# V12 Diesel

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#### B100

##### Well-Known Member
Hi Ross thanks for you reply, it seems we are communicating better which always good for all

"We agree that the BSFC for 4 stroke diesels is better than most SI engines- no argument. Here pump gas is around .83c/ L and diesel is 1.05. This means the diesel is not going to save any money over a comparable SI powered car."

Lol...Luky you! here in Portugal and in most other European countries its the other way round, diesel is cheaper than gasoline! here is a link that should make you guys across the pond realise how good you have it

https://www.energy.eu/fuelprices/ (these are reference prices, they can be a little cheaper or expensive)

Here you only have unleaded 95 @ 1,48 euro/L and 98 @ about 10 cents more! Diesel costs 1,25euro/L

Just for the record my home made Biodiesel has a final production cost between 30 and 40 cents/ L ! so you can understand why I bother to make it and dream of a flying machine powered by it !

Depending on where you are in Europe diesel powers between 50 and 65 % of all traffic on the road even in countries where diesel is more expensive! Just stating a fact that explains why the best diesel engines are developed here!

"At the low specific output levels you are talking here, SI engines easily last a very long time also. Our shop turbo 240SX has 330,000 km on it now after 17 years of being turbocharged, beat on at the racetrack etc. Compression is still excellent, oil consumption 0.5L in 10,000 km. I just change oil in it and drive it. I think you will find that engine life in the aero application (continuous high power) is reduced considerably compared to automotive, especially when the hp is increased over stock levels. My point was simply that diesels can't match the same power to weight ratios as SI engines and weight is important in aircraft. Any turbo engine can have better power to weight ratios simply by increasing manifold pressure."

Well Ross there are good and bad engines out there, both SI and diesel , but the point is the engine examples I mention have decent power to weight ratios that are stock and can maintain high power output all day without undue stress! So you can increase power levels safely between 20 to 25% and some makers actually offer that as an option! But you dont need to , because the power is there already ! While you are right that Si engines can be boosted to produce more power then diesels that comes at greater cost in terms of fuel cosumption and engine life ! and lets not forget that torque plays a part as well ! (no wish to go into the torque vs hp debate) but in aircraft applications it seems to be a bonus in certain conditions .

So correct me if I´m wrong take off on 80 to 100% power for 2 minutes, then back of to 75 to 80 % on climb , and cruise on 60 to 65 % power !
In a current diesel engine that translates into 3600 to 4000 rpm then back of to 3000 to 3200 rpm and cruise at 2400 to 2600 rpm !
For a diesel engine that is easy, in fact they thrive on stable power settings , when I drive across Europe my diesel loves it , I set cruise control for 2400 rpm (good for 120kph). In Germany I push it a bit 2800 rpm and keep there for hours! no problem and this stability also delivers great fuel economy!
My point is a diesel is built precisely for long periods of high work loads sustained by their natural low end torque that is constant from as low as 1800rpm , and max out at around 2800 rpm, which is apparently the sweet spot for best prop efficiency.

#### rv6ejguy

##### Well-Known Member
Well Ross there are good and bad engines out there, both SI and diesel , but the point is the engine examples I mention have decent power to weight ratios that are stock and can maintain high power output all day without undue stress! So you can increase power levels safely between 20 to 25% and some makers actually offer that as an option! But you dont need to , because the power is there already ! While you are right that Si engines can be boosted to produce more power then diesels that comes at greater cost in terms of fuel cosumption and engine life ! and lets not forget that torque plays a part as well ! (no wish to go into the torque vs hp debate) but in aircraft applications it seems to be a bonus in certain conditions .

So correct me if I´m wrong take off on 80 to 100% power for 2 minutes, then back of to 75 to 80 % on climb , and cruise on 60 to 65 % power !
In a current diesel engine that translates into 3600 to 4000 rpm then back of to 3000 to 3200 rpm and cruise at 2400 to 2600 rpm !
For a diesel engine that is easy, in fact they thrive on stable power settings , when I drive across Europe my diesel loves it , I set cruise control for 2400 rpm (good for 120kph). In Germany I push it a bit 2800 rpm and keep there for hours! no problem and this stability also delivers great fuel economy!
My point is a diesel is built precisely for long periods of high work loads sustained by their natural low end torque that is constant from as low as 1800rpm , and max out at around 2800 rpm, which is apparently the sweet spot for best prop efficiency.
There are many stock, naturally aspirated SI engines today which exceed 90hp/L specific output- about the same as the best turbocharged stock diesels. They are also loafing along on the highway, even at 150km/h and they easily go 300- 400,000 km. Add turbos to any of these and you can have staggering power as we see in cars like the Nissan GTR (158hp/L stock, 526hp/L modified).

Cruising on the highway at 120 kph demands only about 10% power on an average small car with a 200hp engine so your cruise conditions in the aircraft are 5 to 6 times higher than on the road, this means at similar rpms, manifold pressure must be 5-6 times higher- more stress for sure.

To be clear yet again, diesels do not produce more torque than the same sized SI engine at the same manifold pressure- complete fallacy. Find me one current production engine that does. Apples and oranges to compare turbo and non-turbo engines in this regard. Area under the hp curve determines the work any engine can perform. Diesels do not do well in this comparison. Variable geometry turbos are responsible for the low torque peak rpm on many modern engines (1300 rpm for the BMW 135i), has nothing to do with being a diesel or not. The new M3 puts out 425hp and 406 lb./ft. of torque at about HALF the boost pressure of the 535D turbo diesel (255hp and 413 lb. ft.)

Finally, we see today that modern SI powered cars like the Prius 4 get better highway fuel economy than a similar diesel like the VW Passat TDI SE. Highway cruising keeps the electric motors out of the comparison. With direct injection and compression ratios around 14 to 1 plus other technologies like BMW's Valvetronic, modern SI engines are also very impressive for fuel economy.

#### BJC

##### Well-Known Member
HBA Supporter
Hi BJC ! I have no idea in regards to the Lyc 540, but I´m sure there will be a lot of people on HBA that would know! In fact I would like to know myself!

:dis:
One of the challenges in comparing alternative engines to proven purpose-designed airplane engines is making a realistic comparison. To be realistic, the entire propulsion system needs to be considered for multiple parameters, including weight, complexity / reliability, impact on drag, volume required, fuel systm requirments, etc. Although there are successful alternative engines flying, it is very hard to beat the overall value of a proven purpose-designed airplane engine. But hope springs eternal.

BJC

#### BJC

##### Well-Known Member
HBA Supporter
Finally, we see today that modern SI powered cars like the Prius 4 get better highway fuel economy than a similar diesel like the VW Passat TDI SE. Highway cruising keeps the electric motors out of the comparison. With direct injection and compression ratios around 14 to 1 plus other technologies like BMW's Valvetronic, modern SI engines are also very impressive for fuel economy.
I consistently got 55 to 56 MPG in my 1983 VW diesel Rabbitt, and it had room for 5 full sized adults. The only problems were slow acceleration and inability to drive with an airspeed of more than about 75 MPH.

Oh, and the emissions seemed to bother the US EPA.

BJC

#### Himat

##### Well-Known Member
Cruising on the highway at 120 kph demands only about 10% power on an average small car with a 200hp engine so your cruise conditions in the aircraft are 5 to 6 times higher than on the road, this means at similar rpms, manifold pressure must be 5-6 times higher- more stress for sure.
I do not quite agree on that statement. In Europe the small van is a popular car, and they have for they size decent load carrying capability and often quite small engines. One example, here in pick up truck format, the Fiat Doblo:

The specifications varies, bit the smallest engine is a 1,3l turbo diesel rated at 66kW (90hp).
Top speed of the car is 158km/h or close to 100miles a hour.
Now, said car with the smallest engine is certified to carry a one ton load and pull a one ton trailer.
With 130km/h and 70 miles a hour speed limits common on European roads, this engine will see something different than easy cruising at 10% of rated power. (Ok, there is often a lower speed limit if towing a trailer, but that one is not always adhered to.)
I'll expect quite a bit of pedal to the metal driving.

#### rv6ejguy

##### Well-Known Member
I do not quite agree on that statement. In Europe the small van is a popular car, and they have for they size decent load carrying capability and often quite small engines. One example, here in pick up truck format, the Fiat Doblo:
View attachment 38959

The specifications varies, bit the smallest engine is a 1,3l turbo diesel rated at 66kW (90hp).
Top speed of the car is 158km/h or close to 100miles a hour.
Now, said car with the smallest engine is certified to carry a one ton load and pull a one ton trailer.
With 130km/h and 70 miles a hour speed limits common on European roads, this engine will see something different than easy cruising at 10% of rated power. (Ok, there is often a lower speed limit if towing a trailer, but that one is not always adhered to.)
I'll expect quite a bit of pedal to the metal driving.
My post said car, not van and 200hp not 90hp. Obviously the smaller the engine and the higher the drag of the vehicle, the higher percentage of full power it takes to go X speed. Same goes for higher weight dragging up a mountain. Just comparing an average 200 hp/ 3000lb. car load cycle at 120 kph on a level road and this situation is nowhere near what a cruising aircraft would require for hp.

