What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Why is aviation so slow in technology?

bret

Well Known Member
And why can I run 11.5-1 CR, 230 PSI static cylinder pressure in the Olds on 91 octane. OK, I know I am going to get slammed here but bring it on, this is how new ideas get started. There are a lot of folks here way smarter than me so lets share some CONSTRUCTIVE criticisms and thoughts. I bring this up because of the ever increasing price of fuel and the possibility that 100LL may change. I know some here are using 91 Oct right now, but at the cost of low compression and HP. I remember reading an article a long time ago about Quench chamber heads, I built and blueprinted a engine, forged full floating pistons, file fit rings, align hone the mains, "0" and square the deck, balance, ported intake, heads, headers, used aluminum heads with Inconel exhaust valves and had the quench area @ .030" this produces a violent and internal turbulent event to both cool hot spots and induce A/F mix across the combustion chamber to reduce detonation. In fact a test engine was built and the lower CR engine, with .060" quench heads had more detonation than the High compression engine. Along with this is a lot of custom cam profile timing and ignition curve profile, O, and carb jetting bla bla bla, yes this is all car stuff but you get the idea. So, then you will say, it is not continuous full load, well then we can look at Mercruiser race engines and Cummins turbo charged 18-1 engines and so on. All I am saying is, why are we still in the dark ages? Is everyone afraid to try something new, and no, I am not talking about car engines in planes, I am talking about aviation engines and stepping up to the plate with all this technology available. Twin quinch non hemi head? anyone, anyone, Bueller.....
 
Brett,
You know that old saying..."If you want to make a small fortune in aviation..."

Technology costs money, and getting new technology FAA approved costs even more money. And so long as current technology meets the need, I would bet the answer is that the potential return on the investment doesn't justify the expense.

I do like your ideas, though. The sound of a P-Port Mazda rotary screeming into turn 1 at Road Atlanta is simply awesome...

Best,
 
The issue we fight is cylinder volume vs compression ratio. The higher the compression ratio, the smaller cylinder volume you need in order to prevent auto-ignition.

What happens is the spark plugs ignite the mixture at the top of the cylinder and the flame front moves outward from the ignition sources. The flame front has to reach the most distant corners of the combustion chamber before the remaining mixture in those distant corners auto ignites <explodes> due to the heating and compression it is experiencing.

We could solve that issue by reducing cylinder size and running the engine faster. We could then gear that engine to reduce the speed to a practical prop speed. Alternately, we could keep the displacement the same, but increase the number of cylinders, reducing the size of the combustion chambers. There are a lot of ways to get there. Most of them are more expensive and more complicated than the uber-reliable and reasonably efficient "tractor" engines we currently have.

Lycoming (and Continental) have produced a pretty good set of mouse traps. It is possible to build a better one, but nobody's developed one <yet> that is commercially viable.
 
OK, I have a bite! did you read the ( What do you do for your day job) thread? there are some amazing peps on here, and it only takes an Idea to start something. My story is building and racing, cars, trucks, boats, jet ski, and street bikes, I know what is out there and it just makes me depressed to get into this field (now) and see the lack luster of performance. I do understand the importance of over engineering for reliability but come on, look at what we drive everyday. 200 mph corvetts, to 1 million mile Dodge trucks.
 
Just a guess, but I would think it is the old "market is too small and the liability it too high".

But an io-360 6-cylinder would be cool.
 
The issue we fight is cylinder volume vs compression ratio. The higher the compression ratio, the smaller cylinder volume you need in order to prevent auto-ignition.

What happens is the spark plugs ignite the mixture at the top of the cylinder and the flame front moves outward from the ignition sources. The flame front has to reach the most distant corners of the combustion chamber before the remaining mixture in those distant corners auto ignites <explodes> due to the heating and compression it is experiencing.

We could solve that issue by reducing cylinder size and running the engine faster. We could then gear that engine to reduce the speed to a practical prop speed. Alternately, we could keep the displacement the same, but increase the number of cylinders, reducing the size of the combustion chambers. There are a lot of ways to get there. Most of them are more expensive and more complicated than the uber-reliable and reasonably efficient "tractor" engines we currently have.

