main rotor blows off

[ambision]

So... I somehow manage to get the Huey's main rotor blades to blow off the fuselage

[yes, they just BLOW the F#ck OFF].

I'm curious how and why it constantly happens???

Any help would much appreciated

thanks :-)

 

[26-J39]

Its called Mast Bumping.

Here : https://www.youtube.com/watch?v=OTTr-vAkce8

[ambision]

thank you :-)))

 

I've learned something today :-)

[Flagrum]

I think, there could also be a bug involved in this (reported a loooong time ago):

 

at least with my G940 stick I can deliberately separate the rotor from the fuselage by forcing it to mast-bump:

moving the cyclic horizontally (bank) or vertically (pitch) is without problems and I can deflect the stick fully. But if I deflect the stick diagonally 100%, mast bump occurs instanteously.

 

I think, this has to do with pythagoras: the range of the diagonal movement is larger than the range horizontally or vertically (= the anticipated max. radius of stick deflection). That way you can deflect directly beyond the safe margin, causing the rotor disc to tilt too far and causing an instant mast bump.

 

You can't even deflect the stick fully deflected in a circular manner - as you then also reach the "corners" of the diagonal deflection ...

 

Imho this should not be possible...

[26-J39]

Hmm interesting Flagrum.. I've never had a real issue with rotor seperation.. I might have to test this out..

 

Edit: Got me thinking Flagrum, I do agree that in the diagonal the stick has a larger range of deflection..( makes sense unless some software compensation in various sticks) question is, is it like this in the RL airframe? I would think we would need to look at the mechanics of the cyclic assembly in the RL huey, does it have a "square stick range" or circular.. I think this is the real question.. :book:

Edited January 27, 2015 by 26-J39

[Flagrum]

Hmm interesting Flagrum.. I've never had a real issue with rotor seperation.. I might have to test this out..

 

Edit: Got me thinking Flagrum, I do agree that in the diagonal the stick has a larger range of deflection..( makes sense unless some software compensation in various sticks) question is, is it like this in the RL airframe? I would think we would need to look at the mechanics of the cyclic assembly in the RL huey, does it have a "square stick range" or circular.. I think this is the real question.. :book:

Not impossible, but I doubt it somehow ... That would be like having an (unlabeled) self destruct button.

 

I watched one of those old instructional filns of the us army. Iirc, they tried to demonstrate how far down the rotor blades can get when the helo is on the ground. Viewed from the outside, the pilot deflected the cyclic in such a circular manner so that the tilted rotor disc was moving a couple of times around the helo. Of course I wanted to try that as well - to compare if our rotorblades come down as much as in the video. Well, and *BANG*, immediately my blades went AWOL ... :o)

[DaveRindner]

Mast bumping. FLy the ship so that there is always at least .5g on rotor. It was/is a real life flight limitation that killed many a Western UH-1 crews in 1960's and 1970's. AVOID NEGATIVE G's. For overhilliing use collective instead of cyclic. I think this is a limitation on any semi-rigid or fully articulated rotor.

[b00ce]

Mast bumping. FLy the ship so that there is always at least .5g on rotor. It was/is a real life flight limitation that killed many a Western UH-1 crews in 1960's and 1970's. AVOID NEGATIVE G's. For overhilliing use collective instead of cyclic. I think this is a limitation on any semi-rigid or fully articulated rotor.

Something like that. If you're planning on doing any crazy loops or maneuvers, make sure you're pulling a bunch of power to keep the G-forces positive in relation to the helicopter (Even though it may be upside down :pilotfly:)

 

This method is not approved for the real life. Like at all.

 

Seriously. Guys. Don't do it.

[Snarf]

The Huey employs a semi rigid underslung rotor head. The under slinging means that the rotor hangs below the flapping hing. Imagine an upside down T and you have the relationship of the blades and yoke to the flapping hing. This increases stability and minimises coriolis effect which occurs when the blades flap to correct dissymmetry of lift. As blades flap up or down from a flat position the tips move through a curve. This effectively means the distance from the blade tip to the flapping hing shortens for a blade moving up and lengthens for a blade moving down towards the plane of rotation. This causes a change in the rotational speed of the tip as the tip is going around a smaller circle when it flaps up and underslinging pushes it out so that the tip no longer moves through a curve but relatively straight up and down.

You can see in this image the effect of the underslinging with the bump stop contacting the mast and the yoke and blades effectively moved to the right.

 

The down side to this is that when the rotor is subject to any negative G the rotor is effectively like a right way up T and very unstable which causes the bump stops to impact the mast and severe it. Typically this will cause the rotor to swing through the co pilots head or through the tail boom.

Edited May 20, 2015 by Snarf

[iFoxRomeo]

As everything was said... but not from everyone, I´d like to add something.

 

Flagrum, the cyclic-stick indeed has the movement range of a square "bk". The corners are not mechanically limited. Modern helicopters have e.g. a octagonal range where the corners are cut, like a "stop sign".

 

I made a picture(yes with ms paint) to show the increased movement range when the stick is positioned in one corner "y".

 

 

 

"g" is the normal movement range, and as long as you stay within the limits(slope!, "stick travel speed", g-load, RotorRPM, bank and pitch) you won´t bump the mast. Within the flight envelope you won´t have the need to move the cyclic stick to one corner.

But if you move it to one corner you increase the travel range from "g" to "y" which is an increase by 41,4% of the normal travel range. This will cause mastbumping and finally separate the rotor.

 

Fox

[Tombstone]

But if you move it to one corner you increase the travel range from "g" to "y" which is an increase by 41,4% of the normal travel range. This will cause mastbumping and finally separate the rotor.

 

Fox

 

It wont, keep in mind that rotor blades pitch is not determined by black rectangle, but by red circle r. By cyclic deflection you tilt the plane, but in that plane lays the swashplate. When you put cyclic into the corner, the corner point (intersection of y with bk) will indeed drop more than intersection of g with bk, but blades pitch is determined by swashplate (intersection of y with r) and that is exactly the same.

[iFoxRomeo]

It wont, keep in mind that rotor blades pitch is not determined by black rectangle, but by red circle r. By cyclic deflection you tilt the plane, but in that plane lays the swashplate. When you put cyclic into the corner, the corner point (intersection of y with bk) will indeed drop more than intersection of g with bk, but blades pitch is determined by swashplate (intersection of y with r) and that is exactly the same.

Sorry, but you are wrong.

 

Of course the angle of incidence(and the resulting AoA) is set by swashplate tilt. But the amount of tilt of the swashplate is set by movement of the cyclic stick out of the mechanical neutral position. The stick travel is bigger in the corners ("y") thus the swashplate is tilted further, leading to bigger angle of incidence as it would when only moved with the amount of "g".

 

As I said, some modern helicopters have a mechanical cyclic pitch limiter. You can not move the stick to the corners of a square. You can move the stick only e.g. in a octagonal shape. If it were the way you think it is, there would be no need for a mechanical limiter.

 

Fox