AEROBATIC SCENE - 03.21

Jennifer Kimball’s BJ Craft Nuance in flight.

Top competition pilot, Keith Jackson sets about keeping us better informed of developments with pattern style model aircraft.

This is Keith's column from RCM&E March 2021, which we will be presenting in two parts.

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Jason Schulman and Jennifer Kimball, with her BJ Craft Nuance.

Our heading photos show the US F3A team for the 2021 World Championships, which will be held at the NCRSA site in Muncie Indiana. This event was last held at this huge site in 2011; it is hard to imagine but the site is so large that there are different climatic conditions across the site dependant on which flight line you are using!

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Greyson Pritchett’s Skyleaf Leader with AMA HQ in the background.

Making his international team debut is 17-year-old Greyson Pritchard, who is the Junior team member. He will be flying a Skyleaf Leader biplane. The reigning Junior World Champion, Kal Reifsnyder will sadly not be attending the event.

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Top US pilot Andrew Jesky with his Proteus biplane.

In 2020 the FAI Sporting Code was amended to allow teams of up to four members, so long as one member was female. This rather ground-breaking rule change has allowed the US team to include their first lady team member, Jennifer Kimball. Jennifer flies a BJ Craft Nuance G2 using a V4 Brenner contra drive. It is absolutely great that women competitors are being encouraged into F3A and I really look forward to seeing how the competition unfolds later this year.

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Third in the US team trials and new to the team is Pete Collinson, who flew this HoruS biplane, designed by Italian pilot Sebastiano Silvestri.

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Epic biplane used by Jason Schulman, now kitted by CA models.

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Andrew Jesky’s Proteus biplane at take-off.

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US team for 2021 World Championships. Left to right: Jennifer Kimball (BJ Craft Nuance), Pete Collinson (Sebart HoruS), Andrew Jesky (Proteus), Jason Schulman (Epic), Greyson Pritchett (Skyleaf Leader).

PACEMAKER
This design was flown by one of the UK’s F3A legends, Ken Binks in the late 1970s and has now resurfaced in the growing UK Classic Pattern scene. The plan of this model is available for builders and can be obtained from the Classic Pattern Association via Martyn Kinder ([email protected]).

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Martyn Kinder with his Ken Binks designed Pacemaker.

Martyn flew his version of the Pacemaker at the last Classic Pattern meeting that was held at Buckminster, just prior to the first Covid lockdown. A novel feature of his model is that it is partially constructed from a paper/foam/paper laminate typical of the material used in commercial displays; apparently Ken withheld his approval for this construction change! Otherwise, the Pacemaker is conventionally built with a balsa fuselage and foam veneered wings and finished in a mixture of white two pack paint and heatshrink film for trim.

The model is powered by a Webra Speed 61 side exhaust engine with a Weston Quiet pipe and turns an APC 12 x 9 propeller at just over 10,000 rpm. A fixed tricycle undercarriage was used in preference to the retracts fitted on the original. The overall weight turned out at a reasonable 7.5 lbs, allowing it to have a good vertical performance. Trimming is still on-going, but Martyn hopes to get more airtime with the Pacemaker later this year when hopefully near normality will have returned to the UK.

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Close up on the gorgeous Webra Speed 61 engine.

I’d hoped to see a lot more of the Classic Pattern scene this year but as with most organised activities this was curtailed due to the Covid pandemic. Looking at Martyn’s Pacemaker certainly brought back memories of my own start into aerobatics. It would be great to see these wonderful models in action again and I do hope that during next year's Nationals a demonstration could be arranged during the lunchtime breaks.

BATTERY BACKUP SYSTEMS
Returning from the 2015 World Championships held in Switzerland, I was at the time flying a relatively new BJ Craft Inspire fitted with a Brenner v3 contra drive. This was very much a transitional time for me, finally moving away from YS four stroke powered models to electric flight, and the performance of these models held much promise going forward.

