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Dec 29, 2013, 06:31 AM
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Build Log

PT-19 - 1200mm Balsa-Ply ARF - (Rating 7/10)


US$43 .... !!!???? AU$85 delivered.....
Oh dear... another plane..... LOL.

The pics looked good, and I have seen a few "Balsa-Ply" ARF's - owned by other people, and that looked great. But after GETTING one, I don't think I will ever get one again!! FOAM RULES!! LOL.
But back to this model.....

SHINY!!! That is the key attribute of the Balsa-Ply model. Covered in smooth shiny covering all over, or the just as shiny fibre-glass cowl.
The part I don't like is... the Balsa-Ply, and that covering! It makes altering/modding much more difficult and even limiting.
Then, if it crashes....... OUCH!! Or if you damage the covering in transit etc.

AU$85.... but needs another $100 by the time it is airborne.... so it is not really any cheaper than any foam aircraft of the same size.

Sitting there all finished, it looks GREAT!! Lacking panel lines and finer details of a foamie - even though on a foamie they are badly exaggerated anyway!
But if TopRC or UniqueModels.... or even FMS etc I guess... made a PT-19... then I would advise those as a better option really!

But this is worth what it cost....

....
Last edited by PeterVRC; Jan 09, 2014 at 12:43 AM.
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Dec 29, 2013, 06:46 AM
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First looks


Beautifully made framework, and also the covering job, It would take a HUGE amount of effort to do all this stuff yourself!! So that AU$85 was a bargain, in labour terms!

There is no manual, no info on who makes it to be found.... and it seems it is so new that no one knows anything about it. This means all the assembly and building has to be worked out yourself... as well as the CofG. But being a low wing trainer, the CofG should be simple to work out within good enough accuracy.

How do you join a tailplane and fin, to a fuselage, when all are covered with 'solarfilm'? I didn't want to cut any, as that would make it pull away. I used some creative 'keying' and then Epoxy (my favourite glue!!). That worked fine.

The wing is two-piece, with a big alloy tube as a spar. And a fair amount of dihedral built in too. It all fits together very well - as do ALL the plane's parts!

The fibre-glass cowl is beautifully made too!! But also no info on HOW to attach it.....

All the hinges are mylar(?), or something like that. Adequate, and nice operation really.

The landing gear is fixed - as per the real one - but has 'spring coils'. It will probably work ok, but it would be good to have some Oleos put onto it. I will think over that....

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Dec 29, 2013, 06:55 AM
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Tail servo, rods, horns etc


The plane is set up for dual elevators AND dual elevator servos! That is a bit overkill, BUT does help setting them up better.
The rudder and tail wheel are set up to be driven by push-pull WIRE! BAH.
I decided to shift the way they do the rudder - to a one sided pushrod with control horn.
This required hacking out the current 'tubes', for the pushrods and wires, and shift their positions around. This also allowed aligning them better to the servo positions I was going to use.

I cut the servo plate 'open' so that servos can be placed anywhere across its width. This also allows having 'half circle' cuts wehre the servo gets fed into the plate, and its wires can get through too - then you slide the servo to its real position.
In the '3 fixed positions' way they had it done, that means you have to feed a servo into its 'hole' and somehow get its wiring through, and to do that it needs the position to be a bit longer than the servo really is AND have a 'half circle' for the wiring to get through... which THEN messes up the servo SCREW placement.
So... the "slide a servo sideways to its position" method is WAY better!

I had to make my own rudder pushrod (easy) and the supplied clevises were no good, so I had to use other ones I had also.
But in the end, it is a nice solid control system!

I used Digital CM9 servos - not MG, seeing the dual elevator servos mean more than enough strength anyway. Though I could have used a MG servo for the rudder! I might change that eventually....

I did all the set up with the rudder and elevator hinging just pushed in.

...
Dec 29, 2013, 07:04 AM
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Tail-wheel


The tail-wheel design is quite nice, but no info on HOW to make it all work!
I decided to fit the wheel 'leg' into the holder and then bend it so it would feed a 'tang' into the rudder. Thus affixed to the rudder to steer with it... which they would have intended in some manner anyway of course.

