Acro Wot ARTF (balsa) chat

[Concorde Speedbird]

Hello Jeremy, welcome!

The Acro Wot is a very good aeroplane and not difficult to fly for a reasonably experienced pilot, but it is not suitable for a beginner. It is a very good first low winger, but you should start off with a high wing trainer. Not all high wing aeroplanes are trainers though! Search trainer in the search box on the top right and there are loads of threads to look through. Any questions you have are ones we'd like to answer! Why not start up a thread to introduce yourself and ask questions?

CS

[David Burrows]

I had an original ,

Powerd by an mds61 bought part built from the air shows at elvington back in 90s

[Jeremy Snudden]

Ok thanks for the help!!!

[Chris Anthony]

Hi all,

I have a few Acrowot related questions.

I've been struggling to get the CG position right in mine since my maiden a few days ago, with an SC52 2s engine. First I flew it without changing the CG, with it around 35mm rear of where it should have been! Needless to say it didn't handle very well. I've found I've had to put in 0.4kg of ballast just behind the firewall in order to correct this. This seemed like a very large increase of mass relative to the plane, and it definitely showed on take-off.

I didn't like this set-up either, and need to find some ideal middle ground between the two options I've already tried. What have you guys done to correct the CG position? Do you put your ballast forward of the firewall, somewhere in the engine bay? How much ballast do you find you need?

I'm also struggling with the minimum speed of the thing. For those running a similar engine to me, what kind of props are you using? I'm on an 11x7 at the moment, and am hoping that changing to a 12x5 will help lower my idling air speed.

I've also seen guys at the club use a "flap" or "air-brake" TX mix in order to slow the thing to land on our patch. Do any of you guys use anything similar?

Look forward to hearing your thoughts.

Thanks,

Chris

[john stones 1 - Moderator]

Hello Chris

Almost a pound of lead, that don't sound right, where is your battery ? move anything possible forward, any lead you need to use, bolt as far forward as possible. A prop with less pitch will help slow up your landings. An acrowot is a pretty friendly model you should soon get the feel of it, stick time is what you need. Check the C.G. again a 52 should not need all that lead to balance it. If its way nose heavy it will come in quick. Flaps, airbrakes..its up to you, but you don't need that stuff for an acrowot. Turn it upside down to balance its easier.

John

[Paul Marsh]

I have no problem with cofg _just put a bigga engine in it - a Thunder TiGer 75 four stroke.

A 52 would be a bit boring...

[Chris Anthony]

Thanks John, I appreciate your reply. Yeah I suspected it was a bit too much mass. Yeah I'd rather have less mass put further forward to achieve my CG position but don't know if putting it in the engine area (in front of the firewall) is a good idea. There also may be a problem with the way I'm measuring CG position, I'll have a go measuring it upside down.

It might just be the patch we use is a bit small then John, all the aces at the club use a small amount of airbrake/flaps so I won't feel too ashamed giving them a try! The finer pitch prop recommended was a 12x6 so I'll give one of those a crack as well.

Yep I can't wait to feel confident enough with the thing to get in a load of stick time John. I'm almost there I think.

Paul, well I've just moved up from a 25 so at the moment a 52 is more than enough for me!

[john stones 1 - Moderator]

No problem

Balance low wingers inverted Chris, No problem if its secure up front,will take less lead. Flaps if you fancy a dabble but its not needed for that model. It gets easier more you do it

John

[Chris Anthony]

I've re-checked the CG position inverted and even with the 0.4kg mass where it is (behind firewall), the CG position is only just in spec!

So I'm going to have to move this mass into the engine bay to have any chance of reducing the total mass used. I'm surprised by how much is needed for my model. RX battery and RX are as far forward in the above-wing compartment as is possible.

Any practical tips on the furthest point forward I could put the mass John? Somehow mounted to the plastic engine mount forks perhaps?

Edited By Chris Anthony on 10/05/2014 00:34:04

[john stones 1 - Moderator]

Yes Chris as long as its secure, it'll be o.k.

John

[Mark a]

I had to use some car stick on wheel weights to get my Arco to balance. They will stick straight to the firewall and won't get I the way of fitting the cowl.

