Technical question for the fly boys
Discussion
more so helicopters
have had a google but all came up radio control models
"Generally the RPMs are around 120 to 400, depending on the size of the blades."
But how the hell do they balance the blades/props ??
One comment was to weigh the blades.
or are they run up to speed on a balancing machine
Ta
have had a google but all came up radio control models
"Generally the RPMs are around 120 to 400, depending on the size of the blades."
But how the hell do they balance the blades/props ??
One comment was to weigh the blades.
or are they run up to speed on a balancing machine
Ta
Marty63 said:
more so helicopters
have had a google but all came up radio control models
"Generally the RPMs are around 120 to 400, depending on the size of the blades."
But how the hell do they balance the blades/props ??
One comment was to weigh the blades.
or are they run up to speed on a balancing machine
Ta
Can't answer for helicopter blades however for aero-engines the fan blades are weighed and paired with an equivalent mass blade. The whole assembly is then balance weighted using the same process as a tyre. have had a google but all came up radio control models
"Generally the RPMs are around 120 to 400, depending on the size of the blades."
But how the hell do they balance the blades/props ??
One comment was to weigh the blades.
or are they run up to speed on a balancing machine
Ta
I imagine a similar process is used on helicopters, however they have fewer blades to pair off and often odd number of blades.
I think it is to do with vibration anaylsis
Basically they look at the shaft and see which way it is pulling while spinning which allows them to balance the blades next time they are stopped. As it will have a tiny weeny bit of wobble in the bearings which can be measured and if it is constantly pulling towards one blade then that blade is to heavy
Basically they look at the shaft and see which way it is pulling while spinning which allows them to balance the blades next time they are stopped. As it will have a tiny weeny bit of wobble in the bearings which can be measured and if it is constantly pulling towards one blade then that blade is to heavy
It's done by a combination of vibration analysis and subsquent weighting of individual blades, usually by adding shims at the blade tip, combined with IR in-flight tracking of the blades to determine that they're all balanced not only in terms of weight but also in terms of the profile they're flying, since this also contributes to the overall balance of the rotor disk. The latter can be adjusted by tweaking individual trim tabs and/or the control linkages for individual blades.
On a helicopter, the rotor blades are matched for weight, but once in situ, you need one of these to 'track and balance'-
http://www.dsi-hums.com/Honeywell-Chadwick-Helmuth...
http://www.dsi-hums.com/Honeywell-Chadwick-Helmuth...
For dynamic blade tracking, how about holding a canvas covered board (the lower end of which is on the ground) up to the tips of a rotating rotor disc, so that the tip of each blade clips the canvas and leaves a mark. If you have previously marked each tip with chalk, (a different colour for each blade tip) you will be left with coloured marks on the canvas. From this you can determine the blade adjustment required to bring the marks into line at the correct height.
So who is laughing? Who thinks I'm talking nonsense?
Think again. This is how I was taught as an apprentice. I've seen it done this way on Gazelle helicopters.
Modern methods use dedicated blade tracking and balancing kits incorporating accelerometers to determine out of balance vibration and a strobe type viewer. The operator will be able to view a rotating rotor disc as though it were stationary. In this way, the position of the blades at the point of maximum imbalance and the 'height' each blade is flying at can be determined. It can be done both on the ground and in flight and is a specialist skill needing dedicated training.
Oh, and it was really a question for the engineers, not the 'fly boys'.
So who is laughing? Who thinks I'm talking nonsense?
Think again. This is how I was taught as an apprentice. I've seen it done this way on Gazelle helicopters.
Modern methods use dedicated blade tracking and balancing kits incorporating accelerometers to determine out of balance vibration and a strobe type viewer. The operator will be able to view a rotating rotor disc as though it were stationary. In this way, the position of the blades at the point of maximum imbalance and the 'height' each blade is flying at can be determined. It can be done both on the ground and in flight and is a specialist skill needing dedicated training.
Oh, and it was really a question for the engineers, not the 'fly boys'.
Edited by JoeBolt on Sunday 20th November 13:47
It is a question for an engineer really, as there are only 2 answers you will get from a a pilot:
1. The blades are balanced??? Really?? Is that why it flies so badly? Is that why I have to do so many airtests?
2. Magic (the real answer to anything vaguely related to helicopter aerodynamics, although pixie dust is an acceptable alternative answer on occassion)
1. The blades are balanced??? Really?? Is that why it flies so badly? Is that why I have to do so many airtests?
2. Magic (the real answer to anything vaguely related to helicopter aerodynamics, although pixie dust is an acceptable alternative answer on occassion)
davepoth said:
So the Fly-Boy answer is "I have a man who does it for me"?
