Hobby king ST 330

[pattern14]

Some years back, I picked up a set of St 330 wings from a now defunct online distibutor. As this was my first foray into foam planes, I had nothing to compare it with, and happily went on modding it, until little remained. I also picked up a fuse, which I cut and chopped to fit an EDF unit, and experimented with v tails and the like. Fast forward uptil last week, when I spied the whole plane, minus radio gear, for $80.00, from HK. Too good an offer to pass up, considering I paid more for just the bare wings, 4 years ago, I decided to grab it and trial it as standard, and then with mods. There have been mixed reviews on this one, which is a blatant clone of the Multiplex easyglider, and no doubt there are other ones out there under different names. Value for money, it is well worth the extra work to get it flying really well, especially considering they were on sale only two years ago for 3 times the priceI'll get some pics, and a "out of the box" maiden flight report next post, before delving into the array of possiblities that can be had. Cheers

[pattern14]

Had the opportunity to try this one out under a variety of conditions over a couple of days. Surprisingly, it all fitted together very well, with no obvious gaps or mismatches, The whole plane is quite symmetrical, and balanced very easily, and the quality of the overall finish seemed as good as the multiplex plane it was copied off, and actually more smooth than the skin on the radian. The power system is all one unit, no connections, and like the servo's, are obviously bottom end of the quality scale ( read cheap). Even if the electronics are junk, as so many arf type planes have, $80.00 is still an inexpensive airframe. The prop looks like it came off a wind up toy store plane, and vibrated alarmingly on start up, although it smoothed out OK at higher revs. If/when it breaks, it will be replaced with a better quality item. You get what you pay for apparently. Everything worked "out of the box", which was good, and I put in my 2.4 rx gear and 1600 mah 3s and checked the cog. A little cramped under the foam canopy, with the larger than stock recommended battery, but it all fitted well enough, although the plastic hatch is pretty flimsy. No worse than the easy star one though..........Cog is 70 mm from the LE, and it balanced at this point straight away, which was also encouraging. Those plastic hinges on the control surfaces did not really inspire me I did not concern myself with the stickers and cosmetics, as I simply wanted to see how she flew as a stock standard item that a beginner or novice might be tempted to buy because of the low price. I will give it a taped finish once tested out, as this covering method really adds strength to the EPS/elapor type foam, with very little weight gain. Included some pics of the assembled item, which took less than an hour, even with the rudimentary instructions. Maiden next post, cheers

[pattern14]

This time of the year, the summer weather varies from freezing cold to humid thunderstorms, with lots of wind in between. 4 seasons in one day is not uncommon. So the first flight was made in 10 knot variable winds, which is pretty mild for this part of the world. The wings on this one are attached to a central aluminium cross, with the wing tubes sliding over the the lateral arms, and held in place by self tappers under the fuse. Not the method I would have chosen, but thats' what i have to work with. The tail section seems to be a slide fit into the fuse end, with no securing method at all. The hand launch on 1/2 power was totally uneventfull, with the plane climbing away quite steadily; must have lucked in with the trims. The gentle wind pushed her around a bit, but still climbed up and away with effortless ease. A couple of circuits to make sure all is well, and time to land and re-check. This plane floated in very gracefully, and seemed to skim over the top of the field of oats for quite some distance before settling, very much like its Multiplex inspiration. Encouraged, I changed batteries, and took off again, this time flying to nearly a kilometre away where the updraft from the mountains start. Power off, she soared and swooped for about 15 minutes, gaining and losing height at the extreme range of my vision. Eventually my caution took over and I bought her back for another gracefull landing. Pretty impressed so far, I put her up a third time and tried some aerobatics. Tight loops, very stable inverted, very tight turns ( better than the radian on all accounts), but woefull barrel rolls;she rolls like a pregnant hippo on a skateboard You can't have everything Also impressive was the lack of wing flex, better than the radian again. Next morning the wind was blowing quite a bit stronger, so I tried again. She was very unhappy, difficult to control, with poor responses. Ended up in a tree, but no damage upon retrieval. Wind plane, it is not. That evening was one of the all too rare ones with not a breath of wind, and she flew superbly, as well as any foam glider could, so the more calm the weather the better. She also flies much better as a glider than powered. Next morning I tried again in the early morning calm, and she spat that cheap and nast prop off about 10 seconds into the flight, so it was a gentle turn and gracefull glide back. So my conclusion.........? Not a beginners plane, as the cheap hardware will let you down when you least expect or need it, but it flies well enough for a beginner to learn on. Ideally, you could buy the bare airframe, fit quality gear, and have a sailplane that fills the bill, for a very reasonable outlay, but you would need some basic experience to do this. As an instructors plane though, for teaching purposes, it would do very well, once sorted. So my plans now are to pull it apart, fit decent hard ware, give it a durable tape finish, and choose a suitable power option. Let you know how I get on...cheers