Several weeks passed before going back to the practice field for more F3A flights, but once there I plugged everything in and it all worked first time, so off I went. The second flight started without any drama until halfway through the session and then the dreaded 'no response from anything' happened! The total loss of power to the receiver meant the flight ended in disaster, leaving me to pick up small bits of what was once a fantastic airframe.

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My ill-fated BJ Craft Inspire/Brenner v3 contra system from 2015.

The issue was due to one of the pins in the JST battery connectors coming loose within the plug and not mating properly with the pins in the corresponding socket feeding into the power switch. The intermittent connection was always going to fail at some point, and I was lucky the accident wasn’t much worse, involving other people or property.

As a result of this accident, I have since used a battery backup system in all my F3A models and have never had a repeat of this kind of power failure. The function of these units is to provide an additional power system should the main system fail.

A typical airborne power system would just include a battery and a switch, so an elementary backup system would include two of these systems in parallel, with some additional electronic components to prevent one system trying to charge the other. There are, however, dedicated systems that provide a more elegant solution to battery backup and two of these products are described below.

Updated Optipower Ultraguard 430
The Optipower Ultraguard has been available for several years and has proven very popular as an intelligent, fit and forget battery backup solution, particularly in helicopter applications. The unit is plugged into a spare receiver output and senses the operating voltage when the model is turned on. This takes about ten seconds, after which the Ultraguard goes into a standby mode where it continually monitors the receiver voltage.

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Optipower Ultraguard 430.

Should the receiver voltage change by a discernible amount the Ultraguard activates and provides its own voltage supply to the receiver until deactivated. This allows the receiver to be powered when its main supply voltage has dropped to dangerous levels or is completely absent, as in the case of a broken power lead or faulty switch.

When the Ultraguard is providing backup voltage this state is indicated by an LED on its main circuit board, and also by an optional ultra-bright, white LED that can be mounted remotely and even externally. The unit is then deactivated by pressing a microswitch on the Ultraguard body or additionally on the LED itself if you have the latest version.

The 300mm long lead to the new LED now means that the Ultraguard can be mounted further away from its typical position near the receiver, allowing the mass of the Ultraguard to be positioned to help with model balance.

In use the Ultraguard would be attached to the receiver but your airborne system would still require a switch and main battery pack.

For this example, the power system components would typically include:

• Optipower Ultraguard
• LiPo pack (2S 850 mAh)
• Switch (e.g., Powerbox DigiSwitch)

PowerBox Sensor V3 switch
An alternative approach to battery backup is provided by the PowerBox Sensor V3 switch. This unit feeds two external battery packs into the receiver via two separate power leads. This system has been around for some time now but has recently been updated to use a much more compact aluminium body and a single push button to switch the unit on or off.

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PowerBox Sensor V3 switch.

In practice it operates very much like the Powerbox Digiswitch but includes two separate switching circuits for redundancy. Dual multicoloured LEDs provides feedback on each battery state in a similar style to the Digiswitch.

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Optipower Ultraguard and PowerBox Sensor V3 schematics.

The Powerbox Sensor V3 system would include: • Powerbox Sensor V3
• LiPo pack (2S 430 mAh)
• LiPo pack (2S 430 mAh)

The weights of the two systems are pretty comparable depending on which LiPos you use and, as it turns out, the total costs are virtually the same as well. One additional advantage of the Sensor V3 is the ability to handle higher current demand, with the specifications suggesting an ability to pass 20A for several seconds.

The Ultraguard, however, only requires one battery pack to be charged instead of the two for the Sensor V3 switch. In addition, if the Ultraguard activates you know there is a reason to check the power supply to the receiver and so any potential fault can be found and rectified.

Weights (g)

Main unit

Lipo Pack #1

Lipo Pack #2

Powerbox DigiSwitch

Total

Optipower Ultraguard

41

49

Not required

15

105

Powerbox sensor V3

35

32

32

Not required

99

Either system would serve as an efficient backup system preventing the potential loss of your model due to the simplest of issues.

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