Why are airplane engine TBO hours so low?

Discussion in 'Flight Following' started by k9medic, Dec 4, 2020.

  1. k9medic

    k9medic Line Up and Wait

    Joined:
    Sep 27, 2018
    Messages:
    693
    Location:
    Florida

    Display name:
    ATP-H, CMEL, CSEL, CFI/CFII Airplanes and Helicopters
    I am sure this has been discussed before but it just came to my mind when I got into my car.

    My car currently has 1213 hours on the engine. That is over a lifespan of 24,000 miles. With that average we are looking at a lot of hours before the vehicle even reaches 100,000 miles.

    Why can we not get the same reliability in airplane engines?

    Is it the RPM that we run them?

    If that is the case, why then can we get thousands of hours out of a turbine engine that has an N1 speed of 53,000 RPM?


    Sent from my iPhone using Tapatalk
     
  2. Rein Hart

    Rein Hart Pre-takeoff checklist

    Joined:
    Dec 25, 2018
    Messages:
    138

    Display name:
    TOGO
    Aircraft engines run at continuous loads for hours. Often at full power.

    Car engines run in cycles of stopping, idling, accelerating with the aid of transmissions too. Cars rarely run at full power for more than a few seconds or minutes.
     
    OkieAviator and David Megginson like this.
  3. k9medic

    k9medic Line Up and Wait

    Joined:
    Sep 27, 2018
    Messages:
    693
    Location:
    Florida

    Display name:
    ATP-H, CMEL, CSEL, CFI/CFII Airplanes and Helicopters
    OK to use that analysis then, I have a Diesel generator with 9000 hours on it. It runs consistently at 1800 RPM

    The engine on my tractor turns at 2200 RPM for 6 to 8 hours at a time while spinning a 20 foot batwing bush hog mower.


    Sent from my iPhone using Tapatalk
     
    N747JB likes this.
  4. bfmetcalf

    bfmetcalf Pre-Flight

    Joined:
    Dec 13, 2011
    Messages:
    88
    Location:
    Cincinnati

    Display name:
    bfmetcalf
    If the engine in your diesel generator or tractor fails, you don't fall 2000-20000 feet...

    A lot of engines will run well past TBO, but for safety sake, they have it at a point before failure (hopefully).
     
    MBDiagMan likes this.
  5. Racerx

    Racerx Pattern Altitude

    Joined:
    May 15, 2020
    Messages:
    1,874

    Display name:
    Ernie
    I look at airplanes similar to Harley's or classic cars. They generally sit for long periods of time. Older technology, seen a many Harley's with oil spots where they sat. And if a car, motorcycle, or generator quits you're probably not going to end up in an NTSB report.
     
  6. cgrab

    cgrab Pattern Altitude

    Joined:
    May 2, 2014
    Messages:
    2,162
    Location:
    Huntsville AL

    Display name:
    cgrab
    It's a probability thing...the 40,000 mile warranty on your tires is determined by when the failure curve starts going up not on when it hits the top. The TBO is the same thing, the manufacturer/FAA started seeing problems at that time. It doesn't mean there will be a problem.
     
  7. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

    Joined:
    Jun 7, 2008
    Messages:
    14,467
    Location:
    DXO124009

    Display name:
    Light and Sporty Guy
    And, how much do those engines weigh?

    Sent from my keyboard.
     
    schmookeeg likes this.
  8. Bill

    Bill Touchdown! Greaser! PoA Supporter

    Joined:
    Mar 2, 2005
    Messages:
    14,299
    Location:
    Southeast Tennessee

    Display name:
    This page intentionally left blank
    I'll take the bait, what the hell, it's Friday!

    Because aircraft engines are built with 1940's technology and metallurgy. Look at car engines from that era, they weren't models of long term durability. Car engines have evolved with science and engineering advances, piston AC engines have not.
     
