Aero Diesels

[rateone]

Folks,

This may have been covered before but as a newbie to the forum please bear with me.

I've been thinking about moving to a diesel powered Warrior or 172 (cheap fuel, blah, blah) but I did hear a rumour that there is a weight penalty that reduces payload and makes the aircraft effectively a two seater. Anyone have any thoughts?

[Andy_RR]

That may be true if you fill the tanks, but if you fuel according to your flight plan, you'll probably find they actually have an increased payload, due to the reduction in fuel burn.

I think, for a PA28/172 you have a choice of two STC'd diesel engines. SMA and Thielert. I'm sure their websites will give you some info on what the ultimate effect is.

A

[Wannabe24]

Hi,

I have just joined a group owning a Diesel PA-28. I believe there are only 9 in the whole of Europe! You are correct about the weight thing. Just the other day (OAT of about 30 deg C), we performed a take off with less than 1.5 hours fuel on board. Speed built up nicely, and we were airborne by about 1200ft. But with two on board we were struggling to climb. I've never been so low on climb out from this airfield. I dread to think what would've happened if we had half full fuel tanks! I've got around 10 hours in it now and can say without a doubt that the weight penalty is certainly much greater than is mentioned by the manufacturers. Add a hot and humid day and it all gets very close. However economy is very good. Power back to 55% and you can really get to places.

[Mariner9]

Wannabee 24 - surely thats a power issue rather than weight with only 1.5 hrs fuel on board? What did your W&B check tell you?

The diesel engine is presumably heavier than the original, but by how much I have no idea. Jet is around 7% heavier than Avgas, but as Andy RR says, less fuel will be required.

Rateone - Ask to see the POH for the a/c - it must have a new W&B schedule after being re-engined.

[Wannabe24]

Mariner9 you are absolutely correct! I was being a fool!

[Mariner9]

W24, interesting experience nonetheless. How does the climb-out compare in more typical UK weather (ie bloody freezing :E ) ?

[rateone]

I will ask for the new W&B schedule. I was testing the water for other people's experience before getting a salesman all hot to trot.

I must admit, I hadn't considered the additional weight penalty of the fuel itself - good point. It seems from the responses that there may also be a power issue when compared with the equivalent Lycoming and the manufacturers are always going to put the best gloss on it. Struggling to climb with two up and with only 1.5 hours of fuel on board (I assume no bags) is not great, even if the temperature is 30 degC.

Thanks folks

[172driver]

Hi,
I have just joined a group owning a Diesel PA-28. I believe there are only 9 in the whole of Europe! You are correct about the weight thing. Just the other day (OAT of about 30 deg C), we performed a take off with less than 1.5 hours fuel on board. Speed built up nicely, and we were airborne by about 1200ft. But with two on board we were struggling to climb. I've never been so low on climb out from this airfield. I dread to think what would've happened if we had half full fuel tanks! I've got around 10 hours in it now and can say without a doubt that the weight penalty is certainly much greater than is mentioned by the manufacturers. Add a hot and humid day and it all gets very close. However economy is very good. Power back to 55% and you can really get to places.

Didn't you get new/revised performance charts when the plane came back from the conversion :confused: ? High temps can degrade performance a lot more than many people realise....

[smarthawke]

It used to state on the Centurion website that the take-off and climb performance to 2000ft was worse with the Centurion engine fitted - despite their being a constant speed prop up front. Tells you something as the real performance gain with a CS prop is with the take-off and climb.

This was confirmed by the CSE salesman when he came visiting with the converted PA28 and also stated that the cruise was down 5kts and that it really turned the 161 Warrior to a 2+1ish seater with any reasonable endurance fuel-wise on board. IIRC the Centurion conversion weighs about 120lb more than the original Lycoming version.

Cheap fuel (if you can buy it at the airfield you stop at) and you can't have it maintained at many places - not good if you have a problem or at times of scheduled servicing.

[IO540]

Roughly speaking, the climb rate of any plane is just the engine HP and the weight. Aerodynamics barely comes into it, at the low speeds involved.

Most diesels are of lower HP than the engines they replace, and given that a part of the engine HP is used to overcome the parasitic drag at say Vx, even a small loss of HP is going to have a big negative effect on climb rate.

