Acrowot Build

[Jon Laughton]

I am about to  start building an Acrowot for flying in the spring. Any tips and helpful commets / photos etc would be most gratefully received as would suggested colour schemes......thanks!

I will post photos etc as I go along

[simon barr]

Hello Jon,

When I had an Acrowot, a long time ago, I built it as per the instructions, but "those in the know" recommend lowering the tailplane position by 3/4 inch...I'm afraid I don't know the reason, but it is reckoned they fly better.  I'm sure someone will have a comment about this...

[Braddock, VC]

Build it as per chris foss instructions, if you lower the tailplane you may experience ground strike problems unless you fly off perfectly smooth surfaces.

If you look at the rear of the extra wot you will see the bulk of the mods, lowered tailplane, increase rudder size, extend the rudder downward with a fairing as per the wot 4 giving you back the ground clearance.

As far as I'm concerned the acrowot doesn't need much modifying, it is a 25 year old design and it has largely been superceded by aircraft that are generally lighter with as much or more power that will self destruct with the sort of arrival that a tube of cyno can fix on the foss design.

It's perfectly possible to build it to 5lbs AUW but this is not critical, my last one had a saito 82 and was marginally more in weight than 5 lbs but this was due to reinforcement following a self induced stall.

Give a great deal of thought to the covering, I would advise glass cloth and epoxy for the wings, do not even consider one of the water based alternatives unless you thoroughly seal the veneer as the water will cause it to swell and crack, this latter can be the achilles heel of veneered foam wings.

Try and use the lightest engine you can, to avoid shortening the nose to achieve the C of G, if you have to crop the nose you will need to give considerable thought to the position and size of fuel tank to feed your heavyweight engine.

I've flown mine on an OS 46 FX, Magnum 61 4 stroke, yamada 45 2 stroke, Os 52 4s and finally the saito 82 which was a match made in heaven.

If I was going 2 stroke I'd take a long hard look at the OS 55AX as light as the 46 fx but with much more power.

I'm building one over Xmas too, so I'll watch your thread with interest; in my mind the hardest part of the build is getting the the wing root angled to get the correct dihedral and ensuring each wing panel has the same incidence.

Good luck and enjoy the build!!!!!! 

[Bob Cotsford]

the only mod I'd do fi I had another is to glasscloth/resin the inside of the fuselage in the area of the u/c mount to strengthen it.

[Stan Pratt 2]

    

[David Ashby - Moderator]

Say again Stan?

[JohnnyB]

Stan, either you're using invisible ink, or you've written on the wrong side of the paper.........

[Howard Tomlin]

I had one of these when they first came out and I only finally managed to prang it beyond repair 2 years ago (and it went in hard at least 3 times!).

 Mine was built as per the instructions and flew (very well) on a laser 75, it was a little nose heavy but this didnt affect its flight characteristics and it always put on a good show (sometimes to a round of appluase!!).

 I wouldn't worry about shortening the nose to suit the engine, the laser I used isnt exactly the lightest engine in the world and I didnt shorten the nose , anyway  i think this would bring more problems than it fixes as theres not a huge amount of room up front anyway!

 As for careful consideration on covering, you'll find solartex or sloarfilm etc are all perfectly acceptable, I painted my solartex covered acrowot with fuel proof paint to look like this:-

 

 The union jack is a p.i.t.a. to paint so i wouldnt reccomend doing this if you havent tried on something else first.

 I cant rememeber whether the u/c is plastic or metal bolt on stright out of the box but i used plastic bolts which were fine and stopped the u/c fixing section from ripping out on a hard landing.

 Overall its a great perfoming plane, i doubled all the throws and found this to be a most satisfying setup for some really hairybatics!. flick rolls are very quick, knife edge spins are very easy ( both sticks in the top left or top right corners after a vertical climb!!), it will blender quite well and I even got a prophang or two from it!!

 Alas a silly mistake with losing all the expo settings during a tx reset resulted in an over correction when recovering from a knife edge spin,and misjudgement of how much space i had resulted in it slapping the ground at full chat at the bottom of a hard yank up

The result, :-

wings sheared in two down the joiner line,

bulkhead removal (complete with cowling,engine and spinner in one unit ending up 35m from the impact point) ,

u/c plate removal

I could have epoxied it all back together but I'd done this repair a couple of times already and it was time for it to fly  into the graveyard. - Funnily enough when i hand launched it into the council waste sites skip it glided beatifully as if to show that it had life left in it ....

