CHT Temp issues advice required

[JJbely]

Hi,

I fly my 260 SE in humid and hot conditions with sea level temperatures permanently in the 90/95 F and I am getting concerned by the fact that I rarely can get my two highest cylinders CHT below 380 in cruise when running LOP even with the cowl flaps open fully. I was wondering if other owners are getting the same type of issues. I usually fly LOP between 8 and 9000 feet with MP at 21 2450 RPM and a Fuel flow of about 11.5, about 60 % power.

I begin to wonder if I should not be flying ROP instead. I would burn more fuel but could keep my CHT down to a lower level and reach my destination faster. The SR22 without cowl flaps and a very tight cowling would never have CHT above 330 in cruise, go figure ?

Are you seeing that type of figures as well ? Any advice ?

Thanks

JJ

[kwmoore]

If you're LOP, 11.5 gph is ~66% power for the IO-470F.

Your fuel flow numbers sound similar to mine in warm weather at those altitudes. In the summer here ground temps in the Central Valley can be 100-110 degrees F and at 8000-9000 feet it'll still be a comfy 70+ degrees F. In my plane LOP I do have to crack the cowl flaps open a notch or two to keep all CHTs at 375 or lower; #1 and #4 are hottest and #6 the coolest. If it's really hot I just lean out a little more and it runs a few degrees cooler.

I have tried ROP, running ~150 deg F ROP. This adds 7-8 knots but at the expense of an extra 3 gph or so. CHTs are NOT cooler; if anything they are warmer. Of course you could go to 200-220 deg ROP by cranking up the fuel flow but I haven't tried it.

Maybe have the shop look at your baffling? Not sure what else to recommend. :confused: The IO-470F in the 182 definitely runs hotter than the SR22's IO-550 in my experience.

[JJbely]

Kevin,

Thanks for the information. The tech note I read on the CPA web site seems to indicate that a range of 350 to 400 is OK. I will experiment a bit this week-end.

JJ

[nworth]

Kevin,

Thanks for the information. The tech note I read on the CPA web site seems to indicate that a range of 350 to 400 is OK. I will experiment a bit this week-end.

JJ

#3 is critical on my plane. I can usually get it under 380f in cruise even on hot Florida days at that (density) altitude by running a little leaner. But, that's way outside the danger zone so my normal routine is to run it a bit richer (but outside the red fin by at least 10 degrees) and crack open the cowl flaps. Two "clicks" on the cowl flaps seems to work.

I would echo Kevin's recommendation to check the baffling. Although it's a bit challenging for me to keep the temps low, it sounds like it's much more difficult in your setup.

At annual this year, I think I am going to experiment and install GAMIs (I have been able to run LOP with stock injectors) and see if I can tune #3 down a bit. All the other cylinders are usually quite a bit below 380 in cruise.

With regard to the CPA recommendation that 400 is ok, I think that is technically correct but aluminum becomes rapidly "plastic" just a few degrees after that. If you are not very careful or if your sensors are not properly calibrated, you run the risk of turning your round cylinders into oblong cylinders by extended operation at those higher temperatures.

Finally, with regard to operating LOP in this way, I just passed 650 hours on the engine and the oil sample report came back stating that the engine is showing extremely low wear results. I'm a believer in the technique and not just for the reduced operating cost.

[nworth]

Please see attached useful "red fin" chart.

You will note that, at 8500 or so (this is density altitude so will be lower MSL on a hot day), you can run right at peak EGT (actually you can run anywhere you like). I am usually about 10-15 degrees lean, WOT and 2500 RPM at these altitudes. Fuel flow is higher than you stated, more like 12.2-12.4.

[n2099x]

Just checking the baffling is not good enough for the correct airflow. All of the extra screw holes should be filled, all gaps should be sealed. When I am done with my annual I take a tube of high temp silicone and make sure everything is sealed. It makes the engine run cooler, and eliminates cold spots if there is holes. And it makes the plane faster. Well worth the 20 minutes and 5 dollars.

[kwmoore]

I flew down to So. Cal. and back to visit my father. Temps were very warm: close to 70 degrees at 7500 feet, above 60 at 9500 and 54-56 at 10,500 (DA ~12,600!) on the return.

LOP at 10,500 I had to keep fuel flows at 11.2-11.5 gph and cowl flaps 2 or 3 notches open to keep CHT #1 (hottest) at or below 380. The other CHTs were 350 or less, so no problem. IAS was between 110 and 115 with TAS 138-139 at best.

For the final hour my patience flagged so I went to ~150 ROP. This gave IAS 120-123 at about 13.5 gph. I liked the way the plane flew better too: a somewhat more nose-down attitude and crisper handling. In this mode I could keep cowl flaps only 1-2 notches open for all CHTs below 375 (#4 is hottest when ROP). The extra ~10 kt of cooling airflow made a difference I think...guess I have to contradict what I said above! ;)

I noted the flexibility of the IO-470 here: at altitude one can run it for very good economy LOP or better speed ROP without using excessive fuel. Contrasting the IO-550, at 10,500 LOP it would be 12.5-13.5 gph for pretty much the same speed as the IO-470 running ROP. :cool: I don't cruise a whole lot at 10,500 or higher but when I do I might change to ROP "go faster" mode a lot of the time.

[JJbely]

Kevin,

That's my experience as well, the engine runs pretty well ROP and I get that type of increased IAS when I am running short of time or patience.

I flew in a Cirrus yesterday helping to do a Gami test for a new owner in Western Australia. At 7500 6 degree C, we were indicating 155 at 16 GPH. The engine had fairly bad fuel spread but she went really fast ROP....

cheers

JJ

[Todd]

Generally speaking I normally fly LOP up to around 8,000 feet with the IO-470 and 12,000 feet with the IO-550. Above those altitudes I generally revert to ROP operations to regain some of the power lost by running LOP. As we all know LOP operations generally reduce your engine power by about two inches of manifold pressure. When I'm running WOT at the higher altitudes and seeing maybe 19 or 20 inches the loss of an additional two inches when LOP is just too much for me. The IO-470 is fuel efficient enough that at the higher altitudes even ROP I am happy with the fuel flows. The IO-550 being some what of a gas hog is a little different in that I will go a little higher before reverting to ROP operations. If CHT's seem to be running a little high I normally use both the cowl flaps and a little extra fuel (if ROP) to keep the temp's down. It has been my observation one can have the cowl flaps open about a third without really impacting cruise speed. The CHT's seem to be very temp sensitive with relatively minor changes in fuel flow so I'll put in a little more fuel (ROP) and open the cowl flaps a little and split the difference.