Resetting the ADI

[Bladestrike]

In a heavily loaded S-61, if the ADI is set level on the ground, it'll be pretty much level in the hover and in cruise. If you're light, you'll be sitting about 3 to 4 degrees nose down in the hover and cruise. There seems to be two schools of thought regarding resetting or not resetting the ADI to level in the hover or in cruise.
I'm curious if there is a standard.

[inthegreen]

My thoughts are that you set the ADI in any aircraft around the particular attitude you need to fly at that time. For example, if you are going to do an ITO you would set the ADI to indicate level in the hover in your present configuration so you could recognize a three degree nose down attitude for takeoff. Later on, after transitioning into cruise and resetting power and airspeed, you would reset the ADI to that cruise attitude because that is most important to you then. Just my opinion though.

[Old Man Rotor]

Company Policy is that you set the AI on the ground and don't touch it again.

The B412 on skids will be about 4 Degrees nose up on the ground and zero in flight.

The folk at Sikorsky have solved this deleamour by not giving you any knobs to play with [older S76's].

But whatever you do, don't go resetting your AI reference in IMC or whilst turning.......yes it does happen.

[GLSNightPilot]

I've never flown the S61, but ISTM this is a general question anyway. In the 412, everyone I know sets the ADI to indicate 4-5 degrees nose-up on the ground, because that's the way the aircraft sits. In the S76, I set it to level on the ground, because that's the way it sits. Then I know what a level attitude is on takeoff and climbout. This often works for cruise flight, but I may change it depending on the load and CG. The only time I see a big difference is when I slow down for an approach, and then you generally have to maintain a nose-high indication for level flight. I used to reset it, but lately I've been leaving it as is, and mentally compensating, because every power change requires a new setting. I'm not sure how others do it.

[Arm out the window]

In general, I think it's a bad move to set anything else than the 'real' attitude on the ground; ie. if your helicopter sits about 4 deg. NU on the skids, set that, and if it sits flat, set zero.
Attitude indicators by their nature have an erection system that continuously (more or less, locked out when there is G on) brings them back to a true vertical reference.
You want the AI or ADI to give you a true picture of where the nose is with reference to the horizon, so why set it anywhere else on the ground?
If you are always setting your AI to give you a 'zero pitch' in the cruise, you're fooling yourself. In my view, it's far better to just get used to whatever 'true' attitudes your particular machine generally flies at.
With respect to what Inthegreen says, it would be better (I think anyway) to note what you're hovering with, eg 4 NU say, and make a mental note to lower that the appropriate amount when you do your restricted IF takeoff, rather than always being programmed to go for some rote-learnt picture on the AI.

[SASless]

Ah dear chap....some regimes demand rote learning and mindless compliance to drill and procedure. Freedom of thought and that horrible threat of a pilot "thinking" in the cockpit puts fear into the hearts of management. Once a seatweight begins to think...why who knows where it will all lead to....next thing you know they will be asking questions and we all know how dangerous that can be. If left to get out of hand....they might even think they deserve better pay, safer engineering standards, improved working conditions, and maybe even reduced loads and more fuel....why just cannot let that happen.

I cannot wait until the UK bunch begin to respond to the issue raised in this thread.....that should be enlightening. What could the colonials possibly know about anything.

[Servo Jam]

I fly a S-76 glass cockpit, and we don't even have the option of resetting the ADI. It will be level on the ground and due to a forward C of G due to all that shinny Glass it will fly level in cruise with a 3 to 4 degrees nose down attitude on the ADI. Sperry Honeywell didn't even give us the option of ressettig in cruise.

So I guess their thought was, if the pilots can't touch it, they can't screw it. :p

[OopsNearly]

If you set the ADI on the ground and in the hover you have pitch up or pitch down indication, then that angle is the angle of your undercarriage with refernce to the ground. This is important if you have to do a serious movement close to the ground such as a reject on take off.
Take the S76, it can have up to 8-10° nose up in the hover, if you then level the ADI, then put the nose down 5-10° for take-off you are in fact only levelling the aircraft and you are going to require a lot of runway for your take-off. Conversly, on landing the max nose up attitude close to the ground is 10°, rotate 10° nose up and you are at 15-20° with an expensive noise comming from the tail area.

In the cruise at whatever speed you fly using all instruments not just the ADI, it does not matter whether it indicates a nose up or nose down attitude, you fly using the information it gives you.

There is nothing magic about instrument flying, practice makes perfect, well almost!

[SASless]

Do we need to arrive at a defintion of "Wings Level" ? Seems we have several of them already? Is it ADI level, fuselage level, rotor system parallel to the ground...???

[NickLappos]

IMHO the gyro is a reference used for lots of things, and it should be set to indicate airframe deck angle relative to the earth. If you have to struggle to remember that a zero climb angle is 2 degrees up or down from the big lateral line, well, that's why they pay you the big bucks. You don't adjust the natural horizon when you fly VMC, do you?

