Diesel aircraft engines

[Ted]

I just based it off published TBO, they are suggesting that the diesels may end up with 2500, which should be possible given diesels longevity in other applications.

Making a comparison between a Cummins, PowerStroke, or Duramax and any of the automotive diesels that have been modified and installed into an aircraft is a pretty poor comparison, and the service histories have shown that to date.

Note, I am making no statement about potential future TBOs, but at present, they just aren't there. What was the Theilert gearbox replacement interval a few years ago? I want to say it was about 200 hours, if not less than that. You'll end up spending more on the gearbox replacement over the life of the engine (even if that was the only part that broke) than you'd save in fuel, and probably then some. And nevermind the other problems...

I know you just fly in NA, but what about the resale of a twin with diesels in the world wide market? Probably a fast mover under $400K.

This is perhaps the biggest argument for a diesel. But, that doesn't impact me.

As I said (and have before), I'm a big proponent of diesels in aviation. However, everyone likes to come in and talk about how easy it is. It's not nearly as easy as it sounds. In foreign markets, it does make more sense, and for me I'd like to have diesels before I do a flight around the world. But they'd need to be reliable diesels. Even with two, I have no desire to have one go out on me over the North Atlantic.

I run a LOT of diesels. The maintenance is more in my world only because of the filter cost and fluid capacity. It they had the same filter and crankcase volume as a gas engine, I can't see how they wouldn't be a lot cheaper than replacing mags, plugs, wires, etc. 4 times in the life of the engine.

I don't know what kind of diesels you run, but I used to run a GM 6.5 and a Dodge Ram Cummins 5.9. They were both bulletproof. They also weighed 2-3 times as much as aircraft gas engines of equivalent power. First you have to get the weight down to something that is actually tolerable in a plane. Thielert and Diamond Austro do this by using a small-displacement automotive diesel that is lighter weight, making light-weight components for it (which, not surprisingly, are weaker and thus more prone to failure), and adding a gearbox. If you were to try to do it to a Cummins out of a Dodge Ram, you'd still be looking at something that has an installed weight of likely 50% more than a TIO-540-J2BD for equivalent power, and who knows on reliability. My guess is similar TBOs, but lower at first.

Don't forget, when someone spends all this money on a conversion and then lets their aircraft sit for 10 years the diesel will probably take it much better.

They'd probably both take it pretty poorly. No engine likes sitting around that long.

Most people seem to think that this is a really easy problem to solve. If it was, everyone would be doing it by now, and we'd be done with our gasoline engines. Clearly, it's not as simple as people think it is...

Also, I'd expect on the 310 I fly for the fuel burn to go from 25 to about 20 or so, not 16.

 

[Dan Thomas]

SMA has spent something like a billion dollars on their diesel so far, with only 50 or so flying to date. They must have really deep pockets. The engines have had considerable teething troubles, too, often at the expense of the aircraft owner. And downtime to go with it.

Thielert has been through bankruptcy and the engine has several ADs in it already. I don't know if Austro has any troubles. Both of those are converted auto engines with speed reduction gearboxes. SMA is a clean-sheet aircraft engine, direct drive.

Thielert's gearbox was at a 300 hour TBO. I hear it's now 600.

Dan

 

[Henning]

I want to convert the Audi 12cyl for a 600hp direct drive.

 

[Ted]

SMA has spent something like a billion dollars on their diesel so far, with only 50 or so flying to date. They must have really deep pockets. The engines have had considerable teething troubles, too, often at the expense of the aircraft owner. And downtime to go with it.

Hence my point about why you couldn't convince me to do it now. Any of the supposed savings would quickly be eaten up.

Thielert has been through bankruptcy and the engine has several ADs in it already. I don't know if Austro has any troubles. Both of those are converted auto engines with speed reduction gearboxes. SMA is a clean-sheet aircraft engine, direct drive.

That is what I like about the SMA engine. It was actually designed from the ground up as an aircraft engine. That said, it has had teething problems (I would've designed it a bit differently). The Thielert concept I don't think is necessarily bad, but I think the execution of it was the bigger issue. And, given the company's financial status, it's a bad place to be.

Thielert's gearbox was at a 300 hour TBO. I hear it's now 600.

I figured someone else would know the numbers better than me. Still, that's a lot of gearbox replacements over the engine life.

Do you know if it's actually a TBO? I thought the whole engine was a TBR - Time Between Replacements. Can't be overhauled. That may be from a few years back.

 

[Ted]

I want to convert the Audi 12cyl for a 600hp direct drive.

And how much does that Audi engine weigh?

 

[Henning]

And how much does that Audi engine weigh?

It's reasonably light, the one they put in the Q7 uses a funky phenolic block and aluminum components. It also puts out the power around 2500 rpm so it can be direct drive; between 12 cyl and common rail injection it should be smooth enough. If not I'd just use a viscous coupling/mount for the prop.

 

[Ted]

It's reasonably light, the one they put in the Q7 uses a funky phenolic block and aluminum components. It also puts out the power around 2500 rpm so it can be direct drive; between 12 cyl and common rail injection it should be smooth enough.

A quick Google search says it makes a bit under 500 HP @ 3750 RPM. So at 2500 RPM you could likely get it to make about 300-350 HP (linearly, it would be 333 HP @ 2500 RPM). However, even with aluminum components, you're still talking about a liquid-cooled, overhead cam V12. Of course, one would need specific weights to see. It might be doable, but I wouldn't be too enthusiastic.

If not I'd just use a viscous coupling/mount for the prop.

If you say "just", that implies you've never tried doing that before.