    Cykoguy, brien23, EugeneR and 5 others like this.
  9. Jim K

    Jim K En-Route

    Joined:
    Mar 31, 2019
    Messages:
    3,271
    Location:
    CMI

    Display name:
    Insert cool name here
    I have a 315 hp tractor that displaces 8.7L. It probably spends 80%+ of its time at full power. I expect it to last 6-8000 hours

    I have a 300 hp airplane that displaces 8.8L. It works just as hard at basically the same RPM. TBO is 2000 hours.

    The tractor engine alone weighs 3x what the entire airplane weighs. It also has a liquid cooling system and the components are built as heavy as practical as weight is a virtue.

    Further, if well cared for that lycoming should be capable of hitting 1.5-2x its TBO. For all the talk about airplane engines being crap, I think they're pretty damn impressive.
     
    Witmo, JoeCFI, mondtster and 7 others like this.
  10. Kevin Eggert

    Kevin Eggert Pre-takeoff checklist

    Joined:
    Feb 6, 2020
    Messages:
    112

    Display name:
    Kevin
    If anything, this is contradictory. The starting, stopping, and power changes would have a detrimental effect rather than help to prolong the engine life.
     
    aterry1067 likes this.
  11. Bell206

    Bell206 Final Approach

    Joined:
    Oct 6, 2017
    Messages:
    6,021

    Display name:
    Bell206
    Define reliability. Aircraft recip engines are designed to be as light as possible yet still required to operate at close to its maximum performance continuously. This leads to poor thermal properties, ie., heat disapation. So they basically physically wear out due to the required mfg tolerances to meet those required performance requirements.
     
  12. Greg Bockelman

    Greg Bockelman Touchdown! Greaser!

    Joined:
    Feb 23, 2005
    Messages:
    10,724
    Location:
    Lone Jack, MO

    Display name:
    Greg Bockelman
    Air cooled vs water cooled. A water cooled engine doesn’t go through heat cycles the same way an air cooled engine does.

    it’s my theory, anyway.
     
    Mason, swingwing, SCCutler and 3 others like this.
  13. RussR

    RussR En-Route

    Joined:
    Jan 12, 2011
    Messages:
    3,095
    Location:
    Oklahoma City, OK

    Display name:
    Russ
    Am I the only one who is curious what kind of car you have that has a Hobbs meter? Or is this in the OBD-II data somewhere?

    And I agree with the others about the tractor engine. Build an aircraft engine that weighs that much, and it will be pretty reliable too. Won't get off the ground, but...

    I certainly don't think aircraft engines are some pinnacle of technology. But they do have to be "lightweight" and still operate at continuously high power for their whole lives. And there are many examples of engines going well past the recommended TBO, especially in uses like powerline patrol and aerial survey work.
     
    Rein Hart likes this.
  14. Chip Sylverne

    Chip Sylverne Final Approach

    Joined:
    Jun 17, 2006
    Messages:
    5,447

    Display name:
    Quit with the negative waves, man.
    But lubricants have.

    Your SM probably specs several kinds of grease.
     
  15. Bill

    Bill Touchdown! Greaser! PoA Supporter

    Joined:
    Mar 2, 2005
    Messages:
    14,299
    Location:
    Southeast Tennessee

    Display name:
    This page intentionally left blank
    Actually when you look at specific power output per pound aircraft engines are quite good.
     
  16. k9medic

    k9medic Line Up and Wait

    Joined:
    Sep 27, 2018
    Messages:
    693
    Location:
    Florida

    Display name:
    ATP-H, CMEL, CSEL, CFI/CFII Airplanes and Helicopters
    OBDII data.
     
  17. David Megginson

    David Megginson Pattern Altitude

    Joined:
    Jul 30, 2018
    Messages:
    2,304
    Location:
    Ottawa, Canada

    Display name:
    Canuck
    First, TBO is only advisory for privately-owned aircraft. Lots of people operate to 3,000 hours and beyond. Even commercially-registered aircraft can go past TBO "on condition". It's just a guideline.

    Second, as others have mentioned, we operate our engines at high power continuously in flight, while a car engine runs mostly at what we'd consider to be taxi power (except merging onto the highway, accelerating to pass, pulling a trailer up a hill, etc).

