Cessna 185 Testimonials
The following techniques produce the best speed, the lowest fuel flow and coolest operating temperatures in my airplane.Â (I had similar results with the original IO520, though speeds were at least 5 mph lower).Â I fly wide-open-throttle (WOT) and lean-of-peak (LOP), even for short flights at low altitudes.
At takeoff, use full throttle and full rpm (2700), full rich mixture (should indicate at least 27gph fuel flow).Â Cowl flaps wide open.Â Maintain during initial climb, about 500â€™ to 1000â€™.
After initial climb, establish about 120mph; leave throttle wide open, reduce rpmâ€™s to about 2400, then quickly reduce fuel flow to about 14.5gpm (LOP), close cowl flaps (leave open on warm days, say above 70 degrees).Â Again, leave throttle wide open.Â
Once at cruise altitude and speed, close cowl flaps and monitor EGTâ€™s and CHTâ€™s.Â If EGTâ€™s approach the limits I have established for my plane, lean slightly; if EGTâ€™s and CHTâ€™s are below limits, enrich mixture slightly.Â I will say it again, throttle should be wide open.Â (I know, I thought the same thing, but it works).
About a minute prior to setting up approach I fully open the cowl flaps to begin cooling the engine.Â Then, just prior to reducing throttle, I close the cowl flaps.Â I reduce power, leaving rpmâ€™s and mixture at cruise settings until final approach speed is established, then prop control and mixture control go full forward.Â This allows the engine to cool slowly, with no â€śshock coolingâ€ť.
EGT limits: I run 50 degrees below peak EGT when LOP (peaks as determined when running the GAMI lean test).Â No. 1 cylinder runs the hottest, and peaks at 1420F, so I use 1370F as the EGT limitâ€¦.all the other EGTâ€™s are well below their limits, the spread is usually 90F according to the UBG-16.Â (GAMI suggests no more than 100F spread).
CHT limits:Â Â I use 380F as the limit for CHTâ€™s.Â In LOP cruise CHTâ€™s will be about 340F, and 4 cylinders will often be within 1 or 2 degrees of each other; all are within 10F or 15F of each other.Â If CHTâ€™s get close to 380F lean a bit and/or open cowl flaps.
EGTâ€™s and CHTâ€™s will rise dramatically if the throttle is reduced, even a little bit, from WOT; I have found this helpful in keeping the CHTâ€™s above 300F during cold winter flying, but I always fly WOT otherwise.
On 3450 floats I cruise at 140-145mph, flow 14.3-14.6gph.
On wheels I cruise at 170mph with the same fuel flow.
Several local friends with 185â€™s have learned to fly this technique and all have experienced similar results.Â GAMI injectors will keep the engine running smooth while running LOP; 6-probe digital EGT and CHT are a must.Â I resisted the digital fuel flow for a few years, but now I realize it is also a must for accurate fine tuning (my analog fuel flow gauge reads at least 1 gph high); in addition, I know precisely how much usable fuel I have in the tanks.
About once a year I say to myself â€śthis is too good to be trueâ€ť; I pull the power back to 24 square, the plane slows about 8mph, I open the cowl flaps to keep temps within limits, and fuel flow goes up 1.5gph.
A good resource for the theory behind LOP operation is available in John Deakinâ€™s articles on â€śPelicans Perchâ€ť, available through a link on avweb.com (in addition to his tales about flying a Spitfire, how to manage engines on a Super Connie, gear-up landing a 747, FL30 in his Bonanzaâ€¦â€¦).
GAMI will readily answer questions as you gather operating data for your engine.