Harness and Speed Bar Set-up

Taken from my notes for one of the Thursday evening meetings.

How To Set Up Your Harness And Speed Bar - by Ian Grayland

This text was generated from my notes for the thursday evening lecture a few years ago. Harnesses are constantly under development, but the basics remain pretty well the same. I hope you find it helpful...

Harness Settings

A properly adjusted harness is easy to slip into on take-off, easy to slip out of on landing and comfortable in flight for hours at a time. Here is how to set it up:

Hang Point

First get somewhere secure to 'hang yourself'. Most harnesses are awkward to adjust in flight and you really should be thinking more about where you (and everyone else) is going. Also, after hanging static for half an hour, any mal-adjustment or discomfort will become glaringly apparent.

You need the hang points to be high enough so you can just about hook in and out standing on tip-toe. This is to give enough ground clearance to check take-off and landing modes. The spacing at the top should give about the same angle of spread as the risers on a glider to make the chest strap tension more or less authentic. Don't forget to load-test by bouncing up and down in a foot loop off one hanger at a time before hooking in.

Loosen off all the adjustments - especially the shoulder straps - and begin the set-up in the following order.

Back Straps

Your recline angle is set with these. If you have separate lumbar and thoracic (lower and upper back) straps, then do the initial setup with just the thoracic and add lumbar support to taste later. If you are inexperienced, or in any doubt, set yourself fairly upright to start with. (Worth noting though, that you will be very slightly more upright in flight than static due to drag) Once you have got the recline angle about right, shorten the lumbar straps until your lower back is properly supported and you are thoroughly comfortable. Re-check the angle and re-adjust both sets, as required.

Shoulder Straps

Shorten the shoulder straps until there is just no slack in them. Viz; not tight, but not actually loose. They should not be tight enough to restrict blood circulation to your arms or head and certainly not enough to affect your recline angle. Now you can set the little elastic cross-link to stop the straps falling off your shoulder when you bend forward. Again, not too tight, just enough.

Leg Loops

The optimum setting for leg loops varies with harness type. If you have fixed shoulder straps, you will need some slack in your leg loops in order to be able to stand up. If you have sliding shoulder straps, set-up is a little easier, although the object is the same in either case. Basically, the leg loops must be short enough to allow you to slip back into the harness without pushing it down with your hands. Conversely, they must be long enough to allow you to slide forward to get your feet down for a landing, but, once again, without being so long as to cause a loss of weight-shift control because you have slid right off the seat-board.

Chest Strap

This should be set initially to the recommended setting for your glider (see the placard on your wing). The set distance is between the bottom centres of the carabiners with the chest strap tensioned. Once you have got everything else right, and after a few hours flying, you can start to tune the chest strap. As you slacken it off, you will get more feedback from the wing. You will be rocked about more by turbulence, but will have more weight-shift authority over the glider. If you go too far in this direction, you may find a tendency to take-out the other wing after an assymmetric tuck until you get used to the loop-response time and get the hang of damping things out. Note that the optimum setting will vary quite a bit depending on your recline angle. The more reclined you are, the more you will get rocked about in rough air.

Other Weight-Shift Limiters

Some instrument pods and front-mount reserves incorporate lower attachment straps as well as the main chest-strap or carabiner attachment hangers. Note that tightening these may severely restrict weight-shift. Also, if you have a harness with leg straps that are attached as usual at the centre of the seat board and are attached high up near the carabiners at the top end, they will very severely limit weight-shift if set too tight. (Some of the latest stirrup harnesses incorporate one or other of these systems to adjust roll damping)

Variable Geometry Harnesses

Most of the more recent harnesses incorporate one or more internal pulley systems or sliders to enable the pilot to alter his recline angle and / or seat board angle in flight. This makes them much more interesting to set up. Some of these use a foot stirrup to provide additional leg support and to permit the pilot to get up and back into the harness on take-off. Also, the seat board may be so flat that the stirrup is essential to prevent the pilot sliding forward and out of the harness in flight. These stirrup harnesses are even more interesting to get right.

