So which of the two is the better aero engine?
Pro Lycoming:
Pro Continental:
Anything else? They are almost twin brothers but there must be more tangible differences.
(requires 6 for Conti!)
I think
- the 200 hp Contis run much smoother than a 360 Lyco.,
- but most of the Lycos last longer. The 320/360 series can be flown troublefree for many years
- the IO-550 is a very smooth, powerful engine that will start always, no matter how cold – while 540 Lycos have more cold start problems
- but in general the big bore Contis will need more cylinders than a 540 Lyco
I love the characteristics of the 550 TCM, but afaik a 540 will be less prone to engine mismanagement. i also think the 540 doesn’t run as smooth as the 520/550
The Lycoming -540 is a great engine but it needs regular use. My experience is that on condition they will run well past TBO. Very smooth and dependable.
My Continental 90-8F is only 64 years old and runs very nicely – uses a bit more oil (a quart every 7 or 8 hours). The -8F is not able to have any accessories: starter, vacuum – it therefore tended to be swapped for the -12F, but now the fashion is for a lightweight Super Cub so I am glad mine is an -8F.
The L18C ‘Mil-Spec’ version has a TOGA five minute rating taking it to 95HP, and a MCT rating of 90HP – you can even pretend you are in a Medium Range Jet Transport.
Forget those yankee donkeys. A Gipsy Major is the real deal
200hp available with 4 cylinders
The upside of only 4 cyls is obviously lower overhaul cost, the downside is that these engines are not officially approved for mogas and won’t be, Lyco thinks the detonation margin is too low.
The injected Lyco 360 is a bitch to start especially when warm, but this is much improved by a SlickStart.
4-cylinder engines and 6-cylinder engines are no comparison in terms of smoothness, comfort, sound and “enjoyment”.
Yes, those extra two cylinders don’t make much sense on a 200hp engine (higher initial cost, more weight, slightly higher fuel consumption, higher maintenance, higher overhaul cost, etc.) but then, what does make sense with these airplanes?
On the 172, Cessna went from the 6-cylinder O-300 (145hp) to the 4-cylinder O-320 (150hp) in the late sixties for exactly these reasons, but some people still regret that.
Either you want efficiency or you want a real engine. A 6 cylinder boxer is a poor compromise between the good economy of a flat four and the real piston engines which are of course radials. To each their own compromise, of course, as always and everywhere.
Re detonation – why do aero engines require 100 octane to achieve 8.5:1 compression whereas car engines don’t?
Re detonation – why do aero engines require 100 octane to achieve 8.5:1 compression whereas car engines don’t?
Because they have to work when the worst pilot in the world does a climb at peak EGT and 500°F CHT in mountains… Car engines have electronic mixture control and are water cooled.
Larger cylinders require relatively higher octane due to the length of travel for the flame front and the associated time to complete the reaction. Relatively large cylinders were chosen to minimize weight and promote simplicity and efficiency, as described by boscomantico. That said, many of the engines now running on 100LL were certified on 80/87 and would run fine on it today.
Franklins were (and are) exceptionally smooth six cylinder engines with relatively low efficiency due to the internal friction associated with extra cylinders. The actual reason they went out of business is more interesting: they were bought by the owner of Tucker cars to bring flat 6 car engine production in-house, and turned away contracts for aero-engines. Tucker then failed famously and after bouncing along for a while, Franklin was sold to the Polish in about 1975 – who didn’t do a whole lot with it even though they also owned the matching Rallye airframe.
