Frames and Chassis, aren't they all the same?

Telford was great and it was nice to get some good positive feedback about these series of articles but while I was discussing points with some people I was noticing bemused expressions on their faces. So I have come to realise that I still need to cover some of the more basic aspects of paramotor construction and design which will help some people understand why I do some of the things that I do on these flight tests.

For instance, I was talking to a troubled paramotorist who for the last year had maybe only flown twice. After I sorted out most of his problems I finally suggested that he consider a paramotor with a corsair engine but then he could choose his own frame and chassis. His reply was then "what do you mean choose my own chassis, aren't they all the same?"

Most paramotor manufacturers will use any one of about a dozen of the most popular engines from various reputable manufacturers, so as far as that is concerned you know what you are getting. Choosing one paramotor manufacturer over another is the vital difference in chassis, frame . materials (covered a couple of months ago)and prop size. Things like fuel priming systems, filters, quality and type of harness, and prop type are just extras and can be easily changed

Most people look at a paramotor frame or chassis and think that there's nothing to it. First of all the chassis is what the motor and hang points are fixed to. The frame is then what attaches to the chassis and protects the lines from the prop. But just like the chassis on a Ducatti motor bike compared to others (as purists will tell you) makes the handling that much better and even the chassis on the early Lotus motor cars definitely gave them the edge, and so it is with the chassis or frame on a paramotor.

Geometry?
One of the main things to think about is the geometry of frame. It's all about thrust lines, weight distribution, position and power of the engine not to mention the hang point, torque compensation system and position of the harness. All these things add up to how the paramotor will handle regardless of the wing or conditions. This subject is most definitely a science and we don't have the time or space to go into it here but we can cover some of the broader strokes.
When considering a purchase speak to the manufacturer or dealer and get them to describe the handling and benefits of the frame, then if you can test fly it do. Talk to a few owners and get their opinions. What has to be remembered when doing this is that these people might actually know less than you do and may not have more experience than of that one paramotor. But you will build a picture of the truth and reliability etc.

Netting
Even netting you would think is, well, just netting. But not quite.
I'm going to go back to basics here but the idea of netting is to stop things going into the prop including things like fingers. So with that in mind we teach people how to start the motor safely and somehow mistakes still happen. Every now and then I get a report back that so and so has had a mishap and either been very lucky and got away with it or just had the ends of a few fingers clipped. And even if you think "Oh that will never happen to me", and that's what they all say, remember it's not only you. Many times there are bystanders around who are always willing to help and they are the first to reach forward to stop your valuable investment from hitting the ground.

So what are you looking for?
Well ideally the netting should be strong enough so that if you're behind the machine, where the harness is, and suddenly, for what ever reason the machine clicks on to full power your automatic reaction is to put your hand forward. Would the netting be strong enough to protect you? The easiest way to discover this is try and pick up the machine by the netting. Let me warn you now I would ask the dealer first because not all people are happy to see you do this to their machines. You should be able to man handle the machine, whatever its weight, quite easily by the netting.

You should also, with the engine off, try and push your hand through and reach the prop, the netting should be strong and tight enough to stop your hand getting anywhere near. You'd be surprised how many machines you can do that on.
On the Colonel Basir's Malaysian video there is an incident when a pilots baseball cap gets sucked in and shredded by the prop through a gap in the frame. Humorous? yes in this case, but there could have been a metal buckle on the hat which could ruin a £200 prop, or worse still it could have been a scarf. I even know of incidences when brake handles have got caught in the props in flight and shredded, once leaving lines dangling out of the back unavailable for landing. The fear is that they could have got caught and wrapped around causing spins etc.

A number of manufacturers still use plastic strimmer chord looped through holes in the frame. However, these tend to have quite big holes, big enough for a hand to slip through and when these break although they can be tied off then leave bigger holes.

When you do get the netting the squares should be about 1.5 inches square. If the squares are any bigger then hands or other bits and pieces can get through but if it's any smaller the extra drag created from the netting can be quite extensive.

The next thing to notice is how the netting is attached. Some manufacturers drill small holes in the tubing and fasten the netting with little plastic clips.
Other manufacturers tie the netting on with little cable ties and although this may look a little untidy it's probably one of the strongest methods around, with multiple attachment points and no holes in the metal.

Hang points
There are 2 basic differences in hang points i.e. low and high hang points, with the high hang points being split into a further 2 categories i.e. swan neck and chest hang points. And then the low hang points split into a further 2 categories fixed or variable. Let's look at each one individually.

