Maximizing Lycoming IO360 Climb Performance

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Chris B
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Maximizing Lycoming IO360 Climb Performance

Post by Chris B »

Hopefully this thread will remain focused on how to maximize the performance of our normally aspirated DA40s.

Not why…
  • the NG is clearly superior in most respects
  • forced induction is the way to go
  • Diamond should replace the 180 HP IO360 with a 200 HP IO360 or 215 HP IO390 (angle valve engines)
I disagree with all of those points, but would prefer to keep that separate.
Image

******

After reviewing my Advanced Pilot Seminar (APS) notes, carefully reading George Braly’s (APS principal) relevant posts on BeechTalk, and taking advantage of John-Paul Townsend’s (GAMI guru) insight and extraordinary patience, here are suggestions for maximizing DA40-180 climb performance:
  • Climb performance is directly proportional to power. IOW increasing power X% yields a comparable incremental climb improvement, so cumulative small changes can make a big difference. This is completely different than improving cruise speed, where incrementally adding power yields rapidly diminishing returns. This is also why the Power Flow exhaust has a noticeable climb performance impact, with less obvious cruise benefits (IMO cruise improvements mostly come from reducing drag and - when LOP - balanced injectors).
  • Baffling is critical, and seemingly trivial openings make a big difference. Air is always going to find the path of least resistance, but we need cool air forced exclusively through relatively high resistance cylinder fins.

    Gaps near the top-center of the engine (front & rear) are obvious and easy to plug with RTV. Ensuring that the rubber baffle seals make good contact with the top cowling is a little more tedious; filling gaps with RTV works fine, but IME requires trial and error. When installing the new engine, we discovered several previously-overlooked leaks, principally hard-to-access locations behind the push rods:

    Image
    Full resolution: https://i.imgur.com/pe1a1dI.png?1

    Image
    Full resolution: https://i.imgur.com/Yw0iPXd.png?2
  • Increasing RPM from 2400 (AFM) to 2700 (maximum) theoretically increases power output 13%. AFAICT Lycoming does not publish IO360 power vs. RPM data. But Superior's charts suggest that close-to-theoretical is available in practice:

    Image
    Full resolution: https://i.imgur.com/gnlGl3c.png

    [BTW, APS explains why higher RPM is counter intuitively easier on the engine when ROP, particularly during climb. ROP mixtures burn faster and push peak pressure closer to Top Dead Center (TDC), which increases engine stress. Higher RPM helps push peak pressure away from TDC, reducing stress.]
  • Small changes in fuel flow have a huge impact on CHT, even ROP. Make sure that your mixture control presses the fuel controller arm firmly against the full-rich stop. When installing the new engine we discovered that our mixture control “throw” did not quite stretch from stop-to-stop, so we adjusted the linkage to ensure maximum fuel flow (rather than splitting the difference). Slightly less than full cut-off still works fine to shut down the engine.
  • Leaning during climb to keep EGT values similar to sea-level full-rich significantly increases climb performance. Your specific EGT values will be different (depending on probe location, etc.), but here is what this looks like on ours (#1 peeking above the 1300F line, taken during the climb referenced below):

    Image
    Full resolution: https://i.imgur.com/PjKylsC.jpg
  • Best glide speed (~76 KIAS, depending on gross weight) is approximately optimal climb speed. The caveat is that air speed must be high enough to keep CHT under control, which is why tight baffling and maximum fuel flow is so critical. Lately I target ~80 KIAS; higher in turbulence to keep the stall horn quiet. This is where the GFC700's FLC (/IAS) mode really shines.
Taken together, significantly better-than-book performance is quite feasible, even with relatively low CHT.

Here is a recent high density altitude (DA) departure in our 2008 XLS from South Lake Tahoe (KTVL) to 10,500’, ~100 lbs under gross, keeping CHT < 390F: https://apps.savvyaviation.com/flights/ ... ff948c4962
or: https://tinyurl.com/y7nk9cyo

TVL field elevation is 6264’, but DA on departure was 8600’, while top-of-climb DA was a whopping 13,700’.

