Chris Foss Acrowot (KIt Built)

[CARPERFECT]

Hi I have a Chris Foss Acro Wot. Debating which engine to put in. I have a choice of OS FS 56 Alpha, OS ax 52 or an ASP fs70. What have you got in yours. I have had the Ripmax Acro Wot. and i had a OS FS 91 in it. It always cam in too fast, so sold it.

[Chris Walby]

Laser 70 in mine and its great, minimal mods and no added lead. flies and sounds great. Expect your fs would be nice as well.

PS - As its at or just under target weight it comes in and lands very nicely.

IMHO its very easy to over power and end up with a heavy/fast model that destroys UC mountings

PPS I think its Tim who uses flaparons on his so hopefully he will chip in at some point.

Edited By Chris Walby on 09/01/2021 19:23:24

[Brian Cooper]

I have found a 91FS to be a good choice in the kit build Acrowot.

If they are landing too fast, the prop pitch is too coarse.

[Brian Cooper]

Try a 14x6 prop. 

Edited By Brian Cooper on 09/01/2021 20:02:47

[Tim Flyer]

Hi Chaps . I have two of the small Acrowots one kit version and the other is the ARTF. The one I often fly is the ARTF with a Laser 70. That has plenty of power for it and a larger motor would just add unnecessary weight. It has upwards flaperons which help shorten landings in light winds. My kit version (a bit heavier than the ARTF)Acrowot has an OS 55ax and that is also a good choice. If you are using 4 Stroke a 70 is perfect, for two stroke a 55 is perfect. I would probably use your ASP 70 as it will sound great and have perfect power ... I once had an OSFS70 alpha in my kit Acrowot and that was great too.

[Tim Flyer]

My kit version now Actually has a tuned (a bit of port work ) OS 55ax and a tuned pipe and is “mental fast”  but I must admit I don’t often fly it but when I do it’s great ... it really screams! 

Edited By Tim Flyer on 09/01/2021 20:06:39

[Keith Berriman]

With a four stroke read instructions carefully about the fire wall distances

[ken anderson.]

mine has an OS 91 4/st in it....nice but I reckon the engine is too heavy...anyway, I would trace all the kit version parts on to a bit of old wall paper in case you know what occurs... …

ken anderson...ne...1..gravity dept.

[Engine Doctor]

An OS 70 FS is an excellent choice for the acrowot or a good Sc/ ASP 70 FS . If you can stretch to it a a YS 63 is more powerful than the OS and lighter. Just don't go too big on capacity and weight. Make sure you can get a low idle with an 11x7 prop. A fast idle will mean a fast landing. Too low a pitch prop and engine can over rev , not a problem with 2 strokes but can be with 4 strokes.

[Dave S.]

I've built at least a dozen Acrowots from the kit since they first came out, and have tried many engines in them - an OS or ASP 70 four stroke is the best all round engine for the model in my opinion - my first one had an old OS 90 (rear pushrod - but the engine wasn't old back then!) and was just crazy.

I have an electric powered ARF Acrowot upstairs, haven't flown it yet and may convert it to glow. I reckon that a Saito 82 would work well.

[Andy Stephenson]

When I built mine back in 86 I had to wait 6 weeks for the Laser75 I ordered to arrive so I temporally installed an HP61 2 stroke. I could get all sorts of crazy aerobatics out of it but after conversion to the Laser it was more sedate and a different plane altogether. Moving the CG to 1/2" behind the most rearward point recommended helped with inverted flight and made the elevator nicely responsive.

A.

PS, A Saito82 or a YS63 would be the best choice for a modern 4 stroke engine.

 

 

Edited By Andy Stephenson on 10/01/2021 11:00:23

Edited By Andy Stephenson on 10/01/2021 11:01:12

[Jonathan M]

Just bought an Acrowot kit.  Have two prospective engines for it:  a NIB Laser 80 and a lightly-used ASP 70 (which powered my old ARTF Acrowot).  Which would be the better matched engine, and why?

 

...i.e. would the Laser 80 just add unnecessary weight (and power)?

 

 

Edited April 7, 2021 by Jonathan M

[Nigel R]

Weights and measures...

 

The AcroWot was originally intended for a .40 size two stroke. That would have been a motor weighing around 15 or 16oz with its silencer. Producing about 0.8hp when propped to pass the usual noise tests.

 

A more recent two stroke, OS55AX, will weigh in at 19oz, and will have gobs more power. Around 1.1 or 1.2 hp. Your .70 four stroke will have about as much as the 55. However that 0.70 will push the weight up another notch, it is no lightweight, 21oz. 

 

A Laser .80 is likely putting out close to 1.3hp - but at 25oz. It is more like a .60 size two stroke engine.

 

More power means more weight which means more speed, faster landing, faster takeoff. How do you want it to fly? It's all trade offs.

 

PS a .70 four stroke will accelerate a 5lb airframe up vertically with no problem.

Edited April 7, 2021 by Nigel R

[Jonathan M]

Thanks Nigel

 

Don't want excessive power/weight/speed, so sounds like the ASP 70 will be just right then.

 

Just one thing, a mate has an Acrowot kit with an OS55AX (it is indeed very gobby!) which weighs 5.9lbs, so I expect mine to come in at about 6lbs rather than 5lbs...

