PA28 CHTs during climb

achimha wrote:

The PA28 has a much smaller and streamlined air intake than the C172.

PA28s usually do not have CHT indicators and there is no warning in the POH, so I assume that a full power climb at Vy would be ok.

The POH says that you should run full rich on climb until 8000 ft. Would it then be a risk of getting too high CHTs if you leaned during climb from the start using the constant EGT method?

Airborne_Again wrote:

PA28s usually do not have CHT indicators and there is no warning in the POH, so I assume that a full power climb at Vy would be ok.

That is an assumption you should not make. When the POHs were written, there was a totally different idea of what CHTs are acceptable. My POH (1979) only says I should not exceed 500°F. With today’s knowledge, that is crazy advice.Airborne_Again wrote:

The POH says that you should run full rich on climb until 8000 ft. Would it then be a risk of getting too high CHTs if you leaned during climb from the start using the constant EGT method?

That is equally bad advice because your mixture is going to be awfully rich, bad for the engine, bad for your wallet. The constant EGT method can only be employed when you have digital CHT display for all cylinders. And there is really no alternative to having that…

The biggest truth writen above is that you cant take what is true on one aircraft to be true on another when it comes to cooling performance.

Take a good look at two aircraft, the PA28-180 & the Robin DR400-180, both powered by the Lycoming O-360, the Robin will haul the same sort of payload but faster, futher & off a shorter runway than a PA28. A quick head on look at the aircraft will show you just how the Robin gets some of its performance, the air intakes for the engine cooling as about 30% smaller than the PA28. the result of this is a reduction in cooling drag and an increase in performance.

The down side is that the aircraft has to step climb to keep the T’s & P’s in limits when climbing to the best cruising levels for the aircraft (6-8000 Ft) on a hot day.

The PA 28 was undoubtedly intended to directly climb to 8000FT on a hot day in Texas and the Robin to do the same on a cool day in Dijon.

Sometimes the manufactures get it drasticly wrong, the Cessna 152 may be good for the riggors of training on a hot day in Texas but it is drasticly overcooled on a cold day in Northern Europe, the result being all sorts of engine corrosion issues resulting from the oil not getting hot enough.

IMO the only valid data on cooling performance it that gathered from aircraft of the same exact type as small variations in the cowling and baffel design can have drastic effects on the CHT & oil Temp.

We (C172N Superhawk – O360 – 180HP – EDM700) have a rule of thumb to (after clearing obstacles) reduce power just a little bit and settle for a 90KT 500FPM climb. On the hottest days (around 30-35 degrees) CHTs will be about 410-420 on takeoff and reduce to below 400 after accelerating as described. We have an alert at 440 and on one hot day I actually reached this by mistake (I know…).

I do progressive leaning during climb, but without looking for something particular at the EDM (the constant EGT technique is something I’ll look into). I will normally start leaning after passing 2000FT and then gradually lean a little bit every 1000FT. The thing is that at “milestone” altitudes (eg 5000-8000FT or final cruise) I will want to do a “full” lean with the EDM, so I’ll go full rich, wait, and then do the EDM-lean. At around 8000FT I will expect to see TAS 110KT, 26-28LPH and CHTs around 370.

The CHT safe range is a hot topic among pilots/engineers with answers in the range of “do as the POH says”, “don’t exceed 400”, “have it grounded if 450” etc

I have never heard about any problems like you guys describe on the smaller engine sizes, unless something is wrong.
CHT’s in the 400-440F range normally belongs with the Big Bore engines and are normally the reason why the cylinders only last so long on these.

I might be wrong, but I think that just adapting your flying to get the CHT’s below 400-440F is not the right way to go. You need to spend some time finding the issue to the hight CHT’s, that being bad baffles or something wrong with your fuel system.
I know you guys can’t adjust the fuel flow, but I know there is a way to have it corrected. I will see if I can find that discussion from another Forum Im frequenting.

“You pay now, or you will pay later”!

Hard to find a Posting that doesn’t get too far of topic, but one of the best experts on Cessna’s in the world, John Effinger, wrote this:

Adjusting the idle mixture wont change full power climb. It is my opinion those CHT Numbers(over 410) are way too hot and I would start with baffle, timing (ignition), Intake leaks etc till those numbers could be brought down. The baffle Insp is easiest step but 350-375 in cruise sounds good so it may not be getting sufficient Fuel on climb. I would start there 1st then go down the list.

Reading quickly through the Non-Fuel Injected Forums, it comes to me that it is often wrong Magneto Timing that is the reason for too hot CHT’s.

+A quick check of the Timings would be an easy cheap start.
+ Then look through the bafflings. Best to do this is a dark environment, using light to see where it comes through. Use heat resistant silicon to seal off holes and cracks in the metal part of the baffling, then consider adding new silicon baffles where ever there is a too wide gap.
+ Have a look over the Induction(Intake) part of the engine. There should be no leaks. I have used air through the spark plug hole with a compression tester, or a blower into the intake system(Turbo), to get overpressure into the pipes. Then use soapy water to look for the leaks.
+ An last resort is to have the fuel system “trimmed” to admit more fuel flow for cooling. This is a somewhat discussed/debated way of solving the problem, but it for sure gets the fuel-flow to where it should be in term of cooling for Take off and climb. John Effinger would be the man to discuss this with. His going rates are very reasonable. Unfortunately he is located in TX, US, but your engine parts will probably go there anyway for repair/upgrade……

Good luck

Hard to see detail but it looks like you might have ~ 5mm gaps between the baffle seal and the upper cowling. A LOT of air will escape through there. I had that too and after re-doing it all (using the PTFE coated material) I got a big drop in CHTs.