airdale
Pattern Altitude
- Joined
- Dec 30, 2007
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airdale
As I was putting together yet another power settings kneeboard chart for yet another airplane, I came to the following tentative conclusion: All these charts with seas of numbers for different altitudes, MP, and RPM are way more information than I need.
For normally-aspirated flying in roughly the 4K-10K feet, I need only the following:
Rationale:
This is really not a new idea, the Mooney Safety Foundation training manual talks about a "key number" where, for example, any combination of MP + RPM/100 that adds up to 50 will give you 75% power in an M20J. Key number for 65% is 47%, etc.
Comments? Maybe I'm just the slow student in the class?
For normally-aspirated flying in roughly the 4K-10K feet, I need only the following:
- The lowest available RPM and associated manifold pressure for the two or three power settings that I might use. Say 55%, 65%, and 75%. So, six numbers total.
Rationale:
- One Engine RPM: The lowest RPM setting permitted by the POH minimizes noise and friction losses. Why would I use anything else in cruise?
- One Manifold Pressure: The manifold pressures for a given RPM at different altitudes differ by only small amounts. And why do I care whether I am exactly hitting 75.00% anyway? 76% or 74% would be fine. I can't read 0.1" increments on the MP gauge plus is it probably not anywhere near 1% accuracy anyway, so that's another reason to skip the fine details.
This is really not a new idea, the Mooney Safety Foundation training manual talks about a "key number" where, for example, any combination of MP + RPM/100 that adds up to 50 will give you 75% power in an M20J. Key number for 65% is 47%, etc.
Comments? Maybe I'm just the slow student in the class?