AEROBATIC SCENE, JULY ’21: PRECISION AEROBATICS

AEROBATIC SCENE, JULY ’21: PRECISION AEROBATICS

Adrian Harrison and Phil Lewis with their BJ Craft Epilogue and Skyleaf Leader and enjoying being back flying at a recent training session.

Keith Jackson returns with more F3A flying news. Additional pictures by Robin Trumpp, Adam Debowski, Thomas David, Kevin Caton.

Its great to be finally back flying! I wasn’t really sure about this until I attended an impromptu flying session at Hurley the other week. Even then it was only until eight flights into this that I realised that I’d actually really missed being able to fly F3A.

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Close up of the new BJ Craft Epilogue.

Also attending were GBRCAA members Adrian Harrison with his new BJ Craft Epilogue and Phil Lewis, whose Skyleaf Leader complimented my own Leader model. Phil’s model was powered by the new version of the BJ Craft X Drive with the latest Force motor, which has to be said had more than enough grunt in the stiffening cross wind conditions.

GOLFBALL ERROR

Unfortunately, I have to start this issue with an apology as I made a big error in my last article and included the wrong manoeuvre image for F21-01 Golfball. The image printed was from the F15 schedule, which, as shown, starts with a 45° pull up. The version of the Golfball used in F21 is quite different and starts with a 3/8 pull to an inverted climb. The two versions are shown in here, along with alternate versions which are also allowed and includes the rolls being positioned off centre.

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F-15.03 Golf ball compared with F-21.01 version.

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Golf ball versions with rolls performed off centre.

It is clear the F21 Golfball can appear quite different but still be acceptable under the FAI rules. At first the F15 Golfball appears to be much smaller that the F21 version. However, for the Golfball there is no requirement for the 3/4 rolls to be performed on centre, just that they are centered within the line in which they are flown, and this is consistent with the general principals of F3A.

ROBIN TRUMPP TSAR

As promised here are some more pictures of German pilot Robin Trumpp’s new model, the Tsar. This is a fully moulded monoplane designed by Robin but constructed and painted in base white by Falcon in China.

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Top German F3A pilot Robin Trumpp with his Tsar monoplane design.

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Vinyl wrap was used very effectively to add colour to the Tsar.

Robin has added his new colour scheme using pre-cut self-adhesive vinyl, similar to that used in car wrapping, thereby avoiding the onerous task of spray painting. The effect is simply stunning and shows real innovation in what to many is an almost insurmountable task due to health and safety issues.

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Underside colours of the Tsar will provide plenty of contrast. Sadly, no retracts on the production model.

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Radio installation in the Tsar.

The Tsar has a wingspan of 1700 mm and overall length of 1990 mm. All up weight using a Hacker TopFuel 5100 mAh LiPo was 4650g. The installation uses a BEC for radio equipment power and a Jeti Receiver Voltage Protector AddCap 10AS helps smooth the supply voltage during periods of high current draw. For propulsion Robin uses the E-factor E-F-506 contra drive system turning Falcon 22” propellers.

GBRCAA TRAINING DAYS

In 2020 the GBRCAA planned a monthly series of training days to allow members to fly together at the BMFA National Centre at Buckminster without the usual pressures of a competition. This allows pilots to practise individual manoeuvres, positioning within the aerobatic box, keeping constant baseline (the bottom height of manoeuvres) and depth (distance in front of the pilot) etc., all of which contribute to a high scoring flight. The pandemic curtailed our plans and, in the end, we were only able to run two sessions.

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Pilots and models attending the recent GBRCAA training day at Buckminster.

This year (2021), after a late start due to the third lockdown, we resumed the training days in mid-April. We had a full turnout of 12 pilots with different levels of experience, although all had flown in competitions before. Even though it was only a couple of weeks after club flying had started again in the UK it was clear that many pilots had been taking advantage of the relatively calm and dry Spring weather and had been flying as much as possible. Some smooth and accurate flying was evident but under the watchful eye of other pilots everyone was able to take away a few pointers for improvement to work on before our next session.

The format of these days is that each pilot makes three or four practice flights, observed by fellow pilots. Being watched by your peers sharpens the mind a little and everyone can learn from the experience of others. Also, we are able to train new judges at these sessions.

The Buckminster site was in excellent conditions thanks to the work of the site staff and we now have the benefit of permanent ground bases for quickly installing the centre and box end markers that the BMFA have provided for the use of ourselves and the pylon racers.

