Al, I haven't had time to read the whole thread so you've probably heard this already.
My main observation is the boundary layer problem. I seriously underestimated the effect it has on some aux scoops since it was not critical (avionics cooling) and was amazed at how big a deal it was. The small pressure inside the cockpit was enough to stop all airflow. I ended up turning the scoop 180 degrees (facing backwards) and using the positive pressure in front of the canopy (not a solution for you but just an illustration of how boundary layer effects scoops).
The 'flair' of the diffuser is almost always under-done. When done properly, it just looks wrong.
When it is working right, the static pressure is pretty close to theoretical for the airspeed of the aircraft. Don't stop working on it till you're there (or until cooling is OK). My right side cooling scoop is pretty terrible (only ~ 50% of theoretical dynamic pressure recovery) since I split it between a rad and oil cooler. The Left side works great & gives me 105% of theoretical (prop blast doing the magic part).
The negative pressure above the wing is a relatively feeble thing (as you have already discovered) so that was a dead end.
Tracy
On 7/19/07, Steve Brooks <cozy4pilot@gmail.com> wrote:
Gentlemen,
I've been following this thread with great interest, as I would still like to make further improvements to my cooling.
Since Ernest lives close by to me, I may see if he can look at my radiators to get his thoughts on improvements.
Steve Brooks
-----Original Message-----
From: Rotary motors in aircraft [mailto:
flyrotary@lancaironline.net]On Behalf Of Ed Anderson
Sent: Wednesday, July 18, 2007 3:17 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Oil cooler inlet
I agree with Ernest (even if he clearly must be completely and totally wrong {:>)), difficult to find any rule of thumb parameters for a vane.
I have marked the region (red color) in you duct that I think is most critical in helping the slower moving boundary layer turn and to prevent/minimize its effect on the rest of the air flow. Once you have helped the boundary layer accelerate and get around the curve, then I believe the vane has done about all it can. I would start out the vane approx 1/2 the depth of your opening in order to try and capture some of the higher velocity air outside the boundary layer. I would then compress that air toward the roof of the duct by reducing the distance between vane and top of duct in order to increase its velocity.
Depending on how fancy you want to make the vane, I though that perhaps adding slots so the higher velocity air in the lower part of the duct could help the boundary flow make the turn and further energize it.
Don't have a clue as to how much this well help, but I do believe it will help some.
Ed
----- Original Message -----
Sent: Wednesday, July 18, 2007 2:15 PM
Subject: [FlyRotary] Oil cooler inlet
Attached is a more accurate drawing of the oil cooler inlet x-section; with a few pressure measurements. Based on temps, the
average flow velocity into the scoop is about 85 fps (57 mph) – all at about 160 mph airplane speed. (Point "A" is really about 4-5" ahead of the scoop.)
Ernest; since you were first to propose the internal airflow, or vane; what would you think is the appropriate shape, position, etc. I can understand your non-participation on the 'other' list after being labeled "completely and totally wrong". (That's what you get for not reading his book
J).
Others ideas obliviously of interest as well – ED?
Al
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