[pattern14]

I was going to wait a bit longer, but I ended up with some time to spend when I least expected it. I disassembled the whole thing, and split the fuse from nose to tail. It was a bit harder than anticipated, but I ended up with two neat halves, and dug out the motor, servo's and associated bits and pieces. The motor would have to be the tinniest, cheapest looking powerplant I have ever seen, even worse than the borderline junk pz put in their planes; same goes for the servo's. Maybe I'll find a use for them in a very light, non-demanding parkflier one day............I intend to make a twin out of this one, to free up the nose for a decent sized battery, proper ESC's, and probably a camera at some stage. The centre section will be enlarged to take the rx, and the tail will have a channel cut to accept the servo leads. The servo's for the tail will be mounted in the rear of the fuse with direct rods and clevises. The tail feathers themselves will be retained, but the control surfaces will be replaced with proper balsa ones, and decent quality horns; likewise the ailerons. Some CF rods will be used to stiffen and strengthen the whole plane as well. Try and get some pic's up in the next few days, cheers

[quorneng]

I too acquired a rather battered ST330 with no motor, ESC or radio and the nose completely snapped off.
It ad been 'glassed' overall which made it feel a really heavy lump so I decided to take it all off. It saved 8oz.

I can live with cheap servos but the snakes along with the 'linear' control surface actuators required a huge amount of force to move the surface to full deflection.
The main culprite was the 'pinched down' foam creating the hinge line.

For example the rudder actually required the servo to generate 400gcm of torque for full deflection and that's does not include any aerodynamic load.

I too elected to use servos close to each surface with short direct links but going right down to micro size.
The 3.7g aileron servo.

The servo (and its cable) weighs less than 1/3 that of the original servo/snake/hinge set up.
With the moulded hinge line cut away the wing and aileron edges were rebuilt with Depron to create a simple tape top hinge layout. It will also have a strong differential action.
I have found that in a 'glider' this provides sufficient control of adverse yaw allowing the rudder to be fixed so saving the weight of its servo.

The elevator servo built into the rear fuselage with just the tip of its horn protruding.

The elevator has the same treatment as the ailerons with a tape top hinge.
The trailing edges of the foam wing are very thick - nearly 4mm.

By adding a strip balsa extension the edge is brought down to less than 1mm.

The fin and tailplane have the same treatment.
This modification should reduce the drag, particularly at speed.
The fin and tailplane are permanently glued in place and by removing the nylon mount actually saves more weigh than that of the elevator servo!
The cockpit area is by far the biggest job but as there will now be no servos in there the moulded in cut outs can be filled to gain some strength.

What started as a cheap, quick, 'lets try a foamy' job is rapidly becoming a serious rebuild.

[pattern14]

Hi Quorneng, good to see someone else modding a cheap foamie into a going concern. Your upgrades look as though they will do the trick, and I'm looking forward to the test flight. I have not progressed any further with mine (too many projects at once) but fully intend to get it up and going when time permits. I am finding myself renovating my aging and battered squadron instead of building these days( run out of room for new planes). Checking in other sites and threads, this one has some mixed reviews, compared to the radian. I would not bother with another radian, as I find pz planes fragile and overpriced, but I am sure there are thousands of owners out there ready to disagree. Good luck with this one, cheers

[quorneng]

Pattern 14 - I only hope it proves to be worth all the effort!

The cockpit rebuilt.

The cockpit sides have also been built up to a new sill line.

As the motor is front mounted the extended nose terminates in a substantial 6 ply mount.

Done this way the motor can be inserted (and removed) through the cockpit.

The new 'solid' (or rather hollow!) canopy under construction. 3mm Depron but amazingly light and rigid (once the last plank goes on!).

