What WOT 4 (ARTF electric)?

[Biggles' Elder Brother - Moderator]

The weight question has filled me with curiousity now! It's perfectly possible my memory is at fault - it was some time ago when I put this together.

I'll try to nip out to the shed this afternoon and quickly weigh the WOTTY. I'll report back.

BEB

[Kim Taylor]

Posted by Kim Taylor on 10/10/2018 20:21:41:

I don't know if they've got heavier over time, but my one which I recently completed, albeit using a 6s 2700 Lipo, weighs 6 pounds.

I know my power train (which I had 'in stock' ) is a bit ott, but I don't think it's a pound and a half heavier than a 'standard' setup.

I you look at the Wot 4 artf thread, most electrics seem to come out at around 5 and a half pounds, which I would agree with.

Kim

Edited By Kim Taylor on 10/10/2018 20:22:38

Edited By Kim Taylor on 10/10/2018 20:23:17

Just for comparison purposes, I've weighed my LiPo which comes in at 425g and the catalogue weight of my motor - EMax 4020/09 - is 290g.

As I said above, total weight of mine is pretty much spot on 6lb, so you should be able to work it back from there.

Kim

[Jonathan M]

Ordered mine now from SMC who had all the particular bits I wanted and threw in 2/3 different props for watt testing.

Overlander power-train: Tornado Thumper Brushless 4250/06 800KV (about 800W), 60A ESC (max 80A 10 secs), and some 4s 4,250mAh batts - all of which is a little meatier (and heavier) than the 4-Max options.

New Power XL-38HMB servos - metal geared standards.

3" foam wheels

Watt-meter.

Will be interesting to see what it all weighs... and how it eventually flies... and for how long per battery!

Cheers

Jon

[Bob Cotsford]

If I could extract myself from this armchair I'd go and weigh mine but I doubt it weighs as little as 4 1/2 lb even without the battery. The supposedly lightweight Wot 4 Pro is listed as 4.4 lb so I would have thought 6 -6 1/2 lb more likely for the full blooded one.

[Jonathan M]

So my Wot4 ARTF, which was assembled and test-flown by a club-mate, is now good to go. I had a single flight at handover this week. It was a bit blustery and was flying on his 'soft' TX which I wasn't used to (my sticks are set to stiff) and 10% expo (I'm normally 15% plus) so it was a bit twitchy... but WOW! Quite different to my comparatively more stately Acrowot with its 70FS. Being back on electric for the first time in the few years since I trained on a foamie, I'm also going to have to get used again to the immediate throttle response!

With a Overlander Tornado 4250 800kv motor, a 60A ESC and a 14x7 prop, the max static draw was 54A with 25N thrust (the 13x8 maxed at 50A and 23N). The model is exactly 2kg plus 0.4kg for the 4S 4250mAh Lipo, so the flying weight is right on spec at 2.4kg (5.25lbs), giving a loading of 20oz/sqft which is almost exactly the same as my IC Acrowot. CG is at 82mm specified.

I was originally going to buy the Wot4 and power-train from 4-Max, but he insisted the flying weight would be 4.75lbs and that the model should take a smaller motor, ESC and Lipo. From the feedback earlier in this thread I wasn't so sure about that, so went down this route - if I don't hooligan it around the sky, I expect to get decent flight times with this setup.

One other thing: despite the coloured trim and decals, white isn't exactly the easiest colour to see against an overcast sky!

Now just the weather...!

Jon

PS my mate is now buying the slightly smaller 43" Balsa ARTF version for himself, as it takes the cheaper 3S 2200mAh Lipos of which he has plenty.

Edited By Jonathan M on 12/01/2019 17:32:44

[Jonathan M]

First flights today on my own TX, working through all four 4250mAh 4S Lipos. Aim was to settle the Wot4 nicely down on mid-rates, do a full stick roll no faster than about 1.5 to 2secs, trim out any warps etc (both ailerons certainly have inherent twist), etc.