    Third, our engines have to be as light as possible, so we can't overbuild them for longer life the way you could with a diesel engine in a truck or tractor—they're light, fragile things, like everything in an airplane. For the same reason, most small piston engines have to rely on air cooling rather than (more-effective but heavier) liquid cooling.

    Fourth, we can't afford gradual power degradation like we could in a lawnmower or generator. It's fine if your lawnmower engine is putting out 25% less power after a few years, but with an airplane, that could mean flying into the trees at the far end of the runway. We need to overhaul before there's significant power loss.

    Fifth, airplanes operate in extreme environments, sometimes going from 20c to -10c in a matter of minutes, accompanied by major air pressure changes. Cars, lawnmowers, tractors, and generators rarely deal with that.

    Sixth, many planes spend a long time just sitting around unused. Corrosion seriously shortens the life of engines. Rentals usually go well past TBO, despite the rough treatment from student pilots and renters, just because they're always flying.

    Seventh, you're right that our piston engines are old tech. The industry could probably do better if there were 10× as many of us with 20× as much money to spend, but there's not (we're getting older on average and gradually dying off), so everyone who tries to introduce new engine tech just loses their money. My prediction is that we'll have improved battery tech (e.g. 4–5 hours endurance) for electric planes before we have modern gas engines in most piston planes, because we'll benefit from all the R&D on electric cars.
     
  18. TCABM

    TCABM En-Route

    Joined:
    Apr 23, 2013
    Messages:
    2,894

    Display name:
    3G
    I’d hazard to guess TBO hours are driven by the data submitted to the FAA for certification and probably includes some type of MTBF analysis.
     
  19. GRG55

    GRG55 Final Approach Gone West

    Joined:
    Dec 29, 2015
    Messages:
    9,306

    Display name:
    Aztec Flyer
    The IO-540s in my Aztec are redlined at 2575 RPM. Typical cruise RPM is 2300. The climb phase of every flight, which tends to last longer than the descent phase on most flights is at even higher RPMs than cruise setting.

    Run your car engine under load at 90+% of redline continuously for hours on end and let's see how long it lasts. :D

    Aircraft engine design and manufacturing deals with goals, parameters and limitations that are quite different from stationary power plant (generators) or land vehicles like your car.

    Among other things, weight is the mortal enemy of lift. The heavier the engine and its support systems/accessories the more lift the airframe needs to be capable of. More lift means a larger wing, which means more structure weight, which needs a bigger engine, which means more weight, the bigger airframe and engine means more fuel capacity, which means more weight, which needs more lift...see where this is going?

    One of the best dissertations I've read on this was many years ago - an article by Richard VanGrunsven (Vans RV) where he described these types challenges he was confronting, and the various trade-offs he was evaluating, as he tried to design a 4-place airplane (which eventually appeared as the RV-10 a few years later).

    If water-cooled automotive style engines were actually capable of substituting for the ubiquitous air-cooled Lycoming or Continental then we would have seen masses of homebuilt airplanes using them - there's no major FAA "overlord" restriction for that. Every trip to the EAA Oshkosh airshow since my first in 1985 has included several booths with "new" aircraft engines - everything from diesels to modified auto engines and even a couple of homebuilt testbeds with small turbines in them. Most of these efforts disappear with time. The well funded effort by Bombardier's Rotax division produced the only widespread piston engine substitute for Lyc or Conti - and those aren't exactly an inexpensive engine either.

    The E-AB fleet is overwhelmingly powered by Lycs and Contis. Now why would that be, I wonder...:rolleyes:

    The implication that there's been no metallurgical and other engineering improvements in our Lycoming and Continental piston engines since the 1940s is patently untrue.
     
    Last edited: Dec 4, 2020
    mondtster, Jim K and Pilawt like this.
  20. Tom-D

    Tom-D Taxi to Parking

    Joined:
    Feb 23, 2005
    Messages:
    34,736

    Display name:
    Tom-D
    The 1949 170-A I maintain has a total time just over 2100. I did the overhaul in 2005, and now the 170- has flown 115 since then.
     
