CHT's on Climb Out

[74657]

Guys,

I have only logged a few hours in the Missile and am wondering what you guys do to keep your CHT's down on climb out.  After takeoff I establish a positive rate of climb, clean up the plane and make my first power reduction (to 25/25) at 400 ft. AGL.  I climb at 100KTS and get approx. 1000 fpm climb rate.  My CHT's are up in the 430 F range which for my liking, is high.  I have read that some Bonanza guys with the IO-550's leave the throttle full and reduce the RPM to 2500. instead of pulling MP and RPM. 

I will dig through all the Rocket Eng. info tomorrow when I go to the hangar.  Any quick insight would be appreciated.....  I can't get my mind of flying since the new plane got here......

Thanks.

 

[Ned Gravel]

Mine is not turbo'd like yours but some of the same things may apply.

Pouring gas into cylinders helps keep them cooler.  Four bangers or six bangers, N/A or turbo'd.  Governor has less influence.  Cowl flaps play less of a role in my IO-360 now that my doghouse (old style Mooney baffling) is really tight for improved cooling.

Two years ago, I was occassionally seeing above 400 on climbout, but after my overhaul and the new baffling - climbout is now often less than 350.

So here is what I do now on climbout: 

• 
  
• MP to the max and leave it there until ready to level off.  Not certain how that might work in your turbo'd engine - but it might not be good for it to be much above station pressure in order to prevent overboosting the engine.
  
• Cowl flaps full open (or whatever you need to do to improve airflow over the cylinders).  I need to keep my speed up to near the top end of the white arc to provide enough airflow over the cylinders, although I don't really need to worry about cowl flaps too much these days.  The better baffling really, really, really helps.
  
• Prop at full power for the first 1000 feet for me, and back to 2500 rpm for the remainder of the flight.
  

Hope some of this is useful to you.

[danb35]

Why are you pulling back the throttle or prop?  Unless there's a limitation prohibiting continuous operation at max power, I'd climb at full throttle/RPM, which would also give you more airspeed and therefore more cooling.

Check your fuel flow--it should be at least 26 gph (27 would be better) on the takeoff roll, at least at or near sea level.  If not, the fuel injection system needs adjustment.

Check baffling; make sure there aren't any holes, cracks, etc.

If all else fails, climb at a higher airspeed--you'll see lower rate of climb, but the higher airspeed will mean more cooling air.  CHTs of 430 are definitely too high--you want them under 400.

[KLRDMD]

Quote: 74657

I establish a positive rate of climb, clean up the plane and make my first power reduction (to 25/25) at 400 ft. AGL. 

[testwest]

If you have a normal STC'ed Missile, you have a Continental IO-550-A normally aspirated engine.....with an auto-lean function. So, in addition to losing the extra enrichening feature at wide-open throttle, you are automatically getting leaned as you climb at 25 square. The slightly slower RPM and the gradually leaning mixture are all contributing to high "peaky" inter-cylinder pressures that are a little too early in the power downstroke, and the too-slow airspeed is yielding less than desirable engine cooling, all serving to raise CHT too high.

Your goal is to climb efficiently with CHTs at 380 degF or less.

The guys above this post are right, there is no need to pull back the engine at all unless it is published in the limitations section of the STC'ed addendum to the AFM or POH. 25 square is an old wive's tale. The only reason to pull the RPM (not MP) is for noise, but I can't imagine a noise issue, at 2650 and with our short props we don't wind up (pun!) as high on the local prop tip mach number (unlike some of those gawdawful 2 blade C-180s or Bo's).

Assuming no such limitation, take off at full MP, RPM and full rich mixture (you should see 29 inches or so at sea level, 2650 RPM and 25.6 gph per the Missile specs published here: http://www.rocketengineering.com/missile/performance.html. and the TCM spec here http://www.tcmlink.com/pdf2/SID97-3E.pdf look at page 27). That takeoff fuel flow is crucial, do not accept 0.1 gph less than spec. Leave the engine knobs alone. Climb at ~120 knots indicated, or faster. If the CHTs stay high, lower the nose and increase the climb airspeed. Most folks have to lean a "little" on climb to maintain the EGTs roughly where they were for takeoff, yours is auto-magically handled!

Once you get to cruise altitude (please please please get it up there, our NA Mooney wings LOVE IT at 8000-12000 feet, altitude is your friend, visit more often), level off and park that engine at 65% nicely lean of peak and go. Hopefully you have a good engine analyzer and a low GAMI spread. Won't go into more than that (thread creep) but there is plenty of info around here on how to operate the NA Conti IO-550 in cruise, check the Ovation posts....

Let us know how your next climbout goes. 

[AustinChurch]

Testwest is correct.  Leave everything full forward and climb out at 120 kt indicated.  At that speed, you should see around a 1000 feet/minute climb rate with CHT's under 400. 

[testwest]

For more on CHT's, check this webinar out. It is FREE. http://www.savvymx.com/index.php/all-about-egtcht

[bsuggs1]

I'd climb with at least 30" and prop set for 2600 or so, the "squared thing" is bull.  Adding fuel (pushing in the throttle) cools the cylinders and the fuel flow should be pretty high (25 gals/hr plus).  If it still won't cool have your A & P turn it up.

[jlunseth]

What they said.  WOT climb.  The science of it is that the fuel does not "cool" the cylinders by washing them, what it does, is slow the combustion event so that cylinder pressures are lower.  Full fuel flow is by far the most reliable way to stay cool in the climb.

[Jeff_S]

Full-rich mixture will definitely help keep CHTs down for all the reasons stated above. But it's overkill for most engines (assuming normal ops of all other components of course) once you start to gain altitude. You're just blowing it through because it starts to become too rich to burn. (For NA engines only, of course...doesn't apply to turbo.)