#### Himat

##### Well-Known Member
My post said car, not van and 200hp not 90hp. Obviously the smaller the engine and the higher the drag of the vehicle, the higher percentage of full power it takes to go X speed. Same goes for higher weight dragging up a mountain. Just comparing an average 200 hp/ 3000lb. car load cycle at 120 kph on a level road and this situation is nowhere near what a cruising aircraft would require for hp.
Yes, I did read your example, my point was more to provide another example that show that how a car engine is used can not be generalized, not from either example. The engine in question is used in a lot of different small to medium size cars, but is probably worked hardest in the small vans. I probably could have found an example with a similar car with a small spark ignition petrol engine.

As is the cost and availability of different fuels. Around here diesel fuel is cheapest, even more so if it is not for a road vehicle use as there is less tax on diesel fuel not intended for use in road vehicles. And while talking taxes, in Europe many countries taxes cars by the engine size, both capacity and power output. Small cheap cars then tend to have small engines. To keep up with the traffic the engines then get worked hard.

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#### B100

##### Well-Known Member
I consistently got 55 to 56 MPG in my 1983 VW diesel Rabbitt, and it had room for 5 full sized adults. The only problems were slow acceleration and inability to drive with an airspeed of more than about 75 MPH.

Oh, and the emissions seemed to bother the US EPA.

BJC
Really BJC ! are you serious ? are you trying to compare a 1983 era diesel engine with current engines? I don't want to be offensive but that is ridiculous! Please, be serious do your homework, and get your facts straight!
What you call a Rabbit on that side of the pond is what is known world wide as a VW Golf ! so while back in 83 that was true, today your "rabbit" lol....would be more like a hare....! And updated specs of current diesel VW rabbits/Golf would be closer to this :

Volkswagen Golf Golf 2.0 TDI 150 GT 5d full specification - BBC Top Gear or the latest 120 cu in engine putting out a miserable 181 hp :roll:

But please, dont take my word for it, check it out yourself :

Volkswagen Golf Mk7 - Wikipedia, the free encyclopedia

Lol...I guess with these bunnies you would have no problem with " slow acceleration and inability to drive with an airspeed of more than about 75 MPH." Would you?

Now I am aware that you dont get the best engine options on that side of the pond but that doesn't mean they dont exist!

#### B100

##### Well-Known Member
Grrrrrrrr........just finished a long detailed reply......and lost it when trying to post it :mad2: So here the short version!

"Cruising on the highway at 120 kph demands only about 10% power on an average small car with a 200hp engine so your cruise conditions in the aircraft are 5 to 6 times higher than on the road, this means at similar rpms, manifold pressure must be 5-6 times higher- more stress for sure."

No ! dont agree! my TDI has 115 hp , set @ 2400rpm = 120 kph that is for a loaded weight of around 2100kg so with your numbers.....no way !
Average car engine in Europe is around 100 hp or less ! We cant afford the big inefficient gas engines you have over there ! Oh! and there is a reason that 60% of all cars on the road are diesel!
Himat:
"As is the cost and availability of different fuels. Around here diesel fuel is cheapest, even more so if it is not for a road vehicle use as there is less tax on diesel fuel not intended for use in road vehicles. And while talking taxes, in Europe many countries taxes cars by the engine size, both capacity and power output. Small cheap cars then tend to have small engines. To keep up with the traffic the engines then get worked hard."

Amen to that and Himat forgot another big component too! emissions taxes ! CO2! so....diesels burn less fossil fuel = less CO2 taxes (some countries have different standards for both fuels)

Quick example: 1,6L engines 100hp , one gas , one diesel! Diesel emits less CO2 pays less tax!
Boost them as you say; Diesel easy 140 hp = same or lower fuel burn! Gas up to 180 hp = more fuel= more emissions= more taxes !

