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Looks Great, so now you can put out a drag chute to keep
you below Vne and run full throttle. That 3 rotor does have a nice sound -
noticed when you took of a Sun & Fun - it just sounded "authoritative" not
whinny like the two rotor can. Sure was sweet.
Ed
Sent: Thursday, April 28, 2011 11:59 AM
Subject: [FlyRotary] Re: Cooling Inlets
So your enhanced pressure recovery with the new inlets is
likely largely due to the better control of the entering airflow and the
reduction of any separation caused by the sharp ages of the tubes.
Also looks great. I noticed the inlets appears to have a
removable cover -- I presume this is so you can remove the inlet
cover in order to remove the cowl (or for further experimentation
{:>)?)
Ed
Thanks Ed,
I agree, that looks like the main
factor.
The inlets were made in 3 steps/pieces, each one
bonded to the others as I went so its all one piece that slips tightly over the
OD of the inlet pipe, sweeps back to fair into the cowl contours and then
secured with a couple of screws into nut-plates in the cowl. Mostly
made from carbon fiber to keep it light.
The inlet lip was the
interesting part to make. I made a tool of aluminum sheet the same shape
as a cutaway drawing of the lip, mounted that in the lathe toolpost, chucked up
a 9" square x 2" thick piece of urethane foam using a piece of all-thread &
plywood washers. Set the 'tool' for the proper ID of the inlet pipe and
then machined the inlet shape into the foam to form a female mold. Painted
the foam mold with melted paraffin for a smooth finish and mold release then
laid up the carbon fiber in the mold. Looked like a part out of a
machine when taken out and trimmed. Only snag is that removing
paraffin residue from finished part is critical. There are several
fish-eye areas in the paint that will need to be sanded out &
repainted.
Tracy
On Thu, Apr 28, 2011 at 9:51 AM, Ed Anderson <eanderson@carolina.rr.com>
wrote:
Great to hear, Tracy.
All of the studies I have read indicates
anything you can do to prevent flow separation near the inlet (which you
undoubtedly had at anything off straight and level with those tubes) greatly
aids cooling.
The studies say that anytime you have a
disturbed/(turbulent) area of air impinging on an area of your radiator face
you do not get good pressure recovery from disturbed air - this in turn
can cause that area impacted to suffer a 20% degradation of
cooling effectiveness and also increased drag. The further
upstream from the core the disturbance occurs the larger the affected
area of the core.
So your enhanced pressure recovery with the new inlets
is likely largely due to the better control of the entering airflow and the
reduction of any separation caused by the sharp ages of the tubes.
Also looks great. I noticed the inlets appears to have a
removable cover -- I presume this is so you can remove the inlet
cover in order to remove the cowl (or for further experimentation
{:>)?)
Ed
Sent: Thursday, April 28, 2011 9:07 AM
Subject: [FlyRotary] Re: Cooling Inlets
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
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