Aircraft engines are supposed to be simple..

[Zeldman]

In a nutshell, the difference is in the length of connecting rods and pushrods.

If you have a car that will do 6500 RPM, it probably doesn't even have pushrods.

Say what.???

My last race car would turn 8500 RPM. My sprint car engines were limited to 9300 RPM. Both built from Chevrolets basic design of over head valves, rocker arms and push rods close to stock lengths. Rod lengths were 6 inch and 6.125 inch, with increased crank stroke. In 18 years of racing I bent only one push rod. Ok, we scattered about 6 engines in that time but push rods were not the problem there.

 

[Bill]

RPM is not what kills engines, load is. Cars very rarely see any real load, and almost never for more than a couple minutes at a time.

Winner winner, chicken dinner.

 

[Bill]

Ok I just decided to be a total nerd and do a little testing to show what I'm talking about in regards to load factor. I recently picked up a little bluetooth OBDII dongle that plugs into the diagnostic port

For the nerds among the crowd, what device did you buy?

 

[Henning]

I still don't understand how running at 2600 RPM is so stressful on an airplane engine and my car will do 6500. both are metal pistons in metal cylinders separated by a thin layer of oil. I could drive across the state in my car at 2600 RPM without a care in the world

^all that being said, I know very little about plane engines. I know a lot about the ford 289 V8 as I had one for awhile. MAybe there are vast differences. I don't know em though.

Because Horsepower is a combination of Torque (inner cylinder pressure) and Time (revolutions per minute). The slower you turn the engine, the higher the pressure in combustion chamber must be. That is why aircraft engines use such big pistons, there is a limit as to how many PSI pressure gasoline will supply before one gets into detonation. So in a direct drive engine, your primary limitation is prop tip speed that's what limits you in 'time', when your pound per square inch pressure is set at a constant, that means your HP is limited in displacement, primarily bore.

Your car engine however has an advantage that most recip planes don't, gear reduction. This allows you to multiply torque and replace it with time. For you to produce 300hp at 6500 rpm requires much less pressure in the cylinder than in the engine that produces it at 2500 rpm. That's why you can do it with 289 CuIn and they need 540-550.

 

[timwinters]

I used to be a Dodge "green sheet" buyer.

I used to have car/truck engine failures all the time.

About 10 years ago I quit driving Chrysler products.

Amazingly, I quit having automotive engine failures too!



P.S. I think it's absurd to say my O-470 is "working hard" when it's cranking out a whopping 230 HP on take-off at sea level or when it's chugging along at a whopping 2300 RPM in cruise.

My Toyota 4Runner engine runs at about the same RPM and cranks out more HP per CI when cruising down the highway at 75 MPH than my plane's engine does in cruise flight. It's working harder, and lasts longer.

Plane engines are limited by propeller speed and will produce far more HP when allowed to spin faster. Of course, geared engines have shorter TBOs yet.

 

[Henning]

I used to be a Dodge "green sheet" buyer.

I used to have car/truck engine failures all the time.

About 10 years ago I quit driving Chrysler products.

Amazingly, I quit having automotive engine failures too!



P.S. I think it's absurd to say my O-470 is "working hard" when it's cranking out a whopping 230 HP on take-off at sea level or when it's chugging along at a whopping 2300 RPM in cruise.

My Toyota 4Runner engine runs at higher RPM and cranks out more HP per CI when cruising down the highway at 75 MPH than my plane's engine does in cruise flight. It's working harder, and lasts longer.

Plane engines are limited by propeller speed and will produce far more HP when allowed to spin faster. Of course, geared engines have shorter TBOs yet.

It's not working harder though, it's working easier, it has gears to multiply torque. RPM for gasoline is most efficient for high power at around 4200-6000rpm (the smaller the bore, the higher the RPM) this allows them to use the fuel efficiently without getting to destructive inner cylinder pressures and big 5"+ bores. We relive pressure by adding RPM for any given HP. The most efficient RPM is an effect of flame front speed and pressure build in the critical few degrees after top dead center. That's why the GTSIO-520 in a 421 is so much better at making TBO than the TSIO-520 in the 414.

 

[Ted]

This dead horse gets beaten every so often.