Following all the other steps shown above (except I do dial back RPM to 2600 just because it seems a bit smoother) I will also start to lean out once I get above 3500'. Very slowly, and just so I see one or at most two CHT bars on the JPI. I know if I see three bars on any cylinder (and for some reason, #3 is most susceptible) I've gone too far so I just dial some back in and that keeps things in line. It's taken me awhile to find that formula so YMMV.

[Cruiser]

An excellent approach to controlling your engine on takeoff and climb from any airport to any altitude is the targeted EGT method.

Pick your LEANEST cylinder and display on the engine monitor. Start your takeoff roll and observe the EGT. As you climb adjust the mixture to maintain the EGT at the takeoff value. This will provide plenty of fuel and adjusts for the thinning air at altitude as you climb. IF you have problems with CHTs slow your climb rate, level off and increase speed. If you still have issues, get the engine checked.

[74657]

I took it up this morning........  Climbed out at 115 knots, CHT's around 380ish and a rate of climb at 1100 fpm.  Fuel burn of 26 gph.  Works for me.

[testwest]

Excellent, thanks for the update.

For those above who discussed targeted EGT and full rich, you are correct, b u t the Missile has auto-lean...it does the "targeted EGT" thing automatically (if it is working correctly)......anyhoo, check this out:

Climbing faster than Vy actually has real science behind it. There is a better way.

It is called Carson's speed. If you want the quick answer, it is roughly 1.3 times Vy plus a tad.

For standard gross weight (2740#) M20Js, that is about 113 KCAS. For heavier Missiles at 3200# gross, ~121 KCAS is better.

For the real science, look here. http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm The article is good but a bit dated, it talks more about cruise and predates a lot of stuff we know from the APS courses about engines these days. My assertion is that Carson's speed is a great speed to climb...

Don't be put off by the triple partial differential equation near the beginning of the article, that's just a joke!

[jlunseth]

I thought I was just imagining things, but no.  I have come to realize that if I level off and let the 231 accelerate to something in the 120's, then start the climb to altitude, it will climb about 10-15 knots faster with the same fpm climb rate, then trying to climb "on the prop" at 96.

[74657]

Quote: jlunseth

I thought I was just imagining things, but no.  I have come to realize that if I level off and let the 231 accelerate to something in the 120's, then start the climb to altitude, it will climb about 10-15 knots faster with the same fpm climb rate, then trying to climb "on the prop" at 96.

[Sector95]

What is the L/Dmax on these aircraft?

[jlunseth]

I discovered it on a couple of flights this summer, and as I said, I though I was probably imagining things, then had a very good Mooney instructor show it to me also.  It works.  What's more, once you pick up that speed it will sustain the speed and climb rate all the way to the teens, at least mine does. 

[74657]

Quote: Sector95

What is the L/Dmax on these aircraft?

[danb35]

No, he's talking about the airspeed at which the ratio of lift to drag is at its maximum.  I believe this is the same as (or at least very close to) best glide speed, and is also the speed at which you'll get maximum range.  Not sure what it is for these models, though.

[jlunseth]

I am familiar with the L/D with respect to best glide, but this is a different thing.  Best glide is with no engine (windmilling).  I am talking about WOT climb.  It may be the same set of equations that determine what is happening with the airplane, I don't know, I am not an aerodynamic mathematician.  All I can tell you is that if you let the Mooney airframe accelerate before putting it into a climb, you will find that the climb speed will be higher for the same climb rate.

[Sector95]

Was looking over Carson's 1.316 theory.  Was basically just trying to justify in my own mind, using that theory, why a  10-15kt faster speed would result in the same climb rate.

I imagine that L/Dmax is the same (or very similar) with the engine on or off as the drag of the prop with the engine off would add the same amount of drag pretty evenly across the lift/drag curve (I'm going to qualify this by saying that this is purely an assumption, if someone knows differently, I'd like to know!).  This would make it so that a fully-feathered prop with the engine off would travel further at the same speed than the props that don't fully feather since it can glide in a flatter trajectory due to overall less drag (which makes sense).

If this is true, one could then assume that best glide is going to be the most efficient speed across the board (which is essentially what Carson's theory says).  I think the L/D graph of these planes would be pretty interesting to have a look at, particularly since it would seem, based on the experience I'm reading here, that there is a flat spot around the 100 to 120kt range.

Does anything my mind is grinding out make any sense?  Or am I missing a large and important chunk of information?

[KSMooniac]

Generally speaking, the 6-series laminar flow airfoils have a "drag bucket" where there is a range of lift coefficient that has a noticeably lower drag coefficient.  It could be that climbing at the higher airspeed reduces the lift coefficient (b/c of lower angle of attack) enough to slide into the drag bucket compared to climbing at a lower airspeed and higher angle of attack.  I think that might explain the phenomen, but I haven't looked up the drag polar for the Mooney airfoils and calculated lift coefficients for various airspeeds...  (I'll leave that as an exercise for the students.  /professor) 

[skyking]

I see about 350-400F at 100Knots on climb out.

[JC252MB]

I see 340-360F, 1450 TIT at 120 knots in the climb. M20K/252.

[Sector95]

Quote: KSMooniac

Generally speaking, the 6-series laminar flow airfoils have a "drag bucket" where there is a range of lift coefficient that has a noticeably lower drag coefficient.  It could be that climbing at the higher airspeed reduces the lift coefficient (b/c of lower angle of attack) enough to slide into the drag bucket compared to climbing at a lower airspeed and higher angle of attack.  I think that might explain the phenomen, but I haven't looked up the drag polar for the Mooney airfoils and calculated lift coefficients for various airspeeds...  (I'll leave that as an exercise for the students.  /professor)