Pilot – June 2018

pilotweb.aero | Pilot June 2018 | 41

significant factor. Nine series
engines are used in over 260
different types of aircraft, and it is
inevitable that some installations
are “perhaps not quite as good as
they could be”.
As I taxied into position I
briefly reviewed our weight and
the ambient conditions. With
almost full fuel and two POB
we were within thirty kilograms
of the 600kg MAUW, while the
combination of unseasonably
high temperatures and Wels
airport’s 1,043ft elevation gave
us a density altitude of around
2,500ft. The wind was seven to
ten knots, straight down Runway
27’s 1,390 metres of concrete.
Unfortunately, although I’ve
flown several 912-engined
Bristells I’d not flown the SW
version, and although the
acceleration certainly seemed

stronger, the rate of climb didn’t

seem to be as improved by as

much as a forty per cent increase

in power would suggest−but this

could easily be explained by the

higher wing loading.

Even before getting in I’d

noticed that the engine was

offset slightly so that the thrust

line wasn’t exactly straight down

the fuselage centreline, and

consequently although some right

rudder was required to keep the

slip ball centred in the climb, it

wasn’t as much as I’d anticipated,

bearing in mind that this aircraft

had so much more power than

the last Bristell I flew in 2015,

and the fin and rudder didn’t

look that different. The initial

climb rate was almost 2,000fpm

at 70kt which (bearing in mind

the density altitude) was pretty

respectable, while at 7,000ft

MSL the increase in performance

really was very noticeable.

The turbocharger worked as

advertised, with no discernible

reduction in manifold pressure,

and having trimmed forward and

set ‘max cruise’ of 5,500rpm and

37 inches of manifold pressure

the IAS soon settled on 135kt

for a TAS of 150 while burning

34-35 lit/hr. Pretty impressive

numbers, and although if you’re a

long-term Rotax pilot you might

be thinking that 35 lit/hr is quite

thirsty, I’d counter that 150kt

TAS is quite fast! Pull the power

back a long way to say 4,800rpm

and seventeen inches, and the

engine is now just barely sipping

litres per hour at 80kt TAS, while

a good compromise (Bristell call

it the ECO setting) of 5,000rpm

and 36ins of manifold pressure

still give a TAS of around 145kt at

7,000ft AMSL.

As the primary purpose of this

flight was to evaluate the engine

I didn’t get the opportunity

to explore the flight envelope

completely, but it certainly seemed

as if the slightly heavier engine

had (as you’d expect) shifted the C

of G slightly further forward.

Stopping the engine back on

the ground at Wels again seemed

smoother than with previous nine-

series engines of my experience.

Tech Log: Rotax 915iS

At 7,000ft MSL

the increase in

performance really

was very noticeable

CLOCKWISE FROM LEFT: 915-powered Bristell SW was fitted with a broad-chord ‘scimitar’ propeller; the

aeroplane’s simple T-bar throttle (no mixture of turbocharger controls are fitted or required) and prop lever;

and the cowl, which featues several extra scoops required for the more powerful engine