Longranger thought
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after working around busy airports with a b47 id have to stop the blades as quick as posible so i could leave the machine to get pax from the terminal many times in the day. i got quite good at slowing the blades with collective. it slows them realy fast at high rpm but as the blade slows the wind effect causes more sailing so you move the cyclic slowly toward the wind direction to keep the disc level. then when the cyclic runs out you start to put the collective back down to keep the disc level. once it gets to the point that the effect is gone, put the collective right down and cyclic in the centre and climb up and stop it with my hands. only did this when i had to, and not realy good in gusty conditions as the disc will tilt verry quickly with the collective up and a puff from a different angle. seems to work just the same with the jet ranger??
those straps are what take the weight of the blades, they twist when pitch is applied, why would it be bad for them to twist without being under strain?? because another thing i do is leave the collective up and the cyclic away from wind slightly which holds the blades over without turning in windy conditions so they dont bounce (if you cant tie it down or going again shortly)
those straps are what take the weight of the blades, they twist when pitch is applied, why would it be bad for them to twist without being under strain?? because another thing i do is leave the collective up and the cyclic away from wind slightly which holds the blades over without turning in windy conditions so they dont bounce (if you cant tie it down or going again shortly)
Join Date: Feb 2005
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Lowest point on the blade's rotation should be 11o'clock if I'm not mistaken. I'de venture a guess that in some wind the blade will come to rest in it highest/lowest flapping points in the disc rotation. All irrelevent if you use the rotor brake. Then the main goal is preventing buying beer for the crew when u stop it off-centre.
I've recently had a engineer tell me that the factory teaches pumping the brake from 50% and applying full rotor brake from 40%. This apparently heats the brake disc enough to prevent the shudder some machines have.
Any opinions on this? I know it works, but since I got the idea from word of mouth, its kinda not enough.
I've recently had a engineer tell me that the factory teaches pumping the brake from 50% and applying full rotor brake from 40%. This apparently heats the brake disc enough to prevent the shudder some machines have.
Any opinions on this? I know it works, but since I got the idea from word of mouth, its kinda not enough.
This is the reply from Bell Product Support Engineering:
Bell Helicopter does not publish what not to do in the manuals, we do not publish any scenarios of things or procedures that are not authorized or approved. We only publish approved procedures.
Failing of carrying the approved procedures (sic) may lead to damage of the helicopter. To answer your question on shut down the cyclic has to stay in the center and collective down, if you pull on the collective it will change the pitch of the blades, create excessive flapping which will result in mast bumping.
Failing of carrying the approved procedures (sic) may lead to damage of the helicopter. To answer your question on shut down the cyclic has to stay in the center and collective down, if you pull on the collective it will change the pitch of the blades, create excessive flapping which will result in mast bumping.
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From my understanding, Lifting the collective on both the 205 and 206 after shutdown of the engine increases coning up on both the rotor blades and can overstress the inboard doublers which can become dissbonded. At normal rpm not as much coning occurs. At very low rpm, more coning occurs inboard.
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Undoubtedly, the loads that stress the blades and head when you raise the collective are induced from the bouncing and thumping the rotors can make under some wind conditions, and not due to the tiny lift forces generated by the blades are they sail aound the mast.
At low rpm, when the pitch is raised, both blades (upwind and downwind) go to the new increased angle, but only the upwind blade sees a lift increase because the other blade is at or beyond stall in its down-wind state, so it is non-aerodynamic. The upwind sweeping blade lifts up more than it would have at flat pitch, and then crashes down as it swings down-wind and stalls and its mate sees the lift. This big up/down swing (we have all seen it, it occurs often enough when the pitch is flat) is vastly increased if you raise the collective, and the shock loads on blades and head are not nice. Additionally, the chance to bump the mast is also increased, as the Bell blurb says.
This crash-bang cycle can be induced if you tilt the swashplate very much with cyclic, too.
At low rpm, when the pitch is raised, both blades (upwind and downwind) go to the new increased angle, but only the upwind blade sees a lift increase because the other blade is at or beyond stall in its down-wind state, so it is non-aerodynamic. The upwind sweeping blade lifts up more than it would have at flat pitch, and then crashes down as it swings down-wind and stalls and its mate sees the lift. This big up/down swing (we have all seen it, it occurs often enough when the pitch is flat) is vastly increased if you raise the collective, and the shock loads on blades and head are not nice. Additionally, the chance to bump the mast is also increased, as the Bell blurb says.
This crash-bang cycle can be induced if you tilt the swashplate very much with cyclic, too.
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john
looks like you got a cut and pasted answer there mate. i dont know what he means by it, but there's definantly published information in the 206 manual about what not to do.
warning: could cause injury or death
caution : could cause damage to machinery
note: important information
eg. caution : vne 69kts with front doors off
caution : do not try an airstart above 12000ft as the TOT will rise too fast to control
caution : do not light off below 12% N1
caution : do not try to start above 150deg TOT
these are just the ones i can remember, if they realy thought pulling the collective up during shutdown would be a problem it would have a caution in the book. eg. caution : do not raise collective to slow blades on shut down.
also at the begining of the general section it says (from memory) :this section is for standardization purposes only and may not be suitable in all aplications!!
of course you can mast bump if you dont do it properly , you can mast bump just by putting the cyclic forward while the engines running, you can watch the bump stops touch. you can cause lots of damage in a helicopter if something is not done right but if it IS done right it works quite well.
warning: could cause injury or death
caution : could cause damage to machinery
note: important information
eg. caution : vne 69kts with front doors off
caution : do not try an airstart above 12000ft as the TOT will rise too fast to control
caution : do not light off below 12% N1
caution : do not try to start above 150deg TOT
these are just the ones i can remember, if they realy thought pulling the collective up during shutdown would be a problem it would have a caution in the book. eg. caution : do not raise collective to slow blades on shut down.
also at the begining of the general section it says (from memory) :this section is for standardization purposes only and may not be suitable in all aplications!!
of course you can mast bump if you dont do it properly , you can mast bump just by putting the cyclic forward while the engines running, you can watch the bump stops touch. you can cause lots of damage in a helicopter if something is not done right but if it IS done right it works quite well.
Last edited by vorticey; 8th Oct 2006 at 06:03.
Surely it's not rocket science to conclude that at low rpm your cyclic control is very ineffective and so you have no way of controlling the disc flapping if you choose to raise the lever to slow down the rotors - therefore as Bell says, mast bumping may occur which I think is universally accepted as a bad thing.
Interested as to a detailed explanation of why the 11 o'clock is the lowest point for the rotors........maybe it is a local time v GMT answer
Interested as to a detailed explanation of why the 11 o'clock is the lowest point for the rotors........maybe it is a local time v GMT answer