Initially found the whole thing a bit too fast (cruise needed about 65% throttle) with the batt down to 40% (my limit for ensuring longevity) after just 8 minutes flying. Next batt decided to slow it up by adding a few clicks of up-elevator trim, which got us cruising nicely at half-throttle and after a few aeros landing on 8 mins with 55% capacity left, although whenever I did need to open up the taps a bit the climb became too steep a bit too quickly. Next batt tried a couple of 3-turn spins, but the model was a slightly reluctant to stall at first and my impression was that it then went into more of a spiral-dive than a flat spin (it certainly both spun and descended particularly fast!). Initial rolls (without any bump of down-elevator when inverted, or top-rudder which I can't yet sequence in my mind) needed a lot of initial climb to compensate for the subsequent dropping out. Landings tended to float a bit then bounce (but this may be more to do with the light wind and my lack of experience?).

All of this should have prompted me to do an inverted dive-test to check CG (set as per instructions at 82mm), but the patch was becoming a bit busy with members doing 3D and random folk talking to me while I was flying. My brain was by now going mushy after such a long layoff and in the cold, so I just pootled around for the last batt.

Now at home, I've just remembered something from Geoff's Wot4 Mk2 electrification thread:

Posted by Biggles' Elder Brother - Moderator on 13/10/2018 13:58:14:

I would agree with Ron here. When I say mine balances fine - it does - but it isn't set at 82mm from the LE as the instructions say. You will find that nose heavy I believe, I know I did. By all means try it, but I bet you move it back!

Personally I think the wing incidence is fine - personal taste of course - but for the CoG I'd say 85mm back is the beginning of the "good zone"! After that it just depends how sensitive you like the elevator to be.

I assume everything I experienced earlier today points to a CG spec that is really too far forward? I plan to add some lead to the tail to bring it to a static 85mm before taking the Wot4 up again, then dive-test and fine-tune etc.

Otherwise a lovely model for the job!

Jon

[Geoff S]

Yes, I use a similar power set up on mine (though with a different motor/esc) with 4 AH 4S LiPos and get 10 minute flights comfortably which is long enough for me.

Mine's very reluctant to spin and I've pushed the battery back as far as it will go so I guess a little tailweight is the easiest solution. When it does go into a 'proper' spin on elevator and rudder it's very fast but recovers instantly on centring the controls.

I'm sorry to confess I haven't been up to the field yet this year. I've been busy playing with a new bicycle and it's just a bit too cold for my ageing bones to be standing on a draughty airfield for an hour or two.

Geoff

[Kim Taylor]

I originally had mine balanced at 85mm but found I was still dialling in about 4mm of up trim on the elevator to fly level at half throttle.

After conferring with clubmates, I have added (in stages) 20g to the tail. Still flies with approx 1.5mm of up trim but goes inverted with just a smidge of down and slow rolls are nearly axial without elevator input. When I've next got the gauge out, I'll measure where it's balancing.

Beware of the rudder / pitch coupling - I broke mine last week when on a crosswind approach, I needed to input a lot of rudder at the last minute and the resultant nose drop was enough for me to drop in about a foot short of the mown patch and it did a somersault which broke the fin away from the fuselage.

Kim

[Ron Gray]

I’ve flown mine quite a bit now but went back to trimming basics. On the 45 degree inverted half throttle climb she gently drops her nose and that’s with the 5s batt pushed back. Similarly when inverted it just needs a smidge of down to keep it level. So c of g ok, but on upright, level flight it drops its nose, power on or off. So I raised the main plane le to give it more incedence but that didn’t make much difference. After removing that I tried to see if I could get it level by using flapperons that I could dial in with a rotary knob. This made it worse! But if I used spoilerons it got better (the reverse to what I expected). I then took the drastic action of cutting out the tailplane and adding - incidence (raised the te) with about 3mm in place it got rid of the nose down in level flight. I’ve got some more tests to carry out tomorrow, vertical power off dives to confirm my settings and if ok I’ll glue it up like that. One thing I will say is that it spins with no problems now (with the batts back). For landings I use spoilerons which result in bounce free touch downs!

[onetenor]

Surely moving the CG back increases nose heaviness or did I miss something?

[onetenor]

Surely moving the CG back increases nose heaviness or did I miss something?

[Jonathan M]

Posted by onetenor on 21/01/2019 03:19:10:

Surely moving the CG back increases nose heaviness or did I miss something?

The more nose-heavy a model, the further forward will be its CG.

Adding tail-weight (or moving the battery in the direction of the tail) will therefore "move the CG back".

[Jonathan M]

Interesting Ron and Kim...

