Pilot – June 2018

44 | Pilot June 2018 | pilotweb.aero

He was then asked−bearing in
mind parent company BRP make
several vehicles (such as Seadoos,
Skidoos and CanAm ATVs and
SSVs)−has Rotax ever considered
building an aircraft? “Well” he
smilingly replied, “we obviously
have some of the skills, tools and
resources to build an aircraft on
an industrial basis−but we have
a high level of respect for our
customers' ingenuity and put
simply, why should we piss off
267 of our best customers?”

It’s all in the numbers
Comparisons are odious,
sometimes unavoidable−and
doubtless by now many readers
are thinking “Rotax make many
engines, but which one would
best suit my needs?”
To answer that particular
conundrum we need numbers,
not words. The installed weight
of the 100hp 912iS is 75.4kg
and it costs around £20,000,
while the 115hp 914’s installed
weight is 74.5kg and it costs
£27,000. Both have 2,000hr
TBOs. Finally, a shiny new
141hp 915iS has an installed
weight of 90kg and costs around
£30,000. Currently the TBO is
only 1,200hr, but it is a very new
engine and Rotax is notoriously
conservative. I would expect
the TBO to rise as operational
experience is gained, and it is
worth noting that although early
912s had a relatively low TBO
of 1,200 hours, this has been
progressively increased to 2,000.

All prefer the same fuel−

basically the highest-octane

mogas you can find, with as

little alcohol in it as possible. I

suspect that for most LSA and

UK homebuilt applications the

912iS is just fine, but for operators

of seaplanes and amphibians,

aviators who are based where it’s

‘hot ’n’ high’, tug pilots and−well,

people like me, who never turn

down a few more ponies−the

915iS will be very tempting.

As for any further development

of the nine series, I suspect

there’s not going to be any. As

the 915 produces in percentage

terms a creditable 41% more

power than the original 912S, it

seems reasonable to assume that

this is probably as powerful as

these engines are going to get. Of

course, you could definitely still

get a lot more out of the same

basic unit, but as power produced

increases, longevity invariably

decreases. It’s worth noting that

many classic American aero-

engines typically only churn out

around half a horsepower per

cubic inch. For example, the

typical O-360 produces 180hp,

O-320s are usually good for

160, while O-200s are normally

around 100. The 915 is only

82.5ci, and it already produces

141hp (with much better fuel

consumption), although a lot

of this efficiency is obviously

attributable to high running

speed allowed by the cleverly

engineered reduction gearbox.

Anticipating a considerable

amount of interest in this new

engine (and it appears to have

been very well received by the

industry) Rotax has already

produced over 200 915 units,

approximately 120 having been

delivered to manufacturers.

Twenty or so of these are installed

and flying. I was impressed by

the 915iS. Will it be as influential

as the original 912? You know, it

just might.

Tech Log: Rotax 915iS

ABOVE: autogyro

manufacturers will

appreciate the 915iS’s

extra power

BELOW: demo fleet

assembled at Wels

Where it’s

hot ’n’ high

the 915iS

will be very

tempting