Wot4 XL Flaps?

[Kim Taylor]

Evening all.

Following a house move, my new 'regular' club strip (I am still a member of and visit my 'other' club) is somewhat smaller than I am used to, and is most times surrounded by waist high grass

I therefore feel that it would be an advantage to have flaps on my largest model, the Wot4 XL of the title. I have previously set up flaperons but I don't think that I can get enough 'droop' on the ailerons to really have any effect on the landing speed - the Wot4 seems a surprisingly slippery airframe, given it's slabby appearance.

I intend to cut the ailerons into two 'halves' on each wing (like the Xtreme) and obviously modify the structure as necessary to fit the relevant servos. So far so obvious. 🙂

Now, my questions are:

1. What proportion of aileron to flap is felt to be right - I'm thinking something around a 60/40% split (in favour of the aileron, obviously)

2. Will it be necessary to link the flaps to the ailerons (when they're not being flaps) or will increasing the throw of the outboard 60% of the aileron be sufficient to maintain the current roll performance.

At the moment the model has been hanging up in my garage (2 garages, in fact) since before the covid lockdowns and it's bothering me that it's a waste. I could just try and sell it, of course, and buy something more suitable for my current circumstances, but I'm unlikely to be able to cover the cost of a replacement as everything has gone up so much. And anyway, where's the fun in that? 😁

If anyone has any experience, or opinion on the above please don't be shy. If you've done this mod to a Wot4 or XL - even better, how did it go?

tia

Kim

 

Edited July 23, 2023 by Kim Taylor

[Frank Skilbeck]

Kim, on my gliders which have flaps and ailerons I use flight modes, so in one mode the flaps are coupled to the ailerons but in landing mode they drop right down as flaps and aren't used for roll control. Can you do similar.

 

Note you may need to adjust the flap hinging to ensure the flaps can drop down enough to be effective.

[Nigel R]

Easiest answer must be to just flat out copy the wot4 xtreme. That looks to have about 60/40 split.

 

That said.

 

The main benefit with flaps on a wot4 will be the braking effect of the drag, come landing time. At the other end of the flight, you're not short of power to haul it up.

 

Assuming you do the split aileron/flap option, I'd think about 'stretching' the chord on the flaps, to bump up their area - aim for as much extra on the flaps' TE as possible.

 

As a refinement to the flaps, you could also add a combined airbrake extension to the top surface - a flat piece of 1/16 or 3/32 ply, extending forward a couple of inches from the hinge point. When close the ply sits against the wing surface, when flaps are down, the ply sticks upward like a spoiler.

 

Alternatively, pre-fab spoilers are available, which could be added to wing top surface, and deployed at the same time as the flaps go down.

 

I've also had success from using rudder airbrakes (although I did have two rudders to play with on that airframe) - so maybe a split rudder airbrake might be another option to consider?

[Ron Gray]

A couple of other things to try, spoilerons (ailerons up) instead of flaperons, I used them to great effect on one of my fast ish models. But the other thing that requires no airframe changes, side slipping on the approach. Not sure of the topography of your strip but it could work.

[Jon H]

I would alter your landing approach before you alter the model. A wot4xl will land at almost walking pace without too much difficulty. 

 

You will likely have to start slowing down much earlier in the circuit and i would practice slow flying with the model a little higher to get used to it. Just chop the throttle, pull the nose up and see how slow you can go. Depending on your setup you might need to hold full up elevator and then use the throttle for pitch control with the rudder for keeping straight and ailerons for keeping the wings level. Come in with a high angle of attack, plenty of back elevator and use power to help parachute down. I think you will be very surprised how slow it will go in its stock form. 

 

It will be fine with a wot4, just dont try it with a warbird. 

 

a c/g check might be a good idea too as most models are built nose heavy and are more difficult to slow down. 

Edited July 24, 2023 by Jon - Laser Engines

[Kim Taylor]

1 hour ago, Frank Skilbeck said:

Kim, on my gliders which have flaps and ailerons I use flight modes, so in one mode the flaps are coupled to the ailerons but in landing mode they drop right down as flaps and aren't used for roll control. Can you do similar.

 

Note you may need to adjust the flap hinging to ensure the flaps can drop down enough to be effective.

Don't know how to do multi quotes, so you'll have to bear with me I'm afraid.

Frank - Yes, I'm sure I can do similar either on my radio - I'd have to work out the programming but I know that others have done it.

 

eta Good point about the hinging - I probably wouldn't have thought of that until I couldn't get the droop I wanted.

Edited July 24, 2023 by Kim Taylor

[Kim Taylor]

1 hour ago, Nigel R said:

Easiest answer must be to just flat out copy the wot4 xtreme. That looks to have about 60/40 split.

 

That said.

 

The main benefit with flaps on a wot4 will be the braking effect of the drag, come landing time. At the other end of the flight, you're not short of power to haul it up.

 

Assuming you do the split aileron/flap option, I'd think about 'stretching' the chord on the flaps, to bump up their area - aim for as much extra on the flaps' TE as possible.