As for engine work load , well consider my real world personal example! on the road my engine is propelling 2,1 tonnes @ 120km on 2400rpm and has to go uphill , cope with the road surface/friction, and air resistance/drag and weather which the plane can fly around/over (adverse weather) . The plane ,(certainly lighter than the car) simply has to deal with drag, with the benefit of altitude and thinner air.
So I ask, in these conditions which engine is working harder, considering the constant load both are subjected to maintain the RPM set ?

My lost post had a lot about you BMW comparison , but short of it is that you guys in Canada and the US get very limited engine options on the European cars sold there, this mostly because of your lower fuel standards in gas and diesel ! Our current M3 3,0L diesel comes stock with 313hp !

"Finally, we see today that modern SI powered cars like the Prius 4 get better highway fuel economy than a similar diesel like the VW Passat TDI SE. Highway cruising keeps the electric motors out of the comparison. With direct injection and compression ratios around 14 to 1 plus other technologies like BMW's Valvetronic, modern SI engines are also very impressive for fuel economy. "

Again , you are right but it only applies to Canada and US because of the mentioned limited engines available! In Europe quite a few diesels beat the Prius in terms of fuel economy . I like you am also amazed at the latest development in fuel injection tech, but Ross you know that dew to limitations involving fuel to air and compression ratios SI engines can never reach the efficiency of a diesel, and while 14 to one is impressive, its about the upper limit for a gas engine and low by diesel standards. And since you insist on comparing apples & apples , a Prius is smaller and lighter than a Passat sedan or wagon ( I actually own one Passat)

Hope this helps to put the discussion into context!

#### Kingfisher

##### Well-Known Member
I don't have a bias towards diesels like you do, I simply look at the numbers and the track record in the air. Talking and dreaming about something does not make it reality. Like I said before, build it, get it in the airplane and fly it for a few years to prove it. Paper engines and paper airplanes mean little in the real world. The only production aero diesel to meet decent weight, reliability and cost goals has been the WAM 2 stroke however it's SFCs are no better than existing SI aero engines. All the 4 strokes (including auto based ones) are much heavier and the aero specific ones are crazy expensive, wiping out any cost savings in the long run, at least over here. Many of these have also had reliability issues along the way.

To be clear, I do not make money from doing auto conversions- we don't sell engines.

With regards to your feelings about diesel engine life, high boost pressures exact a toll on all engine types. The Thielert and SMA both had serious reliability issues (pistons and case fretting). The aviation application is little like the automotive load cycle. Ask yourself why everyone doesn't just run 80 inches in auto diesels all the time? The new EPS V8 aero diesel uses steel pistons instead of aluminum and a CGI block to avoid some of these issues. Weight on auto diesels is always a secondary design factor to reliability. Of course you can use an auto diesel in an aircraft, it's been done successfully many times but it's always heavier and never performs as well as a similar turbocharged SI engine. If fuel economy is your main goal, it could be very successful for you.

As far as performance goes, diesels are way behind. The French installed an SMA in an NXT and went to Reno a few years back and were slower than many normally aspirated fixed gear aircraft. They were not even in the same league as the other 2 NXTs (about 100-150 mph slower). https://www.youtube.com/watch?v=OE7lRu1HhHY Most race diesels can't even match the specific power output of production naturally aspirated SI engines.

Essentially, almost all hp increases on the diesel come from higher mass flow through higher boost pressures. Things like injectors, different mapping, turbos, intercoolers etc. simply help support the higher mass flow and boost.

The Audi is going to weigh more than you think by the time a gearbox is added. Upping hp through added boost works with the Lycoming too- 800hp and with geared SI engines even more so if we want to compare apples to apples. We have 3.8 Skyline engines making a reliable 2000hp (AMS) Texas Invitational https://www.youtube.com/watch?v=pcHumlKI5EE.

Talk like this about the "performance" of diesels comes from people who have little knowledge about turbocharged SI engines. SI engines massacre diesels in every form of racing except endurance racing with fuel limits. Let's remember the best turbo SI engines have specific outputs of around 1000hp/L, far in excess of any race diesel.

I'd add that here in my city, diesel fuel costs about 20% more than pump gas, wiping out any significant savings with diesel engines. Of course this varies depending on where you live.

Anyway, as before, when we discussed this, I encourage you to build it, fly it and show us...
Here you are again, stating that automotive diesels won’t hold up under aircraft engine load requirements, while on the other hand you started this thread:
http://www.homebuiltairplanes.com/forums/ford/18808-auto-engines-arent-designed-take-full-power-more-than-few-minutes.html
In there you point out the rigorous testing the automotive engines have to endure, and the likelihood of any Lycoming to fail under such torture.