If you mess with the ADI, you end up not knowing where you are, and that might make a difference when you need to know fuselage angle. Flare attitude comes to mind as a nice to know absolute, as does slope angle. Mess with the ADI and these are not knowable from the display.

Intelligent seatweights, Sasless! I like the term. How about naming pax Screaming Ballast?

[Arm out the window]

"You vill select 3 degrees nose down...zere vill be no discussion...any kvestions?"
Very amusing, SASless; as you say, can't have any of this subversive thinking going on!

Further to my last, if you're using an AI that has an adjustment to the pitch dot / gull wings or whatever that simply moves those parts in the window, then adjusting it is probably not such a big deal, apart from the fact that you are screwing with the 'true' picture of attitude provided by the instrument.
If on the other hand you re-cage an older-style gyro AI to some false horizon, it will then have the dreaded 'pitch-roll error'. That is, a 3 degree pitch difference between the real and indicated horizon will, when the aircraft is turned through 90 degrees, manifest itself as a 3 degree roll indication.

So hooray for the thinking seatweight, I say!

[GLSNightPilot]

Nick, elsewhere on PPRuNe the breathing cargo in the back is referred to as SLF, for Self Loading Freight. Down here we just call them 'critters'.

[Red Wine]

Downunder, their just ...."Rig Pigs".

[Ga. Chopper]

It's too bad that not all ADI's reference the horizon. This type of ADI is more expensive and is usually installed on aircraft certified for IMC, this is also why many fixed and rotor wing aircraft don't use it. It makes raw data insturment flying much easier.

By having a constant reference point, one can consistantly set a target pitch attitude for a given power setting to yeild a desired performance: such as an airspeed for climb/cruise/descent; or just to maintain level flight. This method is utilized in most turbine fixed wing aircraft for basic insturment flying when not using the Flight Director or Autopilot, (i.e. raw data).

[Bladestrike]

Thanks for the feedback!

I've usually just set it on the ground to what I anticipate it to be in the air and go with that, but I think I may go with levelling it on the ground and leaving it alone. I expect a bit of difficulty adapting to flying 4 degrees nose down or rotating to 9 degrees off the deck (5 from level) but I see the points made for doing so.

I've always thought of it as abit of a heading bug. You set the heading bug so you don't have to remember XX degrees, and I've always set the ADI for the same reason, so I don't have to remember X degrees nose down. Anything to make life easier.

Anticipating poor altitude control for a few flights!

[Nigel Osborn]

We were always taught to have the ADI set to level on the ground. This means when at night or in cloud, if you have to make an EOL purely on instruments, then just before the little bump at the bottom, you will know if your skids/wheels are level for running on. In the Navy as a student we practised EOLs at night on instruments and I was surprised to discover I did them better using instruments than using my Mk 1 eyeballs by day! Fortunately my eyeballs did improve!
By having the ADI on a fixed datum, it meant that you had a fixed angle for whatever speed you wanted which made instrument flying much easier. For example a Wessex did 90 knots at 4.5 degrees I think.:p :O

[IHL]

Your ADI is suppose to give your attitude with reference to the "out side world" . re-adjusting the ADI level for every flight configuration makes absolutely no sense.

Imagine having to do a night auto over water(for what ever reason), it would be good to know your attitude with reference to the earth( water). (Which is basically what Nigel is saying).

The fixed wing guys don't change their ADI in cruise, in fact they are unable to.

[GLSNightPilot]

If they're unable to, why are we able? Exactly what is the difference between a fixed-wing & helicopter ADI?

[Ga. Chopper]

GLS Night Pilot,

Both types of ADI's are installed in fixed and rotor-wing aircraft alike. Many aircraft use the settable ADI because it cost less and it is acceptable for VFR/IFR Flight.

Look at my post on the previous page about why many fixed and rotor wing aircraft certified for IMC have ADI's that can not be reset. These type ADI's incorporate a seperate vertical gyro that references the horizon, which make them "More Expensive".

These type ADI's also tend not to drift and are more accurate, because the reference is always the horizon and not what someone sets to what they think is best. Since there is no setting knob to adjust, it also eliminates the possiblity of mis-setting the attitude.

I have instructed using both in fixed and rotor wing aircraft. My personal preference is the ADI that references the horizon since I think is better suited for insturment flying. I can set target pitch attitudes for any given manuever and always get predictable results in all aspects of flight. By learning the various target pitch settings for your aircraft, it is also a good cross-check for other flight insturment faliures and makes insturment flight in actual IMC more precise. This is the only type of ADI utilized by the Airline Industry.

[Shawn Coyle]

And then there are those helicopters that have the AI set to something other than laterally level on the ground, and have the slip ball deliberately set somewhere other than center as well. The aim is that in cruise, the slip ball in the middle, and the AI wings level gives you minimum drag....
And you thought you were confused before.