Helicopters

This page has been contributed by member Ian Cairns, an enthusiastic model helicopter pilot who is often at the HMFC field flying his helis.

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Ramblings of a Rotor Head

So… you’ve seen the You Tube 3D Heli Videos and think “That looks pretty cool… can’t be THAT difficult!” Think again… my first research into RC Heli’s revealed “RC Heli’s require a significant investment in time and money!” Can’t seem to find that pearl of wisdom again… maybe it was affecting their sales?

My first RC (Radio Controlled) Heli was a Dragon Fly 4 FP (Fixed Pitch) electric model… it (I?) never really flew that well, but it got me hooked... just trying to keep it in one place on the Garage floor was enough of a challenge for me. As a Mechanical Draftee I still marvel at the intricate components that make up the Head with all its linkages and complexities; and as for the amazing mixing that goes on in the Tx (Transmitter) … just incredible stuff… they’ve sure come a long way since the Mechanical systems in use when I was at College.

A friend who worked for the ATSB (Australian Transport Safety Board) as an Aircraft accident investigator said to me:

“Gonna have a go at Heli’s aye?… Wow! They’re so unstable they are like balancing a ball bearing on a Glass plate… if it’s all setup correctly it’s like a flat plate… if it’s not… it’s like it’s a CONVEX plate!”

As you may have gathered from the above… Heli’s are quite different to Planks (Heli talk for Fixed Wing Aircraft). You cannot simply throw together an RC Heli and expect it to fly… especially if you’re a beginner.

Why Join a Club?

Joining the HMFC (Hinterland Model Flying Club) was probably the best thing I ever did.

Having upgraded (?) to an E-flite Blade 400 3D RTF (Ready To Fly) electric variable pitch model I was struggling just to keep it in the Air.

The first pearls of wisdom that Club members offered were:

“You’ll need to get yourself a good set of training gear”

Clearly NOT the ones I had, as they were just too short. Having training gear the same width as your Blades may look a bit funny... but it will save the day (and money) far better than a shorter (cheaper?) set.

The real BONUS was help in setting up the Tx which is quite a head spinner when you first get into Heli’s (or Planks for that matter). The Blade 400 3D ready to fly out of the Box was a fine thing… but it is setup for (you guessed it) 3D straight out of the Box! It has the same (probably better) power to weight ratio to those 90 size Nitro beasts you see on You Tube Videos doing things that should be physically impossible (and there’s only ONE full size French Heli (that I know of) that can do anything that comes close to what models are capable of… Stall turn, Loop, Roll maybe… but phew… try a few Tick Toc’s and see how long your Blades stay attached to your Rotor Head… and I’m guessing the Exec Heli market wouldn’t appreciate spilling their coffee (read Moet Champagne) when inverted); these electric models have a fraction of the mass of the Nitro beasts.

Settings to Tame the Beast

The little beast was tamed by using the following techniques’ by other Club members:

Reducing Rotor Head speed (Throttle curve fiddling), this will:

Make it less intimidating
Slow the response speed down = more time to react

Reducing negative pitch (-3 to -5 degrees instead of -9 to -15 degrees) (Pitch curve fiddling). This will:

Stop the Bird from pile driving itself into the ground when you chop the Throttle back when things get messy (the Throttle is linked (mixed) to the Pitch of the Head through the Tx)
Throttling UP and not DOWN takes some getting use to when things get a bit Pear shaped. That balance of getting things back to some form of stability rather than blasting into the blue Sky and loosing orientation also takes some getting use to
You still need SOME negative Pitch in case there’s an updraft and you need to get the Bird down again

Removing any Idle up setting… we DON’T want ANY surprises when we’re learning to Hover (trust me on this one… don’t ask me how I know)
Making the Stunt mode settings EXACTLY the same as Normal mode settings… again we DON’T want ANY surprises when we’re learning to Hover (yes you MAY knock ANY switch when you’re learning… your fingers will be very busy & sweaty)
Setting up about 25% Expo (Exponential) which will slow the throws down around centre stick movements… but still give full deflections at end stick movements… couldn’t really understand why you’d need such electronic wizardry, but it’s a CONTROL thing e.g. being either IN control or NOT by careful use of Expo

Other Setup Help

Other REAL help REQUIRED if you purchase an RTF (Ready To Fly) is WHEN you duff your model in… and YOU WILL (when learning to fly… again don’t ask me how I know … just trust me on this one). There is an advantage in purchasing a “package” like the Blade 400 (such as a well optioned, reliable and easy to use (MINIMUM) 6 channel Spektrum DX6i 2.4Ghz Tx… (one of the reasons I bought this package)… the new E-Flite Blade SR was not available at the time which is a better setup for the novice Pilot) and a high quality excellent performing Heli, not to mention it being a no brainer not having to worry about electric selections (Motor, ESC (Electronic Speed Controller), S/UBEC (Switching/Universal Battery Elimination Circuit), and LiPo (Lithium Polymer) battery (mAH, number of cells etc) and Servo selection etc)

For setting up (keeping the Bird in the Air) as a MINIMUM you’ll need a Pitch gauge, Ball link pliers, Rod end tool… and an optional Blade balancer is also a great addition to your tool box.

