Bullet Proof Engines?
I have never understood why aircraft engines are not as bullet proof as my regular car engine. Every car I've ever owned has carried me thousands of miles without a hiccup, and it does it quietly with minimal maintenance.
In over a thousand hours of flying I've never had an engine issue, but I read too often about others that have. Some even say that there are only two types of pilots, those that have had an engine failure, and those that are going to.
So my question is, which aircraft engine comes the closest to being highly dependable, and what do I need to do to have that "keeps on ticking" reliability?
Any thoughts on that? Thanks.
That's a million dollar question you're asking Dave, and unfortunately I doubt that there's a once size fits all answer.
Generally speaking, most engines are reliable provided that they are (1) properly maintained and (2) used in the application (operating envelope) for which they were designed. Outside of these parameters the reliability gremlins lie in wait.
For my part, I've only ever owned gyros with Rotax 914 engines which I've found to be reliable and trouble-free. My old Magni M16 I sold with 840 hours on it (new owner reports more than 1000 hours now and it recently passed a compression test with flying colours). My current Magni M22 has just passed the 600 hour mark without hassle.
Engine is always serviced as per maintenance schedule, oil change every 25hrs, properly warmed up within ERPM limits, and flying within the operating specs etc. all contributes to engine longevity.
I can think of a lot of reasons why aircraft engines are not more reliable so let me start with that.
They donít build enough of a particular model to make research and development commercially viable. The money that should be spent on R&D is spent on government silliness and then they are not allowed to change them without spending a lot more on government folly.
They sell them to people who run them hard intermittently and then leave them for long periods of time in a tin shed. These people often operate them outside of recommended limitations.
To put a finer point on that the average experimental aircraft flies 50 hours per year with many certified aircraft operating little more.
Many of the aircraft are from schools or rentals. I have not rented a Hertz car with more than 40,000 miles on them and most are less than 20,000 miles. This type of usage does not promote longevity.
The customers demand more power at the same weight.
They are often rebuilt by semiskilled mechanics in less than ideal conditions without some of the required machining done poorly or not done at all with poor to nonexistent quality controls.
I am running a 47 year old engine that replaced a much older ground power unit and neither has failed me in 1,000 hours of operation. It is a 260 pound engine that will make 160 horsepower and happily operate at 75% power continuously with poorly designed support systems for the air cooling.
What percentage of the fleet of automobiles is still running after 47 years?
The engine is designed to run with support systems that leave a lot to be desired. Operating the aircraft intermittently causes challenges for the fuel, electrical systems and lubrication systems compounded by corrosion.
The numbers I have seen suggest that reliable automobile engines become less reliable than aircraft engines when installed in an aircraft.
The most common cause of engine outs in aircraft is fuel exhaustion.
There is a lot more publicity when an aircraft engine stops than when a car engine stops.
I have read that the average speed of an automobile during its service life is 17 miles per hour and the average power required is less than 20 horsepower.
Reliable aircraft engines:
In my opinion in the world of under 200 house power aircraft engines it is hard to beat a four cylinder Lycoming. The low compression engines tend to stick valves when operated on 100 LL.
If I was to imagine normal use and maintenance in my opinion a new four cylinder Lycoming should last more than 20 years without having an engine generated forced landing.
Thank you, Vance
Vance is correct that the most common cause of engine failure, at least in certified aircraft, is running out of gas, which is not the engine's fault. The second most common cause is probably carb ice from misuse (or perhaps I should say nonuse) of the carburetor heat. Both represent operator error. I think you'll find that most Lycomings in ordinary use make their TBO or well beyond without incident.
On this forum, you will find some people flying ancient two stroke drone engines that were designed to last just a few hours before being shot down, some with converted car engines, some with modern two-strokes, some with certified designs that are past their TBO, and even a few with fairly new certified engines. The rate of engine failure for these (and other types I didn't list) varies dramatically with type, as does the cost.
