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Ok Ross and Ted,
I've been thinking about this.... and I read part of one of the articles L Adamson provided, where it said that two engines producing the same HP at the same RPM, would produce the same torque.

Given my two comparisons: my 300 hp gas suburban vs my 300 hp Diesel pickup - and the Cat powered heavy haul rig vs the same rig with a 550 hp Chevy -

Are you saying that if I were to create some type of optimal gearbox for the gasoline engine - a torque multiplier -, then run the engine at the RPM required to achieve rated hp (300 or 550 in these examples), that the gas-powered rig would pull the same load up the same grade at the same speed as the diesel does? If that's what you're saying, then I think I get it. Not a very practical or reliable thing to do, but doable in theory I suppose, leaving efficiency and power loss from the gear train out of the discussion.

Let me know if I'm thinking straight. It would not make me a convert to the SI Gospel Fellowship, but I may be starting to understand what you're trying to tell me:)

Kurt

I'm glad you kept an open mind through all of this discussion. This shows you REALLY DO want to understand the concept. Nobody expects you to convert to SI engines. What you have achieved in both your 9 and at Bonneville is very impressive in my mind. I'm a firm believer in driving and flying what turns your crank. Clearly you love diesels which is fine by me.

Getting back to the discussion, in fact, just putting a 3 to 1 gearbox aft of the 502 atmo Chevy would allow it to do almost the same job as the 928 inch turbocharged CAT engine running 40 psi boost. The Chevy would output around 1700 lb./ ft. to the main transmission. As Ted pointed out, it is not going to last anywhere near as long as a 2900 lb. giant loafing along at 1500 rpm and part load and it needs to be kept within a narrow upper rpm band.

Ted hits on the other points about design and intended application well. The CAT is practical for heavy duty truck use but would be a poor choice for a Lancair IVP for instance, just as the Chevy would be a poor choice for the semi.

Ted reiterates my stance on CI, torque etc. My whole objection to people stating that CI engines have superior torque merely because they are diesels just rubs me the wrong way because it is simply not true. Modern turbo diesels have high torque because they are heavily boosted, simple as that. If we apply even half the boost pressure to the same size, same stroke SI engine, we'll always have both more torque and more hp as we can see in any of the examples. HP does the work, not torque.

People continually compare a 6.5L turbo CI engine to a 6.5L atmo SI engine and come to conclusion it has more torque and even more hp in some cases- well of course it does since it is running 2-3 atmospheres of boost- a no brainer. Add even one atmosphere of boost to the same SI engine and it will trounce the diesel in both respects. The SSC Aero is an example of what relatively low boost does to a well designed 6L class production SI engine- 1200/1200 hp and torque is far in excess of any comparable size diesel running even double the boost pressure.

No one disputes the superior BSFC of CI engines. When this can be combined with low weight, longevity and comparable cost to SI engines, they make a fine choice for aircraft. The weight part does not matter much in road use and I'd be the first to admit that some of the modern turbo CI engines in auto and truck use today work very well and are vastly different and better from the stuff available 20-25 years ago. Diesels continue to intrigue me, I don't hate them- well maybe the smell part but even that has pretty much gone away lately.
 
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Well the reason there are so many discussions about torque and hp on the internet is because lay people continue to post nonsense and ignore the science and physics. ...

"Physics BS", well what can I say about that?:confused: On this planet at least, the laws of physics are pretty well established, repeatable and apply to all of us and all things last time I checked.

I think that this misconception about torque is due in large part to the abstract nature of "power"; it is a difficult concept to grasp without formal training in physics. Torque, on the other hand, is more concrete and readily understood by anyone, and is therefore more naturally applied as the explanation for how and why things work.

By the way, in case your interested, much more lively (and rude!) discussions on this topic are available in the various truck and towing forums.

John
 
Modern turbo diesels have high torque because they are heavily boosted, simple as that.

I need to get a friend of mine in on this discussion. He's a two time RV builder, prefers Lycomings or clones, but best of all (in regards to this subject), he spent decades with Union Pacific as an instructor for the mechanics of diesel engines. This morning at breakfast, he was able to quote exact figures off the top of his head, including BTU's, compression ratios, turbo boosting, etc.

But he did say one thing, and to quote him on it. In regards to diesel engines..... "torque is everything!"

I also got the impression that at sea-level altitudes, the boost wasn't doing much for a diesel engine, just as within an airplane with turbo boost. And that the high compression of a diesel was much of the factor in terms of torque. And at the same time, because of the higher BTU content of diesel fuel, and the fact that less rpms are required to do the same job.........the diesel will always win in the fuel use department as well as longivity of the engine.

But don't quote me on all this (in case I have misunderstandings)............except his "torque is everything!" statement.

L.Adamson --- RV6A
 
I think that this misconception about torque is due in large part to the abstract nature of "power"; it is a difficult concept to grasp without formal training in physics. Torque, on the other hand, is more concrete and readily understood by anyone, and is therefore more naturally applied as the explanation for how and why things work.

By the way, in case your interested, much more lively (and rude!) discussions on this topic are available in the various truck and towing forums.

John

I was reading some of these last night for entertainment.:eek::confused: Like I said, well entrenched belief in the CI culture.

If you are towing something with a truck a long distance, SI engines are not the best choice simply because they'd burn a lot more fuel getting the job done and there are few production SI turbo powered trucks made anyway.

I've never had a problem saying that turbo CI trucks are not good for towing and get better mileage doing it than an SI engine- total reality The part that bugs me is where people think that torque is all important and comparable CI engines have more torque than SI engines.
 
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I need to get a friend of mine in on this discussion. He's a two time RV builder, prefers Lycomings or clones, but best of all (in regards to this subject), he spent decades with Union Pacific as an instructor for the mechanics of diesel engines. This morning at breakfast, he was able to quote exact figures off the top of his head, including BTU's, compression ratios, turbo boosting, etc.

