RAH'er has forced landing

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...
On Tue, 21 Dec 2004 14:32:57 -0500, Corky Scott
wrote:


The reason for the failure, if I'm remembering this correctly, was
that the lower gears were not designed for continuous transmission of
power, at least not at the power levels required for flight. Whether
it was the width of the gears or the size of the bearings that
supported them, or even if there were bearings supporting the shaft, I
don't know. It could also have been a problem with prop loads on the
output shaft, not sure. But the transmission as a psru failed.

It could be the gears that failed, or it could be that the output
shaft could not stand up to the prop loads, don't know how George
supported the output shaft.

In any case, George should be congratulated for safely landing an
airplane with a decoupled prop that has one of the higher landing
speeds for light airplanes around. Putting down after a total loss of
thrust is never easy unless you practice frequently and even then you
always know it's just practice and a blown approach can be salvaged by
advancing power and trying again.

But the real thing is the real thing, and while some people flying
Long E-Z's manage to be at around 60 mph when touching down, most I've
heard of are faster than that to prevent the nose from pitching down
prematurely and uncontrollably.

Good job George.

Corky Scott

PS, I hope George posts here what failed in the transmission. It
would be illuminating.



What really beats on the gears, and what automotive use does not
experience, is the harmonics. Harmonics load the gears in BOTH
directions, with in the order of 10 times the steady state torque.

That tends to shear off teeth!!!

That's part of what I was also thinking, but there's mo

In the car or truck, the use of the clutch tends, over time, to randomize
the gear teeth in use at any specific parts of the power and compression
strokes. As I understand it, use of the same gear teeth all the time is a
common problem in spur gear transmissions. The problem is much worse if
applied to both gears--although that would be surprising in a jproduction
gearbox.

In addition, many people may omit all or part of the flywheel and clutch to
save weight. That could prevent the harmonic damper on the other end of the
engine from doing its job. And those little springs in the driven plate
should provide a lot of isolation once the engine is up to speed.

Finally, a lot of the support for the gears and bearings inside the
transmission is provided by the pilot bearing at the flywheel--especially on
rear wheel drive vehicles. A missing pilot bushing could place tremendous
bending loads on those little needle bearings between the input and main
shafts ...

Does anyone know which kind of transmission (transaxle or an in-line with a
straight through fourth gear) he was using, and what all failed in the
transmission besides the gear teeth?

Peter

wrote:

On Tue, 21 Dec 2004 14:32:57 -0500, Corky Scott
wrote:


The reason for the failure, if I'm remembering this correctly, was
that the lower gears were not designed for continuous transmission of
power, at least not at the power levels required for flight. Whether
it was the width of the gears or the size of the bearings that
supported them, or even if there were bearings supporting the shaft, I
don't know. It could also have been a problem with prop loads on the
output shaft, not sure. But the transmission as a psru failed.

It could be the gears that failed, or it could be that the output
shaft could not stand up to the prop loads, don't know how George
supported the output shaft.

In any case, George should be congratulated for safely landing an
airplane with a decoupled prop that has one of the higher landing
speeds for light airplanes around. Putting down after a total loss of
thrust is never easy unless you practice frequently and even then you
always know it's just practice and a blown approach can be salvaged by
advancing power and trying again.

But the real thing is the real thing, and while some people flying
Long E-Z's manage to be at around 60 mph when touching down, most I've
heard of are faster than that to prevent the nose from pitching down
prematurely and uncontrollably.

Good job George.

Corky Scott

PS, I hope George posts here what failed in the transmission. It
would be illuminating.




What really beats on the gears, and what automotive use does not
experience, is the harmonics. Harmonics load the gears in BOTH
directions, with in the order of 10 times the steady state torque.

Another myth. All engines and drivetrains are susceptible to torsional
harmonics. Why do you think engines have harmonic dampeners on them?
And flywheels? That is one advantage of automatic transmissions, the TC
damps the torsional vibrations from the engine and prevents them from
reaching the transmission and drivetrain. Most standard shift vehicles
have spring hub clutch disks to help cushion the drive train.

