Prop pitch and length

Hi guys,

Im a rookie on these things still so I need your help.

Ive got problems understanding this prop business, you know, when you guys talk about 75" or 50" or somewhat.

What to all the numbers on a prop mean, and how does the pitch work? More pitch, more speed, or more pitch more climb... etc... Ive never tought asking, but id like to be able to understand exactly!

Thank you guys so much!

Cheers

Fred

In example a 8242 prop would be 82 inches in diameter and 42 pitch.The less pitch the faster it will turn and usually produce more takeoff thrust.I always think of it as an airplane wing,the flatter the pitch the faster it will spin.For cruise you want more pitch.The more pitch the less rpms but more speed.In a constant speed propped airplane you would have flat pitch for takeoff and then increase pitch for cruise.

Canada;
Two numbers: the first is the length of the prop, tip to tip. Second number is the "pitch". This is the distance the prop would travel if rotated thru a solid medium (think real thick jello)...the greater the number the greater the distance the prop will travel. Higher number (pitch) will give higher airspeed, lower number (pitch) will give lower airspeed but better takoff performance.
Mike

prop pitch and length

ok i have a question i understand the numbers on the prop such as 82 x 45 but i dont understand how lentgh plays into it how does say a 76x 45 prop differ from a 82 x 45 prop? i know if i had a 76x 45 prop on it would over rev big time or lets say they were a 76 x 60 and a 82 x 60 i wouldnt be able to spin an 82x60 very fast it would take to much power what is this length doing? i thought what these props do is travel in the case of a 82x45 prop is travel 45 inches forward per revolution is that right? well if so does a 76x45 not also travel 45 inches forward per revolution?

Your on the right track Jay, now lets take it a step further. All this starts to make sense when you figure how much volume an engine can move. Lets take an O-320 for example. Assume it can move a maximum 1400 gallons (air is considered a fluid, so we'll measure it like a fluid) at 2700 rpm. So now we figure how much volume a prop makes in one revolution.

Take an 82x60, theoretically it moves 60 inches per revolution. So figure a cylinder 82 inches in diameter and 60 inches tall, that gives you a volume of 1,371 gallons. Pretty close to the engine's max of 1400 gal.

Now with a 76x60, you get 1,178 gallons. There is certainly room for improvement, either more length or pitch

In theory, a longer flatter prop will give you better take-off and climb performance. While a shorter more corse prop will give better cruise performance. Unfortunately nothing is ever this simple, there are a crap-load of other variables that have to be factored for proper length and pitch. But hopefully this will give you a better idea. I'm no engineer and don't claim to be, but I like trains. This is a semi-easy way to understand the correlation between prop sizes and an engine.

nkh

Blade profile also has a lot to do with it as well. Crash

All the above, and...

All else being equal, you'll get better T/O-climb performance with more diameter and less pitch (same RPM).

But, see http://www.supercub.org/phpbb2/viewtopic.php?p=72546&highlight=rpm+dia+mach#72546