On 22/03/2014 20:16, wrote:
On 22/03/2014 17:40, harryagain wrote:
wrote in message
...
On 22/03/2014 12:28, The Natural Philosopher wrote:
On 22/03/14 12:08, Part Timer wrote:
On 18/03/2014 09:46, Nightjar wrote:
On 18/03/2014 09:02, harryagain wrote:

http://www.youtube.com/embed/Y0XbqHU...yer_detailpage

Heh. I knew these were used on aircraft but not in cars.


A good power to weight ratio, which the rotary engine has because it
needs no additional flywheel, would have been just as important in an
early motor car as it was in early aircraft.

Colin Bignell

I'd have called it a radial engine, not a rotary (Wankel).
No
Radial is engines arranged with cylinders in a circle.
Rotary is when the 'crankshaft' is fixed and the cylinders go round it.

Not needing a flywheel is the least of issues for aircraft - the
propellor itself is a massive flywheel.

It was all about cooling really.

Rotary engines are pigs to get the fuel into. too.

"Another factor in the demise of the rotary was the fundamentally
inefficient use of fuel and lubricating oil, caused in part by the need
to aspirate the fuel/air mixture through the hollow crankshaft and
crankcase, as in a two-stroke engine."

http://en.wikipedia.org/wiki/Rotary_engine

The Wankel 'rotary' is a completely different animal.
It has a rotating piston, not a rotating cylinder.

Radial engines reached their peak at the end of WWII and were then
overtaken but the jet engine and turboprops.

Rotary engines didnt even make it to the end of WWI..

Post WWI Bristol engines went down the radial route and Rolls Royce
down
the inline route.

There were legals reasons for this.

In the US Pratt and Whitney were the big radial engine people.

As far as cars went, the cooling problems meant that water cooled was
practically de rigeur as power levels went up. So inline was easily
possible.

The thing about radials being that they offer better air cooling if the
flat face of the cylinders in=s in a prop blast.

But that is draggy - its better to have an inline arrangement and put
the radiators elsewhere where they can be more aerodynamic



Someone once told me that a water-cooled aircraft engine was about as
sensible as an air-cooled submarine engine ;-)

Air cooled aero engines have major cooling problems when flying.
Eg
When descending they over cool and the cylinders can seize onto the
pistons.
At best it causes high wear and tear.

If you look at radial engines, there is a circle of flaps round the
engine
nacelle which are closed on descent.

One some aircraft it is recommended to side slip in when landing for
rapid
descent to the reduce the cooling effect.

So "someone" didn't have a clue.


Err, it was a joke!

FWIW I've flown a wide range of aircraft, mostly with air-cooled
horizontally-opposed (Lycoming and Continental) engines but a few with
radials, in-line, turbine and part-water-cooled engines.

Your assertions are not correct.
Air-cooled engines do not have "major problems". Power vs speed needs
managing but the clearances are such that cooling is not, in practice, a
big problem up to a few hundred HP. Operations such as towing need
special care not to crack the heads, but this just means leaving a
little power and managing the acceleration in the 10 seconds
post-release (water-cooled is easier here).
Multi-row radials have their own cooling issues, as do high power
water-cooled engines such as the Merlin and Griffon.
Not all radials have cowl flaps but quite a few H-opposed engine
installations do; water-cooled aircraft have rad shutters.

I have never flown an aircraft in which side-slipping was recommended
for cooling - what type are you thinking of?


.... forgot to say: the problem with cooling (leaving aside the exotic
multi-row radials) of air-cooled engines is because of the dissimilar
metals used for the heads and the valve seats. If, after a period at
high power, the power is rapidly reduced and the airspeed rapidly
increased, the head cools quickly and shrinks onto the valve seat; this
can result in a cracked head.