Possibly a silly question... car engines?

[sigibbons]

Most of you may chuckle at this question from a novice like myself, but I'll go ahead and ask anyway...

Why are care derived engines not used in GA?

I think the DA40TDI first used a 1.7 Isuzu engine, commonly found in Vauxhalls, and this got me thinking. How about a 3L BMW turbo diesel, 184/203 bhp depending on variant, and excellent fuel economy. I'm pretty confident it could handle a constant 3000rpm, as these things can sit on motorways for hours at 4-5000rpm.

Would anyone care to expand on this?


Many Thanks,

Simon.

[abgd]

It's not a silly question, though it has been asked before

In brief, there have been quite a few attempts to certify car-derived engines, and homebuilts have used car-derived engines with modest success. Mostly they turn out to be less reliable than the traditional aircraft engines, and may be heavier. If you search around you'll find explanations of why various engines haven't worked.

There are quite a few Volkswagen engines in homebuilt aircraft, though I think this is done primarily for reasons of cost rather than economy or reliability.

Incidentally, even though your car can work at 3000 RPM reliably, this is not directly related to power output in the same way as it is with a fixed-pitch propeller - it won't be working nearly as hard as an aircraft engine at this RPM on climbout. You would also need a gearbox to make full use of its power output (5000 rpm would destroy a standard propeller).

[Pilot DAR]

To add a bit more...

Car engines are used to some degree in amature build aircraft. Subaru engines in particular.

For the "certified" world, the certification requirements for the airplane require that the enigne( s) also be type certified. This is very costly. Yes, it is possible, but it requires the co-operation of the engine manufacturer, and my experience has been that auto engine manufacturers have extremely little interest in what they perceive to be the liability associated with the aviation industry. Large cost, large risk, very small market.

Deisel engines create very unwelcomed impulse loads into propellers, and the troublsome gearbox of the Theilert was only a partial solution of apparently limited life. There is a future here though....

A few lingering airplane certification requirements ramp up the challenge to this, one of them being that the engine must be able to run with no extrenal electriciy applied. some FADEC aircraft seem to have gotten around this somehow, but the certification requirment remains applicable.

Aircraft engine design and car engine design took very different philosophical directions some long time ago. There seems to be little financial incentive (deep GA aircraft market pockets) to bring them back together. If we cannot simply get a 100LL Avgas replacement sorted out, how will we ever cause a wholesale shift in engine design philosophy?

That said, I have an order in for the first available SMA deisel engine for a C182 project for a client. But, the SMA deisel is not a car engine.

(5000 rpm would destroy a standard propeller).

Presently available propellers cannot be operated at speeds greater than their design speed. In general, you cannot operate propellers with the tips going supersonic. If the prop will do it a bit (ever heard a C185 floatplane?) it certainly won't go anywhere near that much faster. Whole new propeller, or propfan designs could work, as long as they can pass the rather rigourous noise testing requirements. However, their small diameters proabably would not work well with existing piston engine size, or cowling arrangement. Propfans have had some success with slim turbine engines, but that's a whole different issue....

[Jan Olieslagers]

A car engine rated for 80 HP will spend most of its time producing 30-40 HP. An aircraft engine rated for 80 HP will spend most of its time producing 55-60 HP, and thus needs to be a good deal sturdier.
From the engine's point of view, an aircraft as a load is more comparable to static use, like in a compressor or generator, than a road vehicle.
That said, in the world of non-certified aviation there are a good many car engine conversions. The low cost of acquisition makes up for the loss in power/weight ratio and reliability. Subaru have already been mentioned but that's mostly a North American story.
For just one European example, the Belgian Calypso microlight can use engines from a Citroen Vista, but also from a BMW motorbike.

[oldpax]

I recently took a photograph of an aeroplane which I did not know so put it on another avaition thread.It was a "Diamond 42"made in Austria and one choice of engine is twin Mercedes diesel engine 1.7 TD?Lookit up on Wikipedia.

[Jan Olieslagers]

That's not a Mercedes you're mentioning, but a Thielert. Yes, it started from a Merc engine, yes, but that's a very long time ago.

[achimha]

A lot of airplanes, both certified and non-certified do actually use engines derived from car engines.

The diesel/kerosene engines from Thielert and Austro Engines (used by Diamond mostly) are based on a Mercedes A class engine. The Austro Engine is still very close to the original engine, Thielert has replaced a lot of parts with custom lightweight parts.

For the certified world with its high development costs, there are a few issues with car engines:

- they tend to be heavy (weight is not such a big issue in a car)
- they are liquid cooled these days (which adds weight)
- they get their power at high RPMs, a typical propeller should not turn faster than around 2700 RPM to prevent the blade tips from going supersonic. So you need a reduction gear which adds weight and complexity. The gearbox is the weakest link of all current car derived engines. Until recently, Thielert required the gearbox to be replaced every 300h (it's 600h now).
- airplane engines tend to operate at around 65% HP on average (constant power setting for hours) while car engines average much lower. Thermal management and stress on the material is a bigger issue therefore, requiring a sturdier construction.
- they have a short life span, aviation is used to servicing engines for 50+ years so as an engine maker you should be able to guarantee parts availability forever
- their advantages are smaller than it looks like, the biggest argument still is fuel availability which is a complete non-issue in the USA where most of the GA fleet lives

The biggest issue is of course the very small and conservative market. There is just no economical reason to move away from the 1940s avgas engines -- for as long as there is avgas available. I guess the SMA engine is promising but it's been an economical disaster so far.