I decided the rudder is so thin that the 'tang' would eventually rip out the side of it for sure! Thus I needed to make some thin aircraft alloy plates to make sure it was strong and unable to break out!

Then I CA'ed all the rudder and elevator hinges in....

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Dec 29, 2013, 07:15 AM
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Motor


I had a Turnigy 3536/8 1000kv motor here already (pre-planned for use in this) which should allow use of 3S and 4S/ You need the 1000kv for 3S to be viable, but for 4S it is a bit high... so you will just have to throttle limit it then.
Once it is flying I will decide what suits it best.. or if both are still really viable.
https://www.hobbyking.com/hobbyking/s...ner_Motor.html

I bolted it to the "firewall tube" that these balsa-ply models often have/use. Then slid the tube to suit the cowling alignment. But I had to work out the cowling mounting method first, and screw that on so it was a definite and final position.
To get some down and right thrust, I used a 1.5mm washer to the upper left motor mount position - between the mount and the motor "X" plate. That looks a good amount to have.... so them I aligned the actual motor position for have the motor shaft come out the cowl opening correctly. It worked out really well... perfect!!

For good 3S thrust, I chose a 10x7 prop. A quick power/thrust test - with the whole plane pieced together with all parts in it - and it was a good amount on 3S. Overkill on 4S of course!

All in all it was a great fit... great look... and great power result!!

....
Last edited by PeterVRC; Dec 29, 2013 at 08:24 AM.
Dec 29, 2013, 07:24 AM
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Ailerons & servos


The ailerons are well designed, made and installed. The control horn, quite a typical method, was well done too.
It seems made to have two aileron servos, and that suits me as I want to have individual control over them both!
9g servos - and even the 13.5g ones I used - 'fell' right into the existing aileron servo slots, so I am not sure how they intend people to mount them. But I made some plates for them. The wing cutouts - into the inner wing rib - suited this perfectly.

I used 13.5g MG Digital servos. (HK15178B)

The final setup was excellent and worked perfectly....

While I was at it, I added a pair of 3mm 'dowels into the wing rib as extra 'locators' for joining the two wing halves. The main spar does this in 'one dimension' so it needed a few more 'keys' added.

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Dec 29, 2013, 07:31 AM
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Battery area


The battery area is very much, again, like they do for balsa-ply models of this type. And that is pretty useless really!!!

I added a LONG battery 'floor' from 2.5mm Balsa-ply sheet. Then some balsa wood sides to that. And a LONG velcro floor strip.
This allows a HUGE range of batteries to be used and adjusted for CofG by placing them as required.

There was GREAT difficulty in getting a battery INTO the "tube", because it goes under the fuselage front area and then into the cowl - a LONG way in total. So I had to cut out the tops of a pair of cross brace formers, so you have much better access to that battery placement.
Again, it all turned out really well..... versus the totally USELESS way it would be otherwise!

I can use:
3S 2200mAH 30C
3S 2650mAH 20C
4S 2650mAH 25C
4S 3000mAH 30C
And balance for correct CofG easily for any of those.

...
Dec 29, 2013, 07:37 AM
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Wings


A hefty alloy spar!
They are strong wings, with great full length ailerons.
Really, the whole plane has excellent 'parts' and how they operate perfectly too!

The way the wing keys into the front fuselage and then is bolted on - very typical to many models really - works great. This means you can transport it as a two-piece wing with no compromises in strength and reliability! (though I will almost certainly transport it intact always anyway).

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Dec 29, 2013, 07:46 AM
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Landing gear


The kit comes with some fixed landing gear mounted into wooden blocks. Those can be screwed in to the wing mounts which are also made to take servoless retracts.
Huh? A PT-19 didn't have retractable landing gear.... but maybe you would want it to! LOL
The wing has pre-cut-out bays for the retracted landing gear, and they give you extra legs to use for that - except they are TOO LONG to work there! No matter... I will not use them anyway. And if I did, I would add Oleos on them anyway.

