RAH'er has forced landing

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!!!

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

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!!!

Torsional resonance has been a problem with many PSRU units, over many
years, including units from big manufacturers of certificated equipment. If
resonance is not carefully studied and tested for, you are almost guaranteed
to have a problem.

Does your car have a harmonic balancer on the crankshaft? Why do you
suppose it is there?

I work with big trucks and we have a problem there with torsional resonance
from the power pulses of the big diesels, especially at high torque and low
rpm (sound familiar?). If, for instance, one removes a clutch with a
dampened disc and replaces it with a clutch with a solid disc, the
transmission input shaft splines might shear -- or the transmission gears --
or the differential gears. It is almost impossible to convince a customer
that his cheap clutch replacement caused his rear axle to fail, but it did!
Truck component manufacturers put a lot of effort into finding and
eliminating resonance. I hope your PSRU designer did too...

Also note that changing ANY component in the drive train can mess up the
torsional dynamics, which is a bad thing for a bunch of experimenter
homebuilders. Even cutting down a metal prop a couple inches. Why do you
suppose that the FAA will allow a 25 hour test period with a certified
propeller/engine combination, but 40 hours without?
Resonance is a big reason.
-Bob

wrote in message
...
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?

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

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

"Corky Scott" wrote in message ...
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


I remember someone talking about a damper that was filled with steel shot or similar, but I cannot find a reference to
it now.

On Wed, 22 Dec 2004 22:39:59 GMT, "Blueskies"
wrote:


"Corky Scott" wrote in message ...
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


I remember someone talking about a damper that was filled with steel shot or similar, but I cannot find a reference to
it now.


I can't recall the name, but they were used by Molt Taylor in his
pusher designs and were also used with the Honda Civic engine in some
BD-5s

Ed Sullivan

On Wed, 22 Dec 2004 16:25:23 -0800, Ed Sullivan
wrote:

On Wed, 22 Dec 2004 22:39:59 GMT, "Blueskies"
wrote:


"Corky Scott" wrote in message ...
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


I remember someone talking about a damper that was filled with steel shot or similar, but I cannot find a reference to
it now.


I can't recall the name, but they were used by Molt Taylor in his
pusher designs and were also used with the Honda Civic engine in some
BD-5s

Ed Sullivan
They were made by Dodge Power products, and I think they were called
FlexiDyne?