Yes have a nice day
tacchi88 said:
George, Have a nice day. BTW, yes I worked for the world's largest brewer, and no George I never drank on the job. However, your ramblings are suspicious..........Hmmm, I even spelled your name correctly.T88
Have a nice day,
Since you are into learning: Gears. Lycoming uses
"Spur" gears. You keep saying
"straight" as if crude, low tech or there's something better. Trust me I know gears. Seemingly simple on the surface, these spur gears are remarkably powerful and quite complex. Spur gears used in the Lycoming use the "latest" gear technology. To be fair many call them straight, but there is nothing "straight" except that it means the gears are parallel, not at angles. The differential in you car can not use spur gears. The accessory gears in the Lyc has to use "straight" gears.
When gear axis are parallel there are only 3 gear "types" available: Spur, Helical, Herringbone or double helical gears. The Spur gear is the way to go, produces no axial loads, and for the low speed and low loads here, it's ideal.
The teeth shape used in spur gears is what's called "involute". In the late 1800's early 1900's many gears had a "cycloidal" tooth design (which where poor). Involute came around the 1890's and dominated after the 1920's. It is still the "state of the art" in gears. There is nothing crude, simple or LESS as you imply when you say "they use straight gears!", OK. There not straight, they are spur gears, high strength steel, proper hardness and very powerful "involute" (curved) teeth.
There are differnt types of gear designs, but they are not suitable for this parallel application:
Bevel gears: Straight bevel, "Zerol" bevel, Spiral bevel;
Hypoid gears: Crossed helical gears, Worm gears
and the special Rack and Pinion, to name a few.
T88, another thing you mention is backlash. Backlash, depends on operation velocities, lubrication, loads, tooth pitch and gear center to center. Trust me the Lycoming accessory case gears as designed are a work of art. It could not be done better if designed from scratch today. Trust me. The backlash is what the design manual calls for. They could make it "tighter" but it would serve little purpose and only increase cost. The "slop" is normal and needed with any gear set, including spur gears.
Nuff said on gears, but please don't keep saying STRAIGHT GEARS!, Backlash! like it is bad or primitive. It is anything but. Gear design is something that seems simple on the surface, is remarkably complex in practice, and by no means is it elementary. Those engineers in the 50's knew their stuff, and I was not even born than. Basic machine elements has not changes much or at all in 50 years (100 years). You insult the engineering profession and the men that designed these engines when you willy-nilly throw comments out implying the design is deficient. With all due respect you don't know. Same with car engines, they are a modern marvels, but they where designed for cars, not planes. Can they be adapted? Yea. It is not the engine itself, it's the adaptation in the airframe.
If you never designed anything, than trying to explain the design trade-offs and compromises in an engine is impossible. It's like trying to explain what sex is like to a virgin. A direct drive aircraft engine with a prop bolted direct to the crank is an engineering challenge. These cranks are OVER BUILT. The reason for the AD's is everything has to be perfect. That is why they recall them, to err on the side of conservatism. Also its good there being monitored so close, not that the recent screw ups (from 1997 on) are OK.
As far as cranks AD's you throw it out like an insult. Yep it sucks and is screwed up, but don't spin it, put it in perspective. We are talking about +50 years of service, and most of the problems have been with NEW parts built-in the last 8 years! The other crank problems are with a few older cranks that where corroded. NOT a design or manufacture fault, dis-use and poor maintenance.
When an auto engine guy post a NTSB report of a rare crank or rod failure and says, "SEE", I shake my head. Many an auto engine has come out of the sky involuntarily. When a 1000 auto engines fly a total of a million hours, lets talk. I guess I'll fall back on my old, flying is dangerous, the engine internal mechanics is the least of any single engine airman's worries, lycoming, mazda, or subaru. There is no doubt the crank on a Lycoming is complicated and critical, but it is designed for it. (see tongue in cheek picture):
Crank me-up Subaru makes a nice crank and has 5 main journals, but that is because its small bore (displacement) engine and there's room to fit them in with out making the engine too long. However clearly its not designed to take torsional loads of a prop directly bolted to the crank, which is fine since its designed for a car. (I don't say enough nice things about Mazda or Subaru, but others do that; the engineers designed these engines well with "compromises" for an automotive application. They can be safely converted to aircraft use, but there are other issues outside the engine case that are still a challenge.)
