Tail Boom 'Crinkling'
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Tail Boom 'Crinkling'
I am interested to know if seeing ‘crinkling’ on the tail is usual on helo’s in the hover.
For instance, recently I saw an aircraft (one of Mr Sikorsky’s finest, think Blackhawk / Seahawk) in the hover, and the starboard side was ‘crinkly’, around the transition section and forward half of the tail boom. The crinkles on the transition section were larger in width, and not as noticeable as those on the forward half of the tail boom, which were smaller in width, but more numerous. These are not visible when on the ground (ie no load).
All crinkles ran aft as they went from top to bottom (ie top right to bottom left as you look at the starboard side). The aircraft has had some additions in this area, presumably the engineers did appropriate strengthening etc.
Is this crinkle a normal thing? I understand why it is on this side, as this is the side under compression due to tail rotor force.
I’m especially interested if this is normal on Blackhawk / Seahawks. It’s not something I have ever seen before, as I’m normally inside looking out.
Thanks,
SUA
For instance, recently I saw an aircraft (one of Mr Sikorsky’s finest, think Blackhawk / Seahawk) in the hover, and the starboard side was ‘crinkly’, around the transition section and forward half of the tail boom. The crinkles on the transition section were larger in width, and not as noticeable as those on the forward half of the tail boom, which were smaller in width, but more numerous. These are not visible when on the ground (ie no load).
All crinkles ran aft as they went from top to bottom (ie top right to bottom left as you look at the starboard side). The aircraft has had some additions in this area, presumably the engineers did appropriate strengthening etc.
Is this crinkle a normal thing? I understand why it is on this side, as this is the side under compression due to tail rotor force.
I’m especially interested if this is normal on Blackhawk / Seahawks. It’s not something I have ever seen before, as I’m normally inside looking out.
Thanks,
SUA
Yes, it is normal.
You will see it on many helicopters, particularly the bigger ships, with sheetmetal tailcones/tailbooms. Smaller machines tend to have semi-monocoque or honeycomb panels which offer much greater rigidity through their design. On the big machines the tails are manufactured with conventional construction techniques, as the physical dimensions, drivetrain requirements and thrust to be absorbed are so much greater - and the necessity to limit weight becomes more significant.
It also not unusual to find skin cracks in these structures as the skins relieve themselves. These cracks tend to appear in the same location on all the aircraft - not surprising really!
You will see it on many helicopters, particularly the bigger ships, with sheetmetal tailcones/tailbooms. Smaller machines tend to have semi-monocoque or honeycomb panels which offer much greater rigidity through their design. On the big machines the tails are manufactured with conventional construction techniques, as the physical dimensions, drivetrain requirements and thrust to be absorbed are so much greater - and the necessity to limit weight becomes more significant.
It also not unusual to find skin cracks in these structures as the skins relieve themselves. These cracks tend to appear in the same location on all the aircraft - not surprising really!
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Sit in a S300 and during start up, at idle rpm, look over your shoulder at the tail boom and gently move the pedals a little and see the effect that the tail rotor thrust has. The tail boom bends.
The construction of tail booms is such that they are required to bend/flex slightly to absorb the forces of the anti-torque effect and vibrations associated with main and tail rotor systems.
Agusta have had to beef up their 109 tails. EC135's early models had problems due to flying heavy police equipped machines and had to be modified to stop the cracking that was occurring.
The construction of tail booms is such that they are required to bend/flex slightly to absorb the forces of the anti-torque effect and vibrations associated with main and tail rotor systems.
Agusta have had to beef up their 109 tails. EC135's early models had problems due to flying heavy police equipped machines and had to be modified to stop the cracking that was occurring.
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The term most people use is appears to be 'oil canning' - after the effect that happens to an oil can when empty.
It's a normal thing that happens to most aircraft structures that use formers, stringers and skin (semi-monocoque) construction.
The B-52 shows it quite clearly just behind the cockpit, and you can see it happen a lot if you watch closely.
If you see large and permanent evidence of it, then I'd be suspicious of the airframe, otherwise, not normally a problem.
It's a normal thing that happens to most aircraft structures that use formers, stringers and skin (semi-monocoque) construction.
The B-52 shows it quite clearly just behind the cockpit, and you can see it happen a lot if you watch closely.
If you see large and permanent evidence of it, then I'd be suspicious of the airframe, otherwise, not normally a problem.
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I have seen the mods on the Agusta. pretty hefty on the model i saw, would my thinking be correct that as the metal/fabric bends or is under stress etc there would be a life cycle on this section of airframe or would it be all relevant to the life cycle of the full air frame.
A curious bravo 99 (AJB)
A curious bravo 99 (AJB)
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oil canning , a german engineer once told me that a sheet metal panel had a frog formation , took me a while to work out this was what the germans call oil canning, when you push it it jumps like a frog. Wonder if Klaus B is still around
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Seahawk oilcan effect
Having flown both Seahawk(S-70B) and Blackhawk(S-70A-9,A-32,UH-60A,L) the interesting thing is that the oilcan effect is very obvious on the seahawk yet not discernable on any of the variant of blackhawk.
Go figure.
Go figure.
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Widgeon, both aircraft have a folding tail boom. However the Sea Hawk's folding hinge in located farther away from the tail rotor, and the hinge is on the opposite side. This might effect the boom stiffness somehow.
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That slight wave on the skin of some helos is quite normal, a product of the tolerances of the components as they are layed up in the tooling.
Shawn has it exactly right, it is quite normal, and often seen in this type construction.
Most jet liners use very thick skin, and have no such issue, and the S-76 main fuselage uses a honeycomb aluminum formed skin that is also quite rigid.
Shawn has it exactly right, it is quite normal, and often seen in this type construction.
Most jet liners use very thick skin, and have no such issue, and the S-76 main fuselage uses a honeycomb aluminum formed skin that is also quite rigid.
