Which engine for a Mark 2 Acrowot ARTF

[David Davis]

I will be assembling an ARTF Acrowot once a few other projects have been completed. I have three engines in my collection which would suit the model: an Irvine 53, an OS 61SF two-stroke and a Laser 80, both of which are new and un-run.

Most of the ARTF Acrowots I've seen seem to fly nicely on a 70 four-stroke. I am a pretty average club-level pilot. I have never been able to master the knife edge, for example, which should give you an idea of the limits of my skills.

My dilemma is as follows: would the Laser 80 be too heavy for the model? It's a fair bit bigger and heavier than my Laser or OS 70 which are in other models. I'm less concerned about the model being over-powered by the 80, the Laser has a throttle after all!

On the other hand, would the Irvine be powerful enough for the model? The OS would certainly fly it. I've had another OS 61 in a kit-built Acrowot.

[sean smith 1]

I had a SC 91FS in my kit built Acrowot, flew really well the only down side was getting it to slow down enough to land.

Edited By sean smith 1 on 12/03/2016 07:35:33

[Rich too]

I agree with Percy on those two engines. However, the engine of choice is the 90 fs - and there is an OS 90 fs currently in the for sale section

[iqon]

Your 53 is more than capable, couple at club fly with a 40

[Brian Cooper]

A decent .91 four stroke is the tool for the job. . Fit it with a 14x6 prop and it will give plenty of grunt for vertical climbing, and the fine pitch will keep the speed down on landing.

B.C.

[David Davis]

Rich, if you feel that a 90FS is appropriate, then why not recommend the Laser 80 over the Irvine?

[Paul Jefferies]

Without a doubt the Irvine .53 would be the engine to use. Back in 1980something I did the original kit review of the Acrowot in RCM&E. In order to test it over the manufacturer's full quoted power range I tested it with an OS .40 and with a Redshift .60. To summarize, with the .60 it was too heavy and overpowered. The .40 had ample power for most flying and the model was altogether "nicer" to fly. If you send me a pm I will send you a scan of the review......

Paul

[Rich too]

Sorry, I completely missed that, it's too early! The Lazer is a bit lardy compared to the OS but I dint see why it should work well, and yes, that would be my choice over the other two. I would try it for balance and go from there. Nice engines

[Rich too]

Here you go, apparently the Lazer 80 is a perfect match:

http://www.rcuniverse.com/forum/kit-building-121/1190558-chris-foss-acro-wot.html

[Rich too]

I have to admit that I have never owned one so no first hand knowledge. Point taken Percy, and I wouldn't want to add unnecessary weight.

[Braddock, VC]

The artf acrowot is larger than the kit built acrowot both in wingspan and also in fuselage girth. It tends to be heavier than the kit built one by a significant margin. Hearsay says it can weigh from 100 ounces up over 104 ounces dry. They also seem to come out tail heavy.

My kit built one comes in at 90 ounces dry with an OS 91 Fx up front and about 1.5 ounces of tail ballast.

If you want to master knife edge you'll need as much power as you can get in the early stages.

I have a laser 80 and, as you say in the op, it's a very heavy engine for its output and I'd discount it simply on that basis. I'd put the OS in with a14x6 to start with then try a 13x6 or 7. I'd also think about replacing the standard silencer for one of westonuk's superb throttle pipes and that combination should give you ample power for knife edge flight practice, though I'd be the first to admit the acrowot, in any of its iterations, isn't an ideal knife edge candidate.

As you say, they seem to fly nicely on a 70 4s; as you also say the 60 has a throttle.

Edited By Braddock, VC on 12/03/2016 09:08:20

[alan p]

Mine flies on a ASP52 FS, moved the servo tray forward to the back of the fuel tank, rx battery in a box on the front bulkhead under the engine, needed some church roof to get CofG but not a lot. Otherwise as mentioned above they need a big lump of engine up front to counter the very rearward servo positions that makes them tail heavy.

[Keith Berriman]

I fly an ARTF mark 2 on an OS 46 and it is a pleasure and relaxing model to fly. I watch a very experience flyer do all the stunts with an Irvine 53 up front. So go with the 53 and throttle back that has been suggested

[Jon H]

Lazer with a Z...tut tut whatever next?

Anyway we normally recommend the 70 or the 80 for both the kit and artf version of this model. Reports back from customers say that with either version lead is often still required in the nose even with the allegedly 'lardy' 80 installed The only snag with the 80 in the artf vesion is they have made the cowl very short and it can be a challenge to squeeze it in.