Automobiles and certified aircraft have been designed to avoid or
control harmonics. Some experimental engine/PSRUs have been also, but
unfortunately, some have not.

Matt

Doesn't the 'mazda' rotary mnimize this pulsation?

"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

Blueskies wrote:

Doesn't the 'mazda' rotary mnimize this pulsation?

It may if the combustion event is more spread out than in a conventional
piston engine, but I haven't seen any power curves for a rotary. It
still has discrete combustion events that are converted to rotation, so
it will still have power pulses of some form. The only way to get away
from that is to have something with continuous combustion as in a turbine.


Matt

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

The continuous use of high power through a auto transmission is
what defeated auto-engine conversion guys in the boatbuilding world
many years ago. Even in the 50s and 60s, when transmissions were stout,
they couldn't get away with using them in a boat. The gears and
bearings would heat up and lose their strength and fail. I'm surprised
that more homebuilders don't know that.
I had a 283 in a 13 foot crackerbox-style boat, and the
transmission was a Warner Velvet-Drive marine unit. Forward was through
a massive clutch pack, no gears, and reverse had some impressive
gearing. The transmission was so heavy I could barely lift it, and it
had a substantial oil cooler to keep it happy.
A local guy tried an automatic trans from a car in his boat, and
had it fail in short order.

Dan

On Tue, 21 Dec 2004 20:30:12 GMT, Dave S
wrote:

It sure matters to me. The mazda rotary is about the only auto
conversion that I have even given any serious thought to. I have one
assembled on a stand at the hangar waiting to be put on the airframe.

Dave, you missunderstand me. What I meant was, whether it was the
engine, psru, fuel pump, carburator, or ignition system that failed,
the end result is the same thing: a dead stick landing.

It doesn't matter to the pilot that the engine is running just fine if
the prop isn't connected to the engine anymore.

The point is to use something that will last. Preferably something
already tested. Or at least that's my attitude. I don't want to be
somebody's test pilot, I just want to fly.

Corky Scott

On Wed, 22 Dec 2004 03:11:51 GMT, "Blueskies"
wrote:

Doesn't the 'mazda' rotary mnimize this pulsation?

Not if the Powersport saga is to be believed. Their initial efforts
resulted in a LOT of psru failures.

See:
http://www.powersportaviation.com/Ho...on%20drive.htm

Ross Aero, on the other hand put together a planetary gear design and
seemed to suffer no torsional problems at all. They told me that some
engineer stopped in to tell them that he'd analized their reduction
unit and claimed that it would destructively vibrate at 300 rpm. Of
course the engine only sees that rpm during startup or shut down. The
rest of the time it's operating well above that.

The Ross Aero psru is what Tracy Crook initially used in his Mazda
powered RV-4. I gather he substantially modified it since then and
may now offer one of his own.

Corky Scott

On Tue, 21 Dec 2004, Ron Wanttaja wrote:

ACFT MADE AN EMERGENCY LANDING NEAR A ROAD 15 MILES SOUTH OF LEESBURG, FL


Hello guys, It was actually on a nice two lane road, no wires over it,
wide berms, no driveways or signs, and no traffic, at least until short
final.

I was climbing through 5500 ft when the note of the engine changed, I
checked the guages, all green, leaned the mixture, and reduced throttle.
Then heard a loud growl and then engine disengage from the prop.

I pressed "nearest" on my gps, and it listed Leesburg first, (I had just
left my friend there). I thought it said 30 miles distance, but that must
have been the heading, since Zepherhills would have been listed first.

Anyway, I had lots of time to select my landing spot, and picked a good
one. Which was near a divided highway. 11.5 miles from Leesburg.

Go ahead with your "I told you so's", just remember that there was not a
good alternative six years ago, and my junkyard gearbox has been good to
me.


George Graham
RX-7 Powered Graham-EZ, N4449E
Homepage http://bfn.org/~ca266