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Re: RAdiator fans and H2o cooled engine
R. Wayne Owens wrote:
> I have been trying to avoid fans. They will be in the way above 30 mph
> and even though Bayard duPont said he flew with some for two years
Hi there Wayne, Big David & David Doshay...
Didn't mean to start a goose chase on fans & pumps. Maybe my thought
for a potential need for 'after-shutdown' fan & circulation pump is
baseless (like my sense of humor...whoever saw a goose wearing pumps
The Charles Alresman (info below) CSA April 97 article indicated his
properly executed (my interpretation of his research & system) exhaust
augmenter can run full-power (6000rpm on his Honda) for 10 minutes and
radiator & augmenter were "warm to the touch"; engine temps were
obviously in the green.
Down side is he'll obviously need to bring along a portable stove if
he's out air-camping.
If that translates into even cooler overall system temperature at
taxi-to-tie-down idle speeds, then there could well be no need for
additional cooling of engine after shutdown. Whether heat dissipating
from engine after shutdown can melt your cowl or not is research I can't
conduct: it doesn't on air-cooled Velocities (that I've heard about)...
and I suppose on afterthought if your engine is not too hot when you
shut it down, it won't get any hotter when it's off. Altho forgetting
to use coolant will do a good job of warping an engine head & steam
cleaning anything around it (chalk up one old MGB). WHICH just dawned
on me: since water boils so much better at our cruising altitudes, do
you use PURE coolant and/or what psi radiator cap are you gambling on ?
A spritzer AFTER shutdown would likewise be no help if there's no
circulation of coolant OR air thru the radiator, or of coolant from
radiator to engine, unless your objective is to maximize radiator
cooling rite before shutdown (before you walk away) and/or then have
some natural or thermal circulation going on 'twixt radiator & engine
after shutdown. Note that if there is no temp differential between
radiator (warm to the touch) and what gets spritzed, your not cooling
A spritzer does seem to be good insurance during your learning
experiences (like how many engines would you want to burn up) and to
your own personal engineering and cost compromises (like not perfect but
close enough), or in the event that a cracked exhaust (not so rare)
causes significant loss in augmentor efficiency. It's obviously quite a
challenge to delicately balance the overall equation among radiator
capability (glad to see you're working with Ron Davis), augmentor
inlet/chamber/exhaust dimensions, and engine exhaust tuning. On the
other hand, a spritzer has the potential of cracking your exhaust pipes
(or at least aiding their demise) inside the augmenter, but so does
rain, so what am I thinking? A major point tho is that a properly done
augmentor should be at it's best at full power so spritzers for climb
should really be unnecessary. How about spritzers for water-injection,
or just a casual gathering of friends at a party.
A note from the CSA article: Charles did have a 4:1 exhaust and said
augmentor performance is improved by more pulses in tube at 1 time,
(another reason it's better suited to auto engines cuz of higher RPM).
Your other post said you thought your pulses were fighting each other
and to seperate the exhaust pipes: that's not an augmentor problem,
that's an exhaust design and tuning problem (pipe lengths, diameters,
weld qualities, and shape). You don't want to lose 10-40hp to an
inefficient exhaust for the sake of cooling an engine that won't get you
in the air. And the fewer holes into your augmentor the easier to make
> The Mustang didnt have a fan. I saw one owner sit with his shutdown
> engine about 15 minutes waitng for the rad temp to come down. A
> definate inconvenience.
--didn't have an exhaust augmentor either, but what's so hard about
hanging out at your Mustang ? ("uh yeah, Miss, this is my 'stang...uh..
just monitoring my rad temp reduction status...care for a spin around
the pattern sometime? " ..yeah I hate when that happens)
> I can manage 15 minutes of idle/taxi rpm on my test stand
> befor the coolant temp gets to 220 degrees.
--You're obviously on the right track. (In mid-Manhatten, you could
manage to wait half an hour at an idle taxi stand.)
> I think i will try the spritzer when I get my new radiator. 275 cubic
> inches was definately not enough for 230 HP. Im pretty sure the one Ron
> Davis in building now will be too large 528 cu.in.
Was the safe 15 minutes on a test stand with the 275 cu.in ?
I don't know how cu.inches factor in; the CSA didn't mention
cu.inches. Nor did it mention total system coolant requirement, which of
course is weight. If that's actually radiator frontal surface area as
recommended by Ron Davis, I'd re-evaluate your overall system efficiency
before saying it's not enough, particularly with cracking augmentor
home-heating ducts and un-tuned engine exhaust..
Was that you or the excerpts from Mark's email regarding cracked
home-heating duct? ...for tube material, I'd suggest stainless or
whatever Arlesman used, compatible in heat transfer and strength to your
exhaust pipes and weldable for perfect sealing, opposed to carbon fiber,
which is brittle and expensive & difficult to epoxy for a HI-heat
applications...my guess is Charles Alresman's unit wasn't "warm to the
touch" within an inch of the exhaust pipe. I don't know if it's
required to weld the augmentor to exhaust pipes for best efficiency, but
remember that your exhaust imparts energy as heat, gas, AND noise so
nothing within it should impede the flow of those elements, like holes
and cracks. OH YEAH, and your exhaust also imparts GASOLINE, so your
augmentor also has afterburner potential when you're running over-rich
or having starting troubles...a consideration for cowling exit and prop
clearance. And now I'm wondering about the sonic effects on the
CSA article said for an 1800cc Honda Acura engine able to crank
6000rpm (3000 on prop at 2:1 reduction), radiator dimensions were 2.75"D
x 9"H x 12"W (15"W including tanks), 14 fins per in, with inlet size
recommended by Ron Davis at 15% radiator AREA (I get 108sq"), and
radiator flow was in one half, out the other half (I think that means
front part/back part). Charles' diagram shows his NACA inlet at 2"H X
8"W for 16"sq. His results were good.
> but a variable inlet should reduce the drag penalty. The final iteration 5 years from now
> will be just right.
--Sounds like your closer than you think.
BTW: I checked my CSA roster & Charles Arlesman is spelled Airesman, so
the roster or CSA Apr'97 is in error. No email addr for him, but his
number is 301-724-4586.
--David Doshay, send me your fax number and/or address & I'll fax the
diagram/pictures or mail a copy as an unauthorized example of the
excellent stuff you get from the CSA $20/yr membership, $20/yr back
issues, sign up info (it's not automated yet) at
http://www.canard.com/csa/. Do join if you haven't, but I'll send
anyway as it took me a few weeks to get my CSA copies (I ordered them
all). I'll even legally loan you my copy if I can't get the pic's to
copy...they're really good half-tones.
Thanks for the updates, it's fun just to think, sorry if I ramble on.