Honest reporting on electric airplanes

Tantalum said:
I don't think this is true. There isn't some invisible presence that knows you've flown X hours and you're becoming "due" .. I go get in a rented airplane that's flown 25000 hours in its life engine failure free, that plane doesn't know if I am a zero hour brand new student or a 10,000 hr seasoned accident free aviator who's 'due' for an event. My statistical chance of an engine failure is the same every time I get in a plane

But I digress, back to the thread..
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That ignores the fact that the older a machine gets, the more likely it is to fail. These engines get (or should get) overhauled at reasonable intervals, and they should get overhauled in strict accordance with the manufacturer's instructions. Field overhauls sometimes fall short of that; I've seen it. It's scary. Even at that, the 25,000 airframe hours have no bearing on the engine's hours. None.

Control surface cables and pulleys wear out. Cables fray and will eventually fail if they're not inspected, and inspecting them involves removing lots of stuff sometimes, and so it gets pencil-whipped. Pulleys seize up. Hinge bracketry cracks. Engine controls are not usually replaced at engine overhaul, but they should be. I have seen one failed throttle cable and two failed carb heat cables. That 25,000-hour airplane you rent, if it has not been meticulously inspected, will have cracked airframe components. Every airframe design has its weak points.

I've had two engine failures. One was a broken crankshaft. The engine had been field-overhauled without the manufacturer-specified NDT during overhaul. The crank had cracked due to a long-ago propstrike. The other failed because its carb fell off due to no locking of the carb's retaining nuts. I later bought that airplane, and when I tore the fabric off the wings I found the rear spars of both wings cracked, one of them 3/4 of the way through, and that crack had been there a long time, judging by the wear of the wood in the crack due to movement. It could have come apart in flight in any real turbulence or spin recovery.

Stuff like that made me a careful mechanic and a skeptical pilot. As the Director of Maintenance for a flight school, the government flight-test personnel told me that our airplanes were the only flight-school airplanes in their whole region that they weren't afraid to get into.
 
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Tantalum said:
I don't think this is true. There isn't some invisible presence that knows you've flown X hours and you're becoming "due" .. I go get in a rented airplane that's flown 25000 hours in its life engine failure free, that plane doesn't know if I am a zero hour brand new student or a 10,000 hr seasoned accident free aviator who's 'due' for an event. My statistical chance of an engine failure is the same every time I get in a plane

But I digress, back to the thread..
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If the past risk is zero (ie. you've never had an engine failure), then the future risk is higher than zero regardless of how small that risk is. I wasn't insinuating that every pilot, plane, or engine, has a time when it's "number is up." You're exactly right: planes are dumb. They don't know who's at the controls or whether they are over land or water. All they know is if the angle between the chord line of the wing and the relative wind doesn't exceed the critical angle of attack, it will keep flying. :)
 
Dan Thomas said:
I've had two engine failures. One was a broken crankshaft. The engine had been field-overhauled without the manufacturer-specified NDT during overhaul.
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I hope you didn't make the newbie mistake of discarding that crankshaft, Dan.
I found a guy who can fix them up for us:

 
Tantalum said:
There isn't some invisible presence that knows you've flown X hours and you're becoming "due" .. I go get in a rented airplane that's flown 25000 hours in its life engine failure free, that plane doesn't know if I am a zero hour brand new student or a 10,000 hr seasoned accident free aviator who's 'due' for an event.
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For some strange reason mine seems to know when I'm over water or other unfriendly terrian ... :biggrin:
 
GaryM said:
"The odds don't remember." One of the first things taught when I took a probability course.
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Assuming each event is independent, like a toss of a coin. But that is often not the case with mechanical failures.
Example: a crack forms in your engine case. It gradually propagates until it fails. The odds of failure increase with each prior flight that does not end in failure, because the crack is longer.
 
Dan Thomas said:
As the Director of Maintenance for a flight school, the government flight-test personnel told me that our airplanes were the only flight-school airplanes in their whole region that they weren't afraid to get into.
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....and fly to POH and/or TCDS limitations?
 
Ed Haywood said:
Assuming each event is independent, like a toss of a coin. But that is often not the case with mechanical failures.
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True, and a fact that is often overlooked. When I taught analog circuit tolerance analysis, we spent some time discussing this. A circuit might have many requirements, and its statistical performance against some specs might be uncorrelated, while others might be highly correlated. The analysis can get unwieldy unless you make some assumptions and approximations.

