GWS Formosa 2 EPO Build

[Dunkelmann]

I plan to buy one of these. I have a 30A ESC and need to source a suitable motor, motor mount, prop and prop adapter. I plan to fly it with a 3S 2200 LiPo. I'll be flying from a very rough field (cows and hoofprints) so I may either, dump the landing gear and go for a folding prop, or beef up the landing gear.

As a very quick starter I thought of a Purple Power 2831/1000 at 205W.

I should finish saying I don't want a rocket, nor do I want 3D. Some nice scale aerobatics is what I'm after as I move up the experience scale a bit.

I'd greatly appreciate any advice or experience you would like to share here for me and posterity.

Cheers

Edited By Dunkelmann on 02/01/2013 14:29:19

[Bob Cotsford]

I've got one of these 2815's turning a 10*7 prop in my older version Formosa II, with a Black Mantis esc, I can't remember whether it's 40 or 50A. With modest movements (especially on ailerons) it flies like a mini F3A model. I replaced the u/c legs with thicker wire as those supplied were a joke. It's an easy model to hand launch but I like having wheels.

Mine was designed for a stick mounted brushed setup so I mounted the brushless motor by gorilla gluing a ply plate to the front of the fuselage with the cut down 'stick' mount helping to peg it on.

The F II you link to looks to be an updated version modified to take a brushless motor, in fact it does say that it comes with motor, prop and motor mount in that listing.

[Dunkelmann]

Bob, I can only find the NPS (No Power System) Formosa II for sale in the UK..

I've done some research and came across a couple of programs to help choosing motor and prop:

Motocalc

WebOCalc

The latter helps more in choosing props but it is quite simple given a motor kV and a few other parameters. The former is better but it relies on knowing a bit about the motor parameters. Luckily 4Max's Purple Power motors are in there and they have the data on their site to add the PP ones that are missing.

After reading that a lot of motors come from the same factories and are rebadged (for example see this page on the "equivalence" between Hacker motors and Purple Power), I came across the HobbyKing Turnigy Aerodrive SK3 series. There are suspicions that these too are Hacker (factory) equivalents. Anyway at less than half the price of the Purple Power I thought I'd not much to lose trying one out.

I had a play and came up with a Turnigy Aerodrive SK3 - 2830-1130kv Brushless Outrunner Motor and an APCE 9x5 prop. It's a good quality motor. Motocalc did some nice graphs that helped pick the prop size (Rate Of Climb and Thrust, versus Pitch - once I had decided on the diameter.

I had a look at your motor and put it into Motocalc. Static Thrust was about the same (19-20oz) but RateOf Climb was down (909 -> 721). Current draw was lower (15A -> 13.4). It was heavier. Price is much the same though.

So I'm off to order the SK3. Now I need to work out how to mount it. I believe the Formosa II has a stick mount system. Since both airframe and motor are on back order I'll have to be patient.

Thanks for your reply.

[Bob Cotsford]

I'm not familiar with these calculators but the value of 13.4A you quoted sounded a mile out so I've just plugged in a fresh 3S battery via the wattmeter and it came up with a slightly different actual current value. 29.5A. It's definitely a 2815/09. Somewhere around 330W which is what you want to get a reasonable performance. 150W will fly it but you are leaving no margin for upgrading if you feel the need later on. The weight is not a problem, I had to add some lead to the nose so the bigger the can the better. Some people move the servos from the tail into the wing area to save adding church roof up front. One of the US sites had threads quoting 400 and 500W being used with retracts and glassing all being added, this model will take it.

Mine just got a coat of plastikote paint - it's the yellow one, the other bronze/white/blue one is a .60 powered Tornado.

[Erfolg]

To start off, I have never owned a Formosa.

However I have seen a fair number at our club field.

From comments of one particular modeller who had a Formosa and the EPO version.

The two types are different, in that the earlier version from polystyrene had many structural weaknesses. These were so well known, that all the club models were suitably modified.

The EPO version, apparently no longer suffered from the body issues with respect to strength. However, there is an issue in that the tail is much heavier, naturally moving the CG rearwards. The good side, it is much more robust.

None of the models used the UC, fat to vulnerable on rough grass.

The natural rearward balance, encouraged the modification of the standard cowling, to one which was re-enforced with GF, essentially becoming a GF cowl.

The other consequence was to select a motor where plenty of power was available, as light weight was not such an issue.

I have seen a EPO version crash, after loosing a aileron. It was completely undamaged. Sees to confirm that the EPO version is much tougher. Although apparently not quite as nice to fly, although I have the impression they are still good.

Without being a aerobatic pilot, modellers seem to prop hang well, knive edge, etc well. In addition, will just fly like a trainer.

[Dunkelmann]

Hmmm curious - that's the problem with putting one's faith in calculators. Mind you, I hadn't a clue and started from rules of thumb like 110W per pound!. The Formosa all-up weight is stated as 24.5 oz - roughly 1.5lb and this motor is rated as 187W/20A so it is above the rule of thumb power of 165W. As you say I've no headroom but it cost £11. What's your model's flying weight?

I've had trouble sourcing the Formosa II. I got the last one in one on-line shop. Another shop said that they may not be obtainable any more. I'll email the importers.

I'm like you and use the same colour scheme now. I use Acrylic paint but toyed with the idea of SolarFilm - maybe it's too finicky but I like glossy paint and acrylic is matt.

