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Apr 14, 2013, 05:33 AM
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Build Log

Piper J3 Cub - Starmax 1400mm (Rating 10/10)[Crashed - Destroyed. BOO!!]


A bit out of character for my usual aircraft type that I like - mainly military jets, or warbirds - I had seen a few Cubs around and always liked their docile flight behaviour, so it was an aircraft up near the top of my list to get one version of.

I had three main choices, when I finally decided to get one.
A 1000mm one ($70), this 1400mm one ($126), and a balsa 1800mm one ($130 ARF). I couldn't bring myself to pay $70 for a "small" one, when $50 more gave a much bigger and more detailed version. Whether the Starmax or the Balsa (unknown version) one - but the ARF would need about another $50 spent on it, which is fair enough to have that total cost for its larger size, but it is a bit big for what I want. Thus the PNF Starmax won out.

I had also read up a lot about it, and it had tons of positive stuff commented about it, and no negatives. So add in that I think Starmax make great stuff generally, that also made it the clear winner.

Having it now... even at checking over the parts from the box it was looking a "100/100" plane!! Assembled, then flown.... it is still "100/100". Excellent value for its cost.... everything well designed and implemented! You could just build it and fly it as it comes and it would be fantastic still.
But there are always little things you can do to improve aircraft......

...
Last edited by PeterVRC; Jan 15, 2019 at 08:13 PM.
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Apr 14, 2013, 05:51 AM
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Elevator Bridge


Some people had mentioned the elevator "bridge" was a bit weak - it is just the same foam as the elevator itself. So I added a 3mm carbon fibre rod across it.
This was much better than just the foam, but it really wasn't that great still. The elevator halves could still flex a bit.

When I pulled the fin and tailplane off again (they are bolted together) the paint on their surfaces had stuck to each other!
This brings up one first point about the plane.....
The PAINT.
It is well painted, but... mine at least... was 'tacky'. Your fingers stick to it a bit! So anything that is against it sticks to it. I WBPU all my planes anyway, so that fixed that fine.... so that is something you really want to do!!

But I did that AFTER assembling it all, so that meant the bolted down fin and tailplane were 'raw' paint joined - and it did join, and tear apart, on removal!
So WBPU the plane totally BEFORE assembling it!! And do ALL foam areas. eg even the upper cabin rear end where the wing rests on foam. Mine stuck there too!

After the first flights I decided the elevator was still a bit weak side to side, so I added a plywood bridge that is a much stronger shape to achieve the required task. I was going to put some 2mm bolts through it (or 1.5mm) but just left it epoxied in the end. I will see how that goes. Though adding a pair of bolts per side would not be hard to do anyway - but if you do that, the upper side would need recessed ply plates for the bolts to clamp against. So it is a bit more work - and thus I was that bit too lazy to do it now!
So I would recommend making the plywood plate idea, and not using the carbon fiber rod idea at all. It needs that area that runs out more rearwards on the elevator, to fully support the bridge properly.

...
Apr 14, 2013, 06:04 AM
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Landing Gear


The landing gear main wire portion jus tplugs into a "plastic slot". The way the rear end of the landing gear assembly gets bolted to the fuselage would hold that wire portion in the slot quite well I would expect. BUT, if some hard landing, or crach landing, did rip it out - which is definitely possible - then it would snap off the rear end mount points pretty surely too! And those a custom plastic parts you would need to buy, or make a new set of.

I decided the best way to 'protect' those rear plates is by clamping down the front wire portion, with a plywood plate. Thus it can never come out inadvertently.
This is just a 2.5mm plywood rectangle, and 4 self tappers that you drill into the plastic landing gear base plate. All very easy to do.

There are definitely potential future damage results that are still likely to occur one day anyway, but I decided it was the right 'balance' to protect it this way for the majorioty of cases you will encounter during 'normal' operations and if it is ever broken off, then a more serious solution would be implemented - seeing you would be repairing the plastic parts wrecked, and other plane damage too most likely!

The best way to replace it all would be aluminium wheel fairings instead, and have then hinged along the fuselage line - like the real Cub has it landing gear hinged. So I will do that IF I ever break the stock assembly....

Another issue I found was the wheel "covers" that you screw on to hold the wheels on. By the time the hit the end of their screw travel, the wheel is still loose! By 4mm or so. To fix this I put in a 3mm wheel collar, that is 5mm wide, at the inner end of the axle - to bring the wheel more outwards. Thus the wheel cover reaches the wheel's holding point just before it runs out of screw travel.
Put some OIL onto the axle and also the wheel cover 'hub', so the wheels will turn smoothly.

