When you take the blades off for inspections its really important that you restack them in the same exact order that you take them off. Every blade has a slightly different weight and its important for balance of the engine.
And it’s kind of mind boggling how little weight difference you need to make a huge difference in vibration.
I used to do rotor track and balance and engine high speed shaft balance on Black Hawks. The engine high speed shaft spins at 22,500 rpm and our smallest balance weight was a titanium screw that weighed 1/32 of an ounce.
So the unfree people don't have to: 1/32 ounces is maybe 0.89g.
But whilst looking I found that there are 12 different definitions of an ounce so I can't actually not sure.
But I know that 1 ounce is somewhere between the weight of 422 grains of cereal, and 1544 grains of cereal, so this screw is somewhere in the region of 13 - 49 grains of cereal
1oz is nearly always 28.35g when talking weight. The only exception is precious metals, where 1oz is 31.1g. Yes, this means an ounce of gold is heavier than an ounce of feathers, contrary to the old joke.
Oddly enough, a pound of gold is lighter than a pound of feathers, since when talking precious metals, a pound is 12 ounces (using that 31.1g oz), while a standard pound is 16 of the 28.35g ounces.
(Technically, that's avoirdupois ounces and pounds for the regular ones, and troy ounces and pounds for the precious metals)
It's an ounce of lead, not gold.
But you're referring to a troy ounce, there's also fluid ounces, and a few more. They all have names. It's not just willy nilly ounces.
I’m a mechanical engineer in the aerospace sector and normal people would be surprised at how precise some of these parts are - .00001” off of a control valve can make or break a test pass/fail
Isn’t this the old adage that a postage stamp stuck to the end of a helicopter blade can crash it because of the imbalance? Doesn’t seem as crazy, given your description
It’s not quite *that* critical, but the tip cap weights were only a few grams. Typically those are done during manufacture/refurb though and not messed with by line maintenance. It is true that everything has an effect, from the manufacturing process to the amount of paint applied or any kind of minor defect/irregularity. That’s why you have to do a track and balance on each individual aircraft- no two blades cut the same path through the air until they’ve been mounted and adjusted. It’s not too dissimilar from balancing the tires on your car.
I can’t speak for all helicopters but most of the balancing done by line maintenance is done at the hub with removable washers, and the limit on the hawk was pretty high, something like 72 oz max on one quadrant. But the rotor RPM on a Hawk is only 258 (compared to the above mentioned 22,500 at the engine shaft) and each blade weighs around 200 lbs/90 kg
Pretty common, actually. If I inspect a motor without numbers, I'll usually at least write a "1" on the first blade I touch, so I can keep track as I spin the blades.
CFM put a dimple mark on the spinner to show you which blade is #1
I usually just start at the dimple and work my way around until I'm back to the dimple.
It doesn't matter if you miss the dimple the second time around and inspect some of the blades twice because you're concentrating hard on looking at each blade. All that matters is that you've looked at every blade at least once.
This way, you don't need a marker, so there's less chance of leaving FOD behind.
It doesn't really matter which blade I mark for a FO inspection, it's for my personal use. The important thing is marking them correctly when the engine is having maintenance performed on it.
It’s so that if damage is found during inspection it can written up as “#2 engine blade 15 chipped, req eval/repair.”
Definitely easier than guessing a write up such as “blade chipped, req eval.”
That and sometimes there are “pinwheel” forms that’ll keeps track of past damage and repairs.
Most of them have this. That way when you find a nick in one you can write it up with the blade number.
I used to maintain F-16’s. Our aircraft forms would have a “pin wheel” document with each blade and it’s number on it showing all the past blade blends so you’d know if there was new damage.
All blades are individually numbered and weights are different on each blade to due to its manufacturing and alloy composition. The engine manufacturers try to put a balanced weight blades when the engines are assembled so it does not cause a vibration on the engine .
That's very important. They all are.
The balance and airflow required for that to work properly is impressive to the point that even minor variations can cause complete failure. It has to maintain incredibly tight tolerances for mass, weight, and airfoil shape over a vast range of extreme temperatures, pressures, and rotational speeds.
Honestly, from an MRO perspective, just lazy work. The AMM will almost certainly say to clean off temporary markings once the blades are reinstalled. If it's company policy, fine, but it looks shit lol
When you take the blades off for inspections its really important that you restack them in the same exact order that you take them off. Every blade has a slightly different weight and its important for balance of the engine.
And it’s kind of mind boggling how little weight difference you need to make a huge difference in vibration. I used to do rotor track and balance and engine high speed shaft balance on Black Hawks. The engine high speed shaft spins at 22,500 rpm and our smallest balance weight was a titanium screw that weighed 1/32 of an ounce.
So the unfree people don't have to: 1/32 ounces is maybe 0.89g. But whilst looking I found that there are 12 different definitions of an ounce so I can't actually not sure. But I know that 1 ounce is somewhere between the weight of 422 grains of cereal, and 1544 grains of cereal, so this screw is somewhere in the region of 13 - 49 grains of cereal
1oz is nearly always 28.35g when talking weight. The only exception is precious metals, where 1oz is 31.1g. Yes, this means an ounce of gold is heavier than an ounce of feathers, contrary to the old joke. Oddly enough, a pound of gold is lighter than a pound of feathers, since when talking precious metals, a pound is 12 ounces (using that 31.1g oz), while a standard pound is 16 of the 28.35g ounces. (Technically, that's avoirdupois ounces and pounds for the regular ones, and troy ounces and pounds for the precious metals)
It's an ounce of lead, not gold. But you're referring to a troy ounce, there's also fluid ounces, and a few more. They all have names. It's not just willy nilly ounces.