[Braddock, VC]

Hey Jon, how's it going?

[Braddock, VC]

I've started mine, as I said earlier I am not confident about trimming the wing root to get a good joint at the correct angle so I built a jig, I can't for the life of me fathom how to upload pix on here so I'll try to describe it.

A piece of melamine faced kitchen shelf 300 x1000 mm, a piece of "L" section aluminium, a 3/4" high jigging spacer to set the dihedral and a long sanding block.

I superglued the alloy to the 300 mm end of the shelf so the long part faced the end and the short part faced up the board. A piece of balsa was glued up tight to this short edge to provide a wide landing face. The wing half panel was offered up with the bottom of the wing root flush with the alloy edge, the leading edge of the wing was lined up with the long edge of the shelf and the 3/4" plus a few scraps of the balsa used at the root end to provide the correct angle. The wing panel was held on with big elastic bands. Checked the root and leading edge were in the correct position and blow me if three swipes with the sanding block pressed tight against the alloy face had it done, swapped the trimmed one for the other wing half and ditto. The joint is absolutely perfect and the whole lot took less time to prepare and execute than typing this in.

When gluing the leading and trailing edges on I use white glue. Cut the l/e and t/e pieces to length, get a large sellotape dispenser and swap the sellotape for masking tape, a glue spreader is needed too. A fillet of glue down the piece of wood, spread it evenly with the spreader and hold it tight to the foam/veneer edge with your index fingerholding the wood tight against the foam, with your free hand, take about 4" of masking tape and put the middle of it under your other forefinger sticky side to the wood, the two loose bits of masking tape can then be firmly pressed onto the veneer. I used 6 pieces per edge. Then ensure the wood overlaps the veneer and there is glue oozing out, spread this and remove the excess with your glue spreader then do the other three edges the same.

Sorry to burgle your thread, this is as far as I'll get today, tomorrow I'll shape the wood and join the wings.

Total time so far, 40 minutes.

Hope this helps.

[batcho99]

Brilliant model to build, and one of the best flying models out there. I've had my Acrowot for nearly 10 years and it's still going. It gets used nearly every weekend too! I have just started building a new one though so I can retire my old one as I think it deserves a break from the abuse I give it. The only advice I can give is think about your choice of engine first. Mine flys on an OS70 surpass but if I had the choice again, I would probably put a Saito82 up front. I would then beef up the front area as recommended in the instructions with thin ply on the inside of the fwd airframe. It will give a longer life to the model for sure, if you dont hit the ground

[Braddock, VC]

Soldiering on with mine, built the tail feathers and fin and rudder, all shaped, I used a palm sander then a long permagrit block, wing l/e and t/e all shaped, now I have to get some 5 min devcon for the initial wing join.

These operations added another 30 mins to the build time.

I have one of those slec fuz jigs to assemble so I'll do that and build the fuz on that.

Like batcho99 I'm going to reinforce the fuz as per the instructions as I'm either going to use a saito 82 or a saito 125 ( well it does say for 90 sized airframes and fossy say you can use a 91 fs) seriously though the prop will be the limiting factor as the 125 performs best with a 16 x 6 apc and my last acrowot had clearance problems with a 14 x 6 apc. In reality, the 82 is more than up to the job, several vertical rolls being entirely feasible.

[batcho99]

Hi John.

Have you considered using a multiple bladed prop so you dont have to use such a long one? I haven't done it myself but I think it would be possible?

 Iain.

[Braddock, VC]

Iain, I did, the 125 would need a14 x 8 3 blade. The price is scary, I could almost buy 2 2 bladed ones....

as an engineer I must also poo-poo the relative lack of efficiency of 3 v 2 blades to corroborate my scrooge like attitude .

As you've never met me you won't have seen my landings and the thought of risking at least £20 at least once per flight is daunting.

[batcho99]

John, ha ha.  I know what you mean about damaging the prop, can be an expensive habit!

I can feel another debate coming along here about props, we're going off topic a bit so I feel the need to start another thread on props, 3 v's 2 blades  

[Howard Tomlin]

they fly very nicely on a gold old laser 75 and a 12x6 prop (yes i know it was under propped but it never complained and went like stink)

 loads of prop clearance too!

