How much Expo and Why?

[ASH.]

I know this is down to personal preference but I'm always interested in how much expo people use when flying.

I use 12% - 15% and find that suffices for my style of flying which is smooth aeros when possible. Anything more than that and I feel less in control, less connected. I know the 3D guys can use around 50% but the norm seems to be 25%+ even for precision aerobatics. Have I got a sensitive touch or am I just too lazy to move the sticks.

Being a firm advocate of expo I always try to get newcomers to use it. I try to persuade it's nothing sinister and helps smooth out the erratic flying.

Your views please - always willing to learn.

 

Edited By ASH. on 28/11/2016 00:36:14

[Geoff S]

I use a lot (up to 25%) because I fly mode 2 and it limits the interaction between elevator and aileron which helps my somewhat wobbly right hand. Expo on the rudder is handy for take off because it means you don't over correct yet still have plenty for things like stall turns.

Geoff

[Gary Manuel]

It's personal preference. Some people like it, others don't. I like it and use and have it set quite high.

For me, expo is all about making low / medium / high rates all "feel" similar around the centre of the sticks.

I might use something like 30% on low rates, 40% on medium and 50% on high rates all adjusted so that the curves look the same around the centre on my JR tranny.

[Rich too]

Interesting thread, as I have had to dial it in for the first time in my 35 flying rc. I go with whatever the manual suggests. My Wots Wot XL suggests expo, but on the trans you can have both + and - expo, which is the correct one to use???

Thanks

[Phil 9]

it is not all down to personal preference a lot depends on the model and how you want to fly. I use it on my sport models because it cuts out the need to use different rates

a 3D model may use more because the large barn door control surfaces are to much an normal flying speeds but come into play during high alpha manoeuvres

also remember the % figure is a relative measurement so 30% on one model has a different effect as 30% on another model that has different size control surfaces or more deflection.

[Don Fry]

Posted by Rich2 on 28/11/2016 06:32:25:

Interesting thread, as I have had to dial it in for the first time in my 35 flying rc. I go with whatever the manual suggests. My Wots Wot XL suggests expo, but on the trans you can have both + and - expo, which is the correct one to use???

Thanks

Use the -, that gives less control movement round stick centre.

I once dialled in + on a plane by accident. The maiden flight was most interesting, as straight and level flight consisted of veering from one wingtip to the other.

[Rich too]

Thanks Donald, that confirms my thoughts.

[..]

Plus or Minus expo is not a general term with radio it's brand specific to always best to check your manual. Futaba & Spectrum are opposite.

[cymaz]

On Futaba kit -% gives greater expo....less sensitivity around the stick centre. I use it because, being a mode 2 flier, it reduces the X control of the elevator and aileron a bit.- 20-25 % is about right for me.

Edited By cymaz on 28/11/2016 07:47:32

[Peter Christy]

On modern helicopters, expo is almost essential - especially on the tail rotor, where 30% is quite common. I typically also use around 15% on the cyclics, as without this, it is too twitchy in the hover when set for aerobatic capability.

On fixed-wing, I usually don't use any - but I do have a couple of (semi) scale models that require a LOT of aileron and elevator on landing. This would be too much for normal flight / mild aerobatics, so I have a choice of using expo or switched rates. Because I already have a lot of switches to flick when preparing to land (retracts, flaps), I opted to go for 30% expo to reduce the pilot workload - and avoid a sudden change in sensitivity at a critical stage of flight!

It works well. I have plenty of control authority when I need it just prior to touch-down, but the controls are gentle enough at speed to produce smooth and realistic looking aerobatics.

--

Pete

[Rick Tee]

I set it up according to the models response, type and intended flying style. Just like trimming, set to suit the model usually aim for a linear feel unless its a 3D model.

[Chris Walby]

I have used expo (40%) and elevator travel on a foam P51 war bird ( the main retracts are set back in the wing and there is a lot of weight up front) so it tends to nose over on landing just as it rolls to a rest + initial take off roll out before the prop wash takes affect.

