Grand Piston Duke Manifold pressure drops
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For the sake of experience, I'm attempting to reach 25,000 and then 30,000 feet in the Grand Piston Duke, following the performance chart where the manifold pressure is listed as 35.5 all the way, with 2750 RPM and a 194 mixture setting up to 25,000 feet with a full load in ISA conditions. However, as soon as I cross 22,000 feet, the manifold pressure starts dropping below 33 inHg. I've tried various approaches to maintain 35.5 manifold pressure, but it doesn’t work, even with different payloads and weather condition the results are the same.
I watched a couple of YouTube videos where at 25,000 feet, their manifold pressure is as high as 41 inHg with full props and fully rich (forward) mixtures. In one video, it was 37.5 inHg with lean mixtures. Can you help me understand where I might be going wrong? Your assistance would be greatly appreciated. -
I can take a look at this on my system later, but I suspect that the problem is simply that you are not leaning above 22,000 ft. The turbochargers are only able to maintain 41 inHg until the critical altitude (~20,000 ft). Beyond this, power will begin to decline, as it would with any normally aspirated aircraft, without leaning the mixture. Continuously leaning the engines for best power as you climb beyond the critical altitude should allow you to achieve that 35.5 inHg, all the way to cruise altitude.
Let me know if that works for you! Always here to answer questions. You can also find more information in the "Turbocharged Operation" section of the manual.
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I understand that leaning is crucial as you ascend beyond the critical altitude. As I mentioned in my previous post, I followed the numbers in the performance charts, with the mixture set to 194 up to 25,000 feet and 190 from 25,000 to 30,000 feet. Even after leaning the mixture to 190, the manifold pressure still drops to 33-34, which seems unusual. In fact, I would only use your performance chart as a reference, but in other videos, the manifold pressure doesn't drop like this. I'll try flying again to see if the issue persists. I'm not sure if this problem is unique to me, but thank you very much for your response. I'll wait for further feedback on this matter.
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I have done couple of flight with both B60 duke and grand duke (piston version) and results are same. I took screenshots. These flights are even after reinstallation of software and this time I disable Norton firewall. I have gone through the manual once again to make sure that I am not doing anything wrong.
First image around 20k every thing is fine
Second image mainfold pressure drops therefore I lean the mixture to keep 194 reading
Fourth image 22.5k even after more leaning with the reading of 194 fuel flow manifold pressure is around 35 but throttles are around 98 % forward. I am following the figures highlighted in orange
Third image throttles full forward and the mixture settings are at best settings. every thing else is normal and in green.
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You can watch both videos where readings are different then what I have posted but both these videos are before the update. It may be that you have corrected the behaviour of manifold pressure at these altitudes or goes wrong. Please guide me on that.
https://www.youtube.com/watch?v=YXenEWyGIoM&t=173s
https://www.youtube.com/watch?v=ooXdnkZChJ0&t=121s
