Lubricants
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Lubricants |
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From "Construction Notes" Falco Builders Letter, December 1997 |
Kim Mitchell asks about where to use the three types of grease specified for the Falco. Aeroshell 7 is tan in color and is to be used in the landing gear retraction gearbox. Aeroshell 17 is the same grease except it has molydenum disulfide ('moly') added, which makes it a black grease. Use this on the screwjack threads. Use Mobil 28 everywhere else. Mobil 28 is red in color.
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From "Goings On at Sequoia Aircraft" Falco Builders Letter, June 1986 |
I've recently learned a thing or two about grease. I always thought that grease was grease, and that's all you needed to know. Actually, there is more to it than that.
The whole thing started with the problems some of the Falcos were having with the landing gear retraction system, which began to pop circuit breakers when the weather got cold. I cast about in ignorance until one day I called Kas Thomas at Light Plane Maintenance. Kas put me in touch with Eric Karnau of Aviation Consumables, whose business is... grease! Here is what I learned:
The ordinary greases that have been used for years are petroleum-based. Like oil, they thicken at cold temperatures until they freeze solid at about 25°F. In the last two decades, Shell and Mobil have developed synthetic greases which are relatively unaffected by temperature. Today, synthetic greases are offered by Mobil, Shell and others for use on aircraft, in two types: diester-based and synthetic hydrocarbons.
These greases have a wide temperature range, Aeroshell 7 is a diester-based grease that is good for 85°F to 300°F. Unlike petroleum-based greases, these greases do not thicken with temperature changes: Aeroshell 7 has the same consistency at 60°F that it does at 250°F. Mobil 28, a synthetic hydrocarbon, goes even higher.
We will shortly put out some information on the lubrication of the Falco, as part of the maintenance manual. On the original production Falcos, the lubrication schedule was very simple: light weight oil on the elevator trim tab hinge, hydraulic fluid for the brakes and oleos, normal aviation oils for the engine, and grease everywhere else at 50 hour intervals, except for the very active parts of the landing gear which were greased at 25 hour intervals. One advantage of the newer greases is that the short intervals can be changed to 100 hours. There is also the problem that no one is going to want to put grease on his aileron hinges or elevator pushrod-you have to take things apart. Grease is the lubricant of choice, but no one is going to use it.
Here is what Eric Karnau recommends for the Falco: Aeroshell 7 in the landing gear motor gearbox, changed at 500 hour intervals. Aeroshell 17 on the exposed gears and screwjacks of the retraction system at 100 hour intervals, and Mobil 28 on the landing gear grease fittings, wheel bearings, torque links, side load struts, etc. at 100 hour intervals. I would rather keep things very simple and use one grease, but there are good sound reasons for using these greases-and these same greases are used on Mooney, Beech and other aircraft.
The synthetic hydrocarbon Mobil 28 is used on the landing gear since it is more dirt-resistant, and it stands solvents and detergents well-although you should relube the landing gear with grease after washing with high-pressure spray and strong detergents or solvents. Mobil 28 offers outstanding performance over a wide temperature range of 85°F to 400°F and is used in the engine compartments of turbine and turbocharged aircraft. Mobil 28 is red in color and meets MIL-G-81322D.
The diester-based Aeroshell 7 will sit in a gearbox without oxidation, hardening and won't cake. It is commonly used in gearboxes with lubrication schedules of 500 to 1000 hours. Aeroshell 7 is used in most gyros, autopilots and instruments. Aeroshell 7 is tan in color. Aeroshell 7 meets MIL-G-23827B.
Aeroshell 17 is Aeroshell 7 with 5% molydenum disulfide-"moly"-for extreme pressure. Moly is a crystaline lubricant like graphite, but moly can also be an abrasive in concentrations above 5%. Moly works best with steel and bronze and is not normally recommended for aluminum. It is used on extreme pressure situations because when a bearing surface is under high stationary pressure, the grease can be squeezed out. The moly provides the first lubrication until the grease film is restored by rotation. Moly does not make the grease any more slippery. Because of the moly, Aeroshell 17 is black. Aeroshell 17 meets MIL-G-21164D.
It is very important that the synthetic hydrocarbon Mobil 28 not be mixed with the diester-based Aeroshell 7 or 17, since the combination forms an acid. When in doubt, remove all previous grease if you don't know what was used before.
For all of the other lightly loaded steel-to-steel, steel-to-bronze and steel-to-aluminum joints of the Falco, Eric Karnau recommends Tri-Flow. Tri-Flow is similar to LPS-2 or WD-40, but it is generally acknowledged by experts to be superior in all respects. In the Falex test for wear and load, it failed at a pressure that was three times higher than WD-40 and 5 times higher than 3-in-1 Oil-Tri-Flow probably contains one of the common extreme-pressure additives. Like WD-40, Tri-Flow is a penetrating and water-displacing oil. Tri-Flow is about the same weight as 20-weight oil, but is mixed with a volatile solvent which allows it to be sprayed in an aerosol, assists in penetrating and quickly evaporates leaving the thicker oil. Tri-Flow has excellent corrosion protection characteristics, and it smells a little like Hoppe's gun oil. Tri-Flow comes in an aerosol can or squeeze bottle, and both have a tiny plastic tube which allows you to put the oil right where you want it.
Tri-Flow contains micron-sized Teflon particles. I had always understood that Teflon engine additives were snake oil remedies-Microlon's Bill Williams once told me that he rubbed Microlon on the wing of his airplane, and it flew faster. Eric Karnau says that for engines, Teflon additives are snake oil, but for other applications they are not. Teflon particles do not decrease the friction or make the oil any more slippery. As long as oil is present, the bearing surfaces ride on the film of oil. Teflon has value only as a dry lubricant and a powdery residue of Teflon will continue to provide lubrication after the oil has been squeezed out. That's all it does. Teflon just provides a dry lubricant that will be there if the oil goes bye-bye, and that's why putting it in your engine won't make any difference.
Tri-Flow is sold at gunshops, hardware stores and is available from Aviation Consumables. You may purchase the greases mentioned above in 35 lb containers from Mobil and Shell, or you can order smaller quantities from Aviation Consumables which offers lube kits for a number of aircraft.
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Aviation Consumables is a specialist in aviation lubricants and is a major supplier of grease and other lubricants to the aviation maintenance industry. They used to supply Lube-Kits for a number of aircraft, but they have stopped selling these lube kits. The Falco Lube-Kit is intended to be a three-year supply. For your information, while they were available, Aviation Consumer included the following items in their kits, which you may want to purchase from other sources.
We say again, these kits are no longer available, and the above information is provided for yor information. If you need to reach the company, they are: Aviation Consumables, Inc., 400 Leadbetter Road, P.O. Box 27205, Cincinnati, Ohio 45227. Telephone: (513) 561-9977. |
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July 2000 |
Please post a notice that Aeroshell has a website at www.Aeroshell.com. They have all oils and lubricants for the Falco available. Good service and prices.
Glyn Russell
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