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  #1  
Old 11-29-2018, 10:27 AM
rvdave rvdave is offline
 
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Default Defrost ideas

Yesterday while flying in northern Michigan marginal vfr conditions below the clouds and freezing temps I was picking up freezing moisture on the windscreen. Although I have defrost fans on the glare shield it wasn?t enough heat to take away or disperse buildup so landed right away with no factor.
Has anyone ducted air from floor heat to optionally divert warm air to defrost fans? I?m thinking of adding somehow a coupling and scat to floor heat outlet and a way to switch between the two. Any ideas?
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  #2  
Old 11-29-2018, 10:39 AM
rocketman1988 rocketman1988 is offline
 
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Default Umm...

If you were getting "freezing moisture" on the windshield, where else might you be getting "freezing moisture"?...
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  #3  
Old 11-29-2018, 10:44 AM
Jpm757 Jpm757 is online now
 
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I assume you wouldn't intentionally fly into freezing moisture, that being said, I mounted a fan on the upper side of the firewall heater plenum, mounted a 2" aluminum flange to it and routed it to a defrost duct on pilots glareshield. I have not used it to remove ice from the outside of the windscreen and don't know if it will, but works nicely to defrost the inside windscreen.
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  #4  
Old 11-29-2018, 11:11 AM
rvdave rvdave is offline
 
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Quote:
Originally Posted by rocketman1988 View Post
If you were getting "freezing moisture" on the windshield, where else might you be getting "freezing moisture"?...
This was just a local flight in the pattern, surprised to see a buildup so quick when there wasn?t real visible moisture but obviously was there, was a dreary day. Learned something again. Wasn?t up long enough to see anything on airframe. I can see though a need for better defrosting.
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  #5  
Old 11-29-2018, 11:21 AM
echozulu echozulu is offline
 
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Quote:
Originally Posted by rocketman1988 View Post
If you were getting "freezing moisture" on the windshield, where else might you be getting "freezing moisture"?...
While that is true, I think with how icing accumulates it'd be pretty helpful to have a defrost duct for the windshield. If you run into icing conditions, at least being able to see out the window might save you, and it's cheaper and easier to implement than putting in prop heat and deicing fluid.
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  #6  
Old 11-29-2018, 11:35 AM
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rocketbob rocketbob is offline
 
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Been there done that...VMC, not in the clouds.

My neighbor's Baron, although not equipped for known icing, has an alcohol prop and windshield. It's nothing more than an AN fitting and a piece of aluminum tube in front of the windshield. I'm sure one could rig up a heated windshield washer nozzle from a car and strap in a small tank/pump to be used in the winter.

Unless you could throw a serious amount of heat at the windshield, hence why hotplates are a thing, I doubt any amount of cabin heat would be enough to keep ice from sticking.
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  #7  
Old 11-29-2018, 11:49 AM
rocketman1988 rocketman1988 is offline
 
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Default Yes...

Yes, a defroster is not a bad idea, however, if you are seeing it on the windshield, it is most likely happening at other areas on the airframe, typically on small radius curves and anything that protrudes into the flow.

It is truly AMAZING how fast the "freezing moisture" can accumulate, if the right conditions are present.

Some years ago a family friend flew a 182 on a cross country and encountered ICE, (there, I said it). Thankfully, he landed at his destination...with almost two inches on the airframe and a ball on the spinner the size of a softball. You may have read about it in the AOPA magazine.

Also, some years ago, my family was snowmobiling in the Northwoods of WI when we came upon a guy flagging us down in the middle of a trail. It turns out the King Air that he and his family were riding in had crashed in a clearcut area. We carried him to the nearest stop on the trail, only to find the Sheriff's department getting ready to walk a grid through the woods to find the downed airplane. Weather conditions, at the time? FREEZING FOG. That King Air was on about a 15 mile ILS final and didn't make it...the crash broke the airplane in three pieces. Amazingly, everyone, including the dog, onboard survived; the worst injury was the pilot's broken leg.

Point is, "freezing moisture" can and will accumulate, sometimes after than expected. Our RVs are wonderful airplanes but they are still no match for Mother Nature.

Be careful out there!
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  #8  
Old 11-29-2018, 12:18 PM
dtw_rv6 dtw_rv6 is offline
 
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The empennage surfaces my be considered small radius curves protruding into the airflow.
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  #9  
Old 11-29-2018, 12:29 PM
rocketman1988 rocketman1988 is offline
 
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Default Yep...

Yes, they are...
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  #10  
Old 11-29-2018, 12:51 PM
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Carl Froehlich Carl Froehlich is offline
 
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Default Be careful of unintended consequences

To clear ice from on the outside of the windshield by blasting heat on the inside would lead me to reflect on my days of stress equations for heat transfer across material. Here the cold outside surface will be in tension while the hot inside surface will be in compression. While quality steel can accommodate some of these conditions, I would not want to test the plexi we use in our airplanes.

I had clear ice once on the glass and leading edge. About a quarter of an inch accumulated on the windshield and leading edges in less than 30 seconds. Departing the icing conditions cleared it up in a few minutes. This experience lead me to study compressive heating (OAT reading is up to 5 degrees or so above actual OAT) and super cooled liquid in cloud tops.

Here is an OAT correction graph:http://aviationandaccessories.tpub.c...225-10_640.htm

Carl
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