But he did say one thing, and to quote him on it. In regards to diesel engines..... "torque is everything!"

I also got the impression that at sea-level altitudes, the boost wasn't doing much for a diesel engine, just as within an airplane with turbo boost. And that the high compression of a diesel was much of the factor in terms of torque. And at the same time, because of the higher BTU content of diesel fuel, and the fact that less rpms are required to do the same job.........the diesel will always win in the fuel use department as well as longivity of the engine.

But don't quote me on all this (in case I have misunderstandings)............except his "torque is everything!" statement.

L.Adamson --- RV6A

Actually the low rpm is not a real advantage here except for longevity and in a loco application, engine weight is no factor in design. A higher revving engine could be geared to do the same job but at the expense of longevity- but this makes no sense to use in this application.

Actually the very high CR in CI engines does not do much for torque as we have seen. I searched a lot over the last few days and could not find a single case where a comparable sized CI engine had more torque than an SI engine. If you can find some examples, let me know. High CRs use a lot more energy to compress the charge and there is a rapidly diminishing hp gain as CRs climb above 12 or so- the curve is very flat.

A diesel needs to be larger and run more boost in fact to do the same work as an SI engine. Many people who come from the CI industry/ world just won't believe this.

Torque IS a factor in determining hp and therefore WORK that an engine can perform. It is a simple fact that the more torque any engine produces at a given rpm, the more hp it also has. If people are impressed that some big CI engine produces 3000 lb./ft. at 1200 rpm, they should only be impressed because it is producing 685 hp at such low rpm. Its specific hp output is actually pretty pathetic for a 1500 cubic inch engine but this is precisely the type of engine design best suited for a boat, heavy truck or locomotive. As such, your friend's statement that "torque is everything" is true from one perspective but scientifically incorrect. A modern atmo F1 engine with say 200 lb./ft. geared down 16 to one from 20,000 rpm could perform the same "work" as this massive turbo diesel at 1200 rpm in reality.
 
I've never had a problem saying that turbo CI trucks are not good for towing and get better mileage doing it than an SI engine- total reality The part that bugs me is where people think that torque is all important and comparable CI engines have more torque than SI engines.

Yes, I do think torque is all important...........in regards to pickups & towing. I get bugged about modern liquid cooled engines in GA airplanes. I really do, as I have not seen one that compares anywhere close to 70 year old technology for simplicity & reliability. My favorite aircraft of all time is the "liquid cooled" P-51 Mustang, and I prefer my liquid cooled Honda motorcycle engine over that of a Harley because liquid cooling is more sutible for ground bound vehicles. Air cooled Harleys sound better though, and Lycs sound better than high reving liquid cooled in airplanes. Of course, that is my opinion, along with some others. My Honda is a six cylinder Valkyrie bought new in 98'.

When WII ended, large commercial aircraft stuck with air cooled radials, and dispensed with the liquid cooled variety. In terms of RV's, it just happens that my air cooled Lycoming at 180 HP/2700 rpm/ & 350 lb.ft. of torque is getting off the ground & climbing faster than the Subaru H6 at 212 HP/ 4400 RPM / 210-247 lb. ft. torque & maximum rpm of 6000.

In this case, is it the torque of the larger displacement airplane engine, or what? I don't have the real answer to this one. Yet, I'll take my diesel pickup over a comparible SI pickup anyday (or, I suppose they really don't make comparibles). My thoughts are due to actual experience over the years. Heavy duty pickups are a part of my job, and I've been driving them for almost 45 years. So yes, I too get bugged when someone try's to tell me different, based on engineering principles, and just a small bit of experience with the actual product. If horsepower is what counts, then that H6 should be flying circles around my prehistoric engined RV, yet it doesn't, and may never. Why is that? I'm rather curious. But for the record, I much prefer SI for my airplane.........at this point.

L.Adamson ---- RV6A
 
Actually the very high CR in CI engines does not do much for torque as we have seen. I searched a lot over the last few days and could not find a single case where a comparable sized CI engine had more torque than an SI engine. If you can find some examples, let me know.

http://www.autoblog.com/2010/03/10/gm-quickly-one-ups-ford-with-2011-duramax-diesel-ratings-releas/

Not bad for an engine stuck on the front of a standard sized pickup, and has more towing ability & better fuel economy at the same time. That really IS, the diesel advantage.

L.Adamson
 
Actually the very high CR in CI engines does not do much for torque as we have seen. I searched a lot over the last few days and could not find a single case where a comparable sized CI engine had more torque than an SI engine. If you can find some examples, let me know. High CRs use a lot more energy to compress the charge and there is a rapidly diminishing hp gain as CRs climb above 12 or so- the curve is very flat.

A diesel needs to be larger and run more boost in fact to do the same work as an SI engine. Many people who come from the CI industry/ world just won't believe this.

Ross, you're forgetting two-stroke. I challenge you to find a "stock" 5.2L SI atmo engine that produces 470 ft/lb, like the 318 inch atmo diesel does. Yeah, you're right, it's not apples to apples cuz it's a 2-stroke, but it really works well, and there's no down-side (other than the smell). When most of us think of two-strokes, we think of motorcycle engines and outboards with their associated quirks, like low life-span, mixing oil, fouling plugs, etc. But the diesel two strokes have none of these issues. And they're extremely reliable.

That's why I'm so excited about them for aircraft engines. As you say, they would be ideal for aircraft if they can meet the criteria (simplicity, direct drive, efficient, low parts count, low weight). All of these have been achieved. Its just a matter of time before the "right" package comes out.

I'm agreeing with all the physic and mathematics you provide, along with all of your theoretical examples of SI engines being able to perform on par with CI engines in the right circumstances. Problem is, no one's producing the truck engines you describe. They're building diesels with incredible pulling power, reliability, and efficiency for the "work" they do. Why don't they produce these incredible SI engines and drive trains they would require to do the same work as a diesel? My guess would be "no market".

