Is this correct?

[rga]

Today I found out that a Hurricane Rotol or Spitfire MkII has much greater speed (at least 20mph faster) at 2400rpm and boost 5 than full throttle, maximal rpm (3000)
I always thought if you want to get fast, you fire-wall your throttle and let the engine fried.

[robtek]

To fry the engine thats the right way, like racing your car in first gear.

For top speed the propeller needs to bite more air per revolution -> coarse pitch.

Also a fried engine really doesn't deliver much power, so keep your manifold pressure below the "fry engine" limit.

For details you've to ask our anglo-saxon brethren.

[CaptainDoggles]

Originally Posted by robtek

To fry the engine thats the right way, like racing your car in first gear.

For top speed the propeller needs to bite more air per revolution -> coarse pitch.

I always hate it when people use the car analogy. This is not true for Constant-Speed units.

Originally Posted by CaptainDoggles

I always hate it when people use the car analogy. This is not true for Constant-Speed units.

I agree emphatically. For max performance (for both climb and top speed) you need the engine to be delivering the most power possible to the prop. This is typically the maximum allowed rpm for an aircraft engine. The constant speed prop governor will then vary the pitch between low and high as necessary to maintain that rpm, maximizing the thrust for any given situation. The only car analogy that fits in this case is a car with a continuously variable transmission, but people almost universally reference simple manual transmissions in their descriptions.

[41Sqn_Banks]

Originally Posted by rga

Today I found out that a Hurricane Rotol or Spitfire MkII has much greater speed (at least 20mph faster) at 2400rpm and boost 5 than full throttle, maximal rpm (3000)
I always thought if you want to get fast, you fire-wall your throttle and let the engine fried.

As both metioned aircraft have a Rotol Constant Speed Propeller highest boost and highest RPM should give you highest (horse-)power and highest speed.

[robtek]

But Banks, to reach and hold 3000 rpm the prop has to have fine pitch, not very efficient.

[41Sqn_Banks]

Originally Posted by robtek

But Banks, to reach and hold 3000 rpm the prop has to have fine pitch, not very efficient.

In the case of a constant speed propeller the RPM stays constant and the pitch depends on your airspeed. At low speed the pitch is fine, at high speed the pitch is coarse.

With a constant speed the car gear anaolgy fails, you have to think of a car with automatic gear where you choose between a economic and sports "mode".

[TomcatViP]

Cte means that the mechanism will hold the rpm you hve selected despite any minor variation in speed. It's not Auto-prop pitch.

This has been alrdy explained (by Maddog ?) elsewhere on this forum.

[jf1981]

Originally Posted by rga

Today I found out that a Hurricane Rotol or Spitfire MkII has much greater speed (at least 20mph faster) at 2400rpm and boost 5 than full throttle, maximal rpm (3000)
I always thought if you want to get fast, you fire-wall your throttle and let the engine fried.

Note boost decreasing over 2650 rpm. I've noted this speed to be optimum.
In reality, you wanted to damage your motor by running it fast for too long.

However taking off done 3000 rpm since you have maximum thrust with minimum torque effect at that rpm setting hence less unbalance. After that reduce, you may use 2800 but 2600 seems fine. Spit IIA you could push the red button preventing throttle to reach its maximum inside cockpit. Then it enables over boost which requires max 2600-2650 rpm for safe use, higher rpm and you'll burn the engine.
There's something similar to a bug since you can use this overboost constantly without any problem, or maybe the engine was fine with this, not sure.
You'll exceed may temp at high boost and high altitude, keep oil 90C or less and coolant 120C max.

[phoenix1963]

In RL, Merlin pilots would set their RPM to 2800-3000 prior to combat.
The point is that 2600 rpm IS about optimal for thrust, but if you momentarily slow down (e.g. in a combat turn), 3000 rpm gives you (non-steady-state) an edge in unplanned slow manoeuvers.
It's a sort of insurance policy!

56RAF_phoenix