Among my circle of pilot friends are many with five to ten thousand hours in certified piston aircraft who have never had an engine out, and who are not likely ever to suffer one. For contrast, ask Stan about how many he has collected in his log, and what engines he was flying when they happened.
I've been stranded several times in my life by GM, Ford, Japanese, German, and Italian automobiles, and with American, British, Japanese, and Italian motorcycles, but never had a Lycoming betray me.
Well my take on it general aviation often run air cooled engines, in the UK often these sit idle for weeks then a 5 minute warm up and as soon as the temp is ok, it's a full throttle climb possibly with the mixture set wrongly on occasion or partial carb icing. Then 1 hour or so later a decent and switch off, cooling it relitavly quickly. That usage profile compares with the use of unreliable garden machinary. In gyros we also have rear mounted engines in a turbelent airflow and prop vibration as oppose to a vehical propshaft.
I run a Rotax 532 2 stroke "water cooled" on my gyro so we are not talking latest technology, running at over 5,500 rpm when my car runs at less than 3,000. I have had a few failures possibly due to vibration, a chafing spark lead, failed ignition coils, radiator pipe detachment etc
para planes and glider tugs have many failures as they are heating and cooling significantly on every flight. For us in the UK fitting a modern reliable engine is very expensive to gain the certification, so we are mostly stuck with old technology. The newer rotax engines seem much more reliable. But running a direct drive VW or Mac engine of 1960s design without propper "as designed cooling" maybe is a reason why reliability suffers. Internal deteriatiing takes place inside an idle engine sitting in a hanger, sump oil has a lot of nasty things in it if not heated till hot and changed often, and open valves allow dampness in to cylinders, along with condensation as the ambient temperature changes internal seals dry out, crack and brake down.
Life as an aero engine is not an easy one.
Just got my videos on over the shoulder Rotax teardown for maintainance from Homebuild Help the other day.
Very interesting and instructive, but made me wonder why they don't fail more often with the previously mentioned abuse they suffer.
I do know at Mentone this year we had 4 engine outs total. 3 Rotax and 1 MZ.
I do not think any engine is bullet proof.
Your car engine has an easy life compared to just about any aviation piston engine. How often and how long do you run your car engine at the redline ? My guess would be almost never, aviation engines basically live there. An aviation piston engine has a duty cycle more closely aligned with a race car engine then that of your daily driver.
Funny you should mention the term "Bulletproof" in your question as there have been a lot of 914 Rotax engines exposed to small arms fire while operating in Predator UAV's. Some of those engines have compound turbo-chargers and work perfectly well at altitudes up to 60,000' !!!
I don't know of anyone - off the race track - who drives any automobile engine thousands of miles on end at 75-85% wide open throttle, which is typical cruise for an aircraft engine. The issue is heat build up on moving parts and bearing surfaces, which greatly increases wear rates, and the difference is HUGE.
Example: Let's consider a Subaru that has a top end of 130 mph. 80% of that is a mere 104 mph.
When is the last time you saw 104 mph in your family sedan, let alone for 10 hours to make your first thousand miles?
There is a GIGANAMOUS difference between loafing a car in top gear at 2 grand forever, cruising the expressways at 65mph, and running it at 6000 rpm for thousands of miles.
You are talking not just apples and oranges, more like apples and orangutans.
If you want reliability then stay away from all 2-cycle motors, including the Kotex variety. Any motor that recommends a top-end rebuild every what, (second hand rumor quote here) 25 hours, to clean the stupid piston grooves and rings just isn't worth the money, time, nor trouble.
