AS 350 hover question

[krautland]

happy new year, everyone.

quick question: I was watching a bunch of tv choppers over san francisco, most seeming to be AS 350, hover for more than an hour over a demonstration earlier this week. they maintained their positions quite remarkably well over a long period of time, which got me wondering if these guys were actively controlling their positions (=lots of work) or if there was an autopilot option that essentially hovered on the spot for them (=lean back and just wait).

can anyone fill me in?

[Fun Police]

hi and happy new year all.
yes, there are autopilot systems available for the 350 and they may well use them. i have never seen one as they are not usually installed in utility configured a/c. the 350 is very stable in the out of ground effect hover and would not be hard to keep stable for extended periods of time (especially of the winds are favourable). in ground effect they can be a bit of a handful but not bad once youget used to them.
cheers
FP

[Nubian]

Seasons Greetings!

Autopilot is one thing, but what you refer to would be 'Autohover' (requiring 4-axis autopilot), which I am quite sure you won't find in News reporting helicopters, specially not in the US. New-ships are generally loaded with enough weight as it is, and to handfly a 350 is not that difficult either. It's done all the time with precission long-line.

Auto-pilot systems in light helicopters as the 350 and Bell 206 series are generally not very common at all. Not to mention with Autohover capability...

[Gordy]

I used to fly for KRON the San Francisco NBC affiliate, (they are an independent news station now)----there is NO autopilot. Unless you are watching continuing coverage, they are not remaining in the hover all the time.

Back in the 90's we would all fly around in an orbit until our station wanted the "steady shot" to go live, at which point we would move into position and hover. We would all talk to each other and work out our own co-ordination and stay out of other peoples shot as best as possible. (The airspace over downtown San Francisco is not controlled by ATC).

[Tango123]

In many AS350 (with and without AP) you have a stabilisation system in the pitch, roll and yaw axis. It is not an auto-hover but due to the rotorsystem (semirigid three rotor blade) the AS350 has a tendency to "wobble" a bit. Therefore you have the stabilisation system for pilot comfort.

In hover you can have feets on the floor, so if you dont do too quick collective inputs the stabilitator will maintain your present heading.

T

[Nubian]

Tango

Would you please explain what this "stabilization system" is??

In all the 350's I have flown over the years(and seen for that matter), B,BA,B1,B2,B3+, I have never come across what you are refering to... In many AS350 (with and without AP) you have a stabilisation system in the pitch, roll and yaw axis.
Maybe, you're referring to an optional trim-system...... which is a trim-system (that would not allow you feet of the pedals tough)

If you keep your feet on the floor as you say, you'll have "heading-hold", that would be around one of the axis, ie. AP installed. OR make you much cooler?! than me...

As for wobbling, yes it does very close to ground when on set-down mainly. (this does not come from the MR design by the way, but the fuselage aerodynamics, TR position and design) In OGE hover it's your own responsability to create the wobble....

Cheers

[SEL]

With respect to Tango's AS 350 remarks....what do you mean by stabilator?

[Gomer Pylot]

With respect to SEL, Tango didn't say 'stabilator', he said 'stabilitator'. Whatever that is. :p

[Gordy]

Gomer Pylot

With respect--do I detect a hint of sarcasm?

Would it not have just been easier to help the man out and tell them that the "stabilitator" is just forward of the isolinear transwarp discriminator coil.

Obviously it does not work unless one locks the the avidyne resonator, and bear in mind to watch out for a failure of the sarium krellide phaser buffer which could under certain circumstances result in a less than perfect hover.

[Gas Producer]

Gordy,

Man, you gotta give aviation away . . . with an imagination like that, you should be writing for the movies!!

GP:)

[SawThe Light]

Tango123

semirigid three rotor blade ? Semi-rigid? do tell.

[212man]

To answer Krautland's question, the aircraft would be hand flown (as has been suggested) but the seemingly accurate hover would be to a large extent be deceptive because of their frame of reference. That's not to say they weren't hovering accurately, but if you were to see the same positional accuracy closer to the ground it may look less impressive!

A comparison would be if you've ever seen a military fast-jet display team : from the ground the poistion keeping looks rock solid, but from the cockpit there is a lot more apparent movement.

Similarly, if you are flying at 3000 ft and maintain your height within +/- 20 ft that seems pretty good, but if you are flying down the beach at 10 feet, that accuracy would be less satisfactory! :eek: On the other hand, you would actually be able to maintain the 10 ft at about +/- 1 ft :ok:

[xxxchopperpilot]

tango123, sorry pal, but someone has fed you a load of hogs wallop! Try "Fully Articulated" Rotor Head System.:ok:

[feathering tickles]

ahh, the great Rotor System Name debate.....

quote AS350 B3 manual; section 7 "The main rotor is of semi-rigid design.."

[pilot_wood]

High Hovering just requires practice - the 350 and 355 are nice machines for this kind of work - especially without SAS.

