A
tour of the T58 Speed Decreaser Gear (SDG)
The
General Electric Speed Decreaser Gear (SDG) for the T58 (series)
Detailed
here is the correct General Electric Speed Decreaser Gear
(SDG) that originally came as optional equipment on the T58-GE-8F
turbine. These massive gearboxes provide a reduction of 3.25:1
and efficiently handle the horsepower of the T-58. Since they
are not considered part of the T-58 engine assembly, the SDG
usually remains with the airframe when the engine is removed
from the aircraft. As a result these units are very hard to
locate for sale.
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These
are the 'as received' photos- it's obviously been sitting
for a while, showing signs of exposure to the elements.
I
opened the case to clean, inspect, and see exactly what
I've got.
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Here
you can see the arrangement of the gears inside the
gearcase. My Maintenance Manual is well written and
guides you through the entire inspection process. I
was pretty amazed to find no noticeable wear on the
bearings or gears.
This
is the view inside the cover. The stickers indicate
overhaul at NADEP Pensacola during the 3rd quarter of
1993, which coincides with the date the T58 motor this
was connected to went into storage. No wonder it shows
no signs of wear- it's never been installed on an aircraft
since overhaul!
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This
is a good view of the massive support bearing (Arrow
'A').
This
General Electric SDG is equipped with a 'torque sensor'.
Actual torque transmitted to the helical gear (Arrow
'B') forces the gears apart. This movement uncovers
an oil port, allowing oil pressure to escape to a transmitter,
sending a signal to the indicator to display the corresponding
amount of torque. This feature is very important as
it allows the operator to monitor torque loading so
as to avoid overloading the gearcase which is a major
cause of SDG failure. (Arrow 'C') shows a scavenge port
for lube oil to return to the pump.
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(Arrow
'D') shows another lube oil scavenge port. A splash
guard keeps excessive oil off the spinning gears (Arrow
'E').
(Arrow
'F' and 'G') show more scavenge ports. A series of lube
oil spray nozzles (Arrow 'H') apply oil to the gears
to cool and lubricate via supply ports machined into
the gearcase (Arrow 'I'). After I receive the O-ring
and gearcase sealant I have on order, I'll complete
my cleanup and get this reassembled.
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After
the new seals were installed, a few coats of high-temperature
paint were applied and it's ready to install.
This
SDG will provide many years of reliable service.
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A
pair of T58-GE-8 gas turbines with starters and gearboxes
is available. Contact me for details.
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Here's
a pair of General Electric Speed Decreaser Gears ready
to install.
This
pair is will be included as part of a T58-GE-8B gas
turbine package.
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This
SDG bolts directly to the T58 Power Turbine and reduces the
gas turbine output from about 19,500 rpm, down to a usable
level of around 6,500 rpm (at 100% power or wide open throttle).
Since the Gas Turbine Generator is independent of the Power
Turbine, a disk brake can be fabricated to stop the output
shaft while the turbine runs. This allows shifting a crashbox,
transmission, or effectively provides a 'neutral'.
The
Rolls Royce Speed Decreaser Gear (SDG)
The
Rolls
Royce SDG (Speed Decreaser Gear) was originally produced
under license by Bristol Siddeley, until bought out by Rolls
Royce in 1966. While the Gnome Speed Decreaser Gearbox is
very similar to the General Electric SDG, one of the more
obvious differences is the lubrication system. Lube oil is
routed through external lines, where the General Electric
SDG (shown at the top of this page) is lubricated through
internal passages. Either gearbox will bolt up to the GE T58
engine and is suitable for powering boats, tractor pull vehicles
or whatever you can install a T58 into.
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This
unit also features a 3.25:1 reduction. This particular
SDG is configured to have the output shaft run forward
under the engine. It is also available with a rear output
or can be easily modified for rear output and a front
shaft brake. These photos show the Rolls Royce SDG with
the external lube lines removed.
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You
definitely don't have a lot of choices when it comes
to getting this much power back to the prop. The Arneson
ASD8
surface drive and Sage
#8 Stern Drive are some of the very few drives rated
to handle the tremendous torque and horsepower loads
expected from this gearbox. I recently acquired an Arneson
ASD8 Surface Drive for my project.
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This
Rolls Royce Speed Decreaser Gearbox is setup for 'rear
output'.
Here
you can see how the external lube lines are routed.
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We have several Rolls Royce Speed Decreaser Gearboxes (SDG)
for sale to bolt right up to your T58 Gas Turbine engine.
These units come with the correct synthetic gas turbine oil,
a copy of the original Factory Maintenance Manual, and are
ready to ship now. E-mail me
for details
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Here's
a good view of the external lube system showing the
lines, couplings, and sensors on the Rolls Royce SDG. This particular SDG is
configured for rear output.
The
SDG tucks in real close to the 'cheeks' of the exhaust
housing when mounted in place. This SDG has all the
lube lines, sensors, and heat shields in place and appears
much the same as you would see it when mounted in the
aircraft.
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The
mounting pads provide an easily accessible, solid mounting
point from which to fabricate brackets to support the
SDG, exhaust housing and the entire rear of the turbine.
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Introducing
the Rolls Royce 'Coupled Gnome' Gearbox
Some
twin engine aircraft like the Wessex
60 helicopter flew twin Rolls Royce Gnome turbines. In
this particular example, a pair of Rolls Royce H1200 Mark
660 turbines were coupled to this gearbox.
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This is the Rolls Royce "Coupling Gearbox"
Type 100. Either engine (or both) would drive the gearbox
with a single (reduced) output.
This gearbox was used in several models of helicopters
including the Westland
Wessex 60. We have a Combining Gearbox available to power your tractor puller or other turbine powered creation.
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This drawing shows the arrangement of the turbines utilizing
the Rolls Royce coupling gearbox type 100. This twin
engine configuration is also known as the 'coupled Gnome'.
Another
view of the gearbox. More details are on my Rolls
Royce Gnome page.
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Perfect for Tractor Pulls or offshore race boats, this gearbox
allows running two Rolls Royce Gnome or GE T-58 gas turbines
with a single output.
More details
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