-
Please take a moment and update your account profile. If you have an updated account profile with basic information on why you are on Air Warriors it will help other people respond to your posts. How do you update your profile you ask?
Go here:
Edit Account Details and Profile
Mast bumping and other helo terror
- Thread starter wlawr005
- Start date
MasterBates
Well-Known Member
Unloading the head in a 60 is nowhere near as "bad" as it would be in a H-1 or 57
It means that if you go inverted the Crew Chief will have a fit. At least thats how they explain it to the Longbow guys who see videos of it being done and think "thats F'ing awesome."
Semi-rigid is what 2-bladed helos are. The two blades are fastened together and teeter over the mast. That teetering motion allows the rotor disc to be aerodynamically balanced. On the minus side, if there are no Gs on the aircraft, the helo is basically floating under the rotor, and the mast can contact, or "bump," the stops underneath the blades, and VERY bad things, up to and including the rotors falling off, can happen.
Fully articulated rotors have more than 2 blades. Each blade has hinges that allow it to swing a little forward/back and up/down to aerodynamically balance the rotor disk. This also allows some envelope expansion, especially in regards to low-G maneuvering.
I know nothing about RW aero so please excuse my ignorance, but how does that typically happen? Chopping the collective?
No, descents cause by collective are fine. It is descents initiated by forward cyclic that is the issue. Think avoiding a bird. The -57 can safely go down to +0.5g's but it feels real uncomfortable below 1 g.
With a semi-rigid head, think of the fuselage as simply hanging beneath the center of the rotor. Flying around in 1g this is no problem because the rotor just pulls the fuselage around. When you get to 0g's, the attitude of the helo and rotor are no longer coupled. The fuselage will experience a right rolling tendency because of the tail rotor. A natural pilot reaction of left cyclic to counter the roll will cause the rotor to roll until the droop stops start hitting the mast. Two important pieces of metal hitting each other hard many times a second = BAD. (Rotor flies off, Rotor starts to cut fuselage into pieces, etc.)
Yes, we are careful about entering autos with the VSI @ or below 0. Doing so otherwise would possibly induce a 0 G type situation in which we'd be bobbling about a loose rotor spinning which is BAD news.
Once VSI = 0 or descent rate, and the auto is safe to enter.
Mast bumping is more like mast BUMP and then mast separation. Helos tend to fly better with rotors attached.
That could possibly do it, but a really drastic push forward on the stick is enough to unload the head. Then, as was said, the helo is basically floating underneath the rotor, so the rotor is free to move in all directions instead of what is intended.
The result can be mast bumping, which is bad. A good visualization is a soda can. If you apply a load to the top or were somehow able to pull directly through the bottom, only in the up and down (z-axis), the soda can is pretty dang resilient and tough. But, you dent the side of the soda can at all, it loses all of that tensile strength. Same thing (basically) happens with a teetering rotor head like what the -57 has.
The same way it does in FW - excessive forward stick/cyclic. One way it happens is entering a steep dive; to follow a sharp cliff dropoff, for example.
Several years ago we had a traffic reporter (recent FW transition) in a R-22 respond to a model rocket climbing up at him by pushing the nose over. Result was mast bump, tail boom speration, rotor blade seperation and fatality.
I think a lot of rotary wing guys miss out on this very subtle but key piece of aero knowledge. Maybe because it is a needle buried in the haystack of flightschool along with a thousand other needles...
yep..."bunting" is a SWTI term for terrain masking down the back side of a cliff/mountain. We encountered that from time to time. It can also happen if pilots input too much forward stick after an aggressive cyclic climb...(also characterized by crewman in gunner's belt bouncing off cabin overhead
)
yep..."bunting" is a SWTI term for terrain masking down the back side of a cliff/mountain. We encountered that from time to time. It can also happen if pilots input too much forward stick after an aggressive cyclic climb...(also characterized by crewman in gunner's belt bouncing off cabin overhead
Say what...? You know what bunting and SWTI are, but you don't know semi-rigid and fully articulating? Are you some kind of spy?