Lycoming (and Continental) have produced a pretty good set of mouse traps. It is possible to build a better one, but nobody's developed one <yet> that is commercially viable.

Yes, my understanding is that the larger Dia the bore, the more prone we are to det. So our other end of this is to increase RPM, and to keep the prop tip speed down, couldn't we go to a shorter Dia prop and go with a 4 or 6 blade?
 
Yes, my understanding is that the larger Dia the bore, the more prone we are to det. So our other end of this is to increase RPM, and to keep the prop tip speed down, couldn't we go to a shorter Dia prop and go with a 4 or 6 blade?

More blades and shorter blades both mean less efficient blades.

Fundamentally, virtually everything there is to know about piston engines was learned during WWII. Today, we just choose the "best" set of compromises from that technology for our application. Magnetos are not as efficient as electronic ignition, but most airplanes use them because they don't rely on an external source of electricity. Big bore, slow turning engines with 8.5:1 compression ratios are a good fit for long (efficient) prop's, without the expense and complexity of a gearbox. It is a long list of compromises, but in the end, those compromises have delivered a product that fits our needs pretty well.
 
To address the original question, which was regarding compression ratio, the answer is wrapped around dynamic compression, not the static compression that most people refer to. In other words, you can run high static compression, then run a cam with long intake duration, which will result in, say, 8.5 to 1 dynamic compression and will make good power at high rpm, but will sacrifice power at low rpm. The new rage (OK, technology) is to use variable valve timing to allow decent performance at low rpm while still achieving the high rpm performace. This is done so that you can make good power with limited displacement and allow you to meet the emissions regs as well.

The easy way, and many times light weight way as well, is to just run bigger diplacement with lower static compression and a milder cam, kinda like a Lyc. There is new technology I would like to see on a Lyc, but make no mistake, a Lyc is not low tech, nor is it stuck in the dark ages.

Tim
 
Last edited:
I understand your fustration. I just returned fron Death Valley and had a great time. I tow a 72 Baja Bug with a stock 1600dp motor. A friend followed in his 2010 Ranger and was bragging about the 30 mpg he was getting. After driving around the valley i averaged 25mpg with three people in the Bug. He did not want to hear that after 38 years he only beat me by 5mpg. I really wonder why. The same must be true in all motors.
Mike

Most 2 seat RV's do get 30 mpg with a motor that is far bigger than the Baja Bug or the Ranger.
 
There is new technology I would like to see on a Lyc, but make no mistake, a Lyc is not low tech, nor is it stuck in the dark ages.

Tim

Very well said. If you look at the BSFC of the Lycon vs most auto engines, the Lycon is very close. Our air-cool engines may look antiquated, but they generally out perform most auto engine on a power to weight ratio. Torque is king in aviation engines. The O-360 should be putting out around 350ftlbs or torque up to 100% continuous, for ~2000 hours or as much as 400,000 miles in the RV (at WOT 200mph Cruise).

That said, if there were a diesel out there with the same power-to-weight and well proven, I would mount one instead of the lycoming. I would love to have a diesel on my plane.
 
couldn't we go to a shorter Dia prop and go with a 4 or 6 blade?

In general terms, prop efficiency is best when there is very little increase in airsteam velocity across the prop disc. With that in mind, in order to get the thrust required for the application, the diameter of the prop disc must go up and the rpm must go down to avoid tip shock.

Another way to look at the velocity comment is to compare the prop to a wing. When one is creating a lot of downwash on a wing (read prop airstream delta V), the induced drag is very high. On a prop, the induced drag sucks HP and lowers prop eff.
Just like a wing, one wants to operate a prop in the best L/D part of the polar.
 
Diesel????

Why is nobody talking about smooth reliable aero diesel engine. Can't beat there economy, there reliability, start up at low temps like no other.

I've been flying diesels of and on for the last three years. No greater joy when it comes to endurance.

