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Mar 20, 2016, 01:21 AM
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Build Log

Pitts Model S12 Python - Dynam 1067mm (Rating 10/10 !!)

With the Demise of the PT-17 I pondered what to do about having a Biplane....
Another UniqueModels PT-17, seeing it is a beautiful and well made (almost totally) plane?
Or something else?
The Dynam Waco was the leading choice in scale terms. But I was also thinking about Aerobatics and a STRONG bi-plane to cope with those!

I went to Hobbyzone (Victoria, Australia) to look over the Dynam choices....
The Waco, The Pitts Model S12 and the Devil 3D.
I was surprised to find they use alloy and carbon fiber strut systems = GREAT! When I checked them over I found them to be very strong - exactly what I needed/wanted!
So which one to get???

The Waco looks the best. Its "1930's nostalgic look".
The Devil 3D looks a bit too 'clinical' and modern. Plus was known to be a bit more twitchy and easier to stall in aerobatics.
The Pitts Model S12 Python looked a bit 'plain' but has the best credentials for aerobatics.... and it still does look quite good too.

The Waco out of stock.... hmmm.... but I could WAIT until they arrived....
With its scale sized, smallish, Ailerons they would need to be modded to be larger so that it could do better aerobatics - not a hard thing to do at all, but it does mean more TIME to get it going.

The Pitts Model S12 is really MEANT to be an aerobatic aircraft anyway.... so the real issue was ME, and altering my mindset from wanting a scale type OLDER biplane, to a more modern scale biplane!
So I accepted that and got the Pitts!!

Last edited by PeterVRC; Apr 19, 2016 at 03:34 AM.
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Mar 20, 2016, 04:10 AM
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First look - then assembled

As mentioned, I had looked over a used/flying Pitts at Hobbyzone, so I knew quite a bit about it already.

When I unpacked it the main thing that 'annoyed' me a bit was how this and flat the tailplane and fin were. Something like 5mm thick, flat, EPO foam. And seeing they are so thin they were BENT!
I had not noted that on the built one I looked over.

The tail surfaces have fitting to run 'diagonal rods', as per quite a few aircraft types also use, and that ties all those surfaces into each other to make them far more rigid. This solves the 'weakness' that 5mm thickness creates.
I just bent the surfaces by hand - no heat - and they ended up close to dead flat again.

Pretty well everything else is quite well done just as it comes! Though there are a few mentions of issues, in the RCG thread on the plane. So there will be some things that are best to fix/improve... but not many.

I painted all the parts with WBPU right away, before assembly. Just to get the first coat on it, and on surfaces that will be 'hidden' once assembled. Then I put it all together, seeing any mods I will 'need' to do can easily be done even after assembly.

I put Blenderm tape over ALL the foam hinges, that means they will last indefinitely. You can JUST see that in one of the pics below.
Then I applied all the stick on Decals - which is a really nice set in total(!) - and then painted over the whole plane with another coat of WBPU. This extra coat really finishes it up even, plus shinier (even though I use Matt WBPU) - it looks really great once all done!

Mar 20, 2016, 04:13 AM
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Wing Struts

As mentioned, the Pitts has carbon fiver and alloys struts.
Carbon fiber on the outer struts and alloy 'frames'/struts on the fuselage ones.
Once they are assembled it forms a very strong wing fixture system and unlikely to ever be able to break in flight! (Unlike the UniqueModels PT-17 strut system!).

Mar 20, 2016, 04:22 AM
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Hatch area

The Pitts sort of has THREE internal areas.

1) Above the lower wing, which is under the cockpit. This is where Dynam seem to have aimed to have the RX placed, but it is somewhat of a useless area to put anything that you ever want to get to because once the Wings are assembled with their struts it would be very painful to ever get into that area again!
I think it is better used from ABOVE, for an FPV setup if you wanted to add that. That would need an opening cut in from above then - but that is fine to do for FPV installation!

2) Under the Top Wing where the alloy strut mount are. This area has a lower area, below the battery 'tray' height, and this is a good place to put an RX, and it also has room to have a Flight Controller in there too.
This area is meant to have its Hatch glued down! It is only a cover piece so that you can fit the struts and then close it up - but that would be a dumb thing to do really!

3) The forwards upper hatch, for the battery. This area is just right for what they intended it to be.. the battery area!
It is large enough to fit even a 3000mAH battery if you wanted to use that. Though for 3D/Aerobatics it is better to use a 2200mAH battery, or even an 1800mAH battery.
But anyway, it has plenty of room for all kinds of sizes, and to place them wherever needed to balance the CofG correctly.
The one thing I did in there was cut out a bit of all the foam 'ribs' because the width in there is only suited to the 1800/2200 battery size, so to get up to 3300mAH you need the extra width. Doing this does not weaken the plane in any way that will matter. Then I removed the stock 'thin' velcro strip and added a long and wider velcro strip so that it allows that wide range of battery positioning and sizes.

