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   the flexwing microlight
 
  how to fly a flexwing
 
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how to fly a flexwing microlight (trike)

  Turn a flexwing
  Land in turbulence
  Fly through turbulence
  Land in a gale
  Get out of a spiral dive
  Recover from a stall
  Land in a short field
  Take off from a wet grassy field
  Fly economically
  Pre-take-off check
  Land Crosswind
  Take-off crosswind
  Not do a Wingover, whipstall or tailslide

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Turn a flexwing

If a flexwing is to turn efficiently, the angle between trike and wing needs to be 90 degrees.  In other words the same as it is in level flight.  It follows that the most efficient and smoothest turn will be where you have chucked the trike out by just the right amount to keep the 90 degrees throughout the turn.  The 'chucking out' is of course done by centrifugal force swinging the trike to the outside of the turn like a ball on a string.

In order to make the trike swing out there are two things you need to do (as well as banking the wing that is).  Firstly it helps if you gain a little speed by entering a shallow dive, then once you have initiated the turn by pushing the bar left or right, you need to push the bar slightly forward. Oh, and at this point tweak the power up just a touch to push the trike round the curve.  This takes a bit of practice until you can time it right and apply just the right amount of forward pressure and power for the steepness of turn.  But get it right and it feels lovely. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Land in turbulence

It's not so bad as you think.  When (if) you can get close to the ground the turbulence usually dies away quite a bit as the air sticks to the ground and you find yourself floating reasonably smoothly in ground effect.  If you can feel it's going to be rough as you come in then come in with some power - maybe 4000 revs until very late.  This has two advantages - you are driving through the crap, and you have instant power to climb away and do a go round if you are not happy.  And the key thing to remember is you can go round as many times as you like.  It may be embarrassing in the club house afterwards to have gone round 4 times, but not half as embarrassing as wrecking your aircraft.  

Make sure you know what the optimum airspeed is for your wing.  For the Blade it's 55mph.  That means you have maximum control over the aircraft's behaviour at 55.  If you come in at 48 it will be much less responsive (same sort of argument applies to 60mph).  The thing that will catch you out is a huge gust tipping your wing so that one tip catches the ground.  When you are 50 ft above the ground you can heave the trike round as much as you like to get her lined up and level, but you can't do that 15 feet from the ground. 

Better to make more gentle corrections and if you are getting tilted too much then apply power, climb away and go round.  Eventually you will make an approach between gusts that lets you get down to 7 or 8 feet with wings level and you can let her settle on to the runway.  (Remember to kill the power if you have used a powered approach.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Fly through turbulence


It seems best to have a heavy trike (passenger or ballast) and to try and fly at the wing's design speed - in the case of the Blade this is 55mph.  If you have the washout set at normal (I don't, because you can increase speed with it reduced), your pitch will stabilise more quickly and without so much manual input. 

Washout is the amount of upturn on the ends of your wings - think of it like the upturned feathers on a pigeon's wings or those of a soaring bird of prey - the more upturn the more stable the flight, but the slower the bird will fly (you won't see swifts or swallows with washout).  when you are learning you need the trike to sort itself out as quickly as possible even if this means sacrificing a bit of cruising speed.  As you become more experienced you find your brain making the corrections automatically but it can still be quite tiring.

If it's thermally induced turbulence, you can try climbing to the cloud layer as long as it's broken.  Above the clouds you will generally find it as smooth as silk - if a little cold.

If it's wind turbulence coming over hills etc, it's a bit more problematic.  You should be able to climb above it.

Brian Milton (who flew round the world in a trike) said that he used to fight to keep the trike level all the time, but in the end just went with the flow and the trike always sorted itself out.

The more you do it the more relaxed you become.  This means pushing yourself to take the trike out in conditions where you are currently reluctant.

Bear in mind that your aircraft is designed to withstand 3 times the forces that can be induced by turbulence.  However you as the pilot can theoretically overload the structure through violently trying to keep the plane level.  This can only really happen if you end up in cloud in a thunderstorm - so don't.  Thermal turbulence might feel bad but isn't dangerous.  Turbulence caused by strong winds in the lee of a range of hills, can be more violent and more dangerous if downdrafts exceed the maximum climb rate of your aircraft.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Land in a gale

You can land a flexwing in surprisingly strong winds.  It's just once you are down that the problems begin. 

