AeroModeller – June 2018

(C. Jardin) #1
11

RPM is very good for an engine of its
period and type. Back in 1972, when it
was released, contemporary RC glowplug
engines would have been hard pressed to
match it. In the following decade, all that
changed, but the Super Hunter still holds
a trump card. Like its predecessor, the
proximity of torque and BHP peaks means
markedly gutsy delivery of available
power, which would benefi t “heavy
lifting” applications. A cruiser operating at
modest speeds. Propellers giving static
RPM between 10,000 and 12,000 RPM
would give good performance. Try 10x5,
10x4, 9x6, and 9x5.

Experiments
Many Clubs have a blanket rule requiring
a muffl er on the engine. It’s relatively
quiet and a short length of ½ inch ID
rubber tubing attached to the throttle
would usefully redirect the exhaust oil
away, with a restrictor bung of reduced
inside diameter in the end to cut back
the noise. Cheap, but not very effi cient.
We chose a very light option for trial
that I already had to hand - a muffl er
from a Fora F2D Combat engine. Weighs
0.2 oz (6 g) complete with rubber
adapter sleeve for fi tting to 12mm
exhaust stub, 6mm outlet diameter. The
throttle outlet can easily be fi led to that
size. The muffl er probably needs no
support, but a wire clip at the exhaust
end would prevent it slipping off. Repeat
testing with 9x5 propeller showed no
eff ect on RPM (despite generous sub-
piston induction) and full-throttle noise
reduction (3 metres behind

the outlet) from
86 dBA to 80-
dBA. Around the
same intensity as the
kerbside of a busy road.
If the throttle control is so good, why

doesn’t every other manufacturer use it?
The answer lies with fuel draw reliability.
Unlike a carburettor throttle, which
adjusts down intake choke area for
lower RPM, the Super Hunter’s generous
carburettor remains unchanged at all
speeds. Naturally, fuel suction
goes down as engine RPM
is lowered. Fine on the
bench, or steering a
slow-moving model
boat, but raise
the engine above
fuel tank level
(as in a climbing
fl ight attitude)
when idling
and it stops.
Using exhaust
pressure won’t
really help at idling
speeds, because
the throttle more or
less lowers its eff ect. A
smaller choke area seems to us a
necessary compromise for reliable fl ying,

but at what cost to top end power and
RPM? We took the simplest approach
of blocking half the choke in the time-
honoured way with a slip of balsa. Tests
showed a 300 – 500 RPM reduction at
full throttle, but decent suction when
idling. Fair trade in our opinion.
Undeniably, conversion of the Super
Hunter to aero spec. cannot change the
original’s fundamentals, but we reckon
there’s more than enough goodness
there to justify fl ying one in an Old Timer
or similar model. Too good to be left to
old druids alone, but if you’re one of
those, a fi ne vehicle for demonstrating
your mythical powers. Super Hunters
are available only from Weston UK, air
cooled for £125.99. Water cooled Super
Hunters and Super Otters cost £99.99.
Muffl ers are also available from Weston
UK. http://www.westonuk.co.uk or phone Alan
Greenfi eld on +44(0)1795 521030. Try
Mike Crossman or Mark Greenwood of
Techno Hobby West for the Fora muffl er
technohobbywest@gmail.com ■

Sticking with the E.D. Hunter/Super Otter outer
cylinder dimensions limited the scope of revised
porting. Even so, three transfer port arrangement
certainly improves performance.

Single circlip retains wrist pin in piston boss.
Unlike usual practice, it can’t slip out or lose a tag

Bottom end should be almost bullet proof.
Crankshaft journal is a solid 3/8 inch diameter.
Note the unusual use of knurling on the tapered
prop driver mounting area.

Fora muffl er is super light and quite effective.
Rubber adapter sleeve suits 12 mm engine
exhaust diameter. Super Hunter throttle can be
machined or fi led to suit. Or if throttling is not
required, our simple machined exhaust stub
weighs only 2 g.

Moulded nylon induction
rotor/backplate
assembly has
horizontal needle
valve assembly.
Marine version’s is
vertical. Contour
of backplate face
reduces viscous
drag against
rotor but retains
crankcase
pressure.

POWER TRIP 055.indd 11 26/04/2018 15:

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