So now we have those TWO upper hatches, which are directly touching each other! So the best idea for those is NOT to glue on the second more rearwards hatch, but JOIN it onto the front hatch so that you have one long hatch!
Just clean up the EPO facing surfaces with some Isopropyl Alcohol, to remove the mold release agent, then score the faces a bit with a knife, and then a smear of Epoxy on each face and close the hatches up so they will end up joined as one!
There is no need to run and spar or rods across that joint, there is no force/pressure on them ever anyway.

Last edited by PeterVRC; May 07, 2018 at 07:50 PM.
Mar 20, 2016, 04:35 PM
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Motor mount additional plate

Pretty well ALL foam aircraft have issues with their motor mount remaining solid for the long term - or even just the short term for some models!
The forces and vibrations cause the surrounding foam to compress and then the poorly glued in motor mount - and even if it had been well glued in! - can move in the 'space' left by the compressed foam.

One way to cure this, or at least improve it a LOT, is to give it more support that uses a larger foam surface area, plus foam areas that are even further away from the main motor mount foam. In most cases the best way to achieve this is to add another plate of plywood as a 'secondary firewall', to the rear of the stock foam firewall they have created.
Another way is to add 'rails' lengthwise down the fuselage, but that is often difficult to add them in a good manner.
So I used the 'secondary firewall' method...

A 50mm x 45mm plate from 2.5mm 5 ply, epoxied onto the rear face of the foam firewall, in the battery area.
Then two 3mm bolts are run through from the main motor mount and out of that secondary firewall plate. Using lock nuts (otherwise captive nuts would do) to lock the bolt/nut setup down.

It is best to do this BEFORE the foam compressing occurs - as in, do it from new! To prevent, reduce, delay, the foam compressing from happening at all. Because once that foam compressing has occurred that foam area is wrecked and fixing it well is even harder. (but not impossible).

Why have a KNOWN issue, that WILL turn up sooner or later, just happen one day and ruin the flying day when you discover it at the field!!??
It is unlikely to cause a crash (loose motor mount) but could be discovered in flight too.

Note: One good aspect of this Dynam plane is that they used BOLTS and captive nuts in their motor mount, to attach the motor. NOT just self tappers into plastic!
You are best to smear a touch of CA onto each motor bolt and re-fit them, so that they are locked in and won't come loose ever!
DON'T use Loctite as it eats plastic and you are likely to get some on the plastic motor mount. The small drop of CA is better.

PS: The secondary firewall can be glued in with Polyurethane glue (like Gorilla etc) to toughen up the foam in that area, plus it will form a hard base for it.
I will do that in the future, if/when it ever needs more support. eg if the foam compresses eventually.

Last edited by PeterVRC; May 07, 2018 at 07:54 PM.
Mar 20, 2016, 04:41 PM
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Detrum Motor

The motor in the Pitts is quite hefty and likely to be more than adequate.
Dynam stuff... labelled "Detrum" are generally pretty good items. Motors, Servos, ESC's etc. But they are still just re-badged Chinese low cost items. They just tend to be a little bit above average compared to what quality is used in many other 'budget' brands of foam aircraft.

I tend to say, over experience with the many other Dynam aircraft I have and have seen, that Dynam are a "Budget brand" BUT whoever runs/controls the company has a Mission Statement of something like "We will make low cost, budget, aircraft but they MUST be made well, have good components, and work properly and well!!"

And that is what you can count on from Dynam! Add a bit of your own tweaking and finishing and you can move them up to being much more than just a budget aircraft!

Mar 20, 2016, 04:49 PM
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RX and Stabiliser position

As mentioned, the "second hatch" area, in the fuselage between the top struts, is a great place to fit the RX, and also a Stabiliser if you are going to use one. There is just enough room in there to do that with ease.
BUT.... getting into that area when the Top Wing is on is messy and difficult - but not impossible.

It is actually not too hard to take the Top Wing off reasonably quickly, so if you needed better access, or wanted that, you could take the Top Wing off.
I did it all with the Top Wing on, and doing that was still ok....

I am half decided over putting in an EagleTree A3 Super2 stabiliser. Mainly because they do not seem to be a very refined unit and in some planes I have had issues in their operation of SOME aspects.
I can do a lot of 3D type things without a stabiliser anyway, but it does give an ever bigger scope to do more 'perfect' manouevers in the meantime too! Versus some aspects of it (any stabiliser) makes things 'worse' too!
So I am thinking over whether I fly it first to get a base reference of the plane without it, and then add it and compare the differences.

A Stabiliser - which I should call a FLIGHT CONTROLLER instead!!! - can give you perfect knife edges.... perfect hovering.... and other things that you might not be able to get 'perfect' yourