16 October, 2011

Paramotors and Safety Chutes.

I see, most reserves in PPG have the bridles connected behind the karabiners, closer to the cage. The idea is, in case of a deployment, the pilot will be 'forced' into a standing position and the legs will absorb most of the force from the (imminent) landing impact. That's at least the theory. In real life things are a bit more complicated because a paramotor pilot can not apply the PFL technique, as easy and meaningful as with a paraglider. Personally, after destroying 2 props and hurting my back a bit, during 'rough' landings, I decided to have a closer look at the issue. It quickly became clear, even experienced PPG pilots have little understanding what it means to land under a safety chute with a 50pound+ and 5feet+ steel/aluminum cage on your back. Fortunately, unlike paragliding, paramotoring is done in less demanding flying conditions, which means a safety chute deployment is less luckily. I was not satisfied though. I wanted a passive system (kind of safety belt in a vehicle), which really does something in the case of a emergency landing. Eventually I came up with a carbon-fiber 'add on' skid, which is mounted/bolted at the base of the cage. Further, a fairly thick (15cm) Hi impact absorbing foam under the seat. The system looks pretty neat and (unfortunately) it did not take long before it did shown its capability.
On a fairly rough Sunday afternoon I was desperate for a flight. But shortly after TO I realized I was better on the ground then in the air. My wing is a very safe one. It is the only wing on the market, which has a factory recommended C-Line (not B!), parachutal stall rating. It even has specially mounted tabs (red color), which the pilot can activate by pulling down to initiate the procedure. On that particular day, at around 100feet above ground, I did just that. In turbulent conditions my wing turned into a (fairly stable) parachute and according to my vario I was descending at 5-5.5m/s. As expected, within 5 or so seconds I was on the ground. To my huge surprise (and relief), the feathering system worked as planed and the fairly hard landing (on grass mind you), resulted in absolutely no damage to the motor or myself. It reminded me of jumping in my swimming poll while hitting the water with my bum. Now, I expected the landing to be cushioned but not by that much. I am not a good pilot, however I know a thing or two about physics and maths (applied maths is my other hobby) and I must admit, even I was surprised at how good the system worked. This needed further investigation.
 When a paramotor lands under a safety chute, the movement is almost entirely vertical and a fairly fast one at that. The legs hit the ground first and then we are supposed to do a PFL to dissipate the remaining energy. But here is the problem! The big cage and weight does not allow that and we end up falling on our bums hitting the ground hard while the cage basically falls on our backs, on top of us! Not good.
It turned out that in my case, the movement was spread over three stages, each absorbing a chunk of the impact force. First the legs hit the ground (obviously I get out of the seat but DO NOT hang out with the cage high on my back as you would if the bridal/safety chute was connected much further back then the usual karabiners !) Secondly, the cage hits the ground - it basically slides down behind your back. Here the fiberglass attachment (tested to 10G's before bottoming out), absorbs most of the motor/cage's impact. Then the cage bounces back a little. And because it is strapped to our backs it basically pushes the body in a forward motion just as the bum hits the ground. Here, the Hi-impact foam absorbs what our legs could not absorb during the initial impact. It is of note that the engine/cage actually helps with the landing, by forcing the body in a correct, spine protective, forward leaning position, mere milliseconds before the bum hits the ground! It took me a while to figure out all this and come up with the right amount of flexing in the carbon-fiber skid. Now it works rather nicely as long as two things are happening before the impact.
1.Have the correct skid and Bum protection in place as a passive safety feature !
2.After activating/deploying the safety chute, get out of the seat as you would normaly do before landing. DON'T lean too much forward!
From here on, nature takes care of the rest. I hope this helps someone out there.
Mario ☺

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