That is my dream for my -8 as soon someone can do it for a better price....that's the only down-side.
 
There is a big thing ignored here, and that's the efficiency of a powertrain system as a whole. Cars have averaged 25mpg since the early 80's. Coupled to a transmission, drive shafts, half shafts, etc. the system is very inefficient. On the other hand a propeller is fairly efficient, and that is where we make up for engine deficiencies. So the systems as a whole are pretty good, but there is a lot of room for improvement particularly in the intake system and cylinder head design.
 
I disagree on the 25 MPG, Honda I DTEC 2.2 Diesel is getting 63 MPG, one of their improvments was to inject the fuel at 1,600 BAR, thats 23,000,000 PSI, our comon rail systems are at around 30,000 PSI
 
I disagree on the 25 MPG, Honda I DTEC 2.2 Diesel is getting 63 MPG, one of their improvments was to inject the fuel at 1,600 BAR, thats 23,000,000 PSI, our comon rail systems are at around 30,000 PSI

1600 bar is about 23,000 PSI.
 
I disagree on the 25 MPG, Honda I DTEC 2.2 Diesel is getting 63 MPG, one of their improvments was to inject the fuel at 1,600 BAR, thats 23,000,000 PSI, our comon rail systems are at around 30,000 PSI

Fleet average is still around 25mpg. My Golf TDI gets 48mpg and is ten years old. The Honda DTEC is not available in the USA.
 
I love all the "I get XX MPG" statements without any information about the weight of the vehicle. Completely meaningless.

If you want to get into real meaningful data, let's talk about BSFC and ton-miles travelled per gallon.
 
That is impressive. Staying on the gasoline engines, my Honda Fit automatic does better than 40 mpg cruising in the 70's. The aircraft engine version don't do too bad either!

I disagree on the 25 MPG, Honda I DTEC 2.2 Diesel is getting 63 MPG, one of their improvments was to inject the fuel at 1,600 BAR, thats 23,000,000 PSI, our comon rail systems are at around 30,000 PSI
 
If you want to get into real meaningful data, let's talk about BSFC and ton-miles travelled per gallon.

I would argue that ton-miles per gallon is also meaningless if 90% of that weight is not required for the journey.

If I drive an escalade with only myself in it to work, I'm getting pretty good ton-miles per gallon vs a 75 lb moped. But which is more efficient?
 
Technology

I find aviation to be a curious mix of conservatism and progressivism. If we look at the history of airframes they have gone from wood and fabric to tube steel, to semi monocoque aluminum to carbon fiber composite. And yet at each change point there were holdovers from the previous technology. If we look at avionics the changes are even more startling, going from mechanical instruments, to tube radios to solid state radios to computerized flight management systems. And engines as well, from IC gasoline engines to gas turbines.

However, in answer to the original question, I think the answer is in the market. We do have alternative powerplants, from auto conversions to electronic controls of traditional aircraft engines, to converted gas turbines, to compression ignition (diesel) engines. And yet how many engines have SMA (Renault diesel), Wilksch, or Innodyne sold. Why did Bombardier/Rotax axe their 300 hp V6 diesel. How many Precision Airmotive electronic management systems have been sold.

So the answer is you and me. If there were a cheaper (big emphasis on this), more reliable, more fuel efficient aircraft engine than the current Lycoming/Continental I would buy one. But after a survey of the market over many years, I have concluded that there is no better choice (Van apparently concluded the same).

Many years ago I watched with great interest when Curtiss Wright and John Deere spent millions on developing the Wankel engine for aircraft use. I thought it was the ideal replacement for the current piston engines. But it didn't turn out that way.

In any case, I think maybe we're on the cusp of as great a change in private aviation as the change from piston engines to turbine engines was in commercial aviation. The recent developments in electric motors driven by batteries or fuel cells may be that change. I think I will go out and buy an electric RC controlled park flyer to get up to speed with the new technology.
 
