Hey Ed, before you change ducts, how about making the delta-T
measurements on the water side of the two coolers, and then repeating with the
measurments with each change in duct. I think we can learn something
fromthe data.
----- Original Message -----
Sent: Friday, April 08, 2005 2:09
PM
Subject: [FlyRotary] Re: Ed Anderson
Cooling System
Hi Doug,
No doubt when you have different (higher?) standards they can be
tougher to meet {:>).
I agree with you assessment about a "reverse venturi"
duct. I have a larger "capture area" before the one duct necks down to
10 sq inches and the other to 18 sq inches. My theory was that would
increase the velocity (dynamic pressure potential) to help maintain that
higher dome of pressure in front of the core that my radical curved duct
walls infringe on. My inlet is 6" long on one side and 3" long on the
other, so did not have a lot of room to play duct with.
I flew a max power/climb take off two days ago with the ground OAT was
85F, by the time I hit 3000 MSL the oil temp was up to 210F and the coolant
to 220F (my personal maxs for short duration). I then leveled off and
let the cooling system catch up with heat load. So it does appear that
for mid summer operation a bit more inlet area is called for. I intend
to open up the 10sq inch side (which is on my hottest radiator - first in
the series) to 18 sq inches as well. That will provide a bit more
margin on those hottest days. My personal experience with the 91 turbo
block and the Teflon coat silicon coolant "O" rings that even coolant temps
of 240F for short periods do not appear to have done any harm - as you say,
coolant and combustion chamber are still separate.
But, I am please with the experiment in that I believe for my HP engine
(I estimate 175-180HP) I have found a "lower" limit on duct size.
Although perhaps with "exhaust augmentation" it could be made to work fine
in hotter days - much easier just to open one duct up a bit.
I total agree, when approaching trees or a ridge line - who cares about
the temps - can always replace the engine (if necessary) provided you clear
the tree line.
It always a personal pleasure to exchange ideas, experiences and
theories with people of the calibrate we have on this list. I always
report my happenings - even when they are a bit embarrassing at times.
I seem to have had an unusually assortment of events happen. I was
awarded the Rotary Round Up "Lightening strikes six times (or more) award
which lists a litany of things from oil pump key drop out, front tire gauges
on both sides by the bolts holding on the wheel pant when I screwed them in
a bit too much and then planted the front tire a bit hard causing it to
balloon out and catch the bolts, flop tube drop off resulting in a 12 miles
engine out glide, etc, etc.
But one of the main reasons I share - is life is too short to
make all the mistakes yourself, so my objective is IF you are going to make
mistakes - advance the state of the art and make one I haven't - we already
know how those turned out{:>).
Thanks for the comments, Doug. We try our best - and what's great
is when you're wrong, folks will bring it to you attention - in a pleasant
manner.
Tomorrow I launch (weather permitting) heading down to join Tracy Crook
and on to Lakeland, Fl for Sun & Fun hope to see a bunch of your folks
down there.
Best Regards
Ed
----- Original Message -----
Sent: Friday, April 08, 2005 11:05
AM
Subject: [FlyRotary] Ed Anderson
Cooling System
There were those who claimed that there was
no way that would work. Well, I reduced my inlet area from 48 sq
inch to 28 and it works just fine thank you. Tracy Crook can vouch
that I have flown with the small openings for well over a year and he
has never seen steam or smoke coming from my engine - yet
{:>).
Hey Ed...that was probably me! All my analysis uses Military
Air outside conditions (+40 deg F over standard conditions), are
climbing at 100 mph TAS (near max rate of climb) and assumes that you
are actually generating 200 HP. At 2,000 ASL and +40 deg F over
standard....I suspect you are not generating 200HP and if you are
indeed capable of 200 HP probably do not maintain that operating condition
sufficiently long (at 100 mph) to reach steady state conditions which
my rules of thumb consider.
Hopefully if you ever are approaching the trees on T/O under the
more severe conditions you can tolerate 245+ deg F engine out coolant
temperature. Been there done that with the Mooney. You know
what? The throttle stayed in WOT and no leaves on the belly!
It defined "pucker" for me. So you'll have to forgive me if I size
my inlets just a little bit larger for our 95 deg summer days.
(Military Air at sea level is 99 deg F)...WOT...generating 200 HP for an
extended period!! Do what Tracy "noodles" and spray water on the
heat exchangers!! Of course you have to carry that two gallons of
water around for the inevitable situation :>). Sort of like a
"gear up...not if, but when...if one flys enough.
Incidentally we unavoidably reached those 245 deg F engine out
temperatures while developing my friends system without "apparent" ill
effects. He does not have sufficient hours to determine if there
were long term effects, but water and oil are still
separate! Being a little experienced with automotive tests I
would estimate that short of rapid temperature "shock" at those
temperatues, no damage was done. Note: one of the OEM
Automotive tests of heads/head gaskets is to dump just above freezing
water into the engine inlet side of the waterpump while running at full
tilt!! That is thermal stress!
SWAG (valuable engineering tool), I believe you have what is almost a
reverse venturi duct and your "effective" inlet area is actually larger
than 28 sq. in. which is probably your smallest area in the inlet
duct. I have "noodled" (another valuable engineering tool!) that
what you are doing might very effectively compensate for a very short
inlet duct....but probably is a small detriment to cooling drag. Too
small to matter IMO.
Hey, you are a terrific experimenter and an invaluable Hummmmmer
flyer who is willing to share even at the risk of us "still building"
asking questions trying to understand what is happening in the Big
RW. It is terrific you share so we can consider what you have
done and if we are smart....will try to implement same in our own
builds.
I truly appreciate your combination of theory, practical application
and ability to write!! Thanks!
Doug in
CO