Aircraft engines do have areas that they could be improved, but nobody wants to pay what an improved engine would cost. Plus, EFI and direct injection won't have any significant economy increase unless you run stupidly rich all the time. For a properly trained LOP pilot, you'll see no benefit.

Where to make things better and more efficient? Combustion chamber design and electronic ignition. EFI would help for reliability. Remove the lead and you could also likely build engines that would work fine with thinner oils, which would help.

 

[timwinters]

Another data point...

Car engines built in the 1960s rarely made 100k miles without overhaul, much less 200k...300k like today's engines regularly do.

 

[MAKG1]

Say what.???

My last race car would turn 8500 RPM. My sprint car engines were limited to 9300 RPM. Both built from Chevrolets basic design of over head valves, rocker arms and push rods close to stock lengths. Rod lengths were 6 inch and 6.125 inch, with increased crank stroke. In 18 years of racing I bent only one push rod. Ok, we scattered about 6 engines in that time but push rods were not the problem there.

Race cars are not the same. Haven't been for several decades, if they ever were.

Tell me, would you take the pushrods from my C10 outside, install them in your race car and expect the same results?

SBC pushrods are also much shorter than O-360s. Take a look.

And most cars sold these days are OHCs. The few that aren't are not high revvers. The public is very much afraid of the redline and will ***** and moan if it cruises at 3000 RPM.

 

[MAKG1]

Another data point...

Car engines built in the 1960s rarely made 100k miles without overhaul, much less 200k...300k like today's engines regularly do.

The reason was simple. Hardened valve seats made necessary by unleaded fuel.

 

[timwinters]

The reason was simple. Hardened valve seats made necessary by unleaded fuel.

I seem to recall most old cars needing to be overhauled due to excessive oil consumption.

But I was a kid...

 

[MAKG1]

Where to make things better and more efficient? Combustion chamber design and electronic ignition. EFI would help for reliability. Remove the lead and you could also likely build engines that would work fine with thinner oils, which would help.

EFI has unacceptable failure modes for single engine aircraft.

It certainly helps efficiency, but a pregnant field mouse can bring it down. Seen it happen. They chew wiring insulation and use it to build nests.

 

[Henning]

Race cars are not the same. Haven't been for several decades, if they ever were.

Tell me, would you take the pushrods from my C10 outside, install them in your race car and expect the same results?

SBC pushrods are also much shorter than O-360s. Take a look.

And most cars sold these days are OHCs. The few that aren't are not high revvers. The public is very much afraid of the redline and will ***** and moan if it cruises at 3000 RPM.

Yeah, no worries, I used to run bone chevy stock pushrods in all sorts of engines up to 6500 rpm/500hp

 

[Ted]

EFI has unacceptable failure modes for single engine aircraft.

It certainly helps efficiency, but a pregnant field mouse can bring it down. Seen it happen. They chew wiring insulation and use it to build nests.

There are ways to mitigate the risks, but I've long said that the primary advantage is ease of starting and operation.

And no, it won't help efficiency unless you compare to someone running stupid rich.

 

[oldShar]

You simply don't hear about it when a car does it.

Mine did -- 32 years ago, on the way home from school on a dark and flurrying nite with -10F temps about mid way between Lincoln and Omaha.

The story of the incident didn't make the World-Herald or other news rag, nor did the skin from my ear that I left on the payphone outside the Sarpy County Courthouse (car totally died in front of the courthouse) when I Phoned Home (iPhones weren't even a glimmer in them thar days).

I kept the parts and pieces of what was left, until I cleaned out the garage day before yesterday and sent them to the landfill <sigh>

 

[docmirror]

Here's a hybrid system that is bone simple, mostly mechanical but offers a bit of benefit for automatic mixture control.

Bosch KE-Jetronic. The K-jetronic is completely mechanical, and it has the advantage of offering a different mixture based on MP demand. The shape of volute in the air damper determines the mixture. So, at high MP we would have a rich mixture, and as we climb or pull the mixture handle the ratio increases. The "E" in the name says it has an electronic closed loop mixture monitor which can automatically change the ratio based on a sample from the exhaust stream.

I've worked on K and KE Jetronic systems for years, and they work fine as long as the car is driven regularly. This could be an issue for planes, but the defect shows up on start up which would be good because it'll die before takeoff if the fuel inj system isn't working right.