...
Last edited by PeterVRC; Apr 14, 2013 at 06:26 AM.
Apr 14, 2013, 07:05 AM
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Battery area


I bought some Turnigy 4S 2800mAH 30C batteries to go with the Cub.
I already had about 8x 4S 2650mAH 20C, 25C, & 35C batteries - all much the same dimensions as each other. Wide and flat.
The new 2800mAH batteries are more square.

The 2800mAH could not fit into the battery "hole" due to being too high - there is a rib to the bottom side of the Cub in there, so I cut that out.
Using my trusty "Long reach kitchen carving knife"! Long, thin, SHARP! So it can get way down into hidden caverns.....

Then I found the 2650's were too wide!
So I trimmed off about 5mm from each sidewall, right down to the front end of the battery hole.

So then both battery types were friction fits into the hole, thus they would not budge in flight. That worked out very well.... for those.


The hatch cover has a 'block' on it to help keep a battery in that forward hole, but it is not really suited to the job. Especially with these two types. So I just cut that all off so it all has more room and closes easier. The tight fits keep them where you places them fine.
But I did as "Fibre Tape Tabs" to the batteries, so you can pull on that to get the battery out. NEVER pull, or even hold, a battery by its power lead or balance lead!

Turnigy 4S 2800mAH 30C
https://www.hobbyking.com/hobbyking/s...dProduct=21242

The batteries typically get 8mins to 10mins of flying time, at constant cruising speed throttle - or a bit more now and then - with plenty of leeway to spare and give them an easy and long life.

Another thing I did was extend the ESC battery lead because it allows more length to make battery connection much easier. It saves having some tightly contorted 'loop' to get to the battery connector. It works very well and is pretty much a must-do thing!

...
Apr 14, 2013, 07:12 AM
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Flight Report


Not much to say.... it flies!
It is very docile and flies very scale-like at about 35% throttle on 4S. It would probably fly fine on 3S too - though it is handy to have the 4S power capability on hand IF you wanted to use it. So I don't really have any interest in using 3S.... or maybe I will, just to get some use out of a bunch of 3S 2200mAH batteries that I have.

As mentioned earlier, 2650mAH to 2800mAH gives an assured 8 mins of flying time... but possible out to 10mins or 12mins really. And more if you really wanted to MAKE it last longer.... but if you fly it like a real one - using power all the time - then those above times are more realistic.

The landing gear works fine, even though it is a bit stiff really.
It can land and take-off from 'average' grass very well, and does not nose-over. The "balloon" wheels are quite wide and a good diameter for the plane.
Last edited by PeterVRC; May 16, 2013 at 08:07 AM.
May 16, 2013, 08:09 AM
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Landing gear ripped off.


On a "silly" landing, I ripped off the whole landing gear assembly. This means it broke, because of how it is partly bolted to the palen and wing struts! Pretty much as I expected would occur eventually.
If you took CARE ALL the time, it could last long term.
But now, time for some new robust landing gear for it!!
Aug 07, 2013, 08:54 AM
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The Cub goes FPV


After a lot of humming and harring over getting some form of FPV setup, I finally decided on the first test setup. And the current best plane I have to put that into, and test/learn about it, is the Piper Cub!!

A lot of pondering over how to mount all the bits.... this install is not just FPV, but also a Cyclops Storm OSD unit, which gives the OSD with Flight Battery Volts/Amps/Used mAH, Altitude, Speed, Home pointer, Distance to Home, Flight Stability, and also ReturnToHome - just in case the plane somehow tries to fly off and away!! hehe

The camera for this setup is the 808 #16 keychain camera, running from a pannable mount - to allow looking left/right at downwards angles, and of course level straight ahead.

I decided to mount the VTX in the upper wing to one side, and the GPS in the other side upper wing. Those are optimal positions, and also allow wiring to be easily run too. They will be 'covered' by PTC painted covers.

The Storm OSD goes in the rear end of the cockpit.
The Camera/mount sits mid-cockpit and has a 'pilot's eye' view out of the plane.

I haven't weighed it all yet, but it is about 200g in total with a separate FPV battery for it. That battery mounts under the mid wing, to the rear end of the cockpit - though can move anywhere along the mid-wing in the cockpit upper opening 'hole'.

I have started on the new landing gear assembly, but still a bit of 'humming and harring' to do over some specifics of that....

.....
Aug 09, 2013, 09:46 AM
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New landing gear


A temporary move from the FPV process.... sort of in parallel....

