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harisund
Mar-25-2014, 16:28
I am trying to get an understanding of the effects of both on engine efficiency/speed/temperatures etc.

If my understanding is correct, there's an optimum RPM range for each planes.And I have seen this message when searching --

"To obtain maximum speed you want to be able to apply full throttle at the lowest prop pitch % while keeping RPMs as close to power band/optimum range"

Why is this the case? Why can't I increase prop pitch % and decrease the throttle? Does that have the same effect?

Can someone provide me with some kind of explanation (or point me to links) where I can understand how the combination of throttle/prop pitch affect planes during take-off/landing; climbs/dives? ..

So far, my Googling has gotten me this far ->
1. Fine pitch 100%, small "bite" of air, needs less power from engine to quickly reach high propeller speed, kind of like 1st gear in a car.
2. Coarse pitch 0%, large "bite" of air, needs lot of power from the engine and so doesn't reach high propeller speeds, good for cruising.

To obtain maximum speed you want to be able to apply full throttle at the lowest prop pitch %, why wouldn't alternating both result in the same effect?

III./ZG76_Keller
Mar-25-2014, 16:39
You can do 50km/h in a car with your foot to the floor if you stay in first, you can also do 50km/h with just a touch of gas if you're in sixth gear. Which one do you think is better for the engine and fuel consumption?

harisund
Mar-25-2014, 16:50
You can do 50km/h in a car with your foot to the floor if you stay in first, you can also do 50km/h with just a touch of gas if you're in sixth gear. Which one do you think is better for the engine and fuel consumption?

haha that's a nice way to put it. I did see the comparison to vehicle transmission in a few places, but I didn't want to literally equate the two.

So, again, just to make sure my understanding is correct, if I want to rapidly gain speed (like passing a long truck in a car ... or take off/climb in a plane)... I use the equivalent of "low gear" .. which would be a fine pitch with a high throttle.

And if I want to cruise, or go high speeds (like in a dive) .. I use the equivalent of "high gear" .. which would be coarse pitch with appropriate throttle ..

Once again, to carry on the comparisons with vehicles .. if I stay too long with high throttle and fine pitch / high pitch %, I run the risk of burning up my engine quickly?

III./ZG76_Keller
Mar-25-2014, 17:28
So, again, just to make sure my understanding is correct, if I want to rapidly gain speed (like passing a long truck in a car ... or take off/climb in a plane)... I use the equivalent of "low gear" .. which would be a fine pitch with a high throttle.

And if I want to cruise, or go high speeds (like in a dive) .. I use the equivalent of "high gear" .. which would be coarse pitch with appropriate throttle ..

Once again, to carry on the comparisons with vehicles .. if I stay too long with high throttle and fine pitch / high pitch %, I run the risk of burning up my engine quickly?


Pretty much spot on. Just make sure you're always watching your RPMs (or listening to them as will come with practice).

Sometimes in a dive I use the propeller to slow my dive speed, basically a low throttle setting with higher RPMs. The resistance of the prop helps to cause a bit of drag thus reducing your speed and acceleration in a descent; it's harder on the engine though so if you're going to try that be very cautious.

*Thread Moved to more appropriate forum.

Roblex
Mar-25-2014, 18:29
An important thing to note is that not only does 100% pitch give you the best acceleration but it gives the best deceleration and so it is worth using when you enter the circuit to land because it gives you better control of your speed and quicker response. Following on with the car analogy though, don't go into 100%/1st Gear while travelling fast as it will over-rev the engine and blow it.

harisund
Mar-26-2014, 02:04
An important thing to note is that not only does 100% pitch give you the best acceleration but it gives the best deceleration and so it is worth using when you enter the circuit to land because it gives you better control of your speed and quicker response. Following on with the car analogy though, don't go into 100%/1st Gear while travelling fast as it will over-rev the engine and blow it.

hmm yeah .. .kinda reminds me of going into a sharp curve on a race track with a low gear knowing I will need the pick up right after the turn for the straight .. in the plane case, I am guessing one of the reasons is that if you screw up your landing you can quickly get back speed for a take off and retry the landing ?

Anyway, thanks for all your responses folks ! Very very helpful :) (And thanks for moving to the right sub forum as well)

Roblex
Mar-26-2014, 03:02
hmm yeah .. .kinda reminds me of going into a sharp curve on a race track with a low gear knowing I will need the pick up right after the turn for the straight .. in the plane case, I am guessing one of the reasons is that if you screw up your landing you can quickly get back speed for a take off and retry the landing ?

Anyway, thanks for all your responses folks ! Very very helpful :) (And thanks for moving to the right sub forum as well)

It is more like entering a corner with no brakes, you need to use engine braking and 5th gear would be useless. It is more about the response though. When you are landing you might need to speed up or slow down by 10kts to get the softest landing. Think how long it takes you to gain or lose 10kts while cruising at 50% or even 75% prop pitch.