Speaking if Oleos.... I want to change the "wire legs with spring loops" into Oleo legs anyway! This is because the wings are strong and rigid, and the mounting system they made is NOT that great. Any harsh landing could very well rip them out of the wing, and a balsa/covered wing will NOT like that at all !! So if you can give it some help to get less shock - via oleos - then it will at least HELP reduce damage cases.

I will maiden it with the wire legs, and need to work out what oleos to use for it.

I changed the wheels/tires to DuBro clones.... a bit bigger diameter and nicer looking.

The landing gear leg Covers need to be affixed somehow, so I epoxied them onto the wire legs... I am not sure how long that will last, but it seemed ok.

...
Dec 31, 2013, 06:48 PM
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Maiden flight report


I chose the set a CoG right at the rear screws of the landing gear blocks. Even that seemed excessively rearwards in terms of the wing chord position, but it would need that to not nose over on take-offs.

I had used a 1000kv motor with the aim to run on 3S, but with a 10x7 prop it was only 250 Watts on 3S !! The thrust felt like it might be JUST enough to fly it, but there would be little (or no) leeway for getting out of trouble!
I did have some 11x8, 11x10 props, and I think 11" would still look fine, but instead I ran 4S on the 10x7 just to be sure of adequate power.
500W to 600W on 4S !!! WAY overkill..... LOL. I would just use 1/3 to 1/2 throttle range! hehe

So off to the airfield it was.....
For some first flights with other aircraft it was quite calm, but by the time I got the PT-19 out it decided to get windy and a bit blustery. Seeing I had it out and ready I decided to press on with the maiden....

The first flight I balanced it (CoG) as per aimed for. It rolled out with a fractional struggle not to nose over but was pretty good all in all.
It was VERY sensitive in Roll and in Pitch!! And I had forgotten to set up Dual Rates and Expo....

I would say it was a bit tail heavy. But the Roll axis instability was large! Very annoying. Whether a Roll move was instigated by Aileron control, or wind, it would 'flick' sharply - it seems like it has no Roll inertia, thus can change Roll angle in a blink!
The Pitch sensitivity was possibly excessive Elevator throw, and/or CofG too rearwards. But the CofG did seem ok to me.

All in all it was TERRIBLE to fly!! The worst plane I have!
MAYBE it can be set up better, but it doesn't seem likely. It just seems like a plane someone made from original full scale planes, which then ended up it doesn't fly well at all as a model.

Power off for landing had it come in beautifully into the headwind. Probably as the 'very shiny' covering finish is so slick and LOW drag. I was expecting a hairy landing process, but it actually was perfectly behaved through that sequence.

Seeing it flew so terribly I was not going to fly it again, but I think the great landing sequence sucked me in.....
I set up some Dual Rates and Expo.... and also set the next battery to move the CoG forwards more... about 5mm or so. As it turned out this made it nose-over almost every attempt to get it rolling for take-off!! So that is no good.
In the air it flew a BIT better.... less Pitch sensitive and tracked better longitudally... except that Roll axis sensitivity was still too crazy! So I think that is here to stay! A resultant of some aerodynamic / physics reason.

The landing sequence was ok again, but it was hairier than the first with the wind flicking it around more this time. And that made for a landing onto one wheel more than the other, and enough shock from it to break that right hand landing gear mount!! I knew this landing gear design was going to be sub-standard and likely to be damaged with any slightest poor landing! BAH.

So all in all I did not like the PT-19 AT ALL !!!!
I don't even really like the looks, because it is 'slab sided' and missing all the true shapes of the real one - so FOAM RULES!!
I will never buy another Ply-Balsa plane again!!! For sure!
And everything added up, I give it a lowly Rating of 2/10 !!

(videos soon)
Last edited by PeterVRC; Jan 05, 2014 at 05:52 PM.
Jan 05, 2014, 06:14 PM
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"waggle" !!!!!


On the Sunday "Dawn patrol" Flying outing I got to fly the PT-19 in close to dead calm wind conditions. Even though it is not a great plane to fly, I really wanted to see to fly in dead calm, as a source of more information on how it behaves when "left alone" to just flying itself, not wind blown etc.