Also, there's an assumption that the mechanical system remains undisturbed, but none of our engines do. We change oil, clean sparkplugs, replace a cylinder, etc.. (You can get into a Ship of Theseus discussion; was the probability of the boat sinking changing as each plank was replaced?)
 
Let'sgoflying! said:
I hope you didn't make the newbie mistake of discarding that crankshaft, Dan.
I found a guy who can fix them up for us:

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That crank is from an auto engine. In the world of aircraft, that sort of thing is so risky it's not funny. An auto crank delivers only torque, and a failure means coasting to the side of the road. The aircraft crank takes terrific thrust and gyroscopic precession loads as well as the torque, and often has fewer but much bigger cylinders that really make torque spikes.

Lycoming says this in their Direct-Drive engine overhaul manual:

1716667976518.png
And this:

1716668025064.png

About bent cranks, Lycoming says this in their manual:

1716667748931.png

FAR 43.13 says this:

1716668945190.png

So the work must be done in accordance with the manufacturer's current manuals. Lycoming forbids the re-use of any cracked crankshaft, which would certainly cover broken crankshafts as well.

We sometimes used a nearly engine shop for cylinder work or NDT after a propstrike. The owner told me that a fellow came in one day, from the airside of the shop, and asked about the O-200 crank that was in the scrap barrel. He wanted it, and the owner would not give it to him. It was cracked between the prop flange and first main bearing surface. That crank disappeared overnight, and nothing was heard until one day the Transport guys came in and asked if they'd sold a used crank to a certain homebuilder. They had a picture of the guy, and it was the guy that wanted that cracked crank. Well, he'd swiped it, gouged out the crack, and welded it up and put it in his homebuilt. In flight, the front end of the crank broke at the weld, and the prop came off and flew up and went through the windshield, killing the guy. Crash. Legal maybe, but really stupid.

In a previous career I was the shop foreman in a machine shop where we rebuilt air brake compressors, valves, and a bunch of other stuff. Compressors are driven by the truck or earthmover's engine, and some of them had weaknesses at the drive end. Some were being driven off an engine pad and internal gearing that was designed for a hydraulic pump. But a compressor is a reciprocating load, not at all like a hydraulic pump, and it lashes the drive every time the piston goes over TDC and the residual air in the cylinder pushes the piston down, forcing the crankshaft forward, that the crank is forced back again by the next compression cycle. This beats up the drive splines.

Those cranks were expensive. Some shops were welding them up and having lots of failures. I developed a process using a MIG wire of equivalent strength to the crank's steel, and after machining all the old splines off and to a level deeper than the the weld fusion would reach, I'd weld them up carefully, two beads at a time, one on each side, and let them cool before doing any more welding. This reduced the chances of cracking in the weld interface as it cooled. Once they were all welded up, I machined them to the right diameter and cut the splines into them on the mill. They worked well unless the mechanic installed them into worn splines in the drive gear in the engine. That lash soon tore them up. That happened with brand-new cranks, too. We also did some cast iron cracks this way, but it was much more difficult due to the high carbon content of gray cast, and I had to use pure nickel wire to get adhesion. With cast, you don't want penetration or the dilution creates a hard, glass-brittle transition zone that will soon fail. The weld has to stick to the iron much like brazing would. After I left that place, they started taking shortcuts with the welding, and crank breakage happened in nearly every compressor of that drive type. I had warned them against that. Keep it cool I had said, and don't turn up the amperage. Take your time. But no, someone ignorant higher up in the company demanded speed, and got big warranty problems. Saving money no matter how much it costs, just like that homebuilder.
 
omg, Dan. My mistake, I thought you’d see a blatant joke for what it was.
 
Let'sgoflying! said:
omg, Dan. My mistake, I thought you’d see a blatant joke for what it was.
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Well, I don't usually take such stuff as a joke. Remember the guy that stole that cracked crank and welded it? Stuff like that happens. And I've seen too many other such "jokes" in airplanes.

There are sometimes people who suggest spray-welding up the worn journals on aircraft crankshafts. The regrinding limit is usually .010" undersize, as opposed to as much as .040" on an auto crank. So .010" undersize bearings are all you can get. Since a new crank can cost many AMUs, the temptation is to use automotive technology to save it.

