This is a page of information that seemed to be a bit technical for the introductory page. We'll add to it as things come to mind!
 

INDEX Ask a Question
Taxiing	Takeoff techniques	Doing a Good Turn
Short Field Landings	Recovery from Attitudes	Stalls and "Mushes"
Aerobatics	About side cables	Pitch stability
Luff Lines and Dive Sticks	Fins and Keel Pockets	More HorsePower?
Glossary of trike terms	Trim Systems	Trike Pages Index
SPECIAL NOTE: We do not sell trike plans.
CAUTION Some of the information presented herein is open to interpretation and may not agree completely with what your instructor may teach or have taught you. The author is not an instructor, just a reasonably experienced pilot. When in doubt, follow your instructor's advice! Luff Lines (a.k.a. Reflex Bridle) Most modern Rogallo-derived flex wings feature cables or strong cords running from the top of the kingpost to the rear of some of the inner battens on both sides. In addition, the rear section of these battens is flexible, usually made of fibreglass.  In most places, these are called Luff Lines, or sometimes, the Reflex Bridle. Under normal conditions, these should be just slack.  Luff lines were introduced originally in hang gliders to aid stability by inducing reflex at very low angles of attack. They, in conjunction with tip sticks, which define a lowest possible washout for the tips are intended to provide a good pitching moment at very low aoa to prevent "tucking". (Early hang gliders had a rather nasty reputation for entering a "luffing dive" in which the aircraft would enter a stable dive with the sail flapping. Later short keel wings with pre-formed battens are sometimes known to "tuck", meaning that they would continue past vertical to an inverted state, usually resulting in a "tumble" where the glider flips end-over-end with resultant structural failure.)  You should never, never, never lengthen the luff lines of any wing beyond the manufacturers spec without consulting them.  Luff Lines and other Trim systems In modern high-speed trike wings, the luff lines are often put to an additional purpose, that of providing a trim speed adjustment. (Trim speed is that speed the wing will fly at "hands off", or with no pitch bar pressure fore or aft.  A winder handle on the control bar can be used to pull on a cable which will tighten the luff lines and induce a slight "reflex" (or reverse camber) in the rear of the flexible battens. Simplistically, this can be thought of as a slight "up elevator", moving the aerodynamic centre of the wing forward, and, since the payload (trike) is still suspended from the same place, the effect is to trim the glider to a slower speed.  You should bear in mind that this system does NOT in general reduce the stall speed of the wing, and if anything, may increase it! It has the effect of making the wing somewhat less efficient, and level flight at the new trim speed will actually take more power than flying at the same speed without the use of the trim. Power-off glide with this trim engaged will be steeper.  Other Trim systems Other trim systems in trikes have usually focussed on providing relief for fast flight bar pressures by either mechanically reducing the amount of bar pressure or by moving the hang point forward (eg: via worm gears, etc...)  A system often tried is to connect a bungee from the control bar to the front of the trike frame. This works, but care should be taken that any such arrangement is foolproof ans allows either instant disengagement or still allows immediately available full and free movement of the control bar. It should go without saying (but we'll say it anyhow) that any trim arrangement should not be capable of freezing the bar position or fouling any part of the aircraft in flight.  Why does a trike exhibit pitch stability You are warned that the following explanation should be considered only a qualitative explanation - it is not rigorous aerodynamics!    At high angles of attack/stall, it is the tips of the glider that provide a natural nose-heavy tendency. Think of it this way. Your wing is flexible, and the root chord always has the highest angle of attack, and the tips the lowest. The wing also has spanwise tension that tries to keep the tips as flat as possible, but as you can see from in-flight photos in magazines, taken across the wing, the tips are usually really heavily washed out. An aerofoil stalls in the region of 16 degrees aoa, and the root is usually close to this, The tips are often at so low an aoa that they're almost along for the ride under trim conditions.  However, as you push out, the aoa of the tips increases. The root isn't going to generate much more lift - it spends most of its time near max lift anyhow. But the amount of lift at the tips increases substantially, so that when the root eventually stalls, the tips are still lifting well. Since the tips are behind you, they "tip" the glider nose downward, hence a good positive "nose-over".  