582 Problems

[Morph]

You will, you won't, more pitch, less pitch

Cruise speed is governed by wing design primarily, and secondly by have a motor capable of flying the wing at that speed.

A finer pitch gives you a higher static rpm, and a better climb. It's similar to a car, climbing a hill in 4th vs 5th, i.e. the lower the gear, the easier the engine runs, albeit at a higher rpm and the easier it climbs the hill.

Once over the crest of the hill, change to 5th for a better cruise (better being lower rpm required for the same performance) If you stayed in 4th you could still achieve the same cruise, except with a higher rpm. This would typically use more fuel. But this is not always the case.

On the other hand if the engine is over pitched, then your static would be low, the pax rpm achievable would be lower than before, and the engine would be labouring. In A climb you would be sitting there full throttle, sucking a moeroffa lot of fuel and going nowhere, until to get to the top of the climb and settle down and then slowly the plane would speed up and become more efficient.

It is quite conceivable that if the prop is heavily overpitched, the static would be drastically low, and max rpm would be insufficient to even attain cruise speed. On the other hand you could have the pitch too fine, static too high, max RPM exceeding the max allowed for safe operation and it too would be unable to attain the cruise speed without overrevving or running out of revs.

Pitching also affects the engine running temps. Overpitching, pushes the EGT's up and underpitching the opposite

So what is it, a very fine pitch would give a great climb but on the straight require higher rpm, course pitch bad climb lower rpm on cruise. Actually in the middle. If you look at the power band of the motor on a 503 your peak torque is at 5500rpm and peak power at 6500rpm. It makes sense to pitch the prop in such a way that your engine is at cruise close to your peak torque settings. This is where the engine is producing the most performance for the amount of fuel being fed. You also want to be able to hit max RPM in takeoff to get the max power. The ideal settings for a 503 is 6250 Static, this will give you 6500 to 6800 at WOT. Once in the air 5200 to 5800 gives you your cruise envelope with more than enough spare rpm for climbs

Through experience I have fiddled with a ground adjustable prop and with fuel flow and engine management and found with the above setting I managed to get the best fuel consumption. Over pitching, giving me a static of 5800 I would get 22l/h at this rpm. At cruise (5000 rpm) I would get around 15l/hour. Setting my engine up correctly I would get 6500 on take off at 22l/h, at 5800 cruise I would get 13l/h at 75mph and at 5000rpm, 60mph I got less than 10l/h on a 503. This same rpm gave me 15l/h when over pitched. Additionally the motor ran much cooler, as there was less loading. Much happier all round.

[Morph]

Note in the case of a Bush baby or Cheetah, 582 versus 912, there is a difference in published cruise speed. On the BB there is about 10mph difference between a 582 BB and a 912UL BB in cruise. A 582 would cruise at 75mph and a 912UL at 85.

In reality the same airframe with the same wing will fly faster with a 912 than with a 582, why? Purely because the 582 doesn't have enough power to fly the wing at it's higher cruising speed without being over revved and even then if it did get there it might run out of revs.

[Flooi]

Santana.

If your 582 is running rough at full power and high revs, and your prop is balanced, it mst likely
indicates that your engine is running too rich. At Reef altitude, the washers should be in the second
slot from above when holding the carb piston with the needle pointing down.

[Flooi]

Santana.

If your 582 is running rough at full power and high revs, and your prop is balanced, it most likely
indicates that your engine is running too rich. At Reef altitude, the washers should be in the second
slot from above when holding the carb piston with the needle pointing down.

[Duck Rogers]

I don't quite agree that you'll get the same airspeed.

Example:
Same throttle setting, same rpm
Let's say a prop of 68x40. One revolution of the prop = 40 inches forward.
Let's say a prop of 68x44. One revolution of the prop = 44 inches forward
Draw your own conclusions

[Morph]

Agreed, that's why I used the gearbox analogy. The finer the pitch, the higher the required rpm to reach the same cruise. If the pitch is too fine you might even run out of revs before being able to reach cruise

When I flew my 912 back from Loeries the prop was pitched very course, static of about 4500. Climb was horrendous but she cruised at 85mph at 4000 rpm, burning 15l/h

Back at Morning Star I repitched the prop, giving me a static of 5450rpm. Now the climb is awesome but she needs 5000 rpm to reach 85mph. Guess what my fuel burn is........13-15l/h. By unloading the motor she is running sweeter, with more power and the same fuel consumption.