Difference between automotive and aircraft engines

[fdcg27]

IDK.
Our family discretionary income is certainly higher today than it was twenty years ago and yet twenty years ago I could have afforded to own a 172, maybe even a 182.
Not today.
Yes, the entry cost of a decent old Cessna remains quite low, but after that, everything from fuel to insurance to hangar space costs more, not to mention annuals and general maintenance and repair. Many of these old planes are also cheap because they have hopelessly outdated avionics and there is no cost-effective way of updating them.
Let's say I don't care. I just want a VFR traveling airplane and I have no desire to earn the rating and fly within the system. Sure, but it's becoming harder all the time to operate outside of the system.
GA has suffered more from the loss of active pilots and aircraft than it has from any economic decline of a decade ago.
As the number of active pilots and aircraft has declined, everything has gotten more expensive in constant dollars than was the case a couple of decades ago.

 

[tom slick]

I have flown with with my boss on business trips in his Cherokee a couple of times. That has ended since the insurance for flying employees in a personal plane is $30k + per year.

 

[dwendt44]

The proliferation of commuter airlines and discount airlines
showing up in smaller markets, has also helped the decline in
private aircraft ownership.

 

[Silk]

You can go the other way too...or you can in New Zealand.



The Lycoming Special.

 

[Cujet]

The real reasons are not what you think:

BSFC: A well tuned Chevy V8 will achieve a BSFC of 0.55 Lb fuel per HP hour. A Lycoming air cooled IO360, 0.38.

Drag: Air cooling reduces drag. As a high temp differential, such as cylinder heads at 350 deg F, requires far less cooling airflow than a much cooler liquid radiator, for a given thermal load.

Note: large bore, air cooled engines run hotter, and therefore have lower thermal loss during the combustion event leading to greater efficiency in cruise flight.

Take a close look at the properly designed cooling airflow inlets for this 200HP engine:

This is a liquid cooled diesel engine of far lower HP. The reality is that until recently, liquid cooled gasoline engines have always been less efficient, and have double the cooling drag. That is changing with modern direct injection and higher temperature liquid cooling systems.

 

[Cujet]

Some other thoughts. BSFC is, for our discussion, by weight. Diesel fuel/jet fuel is considerably heavier than Avgas.

Aircraft carry weight, and weight is the only thing that matters. Diesel aircraft get better MPG, but not necessarily by all that much in cruise flight. What diesel aircraft do not seem to achieve by any great measure, is more range.

Put another way, if our fuel limit is 300 pounds, it's 300 pounds. MPG matters not. An aircraft will not magically be able to carry more load if the engine is a diesel. Diesel aircraft carry less of the heavier fuel, and consume that fuel slower. The end result is near parity with regard to range and capability.

What diesels do very well is consume less fuel during phases of flight other than cruise. As air cooled engines are operated in an "over rich" condition for cooling. And consume a less expensive fuel.

Here is a 160HP diesel Cirrus. This particular one was not a success, despite the amazing effort. Underpowered, slow and incapable. Part of the problem was the overweight engine simply did not have enough HP to compete with the 200HP air cooled engine that previously powered that airframe. The end result was a difficult, slow and long flight from Florida to Wisconsin.

 

[brave sir robin]

Originally Posted By: Andy636
Actually what amazes me is how Rotax can make airplane engines but can't build a half **& decent motorcycle engine...


wat

130hp with Honda tier reliability is apparently not a "decent motorcycle engine"

One of the local dealerships returned their valve adjustment kits because they literally went years without needing to do one on a customers bike. not a "decent motorcycle engine"



pic related

 

[fdcg27]

Thanks for your two posts Cujet.
I had no idea that there was such a dramatic difference in SFC between a ground vehicle liquid cooled V-8 and an air cooled flat six av engine.
Your points make great sense as to why this might be the case as well as to why diesels might not be the answer for light aircraft.
Maybe all those Lycoming and Continental engineers actually knew what they were doing when they laid down this ancient design theme?