Very well said. If you look at the BSFC of the Lycon vs most auto engines, the Lycon is very close. Our air-cool engines may look antiquated, but they generally out perform most auto engine on a power to weight ratio. Torque is king in aviation engines. The O-360 should be putting out around 350ftlbs or torque up to 100% continuous, for ~2000 hours or as much as 400,000 miles in the RV (at WOT 200mph Cruise).

That said, if there were a diesel out there with the same power-to-weight and well proven, I would mount one instead of the lycoming. I would love to have a diesel on my plane.

HP is actually the motivating factor on all vehicles. HP= work, torque = force.

You will notice that BSFC is rated against hp, not torque.
 
Terry is right on several counts. What do I want?

FADEC? You could not give me one.

Auto conversion? You could not give me one

Diesel? I don't know enough about them but the fact that they are not mainstream leads me to believe that they are not ready for prime time.

My one disagreement is that electric power is the future. Not anytime that will impact me. It is largely a failure with cars. It makes even less sense with aircraft.

My questionable opinion is that the biggest improvement is being discussed with cooling air/internal cowl mods in another thread.
 
I would argue that ton-miles per gallon is also meaningless if 90% of that weight is not required for the journey.

If I drive an escalade with only myself in it to work, I'm getting pretty good ton-miles per gallon vs a 75 lb moped. But which is more efficient?

Ahhh, but that gets down into personal choice. Some people will prefer to carry an extra 3000 pounds of steel cage around them on the highway for impact protection, while others are perfectly happy riding around in a ball of tin foil. Going by a seat-miles rating would not be realistic because we would be comparing a Ford Focus to a Chevy Crew Cab.

It takes energy to move mass (as long as friction is considered, orbital mechanics are a different animal) so the ton-mile/gallon would be a truer measurement tool of energy efficiency.
 
See, with a liquid cooled diesel you would not even need to talk about that. You can build much more aerodynamic cowlings.
 
Not that I call real data. There are so many different air frames and propeller pitches going on, nothing all that specific. You can throttle back and see 3.5 gallons an hour (on regular grade gasoline WITH ethanol), general consensus seems to see about 5 gph cruise, but far too many variables yet to set a number in my opinion. Additionally, in my opinion the intake manifold is a joke, the better one coming out will change those figures anyhow.

Hey Don,

If you are talking about Eggenfellner's Viking, is there real world data on efficiency?
 
Ahhh, but that gets down into personal choice. Some people will prefer to carry an extra 3000 pounds of steel cage around them on the highway for impact protection, while others are perfectly happy riding around in a ball of tin foil. Going by a seat-miles rating would not be realistic because we would be comparing a Ford Focus to a Chevy Crew Cab.

It takes energy to move mass (as long as friction is considered, orbital mechanics are a different animal) so the ton-mile/gallon would be a truer measurement tool of energy efficiency.
It seems to me you two are talking in terms of "efficiency" but you haven't agreed upon what that term means. This is a subjective term that needs clarification anytime it is to be used in a discussion such as this. Which is exactly what Greg originally posted (in his own words). Greg's definition is proving to be different than Phylan's. Now the question is which perspective should be used?

Now, for my thoughts on the subject. . . oh . . . well, on second thought, you guys really don't care to hear about that I am sure.

Live Long and Prosper!
 
And why can I run 11.5-1 CR, 230 PSI static cylinder pressure in the Olds on 91 octane. OK, I know I am going to get slammed here but bring it on, this is how new ideas get started. There are a lot of folks here way smarter than me so lets share some CONSTRUCTIVE criticisms and thoughts. I bring this up because of the ever increasing price of fuel and the possibility that 100LL may change. I know some here are using 91 Oct right now, but at the cost of low compression and HP. I remember reading an article a long time ago about Quench chamber heads, I built and blueprinted a engine, forged full floating pistons, file fit rings, align hone the mains, "0" and square the deck, balance, ported intake, heads, headers, used aluminum heads with Inconel exhaust valves and had the quench area @ .030" this produces a violent and internal turbulent event to both cool hot spots and induce A/F mix across the combustion chamber to reduce detonation. In fact a test engine was built and the lower CR engine, with .060" quench heads had more detonation than the High compression engine. Along with this is a lot of custom cam profile timing and ignition curve profile, O, and carb jetting bla bla bla, yes this is all car stuff but you get the idea. So, then you will say, it is not continuous full load, well then we can look at Mercruiser race engines and Cummins turbo charged 18-1 engines and so on. All I am saying is, why are we still in the dark ages? Is everyone afraid to try something new, and no, I am not talking about car engines in planes, I am talking about aviation engines and stepping up to the plate with all this technology available. Twin quinch non hemi head? anyone, anyone, Bueller.....

