SR20 cruise performance

I would be intertested if other SR20 customers are happy with the cruise speed of their aircraft, because our SR20 (C version, 3-blade-prop) really cannot keep up with the book specs.

At standard temperature and 2500 lbs weight, it normally lacks about 5-6 knots and if temps are high and weight are high it even lacks 8-12 knots!

Therefore, we sometimes don’t even reach the 150-knot mark.
Because engine gauges might be inaccurate, I think a good benchmark is to climb to 8000 feet pressure altitude, feed in full power and lean to 75° rich of peak (normally about 1375° EGT on our aircraft). This gives us 155 KTAS in winter and 153 KTAS in summer.

Would like to know your exact observations. Thanks.

I would be intertested if other SR20 customers are happy with the cruise speed of their aircraft, because our SR20 (C version, 3-blade-prop) really cannot keep up with the book specs.

The 20, unlike the 22, does not usually seem to be able to reach the book values. I typically see 150-155 KTAS. Do make sure the plane is clean, however; dead bugs and dirt will easily rob you of five knots or more.

Agree with Dave Katz’s comments.

Also, when I compute TAS on Garmin it seems to be about 3 or 4 knots faster than TAS indicator.

Also, I think forward CG works against attaining max TAS. Wonder about some kind of weight in cargo area. Anyone experimented with this?

I would be intertested if other SR20 customers are happy with the cruise speed of their aircraft, because our SR20 (C version, 3-blade-prop) really cannot keep up with the book specs.

At standard temperature and 2500 lbs weight, it normally lacks about 5-6 knots and if temps are high and weight are high it even lacks 8-12 knots!

Therefore, we sometimes don’t even reach the 150-knot mark.
Because engine gauges might be inaccurate, I think a good benchmark is to climb to 8000 feet pressure altitude, feed in full power and lean to 75° rich of peak (normally about 1375° EGT on our aircraft). This gives us 155 KTAS in winter and 153 KTAS in summer.

Would like to know your exact observations. Thanks.

Cram 50 or 60 lbs. in the cargo and your bird will cruise a bit faster.Also if vfr and for example your cruise will be at 8k.Climb to about 8,300 ft. then come back downhill to 8k.Instead of leveling off at 8k and waiting for your speed to lumber back up.This gives the bird a bit of a bump of momentum. go try it and post your results here. -j

Philipp,

I thought about a lot of what has been brought up in the posts below way too much when I was flying gliders, so I can reiterate a couple of things. First, a more rearward CG will make your plane faster. Most competition gliders have small water tanks in the tail for exactly this reason. We always try to keep the CG on the aft limit for maximum glide performance. A rearward CG will also make your plane more difficult to recover from a spin. Gliding performance was improved for the reason Gordon reported below, less drag from the elevator having to provide less downforce to counteract the heavier nose.

Second, bugs, dirt, dust or rain drops are all enemies of laminar flow airfoils. Your entire plane must be absolutely clean, not just the leading edges of the wings. To give you an idea of how much this matters, it was well documented by the use of drag probes on gliders that glide performance can drop by as much as 15% with significant bug accumalation. Some competition gliders actually have small devices the pilot can deploy from the wing root area that scrape the bugs off the leading edges while in flight.

All that being said, 8-10 knots does seem like a lot to be coming up short and I don’t think you are going to find it moving the CG around or wiping the wings.

You might take a look at both ailerons and flaps when nuetral to be sure they are dead even, check the gear fairings for security, etc.

If you don’t see anything suspicious, I would start recording some accurate numbers in flight and talk to CD. They will probably be able to home in on the problem.

FWIW,

Greg

I would be intertested if other SR20 customers are happy with the cruise speed of their aircraft, because our SR20 (C version, 3-blade-prop) really cannot keep up with the book specs.

At standard temperature and 2500 lbs weight, it normally lacks about 5-6 knots and if temps are high and weight are high it even lacks 8-12 knots!

Therefore, we sometimes don’t even reach the 150-knot mark.
Because engine gauges might be inaccurate, I think a good benchmark is to climb to 8000 feet pressure altitude, feed in full power and lean to 75° rich of peak (normally about 1375° EGT on our aircraft). This gives us 155 KTAS in winter and 153 KTAS in summer.

Would like to know your exact observations. Thanks.

Because both Cirrus products are nose heavy, loading closer to the aft part of the envelope will most certainly help. Keep in mind that book numbers are normal day (ISA), mid weight loading, etc.

Here’s a great article on aft loading:

http://avstop.com/AC/FlightTraingHandbook/EffectofLoadDistribution.html

For those keeping track, my partners and I are taking delivery of SR22 contract #95 (S/N 91) on Sept 18.

Chris SR22 N747SJ

Agree with Dave Katz’s comments.

Also, when I compute TAS on Garmin it seems to be about 3 or 4 knots faster than TAS indicator.

Also, I think forward CG works against attaining max TAS. Wonder about some kind of weight in cargo area. Anyone experimented with this?

I would be intertested if other SR20 customers are happy with the cruise speed of their aircraft, because our SR20 (C version, 3-blade-prop) really cannot keep up with the book specs.

At standard temperature and 2500 lbs weight, it normally lacks about 5-6 knots and if temps are high and weight are high it even lacks 8-12 knots!

Therefore, we sometimes don’t even reach the 150-knot mark.
Because engine gauges might be inaccurate, I think a good benchmark is to climb to 8000 feet pressure altitude, feed in full power and lean to 75° rich of peak (normally about 1375° EGT on our aircraft). This gives us 155 KTAS in winter and 153 KTAS in summer.

Would like to know your exact observations. Thanks.

Yes, rearward CG is faster. Lower required downward force of stablizer/elevator = lower drag = higher speed.

No, the old “step” theory that over-climbing and coming back down to altitude results in higher TAS was long ago debunked. If it gives you jollies go ahead, but you won’t go any faster.

Gordon

Cram 50 or 60 lbs. in the cargo and your bird will cruise a bit faster.Also if vfr and for example your cruise will be at 8k.Climb to about 8,300 ft. then come back downhill to 8k.Instead of leveling off at 8k and waiting for your speed to lumber back up.This gives the bird a bit of a bump of momentum. go try it and post your results here. -j

Is there an opportunity to communicate disagreement more tactfully?

Yes, rearward CG is faster. Lower required downward force of stablizer/elevator = lower drag = higher speed.

No, the old “step” theory that over-climbing and coming back down to altitude results in higher TAS was long ago debunked. If it gives you jollies go ahead, but you won’t go any faster.

Gordon

Cram 50 or 60 lbs. in the cargo and your bird will cruise a bit faster.Also if vfr and for example your cruise will be at 8k.Climb to about 8,300 ft. then come back downhill to 8k.Instead of leveling off at 8k and waiting for your speed to lumber back up.This gives the bird a bit of a bump of momentum. go try it and post your results here. -j

Is there an opportunity to communicate disagreement more tactfully?

No need to - it’s Jeff!