 

[Cujet]

Originally Posted By: fdcg27

I had no idea that there was such a dramatic difference in SFC between a ground vehicle liquid cooled V-8 and an air cooled flat six av engine.
Your points make great sense as to why this might be the case as well as to why diesels might not be the answer for light aircraft.
Maybe all those Lycoming and Continental engineers actually knew what they were doing when they laid down this ancient design theme?


Yes, the Lyc and Cont engineers knew exactly what they were doing. It was well documented, even back in the 1930's.

Large bore, low RPM engines have interesting advantages.

1) Piston ring swept area is lower, per displacement, on large bore engines and can affect sealing losses.
2) Piston ring swept area is the key factor in friction.
3) Due to simple geometry, the heat transfer surface area is lower in a large bore engine's combustion chamber. When compared to multiple cylinders of the same displacement, leading to better thermal efficiency.
4) Air cooling has a lower temperature differential to combustion gasses, leading to better thermal efficiency.
5) Cooling drag is lower on properly designed air cooled powerplants.

Above, someone brought up the Rotax aircraft engine. Interestingly, the common Rotax, such as the 914 (we have one) has exactly the same BSFC as automotive liquid cooled engines. Yes, they don't consume much fuel, but they also don't make much power. HOWEVER, Rotax is now producing an engine that matches a similarly low powered Lycoming in efficiency. They make a big deal of this! They do this by electronic fuel injection, turbocharging, and a complex set of digital controls. Along with excellent design. Efficiency: 280 - 310 g/kWh BFSC at 5,500 rpm. Look at what it takes to match a Lycoming in efficiency.

Equal BSFC!

Possibly even more interestingly, Klaus Savier has modified a typical aircraft engine for efficiency, and has achieved "God-Like" BSFC numbers in cruise flight. Near 40MPG, at 252MPH, out of a 250HP, Lycoming using electronic ignition, timed high pressure fuel injection and lean of peak operation.

 

[Cujet]

Thought you guys might like a look at some modern aircraft diesel engines. They are quite impressive! And, yes, they do achieve excellent BSFC. But $220,000-$250,000 purchases a LOT of Avgas.

Also, of note, diesel aircraft engines are notoriously hard to re-start at altitude, and often have to carry a bit of power on descent to avoid flame out.

I'm not at all "anti diesel" aircraft engine. In fact, I'd love to operate one. I just do not think we are "there yet" with regard to the proper design criteria for aircraft diesel. Cessna tried it and pulled it from the market due to the above mentioned problems.

 

[A_Harman]

Originally Posted By: Cujet
The real reasons are not what you think:

BSFC: A well tuned Chevy V8 will achieve a BSFC of 0.55 Lb fuel per HP hour. A Lycoming air cooled IO360, 0.38.



I worked at GM on the 5.3 Gen V engine for a couple of years, and I can assure you that it does a lot better than .55 lb/hr*hr. It is highly dependent on where you look at the speed and load map. Peak thermal efficiency of the 5.3 occurs at 2500 rpm, 160 HP, which is just before max power enrichment kicks in. It makes .375 BSFC there, which is 37% thermal efficiency. The 5.3 maintains respectable thermal efficiency up to 3500 rpm, where it is still hanging around 33%. Once the engine gets above 4000 rpm, they bring on full power enrichment lower in the load range, so BSFC suffers. At full power, thermal efficiency is down around 25% due to a lot of excess fuel being used to control EGT out of respect for the catalyst.

I also spent some time studying the performance of the LT4 engine, and the max power efficiency is unspeakable.

 

[LoneRanger]

As far as car engines in airplanes, that topic has come up since back in the day when I flew. I'll take a Lycoming just past the infant mortality stage hour-wise, that's been overhauled by a reputable shop and in a non-hangar-queen Mooney M20 that flies regularly.