There are a lot of Subaru engines that seem to do a reliable job on a gyro just fine, and there are plenty of parts and redrive kits available for them. In-line Honda 4s are also a good bet, but they aren't as numerous and the parts are a little bit more along the lines of fabrication and cog belt drives. I would stay away from a Yamaha conversion if you don't know what you are doing and don't have a host of shop tools and build experience yet. There is a lot of proof work left to do and the redrives are not a simple matter of slapping one on a motor, and going flying next weekend. The only conversion kit that is available for purchase to date is very difficult to get in a decent turnaround time. I'm working out something myself for a Yamaha Genesis Extreme 4 (and when the manufacturer calls it extreme, they aren't kidding), but it is nowhere near the stage where I would offer the conversion parts to just anyone I don't already know as a good builder.
If you have, what, $35-45,000 dollars you can always buy a Rotax 912 or 914. Or just get a turbine Helicycle, since you'll have a comparable amount of money into your project in the end, right? I mean, the whole idea behind gyros is to fly cheap i thought, and $40,000 aint' my idea of an affordable power plant.
So that's the reason gyro engines fail: we need to fly cheap, and 2-cycle motors are just that.
As far as your question about engines goes not as it relates to cars, I agree with Vance the Lycoming would be tough to beat for that type of engine, but not too many gyros running them
As for a two stroke engine for a gyro it would be tough to beat the longevity and toughness of the Rotax 503, good HP to weight ratio and Aircooled for keeping it simple.
most mechanics I spoke to have said the 503 is just about the least problematic two stroke as it doesn't make enough power to hurt itself.
Anybody ever consider motorcycle engines. Most are designed to run 8 to 10 thousand or more RPM's And except for a few big lugger engines are lightweight. Most have decent horsepower. My motorcycle is rated for 9,000 rpm and and most of the time I run it around 5000 for about 50 to 55 mph The motorcycle is used almost daily and the only failure I've had was a flat tire.
Aircraft engines -ARE- reliable.
Rotax 912 series, 914 series.
Lycoming 100+ HP range, Continental (though they are known to need a top end mid way to 2000 hours)
These are all reliable engines.
HKS, Jabiru, 2-strokes, less so. Simply because they have not accumulated the hours of field testing and gotten themselves proven.
In 2-strokes Rotax still rules. There is a reason it is the market leader. Rotax 503 and then 582 (if properly flown, good oil mixture, 1050 F EGTs and properly maintained).
For Hirth: Well friends don't let friends fly a Hirth
Car engine conversions are not that reliable. I have done and owned 12 of them. Suzuki mostly.
One of my students just passed away in his Just aircraft accident going down into the woods due issues flying with a Honda FIT car engine conversion which I have to admit, peaked my curiosity as well. But right now, no thank you, I will stick with Rotax 912ULS or 914.
I have not had a single engine out on Rotax 912ULS in about 1800 hours of operation and the maintenance is very reasonable.
Car engines unlike aircraft engines do not operate constantly at 75 to 85% power. Cars only use 25% power on average continuously.
2000 hours of operation on a light aircraft at light aircraft average speed amount to close to 1.8 million miles in your car. Try taking your car engine to that number sometime.
Lots of reliable engines
There is a boat load of light weight reliable motorcycle, snowmobile, boat, car engines. The problem always comes in when you try to spin a propeller with that engine. That is a nut that many people have tried to crack and most have failed. In my opinion, if you want a light weight (proven reliable spinning a propeller) engine, rotax 9 series is the only way to go.
Propellers are just harder to turn than tires. Automobile engines are made to turn tires. You can use pliers to tighten nuts and bolts, but it's a much better idea to use the right tool for the job.
Besides wot everyone else has pointed out, weight is anatha major consideration in aircraft.
How many 100 HP car engines do you know of that weigh as little asa 912?
Theres a fine line walked when your buildn a RELIABLE, light weight power plant.
I hada EJ22 soob pushn a gyro, and it was reliable. I know a bloke who has dun thousands of hours on same, without fail.
But this auto engine is heavy compared to the 912. Same power, same reliability, cheaper, but weighs a ton.
If you cant afford or dont need the 912 reliability and light weight, an EJ22 will do just fine.
You get wot you pay for.
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