We both agreed that there hadn't been the same level of change in engine technology over the same period of time. Most aircraft, certified or not still use Lycoming engines. Rotax has certainly come to be a bigger player in the home built category but still only represents a small portion of the market.
It's been a long time since I have flown anything with pistons but we got to thinking that automotive engines have evolved a great deal in the last 30 years. I know of 3 people that have had engine failures with Lycoming aircraft engines but I don't know of anyone who has suffered an engine failure in a car. Today's engines are far more powerful and reliable than they were 20 years ago and yet most pilots would never consider anything other than a 60 year old aircraft engine.
For comparison, Take an O-360 engine. It puts out about 150 hp using 5.9 L of displacement. I have a 20 year old Subaru in my garage that puts out 280 hp on only 2 L of displacement. Both weigh about the same and have nearly identical length/width/height dimensions. My Subie was rated by Consumer Reports to be the one car most likely to last 450,000km without any major issues. Most people point to the single ignition source of an automotive engine as the biggest draw back. I read somewhere that the Bosch ignition on my Boxer engine was designed with a 20,000 hour Mean Time Between Failure while a typical aircraft magneto was designed with a 600 hour MTBF. That means that on the typical aircraft engine you can count on having at least one to three ignition failures through it's service life. My car, not so much.
Here's where I make a few assumptions. I know Torque isn't linear but for the sake of argument, let's assume it is. If my engine develops peak torque (280 lb-ft) at 4800 RPM it should make 140 at 2400 RPM. That puts it in the same range as a typical lycoming powering a C-172/PA28 which I think develops peak torque around 3000 RPM if I remember anything about pistons. My engine is happy as a clam running at 2400 RPM and could do that all day long.
So, if an aircraft like a 172 takes off with 100% power (give or take 150 hp) then cruises at 75% (112 HP), why couldn't I use a automotive engine with 280 HP to take off with 50% power and then throttle back to 40% for cruise and all the while do this with 2.0L displacement instead of 5.9L? I am pretty convinced that my automotive engine will outlast all the Lycoming's currently installed. What does a Lycoming cost these days? It's north of $20,000. Subaru equivalent? $4000 including Turbos, intercoolers alternators and air conditioning.
What's wrong with my thinking here?
Some other thoughts:
- density altitude: how would a normal car engine behave at 10 000 ft?
- size: I have the impression the average car with all accessories takes up a bunch more space than an airplane engine. The more efficient the engine, the more accessories it usually has.
Also had a slew of ignition problems and rough running, won't idle, etc. Stuff that would be unacceptable in an aircraft.
I've also had two mag failures. Both were uneventful and I didn't even notice until I did the mag check before shut down.
All the attempts that I'm aware of at bringing automotive engine technology to certified aircraft have had two independent engine computers. Most have also been diesel, meaning no spark plugs.
Subaru has a diesel boxer in their Foresters that they sell in Europe. There are a few guys putting them into RV's from the looks of it. 285 lb.ft torque and according to the blog I read 2.5 GPH at cruise. The Vans guys are saying it's pretty much the same size as an IO-360 for size and weight. I've only skimmed the forums so the only thing I noted was that the earlier EE20's had crank shaft problems which were resolved in later versions. Here's a video I found https://www.youtube.com/watch?v=9Wdw_S-WT-g
Speaking of alternate engine solutions, there was a guy who built a Bugati aero racer replica and powered it with two Suzuki Hayabusa engineshttps://www.engineswapdepot.com/?p=7262. Now there's a creative idea. 200 HP out of a 200 lb engine designed to rev super high. People have boosted the Hayabusa engines up to 700 HP which is a crazy amount of horse power - 100 HP more than a Harvard with a 22 L displacement. Imagine that engine swap - a Harvard with a tiny Hayabusa engine up front.
https://www.savvyaviation.com/wp-conten ... r-talk.pdf
Not sure if you're familiar with him, but Mike has created quite a name for himself in the US as an aircraft maintenance authority but like all such "authorities" has his adherents and his naysayers. I think he presents his thoughts fairly clearly however and is worth reading most of the time.
“It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.”
I've also observed another catastrophic failure: was driving behind a SUV when something came loose and exited out the bottom of the engine dumping the entirely of the oil and coolant on the road in only a few meters.
If this had been a single engine aircraft, it would have been a forced landing. Thankfully they were cars and simply pulling to the side of the road was the simple next step.
I did work for a while on a program to type certify a Subaru derivative engine (as it is a derivative of an aircraft engine anyway). The program lost financial inertia. Our industry effort will be better directed to creating a certification basis for electric motors for planes, that's where a lot of future will be!
