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View Full Version : Random thoughts from the PPRUNE bar....


HELOFAN
10th Jan 2008, 18:45
Why isn't there a web site that shows what countries fly under which flight rules E.G., FAA, CAA, CASA, JAA etc?

:confused:

Simply type in a country ( or click ) and it shows all, or select the flight rules and it shows the countries that accept it, a little bonus there would be to show you what it would take to cross over using one type of rules to another.

That would be nice wouldn't it. :)

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Also ever wondered how a set of limits are imposed on a components life?

for E.G., Its a beautiful sunny day & your flying along just you and your instructor when suddenly he unleashes a throttle chop on you.

":mad:" your inner voice says ":mad: me, :mad: me"

"NICE ONE" you calmly say to your tormentor... I mean instructor, as though to throw him off noticing the stench erupting from your side of the cockpit, As you jam down the collective & mash in right pedal, all the little reminders pop in your head like airspeed and attitude and where am I putting it down this time?
And hey..why not make a quick call to someone that cares & let them know that you may not be returning the aircraft to the airport today......wind wind..where is the bloody wind from & don't forget to check the collective just before you flare to avoid over speeding the rotor head, gear box & rotors .....

"Hmm" you think to yourself as you are madly trying to keep everything spinning the way the designers intended...


" I wonder what the actual RPM limit is on the rotor head before the bearings explode into tiny fragmented pieces of shrapnel,:eek: just seconds before the head detaches itself from the mast ,:eek: taking the over sped rotors with it into another direction than the rest of the fuselage is heading thus ending my flight earlier than intended?":eek:

I also wonder how long it is tested for and at what incremented RPM's and then do they just crank up the RPM's on a brand new one at a constant rate until it explodes....I mean fails.

:suspect:

And how many times can it be taken to X RPM until if fails at a normal RPM due to over stress from too many over speeds?

I wonder indeed , and also if these limits can be found on the internet anywhere and are there any videos of this destructive testing?

Would the manufacturers actually show this info to the public as I find this sort of info quite interesting let alone valuable and entertaining but I bet its a liability thing or something of the sort.

Then it makes me wonder how they test the rest of the components and where the heck could one view this sort of carnage being performed in the name of interests in safety?

I mean if we can watch braking tests & wing deflection tests on the A380 aibus, why cant we watch helicopter components being broken too?

:E

Take a seat, first beer is on me.

HF

ericferret
10th Jan 2008, 19:21
From memory the safety factor in normal conditions on a starflex as fitted to a squirrel is x7.
That comes from the AAIB accident report into the squirrel lost a few years ago in the UK.

HELOFAN
10th Jan 2008, 19:46
Thats spinning up pretty darn fast then compared to normal operation.
Not that you count on it being safety margin, its just interesting.


Thanks for adding some input.

HF

Helipolarbear
10th Jan 2008, 21:18
Hey Helofan....Just exactly how many pints have you had?....Get me Double JD....lots of ice and continue with your avalanche of amazing stuff...good on ya!:)

lelebebbel
10th Jan 2008, 22:21
" I wonder what the actual RPM limit is on the rotor head before the bearings explode into tiny fragmented pieces of shrapnel,

precise failure-values are pretty much impossible to determine, especially if you consider metal fatigue. Take a batch of 10 brand new rotor heads, and maybe 8 of them explode at 120%, one at 115% and one at 125%. Take the same batch but use them for 1000hrs before the test, and you might get completely different results, who knows!
The manufacturers are smart enough not to let anyone see those kinds of tests. Their job is to come up with numbers that gurantee an explosion-free component life for every single part they make.

And why did we get to see the wing deflection tests on airliners? Probably because passengers got scared looking at the moving wingtips, thinking it's about to fall off.

alouette3
10th Jan 2008, 23:30
I think Shawn Coyle and his ilk(test pilots ,I mean) should weigh in on this as they have the inside info. on testing.;)
Secondly, I think the public should really see how tough these whirlybirds are. After all, most of the people get their info. from Hollywood. I have yet to see a movie where a helicopter appears and does not crash/explode spectacularly after a few frames.:eek:
Just my .02 worth.

sunnywa
11th Jan 2008, 00:20
HF,

I would say that after what you had to drink at the bar, it wouldn't really matter what Nr the rotor got to as I don't think you would worry about it much (Óh I say, there goes one blade, darn another, well only a couple to go)

I'll have half and pass the crisps.:O

helimutt
11th Jan 2008, 07:22
I hope the instructor who 'throttle chops' you realises you have had a few beers:ok:, oh, and that it's not a practice which should really be used in training.

I was told that an increase of 10% RRPM from 104% on an R22 causes the force on the spindles to go from 4.5 tons of pull to 9 tons of pull. Any truth in that?
I think quite probably.:uhoh:

lelebebbel
11th Jan 2008, 09:49
104% is 530 RPM, 114% would be 581 RPM

if you know how much a blade weighs and how far from the hub it's CoG is, you can just enter it right here and find out:
http://www.soft-calc.com/calculator/centrifugal_force_calculator_e.html

The centripetal (or centrifugal) force increases at a more than linear rate, but I don't think it would double when increasing RPM by only 10%.

helimutt
11th Jan 2008, 09:54
Oh come on, it's early. !!:hmm:

HELOFAN
11th Jan 2008, 15:14
I wasnt aware I was the barman but I will assume the role.

Thanks for taking a seat and joining in on the discussion, hope you like the drinks.
:ok:

* lelebebbel, I would agree with you thoughts on the testing & I too would assume an average is the only way to gauge it.
I am a mech engineer and have a vague idea of what they may do.
I would like to see figures or at least testing and results, not because I would keep in mind the highest result but just the average & then keep in mind the lowest figure and then try to believe that it will be reliable under normal fight ops within the "expected" life limits.

Though we assume that they are a resonably well designed component because we are not reading lots of ( at least I am not seeing them ) crash reports pointing the finger at hubs failing.......right?:ooh:

I also would like to see it because I simply want to see what they do when they do go.:ouch:

I also agree with your thinking that the passengers freak out about the wing flexing, i like sitting over the wing and watching it flex in turbulence.
Maybe we could start telling the manufacturers we are scared that the head will explode and they will show us the testing?:E

*alouette3 I agree. I welcome Shaun or any of the test guys to the bar. A little insight to how and why we are told what is reliable would be great.

*sunnwa, thats about right too but its that darn vibration whilst the forces are fighting to be equal that would annoy me , least till that last big bit departed then all would be smooth & sunny again.


*helimutt, I would think those figures could be close, possibly an exponential formula at work there.

Hmm, my glass is empty.

Another round?
:)
HF