AeroModeller – June 2018

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

[email protected] ■

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.

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