The 25/25 myth

[Sac Arrow]

Per Deakins, I've been leaning during the climb but not doing LOP climbs. Rather I've been noting my EGTs at 500' or higher, then leaning every 1,000' or so to maintain the same EGTs. As I understand it, this is cooling with extra fuel but doing so without dumping even greater amounts of extra fuel as higher altitudes naturally richen the mixture. It's conservative in the sense that at any point, the engine is 'parked' in a safe spot. That is, if I stop leaning nothing bad will happen.

The thing that concerns me about LOP climbs is that engine is not 'parked' in a safe spot for climbing. As the climb naturally enrichens the mixture, pressures and temps will climb as the mixture moves from LOP to Peak or even slightly ROP, aka the 'red box'. This especially would concern me going only 5deg LOP.

Of course the remedy is to monitor the EGTs during a LOP climb and if 5deg LOP is the target, one would need to continue to lean as one climbed. But neglecting this fine tuning could put you right in the red box, especially early in the climb.

If climbing LOP, do you continue to lean as you climb?

All I can say is stay within the limitations within your POH if you lean during climbout. For example, my Arrow II calls for no leaning under 5,000 feet at climbout power. My TA III called for full rich during the entire climbout. What Deakin is promoting is doing the climbout in LOP at wide open throttle using the mixture to control power vs. manifold pressure, vs. ROP climbout per manual. In most instances you need to do one or the other. This can be done safely if you have the instrumentation, and you've figured out the fuel flows that correspond to the climbout and cruise power limitations you may have.

Whether or not you need to lean for climbout at LOP depends on your fuel delivery system, and if your engine is turbocharged.

I do not have the instrumentation necessary to do LOP climbouts otherwise I probably would. I do run LOP in cruise though.

 

[docmirror]

Why does there need to be talk of a "starting point"? You're perpetuating the squared nonsense. The "starting point" is to leave full power and reduce RPM slightly only if you want. And you reduce noise by reducing RPM, not MP. You are not going to hurt anything by leaving full power and reducing RPM to 24-2500 if you want to reduce noise. If this hurts things, then engines with fixed pitch props would be blowing up left and right. Doesn't happen.



Again, why pull the throttle lever back unless specifically advised to do so in the POH? The reason why there's no reason to do this (or even why there are negatives) have already been covered here.

Why, well I guess because it's in the POH? Um, I said 25/25 will make less racket, which it would when reduced from red line RPM(~2700). I don't know which "25" you want it to be, but it represents a reduction in RPM in either case. Which makes less noise. duh

Why I pull the throttle levers back was already explained. If you don't want to do it, then don't. I'm able to manage my fuel flow, temperature, and climb without retaining the full throttle setting. If you can't then by all means, leave the throttles at the forward stop.

 

[poadeleted20]

Hmm, first I've seen of that one, I'll try it. What I have been doing is full rich to 5000msl, then leaning to ~1350 for the balance of the climb. Why 1350? From experience my engine peaks at 1450-1500 depending on conditions, and best power is normally ~100ROP, so leaning to 1350 on climb puts me at 100-150ROP.

Best power is also right about peak CHT. Combine that with the lower cooling air flow at climb speed vs cruise speed, and CHT's go even higher. Make sure you aren't running the cylinder heads too hot when you do this.

 

[Bill]

Combine that with the lower cooling air flow at climb speed vs cruise speed, and CHT's go even higher. Make sure you aren't running the cylinder heads too hot when you do this.

I cruise climb at 120kts, and if it's warm trail the cowl flaps half open on the climb. 375F is pretty normal for the heads.

 

[Ghery]

I had a young CFI that I flew with ONCE who got all over me for over square operations in the Arrow. I asked if he had read the POH numbers. He had not. I had. Got my annual flight review sign-off (club requires the equivalent of the FAA's flight review every year) and never flew with him again. What other old wive's tales did he preach? I didn't want to find out.

 

[poadeleted20]

I cruise climb at 120kts, and if it's warm trail the cowl flaps half open on the climb. 375F is pretty normal for the heads.

With the Lycoming in your Mooney, yes, that's pretty normal in a climb. But since you are monitoring your CHT's, you've got it handled. I just don't want to think of people leaning like that in a climb without watching that unless they're up above 5000 DA or so.

