Ka4-70 Series

Hi.

Does anyone have the Kt Kq J diagrams for the Ka4-70 without nozzle?

Thanks

 

Does anyone know if there are the Kt Kq J diagrams for the Ka-series without nozzle?

 

I found a Research Article (http://www.hindawi.com/journals/ijrm/2012/474785/) that has the Kt Kq J diagrams for the Ka4-70 with and without nozzle, but there are a huge difference between those diagrams, principally for the Kq.

Can anyone confirm those diagrams and explain the difference for the Kq?

Sorry for the english, I am Brazilian.

Thanks.

 

The curves for a Ka4-70 both in and out of nozzles is given in Volume II, Chapter 56, Section 9 of the 1988 edition of Principles of Naval Architecture by SNAME. See also the following threads.
http://www.boatdesign.net/forums/education/propulsion-kort-nozzle-4525.html
http://www.boatdesign.net/forums/education/just-question-5547.html

 

Thank you for the answer jehardiman. I read the threads you recommended and they helped me to understand a few things. But I read the Volume II, Chapter 56, Section 9 of the 1988 edition of Principles of Naval Architecture by SNAME and I didn't find the curves for a Ka4-70 both out of nozzles.

 

PNA Vol II doesn't draw the curves of the propeller characteristics, it supplies the coefficients of the regression polynomials used to calculate Kt and Kq (See p. 217)

It's a similar procedure which was done with the open B-Series wheels.

 

P.217 tables 21/22 give coefficients for Ka4-70 in nozzles 19A and 37. As Ka4 screws are designed specifically for nozzles I don't think there are coeffs for the screws allone. May be in the work of Van Gent et al. (1983)?
However there is a comparisson chart with B4-70 series at pp.219 (both ahead and astern)

 

The Ka4-70 series coefficients are Ct, Ctn, and Cq, which represent the total thrust coefficient, the nozzle thrust coefficient, and the torque coefficient. I think that an approximation of the thrust due to the propeller alone could be obtained by subtracting the nozzle thrust from the total thrust for a given speed of advance.

 

NavalSA, that makes sense to me. So total thrust minus nozzle thrust for 19A should give the same that total thrust minus nozzle thrust for 37, and that's the thrust of screws alone? Has this checkup been made already?

 

Not so easy...

Sorry guys, it's not that simple. The nozzle creates a local velocity inflow into the propeller, which is substantially different from the condition without a nozzle, and measurably different between different nozzle styles. We wrote up this article some years ago that might help explain a bit more.

http://hydrocompinc.com/wp-content/uploads/documents/tex0801.pdf

And regarding the original post, the series of NSMB tests that make up the various ducted propeller series did not include published tests of the KA propeller without a nozzle.

Don MacPherson
HydroComp

 

I looked at the data in PNA again and I see now that the comparison is indeed against a B4-70 not a Ka4-70.

FWIW, I did some work years ago for a custom tube thruster using a wheel similiar to a Ka4-66 but with a different pitch distribution and blade shape. In the tube it was much more efficient than a similiar Ka (65 lb/hp vice 45lb/hp bollard). However, it was very supceptable to tip clearence issues. So I would expect a Ka type wheel out of the tube to be similiar to B series thrust but with more torque absorbed and tip cavitation problems.