would like some technical confirmation

[SFRT - Frenchy]

 http://bbs.hitechcreations.com/smf/Smileys/default/Forum9/HTML/000643.html

For those who don't go to 'aircraft and vehicles' too often, I'd like to that some additional informations about what Flakbait is explaining. (it's about prop pitch).

I'd like more infos.

[texace]

I think that technically, prop pitch is the angle of the blades. Propeller blades are shaped like aircraft wings. As they spin, they generate lift behind them. This is how they are able to pull the aircraft. You can alter the angles to make them cut into more or less air. At low altitudes, you have about half pitch to get the maximum amout of power and good fuel economy. At high altitudes, where air is thin, you give it less pitch to save fuel because there's less air for them to bite. You can also move them to where the entire blade's face is against the wind, stopping the prop. Feathering. I think that at lower altitudes, you can save fuel by moving the blades a bit from middle pitch so they bite less air and save fuel. If you do to much pitch, you'd lose all pulling power cause they would lose their aerofoil type motion. The more pitch you give it, your burn more fuel cause the wind resistance would slow the prop. When your landing, you'd move the blades to bite alot more air so they'd get more lift at low speeds. If I'm wrong, someone clarify, but that's whaT I heard.

------------------
Lt. Col. Aaron "txace-" Giles of the 457th BG
    "Fait Accompli"

[Downtown]

I know a lot of U.S. Fighters were equipped with constant speed propellers (Curtiss made em.)  I do believe they did cause problems.  I thought having adjustable pitch would be better than speed adjustable.  WHen you are climbing you could adjust the prop to cut deeper and pull more air, and improve climb.

The Speed adjustment is about the same effect though better for increasing prop drag to slow the plane for landing.

------------------

"Downtown" Lincoln Brown.
    lkbrown1@tir.com    
 http://www.tir.com/~lkbrown1
Wrecking Crews "Drag and Die Guy"
Hals und beinbruch!

[SFRT - Frenchy]

Downtown, read my last post on the matter please. Constant speed props adjust their speed by changing their pitch blade angle. So what we have is constant speed props and it's the real thing. I believe that ur pitch change with no RPM change is an abuse of language.

Let me know if my explanations are not clear enought, I will re-explain the whole process.

[av8or]

In real life plane i.e. small regional t-props or small light singles the pilot will have direct control over prop speed the pilot sets in t/o power and prop high or flat pitch(low blade angle) now once off the ground the engine is not meant to run at max power for long so the pilot pulls the manifold pressure back to max. continus power and pulls the prop back to recomended speed(25/25 in non turbo GA aircraft)anyway once upto altitude the pilot pulls the manifold press back to cruise setting(best power or best fuel range for that alt.)and then pulls the prop back to match that setting.I have no idea what settings go with each airplane you have to look them up in the pilot operating handbook.anyway so for max climb you want a low pitch or flat pitch or prop high(high rpm)for climb for fuel efficiecy you want prop low or high angle of attack or again low engine rpm. now these props are called constant speed props do to the fact that the pilot sets the prop speed thus engine rpm too and the prop govenor maintains that setting by increasing or decreasing blade angle. now i will and can go more indepth but you all are probably asleep by now. i was in this secion back in mechanic school and in pilot school.

[arhurb]

I´m not a techie, but, for what it might be worth, here I go:

AFAIK, prop pitch work is similar to the gearbox of a car. Imagine an Auto transmission. The lower the gear, the lower the prop pitch, means maximum pulling power, minimum speed (T/O, climbing, accel ...) at a given rpm. On the opposite, the higher the gear, max prop blade angle, means minimum pulling power, but max speed (cruising, running...) at a given rmp level.

If that's wrong, please enlighten my less that .02c opinion.

Cheers,

Pepino

[Renfield]

Texace - a few errors in your post...

Pitch when given as a distance is the distance a prop would move forward in one revolution if it was 100% efficient - i.e. the distance it would move forward if it were turning in Jello.

At climbout is when you lower the pitch - like shifting into low gear. The blades are taking less bite with each turn but the engine is able to rev up a little more and put more power to the air.

At cruise/altitude the pitch is increased. This lets the engine turn slower saving on wear, tear, and gas. Each blade takes a bigger bite. Since you aren't trying to haul a few tons of aluminum up and up, less power is required.

The whole idea of variable pitch is to set the proper angle of attack between the blade and the apparent wind it sees. A slow plane that is turning up the engine very fast (i.e. climb power) will have a shallow blade angle because the apparent wind to the blades will be close to the plane defined by the prop arc.

A fast plane with lower RPM will be at high pitch because the apparent wind for the blades will be more closely aligned with the path of the airplane itself.

Feathering a prop turns the blades to where they align with the path through the air. The blades are not flat to the wind, they streamline similar to the wings of the plane itself. If you are looking at the plane from the front, the blades would look thinnest.

Fixed-pitch props generally have too much pitch at takeoff and are less efficient at climb but have too little pitch at cruise and thus get lower gas mileage and more engine wear.

[av8or]

well i guess that's a simpler way of putting it and it will work. i guess the Friendly Aircraft Association (FAA) wants me to know the technical stuff that not even i can understand with out a few days of studing it.

[Minotaur]

The cool part about all to this is that wooden propellors sometimes designed to "twist".  

Under stress conditions of high load high RPM (climb) the propellor will twist and the pitch becomes less.  

Under conditions of low load low RPM (cruise) the propellor will return to its unstressed (untwisted) position and have more pitch.

------------------
Mino
The Wrecking Crew

"So what do you post here? Poetic love letters?"
Ram

[Renfield]

Some of the composite/plastic props for ultralights do this too I think. They are molded at high pitch but flatten out as more power is put to them.

Also, some planes in WWII had the counterweight pitch adjusters - the little metal pucks would fling out at higher RPM to change the prop pitch. I think the Texan is one and the Hellcat is another but won't swear to that - but they are easy to spot - smaller prop hub and silver hockey pucks - one at the root of each blade.