I'm one of those that would love to fly again even got my old 1998 vintage PP-ASEL reissued in the new card type with no SSN on it, just last yr. And I think progress has been made on substituting a driver license for a 3rd class medical (which I think is a bad idea though). Go through these phases where I think I would like to fly again, maybe get another trainer level a/c like the '67 Pa-28 140/160stc I had for a bit. But then my annoying analytical side kicks in and I think about what it was like paying hangar rent, insurance, annuals (there are always squawks on a 30 or 40 yr old airplane), 25 hr oil changes (did them 25 even though equipped with a spin-on)... and fuel expense. Yeah, fuel. And back then I remember pumping 100LL self serve at the local FBO at their weekend rate for $2.34 a gallon for example and thinking what a screwin' that was. 'Bout 2x the price of auto gas, which seems to be where Avgas tends to hover.

I think of the fun of flying but then the sheer futility of small single engine GA for my lifestyle vs. what the economic burden would be on my income and I go soft on it every time.

What makes GA flying viable today is having a small business which helps justify it and bear the cost burdens. Individually, heck I know lawyers and a doctor who've sold their birds and stopped flying in as many recent yrs.

My Ophthalmologist has a Cirrus SR22. For the Holidays last yr he was talking about going out to California to visit their kids. Asked how he was planning the flight are you taking that corridor around the Rockies in NM or whereever it is.... no he replied, they bought commercial seats because it cost less than taking the SR22 that far.


Originally Posted By: fdcg27
Your use of the term "death spiral" for what's happening to GA in this country is apt.
I drive past one of our county's two public use GA airports on my commute five days a week and I hardly ever see anyone flying even on a nice day. There is a large hanger with its door facing the road and I often see an American (or Grumman) Traveler and a Cessna 337 rolled out and basking in the sun, but I rarely see them fly.
Today is a beautiful CAVU day and the sky should be full of little airplanes.
It isn't.
As GA activity declines, the price of avgas rises, since it is a highly specialized fuel and can only cost more to blend and ship in ever-smaller batches. The number of wrenches qualified to do annuals also shrinks and the cost of having any little thing fixed can only rise as the number of available wrenches declines. The entire parts infrastructure begins to fade away and parts for even a simple aircraft like a 172 or an old Piper Cherokee become less affordable for any individual who seeks to own what should be a very affordable plane.
A number of larger GA airports have but one FBO who basically runs the airport and sets absurd minimum ramp charges for every airplane. The operator can't make any money putting twenty gallons of 100LL in a 172 so they'll price such small craft off the airport.
The list goes on and I don't know what the answer might be. The FAA has tried various things over the years, like allowing STCs for mogas in certain aircraft, more restrictive and less costly to train for pilot licensing and even allowing the sale of low performance factory built aircraft without type certification.
None of this has done much good, so the outlook for all of those old singles that sit at tie-downs and rarely move remains bleak.
It is a pity, but the era of every farmer having an airplane and many ordinary folks owning and flying one appears to have drawn to a close. Organizations like EAA and some of the classic type clubs do what they can to keep the flame alive, but the trend s clear.

 

[Astro14]

I would love to own and fly a light airplane.

But the cost is prohibitive, and fuel is only one of those considerations. My friend's SR-22 costs him $15,000 every annual. They always find something, or he finally fixes some nagging problem. Either way, it's really expensive just to own an airplane, let alone do the maintenance or put fuel in it.

The sweet spot for a light airplane, in my estimation, is the 300-800 mile trip. Fewer than 300 miles, and driving is so much cheaper, and nearly as fast, that flying isn't competitive. Above 800 miles, the airlines are a lot faster, and a lot cheaper.

But in that sweet spot, the speed of the airplane over other options outweighs the cost.

 

[UncleDave]

Originally Posted By: Cujet
The real reasons are not what you think:

BSFC: A well tuned Chevy V8 will achieve a BSFC of 0.55 Lb fuel per HP hour. A Lycoming air cooled IO360, 0.38.


Im skeptical of your Chevy V8 numbers based on my own dyno room and ownership experiences.

My most recent BBC a fuel injected 588 makes 725 & 819FT LB with a BSFC between .379, and .387 with the average being .382


UD

 

[Cujet]

Originally Posted By: UncleDave
Originally Posted By: Cujet
The real reasons are not what you think:

BSFC: A well tuned Chevy V8 will achieve a BSFC of 0.55 Lb fuel per HP hour. A Lycoming air cooled IO360, 0.38.


