Taildraggers © Chief Instructor
Verfasst: Mo 26 Dez 2016, 08:30
If I may make a little contribution here… Hopefully some of you who are finding the Spit, Dora, 109 or P-51 a bit of a handful during take-off and landing, may find it useful!
What do I know about it? Well, I have spent a significant proportion of my professional flying career teaching both experienced and novice pilots how to fly and handle tail-dragging aircraft. This amounts to several thousand hours of tailwheel training alone, though who’s counting! These aircraft include among them modern high performance aerobatic aircraft and a variety of more vintage types from DH Tiger Moths, to Harvards. I can’t recall off the top of my head exactly how many students I’ve worked with over the years, but it’s well over 200! Best of all, they have all gone on to fly extensive tailwheel ops in a variety of types and to the best of my knowledge, only 2 of them have crashed anything since!
As a significant number of pilots here are expressing difficulties with tailwheel handling, particularly with the early access (and quite wonderful) Spitfire now being available, I hope that my experience of teaching real pilots to overcome these challenges may be beneficial to some here. After all, the majority of difficulties being described are exactly the same as you’d encounter in the real world, and therefore, most of the solutions and techniques used to overcome them are also highly applicable. A real testament to the fidelity of the DCS offering.
Having read all of the comments on the new Spitfire forums here, as well as most of the other forums, I wanted to reassure those of you who are finding the ground handling difficult, that what you are experiencing is quite normal and to be expected. I’ve read several posts which question the overall difficulty levels involved and how they are modelled. Some suggest that the DCS Spit (and other TW aircraft) are perhaps too difficult. On balance, I think that they are pretty representative of what real world TW ops are like, and here’s why…
Firstly, the behaviour of a TW aircraft on the ground is fundamentally different to that of a “nosedragger” aircraft. This is because unlike a tricycle configuration, a TW aircraft is positively directionally unstable. This describes a condition where the aircraft wants to turn left or right on the ground, whilst the effect is almost exponential in its manifestation. In contrast, tricycle configurations are almost all positively directionally stable; meaning that any tendency to turn left or right on the ground will, for most part damp itself out until its directional tendency is to remain straight.
The reason for this is simple: A TW aircraft’s C of G is behind the main wheels, where a tricycle aircraft’s C of G is in front of the main wheels. Once the aircraft has kinetic energy and is in motion, the C of G (the point where the aircraft’s mass acts) will always want to “lead” the aircraft. Or, better put, it will want to overtake the point of the aircraft where most of the directional influences are concentrated, which is usually the point of contact with the ground. I.e. the main wheels. There are numerous factors acting on the airframe which will cause it to either swing left or right when it is in motion. Some of these forces will act to make the aircraft swing left and some to make it swing right. Some of them are strong and some are weak. Some of them increase with ground speed and/or airspeed, and some decrease. In addition, some of these forces act together and multiply their combined effects, and some cancel each other out. The overall effect is that in some form or another, the aircraft WILL want to swing one way or another. Indeed, during one part of the take-off or landing roll, the tendency to swing left or right may reverse depending on what direction the lack of equilibrium is strongest at any particular point.
One of the greatest challenges facing pilots who are new to this is knowing instinctively what control inputs are required to maintain a straight roll. An important point to remember (and the one which causes the most difficulty) is that to be successful, it is essential that corrective inputs are made decisively BEFORE the motion they are correcting has developed. This is because of what I described earlier – namely that swinging moments develop at an almost exponential rate. In a nutshell, the control input required to cancel the first split second of a swinging moment is a fraction of that required to cancel the same moment once it is fractions of a second more developed. Simply put, if you cancel a developing swing to the right at 0.3 of a second after it starts, it may only require the smallest and shortest of touches on the required control [*usually we’re referring to the rudder here, but ailerons do play a part.] However, if that same swing is allowed to develop for a full second, the chances are that it will require a far greater rudder deflection to counter it. Probably 2 or 3 times the magnitude.
Now, here’s the real crunch point… You must learn instinctively both the required magnitude of the input that is required (i.e. how much deflection) AND importantly, what duration that input should last for. In nearly all cases, the single most difficult thing to master is modulating the duration, as this tends to have a direct effect on the magnitude, more so than the other way around. The phrase “dancing on the rudder pedals” is often used to describe the kind of control inputs required. Indeed, I recently read a post where Wags said just that, and it’s a doctrine well worth embracing. This describes a situation where you are making instantaneous and very short duration inputs, both left and right in a manner that almost predicts the swinging motions before they actually happen. For the reasons explained above, if you can “kill” a swing the instant it starts, or even better, before it starts, then by definition it will only require the smallest of inputs over a very short duration. By that I mean fractions of a second. If you are having to apply large deflections to counter a swing, then you are behind the situation.
