IMPROVING ENGINE COOLING THe air out if engine is always important and ideally the out area should be 1.5 times min the area of in air at the prop (think 1.5 is the figure)
Original dimona had gills on the underside going in, then later models head these gills extending outside. Tech Bul 44 says add a lip to kick out air and suck out more from inside. Then I saw Dave goldsmiths Dimona L2400 with a big push down panel underside done it Koff and co mod to L2400. I made a mould of that and several people are using same including Russell White on his Grob 109A. It was an improvement Over last week Allen Rundell convinced this koff and co (L2400 suck out) outlet was too small and we cut into it with angle grinder and then put a 3cm big curved lip to suck out the air. Boy did it make a difference and we may have to install a cowl flap (prob too cold on cruise) and add a bit of cardboard in front of part of the oil cooler infact try as I might on full power I could not get oil temp above 72degC in climb and now CHTs are down by another 10degC. (now just <180deg C +/-2deg and STABLE) This is with our Sauer S2500 engine (93hp), but our oil cooler is on underside of prop with a lip to scoop in the air. Previously oil temp would go to 95-100 degC if you kept the power on full. TO explain we did a big curve going in 40% the length of the panel and then the 3cm lip which sticks down at about 40deg angle to the underside of panel. Basically the whole underside of muffler is exposed when you lie on your back.. Germans think they know everything but I can tell you they do not!! So guess my next design has to be a cowl flap to keep engine warm!!! Ian M Ian Mcpheeh