I made up the new landing gear - opting for NOT having pivotting suspension for now, at least. Just an alloy plate assembly that can flex for suspension.

A bit of staring at the Cub... thinking of needs and ideas..... so that I could implement the most useful landing gear solution.
I decided that there are a few needs....

1) The landing gear needs to be very robust, so it won't 'tear out' too easily, BUT it needs to tear out if the forces are too heavy. So that means to remain intact for up to 'fairly heavy landings', and tear out at forces above that.

2) If/when they ever tear out they are NOT to take the wing struts with them! Like the stock system does.... and then break the plastics. So I made the strut mounts a separate structure to the landing gear. Thus the landing gear assembly can 'depart' and the strut mounts will remain behind intact.

3) Keep the spring system, for scale looks, and also to actually DO something of use. So it gives some extra 'return spring' to the legs - much like in their stock form.

4) New decent wheels..... Well, I put on the stock wheels for now, until I get some low bounce DuBros for it instead.

...
The landing gear struts/legs are just one alloy plate made from 50tho aircraft alloy. They were shaped to give a bit of forwards rake too, instead of 'straight' across - just to give a bit more stability and you can't really see it.

The wing struts have a plywood plate well epoxied to the fuselage, deeper up into the fuselage than the landing gear plate which goes 'over' the wing struts plate. Then there is an alloy strip which extends out the edges of the fuselage and the wing struts will clip into/onto each one of those per side.

The landing gear bolts to a 5mm plywood plate that is 'medium strength' epoxied to the fuselage, but NOT to the wing strut alloy or ply plate. In a very hard landing or crash, the landing gear alloy assembly AND the plywood plate, will just tear off the fuselage - and should not do much foam damage then either. The wing struts plate, not being glued/attached to the landing gear plate at all, will remain on the fuselage.

The 50tho alloy is just right to give suspension 'bending' and is a strong enough alloy to not really stay bent (but would in quite heavy bashes!), but springs back. And the stock spring system also helps with that. (Though they sprung back fine without the springs too).

It is not as compliant as it could be with hinged fairing coming off the fuselage edge (as per the real Cub), but it is the next best thing and MUCH better than the stock plastic rubbish!
I will paint it all up eventually, to match the Cub properly.

...
Sep 22, 2013, 05:07 AM
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Cub down !!!!!


The END of the J3 Cub.... too badly damaged to contemplate repairing....

I guess I am a bit annoyed, yet still surprisingly little annoyed really. Probably because a Cub is a bit of a sedate plane for me, but also part because it was more or less MY fault it was wrecked and a "Told you so" moment that came true....

A MAGPIE crashed it !!!!
Yep.... a stupid little bird!! One out of a group of 5.....

Where I mainly fly they are nesting now, and at one end of the oval there are 5... and at the other end of the oval there are another 5. And they apparently HATE Yellow/Orange spectrum colours, for some reason!!
If you fly any other colour, they stay put in their trees/nest - but fly anything with some orange or yellow and they come out in force and attack!!

I used to think it was a bit annoying - they might PECK my plane!!
Then a friend had his Cub CRASHED because of the bird attack!! Birds attack other birds by coming up from below and behind and when they do this to a model plane they hit the tailplane with decent force and pitch the plane nose down dramatically! His 800mm was 'flipped' into an uncontrollable dive and crashed from about 30feet.
I didn't think they could do that to a 2.1Kg Cub version..... but obviously they CAN!!

I had been flying around riling them up, and you can easily out accelerate them and keep them away from the plane - but NOT when you come in to land!! And the wind direction meant coming in right over their tree at one end of the oval!! So as I came around and over, out they came!! All 5.... swarming all over the plane! And one second it was flying along on normal approach, and the next it was flipped to dead vertical and plummetted like a rock from approx 30feet!
And to make it a bit worse, it hit a pipe railing out in the 'bush' area off the oval!!! BAMMMM.... I heard a loud bammm as it went in, out of view amongst the treeline.

I knew it couldn't be a good crash, but as I walked up I was amazed!! Such dramatic damage! Even the alloy motor shaft adaptor was sheared off as the motor hub (the alloy snapped!!). And then I saw the fresh dent in the water pipe railing... OUCH!!

So that is that.... a total write off!!
I will either buy the L4 Grasshopper scheme of the same plane - so as not to have YELLOW again!! Otherwise the larger balsa ARF Super Cub.... and I will almost certainly pick that one instead. Because the foam Cub is space limited and messy to set up the FPV stuff.

...
Jan 12, 2014, 05:26 AM
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The Piper J3 Cub RETURNS!!!!


3.5 months later.....

