RobertGary1 Posted April 24, 2019 Report Posted April 24, 2019 As an engineer I can't help but wonder if there have been any studies on the long term effectiveness of compressing grease into assemblies. For 20 years I've been pushing grease through the fittings on my plane every year. Sometimes they stop taking grease and we have 1/2 dozen or so ways to clear then, the most extreme of which is to disassemble the component and clean it out. But how do we know when we faithful push grease through and see it coming out the other side that we aren't just pushing grease along a narrow clear path and the rest of the assembly is clogged up? Has there been any work to analyze fittings to see how well grease distributes after aging (i.e. when things are no longer clear and flowing easily)? -Robert Quote
M016576 Posted April 24, 2019 Report Posted April 24, 2019 45 minutes ago, RobertGary1 said: As an engineer I can't help but wonder if there have been any studies on the long term effectiveness of compressing grease into assemblies. For 20 years I've been pushing grease through the fittings on my plane every year. Sometimes they stop taking grease and we have 1/2 dozen or so ways to clear then, the most extreme of which is to disassemble the component and clean it out. But how do we know when we faithful push grease through and see it coming out the other side that we aren't just pushing grease along a narrow clear path and the rest of the assembly is clogged up? Has there been any work to analyze fittings to see how well grease distributes after aging (i.e. when things are no longer clear and flowing easily)? -Robert I guess we don’t... great question! Maybe the answer is purging the assembly’s on a time basis (every X number of years)? I don’t know- just a hunch. 1 Quote
Yetti Posted April 25, 2019 Report Posted April 25, 2019 Just last night I was squeezing grease into the finish mower. It found a path and squirted out and hit my shirt. So I pumped again. Again hit my shirt. And why can't people make a decent grease gun. I think the point is that it makes new grease available to be smeared around when things move around. Not so perfect somewhat random. 1 Quote
carusoam Posted April 25, 2019 Report Posted April 25, 2019 There is an answer to this fine question... It comes from the study of Rheology.... The study of flow... and the effects of viscosity.... More the Engineering of Grease Fittings, than the science... The grease nipple is nothing but a seal that allows grease to come in, and not come back out... Procedures, and grease chemistry, does the rest... It is important to grease things annually... if it has been a decade since a plane got greased... the shelf life of the grease could cause problems with changes of viscosity... Problems occur when old stuff solidifies... its viscosity has increased. The new lower viscosity grease coming in, May tunnel through the old stuff and show up quickly at the other end... Tunneling is noticeable to some people that have done the job before... their observation would be something like .... Ooh, that was too quick.... (or... hey, that’s my clean shirt!) Another part of the greasing procedure is an observation of the grease coming out clean... as in tunneling includes bits and pieces of the old crap continuing to show up... If it keeps coming out, not clean... a decision gets made... keep flushing, or disassemble and clean. As an engineer... you can calculate the volume of the space and compare to the volume of each pump... Observe how many pumps it takes for clean fresh material to come out... Two ways to set an expectation, and confirm with an observation... Fortunately our grease system in the landing gear is pretty stable. It doesn’t change viscosity that much each year... the volume isn’t that much, so it gets completely flushed each time... Where we run into challenges is the trim system... the grease can be decades old inside the gear box, it doesn’t flush completely out because of the flow challenges of a gear box.... and on the threaded screws themselves... open to the air leads to the grease drying out and solidifying.... A rheology professor I once listened to explained pushing a high viscosity material out with a low viscosity material... it’s like having the runs, but the old stuff is blocking up the system, still... that can be a pain in the butt. Could have been a biology teacher explaining fluid flow.... one or the other... In the end, it requires us to use the right materials and follow the right procedures to be fine... Somebody has thought this through already... and that’s what makes the experimental aviation world such a challenge... soo many details that may go unnoticed when you are the first to do something in a different way. PP thoughts only, not a rheologist, biologist, or experimental plane builder yet... how was that? Best regards, -a- 3 Quote
RobertGary1 Posted April 25, 2019 Author Report Posted April 25, 2019 3 hours ago, Yetti said: Just last night I was squeezing grease into the finish mower. It found a path and squirted out and hit my shirt. So I pumped again. Again hit my shirt. And why can't people make a decent grease gun. I think the point is that it makes new grease available to be smeared around when things move around. Not so perfect somewhat random. That assumes a joint that rotates bear 360. Some of the ones in the gear only rotate about 10 degrees. That’s a lot of place for bad grease to block voids. -Robert Quote
carusoam Posted April 25, 2019 Report Posted April 25, 2019 Robert is really thinking this evening... Lets look at a bearing that only moves 10° and compare it to one that moves 360°... a simple bearing is a cylinder within a cylinder... the grease occupies the space in between the two... the grease is attached to the surface of both... The grease will stretch, rotate, and flow in the direction of the rotation... Thats a lot of motion... and flow... because the whole bearing is moving... even when it only moves 10° at a time... The thought that goes into this.... is directly applicable to... Buying a hangar queen vs. a plane that has been flown a lot.... There is plenty known about planes that fly often... planes that sit, have systems that fail without being used... Best regards, -a- Quote
Yetti Posted April 25, 2019 Report Posted April 25, 2019 9 hours ago, RobertGary1 said: That assumes a joint that rotates bear 360. Some of the ones in the gear only rotate about 10 degrees. That’s a lot of place for bad grease to block voids. -Robert This one happened to be a caster wheel with 360 degree rotation. So in the fun of mowing, casters and wheel arms have gotten bent. So looking up parts it comes to about $500. I can get a used one for $750. Looks like I may have to hook up the trailer to car. I like craigslist. Then I will probably use the torch to heat and bend things. I really do spend more time on the mower deck than I do the plane. Quote
cliffy Posted April 27, 2019 Report Posted April 27, 2019 Yetti Either you have too much land to mow OR you have too small of a mower :-) Quote
M20F Posted April 27, 2019 Report Posted April 27, 2019 The only science I have learned about grease fittings is they break off. Quote
Guest Posted April 27, 2019 Report Posted April 27, 2019 Ideally the gear should be greased while on jacks in a slightly retracted position taking the pressure off all joints to allow for more even distribution of grease. Clarence Quote
cliffy Posted April 27, 2019 Report Posted April 27, 2019 It is also suggested that the gear be "exercised" up and down to distribute the grease around the bearings in the trunion bearings as it is lubricated Quote
RobertGary1 Posted April 27, 2019 Author Report Posted April 27, 2019 6 minutes ago, cliffy said: It is also suggested that the gear be "exercised" up and down to distribute the grease around the bearings in the trunion bearings as it is lubricated That’s what Maxwell says but with the gear unlocked there doesn’t seem to be much ability to get a grease connector on the nipples, especially the left forward trunion -Robert Quote
RobertGary1 Posted April 27, 2019 Author Report Posted April 27, 2019 1 hour ago, M20F said: The only science I have learned about grease fittings is they break off. I solved that problem with locking tips. They are much tighter but then just slip off with a squeeze of the locking lever. -Robert Quote
cliffy Posted April 27, 2019 Report Posted April 27, 2019 The "secret" is to push the grease in while the gear is down and locked then unhook the grease gun and move the gear to spread the grease around. then maybe do it again. 1 Quote
M20F Posted April 29, 2019 Report Posted April 29, 2019 On 4/27/2019 at 2:57 PM, RobertGary1 said: I solved that problem with locking tips. They are much tighter but then just slip off with a squeeze of the locking lever. -Robert I have those as well, I still manage to gank one every now and then. Quote
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