[Braddock, VC]

Continued with getting the wood for the fus ready today, stap me vitals  but there's a piece of 3mm liteply for the firewall, straight in the bin and I cut one out of 6mm 5ply, spent the rest of about an hour just sanding all the wood smooth, an old tip the late ben buckle gave me donkeys yonks ago. The top stringers are spruce, which I've found doesn't take glue too well so I've some really hard lime/basswood that will be stuck on in it's place. I've got the 5 minute devcon and after gluing the end plates and small aileron shaped trim pieces at the wingtips got that cold decided to call it a day as there's no heating in the loft.

I've also measured out and drilled the wing mounting plate, undercarriage plate and the fire wall for the blind or tee nuts that fasten the wing, fibreglass u/c and engine mount respectively.

As I said earlier, I'm fitting a saito 82 in mine, very light and not too extravagant on fuel but as good as any 91 OS clone in the power stakes, especially when fitted with a 14 x 6 apc.

A couple more hours should see the airframe ready to cover and I'll have to give some thought to the colour scheme, at present I've a thing about yellow but I just might do a red and grey scheme. I'll also probably change my mind at least a dozen times......

[Braddock, VC]

Joined the wings tonight, really pleased with the joint that I took so much care with. Regretably I couldn't do it in the loft so I did it downstairs. If I've had one complaint about the glue smell (devcon 5 min epoxy) I've had 20. ( I'm building it in work, as I own the business nobody normally complains)

Anyhow it's standing there straight as a die.

Onto the fuselage next as you really need that assembled to ensure the correct alignment of the inboard trailing edges.

With regard to the fus, instead of infilling with 1/32" ply, I'm putting a 1/32" ply doubler and adjusting the various formers to suit. My gut reaction is that for a little extra work it will provide  enormous strength. BTW the 1/32 infill is Chris foss's idea if you use a heavy or more powerful motor, the saito isn't heavy but it certainly is a thumper, that's why I'm doing it.

I've a bright shiny alloy spinner to fit up front but I'm still undecided what colour scheme to either paint or use film to make, decisions, decisions.

[Braddock, VC]

Checked the wing again this a.m., still straight, have had one move in the past even though pinned and stayed so quite pleased. Another puncture in my car having to buy a new tyre keeps me from working on the plane as much as I'd like I also had to perform my Father Xmas routine for our parent toddler group Xmas party, spent 1/2 hour in there beforehand showing the mums how to work their cameras etc., nothing spoils the effect for 2 year olds more than mum faffing around trying to get a piccy.

Anyway I got the inboard ends of the trailing edges prepared for fitting, fus tomorrow!!!!! 

[Braddock, VC]

Didn't start the fus until today. I'd originally intended to replace the spruce and balsa longerons with bass, but the spruce sanded out ok and I stuck and clamped it and it looks good. I did a really long scarfe joint instead of the short one shown by fossie. I used the bog standard £5 for 5 litres white glue we use in the nursery. I stuck the 1/32" ply doubler on with epoxy, 30 min stuff and then added the other doublers using the white glue.

The parts are sitting there in work as we've broken up for xmas and I'll pick up where I left off on Jan 5th.

 I've given some thought to the final covering and color scheme, as it stands the fus is going to get nylon doped on and the wings will have glass cloth and epoxy; the tail feathers will have tissue doped on.

The base colour is going to be white gloss dulux silkothene with red and probably black trim.

I'll probaby change my mind again but I'll get some practice in with the airbrush and see how it goes.

A merry Xmas to all our readers!!!!!!!!!!!

[Braddock, VC]

Started back on the fuselage construction, been pondering a few things over the break, one of the failings I found was when the acrowot hit just a bit heavily the fuselage sides split, due I think to the sides bulging outward.

The wot 4 shares this problem so I have devised a cunning plan to reinforce the sides, in between the vertical formers of 1/4x1/4 or 5/8x1/8, I am introducing diagonal pieces of 1/4 x 1/8 bass wood. The weight penalty will be minimal. I've also decided to pop the rudder and elevator servos at the aft end so I have nice short and stiff pushrods. Perkins do a 2 bb MG mini servo with 5.4kg/cm torque that I've successfully used in this situation in the past. I'm sticking with the central wing servo but the throttle servo is going up in the cowl, that will be a mini servo. This will clear up the clutter amidships and allow me to introduce some cross bracing in the aperture where the wing seats to beef it up there.