Kind of a happy medium between EFI and full mechanical. Best thing is, if the "E" part closed loop stops working, it'll just default to a rich position and can be managed by the manual mixture control as it is now.

 

[Ted]

Part of the reason why O2 sensors aren't used in our planes is the lead. They do still work, but would become 50 or 100 hour items. Personally, I'd be all for that if it allowed my engine to run more efficiently.

 

[Phillip]

Here's a hybrid system that is bone simple, mostly mechanical but offers a bit of benefit for automatic mixture control.

Bosch KE-Jetronic. The K-jetronic is completely mechanical, and it has the advantage of offering a different mixture based on MP demand. The shape of volute in the air damper determines the mixture. So, at high MP we would have a rich mixture, and as we climb or pull the mixture handle the ratio increases. The "E" in the name says it has an electronic closed loop mixture monitor which can automatically change the ratio based on a sample from the exhaust stream.

I've worked on K and KE Jetronic systems for years, and they work fine as long as the car is driven regularly. This could be an issue for planes, but the defect shows up on start up which would be good because it'll die before takeoff if the fuel inj system isn't working right.


Kind of a happy medium between EFI and full mechanical. Best thing is, if the "E" part closed loop stops working, it'll just default to a rich position and can be managed by the manual mixture control as it is now.

If you are talking about old Volvo 240 style ignition, then I am firmly in agreement. That system would run underwater. It did require what was then called a lambda sensor, but IIRC would run without it just as well ...

 

[docmirror]

Part of the reason why O2 sensors aren't used in our planes is the lead. They do still work, but would become 50 or 100 hour items. Personally, I'd be all for that if it allowed my engine to run more efficiently.

They could be adapted to take the feed from a type J or K thermocouple to manage the mixture compensation. It's not hard to do, and even if it did fail, once again we are back to using manual mixture just like we do now.

 

[docmirror]

If you are talking about old Volvo 240 style ignition, then I am firmly in agreement. That system would run underwater. It did require what was then called a lambda sensor, but IIRC would run without it just as well ...

Well, it's not an ignition system, it's a FI system. And yes, it was called the Lambda sensor in many applications. I don't recall if that was Bosch's name for it or not.

 

[steingar]

The Steinmobile's engine blew up not six months after I bought it. Didn't make the local paper, I can tell you that. Now if the Free Bird's engine does the same thing you'll likely read about it. Whether or not its front page news depends on how badly I muck things up.

 

[MAKG1]

I seem to recall most old cars needing to be overhauled due to excessive oil consumption.

But I was a kid...

While there are a handful of fancy piston ring designs, most cars these days use the exact same three cast iron rings and 45 deg honed cylinders that were used in the 60s.

 

[MAKG1]

If you are talking about old Volvo 240 style ignition, then I am firmly in agreement. That system would run underwater. It did require what was then called a lambda sensor, but IIRC would run without it just as well ...

A lambda sensor is an oxygen sensor. Same thing. It might limp without it, but it would not make full power.

 

[MAKG1]

Here's a hybrid system that is bone simple, mostly mechanical but offers a bit of benefit for automatic mixture control.

Bosch KE-Jetronic.

As long as it works better than L-Jetronic. JHC, that's a flaming POS, whose time came, went, and isn't missed.

I've no experience with the fully mechanical ones, but at a minimum, you have to have vacuum lines controlling the system.

I do think you meant K-Jetronic, though. With an ECU, you have to worry about incorrect inputs. Many many cars won't get out of their own way if either of the temperature sensors open (and the ACT is quite relevant to a speed density computer, even on an air cooled engine), as the ECU interprets that as outrageously cold temperature operation and enrichens the crap out of the mixture. This could be very unpleasant during an obstructed field takeoff.

 

[Phillip]

A lambda sensor is an oxygen sensor. Same thing. It might limp without it, but it would not make full power.

Nope, old Volvos ran without it just fine. Don't ask me why, I've owned one as a student and did not give it too much attention besides oil changes. There was a warning light on the "lambda" sensor, that worked off the mechanical cable (tach? or speedo off the panel). It was a small box of gears that hung behind drivers kick panel. Once the gears advanced enough the circuit would close and the sensor light would come on. Reset by pressing the button on the box. I think I threw mine away and so did a lot of owners of 240...