Sorry if I overreacted, but that's just me and my experience speaking. That crank that failed me had no reason to be in that engine. The cracked spars in that airplane I was flying had no good reason to be there, either, but they were, even after all the annual "inspections" between about 1964 when the airplane was overturned by the wind, putting all the weight on the wingtips and cracking the spars, and about 1979 when the engine failed on another pilot and it got bent. Water in the fuel or something. I once ferried a 172 that took both hands and feet to keep it straight in the air, and after we got into it we found the forward horizontal stab spar broken all the way through, and a whole bunch of other horrors, including no nuts on the wing strut bolts at the bulkhead under the floor. That busted stab spar could have resulted in stab failure if anyone did a spin or spiral-dive recovery. Only the skin was holding it.
 
Dan Thomas said:
Well, I don't usually take such stuff as a joke. Remember the guy that stole that cracked crank and welded it? Stuff like that happens. And I've seen too many other such "jokes" in airplanes.

There are sometimes people who suggest spray-welding up the worn journals on aircraft crankshafts. The regrinding limit is usually .010" undersize, as opposed to as much as .040" on an auto crank. So .010" undersize bearings are all you can get. Since a new crank can cost many AMUs, the temptation is to use automotive technology to save it.

Sorry if I overreacted, but that's just me and my experience speaking. That crank that failed me had no reason to be in that engine. The cracked spars in that airplane I was flying had no good reason to be there, either, but they were, even after all the annual "inspections" between about 1964 when the airplane was overturned by the wind, putting all the weight on the wingtips and cracking the spars, and about 1979 when the engine failed on another pilot and it got bent. Water in the fuel or something. I once ferried a 172 that took both hands and feet to keep it straight in the air, and after we got into it we found the forward horizontal stab spar broken all the way through, and a whole bunch of other horrors, including no nuts on the wing strut bolts at the bulkhead under the floor. That busted stab spar could have resulted in stab failure if anyone did a spin or spiral-dive recovery. Only the skin was holding it.
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That must suck. Because every joke has some element of serious truth to it, so you must never find anything funny or risk, well I’m not sure what the harm is, but you risk whatever it is.
 
Salty said:
That must suck. Because every joke has some element of serious truth to it, so you must never find anything funny or risk, well I’m not sure what the harm is, but you risk whatever it is.
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I have a good sense of humor. I just don't joke about lousy aircraft maintenance. People who suddenly find themselves with a dead engine don't joke about it, either.
 
Dan Thomas said:
I have a good sense of humor. I just don't joke about lousy aircraft maintenance. People who suddenly find themselves with a dead engine don't joke about it, either.
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I've heard of laughing all the way to the bank ... all the way to the ground - not so much! ;)
 
Dan Thomas said:
I have a good sense of humor. I just don't joke about lousy aircraft maintenance. People who suddenly find themselves with a dead engine don't joke about it, either.
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As one of those people I can say for certain you are wrong. I can still joke about people doing stupid things.
 
I used to joke about people that could hide their own Easter eggs.

I understand those types of jokes.

But once my mom got Alzheimer's, those types of jokes lost all their humor.
 
Bob Noel said:
I used to joke about people that could hide their own Easter eggs.

I understand those types of jokes.

But once my mom got Alzheimer's, those types of jokes lost all their humor.
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I’m truly sorry. I know that pain as well, but I feel it’s important to process the grief and humor is one good way to do that.
 
Salty said:
I’m truly sorry. I know that pain as well, but I feel it’s important to process the grief and humor is one good way to do that.
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I realize that some people really need the humor - but for me not that kind
 
Ed Haywood said:
Pretty good rundown on eVTOL infrastructure efforts in FL, suggesting that the FAA is an obstacle.
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Interesting. Considering there are already a number of FAA certified vertiports in the US, I think the premise of the article was more on the eVTOL certification side with its mention of the Paris Olympics. Whatever issues Florida is having is strictly a local issue except for the fact there is no certified eVTOL presently. But that isn’t stopping other cities/states/countries from moving forward on their UAM/AAM infrastructure plans. Some of these places have actually had these plans on the books for years.

Regardless, neither the FAA or the EASA have certified any eVTOL. Is the EASA going to allow Volocopter to fly for the Olympics under a special flight permit… maybe. 2028 is still the going deadline but from what I’ve seen will probably be a bit sooner if it continues at its present pace.
 
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