|
Occasionally, when experimenting, you encounter a
solution that has far reaching positive effects. This dynamic air bleed is one
of those. Pretend we have 100 planes with dynamic bleed, and 100 without.
We would find greater incidence of overheated engines in the ones without. More
compression seal failures, more pinging, more flights with low coolant level,
etc etc. Your description of effects you experienced makes this clear....along
with all my years of measuring effects, testing concepts.
I think it's hard to appreciate just how
significant this is, because it's easy to get by, or just react to the problem
by taking it thru extra cooling cycles. Since we don't measure how effective a
solution is, we never realize a slight change can dramatically improve safety.
So "ok" solutions get transferred from plane to plane, when a "knock your socks
off" solution gets overlooked.
On my first engine install, I did a bunch of things
that were dumb in hind sight. I had a custom radiator made with the radiator
hose location 2" below the top of radiator. Hello! That meant I had 2" of air in
radiator. So I had them install fitting on top that allowed me to add 1/4" hose
up to filler neck. Dynamic air bleed. With my new engine install, I have no
extra hoses anywhere. It's guaranteed to work, and I can prove it all out before
ever flying.
I replied to your post, but my focus is on the guy
that's designing his cooling system now and in the future. If he just pretends
coolant doesn't flow....and considers how air will exit each component....he'll
have safer system. Ed, you do much better job than I do of combining theoretical
and measurement. I really like your btu calculations leading to diagnosing cause
for high temps. That's good stuff. Valuable. To some extent my post takes
advantage of your open mindedness. Sorry, I don't intend to pick on you.
Just trying to save a crash, or overheat, or whatever.
If you view every failure as a system failure (not
operator), you will find significant solutions. Good systems are insensitive to
operator errors. The dynamic bleed is a good example. I add coolant, it fills
right up. No trying to coerce coolant. No topping it off. Less prone to operator
goof ups. Most aircraft crashes have operator error as major component. Same is
true for manufacturing businesses. If you make most of the systems insensitive
to operator, then he is allowed to focus on those few items that don't have
system solutions. Operator makes fewer mistakes. That's one of the key items I
discovered as QA manager. It's what I've done on my plane.
regards
----- Original Message -----
Sent: Friday, October 05, 2007 10:48
AM
Subject: [FlyRotary] Re: Coolant Water
Pressure
You are absolutely correct, Al. Just did not
think, gas/air compresses, liquids do not (to any appreciable
amount).
If by failure, you mean my system would not have
supported flight in that condition (air in coolant) , then you are quite
correct, on the other hand, one of the reasons to test (as you have often
pointed out) is to discover problems before flight inorder to preclude
failures in the air. In this case, I discovered my configuration
requires a bit more effort to remove the air. Once that is done, the
system is operating within its intended parameters. So does that make
the overheating a system failure or a failure to configure the system to
the proper operating parameters.
Even in the automobile, the rotary is known for trapping
air and requiring burping although many can get away without it because most
autos don't operate anywhere near WOT for more than a few seconds, so the
effects of trapped air (depending on amount) may not be
noticed.
I think there is a difference, for instance
you could design the perfect coolant system but fail to put sufficient coolant
into the system resulting in overheating - is that a system failure or a
operational failure? or perhaps more accurately - operator failure?
I am always impressed by your meticulous attention
to detail and systematic approach. I could certainly have benefit
from your knowledge/approach back 10 years ago in my initial
design{:>). But at that time, there appear to be bigger issues - such
as trying to understand how a rotary engine really worked
- sorted out. Air flow and cooling were just vague notions
back then and I just assume they would naturally fall into place
{:>)
I still have a photo of my first oil cooler
installation to remind me of how ignorant of those matters, I was back
then . It had a "Plenum" that conformed to the area of the core - and
its wall stood 2" way from the core face at every point. Then I had a 2
1/2" dia hose piping air to one corner. Is there small wonder that my
first flight was limited to once around the pattern due to oil
temps{:>). Here is a photo - the oil cooler plenum and inlet are the
brown colored box on the left side of the engine (facing the engine) close to
the firewall with the large back hose (that one is 5" in dia as one of my
several early attempts to address the oil temp problems). The
radiator plenums were only slightly better.
No question, knowing what I now know, I would
have done some things different. As you know, Al, I may
sometimes take issue with your characterization, but not your approach and
insight. A valuable contribution to say the least.
Best Regards
Ed
----- Original Message -----
Sent: Friday, October 05, 2007 12:49
PM
Subject: [FlyRotary] Re: Coolant Water
Pressure
>at 22 psi the air would likely occupy even more
space
The opposite is true. Air space reduces substantially
when you increase pressure. Think of coolant as a solid, and air as a
giant spring. When you add btu's to coolant, it immediately responds by
expanding. This causes the air molecules to compress...a lot.
There are some fun exhibits at the science museum I
volunteer at we use to demonstrate air/ water compression. An eye dropper
inside a pop bottle. When you squeeze the pop bottle, the eye dropper
plummets to the bottom. When you let go, dropper rises to surface. The
pressure increase when you squeeze bottle causes air in dropper to
compress(less air volume). This allows water to displace that air....dropper
is now heavier and falls to bottom.
