High CHT's on Takeoff

[Hank]

Gary--

Do not reduce throttle on initial climb! Our carbs have an automatic fuel enrichment that happens at Full Throttle to help keep temperatures down. Backing off on the throttle will make it hotter . . . If you want, use the Target EGT method, but don't use someone else's EGT number.

Takeoff on a day as close to ISA standard as possible [59ºF, 29.92", near sea level], all knobs full forward. Rotate, gear up, establish your climb and look at your EGT. That is your target.

The Target EGT method uses Full Throttle, Full RPM, and lean to your identified EGT value. As you climb, continue to pull the mixture back to keep that temperature.

Reducing throttle will significantly reduce fuel metering by the carb, and leaning the mixture will simply make it worse. Yes, my Owner's Manual says 'cruise climb at 26"/2600' but you aren't "cruise climbing" on initial departure. Full Throttle, Full RPM, and Full Rich or leaned to Target EGT, all the way to cruise altitude. But then again, Texas is pretty flat, a 400 fpm climb may work for you, it's just really s . . l . . . o . . . . .w . . . if you are climbing to 8000' msl.

[BigTex]

All, Thanks for providing your thoughts on my cooling issue. I'll do some take offs maintaining WOT but will have to back off some on RPMs as they are right at redline (2700).

Both mags were recently IRAN'd recently and timing re-checked so I believe I'm fine there. I do have a FF tied into my 430 but haven't monitored it on takeoff. I'll add that to my todo list.

[jimosborn]

Both mags were recently IRAN'd recently and timing re-checked so I believe I'm fine there.

In the words of one much wiser than me... "trust but verify"!

Cheers

[gregwatts]

All, Thanks for providing your thoughts on my cooling issue. I'll do some take offs maintaining WOT but will have to back off some on RPMs as they are right at redline (2700).

Both mags were recently IRAN'd recently and timing re-checked so I believe I'm fine there. I do have a FF tied into my 430 but haven't monitored it on takeoff. I'll add that to my todo list.

Don't know if you have ever checked..........but.........not all tachs read exact! Mine reads 80 rpms low. Even so....2700 rpms won't hurt your engine.

[jetdriven]

Even on a J model on hot days you often need to see 120 MPH indicated airspeed to keep the cylinders under 380.

Also, "target EGT" on our machine is 1285 on #3, sometimes it takes 1250 EGT to give it enough fuel to cool it. Its OK, give it a bit more on climb on hot days.

Puling power back to 25 or 26 "squared" only cuts the climb rate by 1/3rd to 1/2 and makes it even run hotter.

[Parker_Woodruff]

There is nothing wrong with running 2700 RPM. If for some reason your governor is allowing higher RPM than 2700, that's a problem.

Wide open throttle, 2700 RPM. Best thing for your engine and flying enjoyment. If you want to back the noise off a bit, maybe try 2600-2650 RPM.

[BigTex]

After re-checking my Owners manual, it said to maintain an RPM of 2550 - 2600 for takeoff and for cruise climb go with 25 squared for the power settings.

I've found some gaps in the top of the dog house. I'm going to seal those up and see how that helps.

[Oscar Avalle]

In order to stay during climb below 430 on my m20c with LASAR ignition (OAT 30 Celsius) I leave TWO and keep airspeed at 120mph. If I deviate from that speed the cht goes up rapidly.

Sent from my iPad using Tapatalk HD

[jlunseth]

On the RPM issue, one thing you often see when an engine analyzer is installed, is much greater accuracy on some of the readouts than you had been used to. So you might see 2720 RPM's or so, and think the engine is over revving. In fact, the factory gauge would not have been able to "see" that extra 20 RPM's and would have told you that you were operating at 2700. There is nothing wrong with leaving the RPM's at 2700 during climb out. The engine is certified for that. I sometimes pull mine back until there is a slight reduction in the RPM's, say into the 2650-2680 range, but it is really not necessary. My A&P advises that full RPM's are needed for the extra fuel flow to kick in during full power operations, so you don't want to pull it back too much.

Did I read correctly that you see 380 on the ground before takeoff? When the engine is at idle? Or when you are rolling down the runway? That seems very high to me, and sounds as though there may be a calibration issue of some kind with the 700.