I can blame the eventual repair of the Cub... err, THANK, LOL... on Agediffer - for requesting some parts of the 'throw away wreck', which led me to re-assess it when I went to remove the tail-wheel assembly. I guess that 'rested eyes', after a long time not seeing the Cub, can then see things more afresh and spirited?
LOTS to repair, but each bit I could "see" clearly how I would do it, and how each bit "would not be so hard to do". Maybe a list of 20 things in total....
I could just "see" myself doing those bits, easily and without problems... so now it looked something to do for sure!

I had to make a new firewall, as the original snapped in half. The was so quick and easy to do, and to be better than the original too!
I also needed another motor, as the original had sheared off its prop adaptor and would be hard to get a correct one - but I had a suitable Turnigy in a box, which was actually one of the key points that powered the enthusiasm!
I will be able to mod the original motor to make it useable in something else later anyway....

The main cockpit plastic, which is all the "glass" and the wing mount combined, I had already repaired (glued etc) long ago, so I only had to remount that to the foam fuselage. I decided to add plywood plates to the fuselage so I could just screw the cockpit assembly into those. I did it this way because I don't like the 'glue' idea - though it is a huge area that would hold fine - plus having it removable via screws means it gives easy, and total, access to the internal cockpit for FPV stuff.

I had also repaired the cowl long ago, but it could not mount via the original screws so that also needed plywood plates added to the fuselage, to then screw into for the cowl.

Numerous areas of 'splicing' in new foam pieces and then shaping them to the original shapes.....
Some foam bending and 're-shaping'....
Lots of gluing (Epoxy) here and there....

When I went to test the motor I found the original ESC wouldn't work. Maybe if I find a Manual for it I might be able to get it going, I changed it to a HobbyKing 80A I had lying around.
I also mounted the ESC under the engine mount instead of inside the fuselage. I re-did all the wirings from motor to ESC to battery/RX area.

I repaired the rudder (hinges ripped off) and the wing I had already repaired long ago too so that was almost ready to go .....
The 'special alloy main gear' was still all ok and I fixed that back up, and re-mounted it to the fuselage.

The 'hardest' part was getting new wing struts made up. The original plastic ones were almost fully intact in length, but a few of the ends, and wing mounting points, had broken off. I made up some alloy end bits to fix them, but I am also getting some 30tho aircraft alloy 'strips' made up to replace the struts totally. Then I will decide which way seems best.
The wing NEEDS the struts for a total geometry setup that sets up a very strong final result.

So the Cub should be ready for re-test flying within a day or two! Just those struts waiting to be finalised - everything else is done and ready to go!
I will fill and paint the repairs once it IS actually proven to be fine and flying again! But it does look pretty good as it is anyway, considering!
Jan 12, 2014, 05:51 PM
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Peter..Glad to be of help...Did you glue ply blocks to the fuse for the screws??.I like that idea..from what i can see it doesnt look too bad.

As you know mine is the L4..StarMax did it the cheap way..A coat of paint and you have an L4...WRONG...The glass area is all wrong..When its been flown I might see if there is a way to open it up.. The removable cockpit is a good start.
Jan 12, 2014, 06:43 PM
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Small squares of 2.5mm 5-ply. About 12mm squares. Three per cockpit side.
For the cowl, the same ply but in about 30mm x 16mm rectangular piece per side.
Foam cut to their shape to embed them in.
I forgot to take pics of lots of repair areas, seeing I was zooming along so well - I just totally forgot to.

----
Cub all ready to fly again... almost. Just needs the Strut decision....
It looks better in pics than a close up human eye! hehe
But from 2m or more it is hard to discern the scars etc

....
Feb 01, 2014, 06:09 AM
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Struts and Painting


I made up some Aircraft Alloy wing struts. Though they are a bit thin... almost half the thickness I really wanted. BUT they still work totally fine anyway. (I couldn't get a thicker gauge, for now).
I made them "Swing arm" at the fuselage so that they can remain safely attached to the fuselage for transporting. You just put in 4 screws to the wing plates to attach them - not the stock wing mount points.

I also made a new Alloy hatch cover plate, to replace the 2.5mm plywood one I had made before. Using a hatch that goes flush under the fuselage - instead of the stock foam "insert" style hatch - means a nice bit of extra internal space to keep wiring less cluttered.

I mixed up some very accurate paint, BUT the plane has two slight shades anyway! It seems either from two colours used at the factory, or just lighter spraying and thus it came out a bit lighter. This makes getting everything perfectly matched a bit hard.