If you have a turbo diesel (which most are) then you start to gain at about 8000-10000ft, but while there are patches in the UK where one can do that, to routinely cruise there in most of Europe one needs a full IR, and very few private pilots (outside the N-reg community) have one of those....

[skyjock200]

For any body interested in the SMA powered C182Q go to www.teamvencap.com.

The aircraft is undertaking a mamouth trip to somewhat warmer climates. includes pictures and logs and a diary of the adventures. Some legs of thrip 1,000nm plus.

[Rod1]

Why put a modern engine into an airframe which is based on a 1940’s design? If you go for a PFA two seater instead of a PA28 two seater you will save a fortune and also benefit from 60 years of technical advancement!

Rod1

[IO540]

That's very true; however these engines all seem to be hugely expensive, more so than any petrol engine of similar power, so too expensive for the Permit market.

I also think the diesel manufacturers were hoping for a lot of retrofit business (new certified plane sales in Europe are tiny); this is never justified unless the utilisation is very much higher than the average for the private owner, so they were hoping for a decent flying school take-up. That's not a bad market to aim for because the flights are usually very short (1 hour usually) so one can de-fuel to handle the W&B issues. Whereas a private owner with a decent plane will really want the max range, and is not going to be happy to have his 4-seater (effectively a 3-seater with luggage) transformed into another 4-seater which is effectively a 2-seater with luggage.

[skyjock200]

Why put a modern engine into an airframe which is based on a 1940’s design? If you go for a PFA two seater instead of a PA28 two seater you will save a fortune and also benefit from 60 years of technical advancement!
Rod1

I would guess from these comments you are basing your doubts on a privately owned Pa28 doing around 50-100hrs per year. In this case it might not be cost effective for the Theilert to be fitted ove a short period of time. In this case the PFA aircraft may be beneficail to a private owner but not for every one.

The PA28 Theilert with full fuel, true enough it will only carry two people on board. Which is ideal for the training role which most PA28's are used for. You can fly all day without re-fueling. The economics make sence too. Also bear in mind that the Thielert only uses 5.5GPH in the cruise, you don't have to carry as much fuel to get to your destination enabling the aircarft to carry that 3rd person. Plus the fuel is cheap.!

How many PA28 140's and 161's can you honestly fill full with fuel and 3 people on board legaly.?

There are lot's of benifits for the Theilert conversion and the retro-fit's are proving popular especialy with training schools and working aircraft.

[Say again s l o w l y]

retro-fit's are proving popular especialy with training schools and working aircraft.

Really? Most schools wouldn't touch a thielert engine with a long barge pole at the moment. They just aren't reliable enough. At the end of the day, a flying school needs reliability above all else and there is no way these engines are anywhere near as good as Lycomings or Continentals. They are an unknown quantity and flying schools are amongst the least likely to take the risks of unproven technology. A few days/weeks of downtime is an annoyance to a private owner, but it is a disaster to a busy school.

Why are Cabair trying to dump their DA40's? They have had so many problems.

These engines have the ability to be a huge step forward, but they aren't there yet. We have looked very closely at getting a DA40, but the reliability puts me off every time.

With regards to the power produced by the Thielert. I flew a DA40 TDI last year and was very surprised by the sluggish nature on the T/O roll. It was fine in the air, but that was in a modern airframe. I shudder to think of the performance in a retro-fit.....

If the manufacturers came up with a 150-200hp version, then they would do some business, but 135hp is just not enough and the SMA engines seem to be too large for your average spamcan.

[Andy_RR]

How many PA28 140's and 161's can you honestly fill full with fuel and 3 people on board legaly?

It depends on who you are, but here are my W+B calcs for a PA28-161 I used for my skills test:

BEW - 1533.6 lb
Pilot + Pax - 458.6 lb (2 x lard-arses, I know)
Fuel - 300.5 lb (filled to tabs - i.e. not full)
Baggage - 11 lb (headsets, briefcase with nav kit and stuff etc)
Total - 2303.7 lb, which allows for a 22lb 3rd pax

I'd doubt it ever was a four seater, given that it was sold in the US of A! :}

[Mariner9]

Wonder if there's any research going on into a low cost lightweight turboprop engine. Now that would be worth having :ok:

[IO540]

S.A.S.

Why are Cabair trying to dump their DA40's? They have had so many problems

Didn't they put out a big press release a few weeks ago about buying a load more of them? I was curious about that, too.

The other thing about fittings in Permit planes is that they can't go IFR, and a large part of the attraction is the economy, which tends to imply long flights, which tends to imply... IFR. I know some Permit planes are very capable and some have great range but I don't think these top-end models make up a big market.

Andy_RR

You have just discovered the great secret of aviation :) Next time you see a PA28 Warrior going to Le Touquet, 4 POB, ask yourself that same question ;) And I bet they are not carrying a life raft either.

Mariner

The problem with small turbines is that their fuel flow per HP is about 1/3 more than piston. So, the fairly common turboprop conversions (Malibu e.g.) result in a much reduced range. You save money on the avgas tax but you then spend it on extra maintenance - a hot section inspection is about £5000. Maybe it will change one day but the efficiency issue is tough to crack. That's why jets and turboprops fly high; they need the "TAS gain" to make it worthwhile. They fly at levels at which oxygen would be impractical (high flow rate, poor oxygen endurance from a practical size bottle, discomfort from having to wear a full mask, heating problems) so they are nearly all pressurised hulls, which in turn really jacks up the purchase and operating/maintenance costs. Don't even think of the paperwork involved in fitting an extra GPS antenna on the roof of a pressurised airframe :)

[skyjock200]

Really? Most schools wouldn't touch a thielert engine with a long barge pole at the moment. They just aren't reliable enough. At the end of the day, a flying school needs reliability above all else and there is no way these engines are anywhere near as good as Lycomings or Continentals. They are an unknown quantity and flying schools are amongst the least likely to take the risks of unproven technology. A few days/weeks of downtime is an annoyance to a private owner, but it is a disaster to a busy school.
Why are Cabair trying to dump their DA40's? They have had so many problems.
These engines have the ability to be a huge step forward, but they aren't there yet. We have looked very closely at getting a DA40, but the reliability puts me off every time.
With regards to the power produced by the Thielert. I flew a DA40 TDI last year and was very surprised by the sluggish nature on the T/O roll. It was fine in the air, but that was in a modern airframe. I shudder to think of the performance in a retro-fit.....
If the manufacturers came up with a 150-200hp version, then they would do some business, but 135hp is just not enough and the SMA engines seem to be too large for your average spamcan.

I would suggest any flying school using a barge pole on an aircraft is doing something wrong. Maybe try getting into boats.
I won't comment on Cabair. but i would suggest that it is not as simple as you have made out.

Our PA28 has had no problems and has been happily flying around with this Thielert engine for over a year now.

Look out for new diesels in the future. They are on there way.

[Say again s l o w l y]

The occurances notices we all get seem to show a different picture when it comes to reliability. For example, in the lastest issue, there is one report of a DA40 TDI going pop and at the end of the report "The reporter states that this aircraft is now on it's THIRD engine."

That to me doesn't smack of something I'm willing to risk a business on.

I would love to have Jet A powered machines, since the fuel cost saving alone is staggering, I'm just not sure that I want to do a manufacturers field testing for them.

I'm not sure about Cabair now, since I've just seen that press release, but I've also heard from other sources that they are very unhappy with the reliabilty of the things. They've had a fair few "incidents" with them.

I cannot understand why the manufacturers have gone for such daft sizes. If there had been a 160-180hp model straight away, then the take-up would have been far higher than it has been. Why would you spend more money on a less powerful engine that has potential reliability issues hanging over it? The flight school market is always going to be the hardest to break into since there is little money and a deep aversion to taking risks with new technology. So why produce engines that have limited interest to the average private owner? I wouldn't stick 135hp into a 172 or PA28 even with the most efficient prop around.

I'm not anti AVTUR engines, infact I think they are essential to the long-term future of GA, but they aren't there yet and need some serious PR to get over the problems already faced.

[Rod1]

I was concentrating on private owners/groups.

