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