Our National Centre is certainly a place of excellence and well worth a visit for all model fliers. As well as the GBRCAA Training Days there are also Introduction to Aerobatics days for newcomers run each month at Buckminster so there is something for all skill levels. Anyone wishing to attend any of these events can enrol via the GBRCAA forum.

THE FAI

The FAI is the world’s governing body for air sports. In case anyone wonders who devises competition rules and manoeuvre schedules, I’ll give a quick description of how this is managed internationally.

The Federation Aeronautique Internationale (FAI) is based in Switzerland and is recognised by national aero clubs as the governing body for all air sports, particularly competitions and world records. In the UK our national aero club is the Royal Aeronautical Club and management of model flying is delegated to the British Model Flying Association.

The BMFA generally follows international rules for competitive classes and sends teams to world and continental championships. Each class of model flying has international rules, which are managed by a subcommittee drawn from experienced practitioners across the world. Rule proposals from these subcommittees are then voted on at meeting held every two years for each class, with each country’s national aero club representative having one vote. Not every country has a member of a subcommittee, but every country gets a vote.

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New UK delegate to the FAI F3a sub-committee, Kevin Caton with his Skyleaf Leader.

The best way for any country to have a say in how things are run is to have a member on the subcommittee, so I’m pleased to report that after an absence of over 30 years the UK now has a member. Kevin Caton, one of our top international competitors for many years, is now on the F3A subcommittee and can give us a voice in this important forum. This is something that other classes of model flying in the UK have enjoyed for a long time and I’m sure it will be of benefit to us.

TMCR 21 CONTRA DRIVE

This is the latest version of Adam Debowski’s Twin Motor Contra Rotating (TMCR) drive, having been developed over several years and used very effectively by pilots within the F3A community.

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TMCR-21 contra rotating drive by Adam Debowski.

Weighing just under 600g, the drive features two motors running in opposite directions and mounted on two concentrically aligned shafts. The front motor unit drives the rear propeller via the outer shaft and the rear motor drives the front propeller by the longer, thinner interior shaft.

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Schematic of the TMCR.

The unit is supported at the back using a fixed mounting in between the motor units and also using a sliding mount at the front. The beauty of the sliding front mount is that it just requires the two bolts on the fixed mount to be removed and the whole unit can be removed by sliding it backwards. This leaves the front mounting in the fuselage and doesn’t disturb the unit’s alignment in the model.

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Rear motor view of the TMCR.

Each motor typically draws up to 40A and manages to drive a Falcon 23″ x 20″ propeller at 4300 rpm, which is right at the top of the performance range for current contra drives. The large, open aspect of the motors allows plenty of cooling.

The most important feature of this drive, however, is the reduced Gyroscopic force, typically associated with large diameter outrunner type motors, which can have large effects on the tracking of our F3A models. As neither motor is mechanically connected to each other, aerodynamic load sharing between front and rear propellers is achieved by a careful choice of propeller diameter and pitch.

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TMCR on the scales! Sliding front mount also shown.

Control is via two 60A ESCs, which utilise the same braking control as the excellent D3 controller that has made such a big impact in the F3A world. A single 5100 mAh 10S LiPo is used to feed both ESCs.
More information on this drive can be found on Adam’s Facebook page or via email: adam.debowski@d3motors.com

FLIGHT COACH

I first came across this system at the 2019 Triple Crown, held at the Carron Model Flying Club in Ireland. English team member Thomas David was developing it at the time and recording the geometry of his practice flights, along with flights from other competitors who dared to give it a go!

Since then, the Flight Coach has been further enhanced and released as a free to use tool for any pilot wishing to look at recording their flight data. The recorded data is used to provide a geometric display of the actual flight on a computer. The ultimate intention of doing this is compare the individual manoeuvres in the model’s flight as it progresses through an aerobatic schedule, against perfect manoeuvre shapes. The benefit of doing this is to provide objective feedback to the pilot on how their model actually flew through an aerobatic schedule.

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A recent realisation of the hardware required for the Flight Coach, configured and assembled by Phil Lewis. Power comes via the balance lead from a flight pack LiPo.

Having your flight displayed on a screen completely removes the discrepancies between what the pilot thought he did with what he actually did! Reality, it can be said, is rarely comforting! However, using the Flight Coach should allow the user to address repetitive errors in their flying and hence lead to a better presentation.

The following article was written by Thomas and I hope to assess the Flight Coach for myself in a subsequent edition of RCM&E:

The precision aerobatic competition disciplines involve a pilot controlling their aircraft through a series of predefined geometric shapes. The accuracy with which the aircraft describe these shapes is assessed in real time by a group of judges. The approach is very similar to that used in sports such as gymnastics and ice skating. A common frustration for competitors is with the consistency and reliability of judging. In recent years many competitive sports have increased the amount of autonomy in their scoring systems; a well-known example of this is ‘Hawk Eye’, which can be used to replace the line judge in tennis.

