PVC pipe prop - profile query

[domwild]

Hi,

Please let me know what you think of these three

similar profiles. Mainly two questions:

1. I suppose I should have taken more material off the outer

side for the trailing edge, I chose the inner side.

2. The leading edge can be rounder (blunt) or less blunt -

any suggestions??

Thanks.

[Flux]

As these type blades are only suitable for low tsr I suspect that they will all be fine.

Any of the leading edges will do well but if you want the best possible chance I would thin the trailing edge on the inside from nearer the centre say 60% back from  LE and run it out to a sharp edge. Don't remove any from the outside, they are very cambered already.

They ought to perform well if you get the pitch right, you will have to set them at less an angle than normal carved wooden blades because of the camber.

Flux

[bobn]

 Generally the broader the leading edge radius the broader the range of angle of attack the blade will perform at or the less likely it will be to stall at high angles of attack.

Here is a common cambered airfoil.  a google serch will tell you about its characteristics.

http://www.anotherpower.com/gallery/energy-stuff-and-more/goe417a

BobN

[picmacmillan]

just an idea...would it be possible to heat the pvc, so as to shape it to what you need?...we used to heat plastic in an oven and when it became warm we would put it into a little jig we made and created ashtrays, or candy dishes....i just thought maybe you could maipulate the shape this way...pickster

[Dan M]

Based on intuition, and a few other profiles I've seen, I like the leading edge of the bottom one, and the trailing edge of the top one.

For what it's worth.

Also, what diameter are you dealing with?  I've been scrounging all over for some large dia to play with and keep coming up dry (unless I want to buy it new).

-Dan M

[domwild]

Thanks for all the help. The concensus is that a well-rounded leading edge

is best and a sharp trailing edge which starts in the inner chamber

 (concave side) and ends in a sharp trailing edge.

Very useful was the reference to these profiles, which confirms the

member's statements:

GOE497

NACA6409

Selig 1223

Clark Y

GOE417A

Thanks for the reference to these profiles. They all seem to be similar

to the ones the very first bi- and triplanes used.

All are doubly-chamfered profiles which approximate a pipe profile.

I have found offcuts of uPVC or PVC sewer and mains water pipe.

235mm to 250mm outside dia. with a wall size of 9mm to 12mm.

So we are looking for 9"-10" pipe with 3/8" to 1/2" wall for

all you "imperial" boys.

I am not saying this is optimal; just what one can find.

Full-length pipe would be too expensive.

It has been said that a 3m (10') dia. prop, four blades can even turn

a cogging F&P.

 

[domwild]

Thanks for that. It will probably need a long and narrow oven to heat it to just the correct plasticity.

Great web site.

[ghurd]

Special 'electric blankets' just for this sort of thing can be purchased.

G-

[wooferhound]

[domwild]

Thanks Wooferhound. I am just wondering how much less efficiency one gets

with this leading and trailing edge, which is that much easier to make.

It just means setting the jig saw to 45 deg. and to try to cut radially.

The profile data bases and the members all seem to say the leading edge should

be rounded.