OK to Lean to make TCDS Min RPM?
- Thread starter Ted K
- Start date
In general, no. Check your POH/AFM the aircraft configuration for a sea level take off or to check static RPM which its usually carb heat OFF, full rich mixture, full throttle at sea level for your average SEL. Leaning the mixture to obtain required RPM limits usually doesn't come into play until higher elevation or density values. And given the importance of what your static RPM is indicating its one of those checks you don't want to cheat at.
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Is this a mechanical tach?
Notorious for under-reading as they age.
Notorious for under-reading as they age.
pburger
Pre-takeoff checklist
I'm not an expert, and don't play one on TV. That being said, I don't see why not. What's the density altitude? It will affect power. Why wouldn't you be allowed to lean due to high altitude or in this case high density altitude?
Technically the static RPM is a certification point so the OEM will have some sort of procedure to check either in the POH/AFM Limitations or in the mx manual. However, at certain take-off elevations, there can be an OEM supplement instruction to that static check which does allow a mixture lean to obtain max RPM. For example, below is from a 172 POH:
Daleandee
Final Approach
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I see they give elevation but shouldn't this also apply to density altitude?
No idea. The 1st screen shot I posted is from the POH approved Limitations section. The 2nd shot is from Sect 5 of the POH. The mx manual procedure static check usually states take-off throttle and mixture. But I've never done a static RPM check above sea level. However, its my understanding any take-off throttle/mixture configuration must fall between the stated min/max static RPMs in the TCDS. I'm sure Cessna tech support could give a better explanation if interested.