These are clearly empirical relationships based on some unspecified number of data points. They include implicit assumptions about the heat exchanger configuration (frontal area to volume ratio). Thus, the validity for other HX configs is undetermined. That said, these guidelines provide a reasonable starting point if one is not going to do a full-fledged HX analysis. I always say that all the analysis in the world only tells me where to start testing. I appreciate the input and will consider these parameters in selecting my cooling system comnponents.
Gordon C. Alling, Jr., PE
President
acumen Engineering/Analysis, Inc.
540-786-2200
www.acumen-ea.com
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy
Sent: Friday, March 09, 2012 10:31 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Engine cooling
Sanity check:
1) Requirement: Radiator surface required is 1.5 sq in of surface area per cubic inch of the engine. For example: LS1 V8 Chevrolet = 350 cu in x 1.5 = 525 sq in of radiator surface area required. For this purpose, this applies only to the surface area of the radiator that the air flow first makes contact with.
2) Requirement: Minimum of 3.0 cu in of cooling volume per HP produced.
For example: We only utilize up to 300 HP of an LS1 for aircraft use. Using a dual radiator configuration with two radiators measuring 15” x 18” x 2.25” thick = the total cooling volume is 1215 cu in.
Therefore, our cooling volume to HP ratio: 1215 cu in cooling volume ÷ 300 HP = 4.05 cu in per HP. With this formula, we have been able to maintain climb out temperatures of around 200°F and 190°F at cruise on a 100°F day. With a cooling system like this, we could taxi from Houston to Dallas with no overheating problems.
Is it just me or is the math here bogus?
Tracy
On Fri, Mar 9, 2012 at 9:20 AM, Jeff Whaley <jwhaley@datacast.com> wrote:
I think the approach makes sense for the worse-case hot weather environment but from a northern perspective you have to do something when it gets cold. If you design a system to cool at 100F OAT, your engine it is going to be too cold at 0F OAT; in fact it will be exactly 100F less, typically 80F.
Right now I'm using grills that block off approximately 50% of inlet air flow; at 0F I add tape to reduce to 25% air flow. This is of course only ground adjustable but adequate for typical winter flying. Running synthetic oil a bit too cool is less significant than running the glycol too cool. My long-term approach will be to install an in-flight adjustable flap to restrict the outlet air of my radiator, which does not provide airflow over the engine, only my oil coolers do that.
Jeff
-----Original Message-----
From: Ernest Christley [mailto:echristley@att.net]
Sent: Thursday, March 08, 2012 3:38 PM
Subject: Re: [FlyRotary] Engine cooling
Chris Barber wrote:
>
> Just some data points for discussion. PLEASE if you know some stuff
> that is rotary specific, or just wrong, CHIME IN!!
>
>
>
> Chris
>
> Houston
>
>
>
> Cooling Guidelines for V8 Engines in Aircraft by Bud Warren and
> Phyllis Ridings
>
> After much thought, Bud decided to install a thermostat in the LS1
> engine of the Ravin 500 to do some test flying. During cold weather
> the resulting engine temps have remained stable at 190°F at cruise,
> and near 200°F during climb out; just about what we see during the
> warm months of the year. This has corrected the check engine light
> coming on due to the engine remaining in warm up mode.
This approach makes me nervous. It doesn't hit us much here in the southern US, but things get colder as we move north.
When it is freezing on the ground, it's very easy to get REALLY cold temps at altitude. If it is 0*F on the ground,
then the rule of thumb says that it will be -40* at altitude.
The problem described is that the engine isn't able to produce enough heat to warm the water with the amount of -40*F air that is rushing through. The prescription given is to force the water to stay in the engine longer. This necessarily means that the water will stay in the radiator longer. Now the thermostat opens even less, because what it pulls from the radiator is ice water. At some point, the water gets really hard in the radiator and stops flowing altogether. The there is no flow from the engine to melt it. The engine water keep recirculating and it eventually overheats.
The Mack truck I bought in the late 80's had a shutter arrangement in front that would close when it got to cold and block airflow through the radiator. I think a thin aluminum panel, possibly controlled by a push-pull cable from the cockpit, that slid in to partially block the radiator would be a much safer solution. It would also alleviate the concern over broken thermostats. The panel would require minimal support, as it could simply lay flat against the radiator face.
This message, and the documents attached hereto, is intended only for the addressee and may contain privileged or confidential information. Any unauthorized disclosure is strictly prohibited. If you have received this message in error, please notify us immediately so that we may correct our internal records. Please then delete the original message. Thank you.
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html