An AD caught the 660 affected cranks made after March 1999. Lycoming paid for all cost in full. I believe there was a failure on a brand new late model C182. What really started it was a Piper Warrior that had a crank flange fail due to corrosion in the early 1990's. Again not a defect, just poor maintenance. This put the spot light on cranks, even if unrelated.
Than there is the SB, which as you know is not mandatory. Lycoming calls for the retirement of 5100-serial-number specific crankshafts made between 1997 and 2002. Lycoming says it has found no failures in this lot of crankshafts but, nonetheless, wants owners to replace them at the first opportunity? Whisky Tango Foxtrot? Lycoming will sell you the crank and parts kit for $2000, with no labor. I agree this sucks, but again its not the design, it was a failure of "modern" manufacturing in the late 1990s.
The last AD was for 300 late model engines with counterweights. Again to Lycomings credit all cost are paid in full. Also in this case there where no failures attributed to this AD.
To put it in perspective, very few Lyc cranks have failed in the millions of hours flown over the last 50 years. My circa 1970's O360A1A is a brick house, a proverbial "bullet proof" engine. If you look up the history, up to about 8 years ago, the record was pretty awesome on cranks. I am not sure but the "fatigue life" of the cranks are like 30,000 hours. In large commercial aircraft fleets (freight) cranks go 3 or more rebuilds, but they have to made per design and material specs. There is no almost, it has to be perfect. Made correctly the cranks are robust and reliable.
Teledyne Continental had the Airmelt / "vacuum arc remelt" (VAR) mess in the early 90's. Here they changed process to the better VAR and had problems. They tried this NEW and improved high tech process. See what you get. If it ain't broke don't fix it. Its also a tribute to the fact the engineers and craftsman that made these engines knew what they where doing. Just because it is OLD does not make it bad, take you for example.
T88 the point I am trying to drive home is this is an AIRCRAFT ENGINE designed for aircraft use. To get a light weight, direct drive aircooled engines took lots of skill and cunning to achieve a "balanced design". What you see as a huge design fault, is really a clever combination of choices. Same with auto engines. They have their unique qualities that well suited for a car, but in a plane they may be of less importance or even a liability.
If you where building a scratch aircraft engine and had to balance all design requirements, you very well may end up with an aircooled, direct drive, horizontal opposed engine. Not sure what all the Lyc ax grinding is about. As far as backlash and piston clearances being lawn mower loose, LOOSE is good baby, let her rip, because my Lyc will "mower" right over you.
As far as piston clearance, we went over that several times so no need to repeat, but the
rings seal, not the piston. The piston clearance does not affect the oil use or compression. As you know the rings are "compressed" when installed and are sprung against the cylinder wall, so the gap is as thick as the oil film. As the cylinder wears the rings will adjust some what. After a while the rings wear too much or they cylinder, producing less compression. However with modern materials the wear of the cylinder is very small. Most Ring/Cylinders have compatible materials so the ring is "sacrificial" more than the cylinder. However you can bring a cylinder back up to specs. In the old days they used chrome, but it was hard to break in. The good part was it lasted. Now with new cylinders being cheap you just replace them many times. So Piston Cylinder clearance is for thermal expansion and proper oil control. To say the clearance is somehow crude or bad is just incorrect. To make tighter tolerances, which they could, would only cause more heat and wear. Loose is good.
(see page 12, plasma coated top compression ring)
http://www.eci2fly.com/pdf/titanbooklet.pdf
Last never said you drank on the job, and I am a tea totaler, but I think you are driving me to drink.
Just kidding T88, have a great week. George