Paramotor engine mounts and safety issues

[mcl]

Hello everybody.Engineer and new pilot here with zero flights due to no training in current covid situation,i had the luck to try a tandem flight last summer :).

I got the buzz for the sport and perhaps made poor gear choices due to excitement.I bought a secondhand pap pa125 in pa racing frame.I dont have hands on experience with any other paramotors but done alot of research online since. I have come to the conclusion almost all paramotors are lacking in safety and design issues, most of it has to do with the netting and engine mounting.It seems lightweight is what sells and dictates the design.

1.The netting.The pap i have had the same style netting as on the current tinox models.While it is strong you can easily fit a throttle or your whole hand through the netting.I redid mine with tig welded 1,6mm stainless loops and 200kg line strength dyneema with a tighter square netting,you can literally stand on it and the lines are easily replacable at low cost.I could share the build process/pictures/design if there is interest.Many models use weak flexible netting that will of course keep light objects and lines from going in the prop,but offer no real protection for limbs or forces acting upon the net.Other models like the flat top/fresh breeze use strong netting but the line will chafe on the holes and eventually cut.A cut line(netting will wind up in the prop and your going to have a bad day.

2.Engine mounting.From what ive looked,almost all paramotors share the same rubber engine mounts.The rubber mounts are not designed to use in the configuration they are used in paramotors,your literally hanging the engine on some rubber pieces and hope it doesnt sheer off.Even if it doesnt shear it will start to sag and the prop will get closer to the ground.When i got the pap second hand I was wondering why the prop was just touching the ground and not parallel to the hoop.Found out the rubber mounts were sagged and stretched(not cracked yet).I replaced the mounts with new pap ones and after a week its half way there sagging again.One option seems to be to replace the mounts with polyurethane mounts,although these are not available any more,there will be increased vibrations and the fundamental problem of the mounts sheering and engine getting loose still persists.The other more common option is to use a safety line around the mount,while this should keep your engine from working completely loose i would assume it would allow enough movement for the prop to touch the hoop/ground.

Im currently building a engine mount design which is failsafe to replace the standard 30x30 mounts.It would still utlilize the same style rubber mounts so vibration dampening would be the same.But the mount could not fail and the mount would carry the engine weight without sagging.It would be enough to use these mounts as upper mounts and retain the stock rubber mounts as lower mounts.The upper mounts would likely last a lifetime and the lower mounts longevity would be greatly increased due to not carrying the weight anymore.Im building these mounts for myself using a lathe and mill for my own use and testing.But i was wondering if other pilots consider the current mounts as risky as i do,and would be interested to buy these if I would have them manufactured in larger scale?I cant really speak of the price but I would estimate between 60-100euro for a pair depending of manufacturing costs and also if they would be done locally or outsourced to asia.

[AndyB]

Air Conception use a special safety mount...

https://www.airconception.com/store/produit/silicon-diabolo-engine-rubber-mount-large/?lang=en

However, rarely have mountings been an issue since with proper inspection only one usually fails and the other 3 stay attached. Also, in flight the engine pushes on the mounts.

[Steve]

If you intend to fly a paramotor, inspection and maintenance will be one of the things you should learn and must do. Your thoughts about the mounts have probably been the same for many new pilots over the years but the reality is they don't often fail and in eleven years I've not known any sag (although I generally get a new machine every three years or so). If you look at machines like the Parajet Maverick you'll see that there is also webbing on the mounts. But replace them with manufacturer approved mounts every year if it bothers you, it's an easy job on most machines. Certainly cheaper and less hassle than making your own. 

As for the netting, if you don't start you machine on the ground (which you absolutely mustn't) then it's unlikely you'll need to worry about your hand holding a throttle going throught the netting. 

Give yourself some time in the sport before getting too het up about how flawed things appear. Nothing's perfect and the machines are constantly evolving and improving. If you can add something that will make the sport better that's great but we have been here with a lot of things many times before. 

[alan_k]

I understand your concerns on paramotor design as a newbie. However I used a Fresh Breeze motor for many years and never had any issue with chaffing netting line, that just isn't a problem.

In 13 years of flying I have only had one rubber mount start to split, that was picked up in preflight inspection.

[Ganbatte]

Consider also the location of the mounts relative to the axis of thrust. Typically, the mounts do not "surround" the thrust line, so the engine under thrust will tip upward, closer to parallel with the hoop. Or phrased another way, the upper mounts are under compression and the lowers are under tension when you're generating thrust. Several degrees of "sag" when it's not running are a deliberate design feature intended to compensate for that tilt-under-power effect. Your frame/engine may differ, but at least some are set up that way.

[mcl]

Thanks for the replies.Here are some pictures about the netting design.

 

It uses 1,6mm stainless tig wire bent to a U shape around a 6mm bar,the wire is highly polished so that the netting line wont chafe.I built a guide jig for the drill that clamps onto the hoop,the frame consists of two different pipe diameters so i had to made two jigs for the different pipe diameters.

Its possible to freehand,but drilling with a jig will save your drill bits and make straight evenly spaced holes.I experimented freehanding but  it was a hassle getting the loops through,also snapped the drill bits easily.

I used 2mm drill bits.I tried various cobalt bits.Proper bits are essential,i tried using different brand namely bosch etc cobalt(made for stainless) bits but all of them managed to drill only a couple holes before the bit dulled or snapped.Dont even try with standard drill bits(black ones) for stainless.I managed to find success with drill bits from wurth and drilled all of the holes with only 2 bits. Increadibly quality on these drills,i suspect they are made by ruko or at the least ruko would be the same quality.The drilling was done dry because of welding and lubricants would contaminate the weld.

The loops were tig welded with argon shielding gas on the inside of the pipe,the backside on the loop cut 3mm excess which when welded forms a welded rivet on the backside.

The netting is done with 1,5mm dyneema with 200kg line strength,the line goes over under over etc.Attaching the line was done with clamps from pap and the end locked in place with a thru splice on the end to stop the line from slipping.Its tight as a guitar string and can take the weight of a person.The frame will actually start flexing instead of the dyneema when pushing on the net.