Before setting anything up, you’ll want to balance your Main Blades, both statically and dynamically. Do this by:

Mark the centre of balance of one of the Blades with a marker pen
Transcribe this to the other Blade (Hold Blades vertical with tips on bench)
Now check if the 2^nd Blade centre of balance is the same… if not add Balance Tape to one of the Tips until correct.

As always wrap the Tape so the start/end of the Tape is blown down (so it doesn’t lift and eventually go Phaf Phaf Phaf Phlop! (don’t ask how I KNOW these noises, I just DO) thru the downdraft & create a very unbalanced situation indeed)
I temporarily stick an excess of electrical tape on the Tip & trim bits off till it’s right… we’re talking VERY small adjustments here

Now you can Balance the two Blades together by adding Balance Tape to the Centre of Balance mark of the Higher Blade
If you’re lucky enough to afford high quality Blades, a check is all that SHOULD be required… if you’re not lucky (or you’re just learning & it would be silly to do so anyway) you DEFINITELY need to balance the blades

The real trick comes in knowing how to setup the Head and Tail correctly… in a nutshell setting up involves:

Firstly UNPLUG the Electric Motor to avoid the Head spinning up (for obvious reasons… again trust me on this one… ask me to show you my scars some time… actually maybe NOT!)
Take off (zero) any and all Trim and Sub-Trim settings on the Cyclic (Aileron, Pitch, Elevator) channels in the Tx
With the Rx (Receiver) on (and communicating with the Tx) ensure the Tx sticks are at MID position (Half Throttle)… starting at the Servo’s… trial fit the control horns until the horns are at right angles to the control Rods e.g. rotate the control horn on the splines until it is as close as it can be to be in line with the Servo body (usually)
With this now set you can finely adjust using Sub-Trim (in the days gone old (Analogue Servos) if Sub-trim was used the available torque was reduced at the end of travel, but this has been eliminated with modern Digital equipment)
Start at the bottom & get the swash plate nice and level adjusting the rods from the Servo Horns to the Swash Plate (this is only a starting point & will be fine tuned in flight). An “L” shaped Alan key spanner cable tied (or stuck on using Plasticine) to the Main Shaft is a great free tool to get this perfect
Moving on up through all the linkages ensure each pair of rods are the same length (a User Manual will have linkage lengths to start from… but they should be made up in pairs of the same length). As with the case of the Blade 400 RTF you may need to do some research and find the BNF (Bind aNd Fly (no Tx)) manual or build manual as these lengths are not stated (clearly the manufacturer doesn’t think you’ll be crashing… trust me… you WILL be)
Arriving at the Main Blades and ensuring the Flybar Shaft (funnily enough this is the shaft that the Flybar Paddles (those funny stubby Blades) are mounted to) is parallel to the Boom (Horizontal) you should sight along the Main Blades and ensure the Blade is parallel to the Flybar Shaft (this is Zero Pitch)… if not, play with the rod lengths until this is so (Zero Pitch at mid stick). Often the top short linkage has twice the effect as the longer one below it… fiddle with these, but make sure they’re the same length both sides
This is the starting point & is the best you can get Mechanically out of your Heli (all components being straight & not damaged of course)
If you’re REALLY keen (or a 3D nut) you’ll want to check the CCPM (Cyclic/Collective Pitch Mixing) interaction… but it’s gonna be pretty stable to fly even if you haven’t done this. Check out how to do this here http://www.helifreak.com/showthread.php?t=52530
The Pitch Gauge helps sighting up over the top of the Gauge to the Flybar and has graduated Pitch angles for a more accurate setup
MANY Rod ends are handed too, so you need to pop them on only one way (pushing them on the wrong way will stretch them, then you’ll risk them Popping right back off in mid flight… don’t ask me what happens (honestly) when a Rod end pops off & the shaft it was attached to jams itself into a stationary/rotating object… but it’s GONNA be MESSY!). You may now appreciate why a ball link pushed over the Ball & thru to the other side is not a good idea either (as I have seen on one Plank Pilots Heli build)
Moving to FULL Throttle the Pitch Gauge should be loosened and adjusted to find out how much Positive Pitch you can get out of the Head… again sighting over the top of the Gauge to the Horizontal Flybar shaft
Moving the Throttle to Idle check how much Negative Pitch you can get… this SHOULD be the same as Maximum Positive Pitch
If you cannot get Zero Pitch at Mid stick & the same (within 1-2 degrees) Positive and Negative Pitch there’s something wrong… work out which linkages need to be adjusted longer or shorter to achieve this… you MAY even need to adjust the height of the swash plate. Work your way methodically from the bottom up to the top ensuring

The Washout base doesn’t touch the bottom of the Head Block/Rotor Housing (if it does the Servo’s will be buzzing and being overloaded)
The Washout control arm is level too (probably should have told you that right at the beginning!)

