RAH'er has forced landing

On Tue, 21 Dec 2004 03:00:05 GMT, Dave S
wrote:

The glide distance has since been re-evaluated, but overall everyone is
glad it worked out ok.. and on a secondary personal note its refreshing
that the engine itself was not the point of failure

Dave

Dave, my feeling is that it does not matter that the engine did not
fail, the PSRU did and the result is the same: No engine and a forced
landging.

I wondered about using a transmission for a PSRU instead of a PSRU for
a PSRU. The problem with using a transmission is that the all the
gears except for fifth, are designed for light usage. In otherwords
they weren't designed to be used continuously with the engine pulling
50% or more power. George's transmission is not the first to fail
because of this.

Using the transmission for a PSRU is not necessarily a bad thing, but
the gears that will be used and the bearings that support the gears
may need to be re-evaluated.

Corky Scott

Corky Scott wrote:

On Tue, 21 Dec 2004 03:00:05 GMT, Dave S
wrote:


The glide distance has since been re-evaluated, but overall everyone is
glad it worked out ok.. and on a secondary personal note its refreshing
that the engine itself was not the point of failure

Dave


Dave, my feeling is that it does not matter that the engine did not
fail, the PSRU did and the result is the same: No engine and a forced
landging.

I wondered about using a transmission for a PSRU instead of a PSRU for
a PSRU. The problem with using a transmission is that the all the
gears except for fifth, are designed for light usage. In otherwords
they weren't designed to be used continuously with the engine pulling
50% or more power. George's transmission is not the first to fail
because of this.

Using the transmission for a PSRU is not necessarily a bad thing, but
the gears that will be used and the bearings that support the gears
may need to be re-evaluated.

I've not seen this before. This may be true for passenger cars, but for
pickup trucks, OTR trucks, off-road equipment, etc., each gear is
equally likely to be used and typically full throttle is more likely to
be used in the lower gears. I've never heard of any of the gears being
designed for "light" usage in any manual trans with which I'm familiar,
but I'm not that familiar with pax car manuals.

It used to be that 4th gear in most four-speeds was 1:1 and this was
often accomplished by simply connecting the input and output shafts
directly with a collar. So, I suppose this could have been more rugged
as the gears were just along for the ride at that point. However, some
new transmissions have the 5th or 6th gear as a overdrive gear, and
occasionally even the 4th, and may not even have a 1:1 ratio. In these
designs, every speed is being driven through the gear set/layshaft.

If you have a design reference for transmissions being designed to not
handle full torque in anything but high gear, I'd be interested in
seeing it. Also, if you have a list of such transmissions that would be
interesting as well.

Matt

Matt Whiting wrote:



I've not seen this before. This may be true for passenger cars, but for
pickup trucks, OTR trucks, off-road equipment, etc., each gear is
equally likely to be used and typically full throttle is more likely to
be used in the lower gears. I've never heard of any of the gears being
designed for "light" usage in any manual trans with which I'm familiar,
but I'm not that familiar with pax car manuals.

It used to be that 4th gear in most four-speeds was 1:1 and this was
often accomplished by simply connecting the input and output shafts
directly with a collar. So, I suppose this could have been more rugged
as the gears were just along for the ride at that point. However, some
new transmissions have the 5th or 6th gear as a overdrive gear, and
occasionally even the 4th, and may not even have a 1:1 ratio. In these
designs, every speed is being driven through the gear set/layshaft.

If you have a design reference for transmissions being designed to not
handle full torque in anything but high gear, I'd be interested in
seeing it. Also, if you have a list of such transmissions that would be
interesting as well.

Matt

I would think that if anything the lower gears would have to be be
beefier than the higher ones, at least on the output shaft. Torque
increases as rotational speed decreases, right? This is why axle shafts
tend to snap when starting a heavy load from a dead stop.
I just replaced fifth gear in my Nissan NX a month or two ago. It was
pretty much worn out, and not really beefy to begin with. You do spend
most of your time driving sitting in your highest gear so it will see
the most wear, but not necessarily the highest torque loads. All the
gears are equally wimpy, but the 1st and 2nd shifting collar is a little
longer and engages more teeth than the others. This seems to confirm
that 1st and 2nd are stronger gears than 4th or 5th.This car has the
smallest tranny I've ever worked on and one look inside would make you
REALLY glad you aren't flying behind it. Those gears are tiny, and
eyeball engineering would lead me to believe they aren't up to the job
of swinging a prop. Graham's two failures pretty much confirm this. I
can't imagine the mazda's gearbox is any beefier than this one. Flying
with one of these is 'experimental' all right.

Jason
Challenger-II

On Tue, 21 Dec 2004 11:46:46 -0500, Matt Whiting
wrote:

I've not seen this before. This may be true for passenger cars, but for
pickup trucks, OTR trucks, off-road equipment, etc., each gear is
equally likely to be used and typically full throttle is more likely to
be used in the lower gears. I've never heard of any of the gears being
designed for "light" usage in any manual trans with which I'm familiar,
but I'm not that familiar with pax car manuals.

Matt, it isn't a matter of being strong enough to withstand occasional
pulls at full throttle, it's the continuous use that appears to be the
problem, and also that this may be a problem endemic to transmissions
being used as PSRU's.

My curse is that I read a LOT. One of the many articles I read a
number of years ago was about a builder trying to use a Honda Goldwing
engine for his airplane engine. This engine has an integral
transmission which he used as the PSRU. He used second or third gear
for his output gear and the transmission failed, like George's.

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.

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