From working through a similar issue with my 231 a few years ago, the candidates are: (1) operator error - leave the mixture full in as well as the prop and power for a climb out from a sea level airport (or nearly sea level), (2) baffling can make a big difference, more than you expect, new baffling might be in order, (3) the "spider," that is the fuel distribution system, may need adjustment or rebuild. I am assuming you do a run up and mag check, running on one mag can cause high temps also.

[jetdriven]

We saw 380 on the ground today at Ft. Myers, waiting to takeoff behind a whole line of ground-stopped jets. We had a 28 knot crosswind blowing acorss the plane, and I would guess about zero cooling air through the cowling. After 10-15 mins of this, 380 CHT. Departure was normal, and after 5 minutes or so with the cowl flaps locked open, it finally assumed the normal 340 CHT.

[Hank]

Maybe that's why my Owners Manual recommends 1400-1500 RPM for 'extended ground operations.' It may or may not say something about improved cooling; I need to load it onto this tablet for reference.

"If it is necessary to hold for clearance instructions, run 1400-1500 RPM for improved cooling and reduced sparkplug fouling."

For some reason, I can type but can neither get a cursor nor insert into previously-typed text . . . Samsung Galaxy II, 'Droid.

[jimosborn]

So, Gary.... please don't leave us hanging.  Have you yet resolved the high CHT issue?  If so, what was the solution?  Or else what of the known possibles have thus far been eliminated?  Inquiring minds and all that! 

 

Jim.

[BigTex]

Jim - Actually, over the weekend and worked on some of the techniques mentioned and was able to bring down CHT.  I basically ran with WOT/2700 RPM on takeoff and kept my climb out relatively flat until reaching 120 mph, then climbed out at that speed.  Once reaching 120, I brought it back to 26"/2600 RPM.  This seemed to keep my CHT's at or below 400 degrees.  It looks like the key is to reach 120 as quickly as possible.  At that speed, my power settings didn't seem to matter as much.  Just about any setting would keep CHT's below 380.

 

I also found out that I was missing some screws in the back of my doghouse.  Replacing those could of help as well.  I did notice that my baffle material around the front of the dog house is shot and needs replacement.  That's on my list of to-dos which should also help.

[jetdriven]

Leave that thing at full throttle.  When you pull the throttle off the ful stop it leans it out by quite a bit.  You are disabling the full throttle enrichment circuit on the carburetor.  172s climb at full throttle forever.  There is no longevity issue with full power operation.

[KSMooniac]

I agree with Byron... you are doing yourself a real disservice reducing power in the climb, especially reducing throttle!  Leave it firewalled until you're reducing power for an approach and landing.  Climb at 2700 RPM to get to altitude as quickly as possible.  120 MPH is a fine climb speed, and you could even go a little faster.  

 

Mooney POH's, especially in the 60's, leave much to be desired and we know a LOT better today how to manage an engine correctly.  Reducing power in the climb is not the correct way if you value efficiency and engine longevity.

[BigTex]

FWIW my Owners Manual (POH) has me reducing RPM's to between 2550-2600 RPMs once climb is established. I understand what you are saying but I'm not sure it's a good idea to disregard the Owners Manual either.

[KSMooniac]

Again, those manuals were written 40+ years ago and a lot has been learned since then, and climbing at full throttle and full RPM is one of them.  You can try both methods and you'll quickly see which one is better.  Your engine is certified to run 2000 hours at 30" and 2700 RPM.  Do it however you wish, but if you want to treat the engine well and help it last a long time, there is an optimum way.  (and it ain't by the POH!)

[jetdriven]

Older engines have a takeoff limit in the Type Certificate.  The 360 series Lycomings have no such limit.  My POH has that 26-26 recomendation under normal procedures but the maximum performance climb says full throttle and 2700 RPM.

 

Folks think that running reduced power in the climb "saves" the engine, but in actuality it adds heat, wear, and extra time to the engine.

[testwest]

Gary, I would like to add my voice to what Byron and Scott are saying. Leave that throttle in and leave the prop at 2700. It is a hard thing to find out that nearly everything you were taught about operating CS prop equipped aviation engines was pretty much flat wrong.

 

You may also try climbing with that power setting at 130 mph. That "seems" fast, but it is the best way to climb until you can't maintain around 500 fpm. The climb profile is called Vz, take a look in the forums you will find a lot on that.

