Oh those CERTIFIED plane engines !!!!!!!!!!!!!!!!!

"Montblack" wrote in message
...
("stol" wrote)
So here comes round number three. Too bad they don't have the three
strike rule in aviation.


http://www.lycoming.textron.com/supp...ncePublication
s/serviceBulletins/SB569.pdf


Today's AvWeb lead story:

http://www.avweb.com/eletter/archives/avflash/586-full.html#191678
Lycoming Woes Continue: 5100 Crankshafts To Be "Retired"



But the mandatory service bulletin leaves out O-320's and O-235's.

One wonders if Teledyne is getting its alloys from the same source. I doubt
it.

And where are the reports of deaths or personal injury caused by the bad
cranks? Do we have a cite from a Lycophobe?

jls wrote:

"Montblack" wrote in message
...

("stol" wrote)

So here comes round number three. Too bad they don't have the three
strike rule in aviation.


http://www.lycoming.textron.com/supp...ncePublication
s/serviceBulletins/SB569.pdf


Today's AvWeb lead story:

http://www.avweb.com/eletter/archives/avflash/586-full.html#191678
Lycoming Woes Continue: 5100 Crankshafts To Be "Retired"




But the mandatory service bulletin leaves out O-320's and O-235's.

One wonders if Teledyne is getting its alloys from the same source. I doubt
it.


Just guessing here, but aren't the O-235 adn O-320 cranks solid rather than
hollow (for constant speed props)?

Just guessing here, but aren't the O-235 adn O-320 cranks solid rather than
hollow (for constant speed props)?

They are hollow, and some models of the engines have
provision for a governor. That hollow crank has been the subject of an
AD; the front end of the crank gets cold in flight due to the prop's
heat loss and the hollow bore, open to the case, gets condensation and
oil in it. Those mix and form sludge and acids that eat away at the
inside of the bore and weaken the crank. See:

http://www.airweb.faa.gov/Regulatory...5?OpenDocument

Hollow shafts are stiffer than solid shafts. The stresses are
all concentrated in the outside wall, with no central material to act
as a fulcrum to stretch the outside on bends. Try bending a piece of
5/8" bar and one of 5/8" tube sometime (same material, of course) and
see the difference. The bar will bend, but the tube will resist bending
until it suddenly kinks. Cranks need to be stiff, especially where they
are loaded with gyroscopic forces, and need to be light, so they're
mostly hollow.

Dan

wrote:

...

Hollow shafts are stiffer than solid shafts. The stresses are
all concentrated in the outside wall, with no central material to act
as a fulcrum to stretch the outside on bends. Try bending a piece of
5/8" bar and one of 5/8" tube sometime (same material, of course) and
see the difference. The bar will bend, but the tube will resist bending
until it suddenly kinks. Cranks need to be stiff, especially where they
are loaded with gyroscopic forces, and need to be light, so they're
mostly hollow.


More importantly a hollow shaft that is the same weight as a solid
one will have a larger diameter which gives you much better
stiffness, especially in torsion, for the same weight.

--

FF

wrote:
wrote:
...

Hollow shafts are stiffer than solid shafts. The stresses are
all concentrated in the outside wall, with no central material to act
as a fulcrum to stretch the outside on bends. Try bending a piece of
5/8" bar and one of 5/8" tube sometime (same material, of course) and
see the difference. The bar will bend, but the tube will resist bending
until it suddenly kinks. Cranks need to be stiff, especially where they
are loaded with gyroscopic forces, and need to be light, so they're
mostly hollow.


More importantly a hollow shaft that is the same weight as a solid
one will have a larger diameter which gives you much better
stiffness, especially in torsion, for the same weight.

Yes. The outer diameter of the hollow tube will be slightly larger than
the solid rod. On the drawing board, if the outer diameter is strictly
limited (by crank journal diameter), or slightly limited (if the block
allows slightly larger journals), then changing the crankshaft from
solid for hollow this may or may not be an issue. (Pretty wordy!)

In reality, swapping out a solid crankshaft for a hollow one of equal or
at least sufficient strength and stiffness is not always simple,
prudent, or even possible. (Pretty wordy again!)

Here is a good reference for anyone (regardless of their level of
engineering knowledge):

http://www.engineersedge.com/calcula...re_case_12.htm

You can play with the numbers a bit. Moment of inertia is directly
related to stiffness (in torsion) while (cross section) area is directly
related to weight. Section modulus is directly related to bending strength.


PS- Fred, you (and others in this thread) obviously have a good handle
on this stuff. My post is mostly directed to the audience. Disclaimer,
I'm 99% sure I got the working definitions right. Corrections are
welcome