Jeff, Very nice reporting on the methodical testing that you have been doing on the P-mag timing. Noting oil temperature, CHT, EGT, MAP, etc. does provide lots of info. However there is one parameter that you have not noted: What is the mixture setting? A Mixture Meter would instantly tell you what the actual calibrated mixture ratio was. That has a large effect on all those indirect parameters. I have a presentation on Mixture Meters; could tell all about it at the Gathering if there was some interest.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ---------------------------------------------------------- I tested with a 2" scat intake pointed at the oil tank to help cool it. ?That made a 2* difference in the oil temp. ?Dropped it from 220 to 218, which I consider to be insignificant. ?However, I also discovered that the oil temp seems to stabilize at 220 in cruise and stays there, so while it's a bit warmer than I would like, it's not a major concern. ?I decided to move the scat hose back to the heat exchanger for the cabin heat and not bother with it on the oil tank. ?I'm not interested in adding the weight of an oil cooler to the plane and it's really not a necessity. ?My long term solution is going to be to pull wires back from the Pmags to a toggle switch in the cockpit allowing me to select either conservative or aggressive timing before startup. ?With the conservative timing curve in, my oil temp tops out at 208 in cruise under summertime conditions. ?With the aggressive timing curve, it tops out at 220. ?So, I'll likely select the conservative timing curve (limited to! 34* advance) for summertime operations, then select the aggressive timing curve (limited to 39* advance) for all other conditions. Max performance under both timing curves is the same. ?The difference is that the additional timing advance will allow a bit more fuel savings at lower cruise throttle settings. I was also finally able to complete the trim on the aircraft last night as well. ?Photos are on my web site <http://jeffsplanes.com> at the bottom of page 14 under the KR. ? -Jeff Scott Los Alamos, NM > > > ----- Original Message ----- > > > > On Jul 1, 2013, at 12:54 PM, "Jeff Scott" <jscott.planes at gmx.com> wrote: > > > > > > > > I dialed in the aggressive timing on the P-mags for testing this > > > weekend. I really don't expect better performance from the additional > > > timing advance. It should have a some additional timing advance with > > > lower manifold pressures at higher altitudes or partial throttle > > > operations (cruise flight) to help with fuel savings. Bear in mind > > > that I operate from a high altitude airport, so can not pull more than > > > 23.5 inches of MP, so expect some timing advance even during full > > > throttle climb operations. I found that during climb out, my hottest > > > CHT bumped up from 390 to 405. That is still acceptable, although on > > > the cusp of what I am comfortable with running. As soon as I start > > > dialing the throttle back a little, the CHT immediately drops as the > > > throttle plate disturbs the air flow and the fuel mixes and > > > distributes a bit better across the intake spider. #2 cyl has always > > > been the hottest CHT under full throttle conditions due to an uneven > > > fuel distribution at full throttle, so! has become my measuring stick during climb operations. As soon as the throttle is reduced, the temperature drops into line with the other cylinders. During today's flight, under cruise conditions the CHTs ranged from 300 - 340*F across all 4, with only #2 (back left) running a bit warm during climb out. > > > > > > The biggest issue was the oil temp during cruise flight. I was > > > cruising with the cowl flap closed and 18.5" MP at 11,500'. Under > > > those conditions, the timing curve should be fully advanced to 39*. My > > > oil temp topped out at 220*F and stayed there under those (summertime) > > > conditions. I was able to drop the oil temp back to 210* by opening > > > the cowl flap, but that also induces a significant amount of drag, > > > which is less than ideal for cruise flight. This is about 15 degrees > > > warmer than the oil temp was running with the timing curve topped out > > > at 34* under similar conditions. I am going to leave the timing dialed > > > up while I explore ways to get a bit more cooling air directed at the > > > oil tank (the O-200 does not have an oil cooler). If I can't get a > > > little better results with the oil temps, I may have to restrict my > > > timing advance to 34* during the summer months and dial up the timing > > > for the fall and winter months. > > > > > > This and other write ups are located on my web site at > > > <http://jeffsplanes.com> > > > > > > Jeff Scott > > > Los Alamos, NM