The reason why this then leads to the inevitable loss of directional control is because every input you make WILL have an effect directly proportional to its magnitude and duration. The later you leave your response to a particular swing, the longer the effect of that control input will take to manifest itself, but it WILL happen. This makes the next movement even MORE difficult to predict and after several cycles, the chances are that the swinging moment will have exceeded the control authority of the rudder, meaning you’re going for an early shower.
Everything that I’ve described here is somewhat different to the control sequences required to keep a tricycle configuration straight. Firstly, lateral directional stability is convergent, so the timing is less critical because the deviation from your intended path will not (in most cases) increase in rate. So, as long as you eventually steer the aircraft back to the correct path, it will just follow in a predictable and stable manner. This is fairly easy to master because it relies more on a cognitive response from the pilot, and one which is fairly forgiving, allowing time for the pilot to assess the deviation and make a conscious decision as to what control inputs are required.
Response inputs in a directionally unstable aircraft are less instinctive and require a far greater element of “motor skill learning”, particularly as to be successful, you have to be able to predict what the aircraft will do next and react preemptively, rather than retrospectively. Motor skills take more time to learn. They need to be hard coded into your hands and feet and this takes time. Though some element of natural ability will help, it will at best only reduce the time taken for your motor responses to embed themselves. It will NOT shortcut the process. Therefore, no matter how much you understand it (though it helps), and no matter how much you beat yourself up to do better, everyone will have to put in enough cycles to nail it, because it is not a skill we come blessed with by default.
Is it more difficult in DCS than in the real world?
For those who doubt the validity of how DCS TW aircraft behave, and the difficulties they simulate, I can say with some authority that they are pretty much spot on. Therefore, the problems being described on these forums are also very much representative of the real world. The thing that sets DCS apart from other PC based simulations, and a number of commercial simulators, both leisure and certified which I have experienced, is that so many of these factors deemed undesirable in the real world, are faithfully modelled, along with the challenges they bring.
I have read a number of contributions which ask the following question:
“Is it more difficult in a fixed base simulation such as DCS because you can’t “feel” the physical movement of the aircraft?” Well, you may find it surprising but my answer to this is a fairly emphatic “NOT REALLY!”, and here’s why…
As we’re talking about the specific difficulties associated directional control on the ground with tailwheeled aircraft here, a very significant factor comes into play. According to what I’ve described previously, the only ideal response to a directional deviation is to counter it either prior to, or, immediately in response to its initiation. At this stage, there is so little lateral acceleration as to be usefully perceptible through the “seat of the pants”. In real life, if you’re responding to that said lateral movement at the point where you can really feel it, you’re way behind. This is particularly the case because in the real world, where those sensations are also being combined with other movement sensations from the airframe, ground and air, which can have the effect of masking or even confusing what you are feeling, especially in lighter weight aircraft.
Of course, if you ARE responding that late to a swing, however successfully or otherwise, the fact is that the deviation in question is now easily perceptible visually, regardless of how much you can actually feel it. Therefore, in a fixed base simulator, your eyes have already told you something needs your attention, provided, that is, you’re looking in the right place!
This is especially true if you’re lucky enough to be flying in VR. The added depth perception and more lifelike peripheral visual cues are more than adequate to detect movements as they develop. But remember, the most important thing is to be ahead of the aircraft before it deviates that far. Of course, there are many other differences in the experiences that both real life and simulation can offer but my belief is that most of those differences are not so fundamentally influential in the context of this subject, though some may be more so in other aspects of flying. One other obvious difference is control force and feedback, though in the phase of flight we’re talking about here, the feedback element is less useful and the force element can be “tuned out” to a great extent by using control curves.
I can’t emphasise this enough. You need to “dance” on the pedals… Like you’re tiptoeing over hot coals in bare feet. Trying to make the tiniest, quickest movements you can before getting your foot off again. Most pilots new to tailwheel aircraft, particularly those with extensive tricycle experience (which probably accounts for most people here) are programmed for making long smooth pedal inputs during the ground roll. This I liken more to wading through deep mud in wellies, rather than dancing on hot coals! It simply won’t work, though your instincts may be very persuasive in telling you otherwise. After all, it’s what you’re used to! I can’t explain just how you reach the point where you instinctively know what’s coming in time to make these tiny, fast and decisive inputs. I can say however, that if you practice the correct technique, with the right mind-set and an understanding of what is happening, you’ll get it eventually, but for most humans it will take a lot longer than learning to control a tricycle. It’s simply a very different type of learning, both physically and mentally.
In summary, here are a few pointers:
1. There are an almost infinite number of things which will cause a swing. Engine torque, asymmetric prop effect, prop-wash, asymmetric ground resistance, wind, slope, gyroscopic effects, control asymmetry, and of course pilot input! These are just a few of the significant ones but remember, they can combine in any number of ways to produce numerous effects. The only thing you know for sure is that it WILL swing at some point.