I was not thinking of a JetA1 engine, more a Rotax powered machine. The Rotax is much cheaper than the JetAt burner and is tried and tested but still much more modern than the old Avgas burners.

In my UK touring over 80% of the airfields I visit do not have JetA1, but 90% have Avgas, or increasingly Mogas. With the UK applying to Europe to remove the tax exemption on JetA1 Europe wide, it is likely the cheap fuel will vanish in three to four years. When this happens, if the manufacturers have not achieved critical mass on the number of installations we may see some big problems.

Your PA28 is comprehensively out performed by a modern VLA. The VLA would be new, against 40 years old airframe and it has a long term future. I have just returned from a week long tour of France, two up. My MCR averaged 121kn w to w, airborne in 300m, climbed at 900 fpm at MAUW in 30c heat and burned 18.5 lph. Cruse speed was 128kn point to point with handling and visibility which makes a PA28 look like a Ford Anglia against a modern sports car. Remember we are talking about a fixed gear, fixed pitch machine which will cost me about £500 per year to maintain. Still want a two seat PA28?

Rod1

[smarthawke]

Skyjock

You would praise Thielerts and SMAs wouldn't you seeing as you're trying to flog conversions froma certain Oxfordshire based airfield....!!

The 'diesel' GA revolution will only take place when the Americans recognise them as powerplants for things smaller than a 42 wheeled truck.

[IO540]

The problem, rod1, is that the market is probably a lot more complicated than any of us think.

If you think that a £500 annual cost is a significant thing, then you won't be in the market for anything that costs "real money". The annual fuel costs of anybody doing a reasonable amount of flying will be far more than this saving.

In cruise, a Rotax will not deliver more HP per given fuel flow than a properly operated old Lyco - the power comes solely from burning fuel and once you are at peak EGT, or even LOP, there is nothing more to gain.

The tax exemption is another funny one. Currently, anybody with an AOC can get tax free avgas in most places in Europe - though not in the UK as far as I know, well not below a certain weight perhaps. So, the case for avtur in pistons is much diminished for any commercial operation whose fuel usage makes it worth applying for an AOC just for this reason alone - even if they never make any use of the AOC itself. In Spain, it's even easier... any business customer can get tax free avgas, so a PPL school based in Spain has a big price advantage straight away.

The reliability of any piston, especially a Rotax (based on past history), does not even begin to compare with a turbine. And the old Lycos are actually very reliable; the big ones need proper management to get to TBO but the things rarely fall apart.

These are just random factors I can think of.

I do think it is stupid for diesel designers to not match the existing power output. Mind you, did you see the latest Loop magazine? There is an advert in there for a new diesel whose size and mounting points are identical to the old Lyco - now that's interesting. Don't recall the HP but at least somebody is waking up to the fact that at a retrofit cost of say £50k there will be very few takers.

[whiskeytangofoxtrot]

Hi everybody! :-)

We have a C172N with a Thielert in our club. Comparing to our other Cessna, a 150hp C172M, I would say the performance is more or less the same. I don't remember the exact figures offhand, but the takeoff distances are not really significantly better or worse. Of course if you have a 160hp or even a 180, then it is a bigger difference.

Sure, neither of our planes are particular hotrods or real four-seaters, that's a fact. With 3 on board the diesel is still a very nice flying club plane with good range. But what made the real difference for us is the 30-40 euros per hour difference in fuel cost. That is very important for us, as to keep flying at least remotely reasonably priced and thus maintaining enough hours annually to keep the fixed costs down per hour.

The engine weighs 30kg more than the 150hp O-320, and kerosene is a bit heavier than avgas, so one loses some payload with full tanks, but like mentioned earlier, that would be about 7 hours plus endurance depending on the power setting on cruise. Comparing with four hours of fuel on board should even gain a bit over the avgas plane.

We've had the plane with thielert for 1.5 years now and put in some 600 flight hours during that time without any real problems, and have been happy with it. Of course the sticky smell of diesel that emits from the pilots and the plane could be a problem for someone :)

Does anyone know what kind of problems Cabair has had with their Diamonds? Powerplant, airframe or combining-the-two -related? Some of this could well be related also to mainteinance organizations having a new gizmo to play with, after maintaining a fleet of Lycomings for the last half decade..? :)

[Superpilot]

Not sure if it was Cabair but someone has had a double FADEC (both computers) failiure close to the ground.

