OT ish Really interesting automobile engine.

[harryagain]

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

[Nightjar]

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

[Brian Gaff]

Is this the Wankel one with that weird triangular piston rotaor?

Brian

[Nightjar]

No, it is a 19th century design, with five air cooled cylinders that rotate around a fixed vertical crankshaft. Having the cylinders rotating does away with the need for a flywheel, giving a good power to weight ratio, and creates a forced draught over them that improves cooling efficiency.

Similar designs were used in world war I fighter aircraft. However, the gyroscopic effect made turning them rather interesting.

Colin Bignell

[Part Timer]

I'd have called it a radial engine, not a rotary (Wankel).

[Adrian]

Nope, that's definitely a rotary. It's not a Wankel, but it's not a radial, either.

On radials, the cylinders were static and the crankshaft rotated. Just like a normal V engine but with banks all the way round.

On a rotary, the crank is static, and the cylinders rotate, just like that one. Think WW1 fighter plane.

A Wankel is the NSU/Mazda-style one that everybody thinks of as "rotary", with static cylinders, triangular rotor geared to and spinning around the crank.

[The Natural Philosopher]

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."

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

[Nightjar]

Although described as a rotary engine, the Wankel is an entirely different beast.

Radial and rotary engines both have a number of cylinders arrange around the crankshaft. Visually, they are similar when stationary. However, the defining difference is whether the crankshaft rotates, which makes it a radial engine, or the cylinders rotate, which makes it a rotary engine.

Colin Bignell

[Biggles]

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

[The Natural Philosopher]

Nevertheless most of them were.

VERY few really fast piston engined aircraft had radials.

And the big ones with multiple banks all had cooling issues

[harryagain]

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.

[harryagain]

[Biggles]

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?

[Adrian]

Tailsliders often side-slip on landing - and there'd be a high crossover with such older/smaller engine techs and tailsliders, right?

But - aiui - that's more to do with seeing wtf you're going than any kind of cooling?

[Biggles]

It's easier to fly a curved or slipping approach in aircraft with a long nose or high thrust line because otherwise the runway disappears as you come down the approach, shortly followed by the entire airfield in some cases! By slipping, or only lining-up in the last few seconds, the runway can be kept in sight. These aircraft are usually tailwheel aircraft, often called "taildraggers" (rather than "tailsliders" ;-) )

[Biggles]

... 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.

[harryagain]

Pawnee ex-crop duster, used for glider towing. This was the manufacturers advice.

[Adrian]

I was close, then...

[Nightjar]

...

It isn't in the owner's manual.

Colin Bignell

[harryagain]

It was never intended/designed to use it towing gliders. Lots of take offs and landings/descents from around 3000'. Our grouse was that the front cylinders wore out before the rear. Even though the air is ducted.