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No question, Al, that a cooling system failure can ruin your day, particularly if it detracts you from "Fly the Airplane" mantra. But, I also agree its a tough sell, but I believe it is a tough sell because of whether you or I, or Joe or Bill mean the same thing by a marginal system. Perhaps we could come to a meaningful definition but one eludes me at the moment. I mean consider the nature of the beast, we KNOW of some configurations which have repeatedly shown they perform their function - now, you might think that would mean everyone would adopt them - but, who am I trying to kid - certainly not you, Al? There is always going to be somebody (most folks in this activity?) who are going to want to skin that grape another (better?) way.
I guess the real underlying question in my mind is how do you define a marginal system. I have flown my system for 10 years now in all sorts of Summer heat, long waits while taxing, etc. I (obviously) personally don't view the system as marginal but actually finely tuned to my installation. So while we can all perhaps agree you shouldn't fly with a marginal cooling system - I'm not as certain we could all agree on the definition of one {:>).
I gather (hopefully correctly) that you feel any temperature excursion beyond some point temperature point X in some regime of flight would mean a marginal system. So the next question becomes what temperature point X and why? There should be some meaningful reason we choose temp X. Like beyond X Water boils, coolant boils, metal cracks, spark plugs shatter?
For instance, I fly with no thermostat, for whatever adverse effect that might have on engine efficiency, it does one thing a system with a thermostat can not do. My system begins removing heat from the engine the second the engine is started, with a thermostat no (significant) heat is removed until the coolant reaches the thermostat opening temperature and only then does the cooling start becoming effective in removing heat. I have never had problems with ground operations on hot days. The system cools fine - until I pour the fuel to it on take off and then the temperatures start a slow rise - fortunately so does airspeed and airflow through the cores. Once 120IAS is reached my "marginal" period is over and cooling (if anything) is excessive at my normal cruise power settings.
Yes, hotter coolant does mean more theoretically efficient cooling - but, I don't think that increase efficiency can make up for the fact my system has been removing heat from the system from start up. Now some folks would probably think that without a thermostat the system is marginal - I obviously am not one of them{:>), but, again, my point is how to we define the parameters and how do we populate those parameter with meaningful values.
I suspect the generic parameters would have a degree of commonality for just about all liquid cooled engines - but the values for a Subaru would undoubtedly be different from a Rotary or from perhaps a Chevy V8. Just a gut feel there, but again how do we decide. Exhaust valve temps might be a suitable parameter for some engines but would of course be meaningless for the rotary.
My point is I think it would be difficult to get agreement on the parameters from which to evaluate a marginal system much less agree on the parameter values that will categorize a marginal system. The extremes are easier to define
If the engine seizes from over-heating, if the coolant boils out of the system, the fiberglass cowl catches fire, etc, we could probably all agreed that the cooling system was "marginal". But, if none of that (or similar things) happens - what makes it marginal? 1 Degree F over some set limit? 10F over? You get my point.
Second, I think anyone who puts Evans in a marginal cooling system clearly doesn't understand the thermodynamics of the situation (in my opinion). With a lesser Cp (considerably less than water and even an water/anti-freeze mixture) you will remove even less heat from the engine per unit mass of coolant flow and ensure you will eventually cause even the high boiling temp Evans solution to overheat.
Yes, you can heat Evans to a higher temp before it boils - but all that means is your engine and everything else is at that temp as well. I do believe there is one way you could remove more heat with Evans but that is only if you increased the flow rate of the coolant. That stuff was originally used for racing and racers care more about winning than longevity of the engine - so it does have its uses, I just don't believe aircraft engines is one of them And even if I am wrong about the other aspects of Evans, its higher operating temperature may be withstood by some engines but the rotary is not one of them (again in my opinion).
I always enjoy the pertinent points you bring up, Al. They certainly force us (me for sure) to re-examine our premises and perhaps even change them. I guess we could say any marginal system, be it cooling, fuel, ignition, controls, structural is operating on the "edge" and it could only take a factor or two different to suddenly make the system very, very marginal. So it comes down to the inescapable fact that those of use who 1. Fly, 2. Fly experimental aircraft, 3. Fly with Alternative engines are probably closer to the margin in a larger number of areas than we would care to dwell upon - sanity might be one of them {:>).
