Defrosters

[FlyboyKC]

Why do my Defrosters on my M20G suck so bad? I have ensured that the air ducks are in good shape, but it seems that no matter what I do the airflow on the windscreen is just pitiful!
I have even tried to stuff a sock in the main vent to force the air to the windscreen, while that helped a little, it didn't seem like it had the volume/pressure that the main vent did. Everything seems like its plumed correctly.

Anyone got any thoughts or suggestions?

Thanks
Neal

 

[N201MKTurbo]

No, that sounds about right.

Back in the day in the 80s when I got ice on a regular basis. I have landed with only a 1 inch stripe of deiced windshield to look through. And the side window.

My 56 Cessna project has 2 inch ducts running to the defrosters, our Mooneys have a 1 inch duct running to the defrosters. That's 4.027 times as much hot air.

[ArtVandelay]

I replaced my hoses and it helped a bit.

[David Lloyd]

I get next to no flow or heat from the defrost vents or heat vents until level and the cowl flaps are shut. Then there is plenty of heat and about enough from the defrost vents to defog the windshield in about 30 minutes.  Others here have reported the same on older models.

[Hank]

Are you closing the heater valve under the panel, to force all of the air onto the windshield? My C has a valve in each footwell.

[FlyboyKC]

  On 1/3/2022 at 5:50 PM, Hank said:

Are you closing the heater valve under the panel, to force all of the air onto the windshield? My C has a valve in each footwell.

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Yes, I got all the vents closed underneath. Which surprised me that I am not getting more airflow. Where is all that air leaking out to reduce the pressure??

 

[N201MKTurbo]

  On 1/3/2022 at 7:54 PM, FlyboyKC said:

Yes, I got all the vents closed underneath. Which surprised me that I am not getting more airflow. Where is all that air leaking out to reduce the pressure??

 

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It doesn't have to leak out anywhere. The pressure is the pitot like pressure from the heater inlet duct in the cowl. The pressure stays the same, you are just routing it through more restrictive passages. It is like sucking your soda through one of those big McDonalds straws or a coffee stirrer. Same pressure, but a lot less flow.

[carusoam]

Adding to the collective knowledge…

Getting airflow heated, and through the tubes to the windshield has a lot of restriction, minimizing flow….

The Long Bodies added a blower in the line that turns on automatically with the defrost knob….

PP thoughts only, 

-a-

[FoxMike]

Years ago I owned an E model.  When the humidity was high I used to put a handkerchief on the glareshield and rub it on the windshield several times during taxi and just before takeoff.  Like all the early Mooney's the defroster left a lot to be desired.  Having a blower assist on the new ones is a real advantage.

 

[KB4]

  On 1/3/2022 at 7:54 PM, FlyboyKC said:

Where is all that air leaking out

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Left and right defrost hoses.
 

If old, (chances very good cause not easily accessible) they likely have holes.  Check picks of avionics installs with glare shield and all avionics removed, you will see those 2 hoses I’m referring to. 
 

your IPC should show something like this 

[Guest]

Make sure that the valve at the firewall is opening fully and that the cold air valve is closing fully.  Unfortunately many Mooney models are not blessed with good heating systems.