 

[tlrussell]

I used to be a Dodge "green sheet" buyer.

I used to have car/truck engine failures all the time.

About 10 years ago I quit driving Chrysler products.

Amazingly, I quit having automotive engine failures too!



P.S. I think it's absurd to say my O-470 is "working hard" when it's cranking out a whopping 230 HP on take-off at sea level or when it's chugging along at a whopping 2300 RPM in cruise.

My Toyota 4Runner engine runs at about the same RPM and cranks out more HP per CI when cruising down the highway at 75 MPH than my plane's engine does in cruise flight. It's working harder, and lasts longer.

Plane engines are limited by propeller speed and will produce far more HP when allowed to spin faster. Of course, geared engines have shorter TBOs yet.

Wrong. Do the math.

7.7l@230hp at 65% = 150hp/470ci = .32hp/ci
4.0l@270hp at 25% = 81hp/244ci = .28hp/ci

Airplane motors are limited by more than the propeller speed. The physics of limiting maximum speed have many variables.

Car engines average 20-30% max load capability in a lifetime. You would have to drive your Toyota at over 100mph average to equate the motors.

If you did that your Toyota would be a smoking pile of metal way before 2000 hours.

 

[StinkBug]

For the nerds among the crowd, what device did you buy?

It's called iDiagnose. Like $16 on amazon.

P.S. I think it's absurd to say my O-470 is "working hard" when it's cranking out a whopping 230 HP on take-off at sea level or when it's chugging along at a whopping 2300 RPM in cruise.

My Toyota 4Runner engine runs at about the same RPM and cranks out more HP per CI when cruising down the highway at 75 MPH than my plane's engine does in cruise flight. It's working harder, and lasts longer.

It's not working harder though. Take a look at the data I posted up last night. When your 4Runner is cruising down the highway most of what keeps it moving is it's inertia. That whole "objects in motion" science. The only load you're putting on the engine is that which is needed to overcome the friction of the road surface and the aerodynamic drag that is trying to slow the vehicle down. It's not much. About 10% load is what I found for my car. Your O-470 however has to move enough air to keep your plane from falling out of the sky. Being that props blowing air around aren't nearly as efficient as direct drive to the ground, and that cars dont need to fly, the aircraft engine is working at a higher level of load pretty much all the time.

 

[Henning]

While there are a handful of fancy piston ring designs, most cars these days use the exact same three cast iron rings and 45 deg honed cylinders that were used in the 60s.

They are made of different alloys now though.

 

[N801BH]

RPM is not what kills engines, load is. Cars very rarely see any real load, and almost never for more than a couple minutes at a time. Climbing steep hills, hard acceleration, trucks trying to get a big trailer moving, and that's about it. When you're cruising down the freeway at 80 you're barely on the gas, and using about 15-20% power to maintain that speed. An airplane engine on the other hand is expected to run at 70-75% load for hours and hours on end. This is the equivalent of taking your 6000rpm rated car, and holding it wide open while climbing a hill so steep that you can only maintain 5000rpm and just keeping it there for hours. Trust me, if you could find that hill your car wouldn't survive very long. The only time you actually see those kind of conditions is towing trailers in the mountains, and that's very well known to overheat engines and kill transmissions. I'm betting if you've ever driven any mountain pass you've seen a truck or 2 on the side of the road with steam coming out.

People have been trying to get the GenIII chevy LS engines aircraft certified for a long time, and so far nobody can get them to survive long enough to pass the certification tests. These are motors that we regularly tune to 800+ horsepower and run wide open in heavy desert race trucks in 100 degree heat for 1000 race miles (which is similar to probably 50,000 road miles) at a time and they survive that yet they cant seem to build one that will survive typical airplane use. That says a lot.

Hmmmmm.....

An aircraft engine would not last 1 hour during these tests..........

https://www.youtube.com/watch?v=

 

[StinkBug]

I bet it would. Different engines built for different purposes if taken out of their element will not always do well. That said I really didn't see anything there that's too extraordinary. Racing Baja is hard on a vehicle, and hard on a motor for sure, but a stock unmodified engine is more likely to survive that race than the suspension or rear axle. The rest of it kinda bored me.

