AW189
Yawn,
The Bell 429 went 4 hours with torque being increased from staying in the air, to best range, then up in 8-10% steps at 30 minute increments. And this was with a venting of the oil similar to the S-92.
The Sultan
The Bell 429 went 4 hours with torque being increased from staying in the air, to best range, then up in 8-10% steps at 30 minute increments. And this was with a venting of the oil similar to the S-92.
The Sultan
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Could someone tell me what material helicopter gearboxes are made from?
A cat hydraulic ram rod will bounce a ball bearing of specified density with a ping back up to a specified height, or it fails quality acceptance.
A cat clone looks identical, all nice and shiny, but the ball won't bounce more than half the cat height and only makes a dull thud sound..
The cat rod last five times longer and only costs twice as much.
Each chromium plated rod may be very similar in appearance but the underlying steel is a different kettle of fish altogether, and like coca cola, you won't get the recipe out of them.
A cat final drive will operate dry on oil for a couple of hours if the operator is deaf, but is very heavy on the pocket to fix.
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topendtorque, thanks - I get what you are saying, Caterpillar products are top notch, like Snap-on tools.
So how does this relate to heli gearboxes? Are you saying there are cheap ones and quality ones? I thought aviation laws meant they all had to be top quality?
Interesting to learn that they are made from magnesium, the casing I mean. I guess if they had been steel they would get too hot.
Doesn't magnesium react with salt water though? If a heli ditches will the gearbox have to be completely replaced or just overhauled. How do you check for cracks and stress in a magnesium casing? Can you x-ray it?
So how does this relate to heli gearboxes? Are you saying there are cheap ones and quality ones? I thought aviation laws meant they all had to be top quality?
Interesting to learn that they are made from magnesium, the casing I mean. I guess if they had been steel they would get too hot.
Doesn't magnesium react with salt water though? If a heli ditches will the gearbox have to be completely replaced or just overhauled. How do you check for cracks and stress in a magnesium casing? Can you x-ray it?
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Oh yeah, let's take the AW189 MGB thread and start S-92 run dry bashing again. There is another thread for that....
Good on AW if they have achieved that. 45 minutes run dry at 100 kias shoud be the benchmark.
Good on AW if they have achieved that. 45 minutes run dry at 100 kias shoud be the benchmark.
this means less demand is placed on the residual reserves of oil
For the engineers/technicians (or anyone else knowledgeable), do you know whether the reduction gears in a typical box are spur or helical? I work in the machine-tool industry, and the sturdiest transmissions seem to all use spur gears with ground teeth. Oil changes show barely perceptible sediment. That AW statement says "super finishing of gears", so perhaps that means ground teeth.
Bad requirement -
So what is the Pilot instruction to be in the AW189? loss of oil? No problem, you can fly for 50 minutes, we promise.
How about some way of knowing what your real status in that situation is? Aux lube system, you know the pressure, you have real faith. One demonstration, without flight conditions, attitude, what is your standard deviation in results? This release, and the basic requirement itself, only perpetuates a false comfort to go farther than you should. Landing immediately in cold water may be a bad day, but beats the alternative. What if you really only have 25 minutes that day, because the leak initially caused a loss of cooling that you did not notice?
How about some way of knowing what your real status in that situation is? Aux lube system, you know the pressure, you have real faith. One demonstration, without flight conditions, attitude, what is your standard deviation in results? This release, and the basic requirement itself, only perpetuates a false comfort to go farther than you should. Landing immediately in cold water may be a bad day, but beats the alternative. What if you really only have 25 minutes that day, because the leak initially caused a loss of cooling that you did not notice?
Most Aerospace applications by default require high strength to weight ratio. You need the strength obtained by heat treating, and usually other treatments for hardening. This requires the final precision after hardening which can only be done by grinding. Super finish refers to additional polishing beyond that, to a mirror like finish. Does not matter if spur or Helical for that purpose - but that opens up numerous additional design constraints.
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Gears
RF, Orig design from A109 and carried forward
My concern would particularly concentrate on what happened when the bearings go home with a lack of lube..........
VFR
- Input - helical pinion
- Planetary reduction - spur
- Mast drive from planetary carrier - splines
My concern would particularly concentrate on what happened when the bearings go home with a lack of lube..........
VFR
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Oneperrev,
Surely you dont really expect a pilot instruction to continue flying after losing the MGB oil. I dont know what the emergency checklist will say, but at a guess, it will be along the lines of "Land as soon as possible (30 mins). In the event of .....(eg increased Tq, noise, vibration), ...land immediately"
Personally, it gives me a better feeling to know that the gearbox has given some encouraging results in bench testing, and that I would have a good chance of completing the "Land as soon as possible" or a controlled ditching in the time available, rather than have the whole thing seize up in short order and drop me out of the sky!
Surely you dont really expect a pilot instruction to continue flying after losing the MGB oil. I dont know what the emergency checklist will say, but at a guess, it will be along the lines of "Land as soon as possible (30 mins). In the event of .....(eg increased Tq, noise, vibration), ...land immediately"
Personally, it gives me a better feeling to know that the gearbox has given some encouraging results in bench testing, and that I would have a good chance of completing the "Land as soon as possible" or a controlled ditching in the time available, rather than have the whole thing seize up in short order and drop me out of the sky!
