Introduction: Fly 3D With a Model Plane
Andy Ellison from RCM&E Magazine is your guide.
3D flying has come a long way since Paul Heckles took his WOT4 to the limit with countless '3D' machines now available. Many years ago I was shopping for bits in Steve Webb Models of Frodsham when the man himself collared me and, somewhat excitedly, whispered in my ear: Come 'ere mate, and 'ave a look at this.
Steve then lead me to a small portable television with an integral VHS player. Bet you've never seen anything like this before? The video was shot at a club flying field and focused on a late teens yoof about to fly a Chris Foss WOT4 with a huge Steve Webb Models decal across the wing.
The lad took the model off and flew it around in quite a low, slow and tight circuit before passing himself by very closely and slowing the model to a crawl, holding it against the gentle breeze in very slow forward flight. Slowly and ever so carefully he raised the nose to a position where the model should clearly stall and drop from the sky... But it didn't! I was watching intently now as the nose of the model rose more and more towards vertical until the fuselage was at around 80°, some 6 (2m) or so above ground.
With the rudder working back and forth with demonic possession the lad juggled the throttle and carefully backed the WOT4 towards the ground to a point right in front of his Tx. Slower and lower, it came down until the rudder tapped down onto the grass! Throttling up slightly to avoid damage he took the model back up to where the tail was about a foot (30cm) from the ground, and with a quick grab he deftly plucked the model from the air by the wing before turning around to flash a big toothy grin at the camera. Gyros? I said to Steve. No. What then? Practice, he said. Who is he, then? Some local smart-arse school kid? said I. Paul Heckles, said Steve. I hadn't seen anything like that before. Mind you, neither had anyone else in the UK at that time.
Fact is, we were more used to witnessing the likes of Hanno Prettner putting his thing down at Sandown Park. This was special, though. Even Hanno wasnt playing this game! Paul had discovered his video-demonstrated hover whilst doing back-to-back stall turns with his WOT4 but extending the time in the hover at the top of the turn, causing the model to pause for a spell and leading his mate to dare him to try it lower. Needless to say that at the end of the session the model was fairly wrecked! Paul toured the show scene that year with Dave Bishop glorifying him across the famous DB Sound PA system: Hes British you know, ladies and gentlemen... Paul Heckles... isn't he good? I once stood alongside Paul at Woodvale, trying to work out just what it was he was doing with those twitching thumbs and that waving rudder. I'm not easily impressed with new things in aeromodelling but Paul's performance was something else.
Okay, the famous Avicraft display team were fun to watch, high level prop-hanging in unison with their twenty-odd Panic biplanes, but Paul had brought 3D flight to the masses for the first time and changed R/C modelling overnight!
Since Paul's innovative piloting exploits were made public, the 3D flying scene has become so big that almost every sport R/C model released to the market seems to have some sort of 3D ability, enabling it to perform every manoeuvre in the book. But what are these manoeuvres? How are the models suited to perform them, and how can you go about trying them for yourself to emulate the flight simulator trained Nintendo Generation kids showing off at the local model show, or indoors with a simple Depron Shockie? Before we get into that, lets examine the hotly debated topic of trying to summarise just what 3D flight actually is.
Step 1: 3D Focus
Essentially a freestyle aerobatic flight is a blend of more traditional extreme flight patterns, the new moves being flown in a deeply stalled condition with great assistance from the propellers thrust to keep the model in the air or the assistance of gravity to achieve the effective flight path. Its these stalled flight patterns that really catch the eye as being different, and have given rise to the 3D tag.
Specifically, then, 3D flight is the condition where the model is flying at some level of stalled attitude; most other definitions are a derivative of this one. When the model is stalled it will fall earthwards unless lift is coming from some other source, which is usually the propeller. When the propellers thrust is generating the balance of the lift, and airflow over the wing is too slow to generate usable lift, then you have 3D flight.