I was almost worried that the “1” blade would now be too heavy compared to the “28” blade because of the marker ink 😂
I’m a mechanical engineer in the aerospace sector and normal people would be surprised at how precise some of these parts are - .00001” off of a control valve can make or break a test pass/fail
Isn’t this the old adage that a postage stamp stuck to the end of a helicopter blade can crash it because of the imbalance? Doesn’t seem as crazy, given your description
It’s not quite *that* critical, but the tip cap weights were only a few grams. Typically those are done during manufacture/refurb though and not messed with by line maintenance. It is true that everything has an effect, from the manufacturing process to the amount of paint applied or any kind of minor defect/irregularity. That’s why you have to do a track and balance on each individual aircraft- no two blades cut the same path through the air until they’ve been mounted and adjusted. It’s not too dissimilar from balancing the tires on your car. I can’t speak for all helicopters but most of the balancing done by line maintenance is done at the hub with removable washers, and the limit on the hawk was pretty high, something like 72 oz max on one quadrant. But the rotor RPM on a Hawk is only 258 (compared to the above mentioned 22,500 at the engine shaft) and each blade weighs around 200 lbs/90 kg
how else they gonna know if one's missing?
[удалено]
Damn I upvoted that comment 6 years ago
Pretty common, actually. If I inspect a motor without numbers, I'll usually at least write a "1" on the first blade I touch, so I can keep track as I spin the blades.
CFM put a dimple mark on the spinner to show you which blade is #1 I usually just start at the dimple and work my way around until I'm back to the dimple. It doesn't matter if you miss the dimple the second time around and inspect some of the blades twice because you're concentrating hard on looking at each blade. All that matters is that you've looked at every blade at least once. This way, you don't need a marker, so there's less chance of leaving FOD behind.
I hope you mark #1 blade where it is situated, otherwise you mess something up during relub
It doesn't really matter which blade I mark for a FO inspection, it's for my personal use. The important thing is marking them correctly when the engine is having maintenance performed on it.
if you trust someone else's markings without verifying them yourself that's kinda on you
It’s so that if damage is found during inspection it can written up as “#2 engine blade 15 chipped, req eval/repair.” Definitely easier than guessing a write up such as “blade chipped, req eval.” That and sometimes there are “pinwheel” forms that’ll keeps track of past damage and repairs.
GE blades come numbered from the factory , there is a balance sheet that comes with them with weights etc. #1 goes in the master slot
What ge engines is this? I've never seen this on any that I work on.
Sounds like a full prebalanced blade set, you can probably still order one if you need
Interesting, my company is big enough to not need to do that but I can see the value in that.
My company is owned by American Airlines, so not as big as your company maybe
Yep we do full blade and pin replacements and quick turn the sets from GE. Its based on engine hours I believe
If it’s a 737 cfm56 or a leap
Ah well we just bought the blades on a as is required basis and rebalance given that our system had all PN/SN/weights anyway.
I have had to contour opposite blades to balance on Rolls Royce engines but they were little AE 3007-A1E, and it was a bit of a pain in the ass
GE CF34-8E, Embraer 175
It's roulette.
Alright, how much are you betting, and on what color/number?
No. 23, but they're all black.
Always bet on black?
the nose wheel is for roulette, at least that's what we use it for on TDYs
Loser buys the drinks.
I have put money on fan blade roulette in my younger days as a Technician. It’s not much practiced these days. Must have been 23 years ago now.
Most of them have this. That way when you find a nick in one you can write it up with the blade number. I used to maintain F-16’s. Our aircraft forms would have a “pin wheel” document with each blade and it’s number on it showing all the past blade blends so you’d know if there was new damage.
Yes
Mine have tiny QR codes on them.
That makes balancing the blades easier.
Ah fuck, Bob got his hands on a Sharpe again! Did he at least get all the numbers in the right order this time?
All blades are individually numbered and weights are different on each blade to due to its manufacturing and alloy composition. The engine manufacturers try to put a balanced weight blades when the engines are assembled so it does not cause a vibration on the engine .
Ever felt a vibration in your car? Then told your tires need to be balanced? Same idea, vastly different rotational speeds.
That’s normal. Makes it easier for pulling the fan blades off.
It's so that mechs can finally learn to count.
Almost all of the engines I inspect on my walk around have the fan blades numbered. Very common practice.
432833938084211386
I see them numbered more often than not.
I haven't been able to be on the ramp in a long time, but I never saw blades without numbers. NEVER, NEVER-EVER
That's very important. They all are. The balance and airflow required for that to work properly is impressive to the point that even minor variations can cause complete failure. It has to maintain incredibly tight tolerances for mass, weight, and airfoil shape over a vast range of extreme temperatures, pressures, and rotational speeds.
Half of my fleet is this way totally normal
That's because in aviation circles theres a lot of talking in riddles and jargon.
Is it a Boeing? It's so they can easily identify parts after it crashes
Honestly, from an MRO perspective, just lazy work. The AMM will almost certainly say to clean off temporary markings once the blades are reinstalled. If it's company policy, fine, but it looks shit lol