Im skeptical of your Chevy V8 numbers based on my own dyno room and ownership experiences.

My most recent BBC a fuel injected 588 makes 725 & 819FT LB with a BSFC between .379, and .387 with the average being .382


UD


Amazing numbers! And I don't doubt them. Engine builders can, and do, employ all sorts of methods to increase power and efficiency. However, we only need to look at the marine industry to see the fuel consumption numbers for typical automotive engines under heavy load and higher RPM.

Remember, we need to reduce the RPM of an automotive engine to prop capable RPM's. This introduces significant additional friction and weight.

So far, we in the aviation world, have been utterly unable to achieve the holy grail of light weight coupled with good BSFC numbers from Chevy engines. There are a few reasons for this. Automotive engines are not lighter per HP produced, as automotive engines are de-rated for aviation use, much like industrial versions of automotive engines. Operating an automotive engine at it's best BSFC zone results in poor power to weight.

Many have tried this "better idea". Few have actually achieved the well rounded level of capability of a modern Lycoming. Maybe one of you guys will be the first. Below is an interesting conversion. $45K for the conversion and only 200 pounds overweight.

 

[Cujet]

The above 430HP V8 conversion has been derated to 180HP, and does not have dual sparkplugs per cylinder, as is common with aviation engines.

I also recall one additional certification requirement of aviation engines. The ability to operate for a specified period of time without oil pressure. Lycoming and Continental both have specifications that allow vertical flight, knife edge flight, and zero G flight for up to 10 seconds. But have also published data that shows operation for up to 30 seconds at full power, without oil pressure will not fail the engine.

From the Lycoming operational manual, Quote:

DO NOT FLY FOR MORE THAN TEN SECONDS IN THE FOLLOWING ATTITUDES:
1. VERTICAL FLIGHT, STEEP DIVE.
2. INVERTED FLIGHT, STEEP DIVE.
3. ZERO-G PERIODS.
4. WING-DOWN OR KNIFE-EDGE FLIGHTS.


"Oil pressure may be interrupted momentarily in certain aircraft attitudes or during certain
combinations of maneuvers. These attitudes and maneuver combinations are generally of the type
which can only be maintained for short periods of time, so there is no serious effect on engine
performance. The effect is normal and is not to be construed as a system malfunction...

The main cause of momentary loss of oil pressure is that in certain attitudes, the oil in the sump
(or at the top of the crankcase during inverted flight) is placed so that it cannot be drawn into the
oil pickup line (or breather line, for inverted flight). For example, during a vertical or steep
inverted dive the engine oil will fall to the front or top-front of the engine so that neither the
breather line nor the oil feed line at the sump has an available supply of oil"

The opposed aircraft piston engine has many design features that are not particularly self evident. Splash oiling is one of them. As the crankshaft is bathed in oil, during inverted or knife edged flight.

The below is a 315HP, Lycoming IO-580. One heck of a capable engine at about 2/3 HP per pound, installed.

 

[Red91]

What is the engine pictured third down called?

 

[Cujet]

Originally Posted By: Red91
What is the engine pictured third down called?


I think you mean the "Deltahawk" diesel. It's a 2 stroke, 4 cylinder, supercharged and turbocharged diesel. 160HP (maybe,,, )

 

[DeepFriar]

Some thoughts on this thread:

The Mercedes based Austro AE330's in the Diamond DA-62 look like they represent the state of the auto-engined airplane state of the art. Full, dual FADEC and now with an 1800 hour TBO. Appears to have great payload/range/speed options. And you sure can't argue with how it looks. I don't know how Beech can sell another Baron compared to it.

Medical issues got me but expense would've done it otherwise. Flying clubs, partnerships and LSA/ultralights still provide a path to fly. Bristell has an an interesting shares program that looks attractive too.

 

[Red91]

Sweet mercy....

All technical data aside, you cannot beat the sound of a two stroke diesel.

Do you know what oil this engine takes? Is it fair to presume an ashless monograde such as Delo 100?