Directional control is achieved by utilising the prop wash flowing over the control surfaces. Deflecting the prop wash over the control surfaces whilst maintaining enough thrust to stay in the air will allow you to do many manoeuvres in the stalled condition. Flying on the prop as it were, as opposed to on the wing. This puts a great deal of faith in the reliability of the models motor, and its no surprise that petrol power is preferred over glow for larger models, whilst electric power holds an advantage at the smaller end of the scale.
Step 2: Model Choice
Whilst some typical 3D manoeuvres can be flown with fairly traditional models (the WOT4, for example), theres an ever-growing choice of 3D-specific aircraft to be found. Typically, a model designed with 3D flight in mind will have a thrust-to-weight ratio of more than 1:1 (typically 1.5:1 or more), large control surfaces with extreme throws and a relatively low wing loading.
Some established designs have been re-worked for 3D, reducing airborne weight and facilitating increased control throws. As an example, the Glens Models range has been continually developed to reduce airborne weight and better facilitate 3D flight whilst retaining a scale outline. There are even models available in two versions: one for normal, pattern-style aerobatic flight and a second with larger control surfaces for 3D. Whatever the model type, giving it 3D capability allows for some spectacular aerobatics to be flown. Hover, Harrier, Torque Roll, Blender, Parachute, Wall and Elevator are words that are progressively creeping into flying field glossaries.
Lets take a closer look at these manoeuvres and how to perform them.
Step 3: Parachute
Simplest first, the Parachute (a.k.a. Elevator) is exhibited with the model in a level attitude but with the tailplane fully stalled, like a de-thermaliser on a free-flight model. The model will drop slowly and almost vertically as if it were suspended underneath a parachute (see Fig. 1).
Massive amounts of elevator throw are required to get the tailplane to this point aerodynamically, much more throw than is practical for normal flight. This usually means a rate switch set to a 3D position, though more experienced pilots can handle this with electronic exponential. To perform the Parachute, fly a very short down line at idle from height and then quickly pull full up to rapidly dump the airspeed. With aileron correction through the initial stages as necessary you'll find that the model will settle down to floating flight. Steering can be effected thanks to the residual thrust from the prop washing over the rudder, and any wing rocking can be mixed out with a little spoileron, i.e. both ailerons moving slightly upwards with the elevator.
Note that this is the opposite direction to normal coupled flaps and elevator control. The intent is to stall the tail and de-camber the wing until the model is settled. Exit the Parachute with a slow increase to flying speed or transfer into a Harrier near the ground for effect. A rearward C of G with as much elevator throw as physically possible is beneficial. The Parachute can also be performed from an inverted entry. Power may be added to re-position over the field, assist tracking or flatten the fuselage angle further, but too much power will result in a Waterfall or similar erratic flight and produce airspeed that's above the level of the stall.
Step 4: Harrier
The Harrier is defined as high alpha forward flight and is the perfect way to enter a low-level hover, as the attitude of the model sees it already most of the way there.
Most models require maximum elevator movement to be held on for the duration of the manoeuvre, which helps to achieve stability by pulling the nose up to perhaps 60° or more to the point where the wing is no longer working. Its necessary to balance both throttle and elevator to achieve very slow forward flight whilst keeping the wings level and preventing them from rocking, which is very common with most models and a sure sign that you should be lifting the nose higher still. Steering must be performed with rudder, and a little spoileron may help to achieve a higher level of stability and dampen out any wing rocking tendencies.
The Harrier is another that can be performed inverted, and some pilots use it to good effect to exit manoeuvres such as the resultant flat spin from the Blender. The principles for inverted Harriers are the same but with the majority of models its unlikely that you'll achieve the same high alpha attitude as an upright Harrier. Remember that steering comes via the rudder and that this will be reversed when inverted. If you're having difficulty holding the flight path steady then try raising the nose higher, nearer to the Hover. A twist on the Harrier is to introduce aileron throw to perform a Rolling Harrier or high alpha rolling circuit, but your rudder skills will need to be well honed. With practice, full rolling Harrier circuits can be flown.