My answer is lots of elevator travel to stop it tipping over, problem is it makes it hard to fly scale so the expo helps during flight.

Only down side its don't stick bang at full speed (not a issue if scale flying anyway) a this model has a habit of loosing its tail!

PS it has a 4 blade prop and there are no more spare spinners so I am looking after the one I have

PPS Cymaz I adjusted the tension on my TX stick (aileron) which seems to help so it feels a bit more "centred"

[Don Fry]

Posted by Justin K. on 28/11/2016 07:25:16:

Plus or Minus expo is not a general term with radio it's brand specific to always best to check your manual. Futaba & Spectrum are opposite.

I think they are not opposite. I am Spektrum now, used to be Futaba, and don't remember a chance when I swapped. Don't know about other brands.

[Jon H]

Expo is a wonderful tool but is very often misused and the way it operates is misunderstood.

I fly a range of models from a small 36'' ballistic plank, through sport and scale right up to a wafty old 82 inch biplane and 2 heli's. Only 2 of the fixed wing models, ironically the two at the extreme ends of the scale, use any expo and that is 10% on ailerons.

In general, it is better to set up the model with no expo and suitable rates for a test flight. I tend to ignore instructions these days, but if the instructions have a high and low recommendation i take the low setting, then set my rates 10% or so below that for low rates and 10% above it for high. This guarantees me adequate control without it being excessive.

Once in the air i make up my mind if i need more or less rates before going any further.

Elevator rates are usually easy to work out. If its super pitch sensitive then take some movement out. This is especially true for warbirds where elevator is normally really sensitive.

Ailerons are also easy and irrespective of what model i am flying i set them by running in at full power, pointing the nose up 45 degrees and using full stick travel do a roll. I then reduce or raise my rate to get to my desired rate of roll. In the case of a warbird, this is say 10-20% faster rate of roll than scale. Now that is set, if i find the model is sensitive on ailerons at normal flying speed i add 10% expo and bosh. All sorted.

Where i have seen people go wrong is they have a really sensitive model, with excessive rates and then slap 20 or 30% expo on to calm it down, sometimes more. They then fly around using only 20% of their stick travel. In this instance, they would be better off cutting their rate at least in half and ditching the expo. By using more stick travel, you automatically make the input smoother as a larger deflection of the stick results in a smaller deflection of the servo. On most of my models i regularly end up at the full deflection of my sticks during a flight, especially on my neiuport who's ailerons are soggy to say the least.

The problem with using high expo is the sudden increase in control surface movement for a given stick input. Without expo you get gradually decreasing control deflection for a given input due to the arc our linkages follow as the servo moves. This can be quite handy as the effect on elevator would be to give you more delicate control when the stick is fully aft. This would be very helpful when holding off to land.

If you take the opposite, add some expo and then try the same. As you pull back, you get an ever increasing amount of elevator which often leads to a greater than intended pitch up. This is corrected but often results in greater than intended pitch down...and so the cycle continues. When it comes to flare, the rapid increase in elevator deflection can easily pitch the model beyond stall and everything ends up in a crumpled heap.

I do understand the comments about using it to prevent elevator/aileron interaction on mode 2, but i also dismiss it as i fly mode 2, and i did an experiment with a friend some time ago where i had my setup on one rate setting and his (20% expo) on another, he said he preferred his and asked me to reset my one to his. I did, but actually reset his to mine. He then flew waxing lyrically about how this was much better than on my setting....i smirked and only told him what i had done after he landed. He was quite surprised and now never uses expo on anything.