Don’t forget that he died in the crash of that Bugatti replica after... you guessed it... powerplant failure.
- Top Poster
- Posts: 6867
- Joined: Tue Jan 18, 2011 4:47 pm
- Location: Making aviation exhausting, everywhere
Hmm. TBO is a manufacturer recommendation and not a hard limitation, no? We run our engines on condition, but this might be because our MCM allows it. I’m not sure if this is allowed for non-commercial ops.
I realize that in a certified aircraft, to remain in that category, you have to have a certified engine. I guess I was thinking more along the lines of the home built/OM market where companies like Rotax got started. I remember when I was training Rotax's were rumoured to be garbage engines. Now I'd argue that they seem to be on par with any Lycoming out there. Better even??
I am a little perplexed that the price and innovation in GA avionics has changed so much over the last 20 years but we still cling to the Lycomings. They're fairly expensive compared to the rest of the aircraft components. Arguably, they are one of the most important components but we are still using what I would argue is an outdated model, only producing about 150 HP with a 6L displacement. If a Continental had developed the Thielert at the same rate and expense as Garmin has done with avionics you'd be down to almost the same price as an automotive crate engine. Certified glass panels are half the price they were 20 years ago. One quarter for the non-IFR GA stuff. No one had synthetic vision 20 years ago. Now you can buy a 10 inch screen from Garmin for $2500 USD. Is it unfair to compare the rate of development and the cost to the consumer?
i'd love to see an electric aircraft but the problems with range anxiety are amplified with an electric aircraft. I can't see someone flying up to the north to do a little back country fishing or camping and waiting all day to recharge using a solar panel. You have a hard enough time finding avgas in the north. Just try doing a two leg day with an 8 hour battery charge in the middle of the day. You won't get anywhere.
This thread got me reading a little about some of the newer options that are out there. There's a page on wikipedia about GA diesel engines. Most of them are European and most of them were derived from automotive engines in the first place. No one lists prices on their respective websites which leads me to believe they are likely just as expensive as the incumbents. Shame. I like the idea of the Diesel Subaru engines. Basically an aircraft engine to begin with and I do like my Subarus.
I think that one barrier to people buying any GA plane is the price of an engine. Talk to anyone who has ever thought about it and the first thing they'll bring up is the potential for an engine failure and the cost of replacement of said engine. It's not insurance; it's not operating cost, hanger space, avionics, annual inspections - it's engine replacement costs. I'd argue that bringing all the costs down would only allow more people to get into the GA market.
Lycoming/Continental/Franklin exist at a practical low cost, as their development, and teething was funded by military application decades ago, and we continue to ride coat tails on that much larger market at the time. PMA parts manufacturers got their start filling military contract for these engines, and although that market has dried up, it positioned them well to compete. They will never reach the market size of automotive engines, and thus those very mass produced low prices, but the situation is better than it could be, if the certified engines were being developed at present day costs, for a very small civil only market.
When I embarked on the two year long quest to buy a brand new SMA diesel engine for my client, SMA were delighted to entertain the sale, wining and dining us several times in France, though they never produced an engine for sale to us. Part way through the process, my client was quoted US$105,000 for the engine, and I had to do the approval of the installation. Eventually after waiting too long for his plane to be powered, he bought a Continental 550. The SMA diesel (as any diesel) had very demanding propeller limitations for vibration. The same MT prop on the SMA is very limited as to condition, compared to much greater maintenance tolerance of the same prop on a Continental.
Similarly, the development costs of the really nice Garmin $2500 glass display is borne on the back of military and they high cost commercial development. That unit for certified application is more costly (though probably the same!).
In my opinion, the economics of civil piston aircraft operation are unlikely to see development and certification of significantly different piston engines than we know now, the market just cannot afford it, when Lycoming and Continental can be kept running forever. Thing of it this way, when Superior had a clean drawing board to build whatever engine they wanted - they copied a Lycoming!
- Top Poster
- Posts: 6867
- Joined: Tue Jan 18, 2011 4:47 pm
- Location: Making aviation exhausting, everywhere
Your MCM allows it only because there already exists a huge corpus of knowledge about how safely to run a TCM or Lycoming engine past TBO, and because you as an OC holder have demonstrated experience with an inspection program that shows you can safely make use of that extra time, and are alert to signs of engine deterioration.Aviatard wrote: ↑Mon Sep 10, 2018 5:23 pmHmm. TBO is a manufacturer recommendation and not a hard limitation, no? We run our engines on condition, but this might be because our MCM allows it. I’m not sure if this is allowed for non-commercial ops.
Any new engine design has to build the body of knowledge that would allow operators to move beyond TBO, before anyone is going to be approved to go beyond TBO. For the same reason, TBO is limited, initially.