Instead of writing about the issue and asking the same old questions, why not go ahead and do it and report back on why it works - or why it doesn't work.

There's a ton of stuff written about alternative engines, most of it by dreamers, but not much real world success. Many have tried, many have failed - mostly for lack of market, money and no improvement in efficiency.

Come up with something more efficient, more reliable and at a reasonable cost, it will be a success. Go out an do it and report back. :)
 
I should have been more clear in my first post, I am not a fan of auto engines in aircraft, I was thinking of ways to improve the Lycoming base engine, like head design, most engines, gas and diesel use 4 or 5 valves, roller rocker arms with correct geometry to reduce valve tip side load, compression chamber design. Tuned intake runner dia. and shape to match the speed of the incoming air to utilize air mass for inertia supercharging. Tuned exhaust for max cylinder scavenging, I think 4 into 2 into 1 works well. Piston oil sprayers to cool the piston. A fuel system that atomizes the fuel better and delivers the fuel timed with the intake valve events. ect.....
 
My only beef with a Lyc is cost. It is a great performing machine, but it is a 4-cyl, pushrod valvetrain, aircooled, direct drive engine. How expensive should that be? By my (rough) calculations, assuming the highest quality, the retail value of the engine itself should be around $5k. It should come in fully dressed with a modern fuel and ignition system for less than about $9k. If it did, sales volumes would be much higher than they are today and that alone would spark a considerable amount of innovation and development. I don't know where all of the cost is (or isn't), but it is a killer when you look at a new certified engine for ~$35k or experimental for ~$25k. What I think we should concentrate on is how we can make a 2-place certified ready to fly machine available for ~$50K retail and a 4-place for ~$80k. That's what the 1965 to 1975 CPI adjusted price of a Cessna 150 and 172 is.

Tim
 
HP is actually the motivating factor on all vehicles. HP= work, torque = force.

You will notice that BSFC is rated against hp, not torque.

Very true, but you can increase the HP output of most engines by increasing operating rpm (to a piont). HP doesn't tell the whole story for an engine that must drive an rpm-limited propeller. Most 1 liter motorcyles these days are putting out close to 200hp, that doesn't mean it will work on your RV-6/7/8. The 10,000 RPM peak hp output would be a problem. Aircraft engines run at low RPM because they have to and the design of the engine reflects that requirement. The point I was trying to make by noting the high torque way that just because the hp numbers are low does not me the engine is a poor design. Try to find another engine with the same output at that RPM (even with a reduction) for the same installed weight. You won't.
 
I should have been more clear in my first post, I am not a fan of auto engines in aircraft, I was thinking of ways to improve the Lycoming base engine, like head design, most engines, gas and diesel use 4 or 5 valves, roller rocker arms with correct geometry to reduce valve tip side load, compression chamber design. Tuned intake runner dia. and shape to match the speed of the incoming air to utilize air mass for inertia supercharging. Tuned exhaust for max cylinder scavenging, I think 4 into 2 into 1 works well. Piston oil sprayers to cool the piston. A fuel system that atomizes the fuel better and delivers the fuel timed with the intake valve events. ect.....

I hear you Bret, but the simple answer to your question is probably expressed in two words - reliability and cost.

