Goose(is dead...)
Senior Heliman
Location: UK
| A summation of the Active Throttle Governor (ATG) by CYI’ve penned this note in an attempt to give some clarity of the advantages of the ATG. It starts from the bottom and slowly works its way through the reason for having a governor and builds to the ATG. So I make no apologies for stating the obvious as let’s face it, heli’s and their set-up are anything but straight-forward.
First, how a standard governor operates:
As an example, let’s aim for a head speed of 1950 rpm on a heli with a 8:1 gear ratio (The Vibe 90 has this ratio). If your governor magnet is on the main gear you simply dial in 1950 head rpm on a particular flight mode (N, 1, 2). If the magnet is on the engine shaft your governor needs to know that it is aiming for a head rpm of 1950 multiplied by the gear ratio:
1950 x 8 = 15,600 rpm
**Generally, a the governor is inactive for ‘N’ mode as it used for hovering and also lets you use the pitch / throttle trims on the Tx that are only active in N mode.
So back to flying about with a head speed of 1950 rpm (most likely in Flight Mode 2) the governor has control of the throttle and does its job of holding that pre-determined head speed.
But every governor has a small ‘lag time’ in its operation. Imagine your hovering steady and put in full +ve collective for a fast climb. The force this creates on the blades will slow the head rpm as it didn’t know that a ‘request’ for considerably power was coming. And albeit a split-second, the governor takes a few rotations to identify the head rpm has slowed down. Once it has, it then opens up the carby. And if you don’t have quick throttle servo (higher than 0.10 secs/60deg) the lag will be amplified. Finally, the engine responds with more power and the head rpm returns to its target.
Unlike fixed wing motor setups, the set up of a heli engine also needs to have its torque curve considered. Yes it’s getting the maximum power out of the engine but this is done by identifying the peak torque of the engine as well. A broader, stronger torque curve will also be created by a good pipe; Both the Muscle Pipes and Hatori’s for 50’s and 90’s are faultless when set-up. My preference is the MP 5 range, but the performance of the Hatori’s don’t lie.
But back to the ‘lag’, their was a phase a year or two ago whereby a few smart lads attempted to beat this lag, or ‘bogging down’ cited in pushing the limits of their heli’s;
To use the same numbers let’s say they identified 15,600 rpm as the optimal rpm for power and torque. What they did was to set the governor at ~~= 16,000 rpm anticipating that when a sudden load on the engine came about and the head speed & engine rpm dropped, it dropped to the engine’s most powerful rpm (15,600). It was good for a while but then those lads found their engines were losing power over time. It was due to their fuel mixture set for 15,600 rpm was running lean at 17K and therefore cooking their engines. Time for a trip to the hobby shop…
It must be acknowledged that to date the best gov on the market is the Futaba GV-1. For it’s accuracy, set-up and overall performance. The only thing that didn’t really take off that the GV-1 offers is the ability to integrate a servo controlling the fuel mixture on a special carb. Too much mucking about; requiring a multi-point throttle curve to be programmed. I have heard pilots make this work and work very well but they also conceded it was a long arduous process.
The Pitch Curve
**Just before I go into the next section I should let you know about my pitch curves. And I set them up like this as someone who can fly ten times better than me taught me to do so:
N = 0% stick (idle) 5 degrees negative. At 50% stick 0 degrees. 100% stick +12 degrees.
1 = 0% stick negative 12 degrees. 50% 0 degrees. 100% positive 12 degrees
The pitch curve for FM 2 is exactly the same as for 1.
The pitch curve for Flight Modes 1 & 2 give you 5 crucial points:
Moving the stick from bottom to top you have:
1. Max negative collective (-ve 12 deg)
2. hover point when inverted
3. Zero degrees for stall turns / tail slides / whatever
4. hover point when upright
5. Max positive collective (+ve 12deg)
Because this pitch curve is literally linear, it quickly becomes natural and familiar as there are no ‘tricky’ curves or arcs to contend with. It makes your flying and transitions very smooth. Even though the top radios give a 7 or 9 point option (don’t know about the new JR Tx), they’re better used in scale, maybe in F3C in the hovering maneuvers I’m not sure what the setups of others’ are but we’re covering 3D.
Introducing the CY-ATG
It wouldn’t be fair to say that this lag we continue to refer to is a large problem. Any .91 on a pipe with 30% nitro well set-up can produce the torque needed to handle blinding tic-toc’s or tail slides by Lucas Riva that trim the grass !! (my favorite pilot). It is however, more obvious on 50’s simply because they don’t have the thrust/torque to weight of the 90’s
But Curtis in creating the ATG has delivered a painfully obvious solution, or advantage. Look at it how you will:
The lag time compounds from a pitch inducement, head rpm slowing, gov detecting, servo reacting, opening the carb and finally the engine producing the additional power.
But what if the carby opened at exactly the same time as the pitch of the blades changed, so that the head rpm never dropped?
It’s just too easy as the ATG ‘looks at’ or ‘considers’ your
pre-programmed throttle curves. As you move your throttle / collective stick the ATG is literally ‘predictive’ of your request for more power because of your pre-set throttle curve and uses this data so that there is never a head speed drop. Well, at least to the best of the abilities of the engine & pipe & tuning, etc
I hope this has helped some getting their head around the benefits of the ATG. If there are errors, I apologize. It’s late !!
Tomorrow, part 2 is how to set-up the ATG for max performance.
Any comments please shoot. I’m not the precious type
Cheers
Goose |