  21. Chip Sylverne

    Chip Sylverne Final Approach

    Joined:
    Jun 17, 2006
    Messages:
    5,447

    Display name:
    Quit with the negative waves, man.
    What did the innards look like? How many parts didn't meet spec?
     
  22. AKBill

    AKBill En-Route

    Joined:
    Nov 29, 2014
    Messages:
    3,710
    Location:
    Juneau, AK

    Display name:
    AKBill
    WOW, I did not know the 170 was first produced that long ago. Was 1949 the first production run?
     
  23. Huckster79

    Huckster79 Pattern Altitude

    Joined:
    Nov 22, 2018
    Messages:
    2,154

    Display name:
    Huckster79
    So many variables- I would say the biggest factors (assumptions) would be weight, cooling method and time sitting...

    Big truck diesels go forecer compared to a typical unleaded auto engine - what car (even a Honda) you see with a million miles on em? But tjose big truck engines are used very regularly are heavier than hell and roll with few RPM...

    They are all kinda an apples and oranges comparison
     
  24. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    9,019

    Display name:
    Dan Thomas
    No way. Today's engines are much better than they were in the '40s. TBOs are higher as a result. We have things like sodium-filled exhaust valves now. Much better valve and seat metallurgy. Valve guides are made of much better stuff. Piston rings have improved a lot. Cylinders and crankshafts are nitrided. Cerminil and Nickasil are available. Compression ratios and redlines have risen. There have been many such small changes over the years, but because it looks like an engine that was built in the '40s, people tend to think it's still the same thing. As someone else said, lubricants are a lot better, too. If it was really that easy to build a better engine that would give much better life and reliability, the manufacturers would have done it. They don't enjoy forking out money on warranty claims and lawsuits.

    Aircooled engines have to have more clearances between pistons and cylinders, valve guides and so on, to handle the larger thermal expansions at the much higher cylinder and head temperatures these things encounter. Looser fits mean more blowby, and more blowby means more water and crud in the crankcase, most of it corrosive. A car has the positive crankcase ventilation system (PCV) that constantly draws fresh air though the case to get the (far fewer, due to tight clearances) nasty gases out and run them into the intake manifold and burn them into something less polluting, and that keeps the case dry and clean. At the high power levels in an aircraft engine, the manifold vacuum is too low to make that work. So most of the stuff accumulates and we have to change the oil more often and NOT ground-run that engine and put it away. That alone does terrific damage. I've seen it too often.
     
    Last edited: Dec 4, 2020
  25. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    9,019

    Display name:
    Dan Thomas
    Totally different animal. The turbine runs smoothly with little vibration. The pressures in the system are constant, not changing from 800 psi to less than zero 1300 times a minute. There are no reciprocating loads. The metals used in the turbine are pretty exotic. All of it adds up to many more dollars per horsepower compared to a piston engine.
     
    N747JB and Doc Holliday like this.
  26. Tantalum

    Tantalum Final Approach

    Joined:
    Feb 22, 2017
    Messages:
    8,554

    Display name:
    San_Diego_Pilot
    because they're cheaply built pieces of trash in low volume designed in 1940 and 1950 that have had virtually no innovation since then

    But not really, a 9.6 liter engine being asked to give 230 hp is hardly a tall ask

    One could argue this puts a higher load on the engine the mechanical components.. city driving is known to be much harder on cars than cruising on the highway

    You don't fall in a plane either, you've been reading too many news articles. A ~9:1 glide ratio can hardly be called falling

    I fell for the bait too

    Some people talk about weight and make all sorts of excuses for our trash tech engines. The biggest obstacle really is financial and regulatory. Not physical

    When I worked in the marina we had a lightweight Honda generator (this one).. let me tell you, we abused the living daylights out of this thing. It was kept outside, on a dock, tied to the back of a shed, probably 8 inches from salt water.. when boats would go by it would get splashed in salt water. It never got any maintenance, no oil changes, nothing, we just put gas in it. But, it dutiful ran every day from 7am to 11pm from April 1 through October 15. Some mornings late (or early) in the season there'd be a lining of frost on it.. but it always started on the first pull