High hang point, Swan Neck
For: Probably the most stable out of all the systems. Because the hang points are rigid and high to the frame it makes the whole geometry of the wing solid. That is to say if you are in turbulent conditions less of the movement is transferred to you in the seat. Any paragliding school can demonstrate this on a simulator.
And if you ever do fall flat on your face the swan necks give you some protection so the motor doesn't come straight down on top of you.

Against: If you are going to use the wing for paragliding as well, because of the high hang points, the place where the brakes settle will be different. That is when you fly a paraglider the hang points will be roughly at your stomach and your hands, with the controls, will be at your ears. If you now put the same glider onto a high hang point paramotor then the hang points will be 18 inches higher so even with your hands as high as you can there will always be tendency to have a lot of brake on making take off more dangerous. What's more if for any reason you let go of the controls they will go back up to their resting place - out of reach. In either case a very dangerous position to be in.
So the brakes should be adjusted longer, but with dangling brakes they have sometimes been known to get sucked into the prop. And then re-adjusted when paragliding.
Ground handling can seem to be very difficult and will take a bit of getting used to.
Because of the fixed geometry there will be no weight shifting.

High hang points. Chest.
This comprises of the glider connected to the karabiners which in turn are attached to the shoulder straps either kept tight to the chest or which are forward of the chest any where up to shoulder height.

For: Still quite stable. Not as bad a brake problem as with the swan neck. A little easier to ground handle.

Against: Still need to lengthen the brakes if flying a paraglider as well.
Because the hang points are relatively close together on your chest two problems can occur.
a, when reverse ground handling if you turn the wrong way then the risers cross in front of your face hurting you as it does so. The good news is that because the hang points are close together once you have turned around there is very little force trying to pull you back the right way which can sometimes result in you loosening your footing and balance and falling over. However this same point can also be bad.
b, It has been known that when in flight and full throttle is suddenly applied a twisting motion can occur in the air. This will then twist you all the way round slowly choking you ....not funny.
In reality a lot of people fly these paramotors quite happily with no problems what so ever, but these problems have occurred.

Low Hang points. Fixed and variable geometry

For: Both of these systems fly more like a paraglider - i.e. hang points are the same. Therefore easy to change from one to the other without modifying the brakes etc.
A lot more control and manoeuvrability from weight shifting.
You can counter act most of the torque by simply weight shift.
If going cross country subtle weight shifting can change a few degrees in direction rather than pulling the brakes and causing drag.
Easier ground handling.
Less tendency to yaw, because of the weight being between rather than under the suspension points.
More feel from the wing for soaring i.e. power off paragliding.

Against: More feel from the wing means that in turbulence all that movement comes down to you. You can also be thrown to one side (which is the same as weight shifting) making the situation worse. One way around this is get a more stable wing.

Fixed or variable.
You don't see too many truly fixed low hang point systems any more but they are still around.
However the best system in my opinion is the fully moving system which some of the top manufacturers are using. Two bars which move up and down come out of the chassis at waist height, which at the other end is then attached to a part of the harness and hang point.
The advantage of this is that even under full power torque (depending on the compensation system) can be eliminated by moving an inch or so in the seat the other way. Thermalling is usually a great deal easier and flying in general is more like paragliding.

Torque Compensation Systems
Torque can be one of the paramotorist's biggest or smallest problems. Different prop size and composition can greatly change the amount of torque that needs to be compensated but there are a few other different ways that manufacturers have found to try and combat or minimize this effect.

A few manufacturers use an adjustable strap from one edge of the seat to an opposite karabiner. This system is usually on high chest hang point systems which seems to work ok when set up properly but constantly needs adjustment when changing throttle settings.

Some companies off set one of the arms of the chassis giving a slight weight shift effect others have the arms the same but have a hang point that comes out of the right arm which has a similar effect. Personally I'm more of a fan of this method which also compensates for different weights of pilots too.

Only a few years ago some manufacturers had no compensation at all making flying in a straight line for longer than 30 minutes almost impossible unless you had abnormally huge muscles in your left arm. Some pilots who are still flying these kind of paramotors were talking to me at Telford. What I say to these pilots is "WAKE UP". Why do you think I do the "straight line under full power" tests. You got to take every opportunity to fly other machines and find out what's really going on.
I'm not joking, there really are paramotors around that really do fly in straight lines with very little input needed.

We've only touched on some of the basics here. Hopefully I've dispelled a few of the more common myths. Hmmm. Chassis and frames, maybe there's more to them than we first thought.

If you have a paramotor or even wing that you think I might like to test and feature or any other questions about paramotoring then you can write to me at edi@welshairsports.com

Till next time, wishing you all tight lines and clear horizons, Edi.

© Edi Gezcy 2004