Depending on the head setup (Leading or Trailing edge controlled) you’ll need to find out if throttle UP moves the swash plate UP or DOWN (as is the usual case)… I got rather confused on one Heli build and started swapping things round till the manufacturer advised throttle UP moves the swash DOWN and had to swap it all back again… “You have been warned”
Once you have sorted this out… record the linkage lengths for future reference (one guy didn’t and had to go thru this whole process again after a big crash… don’t ask me who this guy was… I’m not gonna tell ya!)
The Tail (Rudder) Servo MUST also be setup with Zero Trim and Sub-Trim to achieve the best performance from the Gyro (this is the thing that’s trying to keep the Heli heading in ONE direction (sometimes with the help of the Heli Pilot… sometimes not) and is the Servo that gets the most work out)… investing in a good Gyro (like the Curtis Youngblood Mini-G) and Servo (like a Futaba BLS-251) really is worth the extra money for enjoyment. It’s hard enough combating the wind effect, but having to bring back the Tail because the Gyro is drifting Left and then Right just adds to the work load when learning to fly
Minimising any binding on the Tail servo Rod and Tail slides will considerably help the Servo (and thereby the Pilot) maintain the Tail location. Light lube is OK, but may simply attract dirt & make things worse in the long run

Time for Trimming!

You may have noticed there’s often a lot of activity happening in the Heli circle… but they just don’t seem to be getting very far. This could be because the Guy (or not so often Gal) is learning to Hover… one Club I approached told me they couldn’t help me much until I could hover. A painful truth, but not quite correct… if they were setup properly with an advanced buddy box system (and wanted to) the Trainer can relinquish control of one control at a time and then add more controls as and when skills improve

The other thing that might be happening is the Guy is trimming his Heli (probably the Guy that Hover fiddle, Hover fiddle, Hover fiddles… and NOT the Guy you see in the local park that Hover drop, Hover drop, Hover CRASHES!)

Now comes the important bit (remember the polished ball bearing on a CONVEX plate?)… trimming the Heli. It is BEST (ESPECIALLY with a light small bird like the Blade 400) to do this in NIL wind… (Yea right… how often does that happen? I remember often having to Tilt the wee Bird into the breeze about 30 degrees forward just to keep her in one place)… at least this should be performed in VERY light wind with the Heli heading INTO the wind (this will help with the weather cock effect and keep the Heli heading straight into wind)

If you are learning it is BEST to get a competent Pilot (at least one who can Hover confidently) to trim the Model (my Blade 400 is hardly EVER trimmed correctly… it (wasn’t me) had a tendency to CRASH before it ever got to be in perfect trim!).

Again in a nutshell you’re trying to do the following:

Tweak the Swash plate to make allowance for the swirling down wash/Tail sideways forces
Set the Gyro up so that it holds the heading (heading hold) of the Heli

This is achieved by:

BEFORE you launch into Hovering just above ground effect (that nasty swirling turbulent air the Heli creates when it is 0-1m (0-3.3ft) above the ground)… you should always Spool up the Heli and make any adjustments necessary to keep the Bird from wandering off when it is light on the skids…. Wandering Left, tilt the swash Right, wandering forward, tilt the swash back and Vicki me Verka
If the Tail is swinging one way or the other, you’ll need to adjust the Tail rod linkage length with the Gyro in NON Heading Hold mode (doing this is to reduce the work load on the Gyro and Servo… it will be fighting against any Mechanical/frictional problems with the system if you don’t)
With this done you can then be more confident in Hovering a meter or so off the ground to find out what’s really going on
Adjust the Swash plate to Servo linkages to achieve a Hands off Hover (yes it IS possible to achieve with no wind)
The Swash will invariably have a slight tilt to the Right after this adjustment
Some Heli’s have a pronounced cant to one side when Hovering… this is normal and takes a bit to get use to at first
With the Gyro/Servo working without any swinging it’s then time to setup the Gyro gain in Heading Hold mode. Starting off at about 55% (usually Gain BELOW 50% is NON-Heading hold & anything above 50% is Heading Hold) increase Gain by 5% increments until the Tail starts Wagging (moving Left then Right) then take off the last 5% you just added