[Say again s l o w l y]

Pretty much all the problems I've heard the Diamonds have had, are to do with the engine and specifically the FADEC.

The airframes seem to be fairly good, their construction is pretty simple and any potential problems would more likely to be catastrophic rather than minor issues.

The thielert engine has had many problems that have always been explained away as ancillary issues, but I don't consider this to be a true picture. If the FADEC has a fit and goes to get home mode at low power, then you have an engine problem end of story.

There have been occasions of poor knowledge on the part of pilots when failures have occured, ie over-reaction to warnings, but there was certainly an issue with some of the major components such as wastegates, turbo's and the gearbox. These will I'm sure have been corrected now, but it will take a fair while before I feel totally comfortable spending vast amounts of cash on conversions for our machines.

The issue of the potential ending of VAT free AVTUR, would be a deathknell for engines such as these, without the financial benefits, there is no reason to change. Especially as performance is compromised.

When these issues are sorted, then flying schools will start thinking about converting, but until then it just isn't worth the risk.

[whiskeytangofoxtrot]

The issue of the potential ending of VAT free AVTUR, would be a deathknell for engines such as these, without the financial benefits, there is no reason to change. Especially as performance is compromised.


Yep. Last I checked, 100LL was 1.75 euros per liter at the pump.. :bored:

[Rod1]

I have just been paying 1.45 ish inc tax in France, but at 18.5 lph instead of 43 lph to go 8 kn slower I did not really care!

Rod1

[IO540]

The thing is, it's very easy to go from 43lph to 18.5lph. It is called a smaller (particularly in the cockpit frontal section) lighter and slower aeroplane.

The above is only partly tongue in cheek. Composite airframes, properly designed for aerodynamics, will definitely help. But a lot less than most people would believe.

Especially as the difference between operating LOP, and operating the way every UK PPL has been taught, is about 30% in fuel flow rate.

It's all a tradeoff. If I lost my IFR privileges then I would most likely go for a top-end PFA type right away, fit it with the best IFR avionics, a TKS prop, and would be more than happy with the performance.

I suspect a significant chunk of the efficiency of a DA40 comes from its glider-like low wing loading, which will make it tough to hold in turbulence.

[rateone]

Very interesting discussion. Seems like I stirred up a real hornets nest. Some good points though. Rod 1, the IFR ability of the PTCoA is attractive over the Permit a/c although I do acknowledge that the more recent VLAs are very potent in terms of cruise speed and fuel burn.

With respect to adding VAT to Avtur, I'd do the calculations again Sayagainslowly. The discussion within the European Commission is to remove the VAT exemption not to levy UK fuel duty. So the most that would be added is 17% (of course that is not to say that the dour presbetarian of a future Prime Minister would not add fuel duty in the future), but the cost would increase to say between 50p and 60p/lt. Since I'm paying around £1.50/lt at present, I'd say the saving is worth considering.

Current fuel burn 40-45 l/hr @ £1.54 - £60-£70/hr
Diesel equivalent 25 lt/hr @50-60p - £12.50-£15/hr

Not saying diesels are for everyone, but the thread has certainly given me food for thought

[IO540]

Surely anybody who is VAT registered (most schools I guess) will be able to claim back VAT, so this will affect private owners only.

Also if you use the plane for business travel, you can get the business to buy the fuel used on the business flights, and if the business is VAT registered it can get the VAT back on the fuel. The business can incidentally also pay for the appropriate percentage of the total maintenance costs, and get the VAT back on those. This is from my accountant, as of yesterday.

Everything else being equal (which it isn't) I would prefer avtur over avgas simply because of much better availability when looking at the international airfield/airport scene as a whole. However, on farm strips it is likely to be very much the other way round.

[Rod1]

“Everything else being equal (which it isn't) I would prefer avtur over avgas simply because of much better availability when looking at the international airfield/airport scene as a whole. However, on farm strips it is likely to be very much the other way round.”

Most a/g licensed airfields have avgas, a significant number do not have Jet A1, some, like Sywell, are offering Mogas. To refer to such as farm strips is not very fair!