[victor papa]

The 350 MRH is described as a starflex semi-rigid type. It is semi-rigid iaw the old books because it has no drag damper as per the 76, 61, 330 and 332L2 types. It does however allow for dragging via the starflex and damper fitted to the blade root end which practically makes it a "fully articulated" head. The 332L1 has a similiar argument as the frequency damper is not a drag damper thus semi-rigid, but does allow inflight up to 2 degree drag angle due to it's elastomer build. It is difficult fitting this technolagy in to the old definitions, guess Sikorsky has the right idea by calling it a elastometric head. The 350 with it's droop ring allows for 3 dimensional movement inflight which definately does not comply with any traditional definitions in my opinion.

[theavionicsbloke]

Guys, you may be thinking here of the AS355 Autopilot option.

This is the SFIM 318T system. It is primarily a Stability Augmentation System (SAS) with higher modes of operation making it an Autopilot system. There is also an optional Flight Director with Heading, ASI, ALT, VSI and NAV (Including approach & back course modes). The FD can be used independantly or can be coupled to the autopilot. An optional comparator of which is required for UK / European IFR certification.

It is a 3 Axis System and does not have 'Auto Hover'.

[krautland]

guys (gals?),

just a quick thanks for all the answers. I never even knew about 'auto hover' and knowing they all kept manually at it for that long makes it all the more impressive.

[that chinese fella]

The 350 with it's droop ring allows for 3 dimensional movement inflight

VP, Probably splitting hairs here but not so sure that the droop rings has anything to do what the rotor system does in flight. Unless I have misread this line in your post?

Cheers,

TCF

[SawThe Light]

In its original configuration, the 350 had no M/R droop restraint system. It was made available as a field retrofit in a Service Bulletin some time after the aircraft entered service.

For what it's worth, the Flight Manual states - "Of a semi-rigid design, the STARFLEX ROTOR HUB has no bearings nor lubrication system."

Note that it is the STARFLEX that is referred to as semi-rigid, not the rotor system.

[xxxchopperpilot]

saw the light,
absolutely spot on.

[xxxchopperpilot]

Therefore the AS-350 has a fully articulated main rotor "system"

[What Red Line?]

Kinda like this.

"A fully articulated rotor system usually consists of three or more rotor blades. The blades are allowed to flap, feather, and lead or lag independently of each other. Each rotor blade is attached to the rotor hub by a horizontal hinge, called the flapping hinge (Starflex arm) , which permits the blades to flap up and down. Each blade can move up and down independently of the others. The flapping hinge may be located at varying distances from the rotor hub, and there may be more than one. The position is chosen by each manufacturer, primarily with regard to stability and control.

Each rotor blade is also attached to the hub by a vertical hinge (Thrust bearing), called a drag or lag hinge, that permits each blade, independently of the others, to move back and forth in the plane of the rotor disc. Dampers (Frequency adapters) are normally incorporated in the design of this type of rotor system to prevent excessive motion about the drag hinge. The purpose of the drag hinge and dampers is to absorb the acceleration and deceleration of the rotor blades.

The blades of a fully articulated rotor can also be feathered, or rotated about their span-wise axis. (Thrust bearing & self-aligning bearing mounted within the frequency adapter) To put it more simply, feathering means the changing of the pitch angle of the rotor blades."

WRL

[Shawn Coyle]

Having taught a lot of flight test classes on rotor heads, I'm inclined to say that an elastomeric head is not fully articulated, as the articulation part means that while the blades are free to move, the hinges do not allow moments to be passed across the hinge.
An elastomeric bearing will allow the blades some limited movement, but it will also allow moments to be transferred from the blade to the head. They probably deserve their own designation - all the advantages of the articulated head, with few of the maintenance headaches, and some of the benefits of the rigid head without the issues of exotic metals.

[RVDT]

WRL,

http://users.skynet.be/aerosite/P2_H_starflex.jpg

the flapping hinge (Starflex arm)

The Starflex is the method used for the load path for the lead/lag damper (frequency adapter) to reference to the head. As you can see it is flexible in the flapping plane but NOT in the lead/lag plane or feathering plane. It is not the flapping hinge. That is in the spherical bearing.

http://www.aviation-fr.info/helicos/fig20.gif


(Thrust bearing & self-aligning bearing mounted within the frequency adapter)

There is no thrust bearing in the frequency adapter (lead/lag damper, the brown one on the lefthand end of the sleeves in the photo and vice versa in the images). There is a self aligning feathering bearing.

The thrust bearing for want of a word is the spherical bearing which is basically a pile of steel spherical cups separated by elastomer (rubber) elements. This bearing allows feather and flap and lead/lag. (The big black one on the righthand end of the sleeves in the photo and vice versa in the images .) The rubber elements are very thin so that failure of one will be not catastrophic as it would be if it were one big lump of rubber.

http://www.aviation-fr.info/helicos/fig21.gif

[Air2X]

I flew news down there for a while. It was an Astar B2, and I recall the longest I had to remain in one place was for the Scott Peterson trial. It was the day the verdict was coming down, so they had us fly over the couthouse in San Mateo. I left the Hayward airport, which is about 5 minutes away on the other side of the bay with a full tank of fuel. We stayed on site until I was out of gas and needed to return....which was almost 3 hours later.