Now, if your "work" is getting a light vehicle through the 1/4 mile in big hurry, then SI is the best tool, because in this application, HP is king.

So, as you point out, it's all about the type of "work" you wish to perform. In my experience, the SI engine works great for intermittent pulls and bursts of speed, whereas the CI engine works best for the long pull under a steady load. You have pointed all of this out. But when you look at the two "jobs", which is more like an airplane's work? IMHO, it's the "long pull under a steady load". That's why, as L Adamson points out, Lycomings and the like are designed to have more Diesel-like characteristics, ie slow-turning, lower hp, higher torque, and simplicity. Yes, as you say, high-revving, higher hp, lower torque SI engines can be converted to work in these applications (with their associated gearboxes, turbos, etc), but, at least for now, they struggle to match the traditional engines. (but you keep working at it and you'll get there, and I'll respect you for it!)

Just some of my thoughts for tonight....
Kurt
 
Efficiency

Somehow it seems that "efficiency" may be being left out of this Truck discussion.

Trucks need to be efficient to be financially viable. So a compromise might be made to give up some "performance" for "efficiency". For example, a trucker might be willing to be forced to slow down to 40mph going up a hill in order to be able to run a smaller, more cost-efficient engine over the life of the truck. OTOH, a passenger car owner might not be willing to make that compromise, and therefore would choose to buy a larger engine than he might need otherwise.

Sorta like the choice between a 150 hp carbureted Lyc, vs. a 200 hp angle-valve FI Lyc, let's say. I think the term is "Life-Cycle cost".

Physics may well decide which engine is superior in any given application, but economics drives the decision-maker.
 
Yes, I do think torque is all important...........in regards to pickups & towing. I get bugged about modern liquid cooled engines in GA airplanes. I really do, as I have not seen one that compares anywhere close to 70 year old technology for simplicity & reliability. My favorite aircraft of all time is the "liquid cooled" P-51 Mustang, and I prefer my liquid cooled Honda motorcycle engine over that of a Harley because liquid cooling is more sutible for ground bound vehicles. Air cooled Harleys sound better though, and Lycs sound better than high reving liquid cooled in airplanes. Of course, that is my opinion, along with some others. My Honda is a six cylinder Valkyrie bought new in 98'.

When WII ended, large commercial aircraft stuck with air cooled radials, and dispensed with the liquid cooled variety. In terms of RV's, it just happens that my air cooled Lycoming at 180 HP/2700 rpm/ & 350 lb.ft. of torque is getting off the ground & climbing faster than the Subaru H6 at 212 HP/ 4400 RPM / 210-247 lb. ft. torque & maximum rpm of 6000.

In this case, is it the torque of the larger displacement airplane engine, or what? I don't have the real answer to this one. Yet, I'll take my diesel pickup over a comparible SI pickup anyday (or, I suppose they really don't make comparibles). My thoughts are due to actual experience over the years. Heavy duty pickups are a part of my job, and I've been driving them for almost 45 years. So yes, I too get bugged when someone try's to tell me different, based on engineering principles, and just a small bit of experience with the actual product. If horsepower is what counts, then that H6 should be flying circles around my prehistoric engined RV, yet it doesn't, and may never. Why is that? I'm rather curious. But for the record, I much prefer SI for my airplane.........at this point.

L.Adamson ---- RV6A

so are you comparing diesel trucks and SI trucks the same way that you compare aircooled airplane engines and water cooled airplane engines?!

what about that rotax?! :devil:
 
Okay, How About Some Practical Advice

I went looking for some practical advice about a question that is bugging me -- researched aviation fuels and came upon this thread. Helpful and entertaining until the discussion of hp vs. torque, etc. Always amazing what one can learn at vansairforce.

Maybe this belongs in another thread -- but here's my question. I plan to purchase another plane within the next year or two (had to sell my Grumman interest when I moved) -- I'm a slow buyer who likes to shop a lot and understand all the options. RV-4 is probably my price range, though I'd love to have an -8.

After lots of reading I have become convinced that avgas truly is going away. My local FBO says perhaps as early as two years from now.

I'm not educated and experienced in mechanical things, so I can't design, develop, maintain my own experimental FWF system.

So now I'm thinking, why would I buy any airplane right now? At least, any airplane that can't run on mogas. Better wait to see how this all works out?

I'd love to hear your reflections on this.
 
David you would buy an airplane right now because they are at significantly low price compared to the past 15 years.

getting a lycoming to run on mogas should not be a large problem with standard compression pistons.

the only problem with AVGAS is the lead. if any other higher octane unleaded is used it is a pretty easy transition
 
Now, if your "work" is getting a light vehicle through the 1/4 mile in big hurry, then SI is the best tool, because in this application, HP is king.

Kurt

Work is work whether we are talking about a lightweight GSXR-600 accelerating from 0-140 mph or a 7500lb. diesel truck pulling a 10,000 lb. trailer up a 5% grade. Technically there is no real difference here- both are about accelerating a given mass over a given distance within a given amount of time- the exact definition of hp in fact. This is why all engines, be them Lycomings, bike engines, F1 engines, car engines, turboprops or diesels are always rated by hp, not torque.

Hp is really about rate of energy release and work is all about rate. The ability of any engine to perform work is related to the area under the hp curve within its usable or designed rev range. The larger the area, the more work any engine can do and generally the more flexible it is.

Each vehicle type has a transmission mated to it to make best use of its hp curve or area. My GSXR would be pitiful with a 2 speed gearbox despite it's relatively good power to weight ratio whereas a sprint car works just fine with only one gear ratio. It is all about application and engine characteristics.

A semi engine has to have a lot of gears to accelerate that large mass effectively over quite a large speed range because it has such a short rev range and relatively little hp to do the job at hand. It would be unusable for the application with only 3 gears for instance.

