ninedee_golf_tdi
Vendor
So much for the discussion of why it can't be done.
1.9 tdi powered Cessna 172 Silver Hawk
- Thread starter ninedee_golf_tdi
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So much for the discussion of why it can't be done.
oilhammer
Certified Volkswagen Nut & Vendor
There have been several, but the weight-to-power ratio isn't especially great. Diesel also weighs more than gasoline. Plus, on a plane that size, again for weight savings and simplicity, air-cooled engines are typically better (although there have been air-cooled diesel engines).
So it never was "why" it couldn't be done, more a question of "why would you?" In this instance, the same could be said for using a 180hp VAG gasoline engine, too.
So it never was "why" it couldn't be done, more a question of "why would you?" In this instance, the same could be said for using a 180hp VAG gasoline engine, too.
oilhammer
Certified Volkswagen Nut & Vendor
Heh, I wouldn't trust that engine on the ground, let alone in the sky. But that wasn't what I was talking about (those make 200hp). I was talking about one of the old belt driven 1.8t engines. Like my AWM. It has pushed (and continues to push) two tons of AWD Passat down the road through a slushbox for 17 years and 1/4 million miles. THAT I would trust, although in stock form it only made 170hp. I think it makes about 185 now thanks to Rocketchip. 
I never said anyone was an idiot. And I don't appreciate being called an ass.
The TDI powered plane I was most impressed with used the all aluminum 3cyl (1.0L?). It had a much better power-to-weight ratio, and its shorter length made it closer in size to what the airframe that was being used was made to hold (which was a smallish Rotax engine).
I never said anyone was an idiot. And I don't appreciate being called an ass.
The TDI powered plane I was most impressed with used the all aluminum 3cyl (1.0L?). It had a much better power-to-weight ratio, and its shorter length made it closer in size to what the airframe that was being used was made to hold (which was a smallish Rotax engine).
redbarron55
Veteran Member
A problem with Diesel 4 cylinder aircraft engines has been the relatively harsh torsional impulses and the lack of overlap of those pulses unlike a 6 cylinder engine.
The early modified Diesels used in small aircraft years ago had problems with the coupling to the propeller which has it's own torsional vibration issues.
As I remember these engines were modified MB Diesels and the failures were in the DMF and power transmission issues.
All in all these engines were originally well received, but the problems with reliability plagued them.
Diamond aviation produced a twin engined aircraft with the Diesels. The DA 42 was introduced in 2004. By 2008 reliability problems resulted in the bankruptcy of Thielert. Diamond re-engined the DA42 with the Austro Engine AE 300.
Thielert was bought by the Chinese owner of Continental Motors and has been developed still using MB based engines.
Aircraft engine conversions are not as easy as they seem.
The early modified Diesels used in small aircraft years ago had problems with the coupling to the propeller which has it's own torsional vibration issues.
As I remember these engines were modified MB Diesels and the failures were in the DMF and power transmission issues.
All in all these engines were originally well received, but the problems with reliability plagued them.
Diamond aviation produced a twin engined aircraft with the Diesels. The DA 42 was introduced in 2004. By 2008 reliability problems resulted in the bankruptcy of Thielert. Diamond re-engined the DA42 with the Austro Engine AE 300.
Thielert was bought by the Chinese owner of Continental Motors and has been developed still using MB based engines.
Aircraft engine conversions are not as easy as they seem.
I bet the stock application dual mass flywheel provides quite a bit of damping of the torsional rattle.
The pictures show that they did in fact use one of them in there.
Gotta wonder if they could avoid the gearbox on the propeller all together by flipping it over upside down and doing the dry-sump oiling dance. Probably result in needing to pull the glowplugs to drain oil out of the combustion chambers before each start, heh...
Also need to make a custom bracket for the injection pump, it wouldn't like being upside down, end up full of air eventually. Maybe just add a small orifice bleed hole (small enough that the cold start valve is still able to regulate the injection timing) to the return line from the bottom of the case to keep the air bubbles sent back to the tank, though that might not work good without the "separating bowl" of the QA chamber.
The pictures show that they did in fact use one of them in there.
Gotta wonder if they could avoid the gearbox on the propeller all together by flipping it over upside down and doing the dry-sump oiling dance. Probably result in needing to pull the glowplugs to drain oil out of the combustion chambers before each start, heh...
Also need to make a custom bracket for the injection pump, it wouldn't like being upside down, end up full of air eventually. Maybe just add a small orifice bleed hole (small enough that the cold start valve is still able to regulate the injection timing) to the return line from the bottom of the case to keep the air bubbles sent back to the tank, though that might not work good without the "separating bowl" of the QA chamber.
redbarron55
Veteran Member
4 cylinder engines have issues that can be solved. In the case of MOST 4 cylinder aircraft engine they are direct drive with no flywheel. (other than the prop).
Geared engines are (Almost) always six cylinder or more due to the non overlap problems. Diesels are harsher and often have some kind of coupling between the crankshaft and prop.
As a matter of fact the Jabiru (Australian) engine had problems with the 4 cylinder (not the 6) shearing the flywheel bolts due to these torsional vibrations. I was involved with the RAAS investigations of this problem and the solution.
The four cylinder engines sheared the bolts at about 200 hours as the calculations (after the fact) predicted. The six cylinder with 2/6 more horsepower did not have this issue at all.
In the case of the Jabiru the factory increased the size of the bolts, but experimentally we proved that increasing the torque to the bolt manufacturer's limit would solve the problem.
For reference the final bolts always finished shearing (the final bolts) on start up so no aircraft were lost that I am aware of.
To be exact the bolts did not shear, but rather they failed with fatigue fractures due to repetitive stress and the two parts not clamped where they could not move in relation to each other. Very small movement. Flex the bolts about 1,000,000 times and there you go.
Often these failures are misdiagnosed as the bolts shearing, but microscopic or careful study indicated the failure mode.
Geared engines are (Almost) always six cylinder or more due to the non overlap problems. Diesels are harsher and often have some kind of coupling between the crankshaft and prop.
As a matter of fact the Jabiru (Australian) engine had problems with the 4 cylinder (not the 6) shearing the flywheel bolts due to these torsional vibrations. I was involved with the RAAS investigations of this problem and the solution.
The four cylinder engines sheared the bolts at about 200 hours as the calculations (after the fact) predicted. The six cylinder with 2/6 more horsepower did not have this issue at all.
In the case of the Jabiru the factory increased the size of the bolts, but experimentally we proved that increasing the torque to the bolt manufacturer's limit would solve the problem.
For reference the final bolts always finished shearing (the final bolts) on start up so no aircraft were lost that I am aware of.
To be exact the bolts did not shear, but rather they failed with fatigue fractures due to repetitive stress and the two parts not clamped where they could not move in relation to each other. Very small movement. Flex the bolts about 1,000,000 times and there you go.
Often these failures are misdiagnosed as the bolts shearing, but microscopic or careful study indicated the failure mode.
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I kinda figured that the thrust bearings wouldn't be up to it, lol little tiny things that they are.
I was mainly going on the assumption that the gears were mainly used for keeping the thrust axis up where it's supposed to be.
Planes are way neat, but they take way too much math for me. I'm more a "plop it on, weld it up and see how it does" kinda guy. :\
Joash
Well-known member
COOL! Now i can tell my flying buddy that i was right and that it is possible.