    I would trust that thing in a plane well over whatever garbage Continental or Lycoming gives us

    Don't preflight right? Don't sump your fuel right? Don't do a good run up? Don't carefully fiddle with the mixture? Don't look at the plane right? The guy at Continental had a bad day putting together the sand cast engine and didn't safety wire something? All of those things can kill you

    Absolute garbage
     
    PeterNSteinmetz and RudyP like this.
  27. Tantalum

    Tantalum Final Approach

    Joined:
    Feb 22, 2017
    Messages:
    8,554

    Display name:
    San_Diego_Pilot
    ^correct, but I will also add that the first turbines that came out were prone to flame out, and needed a full blown flight engineer to monitor the thing. However, we have billions of dollars of commercial interest behind the advancement of turbine technology, so advances are made. What interest do we have behind GA piston tech? A handful of pilots flying 50 year old bonanzas who tolerate what they're given. There's no economic reason to advance piston GA. By the time you pour the money into it you might as well be buying a turbine
     
    RudyP likes this.
  28. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    9,019

    Display name:
    Dan Thomas
    :mad2:

    The many voices of the experienced engine experts here
     
  29. NordicDave

    NordicDave Pattern Altitude

    Joined:
    Oct 31, 2015
    Messages:
    2,405
    Location:
    Monterey County

    Display name:
    NordicDave
    The beauty of part 91 operations is we can replace or overhaul "on condition". Anecdotal evidence shows many part 91 operators are seeing 20 years or more of operation and exceeding TBO time 2-400 hours over factory figures if kept free of corrosion and engine managed properly.

    My own O-470R is going in for OH in January. The engine was 1500 hr/ 12 year TBO, but ran for 32 years and 1825 hours before it started speaking it's needs an OH. It also has a Rajay turbo-normalized STC.
     
  30. Tantalum

    Tantalum Final Approach

    Joined:
    Feb 22, 2017
    Messages:
    8,554

    Display name:
    San_Diego_Pilot
    they haven't had innovation. My friend's partner nearly went for a swim in Long Island sound because one of the plastic magnetos failed in a peculiar fashion that was causing bad misfirings, limped home and the engine died on the ground. I've got the email from a mechanic somewhere. That's inexcusable that we still rely on tech like that. Our spark plug gaps are so itsy bitsy that the slightest bit of fowling ruins it. Even a 50 year old car engine runs better, check out the guys at Corvair..

    ..and they are cheaply built, sand casting a mold with crummy metallurgy is cheap, requiring careful break ins.

    ..and they are low volume

    I don't know why some engineers take this so personally. There's no defendable objective argument that can be made to justify the "low tech" nature of these engines.
     
  31. GRG55

    GRG55 Final Approach Gone West

    Joined:
    Dec 29, 2015
    Messages:
    9,306

    Display name:
    Aztec Flyer
    Those arguments have been made over and over again on numerous threads on this forum. The belief that they are not "defendable objective arguments" is your opinion. I will continue to respectfully disagree with that opinion (for the reasons articulated above and elsewhere on other threads in the past).
     
  32. WDD

    WDD En-Route

    Joined:
    Oct 16, 2019
    Messages:
    3,616
    Location:
    Atlanta / KRYY

    Display name:
    Vintage Snazzy (so my adult children say)
    Rotax engines (912) are built using new technology. It has a TBO of 1500 hours, similar to the death trap Continentals mentioned above. This tells me it is more of the demand placed on the engine for the weight and size than simply bad engineering and bad construction.
     
    Jim K likes this.
  33. Shepherd

    Shepherd Final Approach

    Joined:
    Nov 24, 2012
    Messages:
    5,000
    Location:
    Hopewell Jct, NY

    Display name:
    Shepherd
    I've heard this argument all my life.
    I think it's totally bogus.

