The Mitchell B25 and the P-38 Lightning projects are both on hold.
Envisioned a different type of rubber model while searching for ways to power the B25. Pulleys, gears, you name it. Once it is figured out, will resume project. Bought a bunch of plastic gears to test ideas with.
One problem with the P-38 is want to do this biggest model with counter rotating props. Found some that were three bladed blanks, still needing carved. I chose to skip the price, then due to Covid they went away.
What to do?
Why not design my own to scale prop, but use the most efficient design possible.
After several searches, found a gold mine of info, for the last several weeks been reading and designing a prop per what I learned about rubber band power.
Now that I know more, decided to do a 2-bladed project first. Not the B25-still too much designing needing done.
Then it hit me, a long thought of project. Something that has history back to when I was a young lad and both my grandpas gave me some control line models. One of them gave me a scar to this day, clearly visible.
Anyway this is about the prop design:
Searched and found some PDF about a Professor Larrabe and his ideas for a prop design. Basically change the whole look of a rubber band propeller to be more efficient.
Wider blade by the shaft that has an elliptical shape to lower drag losses.
The I found a table and instructions on how to multiply your prop needs into a plottable design, just like how I do my aurfoils. Hey I can do this!!
My new project is huge! Needs a 17.3" diameter two bladed propeller. Why not build my own prop for this project and move it to the front of the line?
I've been designing this complicated project for three months part time-weekends, evenings after work. Never had a project last more than two weekends! As close to scale as I can make it and get it in the air. Special 260gsm paper in use.
The prop material will be 300gsm MOAB, thinking to get the curve need to double glue blades back to back and then using a steam iron and piece of PVC pipe to "iron" a shape to permanently form the proper curve needed.
Here is the 17.3 inch diameter propeller and carbon fiber hub drawing. Plan is to make the hub out of the available carbon fiber tubes I have, and the propeller blade material out of MOAB Slickrock Metallic Silver paper to mimic the shiny aluminum version of the real one.
Prop is proper scale diameter, it is not scale shape or pitch; it has a P/D of 1.00 meaning the pitch is 17.3 the same as the diameter of the prop 17.3:
The airplane part of this project is still being designed, a few things left on the fuselage then the printing starts. Going to do the propeller first and test with planned 6-strands of 1/4" Super Tan rubber band. Bought a ten pound box. Plenty to build models for!
Mike