[ken anderson.]

hello chris...get the lead as far forward as possible -indeed put it on the mount or firewall....ask a roofer if he would let you have any off cut's of lead flashing and cut it to suit and fit it to the firewall using a self tapping screw and some silicone to stop it vibrating etc.....the further forward the better-less reqd.......

ken Anderson ne...1 .........flashing dept

[Steve Nash]

Hi Chris,

My Aceowot needed some lead too, but cant remember how much weight. I used an SC52 four stroke engine in mine.

What I did was to put two longer bolts in the front engine mounts and tighten up fully. Then I used some offcuts of flat lead sheet which you just drill two holes in and slip over the bit of bolt that sticks out and secure with another nyloc nut on each bolt. That way the lead is as far forward as possible which means slightly less weight of lead is needed. The lead can be shaped to bend round the mount so that it fits snugly.

I also used a 5 cell RX pack(6v) which I put under the tank right up against the inside of the firewall, which is makes it useful weight.

By the way, mine also still nips along on tickover with a 6 inch pitch prop, so I might try a 5 or 4 inch pitch prop when I get round to getting one. Im trying to set up an on board glow at the moment to try and get the tickover as low as possible. One of my flights went deadstick recently and the plane comes in beautifully slow and perfect for landing, so it is definitely the thrust from the engine that is stopping it slowing down enough.

Steve

[Chris Anthony]

Thanks guys. I managed to mount the steel to the engine forks very similar to the way you described Steve, except I made my own new hole further forward. I've now got 0.2kg in instead of 0.4kg and have the CG just right.

I've also reduced my prop down from an 11x7 to an 11x4. It revs very high on full throttle so I've restricted myself to 75% on the TX just in case. Aircraft air speed is much more manageable at the low end of the throttle now though. I'll keep this prop just for a couple of flights until I'm happy circuiting and landing the thing, then I'll switch back to the 11x7 and try some aeros.

[Paul Marsh]

Posted by Chris Anthony on 10/05/2014 14:55:36:

Thanks guys. I managed to mount the steel to the engine forks very similar to the way you described Steve, except I made my own new hole further forward. I've now got 0.2kg in instead of 0.4kg and have the CG just right.

I've also reduced my prop down from an 11x7 to an 11x4. It revs very high on full throttle so I've restricted myself to 75% on the TX just in case. Aircraft air speed is much more manageable at the low end of the throttle now though. I'll keep this prop just for a couple of flights until I'm happy circuiting and landing the thing, then I'll switch back to the 11x7 and try some aeros.

Why limit to 75% throttle. Should never have less than full throttle, as if you're in trouble and need more power, then won't have any. With only a .52 it would be giving hardly any power!!!

Just put a 11x7 prop on it and use the throttle lever not as a switch., fly at 75%, but have 100% for take offs, etc.

Even better, get a .70, remove the lead and have a larger prop, 12x8 purring away at 1/2 throttle...

[Chris Anthony]

Appreciate the reply Paul. I've limited throttle as I'm worried about over-revving the engine on such a fine prop. I'm not experienced enough to recognise when this may occur. Do you think this is likely to be a problem with a .52 on a 11x4? I understand your concern regarding having power to get me out of trouble. The plane still takes-off comfortably with ~60% throttle on this prop though.

I don't use the throttle as a switch. With the 11x7 I was flying at around 30% throttle the whole time trying to get used to the plane. And for landing I was at 0 throttle (idle) and still going too fast for my liking. Steve confirms that the plane is able to fly a lot slower, so I'd like to get into that region of airspeed whilst still having my engine running.

I've probably been at 100% throttle for around 30 seconds so far. So again, I'm not going to be getting a bigger engine yet. But I'll bare what you said in mind for when I am ready to upgrade. It seems you currently have a much greater confidence level while flying than me.

[Robin Kearney]

Chris, I have 10oz of lead in front of the firewall on mine, and thats with an OS81 four stroke up front. I think some of the people in the factory think the tail surfaces need to be made from Oak.

r.

[Chris Anthony]

Hi Robin, that's encouraging to hear, thanks. If that works out to about 0.28kg, then that's pretty much the same amount of ballast as me. Did you find performance suffered much with the added mass? Take-off, aeros etc? Yes I had wondered why it seemed to need so much ballast, but am not experienced enough with model design to speculate.