Of course, the converse applies. As you speed up, the tips will tend to dump load, the root will be the major contributor of lift, and since the roots aerodynamic centre is forward, you will get bar pressure that will oppose the speedup. Theoretically, you should not need "reflex" to acheive this,  Our really old "standard" hang gliders had such long keels that in order to be stable at low angles of attack, some reflex in the keel tube was necessary. Not so any more, with well defined swept wings, decent tip chords, and short keels.  If you're looking at the diagrams to the right, notice that they show the difference in angle of attack of the root and tip chord, and that this difference varies markedly!  Loops and Aerobatics Aerobatics in weight shift aircraft can be dangerous. Weight shift means just that. Without a positive "g" loading, the pilot has little if any control of the aircraft. This limits the unit to only positive-g manouevers. In addition, since weight shift is a 2-axis control method, some positive-g manouevers (such as rolls) simply are not practical.  "Tail Slides": You could only be in a position to do a "tail slide" by entering a near vertical climb. Should a trike do this and lose all airspeed, you can be assured that the resulting "tail slide" would most likely break the trike and/or injure the pilot as the control bar is slammed back into either him or the front strut of the trike. The latter has happened several times, and it is suspected the former has too, though the victims haven't lived to confirm it.  Taxiing and ground handling Techniques Taxxing is of course, the first practical thing you learn as a trike pilot. There are only a few salient points to remember:  Most trikes have a very simple nosewheel steering mechanism, working just like a "billy cart" (or for the US folks, a Soapbox racer). That is, you push with your right foot and you go left and vice-versa. This is the reverse of conventional aircraft steering, and many a trike has been ground-looped through conventional pilots forgetting just this fact in an emergency. For others, it comes naturally, along with the normal arrangement of a foot throttle for the right foot and a brake pedal on the left. If you're a conventional pilot, you should practice taxiing a LOT. You should also make it part of your pre-landing checklist to say to yourself as you round out "Remember the steering is TRIKE steering!" and it may save your bacon.  Taxiing in light to no wind is a no-brainer. Don't ride the brake, taxi at a fast walking pace, and make sure your feet are not in a position to slip on the pedals. In stronger winds, the wing enters the equation. When taxiing downwind, keep the control bar somewhat forward to the point where the wind is just pushing the trike along. Use brake as required to control speed. In crosswinds keep the upwind wing down, just enough that you feel handleable pressure on the wing. You should be able to keep it at a level that matches your upper body strength. Too far down and you will wear yourself out and put pressure on the undercarriage; too far up and a gust may grab you and turn the wing over.  Upwind taxiing is much easier if you keep the wing at a low angle of attack, making it easier to control the roll and reducing the frontal area so you won't need to rev too high.  When taxiing always keep an eye out for obstacles including holes, puddles (especially dangerous!), runway markers, livestock and people. Look Around! In addition, observe airfield protocols. Never taxi onto a runway if an aircraft is on final - it has right of way. After landing, vacate the strip as quickly as possible, and try to arrange your landings so as little back-tracking as possible is required. Takeoff Techniques There's often an almost religious debate between pilots as to whether you should take off in a trike with the bar in or out. Our recommendations are that both techniques have their place, depending on the circumstances. Here's the basics:  If there's a noticable crosswind, keep the bar-slightly-in till you're sure of having acheived takeoff speed, then apply firm rotation. This is simply to stay in control on the ground and keep the transition time as short as possible. If it's a reasonable field, with no major crosswind, keep the bar slightly forward of neutral, then ease into rotation when the wing 'wants' to fly. This makes for a no-hassle takeoff. If the grass is longer or wetter than normal, or the strip is not the best (prop danger from gravel etc), it's bar-out till lift-off then build speed on breaking ground before climbing. The idea here is to unweight the wheels as soon as possible to reduce the rolling resistance. Doing a Good Turn Back in the early days of hang gliding, one of the measures of a top pilot was how many 360 degree turns they could manage in a row. In water towing competitions, pilots would tow up, then basically 360 till the water rose up and smote them. Extra points were awarded for reversals.  It was amazing how many pilots just spiral-dived out of the sky, while some seemed to be able to turn forever. They knew the secret.  