Step 5: Wall
Moving nicely along from the Harrier is the Wall, which is also known as the Pop-up, Snap-up or Cobra. This is simply an instantaneous dump of airspeed and a transition from level flight to a vertical attitude. In essence its a very deep and rapid stall. Very easy to perform, but it can look a right dogs dinner if the entry and exit aren't smoothly executed.
From straight and level flight and at moderate airspeed (not so fast that inertia will carry you along the vertical up-line but not so slow that the model is near the stall), pull full up elevator at 3D rate, very quickly. Simultaneously and abruptly, remove all power (if you didn't already do it before the pull). As soon as the model has rotated to the vertical, begin to remove the elevator deflection to complete the manoeuvre. Now add power again and fly vertically upwards or use the deep stall to enter a Hover, Torque Roll or Waterfall. Spoilerons may help smaller models achieve the sudden deep stall, and if there's a breeze the manoeuvre is better executed downwind. The abrupt change in direction will show up any lateral balance issues on the model, and care must be taken to re-apply power smoothly if you want to avoid torque reaction in the rolling plane. With practice you can add full aileron at the same time as the initial pull, to snap into a Harrier position.
A Terminator is an over-pulled Wall, starting with the model heading straight at the floor on a vertical line; the Wall is simply over-pulled to raise the nose back to the vertical and into a Hover or Harrier.
Step 6: Blender
Sometimes referred to as the Spin Cycle, Panic or Somenzini Spin (so named after Chilean Tournament of Champions pilot Quique Somenzini, who first wowed judges with it during 1998), this manoeuvre is now more commonly known as the Blender (see Fig. 3).
Still considered by many as the ultimate wing test manoeuvre, the Blender sees the model enter a diving roll, with increasing airspeed turning the model into a blur for a few seconds as the roll is transformed into a ridiculously high-speed flick held in by the pilot. This transitions into a graceful, flat inverted spin that top pilots will take to almost ground level before the exit. Its a visually violent manoeuvre, but after performing many (some with models you wouldn't think capable) Ive yet to see a wing let go.
I doubt there's that much force on it really, as its the rotational speed that's high and not the airspeed. You'll be much more likely to lose a tail in my opinion, unless your model is a big 'un. To fly the Blender, start with lots of height. Throttle to idle and push down to vertical so that the model is diving. Add some left aileron to initiate a slow-ish roll, and then after two or more full rotations with the model going like the clappers, quickly add full down elevator and full right rudder. The aeroplane will violently snap to an inverted spin and the descent will momentarily stop.
At this point, if flown with sufficient speed, the model should turn into a complete blur. If you have confidence in your model try adding full throttle as you snap to the spin! After the violent snap the aircraft will settle into the spin but you may have to juggle the power to keep it flat. With a rearward C of G and a suitable model you can even begin a slow spin back upwards whilst inverted!
Step 7: Knife-edge Spin
Also known as the Hanno Screw, this spin in knife-edge was popularised by many times World Aerobatic Champion Hanno Prettner. Its a difficult one to do right but is not restricted to 3D models alone (see Fig. 4).
Entry is key, which needs to be deeply stalled in a knife-edge attitude unless you have massive control throw authority to bully the model into place. Prettner would enter this manoeuvre by flying knife-edge to the stall, but Ive found it quite reliable to enter from a stall turn, catching the model with instant opposing rudder once its rotated through 90° to the full knife-edge position.
Again a rearward C of G will assist in keeping the wings dead vertical, as opposed to sweeping a cone with the upper wing tip as the model descends. A good amount of juggling with the aileron is also required, as too much throw on powerful ailerons can overcome the rudders effectiveness and flick the model out into a conventional spin. To fly the knife-edge spin, climb to the desired position, taking note that the model will descend very quickly. Stall turn to the right with zero power and at 90° catch the turn with full opposite rudder briefly before adding full down elevator and some level of power to bring about the rotation.