Most Micro strips will supply Mogas in cans if you ask in advance.

Most Farm strips do not have anything, but might have a petrol station near by.

You can buy Mogas on the way to the airfield (as I do)

The Problem with the JetA1 burners is you cannot use Diesel, so if you have no JetA1 at home base you will probably have a very long drive to get some from a licensed airfield.

At most French CCI airfields it is possible to get Avgas via the flying club out of hours (including diner time), but getting JetA1 is much harder.

Rod1

[Say again s l o w l y]

AVTUR at my local field is 60p/L and I can easily see there being both duty and VAT added to it at some point (currently there is 5% VAT on it). The sop to the airlines would be that if you have an AOC you would be exempt.

I can forsee this as most governments see GA as a rich man's hobby.

We currently pay £1.34 litre for AVGAS.

For example our PA 28 averages around 34 l/hr so costs us £45.56/hr or over an engine life of 2000 hrs : £91120 for fuel, add in the cost of the engine in the first place (approx £18K) gives a total life cost (not including servicing and oil) of £109120. This is however a 181 Archer II, with performance that leaves a diesel machine for dead.

A Diesel conversion costs in the region of £50K with costs of approx 63p/l and with an assumption of a burn around 25 l/hr giving a cost of £15.75/hr for fuel.
Again assuming a 2000hr TBR you are looking at a cost over the life of that engine (excluding maintenance and oil etc.) of £81500.

A significant saving yes, but as I have already stated. This isn't about cost solely, but a combination of reliability and cost. The reduction in power is also something I wouldn't accept. I want a replacement engine to be at least as powerful, if not more than the one it is replacing, otherwise why risk it?

We cannot afford unreliable machines in the the flying school/club environment. They have to make their TBO/TBR with few problems, something I haven't seen (m)any diesels do yet. When that happens and I get an agreement from the manufacturers that they'll guarantee their product, then sign me up.

The current promise to pro-rata an engine if it fails before it's due time is good, but what about the reliability of the electronics? I doubt they are included in that deal.

Whilst neither Lycoming or Continental do this, they are a known quantity already.

[172driver]

Everything else being equal (which it isn't) I would prefer avtur over avgas simply because of much better availability when looking at the international airfield/airport scene as a whole. However, on farm strips it is likely to be very much the other way round.

Rod1

IO540 has a point. While this may not be so in the UK, venturing further afield 100LL avail definitely is very high on the list when it comes to flight planning. Being able to use AVTUR would be a godsend ! Horses for courses, really....

What I also fail to grasp is why the diesel guys are offering engines that produce less power than the ones they are supposed to replace. :ugh:

In any case, as long as 100LL and AVTUR in the only GA market that really counts (USA) are roughtly the same price, I doubt the big diesel breakthrough

[Rod1]

What is TBO on the Thielert? I thought it was 1500, but I may be wrong. This would put your cost saving into the red.

I compared a Wilch 100 hp (forgive the spelling) with a Rotax 912s 100hp some time ago. The Rotax was £8600 inc Vat and delivery to my house, the Wilch was £14750. The Diesel was much heavier and the total running time was measured in 100’s of hours.

Rod1

[Say again s l o w l y]

My figures are giving a best case scenario for a diesel. They are nothing more than a rough estimation.

If I'm not mistaken, the current TBO for a thielert is 1500 hrs, but they are hoping to increase this to 2000.

Was the Rotax for a PT aircraft (ie for flight training) or for a permit? That makes a massive difference in cost. Actually a Rotax is a pretty expensive engine for what it is.

[Rod1]

The Rotax912uls was for a permit a/c. I am surprised you find it expensive, it came top of my value for money analysis.

Rod1

[Andy_RR]

In cruise, a Rotax will not deliver more HP per given fuel flow than a properly operated old Lyco - the power comes solely from burning fuel and once you are at peak EGT, or even LOP, there is nothing more to gain.


I'd just like to correct a misconception here. There are several things that the Rotax has going for it as regards efficiency. Firstly, the engine speed at peak power is much higher which allows a higher compression ratio. Secondly, the bore is much smaller, which also allows a higher compression ratio. These two things together should mean the Rotax should deliver better BSFC than a Lycoming or similar. Whether it actually does acheive this is another story...

