Jeff,
It is difficult to build a cooling system that
will keep the water temp on a hot day during a full power takeoff below 212
that doesn’t produce way too much drag and excess cooling at
cruise. I think I remember Tracy
saying that short excursions to 230-240 will not hurt the engine. What happens
after you reduce the power and go around the pattern? Does the temp start
to immediately drop? Take a couple of trips around the pattern at cruise
and see where the temp stabilizes before you start to tear your cooling system
down.
Bill
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]
Sent: Friday, May 15, 2015 10:19
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Return to
Flight - 2
Well, the second
flight occurred last night with same results as before; one short low-level
circuit due to insufficient cooling … looks like Al Wick made the correct
prediction.
There are 3 things I
can try with the current configuration: 1) Increase inlet area 2) Increase
outlet area (adjustable cowl flap) 3) Re-profile the pinched diffuser. I
will do all 3 and see what happens.
If all of the above
show remarkable improvement then repositioning the radiator is the only
alternative.
Jeff
From: Bobby J. Hughes
[mailto:flyrotary@lancaironline.net]
Sent: Wednesday, May 06, 2015
12:36 PM
Subject: RE: [FlyRotary] Re:
Return to Flight
Al,
“Sorry to say,
the pressure you see has no significant effect on cooling efficiency (heat
transfer). The next time you fly, since you’ve removed most of that air,
you will still see 210F. Just like before”.
If the air was trapped
at the top of the heat exchanger I would expect improved temperatures. Could be
wrong.
Bobby Hughes
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Wednesday, May 06, 2015
11:15 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Return to
Flight
Hi Jeff. I’ve
done lot’s of experimenting with cooling sys. Tough to explain all this,
but I’ll give it a try:
Pretty clear you saw 6
psi only because you took off with 3+ cups of air in the system. If you’d
taken off with 2 cups of air, then pressure would have been 9 psi. 1 cup, 14
psi. No air in system, then you would have seen rated cap pressure (16 psi in
your case).
Sorry to say, the
pressure you see has no significant effect on cooling efficiency (heat
transfer). The next time you fly, since you’ve removed most of that air,
you will still see 210F. Just like before. There’s one huge exception to
that statement, that’s if you have air in sys that can’t move to a high point out of the
flow. In that case air in sys has huge negative effect. Causes local boiling
when it passes hot areas and inflates cooling temp.
You don’t have
to fly to prove these concepts. Ground running at idle is all that’s
needed. Let’s assume all air is removed. Then letting engine warm up to
180 F will result in rapid pressure rise to 16 psi (rated cap pressure). Fluid
will exit system. With 2 cups of air in sys, that same 180F will yield slow
rise in pressure to only 9 psi. No fluid will leave sys.
A good cooling design
pretends air is stuck in block, so you add a path for that air to rise out of
the block coolant flow. This is called a dynamic bleed. Air is automatically
removed from engine coolant flow. Super low risk way to fly as you no longer
care if air is in system. It’s can’t affect cooling.
It’s a bit
higher risk to fly without dynamic air bleed, you just make darn sure you purge
all air from block sys prior to flight. Applying vacuum to rad cap is great way
to remove air.
One of the ironies
about cooling design is that air that resides above engine flow is a safety
asset. For example, your cap is highest point in sys and you have 2 cups of air
under cap. Big safety advantage simply because your pressure gage is then a great
predictor of how well your sys is doing. A leak will be detected long before
overheating. A bunch of other assets to this design.
Conversely, air in
engine flow has overwhelming negative affect. Temps soar and risks boil over.
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