'Beanies' aerodynamics.

[Flag Track]

Just seen elsewhere the delivery of the first Puma HC2, I notice they've not fitted a 'beanie' at Brasov, I know the RAF don't have 'em as standard but would there be any benefit and if so how does it achieve it?

Thanks in advance, Flag T

[RVDT]

Don't think 330 Puma's ever had a "beanie" fitted.

[Fareastdriver]

A beanie is a 332 thing. A Puma has drag dampers that has the reservoir mounted above the rotor head. The 332 has frequency adapters that do not use oil so they can fit one.

[Flag Track]

Apart from it being a 'Frisbie' just wondered it it has other qualities, I think I've seen them on other Pumas.

[Fareastdriver]

I would imagine that a beanie would smooth over the air above the rotorhead. You have a lot of blunt bits going in all directions so I would think that isolating some of it from the airflow would help.

[Wizzard]

I think - but I'm not sure - that the beanie is also required as part of the 332 icing clearance

[RVDT]

United Aircraft Corporation now United Technologies Corporation

with a business unit called Sikorsky aircraft.

USPO 3,181,815

ROTOR VIBRATION REDUCTION CAP
William F. Paul, Trumbull, Conn., asssignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware.

Filed Apr. 27, 1962, Ser. No. 190,745

This invention relates to means for reducing vibration
encountered in helicopters, especially during high speed
flight and due to aerodynamic excitation of the tail section.
The vibrations are primarily attributed to the flow
of turbulent air from the rotor head flowing across the
tail area.

On object of this invention is to provide a dome-shaped
device over the rotor head. It is not an object to fair
pairs of the rotor head which are prime contributors of
drag to reduce their drag. The dome or dome-shaped
cap is not used to cover a nonstreamlined object to reduce
total drag.

A further object of this invention is to provide a device
which will reduce vibrations in a helicopter even though
it increases total drag.

In basic terms the air that flows under and over the cap is pushed down to clean up the turbulence created by the head. The flow around the head is generally a mess and the wake from that batters the tail which having a long lever arm, wags the dog, so to speak.

As usual the more you dig into the inner function of helicopters, the more you realise that it is surprising that they actually work at all.