 

[Lance F]

I use a target EGT for climb leaning as well. Actually before I takeoff I set my engine monitor on EGT #2. Based on experience this cylinder has an EGT at full TO power at sea level in the 1250 to 1270 degF range. During climb I continually adjust the mixture to keep it in that range whether I'm climbing to 3,000' or 13,000'. Once I'm in cruise, I reduce rpm to 2500 then pull the mixture for 5degF LOP on that same cylinder #2. I'm WOT from take off roll to near the pattern. This is in a Mooney M20J with Lyc IO360A3B6D.

 

[Bill Watson]

Hmm, first I've seen of that one, I'll try it. What I have been doing is full rich to 5000msl, then leaning to ~1350 for the balance of the climb. Why 1350? From experience my engine peaks at 1450-1500 depending on conditions, and best power is normally ~100ROP, so leaning to 1350 on climb puts me at 100-150ROP.

Yep, if you lean to maintain the same EGT you have right after takeoff you'll save a bit of fuel and get just a bit more power climbing to 5,000. If everything is setup right you'll probably find that you are still >100ROP and EGT < 1350. At that point you are probably <75% power so ROP/LOP/Peak mixtures are no longer a detonation threat.

All I can say is stay within the limitations within your POH if you lean during climbout. For example, my Arrow II calls for no leaning under 5,000 feet at climbout power. My TA III called for full rich during the entire climbout. What Deakin is promoting is doing the climbout in LOP at wide open throttle using the mixture to control power vs. manifold pressure, vs. ROP climbout per manual. In most instances you need to do one or the other. This can be done safely if you have the instrumentation, and you've figured out the fuel flows that correspond to the climbout and cruise power limitations you may have.

Whether or not you need to lean for climbout at LOP depends on your fuel delivery system, and if your engine is turbocharged.

I do not have the instrumentation necessary to do LOP climbouts otherwise I probably would. I do run LOP in cruise though.

Agreed on following the POH. In my case I'm flying an experimental IO540 and only have the engine operator's manual to reference. However, having attended Lycoming engine school it's clear to me that factory guidelines are not always optimal or fully informed.... usually but not always.

Regarding LOP climbouts - the Deakin-informed procedure I'm using is definitely not LOP.

The idea is that a properly setup (non-turbo charged) engine will provide an overly rich mixture for cooling and detonation protection running full power at sea level. As you climb, the mixture will naturally enrich even further wasting fuel and losing power. The proper overly rich mixture can be maintained throughout the climb by monitoring EGTs and maintaining the same EGT you had right after takeoff by leaning the mixture.

For example, my IO540 gulps 21-22 GPH right after takeoff at 350' MSL. By noting the EGTs at 500ft I simply maintain them at or below that figure by leaning. But I'm not leaner than peak, I'm richer than peak, and the EGTs fall from excess enrichment. I'm simply adjusting the overrich setting to that required at takeoff. Fuel consumption only drops to maybe 18GPH by the time I reach cruise altitude. Then I do the big pull back to LOP and run from 9.5 to 12.5 GPH depending on altitude and desired cruise speed.

So the 18GPH I'm consuming during the high altitude part of my climb is still overly rich and providing probably way too much cooling fuel to the cylinders at that point. It is still excessively ROP. Then when I switch to cruise I burn <12.5GPH and am definitely running LOP. Or I could run 14-15GPH for max power at that point.

Personally, I stay far away from any low altitude, full power, climb speed, LOP operations. CHTs will climb and detonation could become a problem.

 

[JHW]

A lot of this talk is written as if this is a steady state operation. It isnt. Just climb, the MAP will take care of itself. If you want 25in, in a couple of minutes that's what it will be.

 

[Jaybird180]

A lot of this talk is written as if this is a steady state operation. It isnt. Just climb, the MAP will take care of itself. If you want 25in, in a couple of minutes that's what it will be.

Did you read the entire thread? Not likely. If so, you'd find that some have time limitations on WOT operation and would exceed that on a SL to 25" MAP climb.

 

[JHW]

Did you read the entire thread? Not likely. If so, you'd find that some have time limitations on WOT operation and would exceed that on a SL to 25" MAP climb.

some do. Most don't. The OP certainly doesn't.

and most planes that do have such a limitation climb well enough that they will indeed take care of themselves within 2 minutes on most days

 

[flyingron]

some do. Most don't. The OP certainly doesn't.

and most planes that do have such a limitation climb well enough that they will indeed take care of themselves within 2 minutes on most days

I have never seen a WOT limitation. I've had two engines that have max power limitations and on both of them (lycoming and continental), the way you bring that down (if necessary) is to decrease the RPMs.

