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|The separate BEC
units were located just underneath the cockpit canopy,
well away from the receiver.
||The two batteries supplying RC system power are housed in this foam-lined box. Each battery is connected to its own switch, seen in the lower part of the photo.|
The main RC battery is a 3-cell 800 mAh pack, while the retract battery is a 3-cell 350 mAh example. These batteries provide considerably more stored energy than an equivalent standard 600 mAh receiver pack.
As a comparison, a 4.8 V 600 mAh pack provides nearly 3 Watt hours of energy (0.6 Ah x 4.8 V = 2.88 Wh), while the 3-cell (11.1 V) 800 mAh pack provides almost 9 Wh (0.8 Ah x 11.1 V = 8.88 Wh). This is plenty of energy for a several flights. The smaller 3S 350 mAh retract pack provides 3.88 Wh, again, more than a standard RX pack and sufficient to power the retract servo for many up/down cycles.
The only downside to this LiPo and UBEC arrangement is that preparation of the model is slightly more complicated because the batteries have to be removed for storage and charging.
Receiver (Rx) location
A 35 Mhz JR system was used for the model. The receiver was located at the trailing edge of the wing, at the bottom of the fuselage. This position kept it spaced well away from the power system’s components, and the low position also maximised the vertical component of the aerial, which should help with signal reception.
|The pair of switches was mounted in the fuselage side. Also seen here is the cover plate which retains the two small lithium batteries.||The receiver is located low down in the fuselage and well away from the BECs and the power system components.|
The receiver is located low down in the fuselage and well away from the dual BECs and the power system components, any of which are possible sources of RF interference. The receiver sits in a bed of foam to protect it and its delicate crystal from vibration. Vibration is still a factor with electric models, and may be generated by an out of balance prop and/or spinner. Take-off and landing also generate vibration as the wheels contact any bumps in the runway.
|A general view of the fuselage interior.||This simple balsa tray keeps the loose RC system wires distanced from the two BECs.|
I had difficulty in sourcing a scale profile 3½ inch spinner which this model deserved. I settled on a metal example which was not too far off the required profile. Out of balance props and spinners show up readily with electric power models, which don’t have the background vibration of an i.c. engine.
Since it was a cast item, I was not surprised
to find the spinner body required significant work to
balance it. This was achieved by relieving its inside
surface. Its back plate was balanced separately and also
required a lot of metal to be removed, which was very
surprising as this was a turned item. It was necessary
to make a prop nut on a lathe as this had to have a threaded
M4 hole in its forward end to accept the spinner bolt.
This would not have been needed if I’d used a plastic
spinner of a different design, and with hindsight this
would have been a better option in view of the considerable
time spent on this area. Still, the shiny polished spinner
did look very handsome.
|The cast spinner required a lot of metal to be removed to achieve a balanced condition.||The spinner back plate was separately balanced. As can be seen, a surprising amount of balancing was required considering it was a turned component. Also seen here is the custom-made prop nut.|
Weight and Balance matters
The instructions specify that the CG should be located 4¾ inches (125 mm) behind the leading edge (LE) of the wing. Unfortunately it was’t specified where this LE reference point was – the wing is tapered and has a root fillet, so I was not sure if the reference point should be the LE at the wing root, an average LE position along the wing’s actual leading edge, or the part of the wing which joins to the fuselage. In the end, I decided that the wing/fuselage joint was the likely intended reference position. Also, being the most forward of the options this was a ‘safe’ assumption.
On checking the model in flying trim, I found that my model actually balanced 4 mm behind this position (129 mm behind the wing/fuselage joint). I did not consider this to be a significant deviation and so I was happy to stick with it, especially as there have been a number of reports on internet forums about the model being prone to nosing over on landing.
I also used a useful on-line CG calculator which confirmed that the 129 mm position was perfectly safe.
(I found this at: www.geistware.com/rcmodeling/cg_super_calc.htm)
The ready to fly weight was measured at 3,998 g, or 8.8 lbs. This is a very reasonable weight for a 65 inch WW2 warbird, and was made up of the following:
6S battery 768g
Before committing to the air, the model’s power consumption was checked. These were the results:
Prop: 15 x 8
Current: 48 Amps
Power: 1,050 Watts
This was well inside the capabilities of the 20C battery which is rated for a continuous 100 Amps, and the ESC which is rated at 70 Amps.
Taxi trials, carried out on grass revealed that there definitely was a nosing over tendency at low speed. On very short, smooth grass this was containable with the use of up elevator. I also found that the undercarriage legs were a little wobbly in a side to side direction. This problem disappeared after extending the limit screws slightly on the retracts. It would have been nice if the instructions had covered this point.
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