Do you think an automotive diesel is not subjected to such testing? I don’t know why the examples SMA and Thielert had their failures. However, I think it is unlikely that the cause is the core engine’s capability, at least no more likely than if one of your converted Subarus is seizing up.

I suppose diesel max power is limited by rpm, since the injection event becomes too short. But not everyone is racing aircraft. What you say about increased mass flow through the engine for more power is true for all engines.

It is only in America (and I suppose Canada as well as its sidekick J) that large pick-up trucks are still powered mainly by gasoline engines, except for the occasional 7.0 litre Cummins. Even here in Australia, most SUVs and Utes (means pick-up trucks) seem to be Diesels (more reasonable displacements of ~3.0 litres), despite the higher price for engine and fuel.

I grew up and drove in Germany, lived in USA for 8 years (only there I could afford to get my pilot license and actually fly) until 2005 and are now in Australia. Of course there is no need to look into more efficient engines if you pay next to nothing for fuel. When I left the US, people were winging because they had to pay 3 US$per gallon, which is less than 80cents a litre! Back then the Euro was about 2:1, so that would have been 40 Eurocents, boohoo! This was considered a crisis! Compare that to the fuel prices that B100 is listing! During my stay in USA I noticed automotive diesels were virtually non-existent. French cars were not sold in the US (at least I did not see a single one except for in the hangar of a pilot friend, who was also a Citroen enthusiast. He owned several former diplomat’s cars of this company). VWs were sold as Diesels, but nearly no-one drove them other than engine testers (my workmate) or enthusiasts. There must have been a GM disaster in the ‘70s, where they tried to introduce a car diesel, and it had horrible performance and massive failures. The image of the diesel for cars seemed to be still heavily tarnished by that, at least in the Detroit area. So I really think most people in North America simply are not aware of how far diesels have come in automotive. That being said, our company in the U.S. did a lot of weird development projects for the EPA, using VW 1.9l TDI engines as the base engine. So the awareness was there on that level that these were the most efficient auto engines in the world. Last edited: #### cheapracer ##### Well-Known Member Log Member Hope this helps to put the discussion into context! Only the context you seek but many of us try to stick to real world context. I actually spend a lot of time and money researching these options and the math for a diesel simply isn't there - and that's why there is next to no diesel options being offered. As this forum is almost specific to 2 seat light aircraft of around 300 to 400kgs, there just isn't a realistic place for an engine that weighs an extra 80 to 100 kgs, or in other words, the weight of one entire passenger, besides the re-engineering of the aircraft. Real world math. Here you are again, stating that automotive diesels won’t hold up under aircraft engine load requirements, . That's not what he said, try to keep up. Last edited: #### BJC ##### Well-Known Member HBA Supporter Really BJC ! are you serious ? are you trying to compare a 1983 era diesel engine with current engines? I don't want to be offensive but that is ridiculous! Please, be serious do your homework, and get your facts straight! Lol...I guess with these bunnies you would have no problem with " slow acceleration and inability to drive with an airspeed of more than about 75 MPH." Would you? Now I am aware that you dont get the best engine options on that side of the pond but that doesn't mean they dont exist! What are you flying "on that side of the pond" B100? BJC #### rv6ejguy ##### Well-Known Member Yes, I did read your example, my point was more to provide another example that show that how a car engine is used can not be generalized, not from either example. The engine in question is used in a lot of different small to medium size cars, but is probably worked hardest in the small vans. I probably could have found an example with a similar car with a small spark ignition petrol engine. As is the cost and availability of different fuels. Around here diesel fuel is cheapest, even more so if it is not for a road vehicle use as there is less tax on diesel fuel not intended for use in road vehicles. And while talking taxes, in Europe many countries taxes cars by the engine size, both capacity and power output. Small cheap cars then tend to have small engines. To keep up with the traffic the engines then get worked hard. In Europe where diesel is cheaper than gasoline, diesel makes a lot more sense than it does over on this side of the pond, hence you have a much higher percentage of diesel cars there. Same goes for diesel aircraft where 100LL is scarce or expensive or both and diesel or Jet fuel is available and cheaper. No argument there. Over here, economically they make less sense especially in aircraft where the engines are double to triple