As previously stated (and the Lycoming docs support this), the last thing you want to do is try to avoid max continuous by moving off WOT on their engines. They actually have already compensated in the engine design (it actually enrichens the mixture at WOT). Even without the enrichment, there are definite cooling benefits to making the power reduction with the prop.

There usually isn't any reason to worry about setting best power unless you're at altitudes where WOT doesn't equate to a substantially reduced power anyhow.

 

[Bill Watson]

As previously stated (and the Lycoming docs support this), the last thing you want to do is try to avoid max continuous by moving off WOT on their engines. They actually have already compensated in the engine design (it actually enrichens the mixture at WOT). Even without the enrichment, there are definite cooling benefits to making the power reduction with the prop.

Yep, that's the message I picked up at Lycoming school.

I run my IO540 WOT from takeoff to my first required speed reduction whether that be for turbulence on descent, redline, or slowing for the approach. Lots of fiddling with the prop and mixture throughout.

 

[Jaybird180]

I should have stated max continuous instead of being lazy and typing WOT on my phone.

 

[comanchepilot]

I'd said it before and will say it again . . . .

If you do Revs per Second and convert the 25" to cm . . . .what do you get?

How does the engine know its operating at inches of MP or revs per min?

 

[comanchepilot]

Did you read the entire thread? Not likely. If so, you'd find that some have time limitations on WOT operation and would exceed that on a SL to 25" MAP climb.

Explain that to me? Every Lyc / Conti limitation I have seen [in NA and TN non-geared motors] says that max continuous[full power - 2700rpm and 30" MAP} at SEA LEVEL is limited to five minutes . . . .

Now I'm based at 1000MSL. I take off and in a min or so I"m at 2000' and 2600rpm. I"m down to 28" of MP and 2600rpm - in 5 min I"m easily at 5000' and 25" and 2600rpm and under 80% power - so I'm NO LONGER at full power, am I? So explain the limit to me again?

I was flying today - and upon landing it was 94F at Brackett Field - density altitude at 2000' pattern altitude was 4770. . . I should be leaning in the pattern [and I was] so understand the limits cause a full rich mixture on a hot day even down low is simply giving up power. . . . now - going a little richer for cooling is one thing - but the best thing for cooling is high speed air -

 

[Jaybird180]

Explain that to me? Every Lyc / Conti limitation I have seen [in NA and TN non-geared motors] says that max continuous[full power - 2700rpm and 30" MAP} at SEA LEVEL is limited to five minutes . . . .

Now I'm based at 1000MSL. I take off and in a min or so I"m at 2000' and 2600rpm. I"m down to 28" of MP and 2600rpm - in 5 min I"m easily at 5000' and 25" and 2600rpm and under 80% power - so I'm NO LONGER at full power, am I? So explain the limit to me again?

I was flying today - and upon landing it was 94F at Brackett Field - density altitude at 2000' pattern altitude was 4770. . . I should be leaning in the pattern [and I was] so understand the limits cause a full rich mixture on a hot day even down low is simply giving up power. . . . now - going a little richer for cooling is one thing - but the best thing for cooling is high speed air -

See post 94

Also, there are many cases where a stepped climb is required exceeding the limitation. It's poor advice to tell everyone go full power from takeoff to descent, unless you know that engine/prop/airframe combination can handle it. That's all I was saying.

 

[John Collins]

Explain that to me? Every Lyc / Conti limitation I have seen [in NA and TN non-geared motors] says that max continuous[full power - 2700rpm and 30" MAP} at SEA LEVEL is limited to five minutes . . . .

Are you claiming that all Lycoming and TCM engines (excepting the ones you excluded - geared motors) have a sea level limitation to five minutes. If you are, this is news to me. On the Bonanza models, the early models use variations of the E185 engine and they do have a take off power RPM limitation for one minute and a maximum continuous operation with a lower RPM. Both are specified with Full throttle. After the switch to the 470 engines, all limitations were based on maximum RPM and full throttle without any limitation.

 

[polaris]

I've been told by multiple instructors that I shouldn't make a power reduction at 500 AGL because engine failures often happen when power changes are made. 500 AGL is not where you want an engine failure. So I wait until 1000 AGL or when I know I have a field made. Thoughts?

