RAH'er has forced landing

"Matt Whiting" wrote

I believe that ANY gear selected in the GW transmission would have
failed under long-term high power output. I don't think this is an
issue preferential to the higher numerical ratio ("lower") gears.

Matt

A short story might provide a little insight to the design factors involved.

My dad had a 80 Chevy Citation. I was driving it when someone lost control
and hit the rear end, sending it off the road, sliding sideways at about 40
MPH.

Seemed like only sheet metal damage was involved. A few months later, the
transmission failed, specifically, the Hi-Vol primary chain drive. My dad
got suspicious about the design, and since he was an engineer involved in
power transmitting to machinery, he looked up the specs for the sprockets
and chain, and the torque and HP rating of the engine. He could not believe
what he found.

GM had designed the primary drive with an over design safety factor of
around 1.1. Yes, 1.1!!! When there had been a slight miss-alignment from
the wreck, the sprocket failed. He still had to eat the repair, as GM
claims the part was correctly designed.

If this was typical, as to the margins involved in design, of major
manufacturers, I am not surprised the 2nd gear failed under this constant
use.

Oh, and I will add that I continue to drive GM, but would not use a gear in
that manner, unless I had verified the parts were up to the abuse I was
going to give them.
--
Jim in NC

Morgans wrote:

"Matt Whiting" wrote


I believe that ANY gear selected in the GW transmission would have
failed under long-term high power output. I don't think this is an
issue preferential to the higher numerical ratio ("lower") gears.

Matt


A short story might provide a little insight to the design factors involved.

My dad had a 80 Chevy Citation. I was driving it when someone lost control
and hit the rear end, sending it off the road, sliding sideways at about 40
MPH.

Seemed like only sheet metal damage was involved. A few months later, the
transmission failed, specifically, the Hi-Vol primary chain drive. My dad
got suspicious about the design, and since he was an engineer involved in
power transmitting to machinery, he looked up the specs for the sprockets
and chain, and the torque and HP rating of the engine. He could not believe
what he found.

GM had designed the primary drive with an over design safety factor of
around 1.1. Yes, 1.1!!! When there had been a slight miss-alignment from
the wreck, the sprocket failed. He still had to eat the repair, as GM
claims the part was correctly designed.

1.1 with what as the reference? Maximum engine torque output?


If this was typical, as to the margins involved in design, of major
manufacturers, I am not surprised the 2nd gear failed under this constant
use.

I'm not surprised at 1:1 for this application. Airplane structures
typically use only a 1.5 safety factor. A bridge designer would shudder
at less than 5 and most use 10. The reality is that safety factors are
very application dependent and there is no "right" value. Most cars
last a very long time and drivetrains seldom fail so I'd say GM and
others have it about right.


Oh, and I will add that I continue to drive GM, but would not use a gear in
that manner, unless I had verified the parts were up to the abuse I was
going to give them.

Why would you continue to drive GM vehicles if you consider them to be
designed poorly?


Matt