Pressurization Air management
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Hi,
i am new to the duke owners club and really enjoying the depth of the systems but i do have some questions relating to the pressurized air (press air) / environmental system. I studied the POH and there are some dissents to the black square manual.
Let´s take a look to the process: Ambient engine ram air is routed to the compressor, hot compressed air passes the sonic nozzle, then the open firewall shut off wall, then the intercooler and then reaches the cabin air plenum through the check valve.
If firewall shut of wall is closed, press air is cut off and dumped in the engine bay.
Ram air scoops under the wing root leading edges controlled by the "Pressurization Air Temp Lever" control the ram airflow over the intercooler which cools down the press air running through the intercooler.
Here is my Problem: Black square manual says:
Quote: "For this reason (...heating cabin air....), the Piston Duke has two pull handles (one for each engine), labeled “PRESSURIZATION AIR TEMP PULL TO INCREASE” above the red pressurization air shutoff handles. When these handles are pulled away from the panel, air heated by passing over the turbocharger intercoolers that is normally exhausted outboard is redirected into the cabin."
As i understand it only the press air coming from the compressor is connectet to the cabin air circuit. I can´t find any entry/valve for the ram airflow over the intercooler into the air circuit leading to the cabin in the POH.
Here are my questions to the press air system:
- Is there an entry for the ram airflow over the intercooler into the cabin air circuit? I don´t think so.
- I think it makes sense if there is a bypass valve for the press air in front of the intercooler that directs the hot press air past the intercooler direct into the cabin air system. In case of pulling the press air temp lever the ram air scoops unter the wing root leding edges are closed and maybe in this case the press air is bypassed beside the intercooler which is useless without the ram airflow from the wing leading edges.
- Where does the ram airflow over the intercooler leave the plane. Is there an outlet at the back edges under the wing?
- Standing on the ground if the air scoops are open (press air temp levers pushed in) the intercooler is fully functional cooling down the press air before reaching the cabin. How is this possible? Is the the back blast turbulence from the propellers sufficient to create an adequate airflow through the ram air scoops over the intercooler?
Thank you for your answers in advance.
Best regards
NoPro
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What a wonderful message! It makes my day to see my users engaging with my aircraft like this, because that is exactly what I designed them for.
You're absolutely correct that the second half of my statement in the manual is confusing and does not create a good picture of what's going on. As I read your summary from the POH, I recalled what is depicted in my tablet's cabin visualizer. The visualizer rings true, but the statement in the manual should be edited to something like:
"...When these handles are pulled away from the panel, ram air no longer passes through the cabin air intercoolers. This effectively increases the temperature of pressurization air entering the cabin from the turbochargers, supplementing the combustion air heater."
To answer your questions specifically:
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You are correct. The only ram air that can enter the cabin is through the ram air inlet on the side of the nose, when the cabin air pull handle is pulled away from the panel, and the aircraft is unpressurized (check valve). This can all be observed on the cabin visualizer.
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I believe it's the ram air that's prevented from passing through the intercooler, rather than the pressurization air bypassing the intercooler, as depicted on the cabin visualizer. I can check the parts manual or ask a Duke pilot if they know. Either way, the end result is the same.
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I believe the intercooler air is exhausted through the flush louvers on the bottom of each wing root fairing, just behind the inlets. You can see them in white in this screenshot, next to the fuel drains. While you're looking at that side of the airplane, you will also notice the inlet air temperature probe in only the left wing inlet, which is used by the automatic temperature controller.
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I imagine the propeller slipstream does contribute to cooling the pressurization air, as I know it does for the air conditioning condenser, but at normal operating power on the ground, the turbocharger boost is low, and so is the turbine inlet temperature, so there isn't actually much cooling to be done. If you pull the pressurization air temperature handles out on the ground, you will see little increase in the pressurization air temperature, but as soon as the engines are brought up to takeoff power, the cabin will start to become uncomfortably hot. Looking at my code, this should all be simulated in the Piston Duke.
What delightful questions! Always feel free to ask more. I will do my best to answer them, and I will probably learn something along the way too!
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Hello,
first of all: i did´t expect an answer that fast and exact by the developer itselft. This really makes me happy. I was rummaging through this forum and i must say: Black Square seems to be a real gem. Resposivness and dedication to the subject is outstanding.
The Duke and its transperency for the systems by the tablet is a real game changer for me. Before the Duke it was often like flying black box (exept the A2A comanche). Now i have an image about the systems working toghether and its real fun to go to the POH and look for details and settle out how the details work. With the tablet i actually tought my kids how a combustion engine works.
The EDM-760 Engine Monitor is another exemple. Reading the Monitor and learnig the correlations makes long cruises enjoyable.
Some will say: ohhhhh some colors changing by pulling some levers, whats the deal?. But for me its a complete new game. For example i really enjoyed flying the flysimware cessna 414 (although it drives like a family SUV compared to the duke sports car). But as i said, for me it was a black box. All those levers and buttons, and all information i could get for exemple for the environmentals was one!!! single temperature number in the tablet-display of the 414. Now i have the tablet of the duke in my mind and i am able to push the 414 to its limits and fly it like she deserves; completely different ball game.
Keep up the good work! I´m looking forward to the starship and others.
Best regards
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@Black-Square said in Pressurization Air management:
I believe it's the ram air that's prevented from passing through the intercooler, rather than the pressurization air bypassing the intercooler, as depicted on the cabin visualizer. I can check the parts manual or ask a Duke pilot if they know.
If you do happen to ask a Duke pilot, we'd love to know how they typically choose to heat the cabin.
Do they primarily rely on the combustion heater, supplemented by the pressurisation air? Or do they try to minimise usage of the combustion heater, as they are notoriously unreliable and problematic (at least as far as I remember reading, or it may have been mentioned in one of your YouTube overview videos).
I know the topic came up in the forums before but we were all unsure. It's not important, but always feels good to operate the Duke in a way that is true to life, rather than by the book, since the book isn't always right.
Anyway, always a delight to read details about how the Duke works and what has been programmed, thanks for engaging with your users in this way! :)
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I was talking with a former Duke pilot earlier today, but unfortunately, I forgot to ask him. I looked into my documents from the Duke Owners Association, and I could not find a consensus on whether to heat from the pressurized air, or from the cabin heater. I found most owners operating in the way the manual describes, using the pressurization air as supplemental heating, but also a couple mentions of starting with the pressurization air. I will let you know if I learn more. I also discovered something new to me, which I have implemented in my simulation. Apparently the heater blower runs when the ambient temperature is above 90°F to provide cooling to the radar and any other avionics located in the nose compartment.
I also found the intercooler assembly in the parts manual for you. Here is the diagram:
Detail B is the valve assembly, and component 11 is the vent overboard, so the system functions by restricting cooling air intake, as depicted on my tablet displays. Amazing questions, as always!
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Fantastic stuff, thanks for the reply and the extra detail.
It seems almost counter-intuitive to use a dedicated heater at all times, when the engines are capable of providing plenty of hot air to the cabin once airborne, but given the age of the aircraft, it was likely a design choice based on cost or complexity or availability of suitable equipment to regulate the temperature. Not sure, but the fact we are asking such questions to understand your aircraft in such depth is a testament to the incredible simulation you've built! :D
