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Diesel Engines - Specifically the SMA offering

Hi all,

Recently a Diesel powered aircraft went up for sale at an airfield near me and it got me speaking to a couple of people about Diesel lumps. I know that a few people on here have also expressed mixed opinions about them and I have read with interest.

But it also got me wondering why the SMA offering from Safran does not seem to be more wide spread. Correct me if I am wrong but I can only really find Cessna taking it serisouly with the 182 offering. I have found some evidence of a Maule and a PA28 with a demo engine.

This surprised me because some of the concerns about Thielert seemed to be around the fact that the FADEC requires power all of the time and if that fails it can lead to some serious issues. Also the fact that it is a converted Car Engine.

The literature I found on the SMA appears to go the same way as Diamond did with the Austro venture - address some of the concerns from Thielerts and work on their own. But I also noticed that the SMA has a mechanical "FADEC" back up so would keep running, although maybe at a de-rated power. Giving 235Hp vs Thielert's 135Hp offering, plus the fact that it is built bottom up as an aviation engine with a 2400Hr TBO vs a 1200Hr TBR...

And I can't work out why this engine is not more widespread...


Jon Any ideas?

EDHS, Germany

As I recall:

  1. Diesels need a CS prop as the power band is very narrow. This immediately adds a lot of money to the installation cost if the Avgas version didn't have one. Hence the 182 logic I guess.

    1. Diesel is 10% heavier than AVGAS so you can carry less of it for same W&B.
    2. In the UK it is taxed at 57p per litre +20% VAT for private use. This killed our market.
Gloucester UK (EGBJ)

Hi Steve,

Yeah, agree completely with your points, the bit that we couldn't understand fully is why say with a PA28 and C172 the Thielert seems popular.

On paper the SMA looks like a very good choice. Is it Thielert got there first, or is there something sinister in the back ground on these lumps?

EDHS, Germany

In the UK it is taxed at 57p per litre +20% VAT for private use. This killed our market.

I thought that any "business" or "training" use was exempt, so if you fly to Airport X and fly an ILS and you call it a practice flight, you don't pay... ? Or does there have to be an instructor in the RHS? Has this ever been defined?

Presumably, anyway, this creates a huge incentive, on a plane with any half decent range, to fill up outside the UK. This will be worth doing only if you are based on the south coast however.

I don't know what the latest is on the SMA... Socata played with it for a few years (they got Britten Norman on the Isle of Wight to do the R&D) and there is a TB10 and a TB20 flying with it. Thielert obviously got ahead early on, on the back of Diamond's high profile. It should be a good retrofit-market engine, with IO540-compatible mounting points.

Shoreham EGKA, United Kingdom

The SMA engine is very expensive, starting at €90k + VAT + accessories. Until recently it had dismal performance at altitude. They don't want to pursue STCs themselves anymore due to cost and lack of experience. Chicken hen problem.

But most diesel conversions have been c. €80k or so, aren't they? I think what has happened is that the Marketing people decided to go after the 500+hr/year FTO market only and priced it at the absolute very top which they thought anybody would pay. A Lyco IO540-C4 is c. $60k brand new, and reportedly one can buy them from some "cost plus" outfit for a lot less.

Also, isn't it turbocharged?

I vaguely recall there were problems starting it at altitude (a cert requirement) but that this was later sorted.

The Socata man involved in the programme told me they had severe vibration problems which they never resolved.

Shoreham EGKA, United Kingdom

The raw engine is €90k already, you need quite a bit extra like oil coolers. It's significantly more than an avgas engine of comparable horsepower. 2400h TBO is a great start (how did they manage to get this, I rather don't want to know) and they hinted something about 2800h soon and then 3000h later. You can believe these statements like people believed Thielert who "guaranteed" fixed maintenance costs per hour.

The problem of the engine is the turbocharger. It needs a lot of manifold pressure (i.e. turbocharging) even at sea level to make its power. Initially they had a standard turbocharger from one of the two GA outfits but it was too weak and thus the bad power at altitude. They then designed their own turbocharger which is a lot better (and bigger). However, it still loses power at altitude quickly, much more so than a turbocharged Lyco/Conti which makes it uninteresting for high altitude cruisers.

For the same reason there is no chance to get bleed air for pressurization from this engine. Turbo diesels like manifold pressures of 90" and more so turbochargers are already quite busy down low and don't have the power to perform well at altitude.

I wonder how they did that in the 1940s Junkers designs, probably the best aero diesel until today...

SMA launched the second generation only this year and that is the engine that you will find in the new C182 jet A.

It is a huge improvement over the first gen. The engine weighs approx 445lbs dry. Which puts it in the 6 cylinder replacement category.

SMA for now only wants to focus on the OEM's. Thus the price is artificially kept high. I think that once they start gaining momentum they will drop the price to 50-60k ish + you will need to pay somebody for the work and the STC.

A 180bhp C172 runs at 7gph and can run on mogas (roughly € 1,70 per liter). An overhaul is will run somewhere along the lines of € 12-15k.

An SMA 230 would be much to heavy. For the Seneca the problem is that the Seneca uses counterrotation engines. It would be ideal for the SR20, Commander 114, TB20 and the Seneca. ... And offcourse the C182.

For more performant aircraft like the SR22 and SR22t (both 310bhp), the Commander 114TC, etc... the engine is not powerfull enough .. even though you may fly at 100%. I keep praying for a 300bhp engine with below 500lbs weight.


yes the diesel engine will be heavier yes Jetfuel is heavier


the fuelburn is a lot less. So you can also take less fuel with you.

2400h TBO is a great start (how did they manage to get this, I rather don't want to know) and they hinted something about 2800h soon and then 3000h later. You can believe these statements like people believed Thielert who "guaranteed" fixed maintenance costs per hour.

Obviously you are right that without an actual track record you don't have a, ahem, track record...

The real question is how much weight people are going to attach to that. One would think that, post-Thielert, the diesel engine business (and Diamond) would be dead. But enough people prefer to "believe" and take the chance.

Have Diamond ever offered a guaranteed cost per hour, like I believe Rolls Royce (etc) do on their jet engines? That could be a great package for FTOs. OTOH Diamond don't need to do that because there is no other option for that market - apart from the Tecnam twin.

So you can also take less fuel with you.

But, presumably, you are still allowed to fill the tanks right up? So you have less cockpit payload. But that means the wings carry more stress, which needs to be certified as OK.

Shoreham EGKA, United Kingdom
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