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Dec 13, 2015, 07:07 PM
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Build Log

Pilatus PC-9 - 1200mm by Unique Models

AU$118 delivered on the HobbyKing Sale, so I decided to get one. I can;t even drive to any hobby shop and get a plane like this for under AU$230 (eg Dynam), so it is basically less then half price and 'zero effort' to order and get! (no driving anywhere!)

It looks great in pics!
Many reviews on it are good - though also some issues with the retracts are mentioned.
But at AU$118 even then it can't be a 'loss'.... can it ????

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Dec 13, 2015, 10:07 PM
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First assessment

I was not overly happy with the PC-9 after assessing it.... ignoring the price it cost.
For a "AU$250+" plane, it is "older generation" design. A lot like a Dynam 1200mm plane, but even a bit worse.

1) Custom 'how they were done back then' retracts - which use a controller unit to drive them all.
If things fail then you will have trouble getting parts to fix those!

2) "Budget" everything - bar the finish is very good. eg minimal foam, no real wing spar.

But anyway, it is not a 'bad' plane, just an older generation minimalist plane. Probably a fraction under a Dynam in value, and they cost AU$230 currently. So I would not want to be paying the full AU$280 (and then add shipping of $30) that this plane normally costs.

Then allowing for price.... AU$118 to the door.... it is GREAT value! LOL
Dec 13, 2015, 10:11 PM
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Starting assembly

I wanted to keep the PC-9 as close to stock as possible.... but that is never quite possible, if you want a truly airworthy model!

I joined the wings, and they have just two very thin (3mm??) fiberglass rods that you run across the join to make that stronger. They are not really 'Spars', more just 'joiners'.
I think there MIGHT be some spars out in the wings, but the wings do flex easily and a lot so maybe there are none at all really!
So high G's could be a problem for this plane!

I then painted all parts in WBPU before assembly, so that you can cover all areas fully - but not joint areas of course!

Last edited by PeterVRC; Dec 16, 2015 at 07:32 AM.
Dec 13, 2015, 10:17 PM
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Battery tray

I put in the RX where I wanted to have that, and then investigated the battery area.

Molded 'narrow' to hold a 3S 2200mAH battery as per the original version was designed for, all that foam needs to be hacked out to make more room.
Another known issue is even balancing the plane, and most people advised how they needed to put the battery right to the rear end of the foam area just to get it to balance. So I made up a Bass-Balsa Plywood battery tray and added that. With the usual Velcro 'floor' and then added some battery straps.

Unfortunately even with the battery as far back as it can go the plane was still MILES out of balance - Nose Heavy!!!
It does have a long nose, and thus the motor is way out front.... whilst the battery is only over the CofG point, or a little bit after that. Thus it can't help offset the motor and ESC anywhere near enough.

I was puzzled how ANYONE could say they put the battery more rearwards to balance it out.... it is just not physically possible! And they often use 4S 2200mAH, and I had 4S 2700mAh and 4S 3300mAh, which neither is still anywhere near balancing it out!

The only way to cure this issue is to add some tail end dead weight!

Last edited by PeterVRC; Dec 16, 2015 at 07:33 AM.
Dec 13, 2015, 10:23 PM
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Electric hatch....

The PC-9 has an 'electric hatch' which makes the canopy/cockpit/hatch section lift off to one side, on hinges to that one side, and driven by the same device as the retracts.
It only opens the hatch to about 30 deg or so.... what a dumb idea....

You can barely get into the hatch area with it only open that much.
And lifting the whole cockpit and pilots, which such an idea has to do, just looks stupid too!

So I removed the drive mechanism, which will be useful for a spare retract mechanism now(!!). I added three magnets on the closing side, to lock the hatch down when you close it.

It didn't take too long to see that the whole idea of hinging a hatch to one side was just painful and dumb anyway! So later I removed the hinges and made it into a 'normal' format of just removing the entire hatch! With another three magnets down the other side.

The electric titling canopy MIGHT seem a cute idea, but it is just dumb really!!!

Last edited by PeterVRC; Dec 16, 2015 at 07:35 AM.
Dec 13, 2015, 10:35 PM
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Tail weight required to balance CofG

The manual does not even list any CofG.
Various people suggest various CofG positions....

Assessing the wing/planform, it seems to me that approx 60mm would be where it should be. Though a number of people suggest 50mm. So all in all I would think somewhere from 50mm to 60mm would be right - flight testing can work it out properly later.
Erring towards 50mm is safer!!

