You can now buy a safety ring, suitable for many brands, from
Skycruiser Manufacturing for $65.
Thanks to Leon Wacker for working with me on this and making it
available. Shipping adds approximately $15. It comes in 3 segments with connectors and Valco snap
buttons. This is just one of several pieces of prevention. You are always the most important
Besides the kit you'll
need four 4 1/2" hose clamps with a 1/2" to 5/8" range to connect
the hoop to your radial arms (spokes). If you build it yourself, the
parts list is supplied below.
Leon's version has a flat area at the bottom which
looks good but that is not necessary if you make your own. It is there
because a tube bender needs a flat area to start and finish bending. What is
important is that the radius be about 1" less than your prop for maximum
protection. In other words, the hoop should be 1" inside the prop.
This video shows how to mount the hoop (watch it on
3. Package of snap buttons for telescoping tubing, available from
4. Four hose clamps, 5/8" diameter.
Skybolt designer Jeff Baumgartner also developed a retrofit for the
same purpose for the Skybolt. Either one works. We do recommend that
whatever solution you adopt goes all the way around to the bottom. There
have been at least two hands chopped from the bottom of the cage--both
by highly experienced pilots who didn't think it was possible. These
increase strength where its needed most—just forward of the prop
tips and in front of the radial arms and will work on many different
brands. His design, based on the "Better
Paramotor" safety ring, was improved after witnessing a pilot suffer a prop
strike injury. As the video below shows, he has succeeded.
In the accident that spawned this, the pilot's quick action prevented
a catastrophe that still cost him several days in the hospital and a large
scar on his arm. Thankfully, he will have full movement of his arm and
hand when it all heals up.
The retrofit puts a hoop around the most vulnerable section of
cage, where the netting would otherwise be easily pushed into the prop.
The idea of this design is that by putting on a solid hoop forward of
the prop tips, you provide both rigid strength there, at the closest
spot to the prop tips, but also keep the netting farther away. Quite a
few prop injury accidents would have been prevented by this design.
It is still critical for the pilot to exercise intelligent starting
technique—insuring that the throttle is at idle before attempting to start and bracing
yourself in a way to handle unexpected thrust.
it's always safest to start the motor on your back so, if you don't
have electric start, and there's a willing someone around, use them.
These accidents happen in a lightening quick flash of inattention.
Treat the motor with enormous care when starting.
I've also created a 3D model of the "Better Paramotor" design that's
intended to show more accurately how some changes could be made to
existing (and future) designs that keep the paramotor's general
character while dramatically improving safety. A screenshot is shown at
right but it will be done as a quick video with narration highlighting
each of the suggestions. There are many other ideas listed on Better
Paramotor web page but these will be the most important. The model will
be included in parts of the Master Powered Paragliding series.
Note: This was done for testing only,
never use the cage to hold your paramotor for starting or runup.
This is one easy way the ring can be fixed to your motor. Only two of
these are needed on each side since the radial arms (spokes) provide
1 & 2. Computer model of a paramotor with safety ring
and other features that could dramatically improve prop safety.
2. The PPGPlans.com
Skybolt with safety cage designed by Jeff Baumgartner.
Aerodynamics of the Ring
I asked Dana Hague for an assessment of the Safety
Ring's drag, assuming that airflow would be much faster at full power
due to the prop. He did not disappoint. Here it is:
The drag coefficient of a cylinder at the Reynolds
numbers we're talking (~20K) is around 1.0. Temperature variation
between 59°F and 0°F are small enough to make no difference in the
coefficient of drag (Cd), and only minor effects on air density (approx
0.5% between 60 and 100F).
So: Drag is ½pV²CdA where p=.002378 (air density) V is velocity in ft/s,
Cd is drag coefficient, A is frontal area (unlike a wing where you use
projected wing area). So, your 1/2 dia x 141 tube has an area of
0.49ft², and 40mph is 59 ft/s, thus the drag is 2.03 lbs. At 60 mph, it
would be 4.6 lbs. Etc.