Engine configuration

On Dec 20, 6:49 am, GTH wrote:
a écrit :

Opposed engines have less drag than a radial

Agreed

or vee

Why would it be so ?
An opposed engine is much larger just behind the prop, when a Vee is
more easily streamlined.
Would you care to elaborate ?

Best regards,
--
Gilleshttp://contrails.free.fr

A vee takes up as much flat-plate area as an opposed, because
it's not likely to be cowled so the slipstream can flow through the
vee between the cylinder banks. The opposed and vee both have
crankcases and cylinder banks that are in the way, and the case of the
vee tends to be larger, forming a three-armed affair rather than the
two of the opposed. Some opposed engines have been very tightly cowled
for racing purposes, with the carb and such behind the engine instead
of under it.
Most vee-engines have some sort of reduction so that higher
hp can be obtained from a smaller configuration. These can be smaller
than opposed engines for the same hp, but they'll be heavier, too. A
direct-drive vee is pretty big. The Argus was one.
The inline engine is much more easily streamlined, but its
crank is longer and so has to be larger in diameter to obtain the
stiffness required, and as it gets larger it gets heavier.

Dan

"cavelamb himself" wrote in message
...
John Halpenny wrote:
On Dec 20, 12:03 am, cavelamb himself wrote:
snip

But that all assumes you are going to use it direct drive - which almost
nobody does. If you use a gearbox, belt PSRU, or HiVo chain PSRU, they
will
all give you an offset of several inches, making for the same center of
gravity without the other changes, and allowing for much greater power,
because engine RPM's can be run much higher for the same prop RPM.

And what does all that do to 1) weight and 2) CG ???


1) A PSRU gives a smaller faster engine, which is usually lighter even
with the weight of the reduction gear.
2) Raising the output shaft several inches is the same as lowering the
CG, and the bulk of the engine that spoils your view, the same amount.

John halpenny



Not necessarily.

Starting with a V8 (or any other given engine) doesnt make the engine
smaller...


This only works for an engine "designer"...

Very true, and perfectly describes the difficulty of this sort of
discussion.

Peter