We lifted off runway 36 prior to the end of the 2000' displaced threshold and averaged 403 fpm during the climb. Which is quite serviceable, and about 32% better than the AFM “cruise climb” charts indicate:

Blue = comparable DA & gross weight.
Image
Full resolution: https://i.imgur.com/xAO8Yoc.png
(link to previous chart: https://i.imgur.com/qtwHPCs.png)

Note that the AFM charts...
  • Specify 2400 RPM
  • Do not incorporate Power Flow benefits
  • Reflect an older (slower) airframe that doesn’t get “credit” for actually being lighter
    (since we are referencing gross weight, not useful load)
  • Do not specify CHT, but probably not < 390F
Chris

Edit: Originally used wrong DA on AFM chart (26C at 6000, not 26C at sea level...)
Last edited by Chris B on Sun Jun 28, 2020 8:48 pm, edited 1 time in total.
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pietromarx
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Re: Maximizing Lycoming IO360 Climb Performance

Post by pietromarx »

Chris -

I really appreciate you putting the effort into this post. I was in Truckee the other day and was *very* focused upon weight, performance, density altitude, etc. The airplane performed well, but I really wish I had a better climb rate.


Peter
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Scottsware »

Short version: Was only averaging 2630 rpm on takeoff, got that fixed to hit 2680. Noticeably improvement on initial climb. It may be worth checking if you are getting all the rpm allowed. I’m not sure if this is completely relevant to the OP as it only relates to the initial climb.

For the last 1 1/2 years we have been flying our plane the average max rpm has been 2630 per the Savvy Report card. This is noted as being “ average when compared with your cohort“. That seems to imply a whole bunch of DA40's are not hitting the 2680 +/- 20 in the POH. I probably should have investigated this earlier. I had asked my mechanic about it and he didn’t seem like it mattered all that much. I noticed on the prop governor that even at full prop forward, the max rpm screw wasn’t touched. The upshot of that was it was impossible to even adjust for max rpm. I then noticed the faceplate of the prop governor looked like it had rotated as the hex screws that were hold the faceplate were rotated 1/4 inch off center. During a recent mag IRAN I asked the mechanic to re-center/rotate the faceplate. Now at prop full forward the stop touches the max rpm screw. The plane now is hitting 2680.

The extra 50 rpm makes a noticeable improvement on initial climb and acceleration. We fly out of KAPA (5800')

Even though we can use 2700 rpm all day, we tend to pull it back to 2500 rpm after we get cleaned up and climbing well. CHT goes down and it climbs well enough.
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Rich »

Lycoming does publish their data. Look for Lycoming-IO-360-m1a-operating-manual.pdf for data for ours. There's also one that covers mucho variants of the 360's.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Chris B »

Rich wrote:
Sun Jun 28, 2020 10:58 pm
Lycoming does publish their data. Look for Lycoming-IO-360-m1a-operating-manual.pdf for data for ours.
Yep. You are correct! :bow

The embarrassing part is that I had that PDF on my computer and annotated the performance sections in 2015. :oops:

Fortunately the performance change from 2400 to 2700 RPM is about the same as shown by Superior.

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Re: Maximizing Lycoming IO360 Climb Performance

Post by blsewardjr »

The DA42 L360 POH has some IO-360 engine performance data for RPMs greater than 2400 -- see
DA42 L360 AFM.book.pdf
(162.92 KiB) Downloaded 4 times
Bernie Seward, IR, AGI
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Rich »

A behavior of my engine ever since new and continuing to this day: If the DA is above about 2000 ft, the mag drops at full rich during runup start to get above the specified 175 RPM drop, getting progressively larger at higher DA. Leaning slightly eliminates this tendency.

Hand-in-hand with this is leaning for takeoff at higher DA. Meaning above around 5000 ft. The normal procedure for doing this with a fixed-pitch prop doesn't work for a CS, so I'll initially use the lean setting I found gave me the desired drop during mag check and monitor EGTs, targeting 1300 deg for TO and climb.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Chris B »

Rich wrote:
Mon Jun 29, 2020 12:44 pm
Hand-in-hand with this is leaning for takeoff at higher DA. Meaning above around 5000 ft. The normal procedure for doing this with a fixed-pitch prop doesn't work for a CS, so I'll initially use the lean setting I found gave me the desired drop during mag check and monitor EGTs, targeting 1300 deg for TO and climb.

