From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: The effects of OAT on cooling
Date: Tue, 24 Sep 2019 21:02:18 +0800
References: <list-12988427@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-12988427@logan.com>
Message-Id: <68A53516-A6EF-4E52-A0F1-444C4890BB50@gmail.com>

Thanks so much Jeff for the information you provided. Very helpful.
Cheers

Steve


> On 24 Sep 2019, at 8:39 pm, Jeff Whaley jwhaley@datacast.com =
<flyrotary@lancaironline.net> wrote:
>=20
> Steve, my experience says it is 100% linear ** inside the normal =
operating range **. If there is no way to control airflow through your =
coolers and you fly at the same airspeed, same power setting, same =
mixture setting, then your engine temperatures will be directly =
controlled by OAT - if your engine runs at 160F with OAT at 60F it will =
be 180F when OAT is 80F - or at least you had better plan for that.
> Now, there may be some slight non-linearization with high humidity and =
at engine temperatures you don't want to run at; i.e., if your engine is =
already running at 230F (I sure hope not) and the OAT increases by a few =
degrees there may be non-linear transfer at this point.  If my engine =
gets above 210F it's time to back off the throttle - I find every inch =
drop of MP reduces the engine temps by about 5F.
> One day after cruising for an hour at 185F I noticed the water temp =
had spiked up to 195F - I thought something was wrong - I was about 30 =
miles from destination with few alternate options, so continued on and =
landed.  ... but here I was, with my wife about 150 miles from home - =
what to do?  I did a precautionary climb over the airfield using water =
spray for the climb to 5500 feet; as long as I sprayed water on the =
radiator the temp stayed around 180F if not it would creep back up to =
about 195F - I backed off the throttle 1" MP at a time from 22" down to =
19" until the temperature settled around 180F and limped back home with =
a tailwind.  As it turned out I had just flown into an area of warmer =
air ... and learned a few lessons that day.
> Jeff
>=20
> Hi Guys
>=20
> Can anyone confirm the relationship between cooling at various OAT's =
and humidity.
> Paul Lamar says that cooling capacity drops 1% for every increase in =
OAT in degree F.
> It makes sense that any reduction in Delta T reduces the heat =
exchanged but by how much.
> But what does this mean in actual temps?=20
> Say we fly exactly the same plan on two seperate days.
> On one day the OAT is 65F and the other 86F - 20F difference.
> Let's say we don't have a thermostat or cowl flaps in operation. What =
will the difference in coolant and oil temps be for the two flights?
> Will they simply increase by the 20F? I didn't imagine the correlation =
would be that simple.
> And how does humidity effect the heat transfer?
>=20
> Can someone with experience, knowledge or both set me straight please?
>=20
> Thanks  Steve Izett
>=20
>=20
>=20
> --
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