With regards to the Subaru H6 engines, the real reason some have not performed well is simply because they are not producing rated hp. This has been found to be due to 4 basic issues:

1. Gearbox ratios do not allow the engine to achieve peak power rpm

2. The installed manifold is very restrictive compared the the OEM manifold

3. The exhaust systems are more restrictive than OE

4. Modifications to lock out the VVT system have compromised volumetric efficiency

We have two late H6 guys who have some of these issues addressed and they are getting 165-170 knots true at 8000 feet now. Obviously they are still down from the stock rated hp as they don't perform any better than your average O-360.

Two other ways of comparing engines is specific power output which is hp/ displacement and BMEP (brake mean effective pressure) which is the average cylinder pressure over the whole cycle. BMEP= 150.8 X Torque/ Displacement for a 4 stroke engine. In both measures, CI engines don't even come close to matching SI engines, in fact most turbo CI engines can't match even most good SI atmo engines in these regards. BMEP is really the best universal way of comparing different engine designs.
 
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New Diesel Unveiled

I came across an interesting explanation in my old Basic Thermodynamics textbook on the question of SI vs. CI engines:

"The smooth addition of heat added per cycle in the theoretical Diesel (CI) and Otto (SI) cycles is a greatly simplified assumption of the actual way that heat develops in an engine cylinder. The spark ignited Otto engine inhales a mixture of air and gasoline vapour and compresses it.

To prevent preignition of the fuel-air mixture the compression temperature must be kept below the ignition temperature. An electric spark ignites the mixture at or near the end of the compression stroke. To prevent preignition the compression ratio of the engine must be kept below about 11 or 12:1. Modern automobile engines (this was written in the 1960s) have compression ratios ranging from about 6 to 10:1; this limits the maximum efficiency at which an Otto engine can work.

In contrast to the Otto engine, the diesel engine depends on compressing the air enough to heat it to the ignition temperature of the fuel. Ideally, the fuel starts burning as soon as it mixes with the compressed air at the begining of the constant pressure process. To achieve ignition temperatures, diesel engines must have compression rations of at least 12:1. Practical diesel engine compression ratios range from about 12 to 22:1.

Because of the fuel-ignition limitations of the Otto engine and the low compression ratios that must be used we find actual diesel engines more efficient than actual Otto engines, despite the Otto cycle being more efficient than the diesel. The practical compression ratios for the engines explain the paradox."

This explains why highway semi trailer trucks use diesel engines almost exclusively (also large marine and locomotive engines): the engine is more efficient and so uses less fuel than an SI engine. (Also, many years ago diesel was cheaper than gasoline).

The higher compression ratio required in diesel engines also explains why they are generally heavier than an equivalent SI engine: the compression stroke loads are higher, so the piston, rod and crank must be heavier to result in the same working stress. Engines designed for long life and high duty cycles such as diesel truck, marine and locomotive engines are heavier yet for durability.

The heavier pistons and rods in a diesel also limit the maximum speed of the engine due to higher inertia loads.

So back to the Wilksh diesel engine, this is why it is a two stroke engine: to achieve a similar power to weight ratio as a SI engine in spite of having to have heavier internal parts. Thus it has one power stroke per piston per revolution (2 stroke cycle) instead of one power stroke per piston per 2 revolutions (4 stroke cycle). In contrast the SMA engine that Continental has licensed is a 4 stroke cycle.

Regarding Subaru H6 vs Lycoming climb rates, in addition to the installed power commented on by Ross, to do a proper comparison you must use exactly the same propeller and the same airframe. Otherwise you don't know whether it is the engine or the propeller making the difference.
 
Good post terrye. These days with better chamber designs and electronic engine controls CRs on auto engines are generally in the 10.5-13 to 1 range. Many of these are designed to operate on 87 octane. Some competition engines run CRs of up to about 15.5 to 1- this being about the practical limit for hp gains for various reasons. Direct injection on modern SI engines has allowed higher CRs for better thermal efficiency without pre-ignition. Some of the latest SI engines like the Toyota 2 ZR-FXE get within 12-15%% of the BSFC figures of modern lightweight common rail CI engines.

It should also be mentioned that the relatively low revving nature of CI engines is not just due to the heavy reciprocating components but also from the characteristics of how diesel fuel burns. It is simply not well suited to very high rpms. Even the Audi race diesels are low revving by comparison to their SI cousins. Of course the engineers are working on this issue too and no doubt this will get better as new technology evolves.

I agree that the 2 stroke turbo CI engine makes a lot more sense for aircraft than a 4 stroke design due to its far better power to weight ratio. The WAM aptly demonstrates this- being very light indeed.

And yes, the propeller is a significant factor in comparing different engine combinations. The typical MT prop used on many is better suited for cruise around 2500 rpm but the only sure test is to use the same prop on both engines.
 
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And yes, the propeller is a significant factor in comparing different engine combinations. The typical MT prop used on many is better suited for cruise around 2500 rpm but the only sure test is to use the same prop on both engines.

My comparison is my RV6A/ Lyc/ Hartzell CS versus RV8/Egg H6/MT 3-blade electric prop.
 
This is why all engines, be them Lycomings, bike engines, F1 engines, car engines, turboprops or diesels are always rated by hp, not torque.

Sorry, can't help but drag this thread out.

I tend to speed read. I read a lot, when it comes to subjects that interest me. I'd have to be "blind", to not have seen, that an amazing number of diesels are rated with torque specifications along with horsepower. It really is a big deal, and should be. And it's far from being almost meaningless.

L.Adamson
 
Sorry, can't help but drag this thread out.

I tend to speed read. I read a lot, when it comes to subjects that interest me. I'd have to be "blind", to not have seen, that an amazing number of diesels are rated with torque specifications along with horsepower. It really is a big deal, and should be. And it's far from being almost meaningless.

L.Adamson

Yep, just builds on the misconception so prevalent in the truck world since they are comparing usually to atmo SI engines. Marketing 101- emphasize the good parts, downplay the less impressive parts. Seems like all diesel guys believe it so why not use it. It is useful in comparing to other similar CI turbos at least.

