Cruise Setting for Normally Aspirated 337

[cjordan]

I try to keep things easy to remember. 73 "G" with long range tanks. All give ~6hr range with decent reserves.

2300 23" to 6k 20gph
2400 full throttle to 9k 18-18.5gph
2450-2500 " " to 11k 18gph

No hurry, tooling around down low 2200 20" 14gph

They seem to like the 7-10k range for best TAS and fuel burn for longer trips.

[patrolpilot]

Well, the insight G4T has already solved a big question for me. My Cessna tachometer sucks. The only place it is accurate is at 2800 RPM, and it quickly starts to error short of what is being produced.

I've been running around with 2600 RPM set, but the engines are only turning 2400. That explains the angle of attack issues at lower RPMs because the error is as great. The only hard running would have been down low, like in the picture (2K) as the MP would have been high. That would not be a problem at my normal cruise altitudes.

Yep, I do monitor the idle RPM, and the check indicates higher than the book, but the idle was set by maintenance with a digital tack, and they have that just right sound. I never drew the connection in that the upper is limit is true.

My Cessna Fuel Flow Indicator is spot on. This doesn't confirm my next expense concerning my airplane, a move to the Electronic International Primary Engine Instruments.

I wish we could add inline images on the forum

[Mayhemxpc]

Thanks for another reason to get a G4T. Great picture. I had my tach and prop checked during my most recent annual. Actually it was part of calibrating the fuel system after that was overhauled. One were off by a little less than 50 RPM, which doesn't bother me too much as I am probably not that précise in my control manipulation. 200 RPM is quite a spread, however and I can see where you were having problems.

For what its worth, I have an O-2A and 65% power is about 23"/2300 RPM at 3,000 ft. That is also the power setting the USAF functional checklist says to use for post-maintenance test flight. Other altitudes and power settings are similar to what was posted by Ernie. The O-2 is pretty draggy and, to me anyway, the minor increase in speed at 75% is not worth the noise and fuel burn.

[hharney]

No claim to the content but very interesting formula


Using the Airspeed Indicator as a Fuel Flow Meter

[Mayhemxpc]

As everything with Stick and Rudder, very interesting. I compared it to the USAF Dash 1 for the O-2A. Best glide is 100 kts at 4400 pounds. The performance charts say best long range airspeed is 104 Kts CAS and best glide is 99 kts at the same weight!

Similarly, at 4400 pounds, service ceiling is 17,500 ft. 2/3 of that is 12,000. By the book, at 12k max MP is about 17 to 17.5 which is the power you need to get ~104 kts CAS! (126 KTAS) Seems like 1944 rule of thumb calculations for SEL planes were still valid 25 years later for MEL!

I don't carry oxygen, but the dash 1 shows 110 kt CAS at 8,000 still gets me 124 KTAS at 8.2 gph/engine. That is just a little slower that 12k at 1/2 a gallon more per engine per hour. But I can breathe, which is a good thing.

But...20 minutes longer for a 300 nm trip vs my normal cruise at 65%.

[general]

Aspirated = 25 Cruise all the time, 336, 337, 02