enginehistory.org

[jjuutinen]

Perhaps the best indication on how much these "modern" Lycomings suck is the fact that their best SFC with 100LL is greater than that of a WW One BMW inline using some 50-60 octane fuel.

[tmcdaid]

Not particularly to defend Lycoming, but I'd like to share a thought on the topic. I note that Herschel Smith, in his book A History Of Aircraft Piston Engines complains several times that more modern aircraft engines, even WWII vintage if I recall correctly, tend to have higher SFC figures than older ones, but with no explanation why.

I'm inclined to think that at least part of the problem is that newer engines are generally much faster turning than older ones. The upside to that is a greater power:displacement ratio, generally yielding a greater power:weight ratio and power-to-physical-size ratio. The downside is increased friction which I suspect is major cause of higher SFC. With engine weight and size being such big considerations in aircraft design, I conclude that the higher specific output must clearly outweigh the minor SFC cost. It's even possible the aircraft may actually use less fuel under most conditions because of reduced drag made possible by the smaller engine.

I'd be very interested in input from some of our engineering colleagues.
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Tim McDaid

[jjuutinen]

I don´t buy that theory. E.g. Argus engines were basically as fast running, yet had lower sfc and were better in every way. However, the Argus model producing some 240 hp had 8 cylinders whereas these Junkmings have usually 4 for the same power.

[rhaus]

I too, am no fan of modern opposed engines. But in terms of the SFC issue I tend to lean toward the view that SFC isn't really the "most important" factor.....if it were, then every engine would be a heavy, slow turning, diesel. Look at some of the low-speed (125-500rpm) diesels that run small power plants, ships, etc.....they sip tiny amounts of fuel (diesels being the most thermally efficient engine yet devised)

........BUT, they'd never get off the ground...in an aircraft, clearly power-to-weight and power-to-drag ratios take precedence over fuel burn rates.

rh

[jjuutinen]

RH, I don´t think these Junkmings excel in power/weight or power/drag. Plus that you have to remember that e.g. a 10% increase in aircraft weight (dimensions not changing) has minimal effect of speed and range.

So, Lycos are no good!

[bshepherd]

If the Lycomings are so bad why are they the most prolific light plane engine? Maybe there is more to the equasion than sfc.

[wallan]

I thought someone else would have answered this, so here goes.

They are so popular because there is nothing else: you can't make an economic business plan to make a better replacement.

To give you an example, to attain acceptance with aircraft manufacturers, you would need the engines to have a TBO of 2,000 hours. This means that for an engine designed to burn 20 litres of fuel per hour, (around 5 US gallons, 4 imperial) you need two engines and test beds with staff 24/7, (say 240 man-hours a week) and you burn 80,000 litres of fuel over 82 days. So, paying a dollar a litre for Avgas, and 20 dollars per man-hour, you have to cough up nearly 200,000 dollars just to get it certificated. That's after you've lost money designing, building and testing it, without anything going wrong and having to start again. Add in product liability insurance and it would take at least 20 years to get your money back: what happens if the bottom falls out of GA by then?

Then what about your distribution and repair network?

Economically, it's not worth it.

[szielinski]

I know what you mean Wallan, but I still agree with Jukka.
a) Unless people start sprouting wings or build railway tracks through every remote region on the planet, I don't think the bottom will fall out of GA in 20 years, or ever.
b) Given the cost modelling software & data available these days, you could get a much better approximation of how much a programme would cost, and likely returns, however delayed - banks won't lend without data like that.
c) If it's a demonstrably better engine then the sales will reflect that. Only people with "I love Lycoming" bumper stickers will stay with the junkmings (PS, love that term - is the J pronounced as a Y?).
A while ago I was speaking to a pilot who has some 4-cylinder Cessna thing, I changed the subject once he told me that ALL piston engined aircraft are air-cooled. I don't think people like that would be able to withstand the sales onslaught of someone with a better product.
d) As for support, NO industry and NO business has ever rolled out a complete support network 'whollus bollus' for one product/service - it's always a gradual thing, same as sales figures.
Why not build a Lycoming engine mount conversion kit and get Lycoming to support the planes?
(I work for a telco, we're used to industrial incest)
e) Things will have to change in GA eventually, forcing Lycoming to change or someone else to take up the slack. Do you think the same design engines will be flying in 100 years?
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“Make everything as simple as possible - but not simpler” – Einstein.

[hfriedman]

"A while ago I was speaking to a pilot who has some 4-cylinder Cessna thing, I changed the subject once he told me that ALL piston engined aircraft are air-cooled. I don't think people like that would be able to withstand ]

Maybe your friend had a point. In a way all aircraft piston engines are air cooled, including the Merlin. There are just different ways of getting the heat out to the ambiant air. As we use it, the phrase "Air Cooled" really means "Not Liquid Cooled."[/quote]

[szielinski]

You had to be there, but if there is a point in saying all engines are ultimately air-cooled then that guy didn't mean it.

On a lighter note, does that mean that planes that crash are geologically cooled?
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“Make everything as simple as possible - but not simpler” – Einstein.