I'm not disputing that most CI turbo trucks will accelerate a given load faster and up a steeper grade than an atmo SI truck- obviously they do because they have more area under the hp curve. I am disputing that they'd have any chance in doing the same against a turbo SI engine of the same displacement.

You can believe what you want but I think (hope) it is pretty obvious to most people that dropping in the SSC Aero SI turbo V8 into any standard V8 diesel truck is going to make it a LOT faster because it has triple the hp and double the torque on less than half the boost. The higher rpms would also allow you to double the final drive ratio from the CI engine, making it even faster still.

Gale Banks touts how fast their new Duramax diesel S-10 drag truck is at 7.77@180 mph. Not very impressive when you consider Lingenfelter's 2.2L Ecotec powered Sonoma drag truck was going a lot faster almost 10 years ago.

From a performance standpoint CI engines are no match for SI engines.

For fuel economy and long life, SI engines are inferior to CI engines.
 
Yep, just builds on the misconception so prevalent in the truck world since they are comparing usually to atmo SI engines. Marketing 101- emphasize the good parts, downplay the less impressive parts. Seems like all diesel guys believe it so why not use it. It is useful in comparing to other similar CI turbos at least.

From a performance standpoint CI engines are no match for SI engines.

I just can't let these statements go unanswered.

Maybe they used to, but no truck manufacturer needs to compare diesel vs gas. The engines take care of themselves in that regard. And IMO, and I know that most modern diesel owners will agree, there are no "less impressive parts" to downplay. They're building those trucks because there is a huge demand for them, not because they're pulling the wool over our eyes (as you infer), and selling us on "torque numbers" because we're stupid enough to buy into it. We KNOW what we're buying. and we KNOW how much better it works in the real world.

Which brings me to my point: what this discussion boils down to is that everyone has a different perception of what "performance" is. To you, it's quite obviously acceleration. To us diesel owners, it's about the "whole package", and we'll gladly give up a second or two in the quarter mile (since we're not doing that very often, or at all), in order to enjoy a MUCH better overall performance package.

You always like to bring up your examples of how well SI engines would perform (against a diesel) if they were boosted, if they were geared, if if if. But, fact is, there's no SI package available for a truck with "performance" even close to what the diesels provide. Sure, you can "roll your own", in order to prove your point - which is what you're doing with the subie - vs Lyc. etc. But in the truck world, no one's headed in that direction that I know of (not just for acceleration, for everyday driving and pulling). I have a few good friends who have spent a lot of time and money trying, but with results so poor that they switched to diesel.

Do you know of any aftermarket firms producing a turbo or supercharged SI engine that the average Joe can buy, put in his truck, and enjoy the same "performance" that he can get from an off-the-shelf diesel? If so, it would be really interesting to do a comparison test under everyday conditions. Maybe that should be your next project:) and I'll put my Duramax or Cummins up against it and see how well it works.

This is the same thing that the Traditional VS Alternative aero engine argument always ends up being about. Traditional engines offer a "performance package" that is very hard to beat. The engines are mission-designed, and they accomplish that mission very well. We always hear (even from Vans) that when there is an alternative engine that offers everything that the traditional engine offers, they'll be all over it. I believe that engine is a diesel. You believe it's a geared SI auto engine. Only time will tell.

The thing I like about you, Ross, is you're not just talkin' about it! You're doing your darndest to prove that what you say actually works in the real world. Someone's gotta do it. I sincerely hope for your continued success.

Kurt
 
Fuel Economy Not Performance

I just can't let these statements go unanswered.

Maybe they used to, but no truck manufacturer needs to compare diesel vs gas. The engines take care of themselves in that regard. And IMO, and I know that most modern diesel owners will agree, there are no "less impressive parts" to downplay. They're building those trucks because there is a huge demand for them, not because they're pulling the wool over our eyes (as you infer), and selling us on "torque numbers" because we're stupid enough to buy into it. We KNOW what we're buying. and we KNOW how much better it works in the real world.

Which brings me to my point: what this discussion boils down to is that everyone has a different perception of what "performance" is. To you, it's quite obviously acceleration. To us diesel owners, it's about the "whole package", and we'll gladly give up a second or two in the quarter mile (since we're not doing that very often, or at all), in order to enjoy a MUCH better overall performance package.

You always like to bring up your examples of how well SI engines would perform (against a diesel) if they were boosted, if they were geared, if if if. But, fact is, there's no SI package available for a truck with "performance" even close to what the diesels provide. Sure, you can "roll your own", in order to prove your point - which is what you're doing with the subie - vs Lyc. etc. But in the truck world, no one's headed in that direction that I know of (not just for acceleration, for everyday driving and pulling). I have a few good friends who have spent a lot of time and money trying, but with results so poor that they switched to diesel.

Do you know of any aftermarket firms producing a turbo or supercharged SI engine that the average Joe can buy, put in his truck, and enjoy the same "performance" that he can get from an off-the-shelf diesel? If so, it would be really interesting to do a comparison test under everyday conditions. Maybe that should be your next project:) and I'll put my Duramax or Cummins up against it and see how well it works.

This is the same thing that the Traditional VS Alternative aero engine argument always ends up being about. Traditional engines offer a "performance package" that is very hard to beat. The engines are mission-designed, and they accomplish that mission very well. We always hear (even from Vans) that when there is an alternative engine that offers everything that the traditional engine offers, they'll be all over it. I believe that engine is a diesel. You believe it's a geared SI auto engine. Only time will tell.

The thing I like about you, Ross, is you're not just talkin' about it! You're doing your darndest to prove that what you say actually works in the real world. Someone's gotta do it. I sincerely hope for your continued success.

Kurt

Nobody thinks you are stupid for buying a turbo diesel truck. They are the best choices for the job you are doing- no doubt in my mind or the millions of other owners out there.