In one of his classic "Pelican's Perch" articles (#63, "Where Should I Run My Engine"), John Deakin outlines his technique for maximizing takeoff power at higher DA:
John Deakin circa 2002 wrote:Somewhere above about 3,000 to 5,000 feet, leaning for takeoff starts to take on significant importance, and even more so with shorter runways, hot days, deep canyons, poor runways, long grass, and other performance-inhibiting conditions. Above those altitudes, the full-rich mixture setting is much too rich, and will cause a major loss of available power. Since the altitude has already reduced your power (less air), you’re not making as much heat, and you don’t need the excess fuel for cooling.

The books are full of various techniques for this, but I find the simplest and most effective is just add full throttle, full RPM, then grab the mixture knob and move it aggressively from full rich to whatever feels like “more power” on the takeoff roll. You can’t hurt the engine with momentary mixture settings like this on normally aspirated engines! Saw that mixture knob back and forth, and feel the power change in the seat of your pants! At some point as you pull the mixture out from full rich, you’ll feel the power first increase, then for a large part of the movement you’ll feel no power change at all, because the “best power” mixture setting is very flat in that area. (In other words, “best power” occurs over a fairly wide range of rich settings, but not at full rich.) Go ahead, pull it a bit too far, and you’ll feel the power drop off from being not rich enough. Push it back in to the point where you first felt the best power, and forget it. It’s quick, simple, and very effective, and pinpoint accuracy is not necessary.

The time to experiment with this is not your first takeoff from a muddy, short, dogleg runway with obstacles deep in a canyon, with a strange airplane when it is 110F in the shade! Work with it a little at a very high-elevation airport with lots of hard-surface runway to get the idea. It’s not hard, but it does take a couple practice runs to feel good about it. (Don’t use this technique in a turbo!)

Use this technique to identify your engine's EGT at maximum takeoff power (mine is Cylinder #1 = ~1300F). This reflects an optimal fuel/air ratio.

While mixture setting obviously varies, this target EGT is the same at any density altitude.

Chris
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Rich »

The full-throttle runup is the preferred method of takeoff leaning if you're really sure about the pristine nature of the runup area. Prop tally so far: 2 :scream: It's also one big reason I'm staying with the MT prop. :D
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: Maximizing Lycoming IO360 Climb Performance

Post by Chris B »

Regarding runup, from the same Pelican's Perch article (emphasis added):
John Deakin circa 2002 wrote:If you did lean, either push the mixture fully in for runup, or enrich it just enough to get runup RPM. A mag check with a leaned mixture is much more diagnostic than the normal runup at full rich, so if I do a mag check at all [i.e., during runup. John advocates for in-flight, high-power, LOP mag checks.], I’ll do it leaned.

I think most people overdo runups. Many go to ridiculous lengths to set exactly the RPM specified in the POH, and they prolong the agony far too long. From the hangar, I hear these folks on the runup pad at high RPM for agonizingly long periods. Folks, this is quick functional check only, and if the POH says “1,700” for runup, anything between about 1,200 and 2,000 will do just fine for the purpose of the functional check.
Higher RPM makes a lot of unnecessary noise, heats the engine up too much if prolonged, and blows dust all over the place, not to mention picking up dust, dirt, and gravel, and chipping your prop and paint job. So run it up to around 1500 to 1700, don’t worry about the exact setting, and get on with it.

One short cycle of the prop with a 100 or 200 RPM drop is sufficient to indicate proper functioning, and further (or deeper) cycling accomplishes nothing, unless it’s very cold outside, and the prop is sluggish. All these oil-operated props on GA aircraft have passages that assure a continuous flow of warm engine oil to the prop internals. Some of the old radials get a bit sluggish and stiff in very cold weather, and a few more cycles on both the props and the feathering systems are often a good thing with them.
Chris
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