I am sure most of you had heard about United Airlines Boeing 777 engine blew up yesterday. Turn out similar incident had happened before and I just heard that both Boeing had asked every user in the world to ground their the Boeing 777 with the same Pratt & Whitney PW4090 engine for inspection.
Here is the news:Boeing Calls for Global Grounding of 777s Equipped With One Engine Model
Now, on another news: Authorities in U.S. and Japan ground Boeing 777s after engine explodes over Denver
There is an interesting paragraph, I copy and paste below:
The crack that led the fan blade to break on the United flight was similar to one that occurred on a 2018 United flight, said a person familiar with the preliminary investigation results who wasn’t authorized to discuss them.
In the latest failure, one fan blade cracked and broke off near where it attached to a rotating hub, according to the person. A second blade was also broken, apparently after it was struck by the first blade.
The fan blades on this type of PW4000 are hollow and made of titanium. The cracks appear to start from within the surface, making them hard to detect. Airlines can use technologies such as ultrasound to find cracks beneath the surface. The blades are only used on some 777 planes, said the FAA, which is stepping up the frequency of inspections.
After reading this paragraph, I decided to wrote this post on our forum,
Many months ago, I was looking for a Titanium parts manufacturer that can produce a custom Titanium Rear Axle to my spec, and most of them did not respond but one good manufacturer respond, I copy and paste below:
Howard,
We made a run of like 50pcs and we hot forged the flange area, heat treated the blanks, then started the machining process, and then PVD hard coated bearing area. Price back then was around $3-4k each. Now the cost would be much more. Sorry no interest in doing this project again.
Basically what this manufacturer said was, he made titanium rear axle in the past for older Ducati model, however, he can't sold enough to make money because all the process he had to do to make sure it is strong enough for that bike application.
And I assure you that the bike he made the rear axle was not as powerful as our Panigale V4 !!!
Now, our rear axle is HOLLOW just like the Titanium Fan Blade on that Boeing 777 engine. Plus both our rear axle and this fan blade are "ROTATING Assembly" so they experience similar stress, but our rear axle actually experience more stress from the vertical movement of the swing arm following bump (those fan blade only experience rotating stress), so our rear axle actually "work harder" correspondence to the design of course.
Please note that we can't really make our rear axle tube wall much thicker if we still want to use our stock rear bike stand, plus thicker wall will add weight making the "weight reduction" less attractive.
So what this means is, any Titanium Rear Axle for our Ducati Panigale V4 will be WEAKER then our stock steel Ducati factory Panigale V4 rear axle due to simple reason, Titanium itself is weaker than steel at same volume. Titanium is stronger than steel if both weight the same, meaning the Titanium need to have more volume to be equal in strength to steel.
In our case, the rear axle made of Titanium need to have much thicker tube wall in order to be equal to the stock Ducati steel rear axle.
Not to mention, if you just machined a rear axle from Titanium Grade V (the stronger grade), but without any "treatment" after machining, there might be weak area due to machining process which make it weaker than the original ingot of Titanium grade V.
That is why the rear axle manufacturer comment above specifically said that he "hot forged the flange area and heat treated the blanks", the hot forged flange area is the key because that is where the stress is the most.
One more thing, our rear axle is for SINGLE SIDED Swing Arm, thus the flange area handle the stress that usually distributed to 2 end of the axle on the double sided swing arm.
Now,remember this post at Ducati UK forum: 899 - Dangerous Rear Wheel Axel Failure
If a Ducati stock steel rear axle can fail, then a weaker Titanium rear axle can fail too...
I understand that some user only use their bike for the street, but... a street use might be more stressful for the rear axle because, street have more potholes and not as flat as a race track. Imagine your tire/wheel is like the head of a hammer, while your swing arm is the handle of a hammer.
Each time your rear wheel hit a bump on the street, that create stress to the "single flange".
That and plus our Ducati engine is very powerful and the "twist" action from the rotating sprocket, create twisting stress on the same "single flange"... do it over and over and over, and crack/stress might start...