Not that it matters a jot, but the prototype acrowot flew with a laser 75 which was developed into the 80. The 75 was significantly heavier and had less power. The current spec 80 is only 1 or 200rpm off my OS91 surpass so its no slouch.

Having flown several acrowots on everything from a 40la to an OS91fs I can say that almost any engine will fly it well. In the end, most of it is down to preference and what you have available.

[David Davis]

Thank you gentlemen. As of 12.30 I've received a wide range of recommendations.

I have a Thunder Tiger 91 FS but a 91 fourstroke is out because I fitted one to a kit-built Acro Wot several years ago and it was too much for me, besides I need to replace the bearings in my engine. Otherwise the majority vote seems to be in favour of the Irvine, yet others warn of tail heaviness in the model which should favour either the Laser or the OS.

Guess I'll just assemble the model and check its balance point with the different engines as Rich suggested.

[Rich too]

Apologies Jon

[SONNY MONKS]

ive just purchased one of these,im putting a saito 62b four stroke in it,fingers crossed!

[Jon H]

should be a nice combination. 12x6 prop would be my suggestion

[brokenenglish]

Mine flies great with an Irvine 53.

A 4-stroke would probably be a good option because, with a 2-stroke, you'll have to hack some of the front end away for silencer clearance.

[SONNY MONKS]

Thanks john,thats the size prop i used when my saito was in the blackhorse sedona.

[Simon Knight]

I used an ASP FS61 in both of mine and always had plenty of power with a 12x6 prop.

[Chris Walby]

Laser 70 for me..... it is nice and one of our club instructor put it through its paces and announced it flies as if on rails.

No major mods (see my post Laser Acrowot for details).

[David Davis]

Sorry to revive my old thread but I've finally finished assembling the ARTF Acro Wot and over the last ten days or so I've been flying it. It is powered by a Laser 70 and now that I've fine-tuned the engine I'm very pleased with the combination. I have made no alterations other than fitting bigger and heavier wheels to the undercarriage bring the c of g forward and pouring epoxy resin into the tank bay because I had heard that the undercarriage was not well-glued into place. I have had no problems with the undercarriage detaching itself despite a few less than perfect landings. Not yet anyway!

 

I am flying it on low rates with the recommended control surface movements. I had 25% exponential on the ailerons but on the advice of the club's president and sometime National Chamionship contender, I have increased the expo to 40%. It seems to make the model fly more smoothly.

[Jon H]

DD i recommend you take out all your expo, but reduce the rates as well. This way you retain the positivity and accuracy you loose with expo, but the model is not twitchy as you have small ish deflections. A friend had one of these set up similarly to the way yours is and i reset it to my no expo setup and he was hardly able to tell the difference. The only give away was he said he thought the model felt more solid and less prone to wandering. This is probably because the controls take instant effect. 

 

Anyway if you are happy with it as is by all means leave it, but you could set up another set of rates or a flight mode and see how you get on. It will take some tinkering to get it set but you can do it in a flight or two. 

 

I know it always causes an argument but i would also recommend you get the rates right first, and then use expo to ice the cake if you cant do it on rates alone. Even so, 15% is probably the most i would ever recommend and i have only 1 channel on 2 out of my 13 models with expo in them and then its only 10%. My bigger AWXL has no expo at all and its awesome! Give it a try if you like and see what you think. 

[Engine Doctor]

Hi DD While I agree with John's thoughts on set up I would have to say that setting up a model is not a one size fits all scenario as we all have different reaction times etc. 

On some of my models the "high" rates may be set at say75% with 25% expo and "low" rates set at 55% with 20%. Some have no expo,its a personal thing like say adjusting your  cars driving seat. Don't forget that suggested throws are a "starting point" and not set in stone. Often with some far east produced models these sugested settings are totally wrong along with CG settings and can catch out the inexperienced flyer.

 

As for engine size, the AcrowWots I've owned tested and helped setup for others have flown best on a good 60 to 70 fs or a good 46 to 60 2s. Again just my opinion as it's a personal choice. 

The over powered brigade that fit bigger engines IMO just make a nice flying model feel like a flying brick. Bigger engines might give fantastic vertical climb and hike in speed but the  overall effect is they make the model too heavy and ruin its low speed handling , a bit like driving a dragster on the daily commute !

Have fun