Keep in mind that the avgas engine industry hasn't even managed to offer something as trivial as electronically controlled ignition (FADEC). It could be easily added to their existing engines.

[Rod1]

VW based engines have been used in considerable numbers, both in certified and permit aircraft and continue to be popular – AeroVee for example. Early home converted VW’s were not reliable, but the bugs were ironed out years ago. In the US and France there are many more examples than in the UK. The French have put PST engines in Jodel aircraft with considerable success.

Rod1

[sigibbons]

Thanks for the replies chaps.

It seems like there are presently lots of difficulties in this idea, although all do seem to be things which could be worked around, if the investment was there.

As achimha mentions, it appears as though aviation technology is stuck in the previous century in terms of engine design. Maybe plonking a car engine in an aircraft is not such a good idea, but there is so so much technology, which has already been developed, which could be adopted and incorporated into GA engine building.

Which GA engine builders are on the front line in terms of R&D?

Are there any exciting offerings currently being worked on, or recently released?


Simon.

[Genghis the Engineer]

Rotax! 4 stroke high efficiency lightweight liquid cooled engines, fitted with appropriate gearboxes to keep propeller tip speeds down. In many ways superior to the elderly lycontinentals that still infest GA. Rotax Aircraft Engines - HOME (http://www.flyrotax.com/home.aspx)

Also look at Jabiru engines from Australia, slow reving air cooled 4-stroke engines.

The best "automotive" conversions that I've personally seen or flown are generally BMW Boxer motorcycle engines. They give a good power:weight, there are modifications copyable to fit Rotax gearboxes, and they are well supported.

Google "BMW Skyranger" and "BMW Huntwing" for two extremes of how this was done successfully.

G

[German guy]

You might want to read the story of Porsche, entering the aviation market in the 1980s: Porsche PFM 3200 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Porsche_PFM_3200)

Program costs of $75 million, 80 engines sold in total. Ouch. :}

Cheers,

Oliver

[Jan Olieslagers]

Are there any exciting offerings currently being worked on, or recently released?With no guess about what excites you, and not knowing how little of the www you have already looked through, here's some names you could look up:
Wilksch, Delta Hawk, Zoche all announce diesels, though AFAIK only the first of them has any offer on the market.
And, more exciting as an engine to me, ISTR some Swiss project for a GA Wankel.
But all of these are aviation specific so a bit off-topic in this thread.
And, sorry GtE, I will not say anything negative about the Rotax 4-strokers, flying behind one myself. But they can't claim to be at the front of technology today. OK, they are far in advance of the US'an offer, but that's not saying much. To be at least more or less up to date, Rotax ought to offer fuel injection.

[sigibbons]

Interesting.

Porsche story must have looked promising at the time. Although I feel economy would not have been too fantastic, and that's where the market has now changed. If a manufacturer is look at producing any new engine, it must be one of, if not the most critical requirements.

Rotax...... I'm sure I recognised that name. Thinking about it further, I had a Rotax in a jetski once, the 582 on their website looks to be a direct take from that! I also had a jetski with a Rotax 912, and although it didn't appear the same visually as the GA one, I'm sure it's just dressed up with varying bolt-ons.

A 2.4L, fuel injected, turbocharged diesel, producing 180bhp, at 15L/ph.........that's what I'm thinking of......

[Jan Olieslagers]

The Subaru EE is not too far off that spec, meseemeth.

[dont overfil]

I was involved selling Mazdas, some with the rotary (Wankel) engines many years ago.
Stunning engines to drive behind but questionable reliability.

The problem was often incorrect proceedures when servicing.

IIRC the quickest way to wreck one was to to turn it backwards. This was often done when setting the points. (Remember them!) The rotor tip seals chattered and broke.

I wonder if this this problem has been cured for the Wilksh engines. Just thinking of the to and fro motion of the prop when the engine stops, never mind mishandling.

D.O.

[Jan Olieslagers]

What's Wilksch (sic!) got to do with Wankels?

[achimha]

And, more exciting as an engine to me, ISTR some Swiss project for a GA Wankel.

I suppose you are talking about Mistral Engines (http://www.mistral-engines.com/)?

I have seen it at Aero in Friedrichshafen but so far I am rather unimpressed. Apart from the usual issues like development costs, certification issues, lack of progress etc., I fail to see the value of their approach.

The SFC (specific fuel consumption) will not be better than what we have today with our 1940s avgas engines, they don't even claim that. The engine requires high octane petrol, avgas or a future unleaded alternative. This makes the whole project pointless in my opinion, something new will have to burn jet fuel (kerosene). They do say that in the future they plan to make their engine run on jet fuel but why not from the start and how credible is this statement? How do they plan to convince the most conservative engine market with an engine concept that has a (unfounded) bad reputation?