Best Regards
Ed
----- Original Message ----- From: "al p wick" <alwick@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, May 15, 2007 7:01 PM
Subject: [FlyRotary] Re: Marginal Cooling contributes to Crash.
I know it's a tough sell. Hard to believe you have significant risk when
you are normally able to just throttle back, wait a while, and temps
start to drop. Tons of times I heard the same response in my
occupation...."If he just reacts to xxx, then the problem goes away".
Marginal systems place you closer to the boil over temp. It only takes a
20F rise in ambient temp to affect marginal system. It takes 80F rise to
affect robust system. If you heat soak a marginal system, that places you
right on the edge of boil over. Add a bubble of air to marginal system,
you are screwed. As your temps rise, your piloting skills drop off due to
anxiety. I've gotten a number of reports from guys who landed gear up
even though their warning horn was blasting away...just because they were
worried about the engine behavior.
The incident I referred to was the guy that took off with marginal
cooling. Landed at Whyoming airport, changed to Evans, then took off and
bit it. Underlying root cause was marginal cooling. He never would have
changed to Evans if he had started out with robust system.
Our day to day problem solving skills set us up for failure. We are so
used to making marginal decisions, that we find it difficult to see the
significance of robust design. Easy to fly for years with marginal
system, then all of a sudden the other contributing factors stack against
you.......
High ambient temp, high altitude, heat soaked engine. Fortunately,
statistically it will only nail a few guys. A few for marginal cooling, a
few for marginal fuel delivery. One common cause....sys designed too
close to failure point.
Certainly agree, spray bar a good solution.
-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing.
Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
On Tue, 15 May 2007 15:10:12 -0400 "Ed Anderson"
<eanderson@carolina.rr.com> writes:
Hi Al,
I would be interested in these other factors you mention referring
to the
crash. I have years of flying under cooling deficit conditions
right after
take off as do others as you mention - without any problem. Every
study I
have read on cooling indicates the designer strives for an optimum
cooling
system- for an operating regime - (frequently for the cruise regime)
and
then uses whatever, cowl flaps, exhaust augmentation, spray bars,
to cool
it under less than ideal conditions- like immediately after take
off. I
understand even the P51 faced that problem on taxi and take off on
hot days.
You can certainly design your system to not have a "take off"
cooling
deficit but, you are now starting to talk bigger radiators (may have
space
constraints), more weight, cooling drag, etc. for some airframes and
flight
regimes a bit more would not be significant, but for other airframes
and
speeds these factors become more significant.
Perhaps we need to be as bit more specific as to what degree of
"overheating" we are referring to. My limit on oil temp is 200F, my
limit
on coolant is 220F and those only for the short duration of launch
and up to
120 MPH IAS at which time my system is on the good side of cooling.
10 years
of flying with that limitation has not yet revealed any problem so
far as I
can tell. Now with a rotary, if your temps are going 240F on oil
and
similar on coolant then I personally would feel that is too high and
something should be done.
A crash to which the overheating was apparently one of a set of
factor is
certainly something that I would be interested in. How bad was the
overheating and how did it contribute to the crash? I (and I
believe all of
us) would be interested in the details of the crash you mention that
was
contributed to by marginal cooling - for lessons learned. A spray
bar does
indeed provide a considerable margin, Tracy flew with one for a bit
(mainly
for racing I believe), I've never experimented with one since I
don't go
racing and once airborne and 120 IAS and my system is happy.
However, it
might be interesting to see exactly how much benefit such a simple
system
would provide.
Gotta put that on my long list of "to do" things. Another thing
I have
been thinking more about is that my GM cores which have served well
are
approaching the 10 year point. They are really not designed for
water flow
as we know, so I would not be surprised that a custom made set of
radiator
cores might lower my coolant temps by 5-10F by simply providing
improved
coolant flow.