 

As a refinement to the flaps, you could also add a combined airbrake extension to the top surface - a flat piece of 1/16 or 3/32 ply, extending forward a couple of inches from the hinge point. When close the ply sits against the wing surface, when flaps are down, the ply sticks upward like a spoiler.

 

Alternatively, pre-fab spoilers are available, which could be added to wing top surface, and deployed at the same time as the flaps go down.

 

I've also had success from using rudder airbrakes (although I did have two rudders to play with on that airframe) - so maybe a split rudder airbrake might be another option to consider?

Nigel

The Xtreme arrangement is what put the thought into my mind and as you say, the approx 60 / 40 split. A clubmate also suggested raising the ailerons at the same time as the flaps drooped, which is about as far as I'd want to go to achieve my goal. Wholesale alterations to the airframe are not on my agenda at the moment (I've learned the hard way recently how quickly circumstances can change). If I can't get comfortable with it as above, I'll sell it on. 🙂

 

eta Got to go out now, I'll get back to the remaining posts later - sorry!!

Edited July 24, 2023 by Kim Taylor

[Tim Flyer]

On my Wot 4XL where I had a powerful OS120ax I used “UP Flaperons” . These act like air brakes cancelling lift and are mixed with a bit of up elevator. The flapperon setting just moves the ailerons up about 1cm . Setting these up only requires a bit of fiddling with the radio. Mine operate from a slider on the side of the transmitter. They enable a rapid slow down and add another fun feature to the plane. 
 Of course they aren’t really necessary at all as it’s certainly possible to come in slow on Wot 4s but I like the extra controls. Even my little Wot 4 uses the great fun air brakes that Chris Foss designed.

 

If you do add up flaperons / air brakes make sure you do plenty of testing high up first! 

Adding this feature adds interest/fun  with extra controls to the flying, and it’s nice being able to come in fast and stop when necessary.  I also use the up flapperons on my Acrowot XL and Galaxy Mystic and It works very well and provides ann extra bit of  interest. 

[Don Fry]

I would take note of Jon’s comments about flying style.
An easy, cheap option for flaps is a hinged barn door arrangement on the fuselage. Width of the fus, about the same in length, so it doesn’t fowl the ground, and a method bendy push cable to operate it so if it does touch the ground, it has some springing to avoid damage. Used on some interwar aircraft, and works well enough.

[Nigel R]

Jon is correct. You can always come in on the back of the lift curve, although it does not allow much wiggle room for errors or heavy handed flying (well, you get away with a lot on a wot4, but still...)

 

Extra features are fun in and of themselves.

 

Good call from Don on the fuselage option. I would note, apparently, such devices are best placed close to CG (well, centre of pressure, I think? but that is very close to CG). Easy retrofit.

 

Some details on adding a "belly board" to a full size homebuilt here http://www.flykr2s.com/bellyboard.html

[Mike Blandford]

I just use a "flight mode" for landing where I have the model trimmed with some up elevator for a slow glide with power off. Makes it quite easy to do a slow approach.

Just throttle back, let the speed drop off, then engage the flight mode and I get a stable, slow approach. I even have it configured so that if I open the throttle more than 20% the flight mode is turned off.

 

Mike

[Jon H]

Similar concept to the elevator flap mix i use on my warbirds. Essentially its the same as retrimming to land and that is standard practice for full size. 

[Nigel R]

Likewise for rudder airbrakes I have an elevator mix which gives a sensible landing trim.

 

I haven't yet set it up so that opening the throttle inhibits both brakes and trim - must do that.

[Kim Taylor]

OK sorry for the sudden departure - I'm back now.

To try to cover everything that's been raised:

Ron - I can easily try spoilerons, would just need to swap the aileron servo leads over to convert from flaperons.

The basic issue with the strip (certainly as it is at the moment) is that it's an approximately 50 - 60 metre diameter circle, surrounded by long (nearly waist height) grass. If you clip the grass with the landing gear it tends to grab the model, with the inevitable face plant looking ugly at best. I have got away with it, but you can't guarantee it. 

Jon - I think that your suggestion re: c of g has merit. I've been out in the garage and checked, and it's set to the front end of the suggested range. I know on my late normal sized Wot4 I had the c of g well behind the rearmost suggested point. The model does land like an express train and it doesn't want to slow down unless you start the approach in the next county. I'll experiment with it when I gather up the courage to take it to the field. I also need to fine tune the engine now that it's run in - I need to get the idle speed down as I think that is also contributing to the difficulties I've had. I've also got 2 or 3 years more experience now, which may come in handy!! 🙂

I think for now I'll wait for a suitable day (could take some time) have a fly with it and try moving the c of g back incrementally until I feel more comfortable with it.

If I still have trouble, I'll copy the split aileron / flap setup from the Xtreme and start playing with that.

Thanks to all for the contributions and I guess that the takeaway is 'if it ain't broke, don't fix it'.

Cheers

Kim

[Denis Watkins]

12 minutes ago, Kim Taylor said:

I need to get the idle speed down as I think that is also contributing to the difficulties I've had.