 

Jon

[Dave S.]

I used to have an ASP 70 in an Acrowot, pretty much the same performance as the OS 70 Surpass. To my mind a 70 FS is the best choice for the Acrowot, though my unfinished ARTF version has a Saito 82 now. 

I expect we'll be able to compare them in the summer as we fly at the same field!

Dave

[Jonathan M]

Cheers Dave

[ken anderson.]

hello johnathan,i would go for the 70 also. Trace around all the kits parts on a bit of old wall paper,just in case ? 

 

ken anderson......ne...1..tracing dept.

[Keith Berriman]

I fly my kit built on an OS 46 AX 11  I have the battery pack under the tank for C of G settings and like the slower approach for landings with lower powered engine

[Low pass Pete]

 

On 09/01/2021 at 19:03, CARPERFECT said:

Hi I have a Chris Foss Acro Wot. Debating which engine to put in. I have a choice of OS FS 56 Alpha, OS ax 52 or an ASP fs70. What have you got in yours. I have had the Ripmax Acro Wot. and i had a OS FS 91 in it. It always cam in too fast, so sold it.

 

Just completed my rebuild and maiden of my old OS70 engine kit build Acrowot.  Re-engined with a new OS55.

I reckon it flies better with the 2 stroke (using 13/6 APC Prop)

Edited April 8, 2021 by Low pass Pete

[Graham Davies 3]

Hi,

I have a 30 year old AcroWot that flies very well on an old ASP65FS. Mine was built heavy (not by me!) and weighs 6lb, but comes in nicely on a 13x6. Any more pitch and it's not easy to stop on our short and depending on the wind direction, downhill strip.

[Cuban8]

In these noise sensitive times, I'd go with a four stroke, they sound nicer anyway and generate much less mess when used with lower oil content fuels.

I wouldn't be unduly worried about the Acrowot putting on a bit of weight. The one I had (flew the pants off it and regret selling it) was well beefed up to cope with a very rough patch that we used to fly off and I reckon was over 7lbs - had a 60 two stroke in it back in the day 25 years ago. My party piece was to climb vertically to a dot and rapidly spin down 100+ to the last moment and repeat! Would fly it in a gale with no problem.

The Acrowot wing is very safe and doesn't flick unless  provoked and can easily take quite a bit of extra wing loading but still fly slowly and land easily. The standard CG position is very conservative and will stand moving back quite a bit depending on your nerves, so don't just stick to what's in the book without careful experimentation.  I know that some flyers fit triangle stock to the tip leading edges to liven up the flick/spin characteristics (the opposite to what stall strips are usually used for IIRC).

I keep saying that I'll build another one because as they say about the DC3, the only replacement for an Acrowot is another Acrowot.

BTW, I currently have a Seagull Sea Eagle as my hack model and it's very similar in its flying characteristics to an Acrowot.

Edited April 8, 2021 by Cuban8

[Low pass Pete]

Flew my Acrowot (Power OS55, APC 13x6) yesterday.  Light breeze.  Acrowots and Wot 4s are well known for floating on.  Mine does have this tendency.  However the trick to get decent landings is in my opinion in a good low tick-over on the engine plus a good line up on finals.  Too fast and she will float on easily.  Fortunately my new OS55 has a great low tick-over and I was easily able to get a nice 3 point landing in a breeze.

I agree that 2 stroke can be noisier than a 4 stroke.  However not always so when you cruise on less than 1/2 throttle. 

My experience with my OS55 has been great as it will provide the power, as and when needed, but will happily cruise my Acrowot on 1/4 to 1/2 throttle.  Simple really, do not bash around at full throttle and use a larger prop.

Plus 1/2 price compared to a new 4 stroke.

I do see the advantages of electric, especially at a noise sensitive site, however I am reluctant to go fully electric as I am not keen on some of the issues that high power LIPOs have.  Namely disposal when Life-Ex.

 

[Dave S.]

In my experience, Acrowots are floatier than Wot 4s, and more likely to bounce unless you get it just right. 

 

I was testing my new 55AX yesterday, 11x7 was far too noisy and over 11,000 RPM, but a 12x7got it down to 10k and sounded better. Hopefully maidening it in a Wot 4 today. I may take a leaf out of your book and try a 13x6 - I'll take a selection of props and see what works/sounds best. I doubt it'll be at full throttle very often though!

[Andy Stephenson]

I find that my Acrowot lands considerably faster dead-stick than it does on tickover. Propeller braking can be significant if you can have a reliable low-speed tickover, you can even hear the wooshing of the air being pushed through the propeller faster that it's trying to drive forwards. Of course having a low pitch propeller helps.

[Doctor Chinnery]

I’ve  come to this thread a bit late in the day but here goes. I have a Chris Foss B.I.Y. Wot4  kit and also a B.IY. AcroWot kit who have come to the front of the queue, with the choice of an Irvine46 and an old OS60 to power them.

Having read Nigel’s contribution, in conjunction with Chris Foss’s building notes I think the AcroWot gets the Irvine which I’m hoping will give me an aerobat suitable  for a “Wrinklie Flyer” (an exclusive minority within the CMFC ?). That means the Wottie (my 4th) gets the OS, which means I can still be a geriatric hooligan when the mood takes me. 
Any strong views/warnings?