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Having significant experience with the reliability and ease of maintenance of marine diesel engines I have found myself wondering about a couple of things.


1. How does an aircraft diesel engine come in light enough to be installed without crippling the aircraft load carrying capacity? Even small four or six cylinder diesel engines are VERY heavy.


2. What kind of fuel does an aircraft diesel use? #2 offroad or #1 low sulfur


3. Are there any successful diesel engines installed on aircraft turbine or otherwise?


4. What are the problems with getting diesels certified for helicopters in the US? Is there a problem getting diesels certified in the US?


Simple questions but I have been stuck on them for a while.

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For fuel there using standard aviation jet fuel thats pretty easy to get at most airports. As far as weight, you have a good point. But it sounds like using variable pitch trurbo chargers and pumping up the boost there getting the HP/torque needed. I'm sure the manufacturers are designing in weight savings measures whenever they can, and hopefully not at the expense of safety/reliability. As your probably aware of, diesels make more torque than gasoline engines for the same hp (typically) and you can use a smaller HP diesel engine (with higher torque) in place of a larger HP (less torque) gasoline engine.


If I missed something, someone please join in and correct/update me.

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4 cycle diesels are a dog without turbocharging, far as acceleration goes. Yep, turbo's increase power/torque, but improves throttle response. Do you have any supercharged fire trucks? The Detroit Diesel's I serviced in the AF had blowers and turbo's on the same engine, of course they were 2 cycle. Deere is selling a lot of small compact turbo'd 3 cyl eng'd tractors this year.

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All of our units are turbocharged thankgoodness! Our 2008 F550 6.4 diesel is twin turbo'd along with our Peterbilt C13 diesels in some of the engines and water tenders here in the county. But most all our diesels are single turbos prior to 2007. It looks like from an emission stand point, twin turbos are being used with particulate filters at the end of the exhaust pipes that burn the unnburned fuel (similiar to a cat but different I am told). I have heard about supercharged diesels, but haven't seen any in person yet.


Jumping into the way back machine, the first diesels we had were naturally aspirated cat 3208 diesels. Talk about smoke and no power hahahaha! We had fun with bike riders next to us at stop signs when we hit the throttle! Speaking of detroits, had a Mack with a 2-stroke 8V92 as I recall. Daily inspections consisted of checking the fuel and adding a gallon of oil! Sorry for hijacking the thread, my hand is out for a slap....

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Oh klmmarine,

When I was in the AF in Italy, FIAT motors have alum block cast iron liner 4 cyl 1.9L no turbo diesel's in Van/trucks. The engine used about a 2 inch wide timing belt like gas engines!! FIAT= Fix It Again Tony, lol..

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No problem hijacking this thread. I wanted to get a conversation going about diesels and that is what happened. We have no emission standards on our diesels so it is not uncommon for some of the companies out here in the gulf to recycle their waste oil and burn it back through the engine in the fuel, talk about smoke... ugh!


I was just having a hard time envisioning a helicopter with a Cat 3508 or even a 3406 hanging off the back.


I didn't realize you could run diesels on jet fuel, so that answers that question for me. I had visions of people trying to run BioDiesel through their aircraft and losing that great smell of burnt jet fuel in place of the french fry smell you get with biofuel.


I love the smell of jet fuel in the morning. Not to mention the sound of turbines spinning up.

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My father inlaw use to own a Merc 190D, slow as Christmas but got 40+ miles per gallon on the highway. He use to manual shift the auto trans all the time to get it up to highway speed. If left in auto a kid on a bike could pass you...


Some pics of the old USAF trucks I worked on..

P-24 Brush/Struct w/Det 6V-92TA supercharged engine, electronic Allision, I think 1250 gpm.

P-4 Crash/Struct w/ Cat 1648 dual cam turbo'd, 325 hp, 1200 gpm @ 240 psi.

P-18 Tanker/Brush w/6V-92TA, supercharged, class B pump, 500gpm.

P-8D Struct w/Det 8.3L Fuel Pincher Turbo, 750gpm, basically same engine used in some boats.

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Thanks for the links Mechanic! Have a friend who was with the USAF, and he spent a bit of time on P-4 / P-19 and some others that I forget. We just recieved a year ago a special built hybrid engine for the county GAl airport. Its a custom built Pierce that can be used for light crash/rescue, and as a everyday engine for other incidents. Someday well get a real crash unit as were getting bigger and bigger aircraft coming in to service the wine country and Infinion Raceway/Sears Point racetrack.


KLM, I would love to see a 3406 strapped under a S300!!!!

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The weight has been coming down in the diesel engine field for a time , with the advent of electronic injector pumps the stress on the engine can be reduced so weight can be saved the modern range of

compression ignition engines have improved beyond all recognition in the last few years to the extent of wondering is it CI or IC they deliver smooth power rev well and are real reliable,

It cant be long before the CI engine is king of piston power

As for the Fix It Again Tony how about F**k Our Retail Dealers :ph34r:

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I take it you are not fond of the FIAT vehicles either??? The Alfa Romeo seemed to give us less trouble than the FIAT. Those Alum 1.9L's rattled like heck at idle. It seemed like forever getting up to speed, column shifting through 5 gears with no turbo..Those stake bed van/truck or what ever they called them, sucked..

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4. What are the problems with getting diesels certified for helicopters in the US?


The problem is same everywhere; There isn't many diesels certified for aviation use. Thielert's 1.7 (2.0 nowadays) and 4.0 engines are the only ones that can be taken seriously. Others manufacturers still don't have certified products. So far Thielert hasn't showed much interest in rotorwing aircraft propably because they have more than enough to do with the customers in the fixedwing market.