In single-engined airplanes, flown beyond gliding distance from home, we WANT performance, but we DEMAND reliability. There are millions of hours of experience with current configurations - when you start to change the configurations, you need to put a lot of money into test time to prove that you haven;t reduced reliability. Guys have done much of what you suggest in the racing world - and they have the engine-out landings to prove it/. Not that you can't make those technologies reliable - but the development costs will be high.

And that brings us to the other point - amortizing the development costs. There are just no economies of scale. you're not going to sell millions to spread the costs around - you're going to sell thousands - so the development costs are spread over very few units. And homebuilders are nothing if not , ahem...thrifty....shal we say....:rolleyes:
 
I should have been more clear in my first post, I am not a fan of auto engines in aircraft, I was thinking of ways to improve the Lycoming base engine, like head design, most engines, gas and diesel use 4 or 5 valves, roller rocker arms with correct geometry to reduce valve tip side load, compression chamber design. Tuned intake runner dia. and shape to match the speed of the incoming air to utilize air mass for inertia supercharging. Tuned exhaust for max cylinder scavenging, I think 4 into 2 into 1 works well. Piston oil sprayers to cool the piston. A fuel system that atomizes the fuel better and delivers the fuel timed with the intake valve events. ect.....

The improvements you mention are appropriate with modern engines running at 6000 rpm.
But with a direct drive at 2700 rpm, the room for increased performance is limited. There is some demonstrated performance improvement doing what suggest if you want pay for it. BPE, for example, did their standard balancing of parts a few other things resulting in 187 hp vrs 180.
 
Very true, but you can increase the HP output of most engines by increasing operating rpm (to a piont). HP doesn't tell the whole story for an engine that must drive an rpm-limited propeller. Most 1 liter motorcyles these days are putting out close to 200hp, that doesn't mean it will work on your RV-6/7/8. The 10,000 RPM peak hp output would be a problem. Aircraft engines run at low RPM because they have to and the design of the engine reflects that requirement. The point I was trying to make by noting the high torque way that just because the hp numbers are low does not me the engine is a poor design. Try to find another engine with the same output at that RPM (even with a reduction) for the same installed weight. You won't.

HP under the curve within the usable rpm band is the whole story actually whether you are driving a prop on an airplane or boat, a bus, car or locomotive. That is why all engines are rated in hp first (sometimes only) because this denotes the amount of work they can perform. Torque is meaningless in that regard.

I'm not comparing different types or sizes of engines here, only trying to put people on track here about motive capability.
 
See, with a liquid cooled diesel you would not even need to talk about that. You can build much more aerodynamic cowlings.

You can build as an aerodynamic cowling as you want, but the problem is you still need to cool the engine.

The fact is that liquid cooled engines need more cooling air flowrate which equals more drag (yes I know the famed Mustang overcame this at 400mph, but no one has ever done it for a 150mph homebuilt)

This means: liquid cooling = more drag= less fuel efficency.

Basically the reciprocating engine is not THAT much more efficient n matter how you slice it, diesels are better but the fact you have to discharge heat to a cooling airstream at 200F (ish) in a water cooled motor, vs 350F in an aircooled one..Well the only way to dump more cooling horse power is more flow.

I.e BTU/Hr = 1.09 * flowrate in CFM * Delta T.

For an outside air temp of 100F

delta T is 200-100F = 100F, in an aircooled engine 350 -100 = 250F

Thus you can see for the same BTU/Hr flowrate goes up by 2.5 times for the same HP in a lquid cooled motor.

if you want to find out how much.. 1kW= 3413 BTU/Hr and 1Hp = 0.746kW.

Frank
 
Back to detonation, Dynamic compression is one thing that limits us, the other is the cylinder head temperature. Detonation is function of temperature.

Now we don't know what the actual temp of the inner wall of the cyl head is, but most likely it is higher than on a water cooled motor as water is exceptionally good at removing heat, thus lowering temperature.

As to what can be run.. I run premium car gas on an 8.5:1 FI'd Lyc with auto advancing EI with no problems.

Rocket Bob runs regular mogas with the same result..I haven't been brave enough to try that ..yet.