So long story short, it will only take a flight or 2 to get used to being more accurate around stick centre, and for Geoff with his rudder (and anyone else on any other surface) i would say to ask yourself 'do i ever need to use full stick deflection?' if the answer is no then reduce the rate first, dont add expo right away. If the answer is 'yes i need full rudder for a stall turn' then great, add a little expo if it helps you on the ground. I also tend to setup different rates for takeoff/landing on some models to suit their behaviour at low speeds. Again, its not uncommon for me to touch down with full elevator applied, and even on a warbird i have no fear of a stall because of the setup i have used.

The setup Gary uses is fair enough, i can understand why he would set it like that but in general its unusual to have 3 different rates set up on a single model. Is that model 3d by any chance?

Anyway there we are, my long and convoluted story is complete.

 

 

Edited By Jon Harper - Laser Engines on 28/11/2016 08:57:37

[..]

Posted by Donald Fry on 28/11/2016 08:46:17:

Posted by Justin K. on 28/11/2016 07:25:16:

Plus or Minus expo is not a general term with radio it's brand specific to always best to check your manual. Futaba & Spectrum are opposite.

I think they are not opposite. I am Spektrum now, used to be Futaba, and don't remember a chance when I swapped. Don't know about other brands.

Yes they are.

[Cuban8]

Posted by Jon Harper

The problem with using high expo is the sudden increase in control surface movement for a given stick input. Without expo you get gradually decreasing control deflection for a given input due to the arc our linkages follow as the servo moves. This can be quite handy as the effect on elevator would be to give you more delicate control when the stick is fully aft. This would be very helpful when holding off to land.

If you take the opposite, add some expo and then try the same. As you pull back, you get an ever increasing amount of elevator which often leads to a greater than intended pitch up. This is corrected but often results in greater than intended pitch down...and so the cycle continues. When it comes to flare, the rapid increase in elevator deflection can easily pitch the model beyond stall and everything ends up in a crumpled heap.

Edited By Jon Harper - Laser Engines on 28/11/2016 08:57:37

My Hanger 9 P47 was a real pig to land nicely until I reduced the elevator expo to 10% from 30%. Appears counter intuitive until you think about it, and what's actually going on.

[Ian Jones]

Posted by Justin K. on 28/11/2016 08:58:34:

Posted by Donald Fry on 28/11/2016 08:46:17:

Posted by Justin K. on 28/11/2016 07:25:16:

Plus or Minus expo is not a general term with radio it's brand specific to always best to check your manual. Futaba & Spectrum are opposite.

I think they are not opposite. I am Spektrum now, used to be Futaba, and don't remember a chance when I swapped. Don't know about other brands.

Yes they are.

Yep, Justin is right. Donald may not have realised it for some reason but I have seen quite a few maiden flights go badly resulting in either a crash or the builder selling the model on because it was difficult to fly.

Futaba "-" reduces the multiplier used to calculate the servo movement around the the centre point with an opposite effect at the extremities.

Perhaps "putting in some expo [adjustment]" sounds like a positive and when Spektrum came along that's how they referred to it. Or is it something inherited from JR?

[Jon H]

Posted by Cuban8 on 28/11/2016 09:18:41:

Posted by Jon Harper

The problem with using high expo is the sudden increase in control surface movement for a given stick input. Without expo you get gradually decreasing control deflection for a given input due to the arc our linkages follow as the servo moves. This can be quite handy as the effect on elevator would be to give you more delicate control when the stick is fully aft. This would be very helpful when holding off to land.

If you take the opposite, add some expo and then try the same. As you pull back, you get an ever increasing amount of elevator which often leads to a greater than intended pitch up. This is corrected but often results in greater than intended pitch down...and so the cycle continues. When it comes to flare, the rapid increase in elevator deflection can easily pitch the model beyond stall and everything ends up in a crumpled heap.

Edited By Jon Harper - Laser Engines on 28/11/2016 08:57:37

My Hanger 9 P47 was a real pig to land nicely until I reduced the elevator expo to 10% from 30%. Appears counter intuitive until you think about it, and what's actually going on.