 

[Jaybird180]

I've been told by multiple instructors that I shouldn't make a power reduction at 500 AGL because engine failures often happen when power changes are made. 500 AGL is not where you want an engine failure. So I wait until 1000 AGL or when I know I have a field made. Thoughts?

You were given the incorrect cause. An engine is most likely to fail under high stress.

I do not reduce, because I want to limit my time below TPA on departure. I want to get to safe altitude ASAP and so I nearly always use Vy climbs.

 

[JHW]

I've been told by multiple instructors that I shouldn't make a power reduction at 500 AGL because engine failures often happen when power changes are made. 500 AGL is not where you want an engine failure. So I wait until 1000 AGL or when I know I have a field made. Thoughts?

keep looking, sooner or later you'll find an instructor who can think

 

[polaris]

I do not reduce, because I want to limit my time below TPA on departure. I want to get to safe altitude ASAP and so I nearly always use Vy climbs.

Genuinely curious -- along the same line of thinking, would it be ok to use Vx until about 500 AGL and then Vy to TPA, then cruise climb? Or is that Vx part stupid unless you are actually clearing an obstacle? If so, what is the reason behind it? Inadequate cooling?

 

[poadeleted20]

Explain that to me? Every Lyc / Conti limitation I have seen [in NA and TN non-geared motors] says that max continuous[full power - 2700rpm and 30" MAP} at SEA LEVEL is limited to five minutes . . . .

Not every Lyc/TCM engine is so limited -- I know my Lyc O-360-A4K is not, and neither were the O-320-D1D's in my Cougar, nor the O-320-E2G in my Cheetah, nor the O-235-C2C in my Yankee, nor the O-320-D2J's in many 172's, nor the Continenal C-145/O-300 in older 172's, nor...well, I could go on for a long time. Also, RPM limits vary a lot from 2700. And not all such limitations specify "sea level".

Now I'm based at 1000MSL. I take off and in a min or so I"m at 2000' and 2600rpm. I"m down to 28" of MP and 2600rpm - in 5 min I"m easily at 5000' and 25" and 2600rpm and under 80% power - so I'm NO LONGER at full power, am I? So explain the limit to me again?

Depends on how the limitation for your engine is written, and they're not all written as you suggested above.

 

[poadeleted20]

I've been told by multiple instructors that I shouldn't make a power reduction at 500 AGL because engine failures often happen when power changes are made. 500 AGL is not where you want an engine failure. So I wait until 1000 AGL or when I know I have a field made. Thoughts?

Old Wives Tale with no data to support.

 

[poadeleted20]

Genuinely curious -- along the same line of thinking, would it be ok to use Vx until about 500 AGL and then Vy to TPA, then cruise climb? Or is that Vx part stupid unless you are actually clearing an obstacle? If so, what is the reason behind it? Inadequate cooling?

You nailed it. Vx climbs are harder on the engine because of decreased engine cooling, and heat is your engine's worst enemy (pretty bizarre, given that your engine is essentially a heat generator, but that's the way it is). If you love your engine, don't climb at a lower airspeed than the book "cruise climb" speed for longer than operationally necessary.

 

[Jaybird180]

You nailed it. Vx climbs are harder on the engine because of decreased engine cooling, and heat is your engine's worst enemy (pretty bizarre, given that your engine is essentially a heat generator, but that's the way it is). If you love your engine, don't climb at a lower airspeed than the book "cruise climb" speed for longer than operationally necessary.

Heat reduces the strength of the metals. Bolts and fasteners should be replaced often enough to not be a factor. I'd argue that friction is the engine's worst enemy, but maybe that's a different thread???

 

[Henning]

Did you read the entire thread? Not likely. If so, you'd find that some have time limitations on WOT operation and would exceed that on a SL to 25" MAP climb.

Hmmm, most of the limitations I'm aware of are 5 min and they are on "high performance" (greater than .5hp/CuIn) engines. Unless you are turboed, in 5 minutes you'll be below 25".

 

[JimNtexas]

Our Warrior has a five minute limit at 2700rpm that came with the Pen Yann 160hp STC. That's kind of an edge case.

After takeoff power reductions are unusual in single engine GA airplanes. They were common with the round engines of bygone days, I thinks that where this OWT came from.