Obviously anyone can get caught out by worsening conditions on a cross-country.  If you are reasonably sure that you have flown into localised strong winds, you can always go back to your starting point where presumably you took off in sensible conditions.  Of course you don't always know if the wind has started howling - it can be a perfectly fine day, but the wind might have picked up to 40 mph without you realising it.  If you have a GPS you can spot this straight away as your speed over the ground will vary dramatically compared to your airspeed (beware though, this might not be the case if you have hit a strong crosswind, but in this case you will find your machine crabbing markedly into the wind).  If you are flying an old XL and you can't afford a GPS you can tell if it's a 40 mph headwind from your shadow on the ground ... it will be going backwards!

Obviously if your speed over the ground in say a Blade has dropped to under 20mph you may have a problem.  You can do one of two things Firstly try and find out from your destination what the wind speed at ground level is, it might be markedly less.  Secondly you can turn round - you'll make it home in no time at something like 85 mph.  If on the other hand your ground speed has gone up to the high 80's or 90s, you have more of a problem, as it's going to be quite a fight getting back home and that is where the stronger weather is coming from.

So you get to your destination and there is a 35mph gale blowing.  What do you do?  Firstly try and get some information on the radio.  Secondly look at the surrounding area.  Is it flat ground where the wind is coming from, because if so it's likely to be steady even if it's strong.  Now make some exploratory circuits at about 1200 to 1500 feet AGL (I'm assuming this is a microlight site rather than Gatwick).  Is there a runway that's directly into wind - if so great.  If not is there grass or a disused runway that is directly into wind.  The important thing here is that you do not need much - remember your landing speed in relation to the ground might be only 20 mph.  You could be down and stopped in 30 to 40 metres.

Once you are on the ground DO NOT TURN.  Keep pointing into wind, and if you have enough runway keep your wing level (it is most stable in this position).  If you are landing on a short bit, pull the bar in as soon as you are rolling in a straight line.  You will be amazed how quickly this stops you.

Finally keep sitting like this on the runway into wind until either the gale blows itself out, or at least two people spot your plight and scurry out to walk your wing in.  Do not try to taxi in across a 35 mph wind - you will end up with some expensive repairs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Land in a short field

The great thrill of our type of aircraft is their short field take-off and landing ability.  What fixed wing aircraft can arrive overhead the field at 2000 feet and spiral down to land in a bumpy grassy field only 80 or a hundred metres long.

Well firstly coming in steep from directly overhead is not necessarily a good idea in a short field, as you may be travelling too fast as you arrive - and this means that you will float on before you touch down.  A relatively shallow approach maybe 10% slower than you would normally come in is best - any slower and you could run into difficulty if you need to go around, or change direction (the wing is really quite difficult to control at say 10% above stall speed).  Aim to touch down 1/3 of the way into the field, any less and you might run into hedge problems if you hit any sink.  As soon as you get down, pull the bar hard in and the drag created by the down-pointing wing will slow you down quite markedly.  Use your brakes - as hard as you like if they are rear wheel brakes but with great care if it's a front wheel primitive kind like the Pegasus XL.

What factors might cause you problems.  Firstly very light winds will mean your speed relative to the ground will be high and your consequent ground roll longer.  Secondly grass is better than tarmac - long grass will slow you down quite quickly.  If you are going to the field to camp, and you have got a mate in the back and all the gear for two, and a crate of beer, you may end up in the field beyond the one you intended. Remember also that you need to get out of the field later, and factors that were helpful in slowing you down during landing, will also slow you down during take-off.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Fly economically

Assuming you have already done what you can to improve the aerodynamics of your aircraft, such as scraping all the dried on mud off, and dispensing with the idea of panniers.  Remember too that the prop's task is to screw you through the air.  If it has to work hard overcoming excess drag on its own surfaces it won't be able to provide the maximum propulsion for the aircraft (so keep the prop clean). 