As always, appreciate your input and perspective, Al. Any risk we
can
eliminate or reduce is worth examining and taking action on. Again,
would
be interested in the details of the accident if you have them.
Best Regards
Ed
----- Original Message ----- From: "al p wick" <alwick@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, May 15, 2007 12:08 PM
Subject: [FlyRotary] Re: First Flight - Renesis in RV-7A
>I know a lot of you guys are flying with conditions similar to what
Ed
> describes. It gets hot during climb, but cools off during cruise.
It
> seems manageable. I encourage you to not tolerate such a design.
This is
> a root cause for crashes. You have marginal system, normally
easily
> managed, but suddenly other factors come into play. We had crash
last
> year with marginal cooling as one of the root causes.
>
> One simple solution that provides extra safety margin is to just
add a
> spray bar in front of radiator. It just takes a tiny mist of water
to
> dramatically improve cooling. Strongly encourage spray bar at a
minimum.
> Great solution for initial testing.
>
> Even then, I would seek improvements that eliminate need for spray
bar.
> There are simple improvements out there. There are guys flying
exact same
> hp as you, yet they have 10 to 20% better cooling efficiency. Find
out
> what they are doing right.
>
> If you had everyone flying record their temp as they climb out
from sea
> level to 12k ft, you would find a couple guys with better
efficiency than
> the others. You'd have to record outside air temp. Coolant, oil
temp at
> start and end of climb. Everyone would have to climb at same rate,
say 80
> mph, then 90mph. Compare area of radiators. With some facts like
this you
> could end up with some genuine breakthroughs. Speculations do not
lead to
> breakthroughs.
>
>
> -al wick
> Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and
cam
> timing.
> Artificial intelligence in cockpit, N9032U 240+ hours from
Portland,
> Oregon
> Glass panel design, Subaru install, Prop construct, Risk
assessment info:
> http://www.maddyhome.com/canardpages/pages/alwick/index.html
>
>
> On Tue, 15 May 2007 07:47:09 -0400 "Ed Anderson"
> <eanderson@carolina.rr.com> writes:
>> Congratulations, Dennis. A great day for sure! A lot of work
and $$
>> coming
>> to successful launch. Unless you make the cooling system
capacity
>> considerably greater than you need at cruise, you will always run
a
>> cooling
>> deficit during climb - high power, low airspeed. So long as it
>> doesn't
>> exceed your limits and cools off once sufficient airspeed is
reach,
>> you
>> should be fine
>>
>> Ed
>> ----- Original Message ----- >> From: "Dennis Haverlah" <clouduster@austin.rr.com>
>> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>> Sent: Monday, May 14, 2007 10:23 PM
>> Subject: [FlyRotary] First Flight - Renesis in RV-7A
>>
>>
>> >I made my first flight this evening!! All systems worked fine
-
>> cooling
>> >was marginal in climb but we had a good inversion and the
outside
>> air
>> >temperature was quite warm. Several neighbors videoed the
flight
>> and I
>> >heard several comments about how quiet the rotary plane was when
we
>> played
>> >the video. We had a 180 hp RV-7A flying chase and on the video
it
>> was much
>> >louder!! Only flew about 10 minutes but made an acceptable
landing
>>
>> >considering there were about 50 people watching. I'll post
some
>> picures of
>> >the plane later tonight.
>> >
>> > Dennis Haverlah
>> > RV-7A, Renesis, James Cowl
>> > Radiators under engine
>> > Catto 76 in dia- 8 in pitch
>> > EC-2, Em-2, RD1-C
>> >
>> > --
>> > Homepage: http://www.flyrotary.com/
>> > Archive and UnSub:
>> > http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>>
>> --
>> Homepage: http://www.flyrotary.com/
>> Archive and UnSub:
>> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>>
>
>
> -al wick
> Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and
cam
> timing.
> Artificial intelligence in cockpit, N9032U 240+ hours from
Portland,
> Oregon
> Glass panel design, Subaru install, Prop construct, Risk
assessment info:
> http://www.maddyhome.com/canardpages/pages/alwick/index.html
>
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub:
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
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Archive and UnSub:
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-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing.
Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
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