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#55806 by RParker
Tue Nov 08, 2011 8:13 am
Have been asked to produce an accurate drawing of an existing wooden propeller. Anyone ever have to measure and draw something like this?
airscrew.jpg (52.08 KiB) Viewed 5671 times
#55809 by Nick Pyner
Tue Nov 08, 2011 11:11 am
Getting the sections right would not be easy but it is probably more important to be sure of the end use of your product, and where you stand legally. I take it you are not qualified as a propeller designer, and therefore I think this could be a dangerous thing to do.
#55810 by Neil Blanchard
Tue Nov 08, 2011 1:24 pm

How large is the image file? If you insert it into DataCAD and use the Enlarge function to scale it (precisely) to full size -- is the quality/resolution good enough to trace accurately?

If so, you can trace it -- splitting the lines as closely as you can, and this will be much more accurate than scaling the paper and trying to reproduce all those curves that way.

But, what Nick says is critical -- whoever is going to use this drawing you make has to understand that even though it is a CAD drawing, it is totally approximate and a close guesstimate and may or may not be accurate to the "real" propeller. The image you are working from may or may not have been drawn accurately, and the image itself may or may not be stretched, squashed, twisted, or otherwise distorted.
#55817 by RParker
Tue Nov 08, 2011 4:42 pm
Think there is a little confusion. I am being handed the actual wooden propeller. I need to be able to measure and produce a drawing of it.
#55819 by Nick Pyner
Tue Nov 08, 2011 6:26 pm
RParker wrote:Think there is a little confusion. I am being handed the actual wooden propeller. I need to be able to measure and produce a drawing of it.

I'm not confused one little bit. So I'll say what I said again. Measuring the sections off the sample will be extremely difficult. You would probably have to make some sort of jig with a moving mounting for a micrometer depth gauge. This would not be far short of the device needed for making the propeller.

And again, it would be prudent to consider why you are doing this. And again, what is the end product? It could actually be a propeller on a flying aircraft.

The legal requirements and safety standards for aircraft are a long way from Joe Overalls swapping the harmonic balancer on your car, let alone doing it yourself. Your client may be an idiot but that probably won't stop the lawyer from the NTSB knocking at your door if the plane crashes due to propeller failure, and the guy standing behind him is probably a lawyer from the Hartzell Corporation.....

Note that the propellers on experimental aircraft work under the same laws of physics as a store-bought one, and theose laws are extensive and interesting.
#55821 by Neil Blanchard
Wed Nov 09, 2011 7:40 am
Hello Robert,

Yes, I was confused -- I thought you would be reproducing the drawing you posted.

3D "measurements" are next to impossible to do by hand. There are laser 3D scanners that are specifically for doing this sort of thing, and they would produce a 3D computer model, and then you can use that to make a drawing like the one you posted, or the 3D file can be used directly to produce another physical propeller.

Doing it by hand would be very hard to do without a lot of training and it would be hard to verify, and unlikely to be very accurate.
#55825 by Ben at TJB Architects
Wed Nov 09, 2011 10:46 am
If your client is simply looking to reproduce the propeller then he needs a "duplicator".

I would venture a guess that you are probably not making the best use of your time with replicating this exact prop in CAD drawings.
There are many online resources that provide designs, even templates, for propellers.
It's both a fascinating science and a beautiful art.

Your client is within his legal right to produce his own propeller for an ultralight or home-built aircraft.
Home-built aircraft have to receive an Airworthiness Certificate through a series of inspections by the FAA.
Statistically, prop failure is not a widespread cause of aircraft accidents.

By the way, don't take this as advocating making ones own prop.
That undertaking should not be taken too lightly.
#55827 by RParker
Wed Nov 09, 2011 12:22 pm
Thanks for all of the info. The propeller in question is a very rare unit from a WWI aircraft. Client is looking for a drawing to send to another collector. I do not know the final use of the drawing but would be very concerned about liability (BIG thanks to Nick).
Anyone have any experience with the 3d scanners and using their output files?
#55943 by Ted B
Mon Nov 21, 2011 4:28 pm
You might try contacting the Hamilton Sunstrand div. of United Technologies. As Hamilton-Standard they made hundreds of thousands of wood and metal propellers going back to the 1920s.
http://www.hamiltonsundstrand.com/Aeros ... er+Systems

Or the Vintage Aircraft Association.

A friend of mine is an antique airplane collector and restorer of 1920s and 1930s aircraft, and I know he's said that designing and making old props is a "black art", not a science. But they do have replica props and new props made all the time.

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