Last night I carefully re-checked the CG, which is already in fact at 85mm. While I've got stick-on weights to tweak things further when next in the air, in the light of Ron's comments it would seem wise to first check wing-incidence on the bench. On the principle that a symmetrical wing aerobatic model should actually have a smidge (0.5° appx) of positive incidence (and my ARTF Acrowot had similar problems until I discovered it was manufactured with 1° negative incidence), a slight re-seating of the wing may be necessary?

Of course increasing the wing incidence will also increase the nose-down flying attitude, so Ron's method of correcting this by packing up the TE of the tailplane would be a smarter solution... but harder to do given my tail-parts are all now permanently fixed!

The other thing to sort out before I next go flying is the engine thrust line. There's a sharp swing to the left on take-off and a sharp pitch-up on opening the throttle from slower speed, which each indicate that the engine probably needs 2° of right- and 2° of down-thrust.

Edited By Jonathan M on 21/01/2019 08:23:04

[Jonathan M]

[oops, double-post]

Edited By Jonathan M on 21/01/2019 08:22:44

[Jonathan M]

So I managed to get out again with the Wot4 this afternoon - colder and windier but had the patch all to myself which made concentrating easier!

The CG at 85mm is actually spot on - no pulling to canopy or undercarriage in a long vertical dive - and have decided to leave thrust-lines at neutral for now, using rudder to correct swing to left on take-off etc.

Ran through the B-Test manoeuvres - not very well but it was starting to blow harder with increased turbulence from various tree lines, a tricky variable cross-wind and slope-related lift/sink beyond the main patch on two sides. Tweaked rates a bit (a bit less rudder, a bit more aileron) and, despite wearing padded gloves, suddenly found myself much more in the groove! Got rid of the previous bounce on landing by coming in slower at a less steep initial descent, then levelling out while watching to keep the fuselage horizontal until it settles. Managed two passable consecutive rolls upwind with a bump of down-elevator at each inverted, but bottled out of the second roll downwind due to the rising wind. Stall-turn fine, figure eight circles of roughly equal size and height/bank-angles with crossover in the middle, but need more practice on setting up the stall and three-turn spin - rudder alone won't do it, but full aileron as well turns it into a spiral dive.

Now that I settled down a bit, have increased the timer to 10 minutes, which is just the right length for each flight, and landing with no less than 35% remaining.

All told a lovely bit of kit with loads of potential, and an ideal electric aerobatic model to get me up the patch as frequently as possible to progress my side of the flying! Glad also I went for the normal size balsa ARTF rather than either of the smaller options - it has exactly the right weight and presence (very similar to the FS Acrowot) and I can easily fly using the whole airspace without losing orientation.

Cheers for all the earlier advice.

Jon

[Geoff S]

I acquired a few wheel balance weights when I took the car in to have a puncture repaired ( a nail right in the middle of the tread!) so I'll try sticking them under the tail plane and move the CoG back a bit (with caution)

I haven't checked the wing incidence but I assume those who have take the datum as the tailplane angle which is what I usually do. So what's the ideal? 1 deg +ve?

Geoff

[Jonathan M]

Yes, as I understand it (Dave Scott's Performance Tuning Guide) the tailplane is the datum and one wants between 0.5° and 1° for a fully symmetrical wing.

[Jonathan M]

Just an update: since my first Wot4 was destroyed soon after completion earlier in the year (Spektrum TX failure), I've maidened its replacement (flying now with Taranis, yay!). With the lighter 4-Max PO-3547-800 motor it is less grunty than the original, but still more than powerful enough for my needs and flying style, and gives me an easy 12 minutes mix of aeros etc with a 4s 4250 LiPo.

The CG came out at 90mm, even after moving the battery forward a bit plus adding some nose-weight, at which it still needs a few clicks of up-elevator for level flight on 50% revs, plus a harder push on the stick than I feel it should need for cleaner inverted, and was almost impossible to stall. So I'll lose some of the nose-weight to move the CG back by say another 5mm.

Perfect model for the job, flying on mid-rates (half way between the recommended range for each surface), and looking forward to less windy weather!

[Jonathan M]

I made a mistake in my previous post: the CG was originally at 85mm (not 90) and needed a heavy lean on the stick for inverted. Its is now 88mm (removed half of the 60g of lead I had in the nose) and inverted needs only a very slight breath.