That no-longer-a-secret is still important today for all pilots who aim for efficient, safe turns. It is Pitch Control. You see, many of the early pilots believed that you turned by putting your weight to one side. It certainly got them turning OK, but it was only half the story.  A well balanced turn requires application of pitch out as well. In a very steep turn, the amount of pitch required can be quite significant.  Of course, a hang glider is always descending relative to the air around it, but most turns in trikes (except during descents/climbs) are done in level flight, and you really don't want to change altitude. In a shallow turn (say 15 degrees), maintenance of the same power level along with some extra push-out will maintain the altitude at the cost of a few knots of airspeed. However, in a steep turn, additional power will be required. If you are doing a steep turn with power off, assure you enter it with some excess airspeed.  The best way to get a feel for all of this is in the air. Your instructor will take you through all kinds of turns till you get a feel for how your own trike type handles and what power levels are necessary.  Stalls and "Mushes" Many pilots report that it is almost impossible to stall their trike by slowly easing the control bar forward till it reaches the front strut. Instead of dropping the nose, the wing enters a mode often described as a "mush", where, with power off, the descent rate is quite high, or with power on, it requires a bit more grunt than normal to hold altitude.  The "mush mode" of a wing is a sustainable mode in which the root chord is fully stalled, but the wing itself remains able to fly simply because the amount of washout is such that a reasonable amount of the rest of the wing remains flying. This is a direct result of the huge amount of washout/twist that there is in most trike wings at large angles of attack. This is an extremely high drag mode, since you have to push the stalled section of the wing through the air, hence the steep descent profile, power off.  Were there enough bar travel available, most wings in a "mush" will *eventually* stall with more pushout. Many trikes are designed with front struts deliberately placed so that a stall under normal straight & level flight is unlikely.  Whether a wing will "mush" or not depends somewhat on the planform. In the extreme case (early Rogallo hang gliders) the planform is such that the wing could enter a "parachutal" mode. We used to take advantage of this for spot landings. Can't do it on today's blade wings though (sigh)...  There are 3-axis machines with enough spin resistance and elevator authority that they will enter a mush mode. Even the humble Cessna 172 will do it. The author has been rapped over the knuckes by his GA instructor for failing to recognise stall onset and allowing the C172 to mush along...  Definition of a stall Put simply, an aerofoil is considered stalled when the airflow over it becomes separated over a substantial area of the upper surface. The separation of flow increases drag sharply and reduces lift. As a rule of thumb, this happens to most aerofoils at about 16 degrees angle of attack (aoa), and this is independent of airspeed.  A wing usually consists of a bunch of airfoil sections at different angles of attack (root usually higher than tip), so for a wing, the "stall" happens when the root section flow separates while the tips are still unstalled. The result is that the nose drops and the aoa is restored. This is called the "stall break".  A stall can happen at any airspeed. For example, a high speed stall can be induced by suddenly pitching up at speed. The wing will still have speed, but the flow will separate, and it will want to drop the nose. You don't even have to pitch up in some circumstances. For example, a strong thermal surge from below can stall you sometimes if flying slow enough.  Manufacturers will quote a "stall speed", but you should note that this is at a particular all up weight. If you increase your payload, the stall speed will increase. If you're in a turn, it will increase too.  Basically, this is because in both of these situations, the wing is required to supply more lift to keep you up. There are several ways of increasing lift. You can change the airfoil (flaps,etc), increase speed or increase angle of attack. Basically, if you add more weight, you either have to fly faster than normal, or increase the aoa.  So, lets say you start adding weight to your trike but want to fly at the same speed. You have to increase the aoa above the normal to do it. It's easy to see that you have just reduced the margin between your cruising speed and stall, simply because there are less degrees of aoa left between you and that magic 16 degrees. Therefore, the stall speed is higher. In a turn, courtesy of "centrifugal force", you magically put on weight, so your stall speed increases in the same way.  [Return to mushes] Fins and Keel Pockets Some trike wings seem to have a "fin" made up of a deep pocket joining the sail surface to the keel (eg: Pegasus XL), and others seem to have the keel pretty much attached to the sail surface, but have a separate "fin" structure above the keel (eg: Edge, Pegasus Q). What is the purpose of these structures? The deep keel pocket was "invented" by Bill Moyes for Moyes hang gliders in 1975/6 as a way of allowing him to improve performance by flattening the sail, while promoting billow shift from one side to the other to keep handling light. He also used it to allow him to shape the root chord aerofoil; in early gliders, this was wasted on a straight tube.  The deep keel pocket was adopted by most hang glider manufacturers, and it was only in the mid 1980's that hang glider manufacturers found that advances in frame design (floating crossbars, plus leading edge flexibility) had rendered the deep pocket unnecessary. The first major Australian manufacturer to do so was Enterprise Wings, and in the USA, Wills Wing. They are almost extinct in modern hang gliders.  Some trikes, like the Pegasus XL and Jetwing/Demon are pre-1985 designs, and still sport these keel pockets on the wing.  Newer trike wings do not have deep keel pockets, but some sport an extra "fin" above the keel. It is above the keel so as not to interfere with the prop arc. The purpose of these fins is to add yaw stability. Yaw stability of a trike wing is acheived through sweep - if the wing yaws one way, more of the other wing is exposed to the airflow, thus generating more drag, and causing a reverse yaw. The greater the sweep, the greater the effect. On wider nose angle wings, and wings with low drag, this effect is reduced, making the machine more susceptible to yaw in turbulence. Not only is this disconcerting, in inexperienced hands it occasionally leads to what are termed "pilot induced oscillations" or PIO's, where the pilot continually overcorrects due to the lag in the wing's yaw recovery time. The result is an oscillating yaw from side to side, for which the best recovery action is to reduce speed and let the wing recover itself (minimal control input).  Short Field Landing Techniques There has been some debate on techniques to be used in approaching and landing in a limited space. The following suggestions are offered based on some experience doing short-field landings in competition, but your instructor may have different advice.  In general there are always a couple of cardinal principles to keep in mind.  Airspeed is your friend. Unless you know that it is an absolutely calm day, you can never be sure what you will encounter in the way of turbulence and wind shear at low altitude. Altitude is your friend. Keep your options open! You can usually go around. Be ready to do it if things turn sour, and be sure to blip the throttle occasionally on approach to keep the engine ready for work. If you can, fly a low pass over the proposed landing area to ascertain conditions at low altitude, this will help you set up your final approach later. With these principles in mind, assuming you have power, always try to fly a standard box circuit approach. Not only does this give you time to check out what's happening on the field, you will get a better idea of the wind conditions.  Set up your final approach so that it is more or less a glide on limited (just above idle) power, at least 10 mph above your stall speed for a modern wing, (or maybe more if the wind is strong), to just clear the last obstruction. This works for me, but you are really placing some faith in your engine. If the engine fails and you encounter more headwind than you anticipated, you won't make it. Your instructor may insist on a more conservative approach involving coming in somewhat high and doing "S" turns on final to adjust your glide slope. I would fully reccomend this latter approach for a forced short field landing with no engine - but stop "S" turning any lower than 50 ft - By then you should be well established in the correct glide slope!  Lock your legs stiffly to keep the nosewheel straight.  Fly the wing down and flare out just above the ground, but do not hold off - allow the wing to settle, or if very short of space, encourage it somewhat! Be ready for your nosewheel steering to be very sensitive at this higher than normal speed, and pull the control bar in and apply immediate brake!  Recovery from unusual attitudes Thanks to Paul Haines of the Sydney Microlight School for additional input.  One of the nice things about trikes is that under normal conditions, they are very pitch stable, and apart from flight in extreme turbulence or deliberate abuse, it is unusual to enter a pitch attitude that the aircraft itself will most likely recover from with little pilot input.  However, sh*t happens, as they say.  Nose very high with normal/excess airspeed. In this case, you're in good shape. Just ease the bar toward you and maintain power, till you get level again. (you may need a tad more power to keep the airspeed up, sometimes)  Nose very high with low airspeed. Watch it! Don't just wham the bar in hard. Before you actually stall, EASE the bar in while feeding in power. If you have actually stalled, be ready for a fairly savage stall break. (Aggravated stall)  Normal stall (result of nose high with low airspeed, uncorrected). Allow the nose to fall gently. As airspeed is gained, feed in power. For minimum height loss, feed out bar gradually and continue applying power as trike airspeed passes about 1.2 times stall speed.  