Cruise Performance

[Chris007]

Hi all!

I noticed that the normally aspirated Plane is pretty underpowered compared to the tables in Cruise.

For example at max Setting (73%) in 10.000ft I get 172kts instead of 182kts! (2.900 lbs, ISA)

So it is approximately 10kts slower in different altitudes (for maximum power)

But the turbo version seems pretty spot on.

Any ideas or explanations?! Am I doing something wrong?

 

[Coop]

I'd recommend trying maintenance (via SR22 menu ->Maintenance tab, just to see if there is something there. I doubt it a 73% power is the expected power. You are looking at KTAS, not KIAS correct? (I would assume so, otherwise it would be excessively fast KTAS if you were getting 172 indicated). I'd say to also check your CG.

[Chris007]

I have tried maintenance already. But I will try to "reset" my plane. I think I have read about two files that need to be deleted?

At least according to the POH the power of 73% is correct. Just the speed is much slower, 172ktas vs 182ktas.

Interestingly if I throttle back to 66% then the speed loss should be 10kts. But in the plane here the difference to full power is only 4-5 knots. As a weird result, the figures at lower power are not so far off.

Thanks for your help so far.

[Chris007]

Hi,

I have reinstalled now and made sure that everything is fine, but unfortunately it didn't change anything. The top speed is always about 10-11 kts slower - it seems that the last 5-10% of power do not change much because the prop rpm increases to 2700 and the speed even decreases a bit.

However I noticed that if I do maintenance it states "replaced all tires...", or "cleaned and primed TKF porous panels" but it doesn't change anything. Because if I fly and do maintenance it always finds the same things to be repaired. This wasn't an issue at my very first install because the expected message was "engine entries, systems entries" so nothing to be done. I think after my first crash it changed and it continues to show up the same messages (even after reinstall).

[Chris007]

I have tested a different machine and it is still the same. Regarding the maintenance I guess the messages are normal and there is no way to find out what the actual state of the components were/if a maintenance was actually necessary?

Unfortunately it seems that the cruise performance is really far away from the actual numbers. (2000ft altitude 176 vs 186) Is this really a shortcoming of the modelling? I didnt expect this deviation in such a highly detailed engine modelling.

[Coop]

Something external must be going on, I've just loaded in those same conditions and got 183 KTAS over the ground. Can you send a screenshot of the engine page while at cruise?

[Chris007]

Hi Coop,

Attached 2 screenshots of the engine pages. (X-Plane 11.55, sr22 version 1.2.2)

EFM is turned on. Although I realized that efm is turned on automatically according to X-Plane Log.

[Chris007]

Have also other tested the performance with same conditions?

Or am I really the only one?

[andreasxb]

Are you sure you leaned it correctly for best power? It's hard to tell since you don't have the assist on in the screenshot, and I'm not sure whether fuel flow would be at the top of the green range at best cruise power.

[Chris007]

Yes. It is the best TAS that I can get.

Leaner or richer is anyway a difference of maybe 1 knot. If I would lean the mixture more towards the POH value of 23.3gph it would be a little bit less power.

[Coop]

Seems we've figured out that there is something going on with the Experimental flight model and Coefficient of Drag (Cd) with the SR22NA under high-power cruise settings. We've recalibrated the Cd curve and will push in the next update.

[Chris007]

Ok thanks for the information, good to know! Perfect.

One last question: regarding maintenance, I guess the messages i.e. "replaced all tires.." are always appearing no matter if something was actually broken before? Can I find out what the actual "wear" is and If a maintenance is necessary?

[Coop]

There are not separate inspections from the actual repairs at this time