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Acro Wot ARTF (balsa) chat

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Jonathan M18/12/2018 10:31:55
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Posted by Tim Flyer on 18/12/2018 10:15:57:

... I also have a Wot 4 kit built plane with OS 80 and I’m very very pleased I put the Chris Foss designed air brake/flaps on that.

Tim

Can you describe wot brake/flaps setup you have on your Wot 4, and how you might do this differently for an Acrowot?

Jon

Tim Flyer18/12/2018 11:36:18
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The airbrake/flap set up I have on the Wot 4 kit build wouldn’t be easy to replicate on the ARTF. It has oversize flaps which are hinged in the centre acting as a brake above the wing and flap below as they rise. They are brilliant and allow a nice steep approach despite having the Laser 80 power. They are mixed with a bit of up elevator too . On the Acrowot there isn’t really room for these . What I will do is program “ upward moving flapperons” this will slow the plane and reduce the floaty tendency and allow shorter landings . I also use upward flapperons on my Wot 4Xl. I will also mix this with a bit of up elevator. Here is a photo of the Wot 4 wing . 598ca135-4b31-4e69-8335-22be913b7c18.jpeg

Edited By Tim Flyer on 18/12/2018 11:59:46

Jonathan M18/12/2018 14:19:14
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Cheers Tim - a good solution.

I've programmed down-flapperons via a swtich into my ARTF Acrowot, but they seem to make the model more floaty rather than slowing it down in light winds. I don't know what the solution is.

The solution I use on my Middle Phase is up-flapperons (on the 'throttle' lever, max about 40deg, mixed in with a tiny amount of elevator compensation) to kill lift for landings in tight spaces - this is very effective in 'pressing' the model onto the ground before slope-lift catches it again.

I'm not a very good power-flyer, but I wonder whether learning to side-slip would reduce lift and slow/steepen the decent on landings?

Edited By Jonathan M on 18/12/2018 14:20:08

Jon - Laser Engines18/12/2018 14:30:42
4230 forum posts
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Posted by Jonathan M on 18/12/2018 14:19:14:

Cheers Tim - a good solution.

I've programmed down-flapperons via a swtich into my ARTF Acrowot, but they seem to make the model more floaty rather than slowing it down in light winds. I don't know what the solution is.

 

Edited By Jonathan M on 18/12/2018 14:20:08

If you want to add flaps just cut the existing aileron in half and then remove the inner half. You can then adjust the bevel to allow greater down movement and with some care you should be able to install torque rods in the root and have a single servo in the fuselage do all the flapping. If something gets in the way of the fuselage mounted servo, fitting another servo in the wing should not be too difficult.

Once its all set up set the flaps to come down almost vertical like on a Spitfire. This should add maximum drag with very little additional lift.

Also be careful with flapperons as they can induce tipstall if you go a bit mad with the travel. 

You also say you arent a good power flyer? I assume you mean you are not experienced with power? If so the its possible the additional weight of the model is catching you out. Its also possible your engine/prop combo are not helping either. If you can give details of the engine, prop and idle RPM you have set we might have more ideas to point you in the right direction. 

I only say this as i have flown one of these with an SC 70 and had no trouble slowing it down to land it. 

Edited By Jon - Laser Engines on 18/12/2018 14:34:13

Jonathan M18/12/2018 15:00:42
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Hi Jon

Your suggestion of cutting the ailerons and fitting flaps is a good one, but (given the massive down-braking you're indicating) surely one would only need to cut say the inner third, leaving the remaining two-thirds for all other necessary aileron duties?

I'm no beginner to power, I got my A Cert a few years ago and I'm a competent flier, but I'm not yet a fully-experienced one as I still have to think what I'm doing (whereas I find slope-soaring more instinctive).

My ARTF Acrowot:

  • ASP 70FS
  • 13x6 prop
  • RPM range 250/300 to 10,000

I don't have a problem landing in normal wind conditions, just when there is very little of it. What do you think?

Jon

Chris Walby18/12/2018 15:40:05
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Hi guys,

My Acrowot flies quite slowly, but has been much improved by moving the CofG back a bit (mine requires very very little elevator between normal and inverted flight. The upside is lower landing speed.

Its typical wot bouncy undercarriage so I bleed all the airspeed off until it just sits down. The roll out after that is not long as it does not weigh much. You could put smaller wheels on it and hence the drag it might then tend to nose over although you have plenty of elevator authority.

IMHO I would not bother with flaps as its likely to give you more problems than you will solve with a light model/short wing. By all means get a model with flaps and practice that way.

What does yours weigh by the way? I'll check, but I think mine is 2.6kg AUW

Jonathan M18/12/2018 15:49:18
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520 forum posts
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You're right about not troubling with an actual conversion to flaps - I'm just curious about the theory of it.

Mine weighs 2.7kg AUW including the bit of tail-weight I added to get the CG back to the specified mark (I was so anxious to not start with a tail-heavy model, that I mounted the 4.8v battery-pack right forward under the tank). I could try it a bit further back still - as I already have huge trouble getting it to stall let alone drop a wing!

Jon - Laser Engines18/12/2018 16:14:29
4230 forum posts
155 photos

1/3 should be fine as a flap. I was just using half as a rough guide.

That said your comments about c/g open up a possibility because if you are nose heavy this could mean you run out of elevator authority before you run out of airspeed. This could be why the model is so reluctant to stall and it would also give that uncomfortable feeling of trying to hold the model in the air with the elevator stick. You could add extra elevator movement, but if the model is nice to fly as is i would leave that alone and move the c/g back a touch.

As you suggest yourself, moving the battery back a bit would be a good start and as chris suggests you should hold it off the ground (about an inch up is ideal) for as long as you can before it settles on its own.