the cost of similar hp SI engines. #### rv6ejguy ##### Well-Known Member Grrrrrrrr........just finished a long detailed reply......and lost it when trying to post it :mad2: So here the short version! "Cruising on the highway at 120 kph demands only about 10% power on an average small car with a 200hp engine so your cruise conditions in the aircraft are 5 to 6 times higher than on the road, this means at similar rpms, manifold pressure must be 5-6 times higher- more stress for sure." No ! dont agree! my TDI has 115 hp , set @ 2400rpm = 120 kph that is for a loaded weight of around 2100kg so with your numbers.....no way ! Average car engine in Europe is around 100 hp or less ! We cant afford the big inefficient gas engines you have over there ! Oh! and there is a reason that 60% of all cars on the road are diesel! As for engine work load , well consider my real world personal example! on the road my engine is propelling 2,1 tonnes @ 120km on 2400rpm and has to go uphill , cope with the road surface/friction, and air resistance/drag and weather which the plane can fly around/over (adverse weather) . The plane ,(certainly lighter than the car) simply has to deal with drag, with the benefit of altitude and thinner air. So I ask, in these conditions which engine is working harder, considering the constant load both are subjected to maintain the RPM set ? My lost post had a lot about you BMW comparison , but short of it is that you guys in Canada and the US get very limited engine options on the European cars sold there, this mostly because of your lower fuel standards in gas and diesel ! Our current M3 3,0L diesel comes stock with 313hp ! "Finally, we see today that modern SI powered cars like the Prius 4 get better highway fuel economy than a similar diesel like the VW Passat TDI SE. Highway cruising keeps the electric motors out of the comparison. With direct injection and compression ratios around 14 to 1 plus other technologies like BMW's Valvetronic, modern SI engines are also very impressive for fuel economy. " Again , you are right but it only applies to Canada and US because of the mentioned limited engines available! In Europe quite a few diesels beat the Prius in terms of fuel economy . I like you am also amazed at the latest development in fuel injection tech, but Ross you know that dew to limitations involving fuel to air and compression ratios SI engines can never reach the efficiency of a diesel, and while 14 to one is impressive, its about the upper limit for a gas engine and low by diesel standards. And since you insist on comparing apples & apples , a Prius is smaller and lighter than a Passat sedan or wagon ( I actually own one Passat) Hope this helps to put the discussion into context! Of course there are smaller and lighter diesel cars than the Prius which give better fuel economy. Just making a comparison of roughly equal sized cars SI and diesel. The interior volume of the Passat and Prius are almost identical, the Passat does weigh about 400 more lbs. The Prius got better mileage than the Passat and probably would even with 400 more lbs. on board. You say inefficient but today SI engines with modern tech have narrowed the gap considerably with diesels. Back in 2007ish, the SAE World Congress recognized in a statement that new SI technologies were rapidly bringing SI BSFC numbers close to diesel engines. Actually, if you compare the best, latest, SI passenger car engines to diesels on a BTU level in the fuel, the SI engines match or exceed the diesel in this regard. Diesel fuel has about 13% more energy content per unit volume. The energy content per unit weight is very similar between the two fuels. There is a rapidly diminishing return in thermal efficiency gain with compression ratio. Modern diesels have actually seen a reduction in CRs whereas modern SI engines have seen an increase- which has narrowed the efficiency gap lately along with other new technologies. Let's take my 2002 BMW 330ci with 3L SI engine. At 120 kph on a level road, it's using 6L/100km. Converting this to hp and using .45 BSFC, that's 21hp used to overcome rolling and air resistance. A Lycoming O-360 develops 135hp at 75% power cruise. That's 6.4 times the hp of the BMW at 120 kph so you see, the load cycle is much higher in aviation use. Most aircraft generally never cruise at power settings below 50%- usually 65-75%. The BMW example- mid sized car, 3500 lbs is using 9.3% power to cruise at 120 kph. I would expect the BMW to last 400,000-500,000 km cruising under these conditions. Let's say 3000-4000 hours conservatively. I'm not sure it would last that long in my RV6 pulling 60% power (135hp). We see the Thielert and Austro 2L aero diesels based off a Mercedes design rated at 155 and 170hp respectively- they have not pushed the ratings up with higher boost pressures since they know longevity is likely to suffer. Initially, the Thielert 1.7 had many piston/ ring issues and many engines were being pulled even prior to 1000 hours because of excessive oil consumption. They eventually solved the problems on these and the 2L is now working very well according to most reports. Generally on auto