Although the kit is the fibreglass one, I'm not fitting the f/g u/c it's far too heavy, I have a nice light carbon reinforced one that fits one of the weston models, I also have a carbon cowl, between them they are 3 ounces lighter than the items they replace as I'm determined to get the weight down below 5 lbs. There's method in my madness, each bit of weight saved requires less power from the engine so the fuel consumption will be less, so I hope to fit an 8 oz tank or maybe even a 6 oz one which will reduce the flying weight further and the saito 82 will haul it round in style, not that it didn't do that with an auw of 5.5 lbs with the last one, I'll just feel that much better at the lower weight.

I'm hoping to get away without any nose weight, if I do have to add some then I'll get an alloy spinner and gradually build up from there.

[Braddock, VC]

Spent a couple of hours fitting the fuselage formers etc, got really tight joints and tight joints mean less glue, that means less weight.

Hope to complete the fus this week and then I'll really have to decide on my finishing method.

If I'm honest I've spent about 10 hours so far on the construction, I reckon finishing should take about the same amount of time if I follow the solartex/profilm route and about twice that if I cover the fus with nylon, dope and tissue on the tailfeathers and glasscloth and epoxy on the wings, but what effect will that have on the auw?

[Braddock, VC]

Glued all the fus together today, all clammped and pinned up and drying off in the boiler room, ready for the razor plane tomorrow.

The final construction work, adding the inboard trailing edges and glassing the wing join will also take place tomorrow, it'll then have the weekend to set properly.

Then it'll be covering time and I STILL haven't made my mind up about how I want to do it. One thing's for sure though, it's going to get a dose of sanding sealer all over.

I've ordered up a few of those velocity stacks for the saito and I'll plonk one of them on the 82 destined for this plane; at the same time I bought a flexible exhaust pipe so I can route the silencer below the wing .

14 x 6 APC props £13.49 god they're an expensive consumable.

As a matter of interest I've just ordered my next build, a mantua models Double, this is an amphibious plane sized for up to 50 2s or 70 4s, and is a pusher. I'll check out the cost of pusher props and, if they are exhorbitantly expensive, I'll send my laser back to neil tidey so he can retime the camshafts and it'll run in the reverse direction using standard props.

[Philf]

Do you not think that a 6oz tank is a tad small for a Saito 82?  Mine seems to drink fuel like its going out of fashion.

[Braddock, VC]

Hi Phil,

            Sorry to take so long to reply, I'd tried twice but my kids have cleaned my registry and I was logged off hence losing the posts.

I did say the 6 oz tank was a maybe, I have a dubro 8 oz for initial installation. Like you I found the saito 82s juicy to begin with (I have three, two in use and one waiting for a job). After about a couple of hours running I reset the idle mixture, taking almost 1.5 turns in to lean it out. In my previous acrowot, with a 14 x 6 apc and 10% Prosynth, much of the flight was at less than half throttle so this measure had a significant effect on the fuel consumption. After I crashed the AW I installed the engine in a 63" span CAP 232 after fitting a velocity stack to the carbie, this also improved fuel consumption; so much so that more often than not after ten or 12 minutes (about as much as I can concentrate in one go) the tank is almost always 1/2 full.

This is not really such a good idea as, I don't know about yours, my 82s are extremely intolerant of water in the fuel and saitos MUST have exhaust pressurisation to run properly (contrary to the benign idiot of Oz's recent article, which I have to say was drivel) the exhaust gas contains water and whilst the amount of gas used up in pressurising the tank is relatively small, the humidity must be approaching 100%. The adding of the dregs of the fuel after repeated flights seems to add significantly to the amount of dissolved water in the main fuel bottle which eventually affects first the bottom end performance and throttling, at that point I used to burn off the fuel in an old steel saucepan and, as the methanol and nitro reduced, the amount of spattering in the remaining oil indicated, to me at least, that there was water settling out as the carrier(methanol) disappeared. I took to decanting my fuel into one litre fuel bottles and reducing my tank size to preclude this build up. I'm on the third gallon now with no such effects so fingers crossed.

Sorry to drone on about this but the end result is there's and 8 oz tank going in, if it's more than a quarter full after a reasonable flight, for me i.e., then I'll reduce it to a 6 ounce tank.

This has worked on my vintage jobs, with my junior 60 and windy aint it, both with os 26 fs in each having a 2 ounce tank and extended flights of 20 mins have been achieved, in fact I tend to fly the planes until they run out of fuel as I have no fear of dead sticks with those.......