Trim or Balance & why
 

I am interested to hear other Rotory Pilots views on flying in trim, or in balance & technically why please? I was trained to fly in trim always.............now after just 20 years of flying I have come across a bunch of Pilots who fly our AS350B3+ in balance & frankly it feels awefull like I am falling off my seat & it looks outside that we are skidding across the sky. Your right a... cheek may be lower in-trim but it feels right, balance ball in the centre feels :confused: :eek: :mad: :ugh: :yuk:

What do the aerodynamics Guru's like Prouty etc have to say on the topic???

Thank You for all your responses & as my ole' mate Guru Instructor who has now passed on to that big Heli Hanger in the sky used to say; 'do everything into wind........except piss' ;)

If I could post it, I'd find my copy of Al Ashley's old article on why it is best in the SH-2 to fly with the ball out a quarter ... but it's an old two pages stuck together copy of a copy of a copy that might not scan. I also don't have the rights to it. His explanation was involved enough that I don't want to try to reattempt it from memory.

Single rotor helicopters will always have a miss match between being in trim with the ball centered and sideslip angle. This is because the fuselage has to balance side force produced by the thrust of the tail rotor. It is particularly apparent at slow speed high power settings when on the back side of the power curve. I fly in trim because there is no way to display side slip angle unless you have special instrumentation. You can put a piece of yarn on the wind screen and with a little practice negate some of this annomolly by playing with pedal position, but I think it is more trouble than it's worth in the Huey I fly. Maybe it might be more usable in a R22.

Flying the trim strings or the ball in the inclinometer?
 

Do you maintain the helicopter in trim by looking at the trim strings or the ball in the inclinometer?

I'm flying R66's and there is a noticeable difference between the two.

Please give me your views on the matter!

Never had to fly a Robinson (thankfully) but in the frog-ships (AS350's) it depends on speed as to which is the most reliable.

Fling wing machines should be flown in 'trim' & not in balance :uhoh:

When in compliance with the string the ball is about half way right out of center in my 355.

With a tail rotor, the helicopter experiences inherent sideslip (the same as TR drift but in forward flight) so the fuselage doesn't travel along its centre-line with 'wings' level (level on the AI), it drifts slightly to the left or right depending on the MR direction rotation and therefore the anti-torque thrust direction from the TR.

The string will give a reasonably accurate indication of the relative airflow over the fuselage and is often preferred in the slower speed bracket whilst the balance ball will give an indication of skid in the turn but will only remain central on a constant heading if there is a little opposite bank applied to counter the inherent sideslip.

'Ball' in my view must be considered more reliable, especially in low speed regimes where the rotor downwash affects the strings. Further, the 'Ball' also behaves exactly in accordance with 'Seat of pants' flying mechanics for balanced flight..... I would personally go with the 'ball' in contradictory situations any day.

The problem is that in slow speed flight you are often out of balance because you have an angle of bank to compensate for TR drift.

This is my experience.

The string only starts to flutter in very slow speed conditions ie. nearing hover but as crab mentioned is often more reliable at "slower" ie. between 20-50kts than the slip indicator.

Well.... we don't have strings in most helicopters, but 'ball' in all..

I assume I am in "Trim" or "Balance" when something centers....be it string, ball, or pedals....in no particular priority. The best indication is when the wind quits roaring through the cockpit doors in one direction or the other.

Do you guys lay awake at night thinking about answers to such questions?

If so...ponder this one.....

If you maintain the aircraft in "trimmed" flight....how much offset do you add to the formula determining the correct heading to be flown to fly a particular track across the ground from your Takeoff Point to your Destination?

It would seem if this TR drift thing is so significant...then CFS trained Instructors would have a colored pencil designated to depict that bit of the Vector Diagram.

SAS, it depends on which direction you are flying, don't forget the earth is spinning below you once you are skids (wheels) up:rolleyes:

It would seem if one maintained a steady hover relative to the spot in space you happen to occupy....you could get about a Thousand Miles an hour out of an R-22 or Bell 47.

Whew....now that is flying!

Thanks for the replies.

I've noticed that when I keep the trim strings centered the ball is always a little off to the left.

Personally I prefer to determine trim with the trim strings but I've noticed other pilots prefer the ball method

not quite true, it is only recently we over here to have balls installed, just think what sort of 'real' results we could have done with them. I never knew the install instructions. Ship level on the rigging jacks or in the hover skids hanging low differently for every type, it's a quandary. Remember one day with a high order F/W department person on board; 'Have a go' I says to Barry, next minute I'm nearly a block of ice in the wind draft. Ol' mate is fighting the ball which is only attached one end, but there cos it's the CP's machine and you all know about the blessed rules eh. I cover the ball and tell him fly what the reckons is right, give it a flick with my thumb and praise his accurate flying once I uncover it as now right in the middle.

As I get older yeah it's hard to work out when I lift off, now do I go faster forward to get there or slower backwards with this earth spinning thing.

I was taught without strings or ball, fly for fastest airspeed at the given power setting, that's when it is in best trim and balance.Try it, you may be surprised how comfortable it feels.That is regardless of what you are doing at the time, turning, climbing or cruising.

Are your strings getting "pure" air.....or is there some interference that influences the airflow a bit?

I generally try and fly where the seat isn't trying to tear my jocks off.

Aircraft Balanced Condition
 

What is the condition of the ball in a hover? If the aircraft is loaded with an off center lateral CG, the ball will be off center in a hover. The string is NA at this point in flight. Now in forward flight, (cruise) put the ball in the same position as observed in the hover and you should be pretty close to trim. Now see what the string indicates in comparison to the ball position? Must agree with earlier post, if you are loosing sleep on this, you are pretty fortunate with no other higher priority matters at hand.