Final Tweaking (Blade tracking)

OK so now the Heli’s not going to wander off without your say so (or without your nervous input). Next step is to check the Blade tracking. This is achieved by sighting thru the Spinning Blades… what we want to see is a Horizontal line looking thru the Head. If it appears you’ve left your Bi-spectacles (glasses) at home and are seeing double, you’ve got a Blade tracking issue. Either you’ve forgotten to balance your Blades or it’s a Head issue…

This can be roughly set by lying on the ground at spool up at mid stick even before it becomes light on the skids, but should be finely set while hovering at chest/eye height

With Red electrical tape on one blade end and Blue/Black electrical tape on the other blade end sight thru the blades (trees in the back ground helps) figure out which blade is tracking higher than the other

Tweak ONE of the long linkages one turn at a time to bring the higher blade down to achieve our Horizontal line.

It IS possible to get the Heli to such a stage that it will Hover HANDS OFF in NIL wind conditions (or just slightly wandering off)… you can’t get any better than that! Again trust me on this one… I’ve seen it happening… with MY model!

Apparently the Head needs to be setup a bit differently once you’ve attained forward flight skills… But I wouldn’t know that yet.

My REAL in roads into confident Hovering were considerably helped by being warn down & succumbing to the smell of Methanol (brings back memories to my Plank flying College days, or if you’re a rev-head that wicked smell at the Speedway). Not only the sheer mass of a Nitro Bird helps in a stable Hover (especially in Windy conditions), but the efficiencies in larger paddles (Blades) cannot be under estimated (just the same as the larger Planks fly better).

I would suggest getting a 400 size (MINIMUM) CCPM electric Heli as a good starting point

Not being one to let a bargain go, I found myself (after struggling just to Hover with the Blade 400 for a year in somewhat gusty conditions) INVESTING in a Twister (American = Genesis) Pantera 50 Nitro Bird. An ARF (Almost [read: not really] Ready to Fly) for just AU$895! BARGAIN IMHO (In My Humble Opinion)! And a few months later the US 2 for US$300 deal was passed onto us Aussies and I managed to pick up a “whole Spares kit” (but not Caboodle) for AU$295.

The physical size of components sure helps us fat fingered adults with the fiddly bits (Pantera = no screw is less than M2.5… Blade 400 = smallest is M2 and 1.5mm Diameter pins abound!). These things are just waiting to be lost under the table… and you may as well forget looking in Carpet! Trust me on this… I have MUCH experience in these matters.

Once the initial intimidation of a 1600 RPM whirling set of 600mm (24”) (about 1250mm (49”) Diameter) blades & a 90 Decibel screaming Nitro engine was overcome the Pantera 50 has proven itself to be a most reliable and stable Bird indeed. Actually being able to SEE the Bird when you are “Two mistakes higher than you need to be” has saved my Bacon on nearly every flight!

I can now confess that I am hooked on the Pantera 50 concept of being designed (and optioned) to run a 90 size Motor with other options for 4-Blade Head, great idea… one Bird… MANY guises. The Web is a terrible thing really, while simply browsing I just happened along a backup Pantera 50 (which had all the fruit (upgraded Servo’s etc) I was working towards) for a mere AU$600 delivered! An even better BARGAIN IMHO!

MANY RC (Heli) Pilots rave about using the SIM (PC RC Simulator) to get your skills up… I have the latest V2.5 Phoenix version which is excellent, but just doesn’t cut the Mustard for me… there’s nothing like the real thing. To quote a phrase from John Beech (designer of Pantera 50) “There are many 2 Gallon experts out there… there’s NO substitute for experience behind the sticks”

There is some excellent (and not so excellent) Web advice out there… indeed there are many THEORIES out there too, but if you’re interested in some informative and entertaining Heli setup Videos from the well respected Bob Finless check them out at HeliFreak http://www.helifreak.com/showthread.php?t=52530. I may even have a CD copy of some (they are large & there are many) in my car if you catch up with me at the field

If you’re interested in a step by step training schedule this 10-day (yea right) plan should do the trick www.rchelicopterfun.com/how-to-fly-rc-helicopters.html

So next time you see that 3D Heli Guy throwing his machine round the sky, appreciate the fact that he’s stuck with it for a while and maybe even “Purchased crash repair kits in BULK” until he got to the skill level (and Heli setup) you see before you… OR he’s a 1 in a 1000 who’s a natural and has NEVER crashed OR he’s a Sponsored Pilot who knows nothing about Heli setup (but that’s just half the fun!)

Anyway enough from me… you should be out there doing it…

Happy Hovering (YES you will need to do this Stunt at least one stage in your Flight… get good at that, you’ll need it)

Ian Cairns

Self confessed Rotor Head

Hinterland Model Flying Club