1. ## Mapped 15/20R vs. stock prop blade profile: surprising results

Ok, so now I have a few props to measure and try and I'm seeing some very strange and interesting things. I've been plotting the blade profiles by measuring the heights every 20 mm of linear tip length. You get 8 data points with the first and last 5 mm from each end. You can then easily calculate the leading edge and trailing edge angles using trig. The props I have are:

Stock (measured around 13/19.5) - 69 mph at 8100 rpm
Stock repitched to 16/24 - 76 mph at 8100 rpm
15/20 out the box (measured dead on 15/20) - 77 mph at 8100 rpm
15/20 repitched to 15/24 (measured 15.5/23) - testing this Sunday

The big surprise here is that the 15/20 has a nearly identical blade profile at the tip to the stocker. The blades measured out withing 1 mm of each other. Basically, you can plot the profile of the 4 stock blades with 1 15/20 thrown in the mix and you can't tell the difference.

Clearly, there is much more to prop performance than the leading edge and trailing edge angles. . .

Mike

2. Originally Posted by engineermike
Clearly, there is much more to prop performance than the leading edge and trailing edge angles. . .

Mike
Exactly, root angle plays a huge role in it (where the blade meets the hub)

3. Jerry, is the root of the 14/19 so different from the 15/20 that a guy cant buy a 14/19 and bend it as he mods and get the results?

or get a 15/20 and bend it back until he mods his craft?

Mike, very nice work!

4. Originally Posted by dav_dman
Jerry, is the root of the 14/19 so different from the 15/20 that a guy cant buy a 14/19 and bend it as he mods and get the results?
I also happen to have a 14/19 that was re-pitched to 15/20 (haven't mapped it yet) and it goes 74 - 75 mph at 8100 - 8150 rpm.

Mike