Page 25 - MFW June 2024

Steel fishing trace used for closed loop controls,
checking for free movement.
Despite my Mills Bomb weighing a couple of extra ounces
over DB’s prototype weight, the flight characteristics felt
surprisingly sedate.

DB’s original build article states “…the model will have a
shallow climb, steepening slightly as the speed increases.
You will find that the control surfaces, although not large in
area, are quite responsive…”.

He also commented that “…the glide is reasonable
without being over efficient, towards the end of the fuel
tank run aim to gain some extra height and plan your
circuit when the engine cuts.” These words proved to be
accurate.
DB Mills Bomb
complete ready I wasn’t sure how long the tank would last at these
for maiden flight.
settings, but the motor quit after about 9 1/2 minutes,
resulting in a fast glide with a slightly nose down attitude. I
mis-timed the landing ‘flare’, so the model nosed over
(kind of expected with the ‘leggy’ undercarriage and small
wheels), but the rubber band loaded undercarriage
absorbed most of the impact, folding back as designed.

16th February 2024 - MAIDEN DAY; A follow up flight, lasting roughly the same time, confirmed
my first impressions that if built according to plan, with the
FINAL SPECS PRIOR TO MAIDEN motor mounted with zero down or right thrust, The Mills
Span 35” Bomb would cruise straight and level at one throttle setting
only, climbing steeply at anything higher and descending
Weight 1 lb 5.7oz (21.7oz) (prototype 19oz with Mills at anything lower; it behaved rather like a guided free-flight
1.3cc, 2ch) model, rather than as a true RC model with a significantly
Wing Loading 16.23 oz/sq.ft (prototype 14.22 oz/sq.ft) wider useful throttle range.
Motor/prop. OS10LA (1.64cc), 8x4” Master Airscrew Suggestions from other club members included raising
Scimitar the wing incidence slightly with a 1/16 ply shim and
creating some down thrust with washers added under the
RX Spektrum Ar610
engine mounting lugs on the rear mounting bolts.
Controls Rudder, Elevator, Throttle
I intend to try both of these suggestions, but I’m also keen
Servos 3 x Savox SH-0253 13.6g
to avoid changing the characteristics of the model. The
Mills Bomb flies very well as is, even if the throttle settings
are somewhat limited, but then, the original did not have a
Wind forecast predicted around 10km/h, but it was a little throttle at all, so in this sense my version certainly
turbulent with all the trees around Kendall Park. However, performs true to the original design. And the best part is it
the OS10LA fired up first time after priming, and after has made good use of a sweet little motor that has been
finally checking the controls, a gentle shove was all The lying redundant for years. The OS10LA is very quiet when
Mills Bomb (MB) needed with the throttle at about 2/3. over-propped with the 8x4, and very cheap to run.
With the 8x4 prop, the model climbed very steeply into the
wind, veering off to the right. Throttling back to about 1/3, The Mills Bomb is a neat little design, providing something
the MB levelled off, but still turned to the right. About half a bit ‘different’. It won’t win any beauty contest but has
the available electronic trim cured this so it would fly more- certainly provided me with yet another interesting small
or-less straight and level, which was a good job as manual model build, resulting in an all sheet design that performs
trimming would mean re-doing the closed loop rudder better than expected.
connection.

Taking the MB through basic circuits with low-ish passes
down the runway, it became clear that just 2 clicks of
increased throttle were enough to go from maintaining
altitude at a steady pace to climbing steeply. This
increased throttle setting was still well below half throttle,
yet required sustained down elevator input to bring the
model back to level flight. As soon as the 2-click increase
was reversed, level flight resumed, and the rest of the
flight was spent happily switching between these two
throttle settings.

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