Now, although single axial rolls at higher speed don't need any corrections, two consecutive slower ones at slightly over half-throttle need a wee jab of down at inverted and a hint of up at each end - just what's needed for the B-Cert manoeuvre.

[jeffrey cottrell]

Hi Guys, could use some advice.

Similar situation to others in that I'm looking for a winter 'hack'. Not too keen on foamies, seem to get more hangar rash getting in and out of the car than I ever do flying.
Also a fan of Chris Foss designs so down to a Wot 4 of some description.
Trying to choose between Wot 4 E at 43" or Wot 4 Mk2 at 53".
Now comes the complication.
In the fleet I have a Limbo Dancer flying very well on a HK Aerodrive motor at 1185 Kv and 3s spinning 11 x 5.5 prop.
Got a spare same motor so would like to use that ( cheapskate, moi?) but my feeling is it would be a little underpowered for the 53" version, but possibly a little heavy to get the c/g right on the smaller one.
Don't intend doing any fancy aerobatics, loops and rolls are the extent of my talents, but I would like reasonable duration.

So, any thoughts?

Jeff

[Bob Cotsford]

In theory it should be ok for the larger version but e-calc puts it at 490W, I think a bit more poke would help. You really need to look at 4S driving something like a 3548 840kv motor propped for 6-700W. I haven't had a smaller version but weight really depends on what size battery you use.

[John Bisset]

Posted by Biggles' Elder Brother - Moderator on 11/10/2018 07:58:46:

The weight question has filled me with curiousity now! It's perfectly possible my memory is at fault - it was some time ago when I put this together.

I'll try to nip out to the shed this afternoon and quickly weigh the WOTTY. I'll report back.

BEB

Your memory sounds fine to me - I checked my rebuilt, electric Wot 4 just now and got 4.4 lbs, with a 4S battery. Mine is rebuilt from a 25 year old style Wot, may not even be a Mk2.

John B

[Geoff S]

I electrified a Mk2 Wot 4 last year. My thread is here.

I used a Foxy C4020/10 755 rpm/volt on 4S with a 12x6 prop which gave 600 watts which flies the model perfectly adequately for me. With a 4AH LiPo I get duration of around 10 minutes but I usually think about landing after around 8 minutes as I prefer not to over discharge my packs. In any case that's enough for me.

I flew it yesterday in quite breezy conditions and it coped very well with several touch and goes thrown in.

I was very impressed with the quality of the model and it's become the one I always take up to the field to get me 'warmed up' before flying something I've built myself and have a bit more of an emotional attachment to.

Geoff

[Bruce Collinson]

The larger version will surely make the better hack as it will deal with breeze and indifferent ground conditions better, especially when the wheels are upgraded. Mine (third!) flies similarly to Geoff's, 4S and it is possible to smuggle a 5A LiPo in there.

Reinforce the u/c fixing plate, change the wing bolts to metric, think about extra ventilation holes upstream of the ESC, bin the plastic clevises, Dubro low-bounce wheels and find your own solution to the awful supplied elevator pushrod.

My go-to plane, the nerve and rust settler, don't think I'll ever be without one. They were in short supply although they were back in stock 2-3 weeks ago.

Report back!

BTC

[Jonathan M]

Jeff, I agree entirely with Bob, your spare motor at circa 500W will be too puny for the 53" ARTF. Mine (see my last few posts above) weighs 5.25lbs with a 4s 4250mAh, and its 4-Max 3547 puts out approx 680W. This equals 130W/lb and the flying reflects this - circuits and calm aeros for up to 12mins or more aggressive flying for up to 10 - and any less grunt would be pointless. In fact I'm going to try a larger motor in this Autumn, a (spare to me) Overlander that puts out 900W, which will theoretically give 170W/lb... whether my flying would then improve is anyone's guess!!

Your spare motor would probably work fine with the smaller Wot4 balsa ARTF with much cheaper 3s Lipos (£20 versus about £60), work out the output/weight figs yourself. A club mate bought the smaller one (because he has tons of 3s batteries) and it flies fine, but I much prefer the size and weight of the full-size version, which has proved itself over and over again this windy summer, and which still fits fully-assembled in my boot.

Jon