Windshield Resistance:
The following resistance should be applicable to a new or used windshield.
Between terminals 1 and 2: -0.720 to 0.974 ohms @ 75 Degrees F +/- 5 degrees.
Between terminals 4 and 5: -0.720 to 0.974 ohms @ 75 Degrees F +/- 5 degrees.
Between terminals 3 and 6: this reading will vary with teprature changes.
the following are three examples, you will have to calculate anything in between.
Between 110 degrees F = 342 ohms
85 degrees F = 328 ohms
50 degrees F = 310 ohms
Showing posts with label Windshield. Show all posts
Showing posts with label Windshield. Show all posts
Wednesday, June 10, 2009
Thursday, May 28, 2009
ATA 30
Moisture Between the Windshields
Have you ever seen a waterline in between the inner and outer windshield panes of a Westwind? That is a result of sealant around the outer windshield becoming hard and brittle like concrete, with a tendency to crack, allowing moisture to seep down between the inner and outer windshields. The waterline forms from the rise of water between these panels, because it is filling up faster than it can drain out. It will eventually drain out through the desiccant bottles and then into the avionics bay (oh, boy!!) near the AC inverters via an elbow-style fitting mounted in the forward pressure bulkhead.
This can cause some very expensive damage if not repaired ASAP. Water can cause the heating network electrical terminals to corrode; corrosion causes electrical resistance to increase; and as resistance increases, so does heat at the point of resistance. It can get hot enough to melt and burn the inner windshield, which is made of a very tough plastic, where the electrical terminals pass through.
If the damage to the inner windshield does not exceed one inch in diameter, it can be repaired with a fiberglass-like plug, saving the owner/operator from having to replace it. If the damage is greater than one inch in diameter, the inner windshield will have to be replaced, which happens to be quite costly and very labor intensive.
Nitrogen can be used to purge moisture from the windshield, per Maintenance Manual 56-10-01. However, I have seen many outer windshields removed in order to clean off the waterline and remove corrosion on the electrical terminals and contact plates in an attempt to save the owner/operator a bunch of money in the long run.
Maintenance Tip:
When re-installing the outer windshield, you should take extra effort to keep the sealant flexible for as long as possible. After it cures, it is a good idea to paint the sealant between the outer windshield and aluminum frame with black polyurethane paint, in order to protect it from the sun’s harmful ultraviolet rays, which harden and, eventually, crack the sealant, allowing moisture in. The sealant on the outside of the frame should also be painted and color matched with the airframe to help protect it as well.
Have you ever seen a waterline in between the inner and outer windshield panes of a Westwind? That is a result of sealant around the outer windshield becoming hard and brittle like concrete, with a tendency to crack, allowing moisture to seep down between the inner and outer windshields. The waterline forms from the rise of water between these panels, because it is filling up faster than it can drain out. It will eventually drain out through the desiccant bottles and then into the avionics bay (oh, boy!!) near the AC inverters via an elbow-style fitting mounted in the forward pressure bulkhead.
This can cause some very expensive damage if not repaired ASAP. Water can cause the heating network electrical terminals to corrode; corrosion causes electrical resistance to increase; and as resistance increases, so does heat at the point of resistance. It can get hot enough to melt and burn the inner windshield, which is made of a very tough plastic, where the electrical terminals pass through.
If the damage to the inner windshield does not exceed one inch in diameter, it can be repaired with a fiberglass-like plug, saving the owner/operator from having to replace it. If the damage is greater than one inch in diameter, the inner windshield will have to be replaced, which happens to be quite costly and very labor intensive.
Nitrogen can be used to purge moisture from the windshield, per Maintenance Manual 56-10-01. However, I have seen many outer windshields removed in order to clean off the waterline and remove corrosion on the electrical terminals and contact plates in an attempt to save the owner/operator a bunch of money in the long run.
Maintenance Tip:
When re-installing the outer windshield, you should take extra effort to keep the sealant flexible for as long as possible. After it cures, it is a good idea to paint the sealant between the outer windshield and aluminum frame with black polyurethane paint, in order to protect it from the sun’s harmful ultraviolet rays, which harden and, eventually, crack the sealant, allowing moisture in. The sealant on the outside of the frame should also be painted and color matched with the airframe to help protect it as well.
Friday, June 30, 2006
ATA 30
Cooling the Windshield Temp Sensor
Summertime is here and in full force, especially down here in Texas. But we still have to perform anti-ice system inspections such as of the “Inspection of Windshield Heat Cycling Contactor (WCC) I.A.W. 30-40-00 para. 1.B.”, which is accomplished at every “A” Inspection. In order to perform the check, you will have to cool the temp sensor within the windshield if the outside air temperature is 100°F or greater. The Maintenance Manual calls out to pour water over the temp sensor to lower the temperature. I use a plastic bag with ice in it and simply stick it under the windshield wiper blade over the temp sensor (this is considerably less messy). By all means, DO NOT spray the glass windshield with any type of freeze spray. There is a caution in the Maintenance Manual in the following paragraph (1.C.) “DO NOT SUBJECT WINDSHIELD TO THERMAL SHOCK OF SUDDEN TEMPERATURE CHANGES…MAY RESULT IN A FAILURE OF WINDSHIELD GLASS THROUGH THERMAL STRESS.” I have seen the “freeze spray” results on another type of aircraft, and I can attest to you that it wasn’t pretty. You also must consider the possibility that the outer windshield on the Westwind might not have been shimmed properly at the last install, resulting in it being slightly stressed already. It may not take much more to break it.
Summertime is here and in full force, especially down here in Texas. But we still have to perform anti-ice system inspections such as of the “Inspection of Windshield Heat Cycling Contactor (WCC) I.A.W. 30-40-00 para. 1.B.”, which is accomplished at every “A” Inspection. In order to perform the check, you will have to cool the temp sensor within the windshield if the outside air temperature is 100°F or greater. The Maintenance Manual calls out to pour water over the temp sensor to lower the temperature. I use a plastic bag with ice in it and simply stick it under the windshield wiper blade over the temp sensor (this is considerably less messy). By all means, DO NOT spray the glass windshield with any type of freeze spray. There is a caution in the Maintenance Manual in the following paragraph (1.C.) “DO NOT SUBJECT WINDSHIELD TO THERMAL SHOCK OF SUDDEN TEMPERATURE CHANGES…MAY RESULT IN A FAILURE OF WINDSHIELD GLASS THROUGH THERMAL STRESS.” I have seen the “freeze spray” results on another type of aircraft, and I can attest to you that it wasn’t pretty. You also must consider the possibility that the outer windshield on the Westwind might not have been shimmed properly at the last install, resulting in it being slightly stressed already. It may not take much more to break it.
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