conversions in aircraft, we do not uprate hp over the stock levels since we know this is just going to reduce life and possibly reliability. The Austro and Thielert engineers are no dummies and understand this. Derating engines is a time proven way to extend life. Few knowledgeable engine people would agree that uprating an engine (diesel or SI) would have no impact on longevity at high, continuous output levels like we see in aviation. The M3 SI turbo still has 110 more hp than the M3 diesel and uses less than half the boost pressure to do it. The diesel has better performance at low loads than SI engines (outside of developments like BMW's Valvetronic). This is a fair advantage in light load auto applications. The BSFC gaps closes at or near WOT like we use in aircraft. The BSFC of the Thielert is .36, only marginally better than a Conti 550 running LOP at about .375. As I've said on other forums regarding engine types, fly whatever engine you like and what turns your crank so to speak. I just find the diesel worship guys often seem to think that EVERYONE should be flying a diesel. I just point out that a diesel is not better than an SI engine is all regards for aircraft in all areas of the world and for all missions. They have their place as do SI engines. Last edited: #### rv6ejguy ##### Well-Known Member Here you are again, stating that automotive diesels won’t hold up under aircraft engine load requirements, while on the other hand you started this thread: http://www.homebuiltairplanes.com/forums/ford/18808-auto-engines-arent-designed-take-full-power-more-than-few-minutes.html In there you point out the rigorous testing the automotive engines have to endure, and the likelihood of any Lycoming to fail under such torture. Do you think an automotive diesel is not subjected to such testing? I don’t know why the examples SMA and Thielert had their failures. However, I think it is unlikely that the cause is the core engine’s capability, at least no more likely than if one of your converted Subarus is seizing up. I suppose diesel max power is limited by rpm, since the injection event becomes too short. But not everyone is racing aircraft. What you say about increased mass flow through the engine for more power is true for all engines. It is only in America (and I suppose Canada as well as its sidekick J) that large pick-up trucks are still powered mainly by gasoline engines, except for the occasional 7.0 litre Cummins. Even here in Australia, most SUVs and Utes (means pick-up trucks) seem to be Diesels (more reasonable displacements of ~3.0 litres), despite the higher price for engine and fuel. I grew up and drove in Germany, lived in USA for 8 years (only there I could afford to get my pilot license and actually fly) until 2005 and are now in Australia. Of course there is no need to look into more efficient engines if you pay next to nothing for fuel. When I left the US, people were winging because they had to pay 3 US$ per gallon, which is less than 80cents a litre! Back then the Euro was about 2:1, so that would have been 40 Eurocents, boohoo! This was considered a crisis! Compare that to the fuel prices that B100 is listing!
During my stay in USA I noticed automotive diesels were virtually non-existent. French cars were not sold in the US (at least I did not see a single one except for in the hangar of a pilot friend, who was also a Citroen enthusiast. He owned several former diplomat’s cars of this company). VWs were sold as Diesels, but nearly no-one drove them other than engine testers (my workmate) or enthusiasts. There must have been a GM disaster in the ‘70s, where they tried to introduce a car diesel, and it had horrible performance and massive failures. The image of the diesel for cars seemed to be still heavily tarnished by that, at least in the Detroit area. So I really think most people in North America simply are not aware of how far diesels have come in automotive.
That being said, our company in the U.S. did a lot of weird development projects for the EPA, using VW 1.9l TDI engines as the base engine. So the awareness was there on that level that these were the most efficient auto engines in the world.
As you'll see in my reply to B100, I was talking about increased specific power output almost always reduces engine life to some extent. He was advocating increasing boost to improve the power to weight ratios of auto diesels for use in aircraft- contrary to what most experts do and contrary to what certified aero diesel manufacturers are doing today. Of course auto diesels are subjected to similar validation as SI auto engines so we don't expect them to expire in normal use at normal factory hp levels. Upping the boost in a stock SI or Diesel with proper mapping usually does not materially affect longevity in road use because the duty cycle is very low for a high percentage of of the operating time- the opposite of aviation use. You'll see that the industrial and marine versions of VWs diesel engines are substantially de-rated compared to their automotive counterparts- again the factory engineers have reasons for this in these high continuous power applications.