We're well set in the 80-160hp range with Rotax covering 80-115 and Thielert/Austro Engine 135-166hp but we're nowhere near sensible products in the 200+hp range.

I guess the SMA product has the highest likelihood of succeeding one day -- provided they realize that they will never be able to recover their development costs. I also believe that whatever the solution is, it will be a US product given that the market is over there. Continental having licensed the SMA is a good thing.

[Jan Olieslagers]

Yes, Mistral it was indeed. I share most of your skepticism, but their website does claim the engine(s) can run on unleaded mogas. Of course the www is a very tolerant medium, even more tolerant than paper - and no sheet of paper has ever protested the untruths written on it.
As always, we have to wait and see what turns up eventually - if anything ever does.

Unmatched flexibility in fuelling options (http://www.mistral-engines.com/Technology/Liquid-Cooling): multi-fue (http://www.mistral-engines.com/Technology/Multi-Fuel)l, MISTRAL engines works on avgas, unleaded mogas, mixtures thereof as well as ethanol-blended fuel

[dont overfil]

Jan,
Re Wilksch. I thought they had a Wankel engine at one point in the '90s. I may be wrong.

Whoever it was had a single rotor demonstrator running in an ARV. The name Mistral somehow doesn't ring a bell.

Anyway, I'm maybe off topic because I don't think it was car derived.

I do remember the (made up) reg. being G-WANKEL. I suppose the correct number of letters would be inappropriate.

D.O.

[Shoestring Flyer]

Being fitted in ever incresing numbers in the US in Light Sport aircraft, RV12's etc is the Viking engine which is basically a re-worked Honda car engine. Time will tell if it really is as good as the manufacturer says it is.

VIKING AIRCRAFT ENGINE USING HONDA ENGINE FOR LIGHT SPORT AIRPLANES (http://www.vikingaircraftengines.com/)

[Jan Olieslagers]

That looks nice! Might well be the kind of engine the o/p was hoping for. Not certified, though!

And no dealers in Europe, as yet. US$ <=>euro rate is also less favourable than it used to be, I think?

13.000 us$ seems like a neat price though, I should think even a basic Rotax 912 (80 hp, non-certified) is more expensive.

[DBo]

Re Wilksch. I thought they had a Wankel engine at one point in the '90s. I may be wrong.

MidWest engines made the Wankels & had an ARV as a development aircraft. They were bought out by Diamond.

Wilksch Airmotive have a 2-stroke diesel engine. The WAM-120.

[abgd]

People here seem to be saying good things about Rotax reliability, which pleases me as much of what I've heard previously has been quite negative. I don't like the thought that progress in aircraft engines has ended.

[dont overfil]

DBo,
Thats the one.:ok:
D.O.

[AdamFrisch]

Well, the 912 has 2000hr TBO these days, so they can't be seizing up left right and centre like they used to.

[Flaymy]

My car, when new, could hit 140 mph. Rolling resistance is low and parasite drag is proportional to the square of speed, so the drag on my car at 70 mph is one quarter that at 140 mph, so around a quarter the force at the wheel it is capable of producing. Power = force x speed so with the speed halved the power is reduced by another factor of two, to around 12.5%.

OK so there are fudge factors in there, but it is a ball park figure. Let's add a margin and say that I am using less than 20% of the power to run at 70 mph. OK it was built in Germany, so assume it was made to run well at around 100 mph or about 40% power. Aero engines typically run at around 70% power in the cruise for a sensible balance between speed and fuel use.

So in order to be reliable as an aero engine, my 170 bhp car engine should probably be derated to around 100 bhp. That is starting to look a lot less useful.

I did some work for a motor racing team at one time. They used a very reliable car engine, and of course rebuilt it every race. Working at high power outputs it rarely lasted 6 hours if the race was that long. OK, that is extreme: racing is a tough environment for a car. However it is the end of a continuum of power vs. endurance.

[Rod1]

“People here seem to be saying good things about Rotax reliability”

The 912 series engine has always been very good provided it is looked after by Rotax knowledgeable people. Apply Lyk or Cont engineers with no Rotax knowledge and there are problems. When I made my decision to build my MCR 9 years ago LAA eng considered it the most reliable engine in the fleet, which was one of the reasons I chose it.

Rod1

[Shorrick Mk2]

Rolling resistance is low


Actually if you do a dyno test you'll see drivetrain losses up to 20% are not uncommon.

[lotusexige]

Shorrik, I often wonder about these dyno tests and claimed transmission losses. If say 20bhp is lost in the transmission that is about 15Kw. That's a lot of single bar electric fires even spread out between gearbox, final drive and drive shaft joints.
I suspect that the rolling road figures extrapolated to flywheel figures have a sort feelgood percentage built in.

[david viewing]

Slightly off-topic for which apologies but I stumbled across this (http://www.gutenberg.org/files/31023/31023-h/31023-h.htm) the other day and found it absolutely fascinating as a study in the mistakes that engineers make. Packard were a car company and their aero diesel set an unrefuelled record (80 hrs+ ) that would be hard to beat today. Some of you might find the article quite interesting.