I'm pretty sure Persu would have selected an aircraft engine based on his background and the considerations given for airflow over the engine.
The Wright flyer and the first car (Benz) both used horizontally opposed flat engines for the same reason I assume, they cause less vibration.
If you had a engine under your seat, you certainly would want a smooth one.
EDIT-1
Perhaps something from Beardmore (Great Britain) was on Persu's mind, maybe even a Diesel.
Beardmore Proposed 12-Cylinder Aero Engine
http://www.oldengine.org/members/die...ford/aviat.htm
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The use of diesel engines in aircraft has a long history going back to the early 1900's. and started with both the British and Americans developing engines for use in airships and aircraft. The French, Germans and Italians were also active in this field.
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http://www.alternatehistory.com/disc....php?p=5840541
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Beardmore aircraft diesel, a flat-12 'Boxer' diesel. This was 12 cylinders of 6" X 6½" with a capacity of 2206 cu ins, and developed 505 hp at 1750 rpm, but with a weight of only 1485 lbs.
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