A system that keeps an aircraft stable in even the strongest winds appears to be making a comeback.
The Gravity Trigger was conceived in 1989, and uses gravity, inertia, leverage, friction, tension,
and centrifugal force to control the decalage of a tip-launched glider [TLG].
History
After extensive developing and testing, the Gravity Trigger was rst used on an 18-inch wingspan
javelin Hand-Launched Glider (HLG) to win the 1991 US Free Flight Championships. Normally, a
javelin-style HLG has poor longitudinal stability because it has little decalage. The Gravity Trigger
system can provide so much stability that it is possible to launch into a dust devil and survive the
violeThe next time it was used was to latch and release my
folding-wingtip HLG. I launched my 19-inch wingspan
model, which opened to a 36-inch wingspan at transition.
It worked beautifully and won a few times, but I dropped
the idea for many years.
The system was used again, with a folding wingtip model,
to take second place at the Nationals the year that Bruce
Kimbal introduced us to TLG by winning!
The Gravity Trigger was tucked away until Ralph Ray
helped develop it for the 2011 Nats, where he won the
TLG competition.
The Nuts and Bolts
The Gravity Trigger system holds the tailboom in the
launch decalage position until the moment of transition. At
that time, the Gravity Trigger uses the model’s change in
speed and angle to release the tailboom into the decalage
for glide. It requires no timer. This model also incorporates
Ken Bauer’s superb radio dethermalizer unit installed inside
the nose of the glider.
The Gravity Trigger lever arm is 1/32-inch music wire
through a 1/32-inch ID brass tube. The long end of the wire
is bent and soldered to a thin piece of galvanized tin. On
the same side as the wire, there is approximately 2 grams of
thin lead sheet on the tin. The wire must be bent so that it
does not bind in the brass tube, yet has little clearance.
The short end of the wire is bent so that the spring
(approximately .7-inch long, made from .009-inch spring
wire on a .09-inch diameter mandrel), with a special split
ring on the end, provides small leverage in the “ready”
position.
When the model is held horizontally, slightly banked
to the right, the Gravity Trigger should not move. As the
model is slightly rolled to neutral bank, the spring should
move the trigger slightly.
At the top of the launch, as the model slows to begin
transition, the bend on the short end of the trigger should
allow it to move faster and faster until the spring slips off
the tin and slams into the magnet in the nose of the model.
It can do this because the bend in the short end provides
more leverage as the trigger rotates toward the forward
position.
The brass tube must be securely attached because of the
abuse the joint endures. The 1/32-inch plywood bits that help
secure this joint also provide the correct standoff for the split
ring on the end of the spring. A slot in the fuselage allows the
short end of the trigger to move all the way forward.
Using the System
You need to know the approximate launch CG for your
design. Add temporary weight to the tail to attain this CG
position. Glide test and adjust the decalage with the usual
screw—the one in the fuselage that the tailboom touches.
Move the CG approximately 1/2 inch forward and adjust
the glide, but don’t move the screw! Use the crimped
aluminum tube shown on the right-hand side of the
fuselage. Fine glide tuning can be done by sanding the
basswood on the bottom of the tailboom, or by adjusting
the nose weight.
To set the system into the launch position, grasp the line
where it is tied to the spring but do not pull on the spring
(it is easy to overextend the spring and ruin it). Pull the line
snug around the turn-around pin.
Swing the gravity trigger out 90°. Work your ngers
gently up the spring and slip the split ring over the short
end of the trigger. Finally, swing the trigger back and the ag
latch forward.
That’s it; you’re ready to launch!
Edition: Model Aviation - 2012/07
Page Numbers: 45,46,47
Edition: Model Aviation - 2012/07
Page Numbers: 45,46,47
A system that keeps an aircraft stable in even the strongest winds appears to be making a comeback.
The Gravity Trigger was conceived in 1989, and uses gravity, inertia, leverage, friction, tension,
and centrifugal force to control the decalage of a tip-launched glider [TLG].
History
After extensive developing and testing, the Gravity Trigger was rst used on an 18-inch wingspan
javelin Hand-Launched Glider (HLG) to win the 1991 US Free Flight Championships. Normally, a
javelin-style HLG has poor longitudinal stability because it has little decalage. The Gravity Trigger
system can provide so much stability that it is possible to launch into a dust devil and survive the
violeThe next time it was used was to latch and release my
folding-wingtip HLG. I launched my 19-inch wingspan
model, which opened to a 36-inch wingspan at transition.
It worked beautifully and won a few times, but I dropped
the idea for many years.
The system was used again, with a folding wingtip model,
to take second place at the Nationals the year that Bruce
Kimbal introduced us to TLG by winning!
The Gravity Trigger was tucked away until Ralph Ray
helped develop it for the 2011 Nats, where he won the
TLG competition.
The Nuts and Bolts
The Gravity Trigger system holds the tailboom in the
launch decalage position until the moment of transition. At
that time, the Gravity Trigger uses the model’s change in
speed and angle to release the tailboom into the decalage
for glide. It requires no timer. This model also incorporates
Ken Bauer’s superb radio dethermalizer unit installed inside
the nose of the glider.
The Gravity Trigger lever arm is 1/32-inch music wire
through a 1/32-inch ID brass tube. The long end of the wire
is bent and soldered to a thin piece of galvanized tin. On
the same side as the wire, there is approximately 2 grams of
thin lead sheet on the tin. The wire must be bent so that it
does not bind in the brass tube, yet has little clearance.