 

It is quite common to get confidence in a motor running leaving an high idle speed Kim, but even at 3000rpm the model can fly past.

You are right to suspect the idle as 2500rpm - 3000rpm is not so different on the ear.

Personally I get mine and the lads motors down between 2200rpm and 2500rpm for apparent in air braking and landing.

[Jon H]

I would be targeting 1800-2000rpm for an idle on an engine this size but it does depend on which engine you have installed

[john stones 1 - Moderator]

Along with c.g a simple change of prop often helps, if it's currently highish pitch fit one with less.

[Jon H]

Yes i was going to ask about the prop, and which engine its connected to

[Kim Taylor]

Hi again,

The engine (don't scoff 🙂) is an NGH GT17 petrol with a 15x7 APC prop. From memory it turns it at around 8000 rpm, although I've struggled to get a reliable idle below about 2200 rpm as it seems to load up (go rich) after 10 seconds or so. If I try to lean it out a bit at the bottom end, it tends to cut out as I open the throttle. I've now put in a throttle slow of 1 second, to try to alleviate this in the usual panic 'go round' situation, which really is where we came in.

I did have a 15x8 on it, but that pulled the revs down at WOT and it just seemed to struggle a bit on pick up, although it is quite torquey through the rev range.

It pulls the plane around the sky quite well insofar as it does everything I want it to do, it'll do all normal 'on the wing' aerobatics and will pull a vertical, although not by any means unlimited. All the above with the stock 'silencer' plus an additional can. It passes the std noise test, by virtue of the relatively low revs it pulls

It's supposed to be equal in performance to a .90 2/ glow and it sort of is, in everything except the ultimate top end.

When the weather improves, I'll get it up to the field, fine tune it and give it a go. What could possibly go wrong??

Kim

[john stones 1 - Moderator]

I have same motor on my Funky Cub, I love it, 15x6 on mine ticks over lovely, have you lessened the oil content after initial break in period ?

 

[Kim Taylor]

Hi John

I've been running it in on 20:1, then iirc 22:1.

I don't recall if I've gone to 25:1 yet, but I've just mixed some Aspen at that ratio for use the next time I fly it.

Have you got yours down to a sensible idle whilst keeping a good pick up through the mid range?

Kim

 

[john stones 1 - Moderator]

Mines good throughout the throttle range, on 30-1 now, did run a little lumpy new on the higher oil mix.

[Jon H]

32 minutes ago, Kim Taylor said:

NGH GT17

 

🤢 im feeling a bit queasy 😛 

 

32 minutes ago, Kim Taylor said:

15x7 APC prop. From memory it turns it at around 8000 rpm

 

That sounds about right, maybe a little slow as a laser 100 kicks out that sort of performance and i would expect a 2 stroke to offer a little more for same cc. 

 

34 minutes ago, Kim Taylor said:

I've struggled to get a reliable idle below about 2200 rpm as it seems to load up (go rich) after 10 seconds or so

 

Its probably a combination of mixture and temperature. Petrol engines are more sensitive to mixture change due to temperature than glow engines are. 

 

I would simply do as you have already decided and spend a few minutes having a tweak of the needles. Also when it comes to a go around there is a tendency to want to firewall the stick but that is rarely necessary as half throttle will be more than enough to stop the model descending and get it accelerating. So you can be fairly quick up to half throttle, and then add the rest of the power more slowly. 

[J D 8]

                   I only fly glow or diesel but would like to know why model petrol engines are sensitive to changes when I never have issues with my lawn mower, strimmer or brush cutter.

  

[Jon H]

Just now, J D 8 said:

                   I only fly glow or diesel but would like to know why model petrol engines are sensitive to changes when I never have issues with my lawn mower, strimmer or brush cutter.

  

 

Most 2 stroke garden equipment runs a warbling rich in a cloud of smoke. They are tuned this way deliberately to make sure they run as a no fire due to being lean is beyond the diagnostic abilities of most end users. In my experience its even a struggle for most model flyers to deal with an engine that will show no signs of life at all and we all have experience with them. The general public stand no chance. There are also fuel/oil/temperature considerations as a chainsaw can be used anywhere in the world and it has to just work out of the box with no adjustment. 

 

In any event, garden equipment is not tuned anywhere near its maximum performance as it just has to run well enough to murder some dandelions and nettles.  its not like you care about the mid range throttling of a chain saw either. As long as it starts, and then runs fast enough to chop your logs that is good enough. Model flyers on the other hand want better performance than that so we have to run our engines closer to peak performance meaning small changes will have an impact on the running of the engine. 

 

Mowers are a bit different but are typically around 150cc so are in a different class all together as small engines of any sort are always going to be more fussy than larger ones. Remember all the fun that was had trying to coax cox 049's etc into life? Glow engines below about 3cc are far less friendly than bigger ones. Equally, petrol engines get more fussy the smaller they get as well, its just the floor is higher for petrol due to the small amount of fuel being used. It takes very little to have a big impact on the fuel delivery. Its why i couldnt use walbro style carbs on the laser petrol efforts. They just didnt work with fuel demand that low. The accuracy and consistency just wasnt there.