What we are talking about here is the way you fly, and the key is smoothness.  If you want to get from A to B using the minimum of fuel you need to do everything gradually.  So it's better to reach your cruising altitude by climbing steadily at 200ft per minute rather than holding her at full throttle and climbing at 1000 ft per min (even a 912 uses 22litres per hour at full throttle).  Then fly at that altitude at the speed your wing was designed for.  On a modern flexwing that means the trim control should be just beginning to bite. 

Any more and the wing will be creating too much drag despite its greater lifting power. You do have to balance this with the revs your engine runs at if it's a two-stroke.  It can be critical when the engine starts running purely on the main jet, as opposed to the needle jet. You should also regularly check the profile of the wing battens - they flatten with use, making the wing fly faster but not providing the lift it should.

Remember that (at least in the northern hemisphere) the wind veers as you go higher.  Imagine one is flying north from Peterlee to Eshott and there is the usual wind out of the west.  It's better to fly at about 1000ft rather than 3000 ft, because higher up the wind is more likely coming out of the north west.  Obviously on the return trip one can make use of this tailwind if Newcastle ATC will let one cross their zone at 3000 feet.  GPS is the only way of finding these different airflows by monitoring your groundspeed and bear in mind it doesn't always work out. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Take off crosswind

More aircraft get damaged in crosswind take-offs than deserve to be.  And usually it's not just the aircraft of the guilty party as he often goes skittling into all the parked air craft outside the clubhouse. 

What usually happens is you are sitting on the runway and there's maybe a 12 to 15 mph crosswind.  At this point you are glued to the ground by the weight of the stationary aircraft.  As you start to move slowly forward, the weight of the machine is still dominant, so at first you follow  the nice line you intended.  But as the wing gains lift, there is less grip for the tyres, and all of a sudden the whole machine weathercocks into wind, and the take off track can change by a remarkable number of degrees (now you are aiming straight for the clubhouse with insufficient airspeed to climb over the assembled barbecue, trikes and picnicking pensioners)

The answer is relatively simple (apart from don't take off in strong crosswinds).  The key is to hold the trike firmly on the ground for longer than you normally would, and well beyond the point when she wants to fly.  Do this by holding the bar in as you accelerate down your chosen track.  When she is travelling maybe 10 mph faster than you would normally lift off, rotate the bar just a touch to unstick her.  You will find that although you weathercock quite smartly round into wind, your forward momentum should keep you on your original track, and anyway you have enough speed to climb smartly away.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Land Crosswind

The key here is to line up your direction of travel with the centre of the runway.  This might mean your trike is pointing

The key here is to line up your direction of travel with the centre of the runway.  This might mean your trike is pointing substantially away from the centre line.  Obviously the more you are pointing away from your line of travel, the greater the potential for disaster.  When the leading rear wheel touches down there is a tendency for it to tuck under and the trike to roll.  Even if it straightens up OK there is a lot of twisting action on the trike, and it's why you should always give the trike a good checkover after a strong crosswind landing.

So what can you do to make it easier on aluminium, skin and bone?  If you have got a wide runway, then land on a diagonal to the centre line (ie more into wind).  If you don't get your touchdown point exactly right you can always do a go-round.

If you have to land crabstyle, the technique is to land with the front wheel slightly higher than you might normally (a touch of extra power helps do this) and to make the back wheels just kiss the ground.  If you can hold it like this a fraction longer than you normally would, you will find that the trike will just click round to line up with the runway, and you are home and dry. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Pre-takeoff check

C - controls

H - helmet

I - instruments

F - fuel  T - trim

W - wind

A - (other) aircraft

P - power

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Take off from a wet grassy field

1.  Apply full power, and immediately push out the bar as far as it will go.  This will take the weight off the wheels and reduce the drag from the grass and mud, and the high angle of attack of the wing will be providing maximum lift at the lower speeds before the wing is ready to fly.

2.  The above is crap, and the high angle of attack will create loads of drag which added to the drag from grass and mud will mean a long take-off run.  Much better to keep the wing in a neutral (low-drag) position so that it is ready to provide maximum lift as soon as you are going fast enough to fly.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Not do a Wingover

(or a whipstall or a tailslide)

Your aircraft manual and the textbooks tell you that it is illegal to do a 'wingover', but no-one tells you what one is.  So how do you know whether you are doing anything illegal. 