BTW IO540, regarding the diesel advert in Loop. Was there any web links published? Could you pm them to me if so? I'm in India at the mo and Loop doesn't get that far! Thanks

A

[Say again s l o w l y]

For a C of A machine, the Rotax comes in an awful lot more expensive, in the region of several grand more! And all for a low 1500hr TBO.

[IO540]

I am sorry Andy_rr I binned the magazine immediately after reading it - like I do with all magazines, and it's gone now.

It was a 4 cylinder engine, with 6cyl versions mentioned. I've just remembered that the image was computer generated and they were looking for somebody to pay for the tooling to make the first one, so this is something at a really early stage.

I am not an engine expert but would be suprised if a higher revving engine would out-do an old Lyco when it comes to efficiency when LOP. More revs means more friction losses, the same airflow through a smaller inlet manifold means more pumping losses, a gearbox means yet more losses. With car engines this is all irrelevant because high revs is the only way to get the HP from a physically small unit.

AFAIK the most efficient engine is one with a single large cylinder, working at very low revs. Everything else is a compromise :)

[High Wing Drifter]

Andy_RR,

Fortuately I retain magazines until either my wife's patience or the physical room available in the bedroom reaches the lowest threshold!

http://www.dieselaero.com/

[spernkey]

I have retrofitted 2 of my 172's with Thielerts and have the other 3 booked in this autumn.
Apart from a few pilot related problems and a dim fuel supply system (now changed) and a need for a more aggressive fuel drains (oil more hydroscopic) they have turned out to be lovely! VVVV smooth, massive endurance better fuel availability (and they are cleared for road diesel if you get stuck).
I got real tired of sticky valves on the Lycomings(now an A/D at 1000 hrs), crankshafts been pulled cos some dimmwit at Lycoming decides to out-source components blended with vanadium to make milling easier, engines consistantly not making TBO even though we do 500 hrs p/a per a/p, mags failing, and bain of my life plugs fouling half way through the 50 hr service interval even though we put long reach plugs in the bottom cyls.
Readers should not be mis-led into thinking that Lycomings are so wonderful - just look at the constant flow of A/D's and S/B's for your engineer to ignore. These people have had 60 years to get it right.
Service the thielert every 100 hours and for less cost - buy my own fuel for 40p a litre - and its far easier to keep than AVGAS. Regularly fly 9 hour missions now - no breaking off to get fuel every few hours - yep i'm not missing the Lycomings yet.
One last point - once you have the initial install done replacement engines are only 12 grand.
There are bound to be teething troubles but dont let the Lycoming/Continental brigade put you off - or they will still be trying to put us off in another 60 years - but hey, maybe they will be they will have perfected their petrol burners by then.

[whiskeytangofoxtrot]

The current promise to pro-rata an engine if it fails before it's due time is good, but what about the reliability of the electronics? I doubt they are included in that deal.


"EUR 25,960 exclusive VAT including engine, FADEC, harness, starter, alternator, vac pump, gearbox, governor, etc. An new engine after 2,400 hr operating time will cost EUR 20,319 exclusive VAT." - First time conversion cost is 45-50kEur, including everything needed. This is from the thielert website. I'd probably replace the electronics as well, even though it is ~5k more.

A few points for stuff presented above: The pro rata warranty and the TBR Thielert wishes to eventually reach with the Centurion 1.7 is for 2400 hours, not 2000. And you *can* use Diesel auto fuel, Jet-A1 or a miture of those. With Diesel the minimum operating temperature is just -5ºC though, as one can not always be sure how "arctic" diesel one has. JET-A1 has a lower minimum operating temp that is below mine :)

The reason why manufacturers have lower HP rating for the engines they want to replace is probably the fact that diesels are heavier and at least the thielert uses water cooling which adds to weihgt also.

Anyways, its an interesting new technology and it is good to know how the engines are working and how people find using and maintaining them. I'm not a salesman, just a user that's so far been happy with the reduced costs.