I agree with several of your points and observations here. All this started when someone posted that diesels offered superior performance to comparable SI model cars. Whenever I see that posted, I attack it because it is BS. That was what I was referring to. Performance in my mind is acceleration (work) not fuel economy. Nobody disputes that diesel cars, diesel aircraft or diesel trucks get better fuel economy on any given mission.

I posted many examples in many different types of vehicles and types of use showing the clear superiority of SI engines in the performance realm. When you say MUCH better performance here, you are again comparing to atmo SI engines again. If the CI engine is "superior" it should be able to compete with SI turbo engines. Yesterday I posted as close to "apples to apples" in a totally performance application- drag racing. Both truck drag chassis, both turbocharged yet the SI engine with 1/3rd of the displacement was actually quicker and faster in the 1/4 mile than the CI engine.

The contest would be no different with street trucks towing a huge load up a mountain. It is a no brainer to take a 6.6L SI V8 and put twin turbos on it to make 1000+hp and 800-1000 lb. ft. The math proves that this is a contest the CI engines can't win yet many still won't believe it. The high rev range allows the SI engine to have a much higher final drive ratio as well.

Interestingly this afternoon I was comparing 2008 CR tests of the Chevy, Ford and Dodge turbo diesel trucks against the atmo SI engined ones. The 1500 ones weigh about 1500 pounds less than the 2500 models which is fairly significant. However in all 3 cases the turbo diesel engines also had 1-1.3L more displacement. So displacement vs. weight was quite similar in all cases. In the 1/4 mile, the smaller SI engines were faster and quicker across the board- a full second quicker in the case of the Ford and Dodge and all without any turbos.

We could compare my 2.2L turbo 4 stroke SI to your 1.8L turbo 2 stroke CI in our RVs. It would be no contest again except at the fuel pumps since I can climb out at over 2000 ft./min. solo and have trued 181 knots at 15,000 feet- all at less than 40 inches MAP and with a poorly matched propeller.

I don't believe that a geared SI engine will be the future for powering RVs. I did mine that way because it is cheap and interesting, not because it is better than a Lycoming. My FF package was under $10K including the propeller. You could well be right that a sound Lycoming replacement will be in the form of a 2 stroke turbo diesel and I think that would be cool!

I salute you too Kurt for actually doing it and testing it. So much more valuable that some people who talk but never do something different and interesting.

In summation, fuel economy is the forte of diesel engines, not performance.
 
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The contest would be no different with street trucks towing a huge load up a mountain. It is a no brainer to take a 6.6L SI V8 and put twin turbos on it to make 1000+hp and 800-1000 lb. ft. The math proves that this is a contest the CI engines can't win yet many still won't believe it. The high rev range allows the SI engine to have a much higher final drive ratio as well.

Interestingly this afternoon I was comparing 2008 CR tests of the Chevy, Ford and Dodge turbo diesel trucks against the atmo SI engined ones. The 1500 ones weigh about 1500 pounds less than the 2500 models which is fairly significant. However in all 3 cases the turbo diesel engines also had 1-1.3L more displacement. So displacement vs. weight was quite similar in all cases. In the 1/4 mile, the smaller SI engines were faster and quicker across the board- a full second quicker in the case of the Ford and Dodge and all without any turbos.

I don't believe that a geared SI engine will be the future for powering RVs. I did mine that way because it is cheap and interesting, not because it is better than a Lycoming. My FF package was under $10K including the propeller. You could well be right that a sound Lycoming replacement will be in the form of a 2 stroke turbo diesel and I think that would be cool!

I salute you too Kurt for actually doing it and testing it. So much more valuable that some people who talk but never do something different and interesting.

In summation, fuel economy is the forte of diesel engines, not performance.

Fair point Ross (though I truly don't see the point), but again not a complete picture. How many miles will your "1000+ hp SI V8" go towing 120,000 lbs?? A Pete with a piddly little 425hp cat can and will probably go a million miles or so before it needs to come out of the frame. Not very fast in the 1/4, but how many gasoline powered Kenworths have over a million miles on the engine? Take your same "contest" (however subjective) and lengthen it out for 500,000 miles...how do you think that'll turn out? :confused:

You can banter back and forth all you want about hp, acceleration, "performance", etc.., but the fact is that airplanes are much more like heavy trucks that drone on for many miles over quarter mile dragsters.

Just my 2 cents as usual and no flames intended...it just seems like many times the debates like this run off into a world where the details being discussed become almost pointless to the application we're referring to. I would argue that fuel economy isn't the only "forte" of diesel engines. Lots and lots and lots of variables to consider!

Cheers,
Stein
 
In summation, fuel economy is the forte of diesel engines, not performance.

And that's your opinion of course, since we're talking a lot of what if's.
I buy diesel trucks for performance rather than fuel economy. For a while, diesel fuel was selling for higher than premium gasoline. These days it matches regular or is lower............which is the way it use to be.

But never the less, I don't see a bunch of people cramming dual turbo SI's in their trucks just to pull trailers up long climbs. I don't see manufacturers doing it either. People are already complaining about the cost of fuel for SI truck engines as it is, let alone installing a super high performance engine just to compete in the hill climb. Therefor, my diesel vehicle has the edge on performance for the job I bought it for. Besides, my diesel easily surpasses freeway speeds, and that often includes uphill pulling a load.

So in a nutshell, your summation is still an opinion from one point of view. Not only is the diesel performance better for the task that I expect of it, but it will most likely last much longer..............as well as the fuel economy.

P.S. ---- I'm glad to see that you finally feel that reduction drives aren't the best method of powering GA aircraft. Just let everyone know! :D BTW someone asked about an Egg H6 last week. He only had 3 post's and might be new to it all. I don't believe that anyone replied.

L.Adamson ---- RV6A
 
TCM / SMA

I found this the other day. Kind of interesting.
avweb.com/avwebflash/exclusivevids/ExclusiveVideo_SMACessnaConversion_ParamusFlyingClub_201827-1.htm
"the most requested plane" in the club.

