- 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)
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:
Full resolution: https://i.imgur.com/pe1a1dI.png?1
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:
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):
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.
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
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.
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
Edit: Originally used wrong DA on AFM chart (26C at 6000, not 26C at sea level...)