Pressure recovery spinners

[CAFplanekid]

Hi everybody. I came across a picture of a tapered spinner on a pusher application. Instead of the usual parabolic curve to the tip, this spinner has a recurve to a taper. See here: http://www.aircraftspruce.com/catalog/appages/ac1dome.php

I understand how it works to decrease drag, but am at a loss to find any online information about their design. Can anybody help me out? Thanks,

Jonathan

[HELModels]

Google afterbody drag. I found some interesting stuff about trucks. :rolleyes:

I found a diagram showing separation of flow around a cone shape(kinda like a spinner). I conclude, right or wrong, that the design you linked is designed to minimize the separation of the afterbody flow.
The length of the "spear" is longer than 1/4 the length of the regular spinner part, but that is my eye estimate. A narrow spear reduces the size of the afterbody and the gradual recurve part causes a concave suction to keep flow attached as it transitions to the narrow lower drag spear. What radius to use for the recurve? I dont know, but gradual is good if it doesnt exceed 7 degrees approximated by a straight line.

When it comes to afterbodies, Hoerner liked 7 degrees. Hoerner probably had some ideas on radii that might apply, but I cant find that.

keep in mind that I'm a modeler and only pretend to be an aerodynamicist.

[Texas Buzzard]

Think...... on a pusher the flow of air around the motor/engine and then through the spinning prop will look like what you see in a Blender running at full speed. But with the pusher's motor off the airflow will smooth out.

I cannot believe that the addition to a spinner will do any significant drag reduction in models. New fix-all items pop up every once in a while.

[Brandano]

there's a nice view of the spinner of a P180 Avanti here: http://www.youtube.com/watch?v=HUJ0i3-_Yxc&feature=related
However I tend to agree with Texas Buzzard, getting any real advantage out of a spinner at model aircraft scales seems quite unlikely. The air close to the hub of the average model prop is a real mess of turbulence. Perhaps using a large spinner to reduce the portion of prop producing thrust to the outer part of the blades will improve things a bit, but this will likely come at the expense of weight, complexity and difficulties in engine cooling.

[HELModels]

That mess of turbulence might get better with a proper shape. Give the mess a reason to play nice. That Avanti is one clean machine.

Here is a NACA report on afterbody drag and bodies of revolution. It isnt entirely relevant because of Mach number, but it is interesting that power on and off drag reduction effects were essentially the same. Some of the shapes they used remind me of the "fancy spinner".

http://naca.central.cranfield.ac.uk/report.php?NID=6067