As per all aircraft anyway, it did fly nicer in the dead calm.
BUT..... an issue stood out very clear....
It WAGGLES along - exactly like the Sea Vixen's waggle!!

I think this ties into (onto ) the roll axis instability.... either as a spin-off, or addition, or a cause of it. For eg, "Waggle" is a Dutch Roll, which means the plane YAWS a bit, which then makes one wing advance more and thus effectively moving faster into the airflow than the other, which then makes that wing have more lift and rise.... so the other wing drops (thus the possible tie in with roll instability). When the faster wing lifts, it loses speed and the plane Yaws back the other way, so the cycle begins to the other side.
Thus you get a plane that is yawing back and forth as it flies along, with the associated wing rising, then falling as it goes along also.

In the dead calm t flew along much nicer - seeing there was no wind to 'blow it over' into excessive Roll on banks for turns. So basically it is an unstable plane, which can fly better when it is with less external wind detriment.

I don't know what aspect of a plane's aerodynamics make one plane Dutch Roll and another not.....
I have never seen a clear cut engineering explanation - except to some degree for high wing sweep aircraft cases, which so show how such a wing leading edge shape can create the process.
But the PT-19 is more of a straight wing... sedate trainer... design. Not a high wing sweep Sea Vixen type wing!

But that is what it does.... so I need to work out how to FIX... improve.... or totally remove it.

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Jan 05, 2014, 06:36 PM
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Flaps - splitting off the full length Ailerons


Waggle Fix - Idea 1: Washout.
The ply/balsa wing of the PT-19 has no... or VERY LITTLE... washout. Could this be its shortfall?
There is no way to add washout to the wing now.
A very rough, poor, Washout 'fix' is to use a slight Reflex on the Ailerons - upwards... like Spoilerons. Except this PT-19 has FULL length Ailerons, and that means "Spoilerons" would NOT add an effective washout because the whole wing gets that reflex, not just the outer wing regions.

I split the Ailerons into Flaps & Ailerons, at a position I thought looked appropriate. The Flaps would run the same as per the Ailerons originally had run, so that was almost done and ready.
With only three hinges on the full length Ailerons that meant the Flap portion needed re-hinging. I cut off the mylar hinge it had and used Robart style pinned hinges for the Flaps (2 for each Flap)

I had already pre-thought the Aileron design layout before starting this of course! The outboard Aileron servos would go into the 'open' areas of the wing that had Monokote covering. This meant making a 'platform' inside that wing panel area to mount the servo onto.
Seeing it is a 'big box' area it meant there was a lot of room, so I may as well make a servo 'holding' structure that the servo could be held down into, rather than any gluing to hold it (like mainly done for foam wing cases).

I made a 'platform' for the servo to lie on, then a frame around it to lock it to a position. A Cover would clamp the servo down to the platform.....
I used servo extension leads to run all the way from the servo position to the wing root. Most often I would cut and solder extensions, but seeing it was a removable servo setup I decided to use a plain extension so the servo could be unplugged easily then too.

So that was that..... now a PT-19 with Flaps and Ailerons!!
Which will alllow a 'psuedo Washout' setup, by giving the Ailerons a bit of upwards angle in their 'neutral' state. Plus I can try Downwards offset if I want also.

Flaps can't hurt either!!
And because they are driven by internal servos and internal linkages, you could just 'never use them' if you wanted to remain true to scale of a PT-19! They would then be just fixed inboard wing sections anyway.

....
Last edited by PeterVRC; Jan 05, 2014 at 06:56 PM.
Jan 05, 2014, 06:51 PM
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Tailplane Incidence problem


Whatever CofG/balance totals I came up with, the plane flew along nice and level with no Elevator trim offset. It also flew along fine... no 'tail dragging' or anything. So this would SEEM to mean everything is set up optimally and best.

But on the Take-off Roll Out... trundling down the runway with the tail lifted at speed.... it runs NOSE DOWN!! By a clear and notable amount!!