It looks like the biggest drawback for the SMA is the cold weather. This, of course, will be the same problem for TCM. I guess that a cold weather kit to close off inlets/outlets is one answer. I'm sure they'll work through it. This is where liquid cooling comes in handy. As far as I know, there are no cold-weather restrictions on the WAM.

Kurt
 
Link doesn't work

Just go to YouTube and type in "SMA diesel aircraft". It comes right up. I wish I was more computer-savvy.
 
Hmmm

Very interesting video.

Seems like it works quite well.

A few things stand out to me, trying to be objective:

I'm not sure about their economic forecast here. If we assume equal oil change intervals and standard spark plug maintenance and use their cost numbers and flight hours per year and assume the 470 and the SMA both go all the way to overhaul without major problems, the break even is at about 3000 hours and ten years by my calcs. If you left the $55K extra in the bank at even 3% interest, compounding over 10 years, it pays for an overhaul on the Conti and you still have that $55K left in the bank.

The temp limitations are surprising and not clear what dictates them. I'd be interested to know why. The airplane would be grounded at least 25% of the year in Southern Canada due to these and perhaps 50-60% of the time during winter months. Completely useless in true cold climates in the North.

I believe they also limit altitude to 12,500 feet due to turbocharger rotational limits because of the very high pressure ratio required to make the hp here (65 inches in cruise). This makes the aircraft not very useful for use in and around mountainous areas and certainly for IFR work around here in the Rockies.

I guess I'd question the whole concept given the limitations. It does nothing different or better from the 470 except burn less fuel and run a bit smoother but at a much higher initial cost.

Seems like they need to get the cost way down and fix a couple things to make it competitive in all markets. Right now, it is more of a flatland/ temperate climate engine. In Europe with higher avgas cost and limited avgas availability, payback would be much quicker.

The different/ cool factor obviously makes it popular to rent in this case. I'd be interested in flying one too!

Thanks for the video link.
 
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First hand report of SMA in the mission field

I have been following the alternative engine developments for quite some time, and since it will be a while before I start to build, I'll continue to do so.

In any case, in March I received the MSI (Mission Safety International) newsletter about a visit they paid to a some missionaries in Niger who happen to fly an SMA powered C182. Very interesting read. Take a look here:

http://www.msisafety.org/PDF/SN-Mar 10.pdf
 
Thanks for posting this, again very interesting. Some unusual maintenance requirements and some teething issues to solve for SMA.
 
Very interesting video.
The temp limitations are surprising and not clear what dictates them. I'd be interested to know why.

Mostly it's due to the minimum peak compression temperature required to initiate combustion. On the ground, this is a startability issue, but once airborne, if you let the fire go out, say in a low-powered descent from altitude, you might have a lot of trouble getting it restarted when you really need it!

A
 
Mostly it's due to the minimum peak compression temperature required to initiate combustion. On the ground, this is a startability issue, but once airborne, if you let the fire go out, say in a low-powered descent from altitude, you might have a lot of trouble getting it restarted when you really need it!

A

Really? I heard the guy talking about flameout in the vid but kind of dismissed it. Wouldn't all diesels have this problem in cold weather? Diesels don't have an issue idling here on -30C days- no boost at idle but they are liquid cooled of course.

Would this be a major problem on air cooled diesel designs? Seems like they just need some simple thermostatically controlled damper doors like my '66 Corvair had if it is an over cooling issue.
 
Yes, it is a major issue, yet to be addressed properly. Diesels work reasonably well on the road because of highly developed glow-plug technology and a relative lack of altitude variation.

On an aircraft at altitude, the peak compression temperature of very low density air (temp and pressure) is a double whammy. Also, once you're up there and the fire has gone out, you don't have any energy for your turbocharger to help boost you out of the problem. It goes mysteriously silent on you also...

It's less of a problem on liquid cooled diesels, but only because you can shut down most of the cooling. IMO, though it doesn't mean that air-cooled aero-diesels are dead. I happen to think they are the best way forward, if you select your technology correctly.
 
Thanks Andy. That problem had never occurred to me in aviation use but makes perfect sense when you think about it.
 
No glow plugs

Yes, it is a major issue, yet to be addressed properly. Diesels work reasonably well on the road because of highly developed glow-plug technology and a relative lack of altitude variation.

On an aircraft at altitude, the peak compression temperature of very low density air (temp and pressure) is a double whammy. Also, once you're up there and the fire has gone out, you don't have any energy for your turbocharger to help boost you out of the problem. It goes mysteriously silent on you also...

It's less of a problem on liquid cooled diesels, but only because you can shut down most of the cooling. IMO, though it doesn't mean that air-cooled aero-diesels are dead. I happen to think they are the best way forward, if you select your technology correctly.

Andy this is incorrect. Most modern diesels aren't running glow plugs. They do frequently use a inlet air heater for starting. Direct injected diesels rarely have glow plugs at all. This would be an issue for aircraft of course. The inlet heaters draw a BUNCH of power to warm up, and you would need suffcient battery power to run one and then crank your engine for a in-air restart.
Bill Jepson
 
Wow, when I posted this I never expected the discussion to get this technical.

Also amazes me how smart everyone is, or how dumb I am. Either way.
 
Wow, when I posted this I never expected the discussion to get this technical.

Also amazes me how smart everyone is, or how dumb I am. Either way.

The Alt Engine threads always generate plenty of views and discussion but usually we all learn something we didn't know before. My theory is that most people are secretly bored with their Lycomings and long for something better/ cheaper/ different- something pretty hard to deliver on all counts, which is why most still fly behind Lycomings! :)
 
Andy this is incorrect. Most modern diesels aren't running glow plugs. ...

... Direct injected diesels rarely have glow plugs at all.

Sorry Bill, where did you get your info from?