On the engine side, assuming you mean 2500-3000 then thats a good idle but i would most certainly aim for the 2500 end of that range. 13x6 @ 10k is also just fine. I was worried you were using a 12x8 or something as that would not be helping you.

Glenn Philbrick18/12/2018 17:55:49
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dsc04114.jpgdsc04113.jpgGoing back to the electric Acro wot, I've put on a couple of pics of how I fitted my hatch and batteries, don't forget this was built as a repair on a crashed fuselage I was given. Also I am comparing to my IC acro wot with a 91fs.

This one pulls 35A, 735W though a dsc04112.jpg 70 A esc with a 12x 7 prop. If I fit a 13 x 6 it pulls over 1000w but thing start to get warm.

Bruce Collinson18/12/2018 19:59:19
202 forum posts

Chris,

Where’s your c of g please? I might twitch mine back a bit .....

BTC

Tim Flyer18/12/2018 20:41:12
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847 forum posts
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I use up flapperons on my kit built Acrowot too to reduce float when coming in . I have only a small movement though ( about 7mm) .  My kit Acrowot is also very heavy, fully glassed and built like a tank but it goes rather fast with its “slightly hotted” OS55 and properly adjusted long tuned pipe😊. I like Acrowots!

Edited By Tim Flyer on 18/12/2018 20:52:56

Chris Walby18/12/2018 22:12:59
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731 forum posts
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BTC,

I'll measure it again as I set it up initially a couple mm in front of recommended spec of 83mm, but had the RX battery in the wing bay thinking it was easy to fit + some lead behind the spinner on the engine casing.

After a few flights I started getting used to it and noticed landing was a bit fast and I needed to hold some elevator in when inverted.

I cut the battery hatch cover out and fitted the RX battery in there and was thinking about removing some lead and then went up the flying field.

I offered Dave one of our club instructors a flight to see what he thought + asked about the C of G and we took all the lead off and put the cowl back on.

The C of G was definitely further back, but still within the +/- 6mm tolerance so I flew it and it was much better, Dave flew it and announced "it flew as if on rails" so I haven't adjusted it further.

PS I had a BH speed air initially electric and then Laser 70 powered and there was something nicer about the IC set up. I assumed it was something to do with the design (for IC) and that the engine centre of mass is different to the motor/lipo centre of mass. I don't think its a common thing as I have electric only models that are equally nice feel.

Jonathan M19/12/2018 08:23:37
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520 forum posts
258 photos

A very interesting discussion, and useful to rule out other factors - thanks Jon. Aside from fast landings and difficulty in getting the model to stall, inverted does currently require quite a lot of forward pressure on the pitch-stick.

So I'm going to move the battery back from the tank-bay to the forward part of the wing-bay, then check the static CG again (fine-tune by keeping or losing the tail-weight). It is currently on the specified 83mm mark (*) but assume it can safely be moved up to 6mm back. Then do a dive-test to re-trim the elevator, etc.

NB * Of course we sometimes forget that the initial 'specified' mark on commercially-produced ARTFs is usually too far forward - makes for a safer, litigation-free start, but not yet a satisfyingly-tuned model.

Stuart Z19/12/2018 08:46:28
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343 forum posts

A very interesting discussion and one that needs a lot of attention. I’m linking in on trimming guidelines used by the aerobatic folks

**LINK**

S

Jon - Laser Engines19/12/2018 09:18:33
4230 forum posts
155 photos

I would throw any manufacturers c/g out the window to be honest. I dont think i have a single model set at the recommended c/g any more and only use the supplied figure for the test flights. After that i usually change it quite a bit. The worst of all was my Hangar 9 pulse. The c/g was so conservative i must have moved it an inch further back and to be honest i think it could stand to go a little more.

The info Stuart provided is good but your acrowot is not as 'straight' as a pattern ship so dont get too obsessed with it. If i were to test my warbirds to that schedule they would all be condemned! Getting a good setup on the model is very important, but dont get caught up in the minutia if you are just looking for a bit of sport flying and dont forget the model you are flying. Not everything will respond to that schedule in the same way and you might end up chasing your tail.

Remember too that trimming is not a static thing and will vary day to day. Wood expands when damp, metal pushrods contract when cold etc. Its not uncommon for models to be out of trim after a change in weather.

Stuart Z19/12/2018 10:57:40
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343 forum posts
Posted by Jon - Laser Engines on 19/12/2018 09:18:33:

I would throw any manufacturers c/g out the window to be honest. I dont think i have a single model set at the recommended c/g any more and only use the supplied figure for the test flights. After that i usually change it quite a bit. The worst of all was my Hangar 9 pulse. The c/g was so conservative i must have moved it an inch further back and to be honest i think it could stand to go a little more.

The info Stuart provided is good but your acrowot is not as 'straight' as a pattern ship so dont get too obsessed with it. If i were to test my warbirds to that schedule they would all be condemned! Getting a good setup on the model is very important, but dont get caught up in the minutia if you are just looking for a bit of sport flying and dont forget the model you are flying. Not everything will respond to that schedule in the same way and you might end up chasing your tail.

Remember too that trimming is not a static thing and will vary day to day. Wood expands when damp, metal pushrods contract when cold etc. Its not uncommon for models to be out of trim after a change in weather.

However, the info will be useful as it covers a lot of general setup items that are well explained

S

Bruce Collinson19/12/2018 13:52:43
202 forum posts

Glenn,

Ta; totally different, as you say following major surgery.

Chris, ta also; still within the +/- 6mm makes me less nervous so I will try a tweak.

Stuart Z; very helpful link. As one who defaults to a Wot 4 immediately followed by an Acrowot, both leccy but see passim, I found this thread very valuable.

BTC

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