eBay

Ultra-Prop Blades - Molded high-strength, glass-reinforced composite. Color: Black. Tip-to-root length: 26-1/4 inches. (Makes a 59” dia. prop including hub). Score lines provided ½” apart near tips for cutting to custom diameters down to 48”. All blades identical and interchangeable. Hub can be setup for almost any bolt pattern. Right hand tractor setup with 18 degree pitch blocks, pitch blocks can be ordered to change pitch from company, I believe they are 7 dollars per pair and 3 pairs is needed to change pitch for all 3 blades.

Recommended RPM for this pitch and prop blade length is 1900 rpm as it is configured now, blades can be down sized to 52 in and 3100 rpm, see chart below.

Diameter	18° pitch	16° pitch	14° pitch
59"	1900 RPM	2400 RPM	2700 RPM
58"	2050	2450	2700
57"	2100	2700	3100
56"	2250	3100	---
55"	2400	---	---
54"	2550	---	---
53"	2800	---	---
52"	3100	---	---

Sample Calculation Using Charts

Use these charts to find the number of Ultra-Prop blades and their angle of pitch to match your specific ultralight.

To begin, you must know your propeller RPM, your engine HP and the diameter of your present prop or diameter that will match your airframe structural limit.

The following typical data is used in our calculation example:

Engine: Rotax 277, 25 H.P. @ 6200 RPM
Reduction Unit: Integral Rotax gear box 2.58:1
Prop RPM: 6200/2.58 = 2400 RPM
Prop dia.: 56 in. (assumed airframe structural limit)

First, we solve for a 59" dia. Ultra-Prop (See Chart A). We find that the 2400 RPM line intersects with a 25 HP curve in the 2-blade, 3-blade, and 4-blade envelopes. Reading the locations of these 3 points (circled) on the pitch degree lines identifies three 59" dia. Ultra-Prop options as 14 degree 2-blade, 11 degree 3-blade, or 9 degree 4-blade. To solve for a 52" dia. Ultra-Prop (See Chart B) we find that the 2400 RPM and 25 HP intersections identify only two different options: 18 degree 3-blade, or 13 degree 4-blade.

Since our example requires solving for a 56" dia., we must interpolate between the 52" and the 59 " dia. data we read from the two charts. A table such as the following is helpful:

		3-Blade
Prop Dia. (")		52 56 59
Pitch (degrees)		18 (14) 11
Thrust (lb.)		163 (179) 182

To complete the table for 56" dia. (that is, to insert the numbers in parentheses), we note that this diameter is 56-52/59-52 = 4/7 = .57 of the way up from 52" dia. The pitch angle for 56" dia. can be approximated as follows:

For the 3-blade prop:
Incremental pitch angle = .57 (18 deg. - 11 deg.)
= .57 x 7 deg. =4 deg.
Pitch at 52" = 18 deg. minus incremental pitch decrease of 4 degrees equals 14 degrees.

We must subtract the 4 degrees from 18 degrees since we are going up 4/7 to 59".