When you look at the Tailplane incidence you can see it is 'tilted up' at the front end... Positive incidence. A Tailplane wants to travel 'horizontal' - level to the airflow - and to achieve that it will Pitch the plane until it does. So Positive incidence will make the nose pitch DOWN.
The problem with that is it will run down the runway nose down too!!

I am not sure what to make of this....
It flies level and great in the air! (In terms of perfect level flight). So in this aspect it is all set up perfect really.
Dead level Elevator to Tailplane, and it flies along dead level and optimal efficiency as it should.

The only real way to 'fix' this it to change the runway behaviour, and NOT the flight behaviour... NOT via any permanent change! Seeing its basic layout is great for FLIGHT anyway!

The only idea I have for now is to use some UP elevator during the take-off run, which will keep the tail DOWN more.
For tail draggers you DO start with full up Elevator anyway, to intentionally keep the tail on the ground initially. Then releasing back to neutral as it builds speed up.
Basically this will need you to NOT release ALL of that Up Elevator, and keep some small amount fed in all the way. And getting that all exactly right is not an easy task!!

It really needs to have a "Take-off mode" switch, where you have Mixed in a small amount of Up Elevator just while you have that mode active. This is because, like a fixed Tailplane Incidence, it is NOT a pilot controlled function - so the pilot can not get it 'wrong'. If it is variable - used by Elevator Stick - the pilot will have a very hard time getting the amount RIGHT.
A "Take-Off Mode" mix is also not perfect, because as the plane flies faster its effect will get stronger. So the plane will Pitch Up more and more as it gains more speed.
But I think if you set a 'good and right' amount it will fix the runway run portion - keeping the fuselage level as it runs along - and then that slight Up Trim offset will become an "Automatic climb rate" function/spin-off also!!
Then you switch out of that mode as it climbs away..... or after it reaches your desired level flight altitude.

I will do some test setups for that....

Hopefully I can FIX all the issues this plane has (Dutch Roll etc) and turn it into a great plane!!
After the CALM weather flying, I decided to upgrade the plane's total rating to 4/10 !! It is possibly even 6/10 really, but I will do a few more tests and think about that....
Jan 09, 2014, 01:02 AM
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Dead calm morning test flights


A PERFECT dead calm, crisp sunny morning today!! (7am). So I got a chance to test the PT-19 out with its new flaps.

Just before flying it I realised the AIM of the Flaps mod was really to have separated AILERONS, to allow SPOILERONS to be use to add a form of WASHOUT to the wing - and I had not even made up a Mix/Switch/Pot for that!! DOH!
Whilst beginning to look into that (TX programming) I noted one Flap was not returning to dead neutral, so I had to do some adjusting of things, which I could not get perfect (easily) so I just gave up ALL programming ideas and just flew it as it was! LOL

If flew BEAUTIFULLY!!! I almost didn't believe it. But all models love Dead Calm conditions, and that was why it got to fly in its best manner. And ZERO Waggle.... which probably more shows the WIND is a big input into that, rather than the Washout.
I thought that also MAYBE the Ailerons being more 'normal' and only outboard, instead of Full Span, could play a part in it all too.... ???

I had mixed is a very small amount of Down Elevator with the Flaps, and that was a bit too much. I adjusted it for the second flight and that was dead right then! Dead right to fly Level.... but then I had a thought.....
If you only use Flaps to LAND..... and really should only deploy them when on an approach path..... why not have the Down Elevator Mix GREATER than required for level flight anyway? To enforce an 'automatic' glide slope.
So then I thought.... why not have another Flap 'stage', so that Full Flaps has the Down Elevator mix for level flight, and one more stage is Full Flaps with MORE Down Elevator mix, to create that descent path. And that might be with a Pot 'adjuster' so you can alter that glide slope to suit wind levels etc. And also, the pot is only active on Flap Stage 3... NOT in normal flight.
I will set that up.....

