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Jan 25, 2017, 01:14 PM
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Here's an interesting Read ..... Phillip Steinbach on aerobatic Aeroplane design


A lifetime RC modeller talks about state of the art fullsize design - interesting stuff !

GB1 GameBirdWhy do modern aerobatic aircraft look the way they do?With an RC model, you´ve got endless options: engine, size, weight, shapes, all can be as you want. It takes an idea, some work and off you go. Best way to learn and to try new things.Model aerobatics are clearly leading the way, at least in Freestyle.Add people to flying machines, and the amount of options for designers gets less:There are pretty much only 2 engines to choose from if the machine is supposed to have sufficient performance for unlimited competition (Lycoming AEIO 580 and M14 radial).Persons require space, add weight and come in all shapes and sizes (but pay, so make sure they feel comfortable sitting in the airplane!) Cockpit design and ergonomics and engine choice are pretty much the starting point. Once you´ve decided how many people (one or two) should be propelled through the box by which engine, the rest is a matter of how many you want to sell and to whom, size of the development budget, plus talent, experience and persistence.It is also important to make sure the design can be produced economically and that the design meets whatever regulations apply so that it may legally fly.I’ve been working at Game Composites the last two and a half years. At Game Composites I have the privilege of working with the best team I could wish for. Building the team is one of the key factors to make such a long and intense project work. Our work has been exclusively focussed on designing and building the Gamebird GB1. The GB1 is a two seater. The front seat opens the market to more people than the few hardcore aerobatic competition pilots, and the GB1 is meant to be used for Unlimited aerobatics, training for all levels, as well as upset recovery training, flying cross country for a nice weekend trip and just pure fun of course. For those 2 people inside, a GB1 offers speeds in excess of 200 kts and 1000+ nm range, at the cost of a Cessna 182. We have put a big effort into designing the control system and cockpit interior to make it comfortable for different sized pilots and passengers. For the engine, we have chosen the Lycoming AEIO 580 engine because of its reliability and certification, and its lower frontal area provides significantly higher cruise speeds than a radial engine.Speeds are higher than on model aeroplanes, which brings things like flutter into the game, and aeroplanes need some bigger tanks than models, because they don´t fit most cars, and hey, cruising around at 200 kts is the next best thing to aerobatics!Control surfaces are actuated by one human arm, which requires some careful design, again for a speed range from zero to 230 kts. Given that an aileron produces about 1 ton of lift when deflected at 230 kts, and stick forces between 5 and 10 kg are considered acceptable, provides an idea of the margin. Not a lot. Better get it right or it won´t win, and won´t sell.Building huge control surfaces like today´s shock flyers (without hydraulic or other assistance) would simply not be controllable for any lesser human than Arnold Schwarzenegger.Another detail easy with models is stopping motions: let go of the transmitter sticks, the servos centre, done. Once you sit inside, the only neutral position is fed back from aerodynamic forces which need to be balanced for a human arm as mentioned above, but a linear force increase over deflection means zero neutral position, so you could never let go of the stick when flying cross country, and stopping rolls would be seriously difficult.For the GB1 we spent 3 months on aileron design alone, and we are still doing final adjustments during flight test. The wing shape was chosen as a function of area required, desired roll performance and damping, and sensible aileron size. Airfoils are custom, to allow high cruise speeds, precise snap rolls and at the same time providing room for a sizeable spar.For neutral rolling, a midwing aeroplane with symmetrical fin would be ideal, but where do you put the legs of the people inside, and how are they supposed to see the runway?The GB1 is a low wing aeroplane, and because of the lack of servo neutral, this is not a disadvantage at all. View from the cockpit is great!Centre of gravity is ideally no more than 3% forward of the neutral point for maximum pitch authority and stick position while changing speeds in lines, but this leads to marginal pitch stability, which is not nice for cruising. Changing the CG is therefore a good idea, also depending on the experience level of the pilot. As pilots differ in weight too, and these engine do like to burn fuel, the CG is even moving from flight to flight, more than on model aeroplanes. To allow for CG flexibility, the GB1 features a water tank in the tail, which can be drained in flight.Weight versus strength: Models can be built with insane power to weight ratios. So far I know of 2 