How an Aerovee gets 80 hp

There is a vast discussion among “experts” that a 2180 cc VW engine can’t produce 80 HP in an aircraft environment swinging a prop. However, I believe that it can. Below here is Aeroconversions (sonex) take on the subject.

Keep in mind this basic formula that applies to this engine:

HP = TQ x RPM / 5252

With Sonex’s publish ft-lbs numbers you can calculate HP.
80.9 hp = 125 ft-lbs x 3400 rpm / 5252
69.8 hp = 126.4 ft-lbs x 2900 rpm / 5252

Assuming 125.5 ft-lbs at 3100 rpm
74.1 hp = 125.5 ft-lbs x 3100 rpm / 5252

Also remember Torque at the prop is what’s doing the work.

The following was taken a post made on the Aerovee discussion group by Sonex on 10/26/2010:

Hello again AeroVee and SonexTalk Groups-

We wanted to address a common question that we field regarding the
horsepower rating of the AeroVee. Specifically, why do list it as an 80hp
engine when our competitors list similar displacement vw-based engines at 70
to 76hp?

Good data is very difficult to find for most of the AeroVee competition.
There are some slight differences in core parts selection of each
conversion, but there are also differences in how horsepower is being
measured, and at what RPM max rated horsepower is being published.

Sonex Aircraft has both Dyno testing data and comparative prop testing data
to support that the AeroVee is an 80 hp engine at 3400 rpm. Our Dyno tests
conducted with the University of Wisconsin-Madison engineering department
shows the AeroVee produced approx. 80.74 hp and approx. 125 in-lbs of torque
at 3400 rpm on-average between all of our test runs. Peak hp was measured at
3500 rpm: approx. 82.12 hp, however torque is on the back-side of the peak
³plateau² of the graph at this rpm: approx. 123.23 in-lbs, so that
factored-in to our publishing max rated hp at 3400 rpm, where torque is a
little sweeter, and we¹re running the prop slightly slower. Absolute peak
torque was shown in our Dyno test runs at about 2900 rpm with approx. 126.36

We know from our extensive flying experience with these engines that these
numbers are within the normal operating range of the props that we use. We
also know that an AeroVee Engine installation that is set up per our
standard instructions can run all-day in this RPM range. We like to see 3000
rpm minimum static rpm in a full-power ground run. Depending on the prop, we
usually see a maximum of about 3500 rpm in level flight at WOT. We rate the
engine¹s red line at 4000 rpm, but the engine core revs more than that in a

With regard to comparative prop testing: when we first began testing of the
³modern² version of the AeroVee on Sonex Aircraft, we wanted to see how the
engine compared to the Jabiru 2200 we were already flying on the airframe.
At that time, the 2200 Jabiru was rated at 80 hp with a published
power/torque curve to support that number (changes in the engine has since
increased its power slightly since then, and Jabiru currently publishes it
as an 85 hp engine). We had conducted a lot of prop testing with Sensenich
to get an optimized prop selection for the 2200 powered Sonex, and we had a
lot of flight test data collected for that setup. For the first flights of
the AeroVee 2180, we simply had Sensenich make a left-hand turning version
of the Jabiru 2200 prop we had worked with them to refine. With that prop,
static rpm on the ground and rpm¹s in the air was approximately 50 rpm
higher than the Jabiru 2200, and performance of the aircraft was slightly
better as you would expect with an increase in rpm. Note that newer 2200
Jabiru Engines have performed slightly better than the 2180 AeroVee due to
the added displacement and other refinements of the 2200 Jabiru Engine in
the past 8 years.

The bottom line is that the power output of all direct-drive big bore and
stroke 2180 VW aircraft conversions is roughly equivalent, but each company
publishes the rated hp at different rpm¹s. We feel our competitors are
confusing max rated hp, the standard by which most engine hp ratings are
published, with max continuous rpm. Our competitors who are rating their
engines at 76 hp appear to be publishing the max continuous rpm of their
2180 VW conversions.

As always, please feel free to contact Betty, John, Jeremy, Kerry, Mark,
Heather Z, Jason, Stephanie, or Heather W at the numbers or e-mails below
with any questions or Comments.

-Sonex Aircraft, LLC
Tel (Info/Orders): 920.231.8297
Tel (Tech Line): 920.230.8324
Fax: 920.426.8333

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