----- Original Message -----

From: Dale Smith

To: Rotary motors in aircraft

Sent: Friday, July 16, 2004 4:18 PM

Subject: [FlyRotary] Re: 11th test flight

Steve Brooks wrote:

I made a test flight today with the new scoop, but also wit cooler OAT (70F)
than I've seen in the last couple weeks.  I flew for 6 tenths of an hour
with temperatures for the oil at 207 and coolant 200 stabilized at 4700
RPMs.  I increased the throttle to 5300 RPMs and the coolant stayed put, and
the oil increased by only 3 degrees.  I was about 1500 AGL for the entire
flight. I did descend a few hundred feet and climb a few hundred feet to
watch the temperatures, but usually was flying a level circle around the
airport.  I reduced the throttle to 4300, and maintained level flight at
about 105 kts.  Oil dropped to 195 and coolant to 190.

I guess that the good news is the I could fly all day at those temperatures,
and I never saw any temperatures higher than 210, though I really didn't do
an extended climb.  I really didn't push level cruise higher than 5300 (135
kts), but the temperatures seemed to be holding, and actually the oil
dropped a degree after letting it stabilize a couple of minutes.

The bad news is that the scoop appears to be costing me about 10 kts, which
I was expecting.  I also don't have any wheel pants yet on the main gear, so
it's not like I'm out to win any speed test at this point anyways.  My oil
continues to run higher than the coolant which indicates to me that I need
to do some more baffling to divert more air to the oil cooler.

I also have not done any filling or finishing to the scoop, so it's surface
is more like sandpaper right now.  Finishing it will probably improve air
flow some more, and also reduce some of the drag.   I left the scoop on the
plane for now, so that I can hopefully get another flight in tomorrow
morning.  My plan tomorrow is to climb up to 5000' and see what I get there.
Then I'll remove the scoop, which takes about 5 minutes, and bring it home
for some filling and sanding.  And after a few more flights, and more
filling and sanding, some primer and paint.

I am still looking at this as a "hot weather scoop".  My plan is to remove
it during cool weather, and re-install it for June-August.  I mount the
scoop using 6 10-32 SS screws into nutplates embedded in the landing gear
cover, plus 2 of the screws that mount the landing gear cover to the
fuselage.  It's not likely to come off on its own.

Steve Brooks
Cozy MKIV
Turbo Rotary - 6.3 hours and counting

  

Steve ... re: the above underlined.

I would say that what you have is just fine regarding your oil temp.  Remember that the "delta T" between where you are running and the temperature at where it quits working is quite high.  Especially if you are using synthetic oil.   Molbil I keeps lubricating quite well up past 400 degrees and beyond.    Thus, if you are running temps near 200 degrees you have near a 200 degree temp spread (delta T) between what the oil can take away and what it IS taking away in BTU's of heat dissipation in a stable system.    That is a pretty fat safety margin, when you figure you can run 100 degrees hotter than what you are now and still have 100 degrees left before lubrication failure is imminent.  Obviously, lower is better.

Water cooling now is a different story.   operating coolant at temps near 200 while water boils at 212 ... gives you a delta T of just 12 degrees to play with.   I know you can kick it up by anti-freeze, pressure on the system, etc. etc.   but the bottom line is that you have a lot narrower delta T range to deal with, and you are always working the system a lot closer to near it's maximum potential for heat dissipation.

Just a thought,

Dale Smith