tests on the propellers for peanuts

[jose12]

I'm trying to improve the construction of my laminated propellers for peanuts, and the techniques I use are the classic ones: 1mm balsa wood sheets molded onto a 4-inch circular form with a 15-degree pitch. I was thinking of changing the pitch of the propeller by increasing the pitch from 15 to 20 degrees. I was also considering changing the diameter of the forming tube from 4 inches to 2.5 inches. I'm not sure if this is a valid approach; what do you think?

[OZPAF]

I guess the only way to know is to give it a try.

I tend to feel that a 2.5" Dia form may give you too much blade camber, while 20 deg sweep on the form may be ok.

Have you tried tapered forms - like coffee cups - so called "Bucket Props"? blades formed on these have washed out tips.

John

[Prosper]

Hullo Jose, I'm not familiar with the classic method you mention. Where on the blade is the pitch 15°? That seems like a very fine (low) pitch to me, and so does 20°, but maybe I'm not understanding correctly.

Stephen.

[jose12]

I've been reviewing data on this system and found a relationship between the diameter of the forming tube and the angle for achieving a suitable pitch, which in my opinion shouldn't exceed 20° to prevent the blade from deforming. I've concluded that a 3.15-inch tube is the best fit. I believe I've found the answer to my question. If you're interested, I can elaborate.

[Jmk89]

Hullo Jose, I'm not familiar with the classic method you mention. Where on the blade is the pitch 15°? That seems like a very fine (low) pitch to me, and so does 20°, but maybe I'm not understanding correctly.

Stephen.

Hi Stephen
I think the 15 degrees refers to the angle of the blade on the cylindrical form, not a pitch angle.
I was confused too for a moment!

[OZPAF]

This article may help to size the style of props that Jose is talking about - it shows a relationship between cup diameter and mounting skew angle and angle setting at 75% radius for required P/D - pitch /diameter ratio.

https://www.flyingacesclub.com/PFFT/PropFromPlasticBottle.pdf

I would not regard it as very accurate but it is a guide.

John

[cvasec]

20 odd years ago Fred Rash produced a spreadsheet with which you could input the size of you "bucket" and prop and it worked out the angle on that bucket. By playing around with the numbers it was possible to get close to a helical pitch.
Ron

[Jmk89]

The spreadsheet and instructions for using it are still available from the DC Maxecuters website - https://dcmaxecuter.org/building-tips/

[Prosper]

. . . I think the 15 degrees refers to the angle of the blade on the cylindrical form, not a pitch angle.

Ohhhh, I seeee. John's 'skew angle' descibes it nicely too. I never considered that method because I couldn't see how it would deliver a helical blade, but Ron talking about a bucket (a cone rather than a cylinder?) is interesting.

Thanks for starting the thread Jose.

Stephen.