It's really ironic. You can design a system that seems
to work fine. You fly with that for years with no failures( well I guess you
could call the pinging and high temps a failure). But a small change can
greatly reduce your risk. There's a lot of value to changing your air bleed
design to one that dynamically removes air. No shrader valve, no repeated
cooling cycles to remove air. By "dynamic" I mean that it automatically
removes air from the system. No muss no fuss.
As you design system, just pretend their is air at the
top of each component. Then find simple way to allow that air to move to
higher component in system. So, my radiator is lowest point in system. If I
place my radiator tube near the top of radiator, then all air naturally
leaves rad and flows to engine. Next I look at highest coolant passage in
engine. In my case I had to drill and tap a little 1/4 npt into the coolant
manifold, then run tube from there up to highest point in system. Suddenly
I've got a system that automatically removes all air immediately. Try as I
can, I can no longer trap air anywhere. If I develop compression leak that
pumps air into system, it has much less effect, because it rises out of the
coolant flow. When I drain and refill, it all immediately and rapidly fills,
I can get every drop back into the system.
Dynamic air bleed is a safety advantage, easy to
accomplish. Each of these safety advantages adds up mathematically.
Likewise, contrary to popular theory, leaving two cups
of air under cap increases safety. You can prove that to yourself with
simple experiment I described earlier.
-al wick
----- Original Message -----
Sent: Friday, October 05, 2007 9:07
AM
Subject: [FlyRotary] Re: Coolant
Water Pressure
Yes, at 22 psi the air would likely occupy even more
space, but since I do my runup with the cap off or loose, there is no
pressure during the process. So while I have never measured it and
it probably varies from one time to the next, there appears to be approx
1/3 of the top part of each core which has air on the initial fire up of
the engine - after a complete drain and refill of the coolant
system.
I must admit that the first several times of
draining and refilling coolant, not being as knowledgeable as I am now, I
almost cooked the engine, because I assumed that when the header tank was
full - the engine had all the coolant it could take. Rapidly
climbing coolant temps and pinging of hot engine cooling off soon make it
clear that just because the header tank was full didn't mean a whole
lot. Of course, I noticed after each run up that the coolant level
in the header tank would decrease permitting me to put more coolant
in. That finally made me realize what the problem was - would have
been very nice to have this list around back then {:>)
After burping the system there is still small amount
of air left, but the overflow tank set gradually removes the remaining air
over a couple of flights. Then the hydraulic "lock" phenomena starts
with initial pressure of 21-22 psi immediately on engine start, dropping
off quickly to zero and then gradually climbing back to 5 - 7
psi as the coolant heats up.
But, other than having to "clear" the air out with a
couple/three run ups to 5000 rpm, it works just fine and has since
97. I occasionally toy with the idea of putting in simple small air
bleed on the top of each - but, like I said, it works fine and other
things to do {:>)
Sounds like your approach will avoid my burping
problem. However, Lynn has mentioned that even in the car
installation it often takes burping the engine to get the air
out.
Ed
----- Original Message -----
Sent: Friday, October 05, 2007
11:12 AM
Subject: [FlyRotary] Re: Problem?
[FlyRotary] Re: Coolant Water Pressure
Hi Ed,
for sure I saw your installation before (numerous times...), but I
do not recall your exact pluming.
Your description below sounds like inlet and outlet are facing
down.
At 22psi it should even be more like 1/2 the radiator with air
:)
Anyway, I assume waterflow is radical enough to strip the air out
in 3 trials.
My system will have a bottom inlet and a top outlet. If it doesn't
fit the outlet may exit the bottom of the tank but will have an internal
standpipe - this way there is next to no space where air can get
trapped, just a small bubble atop the standpipe, won't be big enough to
cause any cooling detriment.
I still see BMW motorcycle oil-coolers mounted this way. Don't know
the exact make-up today, but the earliest ones where simple single pass
bottom feed bottom exit (cheapest solution and esthetically least
disturbing), a big problem to purge. 1/4 was useless because of trapped
air...
Furthermore, if the pump had a little leak or just a long time
between runs would drain the oil fro mthe cooler and at start-up you had
a fresh load of cold air inthe cooler! As it heats up the air-bubble
expands and reduces cooler volume even more...
Best Regards,
TJ
snipped..
In my case, if I do a complete drain
and refill of the system, on the first run up the core's tanks
will be hot approx 2/3 of the way up and then they are much
cooler - indicating that the remaining 1/3 of my core is filled with
air. It generally takes me 3 runups reaching 5000 rpm
before I can touch the core tanks and find them hot all the
way from top to bottom. So depending on your radiator set up
that might be something you can quickly check.
snipped....
--
Homepage: http://www.flyrotary.com/
Archive and
UnSub:
http://mail.lancaironline.net:81/lists/flyrotary/List.html
|