The first step with a variable geometry harness is to have a look at it to determine the type of mechanism fitted. The simplest of these passes the shoulder straps through a slider and down to the rear of the seat board. When the pilot leans back the extra tension pulls the seat board up allowing the torso to tilt back. The limit stop for this may be either systemic, or by an adjustable stop below the slider or an additional pair of shoulder straps with adjustable length.

The latest variants on this theme also use a 2:1 pulley below the slider to reduce the shoulder strap tension required. The principle of operation however is still exactly the same.

The key to setting this up is still to get your basic recline angle right first using just the back straps ie with the shoulders let right off. Next, tighten up the sliding straps progressively until the mechanism begins to activate as you lean back. Once you get these tight enough, you will feel the arse-lifter kick in and you will go pretty well flat on your back. When you have the mechanism operating smoothly over its full range you can set the stops to limit how flat you go. This is a matter of personal taste, but there is little point dropping your back angle much below 30 degrees up from the horizontal as the reduction in drag is small and the loss of visibility is becoming significant.

When To Fit A Stirrup

Loosely speaking, if you have a bucket harness with plenty of back protection, there is little point in fitting a stirrup. Your legs will be comfortably hanging down in front of the body of the harness where they will create very little additional drag and, provided you have got things set up properly, you don't need any assistance to get into the seat on take off. There are a few harnesses, like the Supair Coccoon for example, where the stirrup is not essential but nonetheless does improve all round functionality considerably. When you get to flat seat harnesses you have no option. You simply won't stay back in the seat without a stirrup unless you are reclined almost completely flat.

Stirrup Harness Setup

The first step with a stirrup harness is to set the distance between the tensioned stirrup and the front of the harness to a couple of inches over the length from your instep to the back of your knee (about 50 + 5 = 55cm in my case). Now go and hang yourself. Try a range of stirrup adjustments until you are fitting comfortably in the seat and round the back of your hips. The problem here is if you go too tight, you will be too far back in the harness and if too loose you will be too far forward. Not a problem in itself but this has a big effect on centre of gravity and hence the angle of dangle of the whole system, so you must get this pretty well right before attempting any of the main adjustment procedure. In fact it is probably best to do this whilst the harness is still in its delivered 'factory settings'.

Once you have the stirrup length right, you can go onto the full variable geometry setup as above.

More Complex Stirrups

The stirrup attachment system may also have a separate leg support adjustment. This will alter the angle at which your legs are supported for a given stirrup pressure and also to some degree, the angle of the whole harness. Basically the higher the stirrup attachment point above the seat the more leg support you will get, so, by providing two attachment points, one low, to pull the harness under you after launch, and one high, to provide sufficient support to keep your legs up without excessive pressure, the harness designer has given you a very considerable range of adjustment possibilities.

Pilot Drag

To get an idea of the amount of drag produced by the pilot in a standard harness, if this was halved, which is actually easily achievable, then a glider with a 9:1 L/D ratio would now glide at well over 9.5:1. Also, as you reduce parasitic drag, the speed for best L/D increases and the entire polar gets flatter. (This explains why some of the latest gliders go so well. Despite conservative aspect ratios; their reduced line-sets and low drag airfoils produce a marked improvement at high speed.)

Two factors affect drag at any given airspeed, frontal area and drag coefficient. The frontal area can be reduced by laying back in a more supine position and by raising the legs to align with the airflow. The drag coefficient is largely defined by the shape of the human body and the design of the harness. All you can do as a pilot, apart from buying a better harness, is to set the one you've got at the best angle to the airflow.

At a glide ratio of 8:1 the slope of the glide path is 7.1 degrees. At 9:1 it is 6.3 degrees and at 9.5:1 it is 6 degrees. Not a lot different. Obviously you will end up with your feet only just below your backside in flight.

There may be some mileage in reducing interference drag of the body of the harness by ensuring that no wake from the feet disturbs this part of the airflow. If you raise your feet slightly in flight you will feel the buffeting on your chest and face from the wake vortices of your boots. It is probably less damaging here than on the nicely rounded body of the harness. I've been playing with this a bit lately, but so far I can't be sure if the vario is beeping because of the pressure change in the local airflow rather than an improvement in sink rate.

The other thing that should make a tangible difference is wearing tighter fitting sleeves and shoulders. I'll have more information on this as well when the weather warms up a bit!