[BigTex]

Byron, you refer to keeping WOT to engage the auto enrichment feature. I believe this is only on fuel injection engines. My plane has a MA-4-5 carburetor so I don't believe that recommendation applies. Can you confirm?

[jetdriven]

The carburetors have a fuel enrichment circuit that gives it extra fuel when the throttle is full open. It is a separate circuit from the main metering jet that you can only get with the throttle at 100% full open.  Backing the throttle off the stop loses this extra fuel.

 

There is one way to see, take off and at 500 feet pull the throttle back 1/4" and note the EGT.  I bet it goes up a good bit.

 

According to the manual, many models of the MA-4-5 have this circuit. They call it an "economizer".   

home.comcast.net/~r123rs/Documents/Carb%20Manual.pdf

 

Backing that throttle off of full is a triple whammy to your engine:

1. loss of economizer circuit fuel (leans out)

2. Loss of airspeed and cooling airflow

3. longer time to climb.

[BigTex]

good stuff... Thanks for sharing.  Have have the overhaul manual for my carburetor and there's no reference (at least that I can find) to this feature.

 

I also went back and re-read the MAPA Performance manual and for my  C-Model it does reference the initial climb with a FT/2700.  But it also recommended at some point above 1000 AGL transitioning from initial climb to cruise climb.  Their cruise climb was defined as 26 squared.  It's sounding like from this group that this transition doesn't happen. 

 

Next time I'm I'll climb at WOT/2700 and see what kind of EGT/CHT profile I get.

 

Byron - Maybe at the next MAPA conference you can volunteer to talk about this stuff.  During my transition training, I was trained to fly to the POH by one of the most seasoned and respected Mooney pilots we have within MAPA.  So a discussion on what and why to deviate form the POH might be of interest to the folks attending.

[jetdriven]

I dont advocate deviating from the POH except in the case of LOP (IO-360, well-balanced, engine montior, etc, all the caveats), that 26 squared climb, and the fuel pump on for takeoff.  In these cases, there is strong evidence the those practices are less than optimal.

 

The MAPA and mapalist crowd will probably run me out of town. Old traditions die hard there. Those of you that have seen the light of new techniques, please forgive me for being such a pain in the ass.  Meanwhile, the Beechtalk guys are running TNIO550's and TSIO-520WB's  at 95% power LOP with 330 CHT to 500 over TBO while the Mooney pilots are debating whether LOP burns exhaust valves and if running oversquare will ruin an engine.  One theorized that LOP caused detonation which "slams the valve shut" and ruins the camshaft. A few supported that idea.

 

Today I called the Lycoming factory and explained my #2 injector is flowing 10% more fuel than the other three and I am tired of dealing with it.  The tech rep asked how do you know this?"  Explaining the GAMI lean test was like explaining heaven to a bear.  He immediately got suspicious and asked if "you were running it lean of peak EGT?"  Voodoo.  Bad things happen there.  Well, how else do you determing peak EGT unless you lean it beyond and write it down? The tech rep said "whats the problem, that cylinder runs cooler."  Yeah, except when operating at peak EGT on 1, 3 and 4 they are 340 CHT,  the #2 cylinder is running 400 CHT at 80 ROP.  To him leaner is hotter, and rich is good. He saw no problem with that.  I do.  I asked how do I run at peak EGT, as recommended by Lycoming at 75% power and below if one cylinder is 80 degrees different, and I peak #2 then 1-3-4 are 80 LOP? After explaining that I have swapped #2 injector around and the rich condition follows that injector, he agreed to warranty it out.

[danb35]

FWIW my Owners Manual (POH) has me reducing RPM's to between 2550-2600 RPMs once climb is established. I understand what you are saying but I'm not sure it's a good idea to disregard the Owners Manual either.

Keep something in mind: your owner's manual has in it a section marked "Limitations".  That section is FAA-approved, and operating contrary to what's in there violates the FARs.  Anything else, though, is purely advisory, and you can choose to follow it or not as you prefer.  Throttling back isn't doing your engine any favors.

[JaredDavis]

Byron,

 

Can you elaborate on why you don't like running the fuel pump on takeoff for a m20C?