Subject: [FlyRotary] New Scoop

 

Steve;

 

There are all kinds of things one could say about trying to make the scoop ideal, effective, low drag, etc; and then when you face the reality of fitting to your plane, you can’t do it.  So it’s what works for you.  I’ll add a few comments for whatever it’s worth.

 

The intake area of the scoop should be fine.

 

One would like to slow (expand) and turn the air entering the scoop in a manner that maintains surface attachment for max pressure recovery and minimum drag.  This takes a much longer scoop throat than you have.  The air entering will trip to turbulent at the abrupt corner behind the B.L dam.  This will result in poor flow and pressure distribution, with most of the air going toward the back of the scoop.  I don’t know what happens in your installation downstream from the actual scoop, but you might consider some internal baffles but get a more uniform distribution if the rad is close to the scoop.

 

The boundary layer dam that you have is high drag, and may be close enough to the entrance lip that backup of the B.L. flow will be ingested into the scoop – or it could result in some external diffusion (pressure recovery) and allow the scoop to work just fine.  The idea in the B.L. “bleed” is to try to divert that flow somewhere else, generally  off to the sides.  That would require a much more gradual diverter angle.

 

I made a much more gradual bend in the wall of my scoop (pic) attached.  Still, in doing flow tests, I found flow separation and turbulence which lead uneven flow distribution.  I added to baffles in the scoop get it fairly uniform.  It could be that some of the turbulence was a result of the test rig setup, although I thought I had a long enough duct from the blower to straighten things out.

 

The squared off internal corners will add frictional drag, but probably not significant in overall picture.

 

But, hey – try it. If it gives you the cooling you need, you’ve got 90% of the battle won.  If you feel you need to reduce drag, you can consider that at your leisure.

 

Al

 

 

Ed, and others -

 

Attached are some photos of the new scoop I'm building to replace my old new

scoop.  As you can see the new one actually has less intake area, but

extends further in order to get outside of the boundary layer.

 

I don't want the intake any larger than it has to be, but I want to make

sure also that it is sufficient to allow for enough air flow.  My old new

scoop did improve cooling, but as I found out, it was only marginal.

 

The new scoop, which is patterned after a P51 style scoop, not only gets

outside of the boundary layer air, but also excludes it, with the dam that

you see at the bottom.  Well, actually it will be at the top, once it is

mounted under the belly.  It also gives me an expansion area once inside the

scoop.

 

Using the program that Al sent me, the boundary area calculated out to about

1.625-1.75 inches +/- depending on speed.

 

The scoop intake measures 10.75" inside at the top (narrowest) and 14.75" at

the widest point average = 12.75"

Height of the inside of the scoop measures 4.25"

This should equal about 54.18 sq in of area.

 

The inside of the scoop sits exactly 2" from the bottom of the fuselage, and

overall height to the outside of the scoop is about 6.6"  again, measured

from the fuselage bottom.

 

I haven't glassed the scoop yet, other than on one side to help with gluing

it together.

 

I am interested in any feedback concerning the size of the intake area.

 

Regards,

 

Steve Brooks

Cozy MKIV N75CZ

Turbo Rotary