flyrotary@lancaironline.net Mailing List Archive

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: > > 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 > > Hi Guys > > 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? > 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? > > Can someone with experience, knowledge or both set me straight please? > > Thanks Steve Izett > > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html