The short end of the wire is bent so that the spring
(approximately .7-inch long, made from .009-inch spring
wire on a .09-inch diameter mandrel), with a special split
ring on the end, provides small leverage in the “ready”
position.
When the model is held horizontally, slightly banked
to the right, the Gravity Trigger should not move. As the
model is slightly rolled to neutral bank, the spring should
move the trigger slightly.
At the top of the launch, as the model slows to begin
transition, the bend on the short end of the trigger should
allow it to move faster and faster until the spring slips off
the tin and slams into the magnet in the nose of the model.
It can do this because the bend in the short end provides
more leverage as the trigger rotates toward the forward
position.
The brass tube must be securely attached because of the
abuse the joint endures. The 1/32-inch plywood bits that help
secure this joint also provide the correct standoff for the split
ring on the end of the spring. A slot in the fuselage allows the
short end of the trigger to move all the way forward.
Using the System
You need to know the approximate launch CG for your
design. Add temporary weight to the tail to attain this CG
position. Glide test and adjust the decalage with the usual
screw—the one in the fuselage that the tailboom touches.
Move the CG approximately 1/2 inch forward and adjust
the glide, but don’t move the screw! Use the crimped
aluminum tube shown on the right-hand side of the
fuselage. Fine glide tuning can be done by sanding the
basswood on the bottom of the tailboom, or by adjusting
the nose weight.
To set the system into the launch position, grasp the line
where it is tied to the spring but do not pull on the spring
(it is easy to overextend the spring and ruin it). Pull the line
snug around the turn-around pin.
Swing the gravity trigger out 90°. Work your ngers
gently up the spring and slip the split ring over the short
end of the trigger. Finally, swing the trigger back and the ag
latch forward.
That’s it; you’re ready to launch!
Edition: Model Aviation - 2012/07
Page Numbers: 45,46,47
A system that keeps an aircraft stable in even the strongest winds appears to be making a comeback.
The Gravity Trigger was conceived in 1989, and uses gravity, inertia, leverage, friction, tension,
and centrifugal force to control the decalage of a tip-launched glider [TLG].
History
After extensive developing and testing, the Gravity Trigger was rst used on an 18-inch wingspan
javelin Hand-Launched Glider (HLG) to win the 1991 US Free Flight Championships. Normally, a
javelin-style HLG has poor longitudinal stability because it has little decalage. The Gravity Trigger
system can provide so much stability that it is possible to launch into a dust devil and survive the
violeThe next time it was used was to latch and release my
folding-wingtip HLG. I launched my 19-inch wingspan
model, which opened to a 36-inch wingspan at transition.
It worked beautifully and won a few times, but I dropped
the idea for many years.
The system was used again, with a folding wingtip model,
to take second place at the Nationals the year that Bruce
Kimbal introduced us to TLG by winning!
The Gravity Trigger was tucked away until Ralph Ray
helped develop it for the 2011 Nats, where he won the
TLG competition.
The Nuts and Bolts
The Gravity Trigger system holds the tailboom in the
launch decalage position until the moment of transition. At
that time, the Gravity Trigger uses the model’s change in
speed and angle to release the tailboom into the decalage
for glide. It requires no timer. This model also incorporates
Ken Bauer’s superb radio dethermalizer unit installed inside
the nose of the glider.
The Gravity Trigger lever arm is 1/32-inch music wire
through a 1/32-inch ID brass tube. The long end of the wire
is bent and soldered to a thin piece of galvanized tin. On
the same side as the wire, there is approximately 2 grams of
thin lead sheet on the tin. The wire must be bent so that it
does not bind in the brass tube, yet has little clearance.
The short end of the wire is bent so that the spring
(approximately .7-inch long, made from .009-inch spring
wire on a .09-inch diameter mandrel), with a special split
ring on the end, provides small leverage in the “ready”
position.
When the model is held horizontally, slightly banked
to the right, the Gravity Trigger should not move. As the
model is slightly rolled to neutral bank, the spring should
move the trigger slightly.
At the top of the launch, as the model slows to begin
transition, the bend on the short end of the trigger should
allow it to move faster and faster until the spring slips off
the tin and slams into the magnet in the nose of the model.
It can do this because the bend in the short end provides
more leverage as the trigger rotates toward the forward
position.
The brass tube must be securely attached because of the
abuse the joint endures. The 1/32-inch plywood bits that help
secure this joint also provide the correct standoff for the split
ring on the end of the spring. A slot in the fuselage allows the
short end of the trigger to move all the way forward.
Using the System
You need to know the approximate launch CG for your
design. Add temporary weight to the tail to attain this CG
position. Glide test and adjust the decalage with the usual
screw—the one in the fuselage that the tailboom touches.
Move the CG approximately 1/2 inch forward and adjust
the glide, but don’t move the screw! Use the crimped
aluminum tube shown on the right-hand side of the
fuselage. Fine glide tuning can be done by sanding the
basswood on the bottom of the tailboom, or by adjusting
the nose weight.
To set the system into the launch position, grasp the line
where it is tied to the spring but do not pull on the spring
(it is easy to overextend the spring and ruin it). Pull the line
snug around the turn-around pin.
Swing the gravity trigger out 90°. Work your ngers
gently up the spring and slip the split ring over the short
end of the trigger. Finally, swing the trigger back and the ag
latch forward.
That’s it; you’re ready to launch!