Private owners can do what they want, but if offered an engine design where the manufacturer quotes (albeit because of regulatory restriction) 1200 hours TBO vs. a tried and tested 2400 hours TBO, which is more attractive?
I'd argue that almost all modern electronics technology is driven off the back of the mobile phone manufacturing industry. Billions of units made and sold.PilotDAR wrote: Similarly, the development costs of the really nice Garmin $2500 glass display is borne on the back of military and they high cost commercial development. That unit for certified application is more costly (though probably the same!).
Put simply.. a Subaru engine is far more complex than an opposed aircraft engine and spins too fast to produce power without an RGB and isn’t designed to run at 75% power for hours on end.
You don’t have head gaskets on old aircraft engines. They are air cooled and the heads are screwed and shrunk onto the barrels.
You only have one camshaft on an old aircraft engine that’s driven by a couple of straight cut gears. That’s all you need with a 2700 RPM redline. Your Subaru has four camshafts driven by a complex and failure prone timing belt. DOHC also makes for huge heads and more frontal area.
Timing is fixed on an aircraft engine since it only has to accelerate the propeller, not the whole vehicle. Magnetos are used because they are simple and light forms of independent ignition. Electronic ignition would require two alternators and two batteries to satisfy requirements. Same with electronic fuel control which again isn’t needed because the engine spends most of its time at one speed and power setting.
Even a modern aircraft engine like a Rotax 912 has barely better power to weight than an O-200 based on the 1930s O-175. And it has five additional failure modes (two throttle cables, gear box, coolant leak, water pump, reduction gearbox, dog clutch).
No. Automotive engines weren’t designed for the same purpose as aircraft engines. Most automotive engines are in service on homebuilts which don’t face the same daily rigours as certified aircraft in commercial service.
That said, Subarus are not my first choice, and I prefer to fly behind a certified aircraft engine (preferably direct drive if piston). Auto engines for cars, aircraft engines for aircraft, as well explained, they're simply different.Using engineering owing much to Fuji Heavy Industries' aviation background, 1965 saw the introduction of the legendary Subaru Boxer Engine – a feature that continues to define the Subaru marque.
This is why the cautious folk go for the airplane engines in airplanes, because all the above has been figured out by Lycoming and Continental for decades now. Auto conversions can be done and plenty have been done, it's just a matter of doing a substantial amount of homework and still accepting what is probably a little higher risk.
As quoted above, an automotive engine in an auto at 100km/h is likely producing 20-30Hp. If you ran that same engine at 75% power continuously, they probably would not last. Car engines only see max power for very short periods of time. If you are looking for high HP with a continuous duty cycle, you would be looking at the industrial Diesel engines and then the weight issues would be your problem.Ame213 wrote: ↑Mon Sep 10, 2018 4:24 pmOne thing to consider is that an aircraft engine is designed to make its max horsepower until overhaul reliably, you car is on average running at what? 1/3 to 1/2 hp? Try running any car let alone a high compression turbo engine at full throttle for 2000 hours and see how long it lasts then. A horizontally opposed air cooled engine is the by far the best option for an aircraft piston engine, there is a reason they haven't changed much in the last 60+ years and I'm sure it wasn't for a lack of trying.
The other issue (mentioned in an other post) is RPM. Since you don't want the prop to spin so quickly you need an engine capable of producing HP at low RPM or a gear box.
With an engine spinning below 2700 rpm you really limit HP.
With a gear box, you add weight, complexity and have all sorts of vibrational harmonics issues unless the proper engineering is done.
Look at the homebuilt (experimental)aircraft world. They usually use Lycoming, Continental or Rotax engines (4 stroke) due to reliability. Any alternative engine drops the resale price of the aircraft. It's not ideal to be the one testing reliability while flying when you are operating single engine aircraft.
Even if you're not using a prop speed reduction unit, you still need something to handle the propeller thrust loads. You can't just bolt a propeller to an automotive crankshaft, as car engines do not have a thrust bearing.
To make power you need airflow. You get that either through displacement, RPMs, or high cylinder pressure (turbo charging). High RPMs require a gearbox (not insurmountable) and high cylinder pressures require very careful fuel and ignition management to prevent detonation, which is why many of the traditional aircraft engines use high displacement for their modest power output.
I suggest if you want to use a Subaru engine in your aircraft, use one of the PSRUs on the market and make it run on higher RPMs rather than relying on excessive turbocharging at low RPMs, as it's a fairly proven system. Stock subaru motors don't make peak torque until well north of 3000 RPMs.
http://jdfinley.com/what-happened-to-th ... ft-engine/