Last edited by Non-PC Plod; 21st Apr 2013 at 12:01.
Gears
Vfr440,
Wrong. From existing AW139 literature:
Input: bevel gears
Planetary: spur
No splines between carrier and mast, integral connection
No combining gearbox, this was technology of the 70's. Gearbox design (by all OEMs) evolved significantly since then.
Wrong. From existing AW139 literature:
Input: bevel gears
Planetary: spur
No splines between carrier and mast, integral connection
No combining gearbox, this was technology of the 70's. Gearbox design (by all OEMs) evolved significantly since then.
NonPC,
that is exactly the confidence to avoid. If you wait until the grinding, it may already be too late. Land immediately does not mean without control. A MGB without lubrication will fail suddenly, matter of time, which is unpredictable if you keep sending power through it. I would not count on more than ten minutes, but even that is questionable.
that is exactly the confidence to avoid. If you wait until the grinding, it may already be too late. Land immediately does not mean without control. A MGB without lubrication will fail suddenly, matter of time, which is unpredictable if you keep sending power through it. I would not count on more than ten minutes, but even that is questionable.
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Most (if not all) of us would take the most conservative solutuion available if faced with a MGB malfunction. I think we can agree on this. That's the operational aspect of this discussion.
But the thread stated with a technical question (not the operational issue). MGB technolgy has improved dramatically over the years, both in design and manufacture. To compare today's MGB certificated under JAR/FAR 29 to older designs is not really relevant except to demonstrate how all things improve with time.
I would prefer to fly a MGB which has actually been tested to a level in excess of the minimum requirement rather than the other alternatives. And that demonstration (necessarily in a controlled environment) is still better than one only meeting the minimum requirement or not tested at all.
And, yes, an emergency source of oil lubrication to critical components being available after total loss of MGB pressure is better than running dry.
You make your operational decisions based on your equipment capabilities and weaknesses, along with your situational condition.
But the thread stated with a technical question (not the operational issue). MGB technolgy has improved dramatically over the years, both in design and manufacture. To compare today's MGB certificated under JAR/FAR 29 to older designs is not really relevant except to demonstrate how all things improve with time.
I would prefer to fly a MGB which has actually been tested to a level in excess of the minimum requirement rather than the other alternatives. And that demonstration (necessarily in a controlled environment) is still better than one only meeting the minimum requirement or not tested at all.
And, yes, an emergency source of oil lubrication to critical components being available after total loss of MGB pressure is better than running dry.
You make your operational decisions based on your equipment capabilities and weaknesses, along with your situational condition.
- VFR
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More on the AW189's 30 minute loss of lubrication gearbox here: AgustaWestland Sets New 'Run Dry' Standard for Helicopters
I/C
I/C
From a practical perspective what is the current requirement and how is that demonstrated? i.e. is it a one time demo under a set of conditions set or driven by the manufacturer or is it a standardised format from the regulator?
AgustaWestland has introduced measures to minimise friction through super finishing of gears and the introduction of special treatments and coatings as well as the use of heat-tolerant materials.
For those interested,
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From a practical perspective what is the current requirement and how is that demonstrated? i.e. is it a one time demo under a set of conditions set or driven by the manufacturer or is it a standardised format from the regulator?
From FAA FAR 29.927:
"(c) Lubrication system failure. For lubrication systems required for proper operation of rotor drive systems, the following apply:(1) Category A. Unless such failures are extremely remote, it must be shown by test that any failure which results in loss of lubricant in any normal use lubrication system will not prevent continued safe operation, although not necessarily without damage, at a torque and rotational speed prescribed by the applicant for continued flight, for at least 30 minutes after perception by the flightcrew of the lubrication system failure or loss of lubricant.
(2) Category B. The requirements of Category A apply except that the rotor drive system need only be capable of operating under autorotative conditions for at least 15 minutes.
(f) Each test prescribed by this section must be conducted without intervening disassembly and, except for the lubrication system failure test required by paragraph (c) of this section, each part tested must be in a serviceable condition at the conclusion of the test."
The FAA 30 min. loss-of-lube qualification only requires a single test article passing a single test procedure. On one hand, it is quite difficult to design a high-performance helicopter MRGB capable of meeting this test requirement, and conducting the test itself is quite expensive. But on the other hand, due to the large number of variables that can potentially have a significant impact on the results of this particular test, a single test article passing a single test does not really provide a statistically relevant validation of the system's design and reliability analysis. As my high school chemistry teacher was fond of saying about experiments or testing, "Nothing actually happens unless it happens more than once."
In the article linked, AgustaWestland's chief gearbox engineer (Giuseppe Gasparini) claims there are basically five factors that determine an MRGB's loss-of-lube operational capability. But in reality there is another factor he did not mention which has more potential impact than all the others combined. That is the design trade-off between MRGB weight and reliability. It is theoretically possible to design a rotorcraft MRGB that is capable of operating for hundreds-of-hours with nothing more than a mist of oil for the gears and bearings. But such an MRGB would likely be many times the size and weight of conventional designs.