Aggravated Stall (result of Nose very high with low airspeed, uncorrected). This is a potentially dangerous situation. DO NOT BE TEMPTED TO SNATCH THE BAR IN SHARPLY. The accepted wisdom is that you should maintain power at at least cruise level and keep the bar OUT. The result will be that the nose should drop to below the horizon with the machine in a mushing mode of flight, and hopefully pick up speed to the point where, when the aircraft has stopped loweing the nose and is picking up speed you can let the bar in a bit till full flying speed is reached, then return to level flight.  Should you snatch the bar in, you run the risk of imparting additional rotation to the stall break, in an extreme cae, this can lead to a tuck/tumble. BE WARNED - this has caused several fatalities!  Steep dive Simply reduce power and ease the control bar out gradually till level flight is achieved. Feed in power as airspeed decays when level.  High Speed Spiral Dives In curving flight (eg: a descending 360 degree turn), pulling the bar in and increasing bank angle can lead to a rapidly accelerating spiral dive. Don't do it! It is easy to exceed the Vne of the aircraft in a single turn, wth the attendant dangers of overstressing the airframe, pilot nausea/disorientation and a pull-out height loss that may be less than the available altitude!  The accepted recovery procedure is:  Reduce power Roll wings level Level out of the dive gradually to avoid overstress or a high speed stall Spin or incipient spin Fortunately, it's almost impossible to spin most trikes, but should a spin be entered, the recovery action is to move your weight to the INSIDE wing of the spin, and pull in a bit. This will load up the inside wing causing it to fly faster, and hopefully unstalling it. You can then recover from the resulting spiral dive.  Inverted Flight Fire your ballistic parachute.  More powerful engines Often folks who are keen on speed get excited about putting a more powerful engine on their trike. The unfortunate fact is that this usually doesn't help much. Adding more power on a trike usually simply improves the climb rate, not the top speed. In fact, the addition of the extra weight of a more powerful engine may actually decrease the trim speed due to wing flex and the fact that if the same hang point is used, you have to push out a bit to support the same weight!  Obviously, in order to pick this up, you'll have to move the hang point forward. However, overall speed gains will only be a few mph.  All about the cables on your wing There's been some discussion on the internet Trike list regarding the loading of cables on a trike/hang glider wing in flight, particularly on the merits of two side-wires per side versus one, and also on the loads imposed on the front and rear lower cables.  The major loaded structural members of a traditional trike wing in flight are:  Control bar basetube - column in tension Control bar downtubes - columns in compression Spreaders - columns in compression Leading edges - inboard, compression & bending. outboard, mainly bending. Lower side wires - tension front & rear control bar wires - light tension. keel - light bending, light compression. In general, there is not a lot of load on front/rear wires. In fact, on some modern hang gliders, the attachment point for these has been moved to a point more than halfway up the control bar in order to reduce drag!  The side wires carry the brunt of flight loads.  In traditional hang gliders, a single wire is all that is used per side. Many certified trikes, however, use dual side wires. Why, when you could just use a really thick single wire? There may be several reasons. The first is redundancy, whether required or not - in case one wire fails due to load or poor construction/corrosion/damage.  The most common reason, however, is that it simplifies the structure and increases the strength of the attachment.  Traditionally, in single wire systems, the single wire is attached to a tang which is in turn connected to a bolt which runs vertically through the outboard spreader. This places the bolt in tension, which is NOT its strongest mode, as you're putting the threads of the bolt in tension. For the size bolts used and the loads associated with hang gliding, this is OK, but when you are dealing with higher loads and possible fatigue involved with engine vibration, pulling on the threads is a no-no. By going to dual wires, the wires can be connected to either side of a transverse bolt, putting it in shear; the strongest mode. Obviously, in flight, both these wires are usually tight, evenly distributing the load. If one were to be loose, not only would it be putting a twisting load on the spreader, but if the other were to fail, the resultant sudden tightening of the other cable from slack to tight, on top of the original load that caused the other to fail, would increase the chances of a second, immediate failure!