Cabin air vents suddenly not venting air in flight

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d424u
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Cabin air vents suddenly not venting air in flight

Post by d424u »

So weird observation in my DA42:

Occasionally, (usually in turbulent air or high airspeeds), there is a popping noise and a sound as if the nose wheel gear door had popped open and stayed open for usually 10-30 seconds. However, gear lights show locked and safe.

What I did notice it that when this happens, both panel air vents do not vent any air, as if a flap valve had close outside air supply off.

What could that be?

Thank you.
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cptndavid
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Re: Cabin air vents suddenly not venting air in flight

Post by cptndavid »

Hello Robert, I do not know about the air vent. You might put a spot mirror on your nacelle
to check if your nose gear is down or if the gear doors are open. you can find the mirrors at National Aircraft Parts Association they are very inexpensive get two one for each side.
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d424u
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Re: Cabin air vents suddenly not venting air in flight

Post by d424u »

David, Thank you for your idea and I have ordered these.

I had one more thought: If a front baggage door were to pop open just a little on the front latch, could that cause enough RAM air to vent into the cabin (through the panel basically) to reverse air flow back into the cabin air vents?

From what I am hearing, all noises I am hearing could be explained by the following sequence:

1) Popping / flapping noise as if a window had popped open, usually at higher airspeeds in bumpy air - (as if one of the front edges of the front baggage door had become unlatched)

2) feeling of air pressure changing in the cabin - with some degree of oscillations to the air (ram air through the nose compartment?)

3) no positive airflow into the cabin through the cabin air vents (ram air pressure from the front equals air duct ram air pressure = no net airflow)

4) all of these symptoms disappearing with reduction in airspeed (front baggage door front latch shuts closed again)

Now, I don't know enough about DA42 systems to verify any of that. Here are my concerns with my theory:

- Is there any direct air path for ram air to come from the nose baggage compartment into the cabin?

- Would I not get a 'DOOR OPEN' CAS message on the G1000 if any one of the front baggage door latches had become unhinged?

Either way, this is a puzzle that I feel my plane should not be the only one ever having been affected by, with thousands of them flying.

Is there any more thoughts on this?

Thank you!
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d424u
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Re: Cabin air vents suddenly not venting air in flight

Post by d424u »

I actually have an update following some further investigation - there is simply no way the front baggage compartment doors could have popped open - I have seen the latches and they would prevent any degree of movement in flight. So that theory goes out the window.

The weird sound and air blockage happened again to me yesterday, this time on descent at around 90kts right when I put the flaps down to first notch.

The plane was obviously at that time changing attitude in somewhat smooth air and rather slow airspeed. Yet, again, after about 20 -25 seconds, everything returned to normal.

I looked in my front baggage compartment, and you can literally see through the back end into the wiring for the panel. So air would have a path into the cabin from the front baggage compartment.

I do not believe ram air could travel from the nose wheel well into the front baggage compartment and on to the cabin. That only leaves two options:

1) nose wheel well directly into the cabin. Highly unlikely - the path would have to be along the steering linkages and I doubt that would be the same cross section as the cabin air vents.

2) something weird happening with the NACA duct for the cabin air. I checked it was clear with no obvious parts that could cause that.

I guess I am back to where I started - with a weird problem I don't know how to fix.

My A&P suggested to tape the NACA duct shut to see if I still get this.

Diamond Tech support came up empty.

Couple of DA-42 instructors with thousands of hours in these things shrugged their shoulders and never heard of that.

Ever had a car dropped off to the dealer five times to fix the same intermittent issue? That's how I feel like now.
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