Cox prop question

Thanks for the Update Bernie. I'm in for a couple.

Shawn

By black plastic do you mean flexible as opposed to grey competition?

Yes, the classic "double tough" flexible, as opposed to the grey "competition" version.

The grey, nylon-filled, resin needs to be bought in a quantity that is bigger than the planned production run, so we will mould the grey ones next time we do a production run of another prop size in grey. If the black ones sell that is ...

We already have grey props in sizes

3 X 1.25
4.5 X 2
4.5 X 4
5 X 3
8 X 4

It would be helpful if the pictures showed the actual product?
To me the images of the "grey" 4.5x4 are identical to the black 5x4 props...?

All our pictures are of the actual product.

However, the "grey" compound that the moulder used is identical to the one Cox used but the manufacturer now uses a darker dye. Yes, they are almost black but the difference becomes visible when held beside a black prop.

If we list them as "grey" they are guaranteed the stiff competition version.

Speaking of, we have a small quantity of OEM grey 6x3 props for sale here:

http://coxengines.ca/cox-.049-propeller-grey-6-x-3.html

We have the 4.5 X 4 in grey and yellow. 20,000+ RPM on a .049 reedie

Not too much difference but it's also they way we edit the raw picture files.

By the same token, colour does not matter; it's the material that the props are moulded with

Well here is what I see, I can't tell any difference....?

OOPS!

Definitely wrong picture      

Pictures are now corrected:

http://coxengines.ca/cox-.049-propeller-grey-4.5-x-4.html

Surfer_kris,

My apologies for not listening to you when you first posted this. On your next order with us please mention this and we shall include 3 of those little beasts for you at no charge

Oh, that explains why they looked so similar then...

Thank you for the offer, I will include that in the next order.

Another question, do you have any recommended rpm limits for these props?

Probably around 40,000 RPM with the compound we used.

Don't let the message on the hub scare you. Back in time they were made with a weaker compound.

1/2A Nut wrote:Bernie, you said you noted the .049 reed engine does 20k +  with the 4.5x4  
Out of the teflon, copper, crystal clear plastic, stainless steel and mylar reeds which reed material has been shown to helps provide the highest rpm?

Thank you, also let us know when the 4x2.5 props are ready for sale.

The Beryllium Copper ones are the least suited as they are prone to "float" and likely the reason that Cox discontinued them. Steel, Mylar and the crystal ones (still not sure what they are made of) would all work. The preference out there seems to be the Mylar version but, if you ask 3 Cox engines users, may get 3 different answers.

Of course we will post when we get the props

Among Cox reedy enthusiasts, I have heard significantly more people that think mylar runs fastest, however will become bowed over a fairly short time. For a speed contest, after trying steel(also bows), solid teflon, woven teflon, copper, and mylar, but not crystal, I am 100% in the mylar camp.

The bow does not appear to me to affect it for sport use, and I can't say whether it hurts or helps RPMs. It seems to continue to seal just fine after short and long term bowing.
Rusty

I got curious about the thickness of the different reeds. About 5 years ago, I stocked-up on new Mylar, Teflon and Steel reeds.. and measured the thickness using a vernier caliper. I also had the older "star-shaped" reeds of Copper and Mylar. The "thickest" reed was the "Teflon" @ .010".. Both of the Mylar (star and oval) are .005".. The Steel reed is .002".. and the Copper is .001". How would the "much thicker" Teflon reed function with a tighter circlip clearance/fit? I've heard it mentioned, that the reed should not bind once the circlip is installed. The .009" difference in thickness between the Teflon and the Copper is quite a bit. Maybe that's why the Copper reed tends to "float" as Bernie mentioned? The Steel @ .002" is probably much more rigid than the Copper.. yet it's .003" thinner than the Mylar.

The "flex" between the different materials is probably a big factor.. but the circlips are all the same size wire diameter. I would think that the reed is meant to be held "stationary" by the circlip.. because of these wide variations in reed thicknesses. Pressure-differential valves "in general" don't float "radially" during their operation. The "disc" comes off the "seat" and reseals on a "linear" path.. without any radial movement happening.

The circlip-style reed-holder design has a "tang" in the center. Depending on which way you hold it; you will see that it protrudes one way or the other.. in relation to the "outer-circle" part of the clip, which seats in a groove around the seat. The circlip should be installed; so that this "tang" protrudes "away" from the reed/seat.. allowing the reed to flex away from the seat when there is a vacuum in the crankcase (piston moves "up" in the cylinder..) After installing a reed and a circlip-style retainer.. I hold the assembly up to my mouth.. and gently "blow" against the reed with my lips tightly sealed around the valve. If I don't feel any resistance.. this indicates that the reed is not seating properly.. (sometimes it "whistles") Oftentimes; removing and re-installing the reed/circlip will establish a reliable seal. Repeat the process as many times as it takes (swap-out a different reed/circlip) to achieve a good seal.. before you continue assembling the engine. This (along with cleanliness...) is the single most important thing to get right.. for a "reliable-running" Cox reed-valve engine.

Steel or Mylar,

I prefer steel, only because it seems more robust. It does hold a shape like the Mylar as Rusty mentioned. They both do a fine job though.