    Stress on an automobile engine is much worse, specifically because of all the changes in engine speed.
    That's why automobile engines are built so beefy.
    And therein lies the main design difference between aircraft engines and car engines.
    Weight in an automobile engine is not as critical as weight in an aircraft engine. Lift the crank for a six cylinder Honda engine, then lift a six cylinder Lycoming crank.
    If you have never done it, the difference will surprise you. The same difference in weight holds true for every other part in and aircraft engine.
    All engines are designed and built to the minimum quality that will get a job done.
    Now, throw in government bureaucracy, and you can explain the difference in price.
     
    Sierra_Hotel and Tantalum like this.
  34. Tantalum

    Tantalum Final Approach

    Joined:
    Feb 22, 2017
    Messages:
    8,554

    Display name:
    San_Diego_Pilot
    That's fair, but if cost and regulations were no object we could undoubtedly find ways to improve the engines. Maybe we've reached the realistic max of what a piston ga engine can offer, but certainly not a theoretical max
     
  35. Samuel Seidel

    Samuel Seidel Pre-Flight

    Joined:
    Apr 16, 2020
    Messages:
    86
    Location:
    Georgia

    Display name:
    Sam
    Let’s say driving a car for one hour at 70mph is equivalent to one hour of flying.

    2000 hours on that plane engine means 140,000 miles.
    3000 hours = 210k miles
    4000 hours = 280k miles

    Thinking about it in this way helps me.
    Also the car engine is under less load at 70mph then the plane is, at a higher load for the car engine, let’s say 115mph, you would go 460,000 miles if driven 4000 hours
     
    Sierra_Hotel and SoCal RV Flyer like this.
  36. bfmetcalf

    bfmetcalf Pre-Flight

    Joined:
    Dec 13, 2011
    Messages:
    88
    Location:
    Cincinnati

    Display name:
    bfmetcalf
    No, I completely get that. But there are a lot of places that even a good glide ratio won't save you from landing in a forest with no fields with similar results. Not to mention we see plenty of engine out fatalities in this sport that, though pilot error, may not have happened if the engine hadn't have failed. TBO's help mitigate that at least some.

    I've lost an engine in my truck on the freeway, it was a non-event, I just coasted to the shoulder (in rush hour traffic) and stopped and called a wrecker. I've lost electrical in a plane in VFR and it was significantly more stressful even with the engine there.
     
    Tantalum likes this.
  37. Tantalum

    Tantalum Final Approach

    Joined:
    Feb 22, 2017
    Messages:
    8,554

    Display name:
    San_Diego_Pilot
    Why does everyone say this? Your car engine is probably 2.5 liter and 180 hp. The engine in the club rental is 6 liters and 180 hp. According to the Ultragauges I've had in my car it takes about 30 percent power to stay at a 72 cruise setting.. (30% X 180)/2.5 = 22 hp per liter. In the plane (75% X 180)/6 = 22..and most people run plane engines closer to 65% power. Per displacement they're being asked to do the same thing

    A lyco 360 weighs about 300 lbs
    A Honda civic engine weighs about 400 lbs.. but the block of the 1.6 weighs a mere 150 lbs (roughly)

    ..anyway.. I've resolved to "it is what it is" and just accept it as part of life.
     
    EugeneR and genna like this.
  38. Tom-D

    Tom-D Taxi to Parking

    Joined:
    Feb 23, 2005
    Messages:
    34,736

    Display name:
    Tom-D
    1948 there were 712 of them made, (rag wings) then the -A- was introduced,(1949) then 1953 mid year the -B- came out last of them was 1957.
     
    Last edited: Dec 4, 2020
  39. Greg Bockelman

    Greg Bockelman Touchdown! Greaser!

    Joined:
    Feb 23, 2005
    Messages:
    10,724
    Location:
    Lone Jack, MO

    Display name:
    Greg Bockelman
    My dad’s 2016 Chevy Silverado will display engine hours if you know how to get to that menu item.
     
  40. Tom-D

    Tom-D Taxi to Parking

    Joined:
    Feb 23, 2005
    Messages:
    34,736

    Display name:
    Tom-D
    Pretty much would have met service limits. but we did the whole re-build, .010 under crank, new cam, new lifters, case rebored, new gears, new motor mounts, and assembled with all new hardware.
    2005 = $12,000