12 23 7 786 869 is the part number for the glow plug fitted to the E71 BMW X6 30dX and 35dX and that's pretty modern...
 
Wow, when I posted this I never expected the discussion to get this technical.

Also amazes me how smart everyone is, or how dumb I am. Either way.

Thing is, few people readily divulge their career history so if you knew what people did 9-5, you'd probably be surprised at the level of specialist expertise in many areas floating about this forum.

People who build their own aeroplanes generally aren't stupid, or maybe they are...!? :D
 
The Alt Engine threads always generate plenty of views and discussion but usually we all learn something we didn't know before. My theory is that most people are secretly bored with their Lycomings and long for something better/ cheaper/ different- something pretty hard to deliver on all counts, which is why most still fly behind Lycomings! :)

Nope!!!

Diesels for my trucks, and Lycomings for the RV. Wouldn't have it any other way! :D Besides, my Lyc powered RV just sounds awesome when it fly's over our house.........under the airport pattern. Somebody did a nice recording of it, yesterday. :)

L.Adamson
 
Sorry Bill, where did you get your info from?

12 23 7 786 869 is the part number for the glow plug fitted to the E71 BMW X6 30dX and 35dX and that's pretty modern...

Ok Andy I stand corrected, BMW must still be using them. I am told that some of the V-8s (Duramax, Powerstroke) do use them too, I'm not sure which models. All the Cummins 5.9 and 6.7L engines do not run glow plugs at all, only a grid heater to assist starting. I'm told that isn't even needed unless starting in very cold weather. I'm not sure about the VW and Audi Direct injected models.
Bill Jepson
 
Glow Plugs

Far as I know, Cummins is the only one NOT using glow plugs. The VW TDI's do, as to the Jeeps, Duramax's, Powerstrokes. So does WAM. Simple and effective.

I would think that liquid cooled diesels will re-start in cold weather better than air cooled, simply because they would retain heat a little longer. I ran mine out of fuel on one tank last winter, and I was amazed at how fast it re-started when I switched tanks. It was almost instantaneous, and I didn't use the boost pump either. It was not terribly cold, probably around 0C.

Kurt
 
How about this diesel

Hi All:

I stumbled onto this and thought "is the past the future". I hope you enjoy. The Jumo 205 is a opposed diesel designed in the 30's. It consisted of two crankshafts and numerous gears with a common valve train. From the layout of the liners, this appears to be a 2 stroke engine.

Paul
LAF
RV7A
Fuselage
Still looking for a IO-360

http://en.wikipedia.org/wiki/Junkers_Jumo_205
 
Hi All:

I stumbled onto this and thought "is the past the future". I hope you enjoy. The Jumo 205 is a opposed diesel designed in the 30's. It consisted of two crankshafts and numerous gears with a common valve train. From the layout of the liners, this appears to be a 2 stroke engine.

Paul
LAF
RV7A
Fuselage
Still looking for a IO-360

http://en.wikipedia.org/wiki/Junkers_Jumo_205

This is the same design as this engine that I linked to in post #40..
Has anyone heard anything about this company?
http://ppdgemini.com/
I saw them at KOSH 08 and they were supposedly about ready to start selling the 100HP version for LSAs then work on the 200HP version. Sounded like a promising alternative, but they haven't updated their web site for a couple of years.
 
If you can find ANY diesel engine of the SAME displacement running the SAME manifold pressure as an SI engine that develops the same hp and torque, let me know and I'll retract my statement.

Ross, this might actually come close to happening some time soon. We here are playing with running diesels at Stoic!!! The reason is the extremely high cost of the SRC after combustion treatment of diesel exhaust. If they can run at Stoic then we can use the 3 way automotive emission systems and reduce the installation cost. The SRC systems currently costs more than 1/3 of the installed cost of the engine.

When we run a diesel at these conditions the manifold pressure is much less however the exhaust temperature is much higher. Particulate emissions are rather high but these can be dealt with fairly easily before going into the 3 way cats, or so the hope is. My exhaust system is built out of 2" Sch 40 SS Pipe and I have the pipe glowing dull red for about 3 ft, that is kind of "Cool".
Your HP SI engines probably do that but it is a first for our diesel.

Bob Parry
 
Ross, this might actually come close to happening some time soon. We here are playing with running diesels at Stoic!!! The reason is the extremely high cost of the SRC after combustion treatment of diesel exhaust. If they can run at Stoic then we can use the 3 way automotive emission systems and reduce the installation cost. The SRC systems currently costs more than 1/3 of the installed cost of the engine.

When we run a diesel at these conditions the manifold pressure is much less however the exhaust temperature is much higher. Particulate emissions are rather high but these can be dealt with fairly easily before going into the 3 way cats, or so the hope is. My exhaust system is built out of 2" Sch 40 SS Pipe and I have the pipe glowing dull red for about 3 ft, that is kind of "Cool".
Your HP SI engines probably do that but it is a first for our diesel.

Bob Parry

It sounds like interesting work you are doing but I'm not sure what running at stoichiometric has to do with the power output as this is not where best power is made.

Modern gasoline engine catalysts no longer need to run at stoich to meet emissions, many using WB sensors run leaner than stoich at light load.

It is highly unlikely that a CI engine will ever match the specific output of SI engines at similar MAP since they are presently at about a 5 to 1 disadvantage and it will never happen until they can match the same rev ranges as SI engines. Hp is dependent on mass flow- roughly displacement X RPM X MAP X VE.
 
You are right a diesel running at stoic may not even match the power of a conventional diesel and certainly not a SI engine in a power enrichment condition. This is being investigated to lower manufacturing costs and still meet pollution requirements. But if compared to SI engine at stoic might be in the ball park.

We hear that the EPA wants engines (SI and CI) to meet pollution limits at all operating conditions. This does not apply to aircraft, at least not yet, but GA aircraft will some day have to meet some kind of emission requirements.

Bob Parry
 
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