A little leading aileron may be required to start (to the left in this instance), but management of this and the throttle will keep you in the spin. A full release of the controls will recover the model into diving flight, but as with the Blender, a fast snap to a slowly rotating flat spin can look most effective.
Step 8: Waterfall
The first person I ever saw fly this was Glen Fletcher of Glens Models, who had stripped large amounts of airborne weight from his popular 1/3 scale CAP 232 design. During this manoeuvre the model flies a continuous, negative g, tail-over-nose descending flip that gives it the appearance of rotating around its canopy whilst the wings remain level. Very careful use of elevator and throttle is required to get it right, and you need massive elevator control throws and a C of G pushed rearwards to its limit. The tumbles are performed consecutively by bringing the model into the hover before adding extra power and using 3D down elevator throw.
Directional management is achieved in part by the rudder, especially through the low-speed inverted portion of the pattern, but correct lateral balance is a must (as are equal elevator throws if two servos are used). Each flip is complete when the model rotates back through to the hover position once again. How low you want to bring it will depend on your confidence in avoiding a flick through over-exuberance around the bottom arc of the manoeuvre.
The Roller Coaster is a variation on the theme, swapping from full down to full up elevator repeatedly as the model descends without actually pulling the nose back up to the full hover position.
Step 9: Hover
Whilst it might look simple enough, a good Hover (or prop hang) is perhaps one of the trickiest manoeuvres to master. Its also a staple feeder for many of the other flight patterns we've discussed so far, and either leads into, or quickly follows, almost all other manoeuvres in a flowing 3D routine. Still emphasised by smoke, streamers and in some cases even fireworks, the hover once captured the imagination but has had so much exposure that its become pretty boring to watch.
The Hover sees the model held in a vertical attitude, using the power of the motor and all flight controls to hold it steady. No part of the airframe is flying at all, and the thrust from the prop is the only motive force. Steering and correction is provided by prop wash only, and with practice, less and less control input is required as the pilot pre-empts the fall of the model from the hover to correct its attitude before it gets too far out of shape. Large or very light models with large control surfaces are usually the most capable, but the key is lots of motor power.
Its essential to have some in reserve to climb out from the hover, or at the very least check a slow descent backwards. Whilst Shock Flyer type designs can be pulled straight into a hover from a Wall, many pilots will settle the model into a low and slow Harrier, steadily increasing the angle of attack until the model is vertical and hanging on the prop. You'll probably never reach a throttle point where the aircraft is stationary along the vertical axis, and fine throttle control from a reliable engine is essential.
Steer the model using the rudder (many will benefit from a little right rudder and right aileron held in to counteract torque), and if the hover is belly in, remember to move the rudder stick towards the dropping wing to correct the drift. Be prepared to back the model into the floor in the early stages of learning this manoeuvre; a high-level Hover has virtually none of the impact of a low level one with the rudder tapping the floor. There is one variation on the Hover: the Pogo, which describes a Hover that continually climbs and descends.
Step 10: Torque Roll
Our last manoeuvre to be studied, the Torque Roll is an extension of the Hover, whereby the model rotates as a reaction to the torque from the motor. Whilst the speed of rotation can be affected by small aileron inputs, good rudder control is essential to prevent the model from wagging off the vertical line. Try to use the elevator for correction when torque rolling, though a little extra upthrust on the motor can help hold it steady.
Perhaps the easiest way to dial into the torque roll is to enter from ever-decreasing circles flown in a nose-high, upright Harrier. This way as you near the Hover position you'll already be using the rudder for directional control coming towards you and wont suddenly have to switch into this thought process. 3D models needn't be expensive, this Multiplex Acromaster is a fine little aeroplane. With practice, just as with the Hover, the Torque Roll can be used frequently in a circuit or pattern for maximum effect. This is much easier to achieve on a calm day and with a good element of shallow pitch on the prop.
Step 11: Go Fly!
So there you have it, a hatful of 3D manoeuvres that will test your piloting skills to the max. Hook it all together and the results can be spectacular. All you have to do now is practice!