[Dunkelmann]

That's a good tip about the cowl - add reinforcing weight rather than metal weights.

I saw a video on YouTube where the modeller made a replica cowl from a pop bottle by first making a base by filling a spare cowl with putty and letting it harden. He then used a heat gun to shrink the bottle onto the base.

If I can find wire linkage I may consider moving the rear servo forward if there is room.

[Bob Cotsford]

I've just put mine on the scales, 930gm for the airframe plus 220gm for a battery gives 1150gm rtf which I make around 2 1/2lb in old money. That's with a 2600 pack but I think you would be pushed to loose a full pound even using the smallest pack you could find as they all seem to need noseweight.

On the subject of cowls, I lined mine with a couple of layers of fibreglass tape and it's survived some landings in extremely rough places.

[Erfolg]

Bob

Seems a very common policy that most adopt, that is strengthening a cowl. All seem far to flimsy, particularly as excessive weight up front seems less of a problem than at the back.

You do wonder where the manufacturers get their estimate of finished weight from, it never corresponds to the model I build..

[Bob Cotsford]

No paint, no stickers, geared brushless motor and a very small battery would help get the AUW down but you can't get away from the fact that the servos at the back need nose ballast to balance them. Maybe the AUW is for the earlier polystyrene version and that with a rearward CofG? Maybe manufacturers rent the space station to do their weighing in? Maybe it should just be taken with a pinch of salt.

One good thing is that the cowl is made from some flexible plastic type rather than ABS so it's quite resilient.

 

I've just realised that I've left out the most important piece of info - this is not so much a Formosa II kit, it's a box of plastic from which an aeroplane can be built.  As I remember it the instructions are basic and not at all clear, you need to use a little initiative in the assembly but it does fly extremely well.

Edited By Bob Cotsford on 05/01/2013 09:05:11

[Dunkelmann]

I've looked at some weights published on the Web: 720g(GWS figure), 800g, 950g, 1020g, and yours at 1150g. My battery weighs 180g. Putting 900g + motor weight + battery weight into the calculations mean the plane will have the characteristics of a basic trainer according to the calculator.

I'm now getting depressed with all of this I had my Formosa order cancelled on me as the shop's website was out of date with their stock levels. So I reordered with another place I've dealt with before (who were the most expensive for the Formosa 2 in the UK). The alternative was one shop that wanted £14 in postage.

It's too late to cancel my motor. But if this shop says it is sold out I'm giving up and will try to find an equivalent. There just doesn't seem to be one however, making the jump from reasonable aileron experience and slow aerobatics to more precise and fast aerobatics difficult. I did consider spending a lot more but I felt the risk of crashing an expensive plane too much. Apart from that I have a bunch of 3S LiPos I want to continue using and the planes I looked at all used 4S. My club is into IC/Balsa and gliders so I'm on my own here.

I can't understand how people pick a motor and prop. I thought I was being scientific. I've spent days of my Xmas hols doing this. I've been amazed at the web shops listing many motors by physical size yet not providing a simple search mechanism (e.g. search for a motor within these weight limits, giving out this power and within this range of kV). Instead I've had to spend hours painfully going through each motor in turn.

IF... I do get a Formosa II, I'll stick a wood firewall on with a decent mount, pushing the nose a bit further out perhaps to help balance. I guess (yes - I'm not using a calculator) I should get a 300W to 400W, 1000kV to 1500Kv motor.

[Erfolg]

Selecting a motor etc. can be made into something difficult. I find that it is helpful to remember it is not a mathematical function, where only one result is correct.

For most, if not all applications, it is about ball park figures, with an aye on what you expect from the model.

The indications are that the model will weight 2lb or 1 kg, indicating something better than 200w is needed. Say 250-300w, will cut the mustard.

The instructions with the kit will indicate a motor, just check what the suggested prop size is. Say a 9" *4". May even give a Kv. I personally would just look for a motor which can draw the current and swing that typically sized prop, the Kv will help. Low Kv bigger props, at lower revs.

The Formosa, is intended for a outrunner.

As most things , it can be made to seem difficult.

Oh, I would also check back here, with your ideas.

[Bob Cotsford]

DM, first remember that my 930gm was with the motor, esc, servos and receiver. Second, the Formosa II is fantastic value for money compared to Mpx models, it just needs a little more input in the build. A quick google shows just about everywhere listing it as out of stock, I wonder if they've stopped production?

[Dunkelmann]

Well, I have received my Formosa II. Since this was a no-power-system model, I wasn't expecting certain bits. However nowhere does it say that servos are to be provided by the builder. I have a couple of 9g Hextronik XT100s from Hobbyking and I'll buy a couple more.

Bob - I see what you mean about a box of bits. There's nothing about fitting servos or your own motor but that's OK, I'll improvise something. Half the fun will be in designing how to reposition the elevator and rudder servos centrally. It looks straight forward enough.

I've thus been trying to source tube and pushrod and swithering between carbon fibre, piano wire, Bowden cable etc. The pushrods supplied come in two diameters 1mm and 1.4mm (according to the manual but I think they are smaller than stated). It's not clear which is for which control surface. I'm thinking of getting about 1.2mm wire as my Parkzone T28 Trojan (about the same weight) seems to use that size.

Erfolg, I mailed the distributor who replied: "I have been looking into this but our purchase department still do not have a delivery date for these so we can't confirm any date at this time. Once we have the delivery date it will show up on our web site." So it looks as though they do expect more.