Safer machines for the real world. Updated
Apr 22, 2015 to add brake toggles/prop protection.
& Flying Feel Cage Intelligence
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Yes, they have to be fun, comfortable, light, powerful, look cool and be
convenient. The most talented
designers will accomplish all that and
provide decent protection. No, they won't be foolproof and
yes, training is just as important. But, as the airlines have discovered, the
best safety improvements come through both passive-safety hardware and
hand at left is an example of why one feature, frangible props, are
so beneficial: this hand went into a prop and survived. The
lightweight wood exploded, minimizing damage to the hand which eventually healed. Of course having other features, namely a
cage that keeps the hand out of the prop, would be far better.
Prop Safety and A
Better Throttle which includes
animations with some of the safety
ideas mentioned here.
here are some recommendations that could improve safety in order of
importance except that item 5 would probably be better placed at #1.
Paramotor cages should:
A. Prevent an open human hand from going into the prop at full rated thrust.
The netting openings must be small enough and far enough from the prop,
especially outward where the tips are closest to the net.
B. Prevent loose brake toggles from reaching the prop in case the
wing goes back and/or cage tilts forward. Of course pilots should
avoid this condition but reality is that they will eventually forget
and it shouldn't be a death sentence. This requires a tighter weave,
no more than about 2 inch squares, net in the area where the brakes
are. That's openings of no more than about 4 sq inches. At least two
fatalities have resulted from having a brake toggle wrap up in the
C. Prevent the throttle cable from going into the prop
even if the pilot tries with two hands. What sees hard to do becomes
possible in the melee that is a fall or crash.
two-hoop design is best (see
illustration) where one hoop
is mounted forward of the radial arms
with a radius slightly smaller than the prop's (by 1-2 inches). That is the most critical
radius since it is closest to the prop. Plus, this is an easy retrofit.
Props should be frangible—strong enough to push air nicely but
weak enough to break before bones break. I’ve seen some that would be unforgiving at best.
Usually this also matches the engineering goal of being lightweight
for quick spin-up. Aerodynamically, rigidity is desirable to reduce
deforming at high load (high RPM).
The pull start and hand hold should be arranged so as to put the
human in a position to easily handle unexpected sudden thrust.
The netting and cage should protect the pilot during landing flare
or if the pilot falls and instinctively puts his hands back towards
the prop—a natural reaction.
Protection must be included down low on the cage. It should also keep hands out of the prop for pilots reaching
Motors should have
some form of
SafeStart (See below, this panel), or
similar, a system that prevents the motor from exceeding idle RPM while starting. It should be accessible from the pilot’s seat and double as an emergency shutoff in case of a failed kill switch.
Scout Paramotors has developed one -- the motor
shuts off if the RPM exceeds a set value within the first 5 seconds of
would prevent a full-throttle situation from driving the motor forward
Another version, with "Off, Start, Run"
would be similar.
You’d start it in the start position then, once running, put it in the
run position where full throttle is available. This would also serve as an
alternate kill switch (“off” position) should the primary fail. The
motor won't start in the run position.
The gas tank should be far enough away from the propeller tip to
keep the propeller from slicing into it during a hard landing or crash.
That has occurred at least 6 times that I know of, leaving the pilot
engulfed in an explosive vapor—one spark away from igniting.
4" for short props (less than 40" long) and 6" of clearance
on longer props.
Even better is a design, as shown on the illustration, where the
tank curves away from the prop near the bottom.
The harness buckles should be of a quick-release type. Old style
rectangular fittings that require angling one part out of the other are
unacceptable since they would make escape difficult after a water
A single buckle that undoes both legs at once is unacceptable
because it allows the occupant to make one lethal mistake. A quick
release for all but one leg loop would be beneficial to allow for quick
escape in the event of immersion.
harness should not be able to slide, or allow any fittings to slide
such that the flight characteristics are significantly altered. Most
notably, the clip-in points must not be allowed to slide or be easily
connected improperly. Adjustable
settings should prevent errors as much as possible. Examples are the free-flight
harnesses that prevent pilots from forgetting their leg straps—that is a
design that has saved lives!
Harness and general design must also minimize torque effects.
Torque-related issues represent probably 20% of inflight accidents although
many are minor because the crash happens just as the pilot takes off.
Torque effects can be minimized.
The harness and frame should offer
some protection in the event of a
near-vertical type crash such as would result from a parachutal stall. In
flight, the motor hangs from the harness, but in a crash, the pilot will
be forced down against the seat and frame. The frame should absorb impact
and the harness should be mounted stoutly enough to stay attached. The
common criteria for airplanes is a 9 G deceleration, meaning that if the
frame hits the ground with a deceleration force of 9 G’s, it would
remain intact enough to protect its occupant. It may deform along the way.
Another method may be to use several inches of
crushable foam (such as what goes in helmets) on the seat bottom and
an inch on back, in addition to any padding that's normally there.
Implementation must allow the seat bottom to fold completely up against
the frame to allow easy running (foot launch only).