Thats it exactly. I flew one of these for a friend who had some....interesting rates/expo set up and wanted it sorted out. Once set (no expo, cant remember the rates) it was a delight to fly, although the DLE20 in the front was offensive!

Another chap as my club has one too with an Enya 155 in it. Its very nice indeed

[Bob Cotsford]

Well I'm with Geoff, as you get any sort of limitation to your dexterity it becomes more difficult to prevent interaction between controls because you can't feel the stick tension to gauge your movements. Over the last five years I've started to use expo as a matter of course. I find it helps enormously with slow rolls and similar, not to mention landings with a standard Acrowot which for some reason gets really ticklish on the last 2' above the ground.

Some models - eg Cougar 2000, Panic - I might use 50% or more on full rates, classic pattern models very much less. For rudder on take off I prefer to use low rates rather than lots of expo for some perverse reason.

[john stones 1 - Moderator]

Humbug

Next you'll be mixing out pitch+roll for straight n level K/E flying n telling us your a wonderful flyer. Kids today eh, n you say MR's don't require any skill to fly them.

John

[Peter Christy]

Posted by Bob Cotsford on 28/11/2016 10:41:37:

...... more difficult to prevent interaction between controls because you can't feel the stick tension .......

Exactly! Why do modern transmitters have such feeble springs on the sticks? And why are the sticks always so short?

I much prefer long sticks with proper springs in them, but the only way to get the right feel seems to be to mod it yourself!

Grrr!

--

Pete

[Biggles' Elder Brother - Moderator]

Well first of all another voice to say Justin is right! Whether +ve or -Ve expo "softens" the centre depends on what brand of radio you use. Fubtaba is -Ve, Spektrum is +ve, Taranis is +ve, JR is +ve (I think?).

Second - this is a very personal thing - I do not believe you can really say there is a definative "rates are better employed than expo" or vice-versa - or that people in general "don't understand" expo! In my experience I've seen models well set up from a "primarily rates" position and equally I've seen models well set up fropm a primarily expo position - both can work well. Its very much a matter of preference and secondly (to a lesser degree in my view) it's a matter of model characteristics. I feel that because I believe it is possible to get a good set uo on any model using either rates or expo as your primary tool, but its probably also true to say that with certain models one route may be easier than the other.

There is nothing at all to stop you uisng both of course!

Personally I use expo primarily - I tend not to use rates. I use expo on elevator and ailerons - I very rarely use it ion rudder, I don't seem to feel the need. The amount I use varies enormously depending on what the model's flying caharacteristics are. For slower, more ponderous, models (biplanes the Cub etc) it tends in general to be a smaller amount - typically 10-15%. In a few cases it could be 0%! At the other end of the scale very fast flying models - deltas etc - I use more - maybe as much as 50% in very extreme cases.

I often have variable amounts of expo available via three position swithches - sort of "rates for expo" if you like! This can be used to address issues where you might want more expo in flight than you do say on take-off or landing.

BEB

[Biggles' Elder Brother - Moderator]

Posted by Peter Christy on 28/11/2016 11:10:13:

Posted by Bob Cotsford on 28/11/2016 10:41:37:

...... more difficult to prevent interaction between controls because you can't feel the stick tension .......

Exactly! Why do modern transmitters have such feeble springs on the sticks? And why are the sticks always so short?

I much prefer long sticks with proper springs in them, but the only way to get the right feel seems to be to mod it yourself!

Grrr!

--

Pete

I agree!

BEB

[Jon H]

You can tighten your springs guys. Most radios are adjustable these days and this should help find the middle

I agree that long sticks are superior as well but not to the extent that i need one of those tray radios our European..err, friends? like to use. I feel that strapping on a radio like im about to go rock climbing is a little excessive.

[john stones 1 - Moderator]

I wind my sticks all the way down and tighten the springs up, it feels awful when there's no positive feel for the center, long sticks are not superior......hands/thumbs come in differing sizes

John