Thank you Sergeant.
Your knowledge on the Spit is truly remarquable.
You are right, +12 psi maximum for brief moments like takeoff, and climb: +6.25 to 2600 rpm.
The challenge is to read the pressure when opening full throttle, the needle stops at the mark-4psi, which really corresponds to 5 psi ... How can I do after what real boost is applied beyond 5 psi?
I'm really shy.
A question comes then, is it appropriate to reduce the power, when after takeoff, I will increase the propeller pitch to reduce rpm?
An example: I take off with +6.25 psi of boost and 3000 rpm.
Once 140/160 mph reached (undercarrier up), I want to set up to climb power.
Normally, I have slightly to reduce the boost before change the pitch to 2600 rpm, and then applying +4 or 5 psi of boost, in order to not exceed the maximum torque.
But if my Merlin can support +6.25 psi at 2600 rpm, why not go directly to the right rpm, without decrease power juste before?
Although I feel that I would never inflict such a thing to my poor Merlin...
But in this case where I am a good student
, what strategy to adopt when one wants to reduce the rpm?
This little following rule could be pertinent: reduce power before rpm, in the same ratio?
My set up after take-off is 160 mph, 3000 rpm and 6.25 psi.
I want to switch at 2600 rpm.
1) I decrease my absolute intake pressure (14.5+ 6.25) / 3000 * 2600 = 18 absolute psi. (14.5 for atmo pressure at sea level)
18-14.5 = + 3.5 psi of boost.
2) Once my boost to 3.5, I can quietly increase speed to 2600 rpm, keeping a constant torque in my mind.
3) Ajusting slightly power to get a correct couple rpm/boost
What do you think about?
Thank you for supporting these banalities of a beginner. And sorry for my bad English, I should have learned better in school ...