flyrotary@lancaironline.net Mailing List Archive

So Ed, you're bored?

Want to take a stab at helping me understand the below graphs and how they lead to the selection of the optimum outside/inside lip radius ratio?

I understand that Cp is pressure coefficient, pressure relative to other pressures in the vicinity.

Not clear to me if we're looking for positive or negative Cp inside the diffuser, I assume positive? (Converting airspeed into pressure)
I also assume we're looking for a profile with maximum Cp over a wide AOA range.
Why did they pick A-20 and Vi/Vo = 0.4 for figure 36d?
Aren't we shooting for a Vi/Vo of 0.2 or better? (slowing 100 mph down to 20 mph)

Finn

On 6/30/2021 11:18 PM, Finn Lassen finn.lassen@verizon.net wrote:

Thanks. I guess I kept missing it because I don't understand what I'm looking at.
Can anyone help me understand the following and show me the optimum inside/outside radius ratio (which I assume is one of the A-10 to A-40 contours):

Finn

On 6/30/2021 9:45 PM, Charlie England ceengland7@gmail.com wrote:

Seems likely; I don't recall seeing a CR3485 referenced anywhere, either.

On 6/30/2021 4:42 PM, Finn Lassen finn.lassen@verizon.net wrote:

I tried in vain to find NASA_CR3485 (well, I found a NASA contractors report on animal studies).

I wonder of he meant 3405?

Anyone found a better match?

Finn

On 4/28/2011 9:07 AM, Tracy wrote:

Finally got around to finishing my cooling inlets. (pictures attached)� Up until now they were simply round pipes sticking out of the cowl.�� The pipes are still there but they have properly shaped bellmouths on them.�� The shape and contours were derived from a NASA contractor report (NASA_CR3485) that you can find via Google.� Lots of math & formulas in it but I just copied the best performing inlet picture of the contour.�� Apparently there is an optimum radius for the inner and outer lip of the inlet.�� There was no change to the inlet diameters of 5.25" on water cooler and 4.75" on oil cooler.

The simple pipes performed adequately in level flight at moderate cruise settings even on hot days but oil temps would quickly hit redline at high power level flight and in climb.�

The significant change with the new inlet shape is that they appear to capture off-axis air flow� (like in climb and swirling flow� induced by prop at high power)� MUCH better than the simple pipes. �� First flight test was on a 94 deg. F day and I could not get the oil temp above 200 degrees in a max power climb. �� They may have gone higher if the air temperature remained constant but at 3500 fpm the rapidly decreasing OAT kept the temps well under redline (210 deg F).

I have an air pressure instrument reading the pressure in front of the oil cooler and was amazed at the pressure recovered from the prop wash.� At 130 MPH the pressure would almost double when the throttle was advanced to WOT. � That did not happen nearly as much with the simple pipes.��

These inlets ROCK!

Tracy Crook

Virus-free. www.avast.com

nadfchpfafimnegl.png

kbdejbnihmgdehea.png

bnmfmdnlndmefidc.png