That said, I doubt it'd be needed. If the propeller vibrations induced by the SMA diesel (which are enormous) can be handled by a direct drive prop, I'd be highly surprised if a V12 would need some weird coupling.

 

[Henning]

If you say "just", that implies you've never tried doing that before.

That said, I doubt it'd be needed. If the propeller vibrations induced by the SMA diesel (which are enormous) can be handled by a direct drive prop, I'd be highly surprised if a V12 would need some weird coupling.

I've worked with hundreds of viscous drives, each has its problems with their own solutions; although I don't think it will come down to it either.

For me they'll be fine at 350hp and to meet my personal mission, but a Lenco drive would let me shift gears & spin up the engine without over speeding the prop for getting that Transpac load of fuel off the ground.

 

[Ted]

I've worked with hundreds of viscous drives, each has its problems with their own solutions; although I don't think it will come down to it either.

Boats and cars don't count. Try doing it on an aircraft, and then get back to me on how well it works for you.

For me they'll be fine at 350hp and to meet my personal mission, but a Lenco drive would let me shift gears & spin up the engine without over speeding the prop for getting that Transpac load of fuel off the ground.

300-350 hp would be fine. Of course, it would effectively be naturally aspirated, because at the pressure ratios required the turbos would quickly run out of capabilities.

I'm sure the multiple-speed drive would work wonders, especially for the extra couple hundred pounds.

 

[Henning]

Boats and cars don't count. Try doing it on an aircraft, and then get back to me on how well it works for you.



300-350 hp would be fine. Of course, it would effectively be naturally aspirated, because at the pressure ratios required the turbos would quickly run out of capabilities.

I'm sure the multiple-speed drive would work wonders, especially for the extra couple hundred pounds.

Well, you need something spacing between the crank and bellhousing bearing anyway, a Lenco isn't that heavy for all the extra power it puts on tap.

 

[Ted]

Well, you need something spacing between the crank and bellhousing bearing anyway, a Lenco isn't that heavy for all the extra power it puts on tap.

I think you'd find the results wouldn't work very well.

Either a machined spacer or a gearbox of some form (if a reduction was desired) would be fine.

 

[Dan Thomas]

Do you know if it's actually a TBO? I thought the whole engine was a TBR - Time Between Replacements. Can't be overhauled. That may be from a few years back.

That's correct. Can't be overhauled. Very little can be done by the field mechanic, and even then you need the Thielert training and a bunch of special tools.

Dan

 

[zaitcev]

This may be another of Zoom's vendettas, but I see nothing but ADs for Thielert. Almost like a new AD every month. Nothing for SMAs (but it may be selective journalism and/or the difference between STCed and OEM engines).

 

[Dan Thomas]

Nothing for SMAs (but it may be selective journalism and/or the difference between STCed and OEM engines).

SMA ADs:

SR 305-230

2007-24-06
Electronic control unit (ECU)

2007-18-05
Exhaust collector assembly

Dan

 

[Henning]

I think you'd find the results wouldn't work very well.

Either a machined spacer or a gearbox of some form (if a reduction was desired) would be fine.

A Lenco is simply a planetary gear reduction unit, a Lenco CS3 5 speed which is 4 2 speed units + a reverse unit only weighs about 45lbs and will hold up to 1800 HP of hard hitting abuse. Each 2speed section only weighs about 10 pounds and allows me to use a direct drive and allows me to select a reduction (I'd use around 1.96:1) for high power; high pitch use on take off and when required/desired.

Here is what it is in 5 speed race car form, a plane only needs one section of it.

http://aberdeen.craigslist.co.uk/pts/2779006670.html This is the lowest rating of the standard transmission for high power racing applications, Lenco. This one takes 1800hp The CS 1 I believe advertises 3500hp. Go look what's behind the Top Fuel engines racing...

 

[Ted]

Well, when you actually go do any of this stuff you talk about and can prove it will actually be viable and useful, then my hat will be off to you.

It would also be useful if you realized that the design constraints for top fuel dragsters are not the same as for aircraft. Just because something works well in one does not mean it will work well in the other.

 

[RotorAndWing]

Well, when you actually go do any of this stuff you talk about

 

[airguy]

It would also be useful if you realized that the design constraints for top fuel dragsters are not the same as for aircraft. Just because something works well in one does not mean it will work well in the other.

Oh come on now - just because most of your flights last longer than 8 or 9 seconds does not mean you should bash others who like short ones with race components before gliding back!

 

[Ted]

Oh come on now - just because most of your flights last longer than 8 or 9 seconds does not mean you should bash others who like short ones with race components before gliding back!

When the Bugatti Veyron was designed, the guy who designed the transmission about had a nervous breakdown in the process. This man developed F1 transmissions regularly, and when asked what the trouble was, he said "You don't understand. An F1 transmission needs to only last a few hours. This needs to withstand 1001 horsepower for 100,000 miles or more!"

But hey, what do I know about aircraft engines...

 

[Capt.Crash'n'Burn]

Does anyone know if biodiesel has been successfully tested?

It would be nice to be able to grow your own fuel in casae of the Zombie Apocalypse.

 

[Henning]

Does anyone know if biodiesel has been successfully tested?

It would be nice to be able to grow your own fuel in casae of the Zombie Apocalypse.

There is an approved Algae based replacement for Jet A....

 

[airguy]

There is an approved Algae based replacement for Jet A....

And I think the US military and at least one commercial airline have tested it in the aircraft, if I remember correctly. I don't of any operators that are using it consistently though.

You're gonna have a heck of a time keeping your algae farm running while shooting zombies!