Lear 20 Drivers-Plastic Windows

[cj610]

I'm looking to find an affective way to keep my windshield from fogging up when comming out of altitude. I've tried a few different methods but turning on the "Windshield Heat" 45 min before landing seems to work best so far. I was wondering if any of you guys have come across any better ways of preventing this problem.

 

[SeaBass]

Once at cruise altitude...just crack open the windshield heat and that should keep up with it during the descent. Sounds like that is what you are doing though...Maybe the only other way to deal with it is to quit going to those nice warm humid climates...stay up in the frozen tundra!

--Seabass

 

[avbug]

CJ610 suggests it's a 20 series Lear; you have the option of windshield heat or defog, with the knob in the "in" position. Push the defog knob all the way in, crack the defog valve open and come down with it open. Do it when you start your initial descent, and you shouldn't have any problems.

 

[troy]

Are any of the "Rain-x" products leal for inside aircraft? I know there are many products that prevent fog, but was unsure of the legality of them........

 

[Starcheck]

Just like avbug said, just crack the windshield heat when you get to cruise, or for longer legs about an hour out works. You may have to adjust how far the valve is open if the windshield overheat light illuminates. Then if need be in the terminal area run it in auto, though this tends to be pretty noisy.

I've found that the inside of the windshield seems to be the real problem in flight when in the terminal area, as the outside tends to be kept clear until you slow to taxi speed on the ground. In that case if you don't have the "hairdryers" to blow warm air over the inside of the windows, running the freon system should help keep the interior humidity level down. Though in some cases, Floride, Lousiana etc... you're going to have to reach up with your hand and clear the fog on the inside so you can see to land.

I don't know the legality of using rain-x or the like, but the only thing Learjet recommends be put on the windshield is mild soapy water. Anything else will probably craze or disort the window.

 

[UPSer]

When I worked for USCheck I always used Rain-X Anti-Fog. It worked great, I never had a problem with fogging up either on the inside or outside of the windshield, even when doing the usual steep decents into warm and humid terminal areas. It sure beat flying an approach with a towel in one hand wiping the windshield.

 

[avbug]

I would definitely avoid using rainex or any other such product on the window. You may not see the damage now, and it won't necessarily be visible, but it will be there. Rainex and similiar products are solvents which work by removing grease and condensation nuclei on the window, and reduce the liklihood or opportunity to fog up. However, you can accomplish something simliar by using some Zep surface clearner approved for plastics.

Look closely at the maintenance manual and be careful what you use on those window panels. At forty thousand dollars a pop, they're expensive to replace. (Depending on the s/n and model).

Be careful running in auto. You can quickly distort and craze the window from heat running on the ground, weather or not the high or low temp thermoswitches are working.

 

[UPSer]

Used it over 13 yrs ago, I haven't heard of Airnet losing any windshields because of it.

 

[abexpilot]

Correct me if I'm wrong, but shouldn't you be using windshield heat at ALL times during flight? Aside from the obvious reason for windshield heat, a secondary and very important function is to make the windshield more pliable (spelling?) thus more resistant to birdstrikes. At all of the airlines that I have flown for, the use of windshield heat has been standard practice for all of the aircraft (turboprops to jets). In fact, on the DC-9, There is an airspeed limitation if the windshield anti-ice is inop.

 

[avbug]

There is a difference between an electrically heated NESA type winshield made of glass, and a plastic windshield such as found on the Learjet. The glass windshield won't melt or distort from the heat, but the learjet windscreen certainly will.

(That's not entirely true: I have seen a thermal runaway on a NESA pan which did indeed melt it).

The learjet can be ruined in short order by too much heat. Additionaly, the Lear has no airspeed limitations related to heat. The Lear has a thck, multi layer (three layer) pliable windscreen that is highly impact resistant, and the angle at which it meets the relative wind provides a greater opprotunity for deflection than the windows on the DC-9.

The winshield heat on the 20 series lears also doubles as the emergency pressurization system. When acting as windshield heat, air is ducted outside and flows over two narrow columns on the windscreen. When directed as defog, it's inside, and can act as emergency pressurization.

Very different systems. Generally windshield heat is not used except for icing conditions, and descent. It should always be turned off on the ground, and auto shouldn't be used on the ground (or at all, if possible) due to the potential for windscreen damage. It only takes a failure of the high limit thermoswitch to cause permenant damage to the windscreen.