Safer machines for the real world. Updated Mar 10, 2020 to add illustration.
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 sound procedures.
The 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. This injury was relatively rare in that it happened during landing. Most happen during start, frequently to people who buy a machine and start it without proper instruction, or the machine has a throttle lock system, aka “cruise control”.
See Prop Safety and A Better Throttle which includes animations with some of the safety ideas mentioned here. SafeStart
So 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 we forget, and it shouldn’t be a death sentence (it has been). This requires a tighter weave, no more than about 2-inch squares, with 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 prop.
C. Prevent the throttle cable from going into the prop even if the pilot tries with two hands. What seems hard to do becomes possible in the melee that is a fall or crash.
A 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 back.
- 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 starting. That would prevent a full-throttle situation from driving the motor forward unexpectedly.
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 landing.
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.
- The 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, the 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.
- There should be some way to verify the carburetor is at idle when starting.
- 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 damaged during aborts.
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.
Low hang 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 machines (shown 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, 2019, 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 interruption. 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. And in interviews with Scout pilots, they are frequently disconnecting it because it triggers at too low an RPM. It needs to allow a high enough RPM that it doesn’t trigger unless it’s at a higher RPM for maybe a second. In other words, false triggers must be avoided.
SafeStart™ PDF | Previous SafeStart™ PDF
The 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 Harness Adjusting and 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.
Control 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.
Insure sufficient 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 style.
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 weight shift).
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 motion.
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 before.
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).