[Robin Kearney]

No Chris, the 81 produces far more power than is needed, in fact even at tick over the thing floats on and on I've tried a bigger prop but it doesn't seem to make much difference. I've just moved to a club with a bigger strip but if I still suffer, I'll try the flaperon trick I've seen others used. Chris' glider designing heritage seems to show through with the Acro !

There seems to be a huge variance in the ARTF, a club mate had one bought at about the same time with a lighter motor up front (OS 55AX) and he needed no lead despite using same servos, RX battery etc. Maybe it's just one bloke at the factory who missed the wood selection day in training

[Robert Armstrong 2]

ARTF AcroWots seem to vary a lot on GofG. I remember the magazine review item needed a lot of lead even with a 70 four stroke, but mine, also with a similar engine, balanced at the recommended cofg with the (4 cell) battery under the fuel tank and no additional lead.

With a 13 x 8 prop, I find difficulty in slowing it down to land if there is no wind though. Quite a lot of thrust still at idle.

[Chris Anthony]

Posted by Robin Kearney on 10/05/2014 17:30:50:

Maybe it's just one bloke at the factory who missed the wood selection day in training

[Steve Hargreaves - Moderator]

As the others have said a heavy engine helps reduce the lead....mine has an ASP91 four stroke up front &..er....no lead!!! A 14x6 prop provides the thrust & I don't think it comes in too fast......

How is the idle on yout engine? Might it be set a bit high?

I think an 11x4 will be too small for a 52 Chris....I have an ASP52 (same engine different badge) in an Irvine Wildcard on a 13x4 & it cranks out a fair few revs.....an 11 inch prop will really make it scream.

Personally I think I'd try a 12x6 on the 52 in an AW.....make sure you have a slow tickover & it should be fine....AWs are pretty easy to land...

[stuey]

A 12x6 works well on the Irvine 53 in my Acrowot, landing speed is fine. Not the fastest in the world though!

[Flanker .]

Hi Chris. Re speed. It is important to understand that the speed of an aircraft is not really dependent on the THROTTLE . The speed of an aircraft is regulated by its angle of attack. If your acrowot flies too fast all you have to do is add some UP TRIM and the reduce power until the plane flies straight and level. Too much up trim will require too little power for S&L flight and the aircraft will stall. It is fundamental to happy flying to understand that speed comes from TRIM. Our models fly just like the big ones and in a big one your instructor will say things like "trim for 80 knots" . Power controls climb or decent . Imagine that you are at a nice height in the circuit, but the plane is too fast to be comfortable. So add say 3 beeps up. The machine will begin to climb so reduce power gently until she flies level. Now if you whack open the power she'll climb like mad. If you back of power she will sink. This is the key to nice landing approaches too. My Acro has the ailerons set up to drop 3 or 4 mm when I pull the airbrake switch and the elevator moves up a bit to compensate for the pitch change. Now I have a nice draggy set up and need only to add or remove power to control the decent. All very calm. Remember we TRIM FOR SPEED and control hight with power. If you want to fly fast for aeros just trim back to neutral and watch the plane speed up. Limiting your throttle is as king for trouble and won't really give you the best for the model. It will also keep you in a bad habit ! IE trimming once and then never touching it again. Have fun, go well, F

[Chris Anthony]

Thanks for the write-up Flanker. That's an interesting approach to aircraft control; trimming elevator for speed and then controlling any consequential height gain/loss with power. I understand it, and will try to think more along these lines when practising my approaches in the future. Is this the way they teach you flying in the real/non-RC world?

As to how this approach translates to my problem. What I would find is that if I added in up-elevator to try and reduce my forward speed to an acceptable level, I would not be able to reduce the thrust created by the engine/prop to stop ascending/begin descending. And so, I would have to set a new attitude again, lessening AoA, having to deal with what I considered to be 'more forward speed than I needed' to stay airborne, until the aircraft would descend enough to land.

However, I'm pleased to say that I have progressed with the acrowot since typing up my previous comments a few days ago. I've got the CG nailed and so feel much more confident flying with full throttle and playing about with my airbrake mixes in the air etc. I've sacked off the 11x4 prop as it wasn't really helping to slow my approach speeds as much as I wanted. So I'm back on the 11x7 prop and loving it. My landings seem controlled enough for me by using the airbrake mixes when I need them. I reckon a couple of weeks like this and I'll be looking to move onto a different engine as Paul suggested previously, think I'll go for a 4-stroke next.