Acceleration on the track usually more rolling acceleration, but acceleration on the street, can happened a lot on that from the stop light drag race... that is harder than rolling acceleration on the track...
Plus, when Titanium break, it just break without warning, unlike steel. Yes, aluminum is worse in sudden breaking but Titanium is also like that although not as bad as aluminum.
Back to the article above, the hollow titanium blade of the Boeing 777 engine start crack from within / beneath the surface so you cannot detect it from the surface, and you need X-Ray or Ultrasound.
Basically, a titanium rear axle on our bike, if it broke might also be similar (crack might start from within/beneath the surface where you can't really see).
Yes, many rider had used Titanium rear axle in the past without problem or failure, however, that doesn't mean it is 100% safe.
It might be because, the bike they are using is not powerful enough to break the rear axle, or maybe they don't ride that much or that hard, or maybe the thickness of the wall is thick enough or they were made with many special step like forging to properly enhance their strength.
I also don't think any titanium rear axle manufacturer actually test their axle to the breaking point and have measurement to know the critical limit...
If racing team use titanium rear axle, well, they use every parts as consumable parts and replace them routinely... we on the other hand most likely won't replace our titanium rear axle every few thousands miles or so...
Those passenger on that Boeing 777 was never thought that the world class engineer at Pratt & Whitney and to some extend Boeing's engineers might made mistake when designing this engine hollow titanium blade... and again if those world class engineer can make mistake...
well, I am pretty sure most titanium rear axle for Panigale V4 were not as thoroughly engineered and tested as the titanium fan blade of this 777 (which still fail)....
Again, the key points are:
a. Single sided swing arm (unlike conventional dual sided swing arm or front axle with pair of forks application)
b. Wall thickness is about the same as steel stock rear axle
c. Titanium broke more suddenly than steel
d. Our bike is very powerful, more powerful than previous generations of superbikes
e. CNC Machining only without extra process/treatment might not be strong enough
f. Even world class engineer at Pratt & Whitney and Boeing can made mistake
g. cracks might be below surface and undetected
h. rear axle is hollow just like the titanium fan blade that fail
i. We only have 1 life
Here is the news:Boeing Calls for Global Grounding of 777s Equipped With One Engine Model
Now, on another news: Authorities in U.S. and Japan ground Boeing 777s after engine explodes over Denver
There is an interesting paragraph, I copy and paste below:
The crack that led the fan blade to break on the United flight was similar to one that occurred on a 2018 United flight, said a person familiar with the preliminary investigation results who wasn’t authorized to discuss them.
In the latest failure, one fan blade cracked and broke off near where it attached to a rotating hub, according to the person. A second blade was also broken, apparently after it was struck by the first blade.
The fan blades on this type of PW4000 are hollow and made of titanium. The cracks appear to start from within the surface, making them hard to detect. Airlines can use technologies such as ultrasound to find cracks beneath the surface. The blades are only used on some 777 planes, said the FAA, which is stepping up the frequency of inspections.
After reading this paragraph, I decided to wrote this post on our forum,
Many months ago, I was looking for a Titanium parts manufacturer that can produce a custom Titanium Rear Axle to my spec, and most of them did not respond but one good manufacturer respond, I copy and paste below:
Howard,
We made a run of like 50pcs and we hot forged the flange area, heat treated the blanks, then started the machining process, and then PVD hard coated bearing area. Price back then was around $3-4k each. Now the cost would be much more. Sorry no interest in doing this project again.
Basically what this manufacturer said was, he made titanium rear axle in the past for older Ducati model, however, he can't sold enough to make money because all the process he had to do to make sure it is strong enough for that bike application.
And I assure you that the bike he made the rear axle was not as powerful as our Panigale V4 !!!
Now, our rear axle is HOLLOW just like the Titanium Fan Blade on that Boeing 777 engine. Plus both our rear axle and this fan blade are "ROTATING Assembly" so they experience similar stress, but our rear axle actually experience more stress from the vertical movement of the swing arm following bump (those fan blade only experience rotating stress), so our rear axle actually "work harder" correspondence to the design of course.
