In a 500 nautical mile flight, how does the normally aspirated SR22 compare with the Cirrus SR22TN turbonormalized aircraft? Is the SR22 more efficient than the SR22TN Turbo? Which plane consumes more fuel on the trip?
Reason 5 – Better NMPG Performance Cross-Country
The Cirrus SR22TN Turbonormalized delivers the best balanced performance. It offers better combined Nautical Miles Per Gallon (NMPG) and True Airspeed (TAS) performance than the normally aspirated SR22.
NMPG and TAS Performance over 500 NM
Note: SR22 NA altitude 8,000 and SR22TN Turbo altitude 16,000. (see SR22 POH, Section 5-24, Revision 2).
In this no wind example, the normally aspirated SR22 needs a flight altitude of 8,000 feet and 2600 engine RPM at 75% power for 180 TAS. The SR22 NA will arrive about 10 minutes later and use more fuel than the Cirrus Turbo.
For better NMPG performance the normally aspirated SR22 must give up TAS, use reduced engine power and accept a more extended time in cruise.
Last week’s post compared the normally aspirated SR22 climb performance versus the turbocharged Cirrus. It takes the SR22 NA almost twice as long to reach 16,000 feet, and at that altitude the normally aspirated engine cannot produce best power.
With piston engines, time-in-climb will affect a pilot’s choice of altitude. Normally aspirated planes breed a lower routine range of cruise altitudes best suited for the engine, and not so much weather considerations or comfort.
In the above no wind example, the Cirrus SR22TN Turbonormalized obtains 193 knots TAS at 16,000 with 2500 engine RPM at 75% power. The lower RPM is easier on the engine. And, the better TAS does not require a maximum engine power setting.
Overall, both high performance advance composite designs offer comfortable, fast, and efficient cross-country travel.
1) SR22 Normally Aspirated, Example 500 NM Cross-Country
2) SR22TN Turbo, Example 500 NM Cross-Country
see wikiWings, Reason 5 – Turbocharged Cirrus, February 6, 2013, Appendix for details
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