My Repitched Prop

When I bought 70L, I discovered that the top speed of the plane was somewhat faster than I had expected. Then I discovered that its climb performance -- how fast it will climb when taking off or how fast it will climb from one altitude to another -- wasn't as good as I expected it to be.

It turned out that 70L had what's known as a "cruise prop". Propellers are not flat but are, instead, twisted a bit. The length of the propeller (70L's propeller is 76 inches long) and the amount of twist in the blades determines it's performance characteristics. A cruise prop is a prop that is designed to give maximum speed when cruising along in the air.

Conversely, a "climb prop" is designed to give maximum takeoff performance but can't deliver as high a top speed as a cruise prop. Since I enjoy landing at and taking off from short strips, including short grass strips, I wanted 70L's performance to be less oriented towards top speed and instead shifted back toward climb performance. When a strip is short and surrounded by trees, it's good to know that you can get off the ground and over the trees in time. :-)

The solution: instead of buying a new propeller (the cost of propellers starts in the thousands of dollars and goes up from there), I decided to have the propeller overhauled and "repitched". As a propeller ages, it invariably picks up a bit of damage. A spinning prop can easily throw small stones and gravel into the air on an unimproved runway and these can damage the prop. Each year, when a plane has its required annual inspection, the mechanics are obligated to examine the prop and file out any particularly bad damage. Some mechanics are better at this than others.

70L's prop had been on the plane for a long time. We're not sure if it's the original prop from 1966 (we suspect not) but it showed the inevitable results of years of wear. Overhauling the prop resurfaces it and smooths out the prop and restores all of the correct angles. It essentially makes the prop close to new again. I also wanted it to be repitched -- twisted a little bit more to make it a bit more like a climb prop.

We got the prop installed today and it's beautiful! It looks like a brand-new prop. It also has made a huge difference in 70L's climb performance. Where before it would lift off the ground, today the plane was leaping off the ground. :-) I'll find out soon how much I've paid in terms of lost top-end speed but it shouldn't be too terribly much. Whatever it is, I will gladly accept it for 70L's new-found ability to leap free of its earthly shackles.

You can see the newly-overhauled prop in the picture posted above. :-)