2. The earlier you respond, the more instantaneously your input will take effect, requiring much smaller inputs and therefore, much fewer counter inputs. Over-controlling is one of your biggest enemies and becomes more likely as your inputs increase in magnitude and duration. Remember, if you’ve put in a large boot full one way, the chances are that it’ll take some time to be fully felt, by which time you’re focussed on the next movement. Then, it’ll be too late and it’ll get you! If you’re on top of it, there should be no need to make anything other than very small, very short inputs.
3. Some swinging tendencies ARE predictable. Use this to your advantage! If you can remember how increasing power makes the aircraft respond, you should be countering that motion in anticipation and stopping it before it happens. Similarly, experiment with setting the rudder trim to lessen the effect of whatever is causing the most significant swing at the beginning of your roll.
4. Primary causal factors vary according to ground and airspeed. For example, the gyroscopic effect of raising the tail during take-off, or lowering it during the landing roll, will be more pronounced at lower airspeeds because you have less aerodynamic control authority. Similarly, increasing the power causes torque effects which in turn cause a swinging moment. However, with increased power comes increased slipstream effect from the prop and therefore, greater rudder authority to deal with it. DCS models this effect very well. My advice here is to be confident with the application of take-off power. The key is to get take-off power set promptly but as importantly, smoothly. Again, use your experience to preempt the effects before they cause problems. Do everything SMOOTHLY and CALMLY.
5. The left swinging effect of engine torque and the ground interaction as a result can be countered with the application of right aileron during the take-off roll. However, you must be proficient at modulating this input as aileron authority increases with airspeed. Failure to do so will only result in a swing and/or roll in the opposite direction, which you may not be expecting. Overall, that may add to your problems rather than helping, so experiment with applying right aileron and holding it prior to starting the ground roll, OR starting neutral and feeding in some aileron immediately prior to the torque causing a swing. There’s no right or wrong way here, it’s down to what works for you.
6. RELAX! It’s a physical fact that when your muscles are tense, you can’t make quick accurate and short inputs. This is a major consideration because the nature of the scenario makes you tense and it’s difficult to counter that! It’s so important though. Before you start your take-off roll, chant a little mantra to yourself… “wake up feet! Wake up feet! Wake up feet!” Do this while doing a little light dance on the rudder pedals. It may sound daft but subconsciously, it will focus a little bit of your brain on the job in hand. It will also help to relax your muscles which have probably already tensed up without you realising it. Do this on final approach to land as well. It helps!
7. SIT BACK IN YOUR SEAT! When faced with a situation that you perceive as being difficult, your tendency is almost always to lean forward and focus on what’s immediately in front of you, effectively narrowing your field of view. Believe me, I’ve seen pilots almost planting their faces in the panel as workload increases. It’s just what we do but the effect of decreasing your field of view and by definition, your peripheral vision, makes detecting lateral movement very much more difficult. It also has the secondary effect of re-tensioning your muscles, something we want to avoid!
Does VR help?
VR technology is still in its early stages of development. However, if you’re are lucky enough to have an effective VR rig that works well, use this to your advantage. The sensory effects gained through vision are much underestimated and VR’s increased depth perception and peripheral cues are singly more persuasive when it comes to movement perception than many physical movements. That might sound far fetched but it is true. Evidence to support this is in the large number of people who appear to experience motion sickness when using VR. Counter intuitively, motion sickness is poorly named and is not a direct result of motion, rather it’s a physiological response to conflicting sensory stimulation. The fact that these effects are so readily triggered by the use of visual equipment alone is a powerful demonstration of just how much we rely on our visual senses to make sense of our surroundings, both on a conscious and subconscious level.
I hope that some of this helps to ease your concerns and to develop the right technique for enjoying the DCS taildraggers. Just remember, if it’s not working for you, the very worst thing is frustration. It will numb your senses and be highly detrimental to your motor skills. The best thing you can do is take a break and do something else for a while, then go back to it. You may have to do this quite a few times over several hours, days or even weeks. If you do though, I can almost guarantee that at some point, you’ll come back to it and it will just click into place. When it does, you’ll wonder why it was so difficult whilst enjoying a whole new aspect of your simulator.
Don’t underestimate the cognitive complexity what you’re teaching yourself to do, and don’t fall into the trap of assuming that handling a taildragger on the ground is just another component of what you’re already used to, because it isn’t. It’s an entirely new skill, almost independent of all of the other skills you’ve amassed. It’s a new skill that’s as difficult to master (if not more so) than all of the other things you’ve had to learn and it’s going to take some time. Of course, there is a simple way to shortcut all of what I’ve said… Start your missions in the air! You’ll be missing out though!
If you’re interested in some further reading and to add more detail to what I’ve written here, I can’t recommend this book highly enough. I used it as my tailwheel teaching bible for many years and it’s as relevant and helpful today as it was then: https://www.sportys.com/pilotshop/th...ger-pilot.html
Happy ground looping!