To balance out at 50mm, with the 4S 2700mAH battery - which is the smallest I will use, and thus you need to account for what the 'least help' battery weight would result in - it needs 80g on the tailplane!!

I found a 1/2" bolt and cut it down in length to be 80g and drilled a hole for it into the fuselage underside at the rear end. Then pushed it into that hole - which is a tight fit and no glue at all will be needed!

Now I can balance anywhere back to about 65mm, and a lot more forwards! eg 40mm even. So now it has great CofG range flexibility!!

Dec 14, 2015, 06:19 PM
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Maiden flight done

I was VERY surprised by this PC-9 by its flight! It was fantastic!

I used 55mm as the CofG - seeing I think 60mm will be about right but it is safer to err towards nose heavier first!
I did not get to test for the CofG 'accuracy' in flight, but it flew great at 55mm for a start. eg It can still be 5mm either way to be optimal, or maybe 55mm is it. That needs specific testing to find out/verify.

What a GREAT plane it is, as it turns out!
Not because of Unique Models themselves - although a model manufacturer can ruin a good plane, or make it at least the best it could be - but because the Pilatus PC-9 design and planform makes for a fantastic aeroplane!
By its design, layout, planform, as chosen by PILATUS, it is just an awesome airframe / aeroplane!

It is extremely sleek - extremely low drag. So that means it is extremely frugal on energy required to make it fly along - just 10Amps flies it quite fast! Versus typical 1200mm aircraft need more like 17Amps to 22Amps regions to fly at the same scale-like speed. (all on 4S)

It rolls very clean and axially - which even with its low wing that does not 'bother' that. I suspect the dihedral brings the end result into a good alignment for the axial roll.

The dihedral also makes it very stable - yet it remains highly aerobatic too!

It is just a great design!

Unfortunately the UM Retracts are not that great.... seeing I have had issues with the nose gear extending since the start.
The retracts jams when "in", seemingly because they over-drive the mechanism and only stop the drive when they sense the current reaches X amount. By then the retract is jammed hard to that end and then cannot reverse when it wants to extend again, because the current required to even try to get it started means it trips out and stops right away!

It does that if the retract is screwed in, but not if it is totally out of the nose.... except, even if the screws are undone and totally sloppy and loose, but you leave the retract in the foam, it still can't move to extend. It has to be out of the channel.
I think there just a bit of 'squeezing' pressure - it hardly feels there is any really - and that narrows the housing that micron, and thus the worm drive block is driven hard into the narrowed end area.
So maybe cutting some foam will resolve it, or even a bit of oil (also) to help it all slide freer.

So of course, after doing other things that seemed to fix this issue when at home, and testing that it was totally reliable every use, when it was FLOWN it did not work....

When I came around to land the nose gear did not go down, so I had to land and try to have the most flare/nose-lift possible after the main wheels touched down. I actually did not even look/notice that the nose leg was not down until the last 2 metres in altitude approx! lol.

But nothing broke... not the prop... and not the nose gear door, seeing the prop took all the nose weight. I guess I was lucky that it was a slow enough speed when the nose/prop came down to hit the grass!

I could not fix it and get it working on site so that was it.. one flight.....

Oh, and the 'extremely sleek' aspect meant it was a quite fast landing approach!
You can set up a plane's flying state to be more nose up and descend slower then, but that is quite difficult and fraught with dangers of stalling if your calculation, or wind, make it amiss. A nose down approach is always much safer and can never stall! But in a slick aircraft, such as a jet, or this PC-9, that means it GAINS speed on descent!
If an aircraft has Flaps then it can slow down even on a safe nose down descent - which is why pretty well all full scale aircraft do have Flaps!
Thus this PC-9 would really benefit a LOT from having Flaps added to it!! So I will do that.

I can fly my 2.65Kg AUW Sea Fury (PC-9 is 2.1Kg AUW) in at 5deg slide slope nose down, and it is SLOWING DOWN under Full Flaps. The PC-9 is gaining speed instead! Both using zero throttle for decent seeing Potential Energy from altitude provides more than enough energy to fly down the glide-slope perfectly.

So anyway, some Flaps would help a LOT!!
Dec 20, 2015, 01:42 AM
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Maiden Flight Video

Pilatus PC-9 - 1200mm by UniqueModels - Maiden Flight (6 min 51 sec)
Dec 20, 2015, 01:44 AM
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Pilatus PC-9 - Flight 2 Video

I have 5 flights so far. This was Flight 2.