For some time, I have been working on a project which has the potential to do the same for precision aerobatics. The idea is to fit a ‘black box’ type device in a competitor’s aircraft to record its position and orientation, and so provide post flight feedback and eventually even automatically calculate scores for each manoeuvre.

The first part of the project has already been solved and made readily available by the UAV industry – you can buy the flight logging hardware for under £100. There are also many plotting tools but most of those currently available are not tailored towards aerobatic flights. The first publicly released part of the project has been developed by Artur Uzieblo in Australia and fills this gap. This is called ‘Flight Coach’ and is free to use on our website www.flightcoach.org. The final step is to identify and score the flown manoeuvres, this is the part I’m working on and this is still in development.

The Hardware

There are a number of setups that have worked well for us and these are described in detail on our website www.flightcoach.org. The hardware consists of a GPS and Magnetometer feeding into a flight controller which adds inertial measurements and then combines all the readings to generate an accurate estimation of the position of the aircraft in six directions.

The advantage of this approach over GPS only systems such as the Jeti MGPS is that we get orientation as well as position data. Additionally, the fusion of inertial sensor data with the GPS provides a far more accurate and higher frequency position trace than the GPS alone can provide.

This data is stored onto a flash memory card, which is removed by the user to download the measurements onto a PC, whereupon it is processed by the Flight Coach plotting software.

The Plotter

The Flight Coach plotter is available on our webpage as a web application to run in your internet browser. It reads the binary data recorded by the flight logger and generates a ribbon plot, so you can see the position trace of your flight in 3D as well as the roll angle. It also gives handy tools to display subsets of the flight so you can look at single manoeuvres or groups of manoeuvres.

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Playing back P21.08 Shark Tooth with two 1/4 rolls using the Flight Coach plotter.

You can also playback the flight so a representation of an aircraft will follow the flown path against a schematic of the aerobatic flying area, otherwise known as the ‘Box’.

The initial release of the flight coach plotter has caused quite a stir within the F3A and IMAC community. As far as I know at least five of the top 10 pilots at the last F3A World Championships are already using it.

Automated Analysis

Developing tools to automatically identify and score manoeuvres is the area that I have been focusing on. The problem can be split into three stages,

1: The aerobatic schedule, otherwise known as the Sequence Definition and the relevant scoring criteria must be separated for each manoeuvre.

2: The individual manoeuvres and elements of each manoeuvre in the sequence flown and recorded by the pilot need to be correlated with the expected sequence definition.

3: The judging criteria needs to be encoded and applied to each element.

Good progress has been made on the first two stages and I’ll go into a little more detail on aligning the flight data to the sequence.

Sequence Alignment

The scoring criteria for aerobatic disciplines differs depending on the element and manoeuvre being flown. For example, if the pilot is performing a looping element downgrades are applied for visible changes in radius. Alternatively, if a pilot is flying on a line, downgrades are applied for the error in the angle of the line i.e., whether it is horizontal, vertical or at a defined angle such as 45°. If the model is flying along any other angle, then a downgrade is applied.

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Playing back a flown Vertical 8 with the elements automatically identified.

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A vertical eight as flown by Thomas David (grey) compared to a perfect figure (orange).

In order to programmatically extract the subset of data relating to each element we have seen good results with an algorithm called Dynamic Time Warping, a technique more commonly used in speech recognition. The algorithm compares a set of parameters from a template sequence to the same parameters in the flight data recorded by the pilot and produces a lookup table between the time indices of the two. As the template sequence has been generated from the manoeuvre descriptions the elements are known and so positions of the elements within the flight data can be inferred.

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An excellent Golfball flown by Thomas (grey) compared to a perfect figure (orange).

The possibilities that these technologies offer to precision aerobatics are exciting. In the short term this project will help to improve the standard of flying and judging. In the longer term I hope to see some ‘postal’ competitions, where people record their flights and send them in for analysis.

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A few manoeuvres from FAI P-21 shown in the Flight Coach Plotter. View positions and angles can be fully adjusted to suit. As anything which isn’t perfection is downgrade-able the feedback from the Flight Coach is invaluable.

My dream, when I started this project, was to replace the judges completely and I think we have come far enough to show that a World Championships could one day be judged by computers. However, there are many hurdles to overcome and solving the technological ones is just the start. I now suspect that the human judge is just as important a part of the competition as the human pilot.

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