I'd love to see a certified diesel helicopter (and i know i'm not the only one) but i'm afraid it'll still take another five years or even more...

Edited by FinR
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  • 2 weeks later...

Hey all! I'm new here, and norwegian so if I write a bit wierd I'll blame that :P This is a great website by the way.


I'm no mechanic, but the way I understand it diesels have more torque than petrol engines compared to HP, but they tend to deliver it in a shorter band, thats why a diesel car tends to have allot of omfh from from a stand still, and then dies off rather quickly. but seeing how we as helicopters operate on a narrower rpm range than say a family car, I always thought fitting a light Helicopter with a diesel engine would be a great idea! not to mention that a diesel doesn't nees the magneto system, so it should be more reliable..


and with the gas prises and that whole situation, biodiesel might eventually be the way to go and seeing how all development in aviation takes a while it would probably be easier to use biodiesel in a diesel engine or say fuel cells.


Most of you seem to know allot about engines, way more than me, but if someone is wondering about the pros and cons of diesel in aviation you could try oxford aviations powerplant cd-rom, they have a whole chapter in there abut how the diesel works and how it relates to aviation. (they are talking about fixed wing though, but the lycombings in the Robbie and Schweizer aren't too different from the one in the Cessna ;) )

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Frank really wanted to get a diesel in his new R66..but it wasnt meant to be just yet..too much weight.


However, 2200 hours on a diesel is nothing. You could take out significant weight in a diesel ( less bullet proof) if you knew you were throwing away the engine after 2200 or 2500 hours...


Also, all technology for diesels has been on improving power and reducing emissions...no manufacturer has really made weight reduction the number one priority.



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Not to take this to far off the beaten track, but there are auto manufacturers that are trying to get the weight down and power up on the oil burners. VW Touareg with a V10 diesel spits out 310hp and gobs of torque. I couldn't find the engine weight, but suspect its not too much being in a mid sized SUV.


And here is how this ties into aviation, so check out a few pics from a PR stunt by VW using a 747:


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  • 5 months later...


I thought I would bring this up again, lol.. I was reading an AOPA e newsletter and ran across a Cessna Skyhawk with factory installed Thielert Centurion 2.0L Turbo Diesel STC!!!

Link, Cessna Skyhawk TD Factory STC.


The 2.0L power is almost identical to the Robbie O-360-J2A Lycom.

Link, Centurion 2.0L



Excellent climb performance up to 13,500 ft and approved to 18,000 ft

135 hp take off power

122 hp in 10,000 ft

97 hp cruise power in 17,500 ft


Link, O-360 Type Cert Data Sheet


They claim the 2.0L burns between 3-5.3 gph.

The O-360 about 8-10 gph.


6.0 gph X 6.9 Jet A = 41.4 lbs


10.0 gph X 6.0 100LL = 60.0 lbs


So, seems the fuel savings would offset the few extra pounds in the engine??


Good fuel calculator, link.




Verrry Intresting....

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I said it in a previous thread that I think Diesels are the future of GA.... it will take a good 15-20 years due to the new cost and phasing out of the traditional recips... but long term it's coming. I'm in no rush... I don't care if it runs on diesel or avgas... as the pilot it won't make any difference.


Don't think you'll be seeing biodiesel in aviation... Jet-A all the way.


By the way.... jet-a is basically diesel.... just barely up the distilling tower and often mixed with additives to get rid of some of it's problems (gelling, bacteria)

So a diesel will run on jet-a.... of course! It would probabally prefer it... much cleaner

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Towing a 747 on wheels isn't impressive at all. Have you bothered to look at what they use for pushbacks from the gate at airports? It doesn't take much to get something on wheels moving.


JetA is kerosene, lighter than diesel. JP4 is kerosene mixed with gasoline. Both diesels and turbines will run on a wide range of fuels with little problems. You can run a turbine on pure avgas, but you have to be very careful on the start, and an overhaul is necessary after only a few hours because of the temps. You could also run diesel in a turbine, but it's harder to get started.


You're not likely to see diesels in aircraft for the same reasons you won't see automotive engines in them - bureaucratic certification costs. You can put any engine you like in an aircraft in the experimental category, but you can't use or sell it commercially.

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You're not likely to see diesels in aircraft



This is the point I was making. The manufactures need to do all they can to keep operational costs low to keep sales up! There are currently only 2 fixed wing models available from the factory with the 2.0L Centurion diesel engines. I was thinking there is a kit copter company trying to use the Centurion engine to get their copter certified???



Cessna Skyhawk TD. I don't believe there is a restriction on the 2.0L, because American Flyers are converting all their 172's to the engine at overhaul.

Diamond DA-42 Twin.- The TCDS A57CE states "Normal Catagory".


American Flyer has 55 training aircraft of the type Cessna 172, which can be converted with the Centurion jet fuel engines. Epic Aviation, Inc., located in New Smyrna Beach, FL, a distributor for Thielert engines for Central and South America partnered with Thielert and American Flyers on the sale and installation of the first conversion displayed at Oshkosh.


Further FAA type certifications for the Robin DR 400 and Diamond DA40 will be awarded before the end of the year. The FAA type certification for the installation of the powerful 350 hp Centurion 4.0 in the Cessna 206, 340, 414 and 421 is planned for the coming year. "This will enable the students of the flying school to experience the feeling of flying a jet from the outset", says Thielert.
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I don't quite understand how having a diesel engine enables students to experience the feeling of flying a jet from the outset. Diesel engines aren't jets, by any stretch of the imagination.


The only thing I was thinking about their claim to fame, was that the Centurion engines use the FADEC system, simular or not??? Maybe they are commenting on the high HP output of the 4.0L?????

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