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Failed Propeller Design Test

4 Bladed Propeller Test

We were wanting to do some tests on the aircraft after analyzing the propeller that were currently using. for test purposes we wanted to increase the number of blades. And for the simplicity factor making (2) two bladed propellers was simpler than trying to manufacturer a 3 bladed propeller.

With this configuration we could simply increase the bolt length through the hub and test the (2) 2 bladed propellers as if it was a 4 bladed propeller.

After installing the propeller we did some test runs and found that we were way over the amount of propeller area that we needed to be. Using the mahogany and yellow poplar mix was still extremely heavy and during the manufacturing process we were kind of under the assumption that this was going to be a test that would fail.

We were able to gather some baseline propeller information that we can use in the future for prop loading.

Even though the propeller design and testing was a complete failure from the standpoint of having a usable product we will share with you the process that we went through to get to the point that we could actually test the propeller. This was from the blog 2 weeks earlier.

New 4 Bladed Propeller for the Polini 250

We have designed a new 4 bladed propeller. Basically ju
st two 2 bladed propellers bolted together. Since we are still in the testing phases for the Polini 250 we will probably be trying several different configurations of propeller to optimize its performance for the EMG-6. this blade will be a 48 inch diameter x 26 inch pitch x 4 blades. the 2 blade propeller that is on the EMG-6 right now is a 48×30. As the engine has begun to break can we are now under loading the engine slightly getting right around 7700 RPM. We have about maximized the blade size for a 2 blade propeller and should be able to substantially improve the climb performance by going to a 4 blade.

We begin the setup process to hold the propeller blanks in place while we machine them.


The prop hub will be the primary indexing system for the propeller blade during the machining process.

The bolt pattern in each propeller will need to be rotated 90° from each other. And the large 1 inch diameter bolt will hold pressure against the machining fixture.

On the prototype blade we start off with the 2 center cores of material in this case we elected to use two colors of wood one layer of mahogany and one layer of yellow poplar. We machine the outline of the next layer and then glue it on while it’s on the machining fixture. This will help us Orient the lamination’s.

Once we have all the lamination’s glued together we begin the machining process using a 1/2 inch ball nose in the mill starting on the bottom side of the propeller 1st.

This is the finished cut on the bottom half of the propeller blade. After each machining cycle we simply rotate the blade on the machining fixture 180° and duplicate the same process on the other side.

Once the bottom halves of the propeller blade have been machined we flip the blade over and re-index before beginning the machining process for the top half of the propeller blade.

In this picture here we can see that were just finishing up on the top surface of the 1st blade.

After we have completed both blades we will machine the hub area to eliminate any fixture marks left from the machining process and ensure proper tracking of the propeller blade.

 As the 1st propeller blade nears completion we are preparing the 2nd blade and will begin the machining process all over again.

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About Brian Carpenter (255 Articles)
CEO Rainbow Aviation / Adventure Aircraft

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