[ANW]

The following has appeared in the PFA magazine.
http://www.howells-aeroengines.co.uk/
The first of the new production batch is due for bench testing very soon, to be followed by flight testing in a couple of months.

[A and C]

So far the new engines deisel engines have turned out to be a poor lot all missing the target by a mile, The bigest market has to be to replace the 115-200 HP Lycoming engines and this has not been done.

Thielert have taken a very good car engine and bolted a gearbox and cluch on the front and come up with something that turns a PA-28 or Robin DR400 into a short range two seat aircraft, at the moment with the Lycoming my Robin DR400 will fly two people safety equipment and a weeks worth of baggage 550 NM+ with 1 hour reserves. Why on earth would I want to fit an engine that cant lift the payload without the fuel that the Lycoming can.

The SMA is to big for the mass market, I think that the company had its eye on the French military trainer market but seems to have failed to ge a hold on this and so seems to be slow to get any sort of market hold.

Wilsh...... this seems to be a long running project to extract grants from the goverment, if you go to the company and try to offer to fit the engine to a well known airframe they run a mile......... I don't think that the thing is even half as good as they say it will be, however I would be very pleased if I was totaly wrong about this but only time will tell.

Deiselareo (TDC) At last a bolt in Lycoming replacment, it,s early days yet but these guys have here eyes set on the biggest sector of the market with an engine that should fit right into an engine frame that a Lycoming has come out of. They also are looking at other uses for the engine one of which is in the agriculture industry, this is an interesting turn of events as it is by understanding that the Lycoming started life as the power for a water pump!

[LD Max]

Recently submitted an MOR for a thielert-powered diesel 172. Engine quit on short finals into Gloucester last month. The reason was the tanks were down to 22 Litres (about 1 hour remaining) and I had sideslipped (on idle) for about 30 seconds to lose a bit of excess height on final approach.

This turned out to be long enough to not only uncover the fuel outlets, but also to exhaust the reservoir. Now this is something you should know, (which I didn't at the time - but will now never forget). If a Diesel gulps air, it will cause an airlock. The engine WILL quit, and you WON'T get it restarted in the air!!!

This fact is omitted from the POH!

[Bahn-Jeaux]

So these new diesels are not self priming like modern diesel engines?
My car has a 2.5 diesel and having run out of fuel twice now (onboard computer glitch telling me I still had sufficient fuel left) a topping up of the tanks did not see me having to bleed and prime the system.
Surely, technology like this should be paramount in aviation.

[Andy_RR]

AFAIK the most efficient engine is one with a single large cylinder, working at very low revs. Everything else is a compromise :)

IO540, this is true in theory and carries over well for diesel engines (which is why we have 1000hp/cylinder marine diesels with peak power at 50rpm!) but for gasoline engines you always run into the limitation of knock. At low speeds this can degrade your thermal efficiency significantly, so you usually have to compromise your compression ratio to make it work.

The alternative is to spin it faster, because knock takes time to happen, and use smaller cylinders which increases the relative burn rate, again, reducing the chance of knock.

Also, it's possible that a smaller cylinder size can be made more lean-tolerant, extending the lean combustion limit compared to a monster bore size.

re: the advert, was it these guys? (excuse the link!) http://www.dieselaero.com/

A

edit: whoops, missed HWD's post - sorry! :)

[Andy_RR]

The engine WILL quit, and you WON'T get it restarted in the air!!!

I have spoken to the designer of one of the diesel aero engines out there about this concern. He says the mid-air re-priming is a non-issue if the system is designed correctly. He stated that his engine would re-prime and re-start within 2-3s. Comparable with a gasoline engine I'd say.

A

[IO540]

Yes Andy that's the picture I recall.

[LD Max]

He says the mid-air re-priming is a non-issue if the system is designed correctly. He stated that his engine would re-prime and re-start within 2-3s. Comparable with a gasoline engine I'd say.
A

Well obviously mine wasn't designed correctly since CSE categorically state the TAE isn't self priming. Wish it had been!

Indeed I watched them do it on the ground and it took a couple of attempts to bleed all the air out of the HP rail before it would start. According to the FADEC it was starved of fuel for about 9 seconds. Wouldn't restart at all either in the air or on the ground on either fadec.

Definately a problem here!