FIKI.
The SR22T rotation speed was increased a few years ago and that results in most of the longer take off roll.
The pumping losses in the Turbo system are significant, once the Turbos start doing some work, they quickly pay overcoming the parasitic losses after a few thousand feet.
In other words, we can’t get all 315hp to the prop down low.
I don’t know if true for the Ts, G5/6 NAs etc., but maybe you can comment. The G3 Composite prop supplement mentions that aircraft fitted with this prop require higher IAS for cooling in the climb. I would think that the NA with the std prop could climb faster down low if flown at a lower IAS/ higher deck angle. But, if you slap a composite on an NA, I wonder if they too must be flown faster in climb (lower rate of climb).
I honestly don’t know the parameters where we need higher IAS with the composite prop. The TN manual does indicate a change from 120 to 130 knots at 7,000’msl. The SR22T is not specific about the altitude for transition to 130 knots but does show a range of speeds between 120-130
I have a G3 NA with a composite prop and my current record is a 40c takeoff. The DA was 7,000 feet at the field and I was at full gross. Very glad to be in Midland, TX that day, where anything above 6’ AGL is man made. My CHTs were 340 on takeoff and 380 before I lowered the nose to 130 indicated, yielding a solid 300-600 FPM climb. Generally don’t see more than 350-360 degrees in the climb between 120 and 125 indicated, producing 600-800 FPM. I do see the mention of higher climb speeds in the supplement but based on my experience, 120 indicated keeps the CHTs below 360-365 on all but the hottest days.
I’m gonna win the lottery tonight and just get a Gulfstream so I don’t have to deal with this anymore.
The NA SR22 will outclimb the Turbo at lower altitudes, up to 8K or so. Where my home field is 6200 and I’m virtually ringed by 10K ridges the Turbo climbs over those mountain ridges much better. Also in the real world, takeoff at those alts are better with the T (mine is a TN)
I just returned from a sea level journey and am always fascinated at the quick pop up on takeoff and what seems like the plane nearly parks in the sky on landings, compared to higher altitude fields