The original SMA and Thielert designs underestimated the aviation cycle stress IMO. They have both been updated. The improved Thielert now has a good record. The SMA does not have enough fleet time to know but I believe the engineers will lick their problems as well. People seem to think that truck diesel longevity somehow automatically translates into lightweight (relatively speaking) aero versions. Clearly to date, it has not. Austro has been able to apply lessons learned form the failures on the similar Thielert and has had decent reliability out of the box but the engines are still heavy (414 lbs.) and very expensive.

Actually in the North America, 30-50% of light pickup trucks are turbo diesel these days. I can't drive 10 seconds in my city without seeing a cluster of them, especially those used for hauling on the highway, private and business use. Ford, Dodge and GM all have turbo diesel trucks here and they've sold millions of them.

Absolutely as I said before, diesels make huge sense if the fuel in cheaper than gasoline and more readily available and the engine options are the same prices. Here is North America, that simply isn't true.

I follow all engine developments as that used to be my field, pretty up on the latest technology out there and being developed for SI and CI engines. The fuel economy gap is closing every year.

We have relatively cheap petrol and that's the main reason why most people drive SI powered cars here. Lots of people simply prefer the quiet refinement of SI engines. I assume that any OEM could offer more diesel car models here but they just don't seem to sell. Most diesel cars over here are VW, Mercedes and a few BMWs. VWs are by far the most plentiful, perhaps 30% of those are diesels.

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#### cheapracer

##### Well-Known Member
Log Member
Ross, I compliment you on your patience, sadly it seems I've run out of it in recent times.

#### B100

##### Well-Known Member
What are you flying "on that side of the pond" B100?

BJC
LOl..... my sofa! but I have to admit that your reply is a funny way of manning up to the fact that you Rabbit example was just ridiculous! :gig:

Dixit!

#### B100

##### Well-Known Member
Ross, I compliment you on your patience, sadly it seems I've run out of it in recent times.
Yes ! Indeed Cheapracer, You probably know all, and best, and everyone knows that progress comes from closed minds and not pushing boundaries and new possibilities ! Fortunately those pesky bicycle builders known as the Wright brothers didn't think like you !

#### B100

##### Well-Known Member
Only the context you seek but many of us try to stick to real world context.

I actually spend a lot of time and money researching these options and the math for a diesel simply isn't there - and that's why there is next to no diesel options being offered.

As this forum is almost specific to 2 seat light aircraft of around 300 to 400kgs, there just isn't a realistic place for an engine that weighs an extra 80 to 100 kgs, or in other words, the weight of one entire passenger, besides the re-engineering of the aircraft. Real world math.

Cheapracer, its your choice to continue to ignore facts , perhaps you declared lack of patience is affecting you, because if you bother to check out my link, it is precisely what you are describing, a two place home built that weights 450 Kg with two adults on board, powered by an automotive diesel engine ! (in fact an outdated one no longer in production) But for your benefit here is the link again ;

http://gazaile2.free.fr/englishInformations.pdf

Gaz'aile 2 : caract&#233ristiques et performances

That my friend, has been flying for years now and that is as you mention "real world math" But you are free you choose to ignore it, either by choice or as you state elsewhere lack of patience.....or some, in the real world might call it something else!

-----------------------------------------------

"Progress is impossible without change, and those who cannot change their minds cannot change anything" - George Bernard Shaw

"There is nothing more dangerous than a closed mind " - ancient proverb

#### cheapracer

##### Well-Known Member
Log Member
Fortunately those pesky bicycle builders known as the Wright brothers didn't think like you !
Ironically it was very fortunate that others did not think like the Wrights, and that the Wrights blocked others from following their methodology turned out to be a good thing forcing individuals to discover far superior solutions. Don't try using history as a weapon unless it's properly loaded.

I have "pushed the boundaries" many a time and my aviation based patents/applications are all about "new possibilities". I spend time and money researching stuff like the possibilities of diesels and in fact, a product of mine being currently developed is advantageous in it's market place through it being diesel powered (modern 2.0 turbo common rail), so overtones of me having anti-diesel bias or ignorance in anyway is nonsense, but it's just not a fit for HBA typical light aircraft. It always comes back to the math and 2+2 needs to equal 4.

You probably know all, and best,
Ask rv6ejguy , he is the ultimate know it all reference on this site !
You have an unfortunate short history here of not liking other people actually having experience in matters overriding your veritable delusions, but anyway, no problem as I don't actually answer for you, there's many others reading here as well and I'm sure they enjoying reading and learning, especially from Ross's posts which are book worthy.

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