The cockpit layout.

With the 1500mAh 3s right forward the CofG is at the recommended 70mm from the leading edge. With its long flush cockpit area other sizes of battery can be fitted. For example, the same CofG is achieved with a 3000mAh 3s positioned at the back of the cockpit.
The completed ST330 finished in my 'house' colours of white with red control surfaces. It has a 12x6 prop.

With the 1500mAh battery it weighs just over 29oz, some 3oz below 'stock'. With a 3000mAh this rises to 34oz.

Nevertheless it feels quite a heavy lump when compared to my similar sized 'feather weight' Depron job which only weighs 23oz and that's with a 3000mAh 3s battery!

I do have serious concerns of the strength of the wing joint as it relies almost entirely on a single 10mm diam aluminium tube. To make matters worse it has two holes drilled in it (to pick up two wing retaining screws) but unfortunately they are positioned right at the point of maximum bending load!
The old and new wing joiners

As this close up shows it looks like the joiner had been bent and straightened several times as the ally has been permanently deformed and cracks have started to propagate.

I had intended to replace it with some 10mm CF tube but unfortunately its internal diameter is just too small to slide over the wing tubes, however the new ally joiner has no holes (the wings are now retained by rare earth magnets) so it should be a bit stronger.

Just have to wait for suitable weather.

[pattern14]

Hi Quorneng I wish my camera was working properly so I could post the wing mounting mod that i did. I actually joined the wing together with cf stiffeners, and used bi directional tape in a criss cross fashion to secure both halves-it turned out really stiff, with just enough "give " to allow for normal "bend without breaking" flex. I then cut the top section of the wing saddle out of the fuse, placed the wing back in the saddle, and then put the top half back, effectively sandwiching the wing centre section. I cut a groove in the top to allow placement of a another short cf rod, with the ends extending either end, and then taped the whole thing in place. Easy to change, very little weight gain for the strength involved, and the whole section will tear out in a crash instead of breaking wings( been there done that etc) Worked perfectly on my first one. The mods you are doing look great, and looks as though you have a winner on your hands. Watching with renewed interest

[quorneng]

Its maiden flight this morning - edited down from 5 minutes.
https://vimeo.com/53207726
Not too bad.
The roll is pretty sluggish although pitch is rather sensitive but overall quite pleasant and well mannered.
It will need a bit more down thrust to really handle full power - at the moment it wants to pull up almost into a loop.
Seems to glide quite nicely.

Pattern 14
Does your mod wing mean you have to un-tape the top of the fuselage to remove the one piece wing?

[pattern14]

Originally Posted by quorneng

Its maiden flight this morning - edited down from 5 minutes.
https://vimeo.com/53207726
Not too bad.
The roll is pretty sluggish although pitch is rather sensitive but overall quite pleasant and well mannered.
It will need a bit more down thrust to really handle full power - at the moment it wants to pull up almost into a loop.
Seems to glide quite nicely.

Pattern 14
Does your mod wing mean you have to un-tape the top of the fuselage to remove the one piece wing?

Well done on the maiden With a wing span like that, sluggish rolls are the norm. My radian does not roll as well. You're right about the floating forever.....the St330 has a very similar glide pattern to the Multiplex easyglider that it was cloned from, and skims over the grass for ages before settling. As for the taped wings to fuse setup, I have to remove the two strips of bi-directional tape to take the wings out, but this very easily done, and is no hassle. Bi-directional tape degrades fairly quickly in sun light, so I replace it regurlarly anyway. Flying from home means I just leave the plane in one piece unless I travel with it , which is rare. You did very well to get a decent flight out of a very budget priced foam glider, and here's hoping there are many more to come. Happy flying

[quorneng]

After some thought I added the extra down thrust by the rather radical method of cutting off the ply motor mount, adding a foam 'wedge' and glueing it all back together.

It has had exactly the effect I had hoped for.
This edited video includes a loop and a roll, quite high but then it was only its second flight!
https://vimeo.com/53497385
It now has quite an impressive full power climb.
If I do build a new set of wings for it I will definitely include air brakes or flaps to reduce that landing 'float'.