When I went to FLY the Cub, the FR-Sky RSSI report was TERRIBLE!! 42dB at close range (not too close!) - which is typically 60dB. I am pretty sure this is because of all the ALLOY over the plane now!
LG plate... hatch cover plate... struts.... merrily reflecting RF I expect.
But it flew totally fine.....
The RSSI increased a bit in flight, but remained in a range from 49dB down to that 42 dB,
39dB = signal too weak to be viable !!
So now I have changed the RX aerials to long (20cm) ones which have base loading at their ends, for higher gain, too. I will mount them both down the tail end if the aircraft region, at a 90deg angle between them, for optimal diversity. And then see if that is enough to bring it back to normal reception, or better.

....
Feb 23, 2014, 04:36 AM
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A BIG Boo Boo !!!! WARNING !!!


With my prior Turnigy 9X radios, re-flashed to use ER9X (An OpenTX derivative) and with FR-Sky RF stuff..... they do NOT have Model matching. Which generally is not a big issue, seeing usually you only fly... or POWER UP... one plane at a time....
And even with the Taranis now, which does have Model Matching on its new RXes, if you use the older D Series RXes they continue to have no Model Matching... and that is what is in the J3 Cub.... NO Model Matching.

So after 3 or 4 flights today, I put it in the van and got out other planes to fly and off I went..... flying away merrily. Eventually I needed some more batteries and I went to the van... slid open the side door... and SMOKE and FEATHERS poured out!!!
BRRRRRRRRR...BRRRRRRRRRR... WARNING... WARNING... DANGER Will Robinson!!

SMOKE means fire or HEAT.... and I instantly knew it was a Lipo Battery!!!
I feverishly hunted for it !!!
When I grabbed the J3 Cub it was HOT!!!
"Oh!! I left the battery in it and connected!!!" and I rapidly got it out of the van to the grass outside!!

Seeing the battery cover is SCREWED ON that took a bit of time racing to find a screw-driver and get it open!!
I dragged out the battery and it was HOT and very obviously burst and grey - though still 98% intact really!
Even more amazing was that INSIDE the Cub was NORMAL.... no burn marks or anything! So I would say the pack split a cell, or more, but that stayed within the heat-shrink jacket so all that got out was a plume of smoke - like an old fireworks fizzer I expect.

That was SO LUCKY!!
If the plane had caught fire, the foam would burn big time... and so would have the whole van I am sure!!! Sheesh.
VERY lucky really....

Feathers? Feathers everywhere..... carried around in the heat and smoke, to plume out of the van.... but WHERE did FEATHERS come from!!???
I knew.... seeing I have a double bed Doonah on each level in the van, to pad the planes sitting in there. But if the battery over-heated and DID NOT catch fire.... and no damage to the plane.... HOW did feathers get out everywhere!!!???

A bit more investigation high-lighted an interesting thing.....

The Doonah was torn/shredded.. and Cub's WING had hacked gouges in it!!! Right in line with the Cub's PROPELLER - seeing the wing lies across the front of the Cub underneath its nose in transit.
The Cub had powered up the motor!!!

This also explained why the Lipo cooked.... whereas a plane just sitting idle, and left connected, could last 24 hours before ending up flat most likely.

NO MODEL MATCH !!!
So for every plane I flew after putting the Cub away, it was TRYING TO FLY also!!! Go to WOT on another plane.. and Cub was too !!!
So the prop hit the wing and hacked through it over those many times...
And eventually the Lipo went flat, but was kept trying to power the Cub as I flew other planes still !!

OMG.... yet another "Amazing model aircraft disaster discovery!!"... things that can happen.....

The Wing won't be too hard to repair....
I have not checked the ESC and Motor yet, so hopefully they are both still ok - but might not be....

That is the first time EVER that I have forgotten to remove a battery from a plane right after landing it.... OOOPS!!!


LATER ADDITION:
The motor and ESC are both DEAD!! What has happened is that eventually the much higher load of being a "Chainsaw" on the Wing and Doonah would have had the motor and/or ESC cooking hot!!
One of those COULD have died before the battery did, but obviously not quite - if one had, then the battery would have survived.
So LUCKILY something blew up and ended the chain-sawing!! Possibly the battery just died 'fairly badly' not 'catastrophically' as it could have, and then catch fire!
PHEW....
$100 or so in total, of "Fuse".... but better than a burnt down van!

...
Last edited by PeterVRC; Feb 25, 2014 at 01:24 AM.
Feb 25, 2014, 10:58 AM
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You have to have XJT module in Turnigy 9x and X series receiver if you want model matching.


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