A true wingover is a 90-deg. climbing turn followed by a 90-deg. descending turn resulting in a 180-deg. change in direction. Trikes can't perform true wingovers because bottom rudder is needed at the top of the climbing turn to keep the aircraft coordinated. Trikes and hang gliders perform "wangs" (see drawing below).

Is it safe?........depends on pilot skill, technique, judgment, experience, etc.

click thumbnail to expand

And here's a description of the other two big 'no-no's

a whip stall is an exuberant stall. Instead of continuing as long as possible to fly straight and level with the throttle shut, you push the bar out as you shut the throttle, so that you enter the stall in a climbing attitude. The angle through which the wing has to recover is therefore greater.

As you increase the effect, the rotary inertia of the wing/trike starts to kick in, tending to make the whole thing rotate beyond the point at which the wing would otherwise start flying again.

The eventual consequence is a tumble, such as on the video clip that did the rounds a few months ago.

If you do a sufficiently exaggerated stall entry, the aircraft may actually slide backwards before rotating.

A whip stall is a deep stall induced by an accelerated entry. The CAA definition of a standard stall entry is a reduction of speed by 1 knot/second. A typical whip stall on a flexwing is entered by speeding up well above a fast cruise, and shoving the bar hard forward onto the front strut. Dont try it until you have tried several more gentle entries gradually increasing in severity. The severe cases are best left to test pilots with parachutes, since the deeper the stall, the more severe the nose down rotation speed; at its extreme, it can either result in a tail slide or a tuck or both.

A tail slide is most definitely to be avoided on all flexwings. If you end up in an extreme nose up situation (probably with power on) and the wing stops flying, there is a chance it will slide backwards before rotating nose down. If it is extremely well pitch-damped there is just a chance that the rotation is slow enough for a tuck not to result (I know of one case where this happened). Best avoided.

Here is a superb diagram published by Pegasus which details what happens in a tail slide and gives you two clues as to how to get out of one. Mind you if you have to think about getting out of one it's probably too late.  This diagram was published at the time of the fatal accident in the USA in Oct 00, but may date from some time earlier.

click thumbnail to enlarge

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Get out of a spiral dive

A true spiral dive is defined as a continuous descending turn in one direction where the speed is increasing.  Obviously in a flexwing once this airspeed gets up to 75 or 80 mph, it's getting dangerous.  There is also the real risk of hitting your own wake turbulence so it's best to know how to get out of it.  On the other hand it's difficult to know how you get into one of these accidentally.  The key is to remember to get out of the turn first before thinking about controlling the speed.  If you try to do it the other way round you are likely to tighten the turn and drop the inner wing even more.

So let's say that you are diving clockwise at about 70mph.  First shove the wing out to the right.  You don't have to be too aggressive.  Gentle but firm pressure will eventually cause the aircraft to shoot out of the dive at a tangent - but still pointing down and probably accelerating.  By now the wings should be level, and you should be heading in a straight line.  Now all you need to do is get out of an ordinary dive.  You shouldn't have any power on (I am assuming that you took the power off as soon as you realised you were in a spiral dive), so all you need to do is make sure your forward pressure on the bar is gentle - so that you don't swoop the trike up into a stall. If you hold this slight forward pressure, you will eventually slow up and can resume normal straight and level flight.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Recover from a stall

For some reason let's say you have stalled your aircraft in level flight - maybe you were trying to get it into a very small field and you decided to fly it very very slowly.  You have to hope that you aren't too close to the ground as even with the standard technique you are likely to lose 50 feet before you can recover.

The first thing you notice is a buffeting through the bar - this is a thump thump of back pressure.  At the same time the aircraft becomes pretty unresponsive to the controls - so don't bank whatever you do.  If the trike is about to stall in level flight, entering a turn will undoubtedly cause the lower wing to stall, and pitch you into a steep side slip.

At the point of stall, pull the bar back (just sufficiently to reduce the angle of attack of the wing below the critical stall angle), while simultaneously applying full power.  Initially the nose will drop in a fully developed stall, but as the air speed increases to a safe figure raise the nose positively into the (full power) climb attitude. If a wing drops at the point of stall then recover as above, but roll the wings approx level before raising the nose into the climb attitude. When at a safe height from the ground return to aircraft to level flight.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

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