Both of us run corner store ethanol blends.

The other thing you really should have is a proper fuel pumping system to avoid vapour lock..But I'm not going there..:)

Frank
 
It is all about mind set. More so in the US than anywhere, Lycoming and Continental piston engines have almost a cult following. Yes they are an adequate engine (and I love my XP-360), however, I always laugh when I see people refer to them as RELIABLE.

If a car or truck manufacturer brought out a vehicle with an engine that needed cylinder replacement due to cylinder heads cracking, worn valve guides, broken valves, piston pin wear leaving a little metal in the filter, broken rings, sticking exhaust valves etc etc etc, they would go broke. What if the engine spalled lifters and cams etc all the time?

Ok, there may not be a heap of catastrophic engine failures but there are way more than in the automotive industry, so I don't agree that they are hugely reliable.

In Australia and Europe, the Rotax 912 is a very prominent engine in the LSA class and have been flown there for many years. They are high revving, water cooled heads, electronic ignition and now electronic fuel injection etc. They are such a beautiful engine which except in very rear circumstances, always make it to TBO without much more than an oil change every 50 hours. And guess what, you don't have to fly them for an hour once a week to make them RELIABLE. Lycoming is trying to match their success with the IO233 but they still can't match the installed weight per HP.

On the other hand, the US seems to love the Australia Jabiru engine. In Australia, the fields are littered with them. Most Australians will not fly behind one and prefer the Rotax 912. I used to own a Jabiru and refused to fly it over anything except open paddocks. I sold that aircraft as the WORST ever aircraft I have owned or flown.

So what is GOOD about Lycomings?

1. Easy to top overhaul (which is handy because it always has to be done).
2. Simplicity (the thing is a tractor engine but things still go wrong frequently) It is reasonably easy to fix in the field.

What is bad?

1. Lifter and cam spalling. I roll my eyes every time I hear the old wives tale (most likely spread by Lycoming) that the reason for spalling is due to the position of the cam. I am a Diesel Mechanic by trade and have built numerous diesel and gas engines with overhead cams. You don't get much higher than that and yet I have NEVER seen a spalled cam.
2. They are a heavy, hugely inefficient, slow revving, noisy, dirty engine (that is part of the romance of the engine for me).

Mark.
 
Nice formulas Frank, but don't forget the surface area of an aluminum radiator, right now we are using cylinder cooling fins AND an oil cooler cause the fins just don't cut it. Did any one see Mikes post # 36 about ADEPT engines? go to their site. these guys may have something. Water cooled engines are way more efficient and you have equal cooling at around 180 to 200 Deg F. compared to a head at 450 F. det can be controlled at a lower temp. I think all things equally, one small water radiator is no more than a big oil cooler, and take away all the cooling fins and the cooling drag may be a wash. what do you think?
 
Another way to look at it...

I've often wondered how the general consensus is that auto engines aren't 'reliable' when we get in our cars and drive for hrs and miles without nearly the prep and nurturing we give our airplane engines and more times than not, with success. If we gave as much attention to our auto engines, were they installed in an airplane, as we do our airplane engines, they'd WOULD be reliable and they WOULD last despite not working as hard, etc, etc. A lot of the fear is centered around the unplanned landing using an auto engine in an airplane vs just pulling over to the side of the road. Design for redundancy (ignition, fuel, electrical, etc) and the reliability will be there. I'm not planning to install a Lycosaurus (yet) and am convinced there is something 'better' (for me anyway) out there! Fortunately Mistral has venture capital investors interested in the way forward...that would be my installation of choice. Just my $0.02 but a good thread nonetheless.
 
Last edited:
2. They are a heavy, hugely inefficient, slow revving, noisy, dirty engine (that is part of the romance of the engine for me).

Mark.

Again, we are getting at the same point that were mentioned before in this post...

-Slow Revving... --> You can't turn a propeller too fast or the tip will break the speed of sound and will then destroy your prop... You have to be slow revving but have more torque so you can increase the pitch instead!
No point in using a 10000rpm engine then... Even with a gearbox, you would be adding weight and reducing reliability to get almost the same result!

-Heavy... --> To reduce weight, you would have to use different metals, but then again, it would cost more to produce and add to this all the required test it would need to get the new parts FAA approved...no way a homebuilder or small private plane owner could afford a 40K$ engine for a such a small increase in gas consumption/performance!

-Noisy --> To cut down on noise, you would need to install mufflers... This means, more weight and performance loss... Who would want that!

As for the dirty engines, we could improve a little on this with better ignition system and fuel injection systems...but again it means more R&D and FAA approved modifications which means you pay more for your engine!

Not trying to be rude here, but just trying to explain why it is that we can't really improve on these points when we have something that is already "Reliable" for an already high price!
 
You can build as an aerodynamic cowling as you want, but the problem is you still need to cool the engine.

The fact is that liquid cooled engines need more cooling air flowrate which equals more drag (yes I know the famed Mustang overcame this at 400mph, but no one has ever done it for a 150mph homebuilt)

This means: liquid cooling = more drag= less fuel efficency.

Basically the reciprocating engine is not THAT much more efficient n matter how you slice it, diesels are better but the fact you have to discharge heat to a cooling airstream at 200F (ish) in a water cooled motor, vs 350F in an aircooled one..Well the only way to dump more cooling horse power is more flow.

I.e BTU/Hr = 1.09 * flowrate in CFM * Delta T.

For an outside air temp of 100F

delta T is 200-100F = 100F, in an aircooled engine 350 -100 = 250F

Thus you can see for the same BTU/Hr flowrate goes up by 2.5 times for the same HP in a lquid cooled motor.

if you want to find out how much.. 1kW= 3413 BTU/Hr and 1Hp = 0.746kW.

Frank

Way more variables involved than just these to say that liquid cooling causes more drag- mass of water vs. air, specific heat of water, thermal conductivity, radiator efficiency vs. those of thick cooling fins, duct design, momentum recovery, etc.

There is no evidence to suggest that a well designed liquid cooled installation has more drag than an air cooled one, in fact there are various examples which I've brought up before numerous times showing just the opposite. The fuel burn vs. TAS on the STI RVs is comparable or better than those powered by Lycomings and these don't even have optimized radiator layouts- just stuffed in the cowlings and using the stock Vans inlets.

With regards to new engines, I just don't see anyone being able to design, test and produce a clean sheet design in the small numbers used by this industry and be any cheaper than a Lycoming. While you might, maybe, possibly get 10% better SFCs with a really modern design, would all that trouble, risk and liability exposure be worth it? Doesn't seem like it to me.

The diesel is intriguing but nobody has demonstrated comparable reliability, pricing and longevity in any aero diesel yet and some have been pretty poor. With time, I believe we will see some of these improve and/or prove themselves and if so, these might make more sense in this application of relatively constant rpm/ high power than spark ignition engines.
 
Has anyone read up on Mikes post #36 a V6 smaller than an IO 360 and lighter, up to 320 HP.

adept.jpg
 
...You can't turn a propeller too fast or the tip will break the speed of sound and will then destroy your prop...

A minor quibble: When the prop tips go supersonic, it is not necessarily particularly damaging to the prop itself. There is no magical power to a shock wave that immediately rends asunder anything it touches.

What is bad about pushing the tips transonic is that it is a lot draggier than when they're subsonic. The shock waves pretty much hemorrhage energy by converting it into noise and neighborhood complaints.

In fact, prop tips go transonic and create shock waves pretty regularly. The tip speed doesn't even need to be supersonic; when the tips get to between 60% and 85% (depending on the blade section), the curvature of the airflow around the blade section causes enough local acceleration in the air to get it to go super sonic and rip out some shock waves.

I don't know what happens when the prop is forced solidly into the supersonic realm. I can imagine that a prop runaway caused by a bad governor or something like that would cause some damage. But probably mostly to the engine.
 
Back
Top