No....I normally have many men who do it for me!!! Well they mess around with weights, adjustments to pitch change rods and other assorted engineering stuff and then make me go and fly the thing and see if it kills me. Not really that different to normal helicopter flying, the cab will kill you as soon as it can!
seemed more of a plane train boat type question rather than in
the technical section which may be deemed as more car based
which i could not find any hoo, did not want to upset an engineer chap, soz
in that case you might know the answer to this one,
on boats if a prop spins too fast it has zero effect and cannot push water to gain movement,
it's called cavitation.
is this the same case in planes or copters,
assume it could, if a plane/copter prop was to spin so fast
would the same happen, going too fast to have any effect on the air around it ??
my thoughts are that it would be the same but are there any examples.
not trying to be a smart ass, just woundering if the same princepals(ish) are present in air and water as i am water based in my playing.
the technical section which may be deemed as more car based
which i could not find any hoo, did not want to upset an engineer chap, soz
in that case you might know the answer to this one,
on boats if a prop spins too fast it has zero effect and cannot push water to gain movement,
it's called cavitation.
is this the same case in planes or copters,
assume it could, if a plane/copter prop was to spin so fast
would the same happen, going too fast to have any effect on the air around it ??
my thoughts are that it would be the same but are there any examples.
not trying to be a smart ass, just woundering if the same princepals(ish) are present in air and water as i am water based in my playing.
Marty63 said:
seemed more of a plane train boat type question rather than in
the technical section which may be deemed as more car based
which i could not find any hoo, did not want to upset an engineer chap, soz
in that case you might know the answer to this one,
on boats if a prop spins too fast it has zero effect and cannot push water to gain movement,
it's called cavitation.
is this the same case in planes or copters,
assume it could, if a plane/copter prop was to spin so fast
would the same happen, going too fast to have any effect on the air around it ??
my thoughts are that it would be the same but are there any examples.
not trying to be a smart ass, just woundering if the same princepals(ish) are present in air and water as i am water based in my playing.
Cavitation is when you get a phase change in the water and it flashes to a steam bubble. You can't get precisely the same effect in air. the technical section which may be deemed as more car based
which i could not find any hoo, did not want to upset an engineer chap, soz
in that case you might know the answer to this one,
on boats if a prop spins too fast it has zero effect and cannot push water to gain movement,
it's called cavitation.
is this the same case in planes or copters,
assume it could, if a plane/copter prop was to spin so fast
would the same happen, going too fast to have any effect on the air around it ??
my thoughts are that it would be the same but are there any examples.
not trying to be a smart ass, just woundering if the same princepals(ish) are present in air and water as i am water based in my playing.
If you put more power into a piece of turbo machinery what happens is it spins faster you get more pressure rise until you move into an unstable region and you get a compressor stall as the flow briefly reverses. The effects of this range from a bang or a pop to a flame out or major compressor damage.]
Crossflow Kid said:
Who by? Trenchard himself? Not been done like that for decades.
You're not far off with the reference to Trenchard. I was one of his finest, but in the 1980s not the 1920s. I last saw the 'chalk' method of Gazelle blade tracking being carried out in 1997, which is the last time I was at that particular foreign airbase. There is no reason for them not to be still doing it that way today. It's a tried and trusted method, needing no expensive equipment.JoeBolt said:
Crossflow Kid said:
Who by? Trenchard himself? Not been done like that for decades.
You're not far off with the reference to Trenchard. I was one of his finest, but in the 1980s not the 1920s. I last saw the 'chalk' method of Gazelle blade tracking being carried out in 1997, which is the last time I was at that particular foreign airbase. There is no reason for them not to be still doing it that way today. It's a tried and trusted method, needing no expensive equipment.I was at Halton in '87 btw.
It's very nice having a man who T&Bs the blades to perfection before flight. But then stuff happens in flight to mess it all up again.
I once had a metre of blade tape come unstuck from the leading edge of one blade. For about a minute it was still hanging on by a thread, so making one blade significantly longer and less slippery than the others.
That baby shook.
I once had a metre of blade tape come unstuck from the leading edge of one blade. For about a minute it was still hanging on by a thread, so making one blade significantly longer and less slippery than the others.
That baby shook.
Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff