Today's Message Index:
----------------------
1. 06:10 AM - cooling air requirement (Gary Casey)
2. 06:47 PM - Re: cooling air requirement (Tim & Diane Shankland)
3. 08:51 PM - Re: Run-in and Break-in (flyseaplane)
4. 11:38 PM - Re: cooling air requirement (albert piccioni)
Message 1
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | cooling air requirement |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
The calculations for cooling air requirements aren't too difficult if you're
only looking for a rough order of magnitude answer. A 100-hp engine will
dissipate about 25hp through cooling. Some goes into the oil, so let's say
the cylinder cooling requirement is 20 hp. There are 2545 BTU/hr in one hp,
so the heat to be dissipated is 850BTU/min. It takes about 14 cubic feet to
contain 1 pound of air and the specific heat of air is about .24 (it takes
.24 BTU to heat one pound of air 1 deg F). You could probably assume the
air temperature rise across the engine is 30 degrees: 14 cubic feet of air
will absorb 7.2 BTU's. To absorb 850 BTU/min of heat you need 1,650 CFM air
flow (850 X 14 / 7.2). Problem is it takes a significant pressure to force
that much air around the cylinders - a few inches of water maybe. Normal
ventilating fans are rated at zero pressure drop (blowing into free air) and
may not be able to flow nearly their rated flow with a significant pressure
drop. The best suggestion I have heard is simply to build a reasonably
large plenum that will capture propeller blast and use that, watching the
cylinder head temperatures. A very effective cooling method would be to add
water mist to the air, but the steam cooling that will result is probably
very uneven and that would worry me.
Gary Casey
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: cooling air requirement |
--> Engines-List message posted by: Tim & Diane Shankland <tshank@megsinet.net>
Regarding the cooling of the Suburu, I thought I might add something
since I sped more of last winter working on the design of my cooling
system. First my research has indicated that an engine will an almost
equal amount of heat to the cooling system (i.e. the water) as it
produces in useful power. Using that a stock 80 hp Suburu would reject
3392 BTU/min. According the the spec sheet for the engine that someone
on this list was good enough to provide the actual number is 2690 BTU or
so for this engine the percentage rejected would be 80 % of the output.
Thus for a 100 hp engine it would be 4241 BTU/min. Next I spend a great
deal of time testing heater cores of heat transfer and flow rate.
Slowing down the flow of water will make the change in temperature
across the radiator larger but the flow rate will be smaller. The amount
of heat transferred by the radiator is volume/min (gal/min)* weight of
water (lbs/gal)* Specific heat of water (1)* change in temperature (F) .
When you reduce the flow you actually reduce the amount of heat
transferred. If someone wants I can give you all the equations, but the
result is that for a given air flow though the radiator an increased
water flow will increase the heat transfer but at a diminishing rate,
that is the curve flattens out. If you increase the airflow the whole
curve moves up (more heat transferred).
Tim Shankland
601HD
plumbing the cooling system
>
>
>
>
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Run-in and Break-in |
--> Engines-List message posted by: "flyseaplane" <flyseaplane@netzero.net>
Of all the engines I, or others I know, have installed on certified
aircraft, there was never any ground run time other than to make sure
everything looks OK and all systems "GO".
1) Pull the cowling
2) Look for oil leaks
3) Put the cowling back on and go fly.
One hour of accumulated ground run while taxing at low power settings
will likely not generate enough heat to do cylinder damage. Make sure you
watch your CHT. Every new engine/airframe combo needs one. You won't find a
CHT gauge in some small certified planes because the factory already did all
the research for you when they certified the plane. They determined how the
baffles and cowling needed to be constructed early on by using a probe at
each cylinder, and once they got it all figured out, they make many, many
copies of that set-up.
Since many of us don't have a "tried and true" baffling-and-cowling
set-up, we need to see where the CHT will be for ourselves. I have seen 100
degrees difference between cylinders on a poorly built set of baffles. I
have a Westach "quad" CHT so I can see where each cylinder is when it comes
time to get ready to fly my plane (it will be a while still). Some system
that will allow reading of all CHT's in a new installation would be a smart
idea.
Just my 2 cents,
Linc
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: cooling air requirement |
--> Engines-List message posted by: "albert piccioni" <adpiccioni@cnx.net>
I have taken photos of the water manifold for my ea81 I have made if
anyones' interested I can send to u directly.
alberto,,,in the okanagan
----- Original Message -----
From: "Tim & Diane Shankland" <tshank@megsinet.net>
Subject: Re: Engines-List: cooling air requirement
> --> Engines-List message posted by: Tim & Diane Shankland
<tshank@megsinet.net>
>
> Regarding the cooling of the Suburu, I thought I might add something
> since I sped more of last winter working on the design of my cooling
> system. First my research has indicated that an engine will an almost
> equal amount of heat to the cooling system (i.e. the water) as it
> produces in useful power. Using that a stock 80 hp Suburu would reject
> 3392 BTU/min. According the the spec sheet for the engine that someone
> on this list was good enough to provide the actual number is 2690 BTU or
> so for this engine the percentage rejected would be 80 % of the output.
> Thus for a 100 hp engine it would be 4241 BTU/min. Next I spend a great
> deal of time testing heater cores of heat transfer and flow rate.
> Slowing down the flow of water will make the change in temperature
> across the radiator larger but the flow rate will be smaller. The amount
> of heat transferred by the radiator is volume/min (gal/min)* weight of
> water (lbs/gal)* Specific heat of water (1)* change in temperature (F) .
> When you reduce the flow you actually reduce the amount of heat
> transferred. If someone wants I can give you all the equations, but the
> result is that for a given air flow though the radiator an increased
> water flow will increase the heat transfer but at a diminishing rate,
> that is the curve flattens out. If you increase the airflow the whole
> curve moves up (more heat transferred).
>
> Tim Shankland
>
> 601HD
> plumbing the cooling system
>
>
> >
> >
> >
> >
>
>
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|