Please note that we can't really make our rear axle tube wall much thicker if we still want to use our stock rear bike stand, plus thicker wall will add weight making the "weight reduction" less attractive.
So what this means is, any Titanium Rear Axle for our Ducati Panigale V4 will be WEAKER then our stock steel Ducati factory Panigale V4 rear axle due to simple reason, Titanium itself is weaker than steel at same volume. Titanium is stronger than steel if both weight the same, meaning the Titanium need to have more volume to be equal in strength to steel.
In our case, the rear axle made of Titanium need to have much thicker tube wall in order to be equal to the stock Ducati steel rear axle.
Not to mention, if you just machined a rear axle from Titanium Grade V (the stronger grade), but without any "treatment" after machining, there might be weak area due to machining process which make it weaker than the original ingot of Titanium grade V.
That is why the rear axle manufacturer comment above specifically said that he "hot forged the flange area and heat treated the blanks", the hot forged flange area is the key because that is where the stress is the most.
One more thing, our rear axle is for SINGLE SIDED Swing Arm, thus the flange area handle the stress that usually distributed to 2 end of the axle on the double sided swing arm.
Now,remember this post at Ducati UK forum: 899 - Dangerous Rear Wheel Axel Failure
If a Ducati stock steel rear axle can fail, then a weaker Titanium rear axle can fail too...
I understand that some user only use their bike for the street, but... a street use might be more stressful for the rear axle because, street have more potholes and not as flat as a race track. Imagine your tire/wheel is like the head of a hammer, while your swing arm is the handle of a hammer.
Each time your rear wheel hit a bump on the street, that create stress to the "single flange".
That and plus our Ducati engine is very powerful and the "twist" action from the rotating sprocket, create twisting stress on the same "single flange"... do it over and over and over, and crack/stress might start...
Acceleration on the track usually more rolling acceleration, but acceleration on the street, can happened a lot on that from the stop light drag race... that is harder than rolling acceleration on the track...
Plus, when Titanium break, it just break without warning, unlike steel. Yes, aluminum is worse in sudden breaking but Titanium is also like that although not as bad as aluminum.
Back to the article above, the hollow titanium blade of the Boeing 777 engine start crack from within / beneath the surface so you cannot detect it from the surface, and you need X-Ray or Ultrasound.
Basically, a titanium rear axle on our bike, if it broke might also be similar (crack might start from within/beneath the surface where you can't really see).
Yes, many rider had used Titanium rear axle in the past without problem or failure, however, that doesn't mean it is 100% safe.
It might be because, the bike they are using is not powerful enough to break the rear axle, or maybe they don't ride that much or that hard, or maybe the thickness of the wall is thick enough or they were made with many special step like forging to properly enhance their strength.
I also don't think any titanium rear axle manufacturer actually test their axle to the breaking point and have measurement to know the critical limit...
If racing team use titanium rear axle, well, they use every parts as consumable parts and replace them routinely... we on the other hand most likely won't replace our titanium rear axle every few thousands miles or so...
Those passenger on that Boeing 777 was never thought that the world class engineer at Pratt & Whitney and to some extend Boeing's engineers might made mistake when designing this engine hollow titanium blade... and again if those world class engineer can make mistake...
well, I am pretty sure most titanium rear axle for Panigale V4 were not as thoroughly engineered and tested as the titanium fan blade of this 777 (which still fail)....
Again, the key points are:
a. Single sided swing arm (unlike conventional dual sided swing arm or front axle with pair of forks application)
b. Wall thickness is about the same as steel stock rear axle
c. Titanium broke more suddenly than steel
d. Our bike is very powerful, more powerful than previous generations of superbikes
e. CNC Machining only without extra process/treatment might not be strong enough
f. Even world class engineer at Pratt & Whitney and Boeing can made mistake
g. cracks might be below surface and undetected
h. rear axle is hollow just like the titanium fan blade that fail
i. We only have 1 life