Pilatus PC-9 - 1200mm by UniqueModels - Flight 2 (13 min 44 sec)
Dec 26, 2015, 06:56 AM
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Extended hatch and lock setup

Hmmm, it seems my mod to have a hatch/canopy held on only by magnets has a slight flaw..... even with SIX magnets!

I was flying the PC-9 around and I heard a strange noise....
It sounded somewhat like the plastic strips you would use in bicycle wheels to make noise! It also varied according to 'something'.. the Angle of Attack it seemed. So I decided it was more likely to be something plastic that was 'vibrating.... or, something else, who knows what.

I landed and checked everything and all was fine. No noise when powering up to WOT on the ground. Hmmm, it was something affected by airflow....

The next flight, as I did a Roll the Canopy flew off....
Ahhh, that is what the noise was - the leading edge of the canopy is not 'bordered' and just sits against the forward upper fuselage. This meant it could LIFT a bit, and vibrate in the airflow then! And this time the whole hatch came off was because it got too much airflow under the canopy lip, and pressurised the inside - which then could beat the force of six magnets!

I decided this was an unacceptable situation, and the best fix was to make that canopy front edge fixed to the plane. To do that I needed to cut out some of the upper fuselage, to join to the hatch portion, so that the canopy DID have one solid base right to its front edge at least!

I probably could have done ONLY that, and it would probably survive fine and not come off - but that was not assured! What about HIGH G's!!?? An outside loop....
Thus I added a tongue to the front end, and added a Slide Catch Mechanism to the rear end. So now it IS locked down solidly... FOR SURE... at all times!

Dec 28, 2015, 06:48 AM
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When I assembled the PC-9 there was no way I was going to fit the ridiculously large exhausts they give with it! They are WAY over-size, plus silver (which you could paint easily anyway).

It took quite a while to decide on how to replace them, and in the end I made up scale 3D drawings to match the PC-9 size and then made new exhausts from balsa wood 'block' (pieces layered together).
These are a LOT smaller than the originals.

But, oddly, even though they were from scale blueprint drawings they still do not really look the same as all the pictures of PC-9's I have! Though I have seen there are a number of variants on the many PC-9's around the world. Just none that match the blueprint ones!
Though they are close enough anyway.
I should have sanded them down a bit 'lower', once I checked against those other pictures....
I do still need to finish their paintwork, to be shinier and with a touch of 'brown rust', so I might thin them down a bit before doing that.

Dec 30, 2015, 03:10 AM
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Nose gear repair (and main gear)

When I pulled out the Nose Retract I found that the Trunion Pin had moved a fair way across and out of the Retract Casing! The pin in just an interference fit into the plastic casing and that is not enough to stop it working its way 'sideways', and in my case it had come completely out of one side's hole, and thus the Trunion had no support on that side so it ended up all loose and sloppy!

It is easy to push the pin back across, but how long is that going to last!!?? Not long!
After a bit of thought about it I decided to make some very small alloy plates to cover the pins and thus prevent them from being able to move out of the casing! The plates are held on by small self tapper screws.

One main gear was a bit sloppy too, so I got that out and found those retracts use a much longer Trunion Pin - not just the equal width of the Retract Casing, but something like 4mm sticking out each side of the casing! Weird! Why?
On the sloppy Retract side the pin was still in the casing on both sides, but almost across enough to not be in that side anymore. eg The other side had 8mm sticking out, and not much left in the Trunion Casing Hole on the other side!

The pin was a reasonable resistance so for this Main Gear one I just centred it again. I though about roughening it up and then putting a bit of CA onto it, which I should have(!!), but I decided not to - but after I reassembled all the Landing Gear I decided I should have CA'ed that! BAH. Next time I will.... because it is very likely to work its way across again!

The next issue I found was at the Nose Gear again....
The Retract rests on some foam, and is bolted against a plywood plate inside the upper nose area. If you do that (as they did) then the clamping of the bolts means the FOAM will be crushed sooner or later! And in my case that had happened - it crushed more to the rear, so the whole retract tilted into the plane more at the rear end.

To cure that problem you really want a plywood plate for the retract on that LOWER fuselage side also. To spread the load across a much larger area of foam - seeing foam is WEAK!
The easiest fix, that should still work ok, was to add a 1.2mm basswood ply plate under the Retract. To also bridge a bit of the Upper fuselage plate to this new lower plate, I added a small balsawood block into a recess that is at the rear end of the Retract area.
I Epoxied this lower plate in, as Epoxy is good to give a solid base to that too.

Hopefully now the nose Gear will be far more resilient!!!


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