A propellers performance depends on the distribution of blade angles along its radius. The blade angles must correspond to the advance ratio, the ratio of forward speed to rotational speed, plus an attack angle. For a fast climb, a low pitch is preferred. For slow climb, cruise and descent, a higher pitch is preferred. For moderate performance in all phases of flight, a mixed pitch might be preferred. I have measured the blade angles of several propellers. These reports may be useful in judging the performance of various props.

I will list them in order of increasing diameter.

**6″ Orange Chinese Prop**

Here is my plot of the blade angle versus radius fraction, r/R. Measurements were made at 1/4″ stations along the radius. The prop was rigidly mounted on a vertical shaft. Chord (c), leading edge (LE) offset above table and trailing edge (TE) offset above table were measured to the nearest 0.01″ at each station. Blade angle (B for Beta) was calculated trigonometrically. P/D was calculated from the usual formula.

B = arcsin((LE-TE)/c)

P/D = pi tan(B)r/R

Wobbles in the graph result from measurement precision limitations rather than manufacturing irregularities. The 0.01″ precision corresponds to about 1 degree.

The blade angle plots in the background are for helical props with the P/D as shown along the right edge. You can see by comparison with the helical plots that this is not a helical prop. The P/D ranges from 0.7 to 1.4. The washin at the tip is due to the sharply swept tip rather than twist of the basic shape.

I calculated the representative radius at 1.73″, 0.577 radius. The corresponding P/D is 0.957. The P/D varies so much that it would not be especially efficient at any particular advance ratio, but it might be somewhat effective over a wider advance ratio range than a prop with a higher maximum efficiency.

Representative radius is calculated by multiplying each chord by the square of the radius, summing the results, dividing by the sum of the chords and taking the square root. It is different for each blade shape. This is a rule of thumb number, like the P/D, and should not be taken with too much seriousness.

Two props weigh 5.6 grams, 2.8 grams each. The cylindrical hub is 0.31″ in diameter and about 0.59″ long. The hole is different diameter on front and back. The front hole is larger to clear the bend in the wire shaft. The back hole was a sliding fit on a 0.0593 drill shaft and 0.34″ deep. The front hole was snug on a 0.985″ drill shaft and about 0.18″ deep. The ramp is about 0.10″ high. For measuring, I put a 0.05″ wide strip of 0.0041″ thick paper through the hole to get a snug fit.

**9 1/2″ Orange Chinese Prop**

There is an article in Free Flight Quarterly, Issue No. 53, October 2014, pages 31-32,”A New Propeller for P30″ by Paul Rossiter, about the new Orange Prop. It is a continuation of the article in Issue No. 15, “P30 Propeller Analysis” that evaluated IGRA, Peck, Gizmo Geezer and Modella props. It concludes “The Orange propeller is an excellent replacement for the Peck prop and one of the best (if not the best) available for P30”.

Here is my plot of the blade angle versus radius fraction. Measurements were made at 1/2″ stations along the radius. This is the average of six measurements, three on each blade. Standard error is about 0.81 degree. High and low measures are plotted. The measurements of each blade were within tolerance of each other. The tips track well.

You can see by comparison with the helical plots that this is not a helical prop. The P/D varies tremendously. The tip washin is due to the swept leading edge.

This plot matches that in FFQ except at the mid radius, where I think there is an error in the FFQ measurement.

I calculated the representative radius at 2.93″, 0.614 radius. The corresponding P/D is 1.03. It is misleading to quote a P/D for a non helical prop.

Representative radius is calculated by multiplying each chord by the square of the radius, summing the results, dividing by the sum of the chords and taking the square root. It is different for each blade shape. This is a rule of thumb number, like the P/D, and should not be taken with too much seriousness.

Two props weigh 14.45 grams, 7.225 grams each. The hole is different diameter on front and back. The front hole is larger to clear the bend in the wire shaft. There was flash about halfway through. The back hole was slightly loose on a 0.0593 drill shaft and 0.38″ deep. The front hole was slightly loose on a 0.0972″ drill shaft and 0.27″ deep. For measuring, I put a 0.05″ wide strip of 0.0041″ thick paper through the hole to get a snug fit. The tips tracked within 0.01″ of each other.

The FFQ article compares the props in a computational model. Such models make simplifying assumptions. There is no sensitivity analysis of how the outcome could vary with discrepancies in the inputs. It calculates prop efficiency at each revolution, total height and flight duration. A calculation is made for motors of 4, 5 and 6 strands of 1/8″. It finds maximum height of 82 m with 5 or 6 strands of 1/8″. It finds duration of 219 seconds with 4 strands, compared with 225 for the Peck. All of the props show maximum duration with 4 strands, which suggests the optimum motor is of smaller cross section. Each prop is likely to have a different optimum motor cross section with different durations. The Peck prop is closer to helical and may maintain its edge with a smaller cross section.

**12″ Orange Chinese Prop**

These differ from others in this series in that the plastic surface is glossy rather than frosted. Here is my plot of the blade angle versus radius fraction. Measurements were made at 1/2″ stations along the radius. The prop was rigidly mounted on a vertical shaft. Chord (c), leading edge (LE) offset above table and trailing edge (TE) offset above table were measured to the nearest 0.01″ at each station. Blade angle (B for Beta) was calculated trigonometrically. P/D was calculated from the usual formula.

B = arcsin((LE-TE)/c)

P/D = pi tan(B)r/R

Wobbles in the graph result from measurement precision limitations rather than manufacturing irregularities.

The blade angle plots in the background are for helical props with the P/D as shown along the right edge. You can see by comparison with the helical plots that this is much closer to a helical prop than most plastic props. Although it varies slightly, P/D is very consistent over the working part of the radius. The sharp washin at the tip is due to the sharply swept tip rather than twist of the basic shape.

I calculated the representative radius at 3.65″, 0.608 radius. The corresponding P/D is 0.727. This is a low pitch prop suitable for fast climbs, but not so good for long, slow flights under power. I expect it will operate best with advance ratios around 0.4 to 0.55, assuming a most efficient blade attack angle of 4 to 6 degrees.

Representative radius is calculated by multiplying each chord by the square of the radius, summing the results, dividing by the sum of the chords and taking the square root. It is different for each blade shape. This is a rule of thumb number, like the P/D, and should not be taken with too much seriousness.

Two props weigh 24.4 grams, 12.2 grams each. The cylindrical hub is 0.35″ in diameter and about 0.75″ long. The hole is different diameter on front and back. The front hole is larger to clear the bend in the wire shaft. The back hole was slightly loose on a 0.0593 drill shaft and 0.62″ deep. The front hole was snug on a 0.1028″ drill shaft and about 0.11″ deep. The ramp is about 0.08″ high. For measuring, I put a 0.05″ wide strip of 0.0041″ thick paper through the hole to get a snug fit.