|Give Bad Boots the Boot|
|Written by Jacqueline Shipe|
|Thursday, 24 February 2011 09:23|
Twin engine airplanes are fun to fly because they are generally much more complex than singles with more knobs, buttons and gadgets to keep track of. They are also better travel airplanes, designed to get from point A to B in a shorter time and to be functional in different types of weather. Many of these airplanes are equipped with de-ice boots to facilitate flight in some icing conditions.
The boots are made of a high quality rubber and have rows of hollow chambers that inflate when the system is activated. The air source for twins with reciprocating engines comes from the exhaust outlets on the vacuum pumps. When the pilot activates the boots, a valve routes air from the exhaust outlets to the boots through a series of hoses. A timer in the system keeps the boots inflated for a specified time and deflates them in the correct sequences. As the boots inflate, any ice that has built up on the leading edges breaks off. (Turboprop planes use bleed air off the compressor to inflate the boots. Most jets have anti-ice systems which heat the leading edges of the wings and tail to prevent ice from ever forming in the first place.)
If the boots are not inflating properly, they are either not getting air or not holding air. Loss of one of the vacuum pumps on a light twin can adversely affect boot operation. Boots should inflate with only one pump working but many times the performance of only one pump gives sluggish boot operation. If there is a leak in the system or in the boot itself, performance will also be degraded. Leaks in the boots can be found by connecting an air hose to the hose connection on the boot and gently inflating it. With the boot inflated, spray a soapy water solution on the boot; bubbles will begin to appear wherever there is a hole.
Boot manufacturers make patches which are used to repair holes and small tears in boots. These patches work pretty well if they are installed correctly the first time they are used in a certain spot. Old patches that have the edges peeling up are difficult to re-adhere to the boot. Small holes can be covered with a small amount of PRC, a thick two-part sealant and adhesive. It adheres well and generally never has to be reapplied once a repair has been made.
Once a boot has numerous places that are leaking, a new boot may need to be installed to guarantee de-ice protection. Boot replacement is an expensive repair, with the average price for a light twin being around $4,000 for a wing boot and around $2,000 for each tail boot. The boots themselves are costly and they require several hours of labor to install. It is best to use a shop or mechanic that has experience installing boots to ensure a good job.
A new boot installation begins with stripping off layers of rubber and glue from the old boot. Abrasive pads and solvents are used to get all of the old adhesive off. Once the airplane surface is completely clean, a thin layer of 1300 glue is applied in two or three coats and allowed to dry. The new boot also has a layer of glue applied to it which is also allowed to dry. A chalk line is made along the leading edge of the wing or tail surface to provide a reference line so the boot is glued on straight.
The new boot is rolled up neatly with the hose connection and glued surface on the outside. The new boots come with a straight reference line that is marked along the center of the inside surface of the boot. This line is matched up with the chalk line on the leading edge. The glue is activated as the boot is pressed on by spraying methyl ethyl ketone (MEK) on the surfaces. Special rollers are used to ensure the boot is stuck down well with no air pockets between the boot and structure. A layer of black rubber cement is painted around the edges to complete the installation.
Owners can do several things to help get the most longevity out of their boots. Sunlight and bug strikes are the two biggest culprits in de-ice boot wear. Storing an airplane in a hangar as often as possible helps to prevent aging and cracks caused by UV light. Bugs should be cleaned off often with water and a mild soap solution. The acid from the bug bodies actually eats into the boot if allowed to remain on it. A couple of different manufacturers make a boot protective coating that is applied by wiping it on. Once it dries, the coating makes the bugs much easier to remove and keeps them from penetrating into the boot. The coating gives the boot a glossy look which improves appearance as well. Once or twice every year, boots should also be treated with a chemical product called Age-Master. This soaks into the boot and rejuvenates the rubber, making the boot more elastic.
The boot treatment chemicals can be expensive to buy and slightly time consuming to use but compared to the cost of new boots, they are worth it. A little extra care here and there can help keep boots looking good and working properly.
From the February 2010 of Cessna Owner
|Last Updated ( Thursday, 24 February 2011 09:37 )|