aerobatic planes capable of accelerating out of a hover, both of which are one-offs and not really made to be sold (the Turbo Raven and the an M-14 equipped Sbach).The GB1 prototype, with full two-seat equipment, is targeted to be as light as the best certified single seat aerobatic plane on the market today, while having a wider envelope, i.e. higher speed to fly manoeuvers. This has not happened by magic or just leaving things off, but by 2 ½ years intense work of engineering, testing and planning.Achieving excellent handling, lower weight than anything comparable before, better performance and at the same time making sure the aeroplane can be produced with a profit nearly automatically leads to the shape the GB1 has taken. There are very few lines left which leave room for styling. Every line and shape has its purpose can be explained by rational reasons, from the cowling inlets over the canopy and wingtips to the shape of the rudder. Form follows function is the guiding design principle.The list of work goes on: after the initial layout tool design follows, production drawings for each part and finally the construction of a prototype.The first part for the GB1 prototype was build early December 2014, the first flight happened July 16 2015.All the assumptions are worthless until proven by tests, which get more detailed if the aeroplane is meant to be sold, and therefore certified by regulatory agencies, the FAA in the US and EASA in Europe for example.- Fatigue test to make sure even a 30 year old aeroplane is safe, regardless where it is kept, ultimate load tests for all structural components (ultimate means the chosen safe load determined by load assumptions / calculations, multiplied by a safety factor)- Ultimate load tests with every structural component- Ground vibration analysis to make sure the aeroplane does not flutter- Landing gear drop test- Emergency escape test- Tank pressure tests- Crew harness attachment point tests- Electrical system test and load analysis- Control system test- If composites are chosen, a material qualification program: make a metal aeroplane, buy aluminium sheets with known properties. Use carbon fibre and resin, and you have a lot of ways to do it right, but even more ways to get it wrong. This program shows that chosen materials and procedures are stable and capable of doing the job.- Flight test: Aerobatic aeroplanes are mostly defined by their flight characteristics and performance. Everything has to be tested and documented. There is a book describing acceptable characteristics, which is there for a reason and should be followed. When there is a good and safe reason to deviate from that book it can be discussed with the authority, but so called an “equivalent level of safety” has to be shown. For example, if the aeroplane has a rather sharp stall, because it is meant to snap roll easily, the mitigation could be excellent slow speed controllability and good acceleration out of the stall.All of these things need to be tested and written down, the reports will get checked and before a new aeroplane can be sold, everything has to be accepted by the regulators. It has to be said, that any of these rules are based on accidents. Ignoring or bending any of them bears the risk of writing that rule again with new blood, which will not help selling more aeroplanes… Customers, regulators and insurers don´t like crashed aeroplanes. The GB1 will be certified in Europe and validated in the US simultaneously, which means we do work with both agencies in parallel. Type certification may imply some compromises over a pure aerobatic design, but it does provide a huge level of safety and security for both customers and manufacturer and therefore makes a better and safer aeroplane.Personally, I enjoy building and flying model aeroplanes a lot, I started when I was 6 years old and never stopped since. It allows experimenting at no personal risk, it helps understanding flight mechanics (spin behaviour, stall characteristics, stability and even most performance parameters are scalable) and it helped me to imagine my full scale flying from a judge´s perspective.But, sitting in one of these awesome modern aerobatic aeroplane, feeling the speed, agility, the G´s, and being able to make some acceptable flights after lots of training is the best thing I´ve ever done with pants on. Period. It is worth every minute of the intense work. I cannot imagine a more interesting and satisfying job.The GB1 has been designed and is now tested to be produced and sold, I hope that it will bring a lot of fun and the joy of aerobatic flying to a lot of people…watch this space!Philipp Steinbach's photo.
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Jan 25, 2017, 09:47 PM
Modeling Retread
I know this kind of a school marm type of thing but this is almost impossible to read. You need to break it up into smaller paragraphs. The added white space eases the strain of reading. If you cut and pasted this you may have lost the readability formatting. That's common for these types of forums. Extra line feeds need to be added by the poster.


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