Anyway..... it flew great!!
I was flying at about 30% throttle, for a good scale pace... but even 20% was possibly a more perfect scale pace. The Power available on the 4S 1000lv 10x7 is way too much. Soon I will have a bunch of 10x4 and 10x5 to try, so that will bring the RPM and Throttle Stick position up to more correct levels.

5min 30secs till Landing Warning (thus 6mins by landed) and the 4S 2200mAH was as cool as when I got it out of the car. Obviously nowhere near depleted, and had not been stressed at all through the flight. Only using 30% throttle.... so maybe it could be pushed out to do 7 or 8 mins as a maximum?
One thing this made me think about is that MAYBE the 10x7 and low Throttle position IS in a very efficient power area anyway!? But changing props to see will tell that.....

CARE when landing!! With the very fragile landing gear mount system, you need to GREASE it in every landing! On a dead calm day that is very easy!
The Flaps must have slowed it down a bit, but it didn't feel like it. Though the Maiden day (2 flights) it was windy, and thus landing into that wind might have produced the same speed as it did today in dead calm - thus it was FLYING in slower today really.
Whatever it was, it landed beautifully too.... looking very accurate to scale speed and process.

So all in all, it is either better all round 'permanently', due to the Aileron/Flap mod.... or just thanks to dead calm conditions. I decided that it flew so nice I upgraded the Rating to 7/10 !!!
This could be a "Special 7/10" if it was the mods NEEDED to have this situation. That would mean if you wanted 7/10 result, you would have to do most of the things I have done to it. Which are a bit of time and effort... but that is what model aircraft are about!! hehe. If you want truly GOOD models, you pretty must HAVE to mod and improve them.
Though not much fun having a lemon and having to make a gem out of it yourself!
I will see what I think on the next windy flights!! Probably this evening....

.....
720p 808#16 video.... lousy compared to Mobius 1080p!!
.....

PT-19 1200mm Balsa-Ply - Calm morning (7 min 20 sec)
Mar 10, 2014, 06:40 PM
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A terrible plane??


Did I mention that this is a pretty lousy plane all in all??? LOL

Out for some flights (or intended flight..S ) this morning and off it trundled on its slow long take-off run.... Nose DOWN about 20 degrees! A very notable amount!
I guess it must be tailplane incidence created - as I mentioned once before.

It flew so-so in the LIGHT breeze. Waggling along.... terrible through turns... and I decided it MIGHT be related to the dead flat wing bottom. (And/or the lack of washout).
So it was a pretty lousy flight.....

For the next coming flight, the first aim was to test "Take-off Flaps" to see what that did to the nuisance Nose Down run-out it has.
I used about 15 deg of Flap.....

PERFECT!!! As it ran out it was dead level!! No Nose Down!
So for that short lived time frame I was happy with the "Fix" for that problem. BUT in flight, it also flies a bit tail DOWN, so that was making me ponder over a total proper fix - if one is even possible.

So it runs along the "runway" nicely, but at the very low power level I use to make sure it does take time to get airborne, it wasn't happy when the extra lift of the Flaps - AND a small gust of angled cross wind - made it leap into the air suddenly, at only maybe 25deg incline..... but it was travelling WAY too slow to be able to do that, and of course tip stalled in that split second instant!!
All I saw was "Yikes, it has leapt into a climb, and is now falling to a side!" before I could even do anything, or think of what to do..

Balsa framed aircraft do NOT like to cart-wheel.....!!!!!

It is quite a heavy plane, and the force on the prop/motor, then motor mount, then fibreglass nose, meant it tore the motor out - which then fractured the fibreglass cowling!! DOH!!!
A MAJOR issue.... for a "simple" incident....
Did I mention I will never buy a balsa-ply aircraft ever again!! hehe
FOAM sure beats balsa/fibreglass !!
Mind you, you CAN break a plastic cowling too... but they are easier to fix, and cheaper to get a new one - this PT-19 won't even have spares, and I would not waste one cent on a spare part anyway!!

AMAZINGLY.... both landing gear survived fully intact! Even though they are the 'glass jaw' of the plane! LOL
Last edited by PeterVRC; Mar 10, 2014 at 06:49 PM.


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