Cabin heat

[A64Pilot]

81 J model, 

My cabin heat has low airflow when cowl flaps are open, close them and you get way more airflow.

Is this normal? I’ve never noticed a decrease in airflow in other aircraft

[milotron]

My K does the same. I think the additional air flow of open cowl flaps cools the exhaust muff down enough to change the temperature. Either that, or the pressure delta between upper and lower cowl sections is changes with flaps open to reduce the air flow through the muff.

I am an electrical engineer and also have no idea what I am talking about, but this what had been explained to me.

[jaylw314]

2 hours ago, A64Pilot said:

81 J model, 

My cabin heat has low airflow when cowl flaps are open, close them and you get way more airflow.

Is this normal? I’ve never noticed a decrease in airflow in other aircraft

Yes, the heater muff goes to a divider between the cabin and the dump into the lower cowl.  When you open the lower cowl, the pressure drops and more hot air goes out dump.

On cold days I'll keep the cowl flaps closed, otherwise the defrosters do pretty much nothing

Edited November 6, 2021 by jaylw314

[KSMooniac]

Normal. Modulate the cowl flaps as needed in cold weather to heat the cabin, and keep the engine cool enough.

Sent from my LM-V405 using Tapatalk

[A64Pilot]

On 11/6/2021 at 10:53 AM, milotron said:

My K does the same. I think the additional air flow of open cowl flaps cools the exhaust muff down enough to change the temperature. Either that, or the pressure delta between upper and lower cowl sections is changes with flaps open to reduce the air flow through the muff.

I am an electrical engineer and also have no idea what I am talking about, but this what had been explained to me.

I think it’s the pressure delta, many aircraft the heater air intake is on the  the outside of the cowl sort of like a ram air intake, I haven’t looked but believe our Mooney’s must be inside of the cowl and subjected to air pressure differences with flaps open or not.

The heater hose inlet on my Maule made removing the cowl a PIA as you couldn’t remove it until the cowl was dropped some, but had to remove it to drop it completely, had great heat though as it had dual heaters, but a pain to remove the cowl

[PT20J]

Cabin heat air intake on a J is at the left front cowling opening next to the engine air filter. Ducting runs from there to muffler shroud and from there to valve on upper right firewall.

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[A64Pilot]

On 11/8/2021 at 11:05 AM, PT20J said:

Cabin heat air intake on a J is at the left front cowling opening next to the engine air filter. Ducting runs from there to muffler shroud and from there to valve on upper right firewall.

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Well there went that theory, so long as it’s normal behavior I haven’t concerns though

[Browncbr1]

Operating my heat valve has always made me think the blend door is sloppy because it’s either all or nothing and seems to change on its own in cruise.   So, I’ve inspected my blend door at the front right firewall and the linkage and door all seem tight, no slop.   Is there anything else I can check?

[jaylw314]

4 hours ago, A64Pilot said:

Well there went that theory, so long as it’s normal behavior I haven’t concerns though

No, you're mostly right   Opening the cowl flaps doesn't reduce the inlet air pressure to the muffler shroud, but it does reduce the lower bay pressure, which means more (or most) of the hot air goes straight out the dump instead of going into the cabin heat valve.

[jaylw314]

4 hours ago, Browncbr1 said:

Operating my heat valve has always made me think the blend door is sloppy because it’s either all or nothing and seems to change on its own in cruise.   So, I’ve inspected my blend door at the front right firewall and the linkage and door all seem tight, no slop.   Is there anything else I can check?

Mine is that way, too.  In flight, if I open it up past the first notch it's like an inferno, although I haven't noticed it changing in cruise.  It's so sensitive that I usually leave the cabin vent fully open so I get a blast of warm air instead of a breeze of flaming air.

I suppose that makes sense since it's getting heated by the 1400F exhaust...

[Browncbr1]

I’ve seen some people polish the firewall, so I got a buffing cone and some polish.  It cleaned up, but it’s not worth the time and effort.     It does look cleaner though.  My real thought now is to polish my exhaust.   The exhaust seems to have a lot of life left on it, but I have had to weld a crack in the muffler where the tail pipe comes out.  It kind of looks cobbly, so I’m debating buying a new muffler @~$1000-1300….    I’ll go get some more coarse polish and see what I can do to the risers.  
 

meanwhile, I had the copilot side panel in WIP for a couple years.  It was ugly and I’m glad I’m finally getting the down time and energy to finally finish the panel.  I’ll be flush mounting the jpi, possibly a flush iPad mini, usb, etc with 3D print fixtures.  Will post progress.  Got most removed today.  Also, I got the pilot yoke off for leather wrapping.

Edited November 11, 2021 by Browncbr1