The motor should be stable when sitting. Tippy motors tend to fall
over making it more likely for gas to spill onto the harness. Plus,
frame bottom should prevent a pilot's leg from getting into the prop. That
sounds unlikely but it has happened. Last, the bottom frame should be sufficiently rounded so
as to slide upward if it hits something sharp on the ground.
The prop should
not stick out the back too far. Being enclosed enough prevents a hand from reaching it
even with the pilot stretching wildly.
The diagramed unit does this, see #10 and hand
#1s. An extra hoop behind the main cage rim could add sufficient
protection while being an easy retrofit (see diagram).
Several accidents have happened where pilots got their hands in the prop
during launch, in flight, falling or landing while the motor was
jostling. Some when their hand went around the cage even though they
found it impossible to do so while trying just standing or sitting.
The gas tank should be protected on the prop side with a material (maybe
a sandwich of external aluminum with foam on the gas tank side) capable
of taking a prop strike without breaching the tank. Not required on
machines where it's impossible for the prop to hit the gas tank.
should be some way to verify the carburetor is at idle when
A clutch reduces some risk during idling
and by allowing the prop to slow when the throttle is reduced without
having to hit the kill switch. That mostly saves lines from get
But clutched machines are every bit as dangerous in cases where the motor unexpectedly
goes to power.
Reduce the likelihood of the brake toggles going into the prop.
point machines, where the cage tilts forward with thrust, are particularly vulnerable since the top of the cage tends
to move toward the risers on launch, putting the prop disk closer to
the brake toggles. I've seen this happen myself and heard about quite a
few more. It may simply require a bigger cage, another hoop (see above),
different hang point, or better netting.
The throttle cable should not be able to get into the prop regardless
of hand motion. Techniques can be employed to prevent this on some
here) but no quality design should require certain techniques.
This improved design (with help from Dennis Webster) makes the design even
more reliable while decreasing hassle.
As of Apr 22, 2015,
Scout Paramotors has built a version of this. Their advice is to
have SafeStart on, get the motor running, then turn SafeStart to off
which takes SafeStart out of the equation and prevents it from shutting
off you motor in case of a device failure or momentary power interuption.
Unfortunately, from a human factors perspective, this removes the
passive safety aspect since the pilot must remember to turn it on for
each start. Here is my page with a video showing how
an ideal installation might work.
Powered Paragliding Bible covers this in detail but here are some design
highlights to reduce torque. The book is more from a pilot's perspective
while this is more from a designers perspective. See also
Understanding Paramotor Torque.
Offset the motor. If it wants to push on the pilots right
shoulder blade, offset the harness/motor so that, even at power, it's
pushing on the left or middle. That may require moving the thrust line beyond the
center so that it looks like it's pushing on the left shoulder.
hangback. The more a motor tilts back, the more it will torque twist.
It's called the horizontal component of torque and acts around the
vertical axis. One method to reduce it is raising the hook-in
points. An aft-tilting motor causes the most torque-induced crashes
than any other cause but is usually accompanied by some other factor
like having the risers too close together.
riser spread and prevent spreader bars (whatever method pushes the harness
away from the pilot's chest) from moving in a torque-inducing direction.
Allow differential riser
height hook-in. If the propeller spins counter clockwise (viewed from
behind), the pilot will be pushed into a right weight shift turn.
Make the right carabiner a bit higher. Note that this weight shift
turn is a small effect, though.
Allow left-right angling
of the thrust line so that, while hanging, the thrustline points left or
right to counter the motor's natural tendency.
Comfort & Flying Feel
This is probably the single biggest reason why most people stick with a
machine--it's comfortable and fun. The ideal machine would incorporate
the above safety features, look cool and have the comfort/feel
attributes mentioned here. If you want to find out what people like,
talk to those who are on their 2nd or 3rd machine. The first machine is
frequently the one sold by the instructor (which is a good reason to buy
it because the instructor knows how to teach it) and a pilot who's only
flown that machine won't have anything else to go on. The same is true
for wings, of course, but this only deals with motors.
A lot of what pilots perceive as comfort and feel depend on their
The seat and back support should be comfortable.
The motor should be well balanced on the ground and in flight with
minimum moving around except for that desired by the pilot (such as
For pilots who like to use weight-shift steering, it should be
effective and require the least amount of effort. This will trade a
"busy" feel as the wing imparts feel back to the pilot in the same
way the pilot imparts steering inputs to the wing.
The risers should be far enough from your arms to avoid impinging
There should be adjustments to accommodate individuals or desires.
Torque effects should be minimized. Yes, this is a safety feature
too but it's just no fun to manage a unit that twists too much every
time you add power.
You should be able to easily launch it. A machine that won't get you
airborne is worthless. The wing is obviously important, too, but a
poorly designed paramotor can be unlaunchable. I've been there
Vibration should be minimized. Some makers have achieved good
results by having two sets of motor mounts but this may motor
farther from your back (less comfortable).