[quorneng]

Just to get up to date I am impressed how docile the handling is.
Aerobatics and low slow flying low just for the camera.
https://vimeo.com/53591661

[pattern14]

Just had a look at the Vimeo you put up; that is one nice slow flyer If life was not so full of priorities right now, I'd have mine up too. Excuses, excuses..........

[pattern14]

With some time on my hands following a "forced" holiday for a few weeks, I'm going to get mine back together and up in the air again....let you know how she goes

[quorneng]

pattern14
Are you still using the original servos, snakes and hinges for the ailerons?
I never flew my secondhand ST330 with its original bits as the surface movement was so poor I didn't even want to try so I have no comparison but the tiny servos with direct short links coupled with a very free moving top tape hinge certainly seems to give positive control.

[pattern14]

Hi Quorneng; good to hear from you. All the OE has been removed, and just the bare foam remains. I'll be doing a similar set up as previously, with "proper" servos', short control rods, etc. Cutting out square chunks in the tail section of the fuse to mount them takes a little cosmetic surgery to make them blend in of course On my first one, I mounted a HET 6904 70mm EDF power plant on the "bridge" section above the wing centre section ala' He 162, and then went to a twin motor wing set up, which I swapped and changed to a variety of KV and prop sizes. It would be really nice to reach a point where you think "this works great; I'll just leave it as is", but the endless experimenter keeps rearing its' ugly head. The aileron set up will also run direct servo's, and I am still thinking along the lines of cutting off all the control surfaces, gluing balsa leading edges to them, and then using tape hinges along the bevelled edges. Apart from that nothing will be glued on this plane, everthing will be taped to allow easy access, including splitting the fuse. I'll go with the conventional nose mounted prop/motor system for the sake of simplicity this time, although I have been secretly working on a "V" tail pusher set up for my custom radian. All the left over mini servo's/wires, tubes etc will be used for a very light weight park flier I am designing for the 3 days of the year when the wind dies down. Let you know how it comes together over the next week....cheers

[pattern14]

Taking longer than anticipated, with lots of little interruptions, but should be together this afternoon.....more later

[pattern14]

Decided to try her with just rudder/elevator this afternoon, out of a combination of curiousity and impatience. Neeeded to see how the power set up would go as well.... I taped the ailerons flush with the wings, and swapped batteries until it balanced at 70mm. The 8" prop seemed to have plenty of grunt on 1/2 throttle, and she flew out very sedately. 3/4 power gave a good climb attitude, and seemed responsive enough on just the R/E combo. Nice big circles, flat glide etc. I'll use the original motor until it packs it in for now, then go back to a wing mounted twin set up again. Moved the COG back a bit, and she became very unhappy, and tried it forward, but really nose dived when the power was cut. So far I have not added any stiffening yet, but I'll put a ventral CF spar, and Horizontal/vertical stab re-inforcing too. The elevator is as floppy as, and the rudder wobbles like a harley on a mountain road. Foam control surfaces are marginal at best, and I usually replace them with decent balsa ones eventually anyway. I'll put on the aileron servo's next, and see how that goes........

[quorneng]

Well done!
Unless I had actually flown an ST330 I would have been very nervous on rudder and elevator only as there is only tip dihedral but it does seem remarkably stable in roll.

The balsa trailing edge extensions I added to mine to reduce the trailing edge thickness also add considerable stiffness to the control surface.

What weight are you flying at?

[pattern14]

Originally Posted by quorneng

Well done!
Unless I had actually flown an ST330 I would have been very nervous on rudder and elevator only as there is only tip dihedral but it does seem remarkably stable in roll.

The balsa trailing edge extensions I added to mine to reduce the trailing edge thickness also add considerable stiffness to the control surface.

What weight are you flying at?

Thanks for the encouragement there Quorneng. The wind died down enough for a test flight with aileron control, and she was far better behaved than just R/E. Turns are tighter than on my radian as well, but that would not be hard. No idea of what the AUW is, although it would be roughly about standard. I'll have to invest in scales one day..........She did handle the wind better with ailerons, but there is no comparison to my flying wing tailless planes, which I can usually send up in a hurricane . Still, as a fair weather summer plane, and thermals about, it is nice and relaxing to fly. I'll get onto the stiffening and coloured packing tape finish as time goes by, and may even play with a V-tail yet....work in progress...cheers