 

[txflyer]

I don't have my POH here with me, but I'm pretty sure it says I'm one of those 5 minute full power guys with my 0-470-R.

I've been pulling MP then the prop when I'm about 1000AGL, but I'm going to rethink this after this thread.

It makes sense. More fuel, less heat. More air, less heat. Turn the engine down with the prop. Over squared never hurt anybody. Besides, like other motors, if you run it under-powered, like lugging a diesel, or not enough current to an electric motor, that will burn an engine up quicker than anything.

 

[docmirror]

I don't have my POH here with me, but I'm pretty sure it says I'm one of those 5 minute full power guys with my 0-470-R.

I've been pulling MP then the prop when I'm about 1000AGL, but I'm going to rethink this after this thread.

It makes sense. More fuel, less heat. More air, less heat. Turn the engine down with the prop. Over squared never hurt anybody. Besides, like other motors, if you run it under-powered, like lugging a diesel, or not enough current to an electric motor, that will burn an engine up quicker than anything.

7:1 C/R, 80 octane engine. Yeah, go ahead leave it full MP and full rich. Your AP will love you. It'll be about a cylinder per year.

 

[GeorgeC]

I was just looking over the checklist to an Arrow IV and it recommended to climb out at 25"/2500 rpm. Looking at the performance charts, this is around 70% at sea level. No wonder why it climbed like a Cherokee 140...

 

[asechrest]

The POH of the 1977 Archer II that I fly appears to give a 5 minute limitation at full takeoff power of 2700 RPMs.

 

[JC150]

@George: Is that the checklist in the POH? I looked in the Arrow IV POH and saw no mention of 25"/2500RPM, only a slight reduction of rpm to 2650 when safe to do so. The climb performance tables also say full throttle. I've tried the full throttle method now 4 times in my arrow iii, and so far no problems! Now if only some of the young CFI's at my local airfield would take a look at this thread...

 

[GeorgeC]

No, it was a third party checklist. It didn't mention the 5 minute limit on full throttle, the reduction to 2650, or the cruise climb speed.

 

[Computerjim]

I have been flying Lycoming O540's and TIO540's for close to 30 years and have never seen any limitations in any Lycoming publication. I see them in third party stuff that spreads common myths, but nothing official.

When a small throttle reduction is done after take off during climb there is a risk of over heating the cylinders. The manufacturers have set an extra fuel enrichment setting at full throttle to guard against detonation and get a little extra fuel into the cylinders to help with cooling.

I use fuel throttle and max RPM at take off, and leave it there until I level off for cruise. In the O540 in the Comanche over 4,00 feet, that means I do not touch the throttle, only reduce RPM and lean. With the TIO540's in the Aztec I set up 70% power with a low RPM, 2300 or less, high MP, 26", and lean to LOP.

 

[gismo]

Depends how hard you climb, I'm still on board with fuel being cheaper than jugs.

In cruse, if equipped for it, LOP is cool, but for a aggressive climb no thanks.

Ask the big DZs, they climb for a living, won't find one running LOP, even the ones with nice JPIs.

I'd consult with your POH or the engine manufacturer, most CFIs are like dogs, one pukes up something interesting, the other eats it, pukes and so on.

LOP climbing is actually easier on the cylinders than ROP but it's something you have to pay close attention to during the climb unless the engine it turbocharged (with an automatic wastegate) or has an altitude compensating fuel injection system. The downside to LOP climbing is that if you get distracted below about 8000 DA you can accidentally slip from sufficiently LOP to a mixture that's detrimental to engine health because the mixture gets richer as you climb.

The 25/25 SOP OWT came from operators of certain engines which had a METO (maximum except takeoff) power setting which typically involved a reduction in both RPM and MP. Engine manufacturers also often recommend avoiding high MP combined with low RPM because this can produce the highest internal stresses. And somewhere along the way this led to the notion that engines shouldn't be run "oversquare" (MP in inHg higher than RPM in hundreds) even though there's nothing to suggest that "square" operation coincides with many engine manufacturer's specific recommendations.

Reducing RPM once you're safely above any nearby obstacles does have one thing to recommend it and that's the associated reduction in noise. But it usually doesn't require a much lower RPM to have that effect. Reducing MP when you lower the RPM would lower the peak internal cylinder pressure if it weren't for the fact that on most engines a throttle reduction also lowers the fuel flow and that can more than make up for the MP reduction.