Q&A Session and Beer Break...

Speed Bar Set-up

How The System Works

The typical speed system fitted to most gliders simply pulls the nose down for a short distance then de-cambers the wing progressively as the nose is lowered the rest of the way. More complex systems apply a reduced effect towards the wingtips to limit any forward horseshoeing or tip-tucking tendency. A few manufacturers use a semi-balanced system that lengthens the rear risers as the front ones are shortened in order to reduce the control system force. In the majority of systems however, the overall force required means the bar travel has to be longer than the pilot's single motion leg travel, necessitating a two-stage bar. The commonest of these uses a webbing loop for the first stage and the bar itself for the second stage.

Objectives Of A Good System

The speed bar must be easy to step back into without looking down or reaching down with the hands. The first stage ('half-bar') should be set to coincide with the 'knee' in the glide polar; the speed just below the point at which the glide really begins to deteriorate. The second stage should just be able to get max speed on full tip-toe. Note that you don't normally fly continuously with the system 'to the stops' since you require a little movement each way for pitch control. Thus half-bar is achieved with one heel in the centre of the loop and your leg slightly bent for pitch control, whilst full-bar is both toes engaged in the bar, legs fully extended (comfortable), with use of the toes for pitch control.

Engagement

Unless you have one of the more sophisticated 'sit-up' type speed bars and it is set-up just so, you will need an elastic engagement assister of some sort. This is simply a foot or so of bungee firmly attached to the centre of the speed bar loop with the other end fixed to one of your boots. To engage the speed system all you have to do is step back with the other foot; the first stage loop will always be in exactly the right place for your heel.

This system works equally well on stirrup harnesses by attaching the bungee from the speed bar loop to the centre of the stirrup. (It also ensures that your trouser legs are supported up out of the airflow by the speed bar loop!)

Pitch-Balance

The location of the primary pulley (generally the first one in the harness that the speed bar line goes round after it comes off the risers) is critical with regard to centre of gravity. If too rearward, you will tilt forward as the bar is applied, if too forward you will tilt back. The height of the foremost guide pulley sets the amount of leg support you get. The higher these guides the more the speed system will support your legs and the higher your feet will lift as you push on the bar. In the event that you are having any pitch problems with your system, you need to be able to discern the difference between these two mutually interactive effects.

Variable Geometry

Some harnesses incorporate a geometry change system that allows you to go more supine as the bar is applied. The primary pulley is attached to the back of the seat and pulls it up as pressure is applied to the bar. There should be an adjustable limit-stop for this system, or an alternative pulley, should you not require this feature.

Brummel Hooks

Most gliders seem to be fitted with Brummel hooks these days despite the fact that they do not comply with the DHV Certification Standard which requires a means of locking on all fasteners. If you must use them, slide a one inch length of half-inch diameter silicone rubber tubing over them to prevent them coming undone. This is easy to slide on and off when swapping gliders.

How To Set The Line Lengths

Your first step is to measure the distance from the bottom of the risers up to the Brummel hooks (around 7-10 inches on most gliders). Now mark this length down from the Brummel hooks on your speed bar lines as a reference point for the top of the carabiners. This will save you having to hook up your risers to get things set-up. Thread the lines down around the outside of your back straps, through the guide-holes and around the primary pulley. From here there will be one or more guide pulleys or loops before the lines emerge at the seat front.

Put a sack of potatoes, or one of your mates, in the harness to hold the seat down and set the length initially to give, say, two inches of slack before the speed bar jams against the seat. This is easy to ascertain using the reference marks against the carabiner tops. Make sure that you have got the same slack both sides and that there is still some slack when pulling both sides simultaneously (in case the seat-front guides are wider than the bar). Now connect up your glider and get in the harness yourself.

Sit on the ground and whilst holding up the risers ensure that the system runs smoothly and that you can get full travel with nothing jamming. You should now be ready for a test inflation to make sure nothing is jammed or cacked. Get a friend to verify that all is well before you launch.

System Limitations

It is worth noting that unless you have very long legs or a very short pulley travel, with some gliders you may not be able to get full movement even with the bar as tight against the seat as you can set it.

Q&A Session and more beer...