How does the F4U-1A beat the Spit 16

[hitech]

I kind of see what you mean though. The conversion from horsepower to thrust is not exact because the propeller still has to cut air and it's not a 100% efficient transfer of force from the engine to the surrounding air - the turbulence caused by the prop reduces the efficiency.

Whereas a jet's thrust can be more easily measured by finding the output, I'm guessing? The output from a jet seems to be a more efficient transfer of engine power to usable thrust.

boomerlu, it is more because on a constant speed prop the basic thrust equation is T = (HP / Speed) * PropEff.  Hence thrust changes drastically so terms like Trust to Weight must also specify a speed. Prop design can drastically effect the PropEff at different speed. Think Helicopter as an extream example Its thrust = weight at zero Vel. But if you would view it moving vertically with out gravity. Your PropEff would drop of very quickly as speed increases. Vs a high speed fighter whos PropEff at very slow speeds is extremely low but is very high at higher speeds.. In many ways it is just using the generic term torque with out giving an rpm with an infinite ratio gear box.

Jets tend to be much more constant thrust, and hence there HP increases with speed.

HiTech

[boomerlu]

boomerlu, it is more because on a constant speed prop the basic thrust equation is T = (HP / Speed) * PropEff.  Hence thrust changes drastically so terms like Trust to Weight must also specify a speed. Prop design can drastically effect the PropEff at different speed. Think Helicopter as an extream example Its thrust = weight at zero Vel. But if you would view it moving vertically with out gravity. Your PropEff would drop of very quickly as speed increases. Vs a high speed fighter whos PropEff at very slow speeds is extremely low but is very high at higher speeds.. In many ways it is just using the generic term torque with out giving an rpm with an infinite ratio gear box.

Mm... more to read about on wikis. Thanks. Out of curiosity - what are some general ranges of the PropEff number?
From a theoretical standpoint, it looks like it should be (0,1). What are some "normal" ranges for aircraft, e.g. ours in Aces High?

Jets tend to be much more constant thrust, and hence there HP increases with speed.

Yup, this is why I'm guessing with the advent of jet engines, aircraft stats started to quote thrust rather than HP.

[hitech]

0.80 is a good starting point for most speed ranges. Those being best climb speed to max level speed.

HiTech

[boomerlu]

Cool thanks! I'm actually surprised to see prop efficiency is that high. After I learned thermodynamics, I kind of got used to the idea that most things are very inefficient.

[Stoney]

Cool thanks! I'm actually surprised to see prop efficiency is that high. After I learned thermodynamics, I kind of got used to the idea that most things are very inefficient.

Theoretically, prop efficiency is very bad at low speeds.  Its a very dramatic curve, with your 75-80% peak efficiencies coming near a planes best speeds, like Hitech said.

[Badboy]

Thanks. Out of curiosity - what are some general ranges of the PropEff number?

Here is a prop chart for the F4U-1 as an example...



At 100mph (close to the stall speed) the advance ratio is 0.55, so the efficiency can be read from the chart at 59%. The maximum efficiency is just over 83% at an advance ratio equivalent to about 300mph. In general, you might expect prop efficiency to vary between about 40% and 85%.

Badboy

[Reschke]

I'd much rather take a crossing snapshot from the Spixteen's gun package into the wing of a Hog than I would a snapshot from a Browning 6-pack into the wing of a Spit.

Didn't read all the way through but this snapshot on a pusfires wings has been very effective for me on the crossing shot.

[Enker]

Didn't read all the way through but this snapshot on a pusfires wings has been very effective for me on the crossing shot.

Agreed, their wings are like peanut brittle. Peanut brittle being pounded with a .50 caliber sledgehammer.