 

[Dan Thomas]

They are made of different alloys now though.

I think the oils we use now are a long ways from the oils of 1963, too.


Dan

 

[timwinters]

Wrong. Do the math.

7.7l@230hp at 65% = 150hp/470ci = .32hp/ci
4.0l@270hp at 25% = 81hp/244ci = .28hp/ci

My 2000 4Runner has a 3.4 liter engine. Dyno graphs typically have it topping out at about 170 HP (even though the book is 183). At 75(ish) MPH it's turning 2300 RPM the dyno graph shows it producing about 85 HP.

85/208 = .41hp/ci

 

[JHW]

My 2000 4Runner has a 3.4 liter engine. Dyno graphs typically have it topping out at about 170 HP (even though the book is 183). At 75(ish) MPH it's turning 2300 RPM the dyno graph shows it producing about 85 HP.

85/208 = .41hp/ci

The dyno graph is a maximum. At any given RPM you can operate at any power from that number down to zero. Odds are, cruising down the highway you are a lot closer to zero than to the maximum.

 

[timwinters]

The dyno graph is a maximum. At any given RPM you can operate at any power from that number down to zero. Odds are, cruising down the highway you are a lot closer to zero than to the maximum.

it doesn't take much of an incline to make it shift down out of overdrive.

 

[JHW]

it doesn't take much of an incline to make it shift down out of overdrive.

not familiar with the engine and transmission calibration charts for your vehicle, but let's just leave it that electronically controlled powertrains are often programmed to do non-intuitive things and you can't make too many assumptions from casual observation

 

[StinkBug]

also that math on hp/ci is completely wrong. Well, technically the math might be right, but it has no actual bearing on how an engine works and what's going on with it.

 

[Ted]

not familiar with the engine and transmission calibration charts for your vehicle, but let's just leave it that electronically controlled powertrains are often programmed to do non-intuitive things and you can't make too many assumptions from casual observation

The man with the twin is correct.

 

[docmirror]

I've no experience with the fully mechanical ones, but at a minimum, you have to have vacuum lines controlling the system.

I do think you meant K-Jetronic, though. With an ECU, you have to worry about incorrect inputs. Many many cars won't get out of their own way if either of the temperature sensors open (and the ACT is quite relevant to a speed density computer, even on an air cooled engine), as the ECU interprets that as outrageously cold temperature operation and enrichens the crap out of the mixture. This could be very unpleasant during an obstructed field takeoff.

Actually, you don't. The vac lines were added as the years went on to manage emissions improvements. There are warm up regulators of the type 1 which use no vac to manage the cold start, or even the engine overrun deceleration. They are typically on the late 70s Merc. By the time the KE-Jetronic came out, they were fully optimized for vac mixture reduction again for emission control, which is what the Lambda sensor and the frequency valve did to lean the mixture. Modified for av use I would run a type 1 warm up reg(no vac), with a KE-jetronic freq valve and lambda sensor. It would have a discrete cutout switch when the mixture and throttle are full so the Lambda sensor is not even in operation.

Like I said it's a hybrid system, and they do not run that bad when the Lambda sensor is malfunctioning. I will agree that high altitude, cold operation could be a challenge, but nothing is without some compromise. Current mech FI on airplanes often have horrible hot start issues, but once running, they seem fine.

It's dead reliable, and can manage mixture control automatically in long cruise cycle as we commonly have on aircraft. One could even have the Lambda sensor disabled all the time, and have a panel switch to engage "Cruise econ" switch to enable the frequency valve and Lambda sensor. Lots of ideas, and it's even fairly light weight being most parts are already made of Aluminum.

 

[tlrussell]

The dyno graph is a maximum. At any given RPM you can operate at any power from that number down to zero. Odds are, cruising down the highway you are a lot closer to zero than to the maximum.

dyno is not what it is using on the road. Car engines use 25-35% power at 55mph. Dyno is a false loading system. The math isn't hard but this will help

 

[Henning]

I think the oils we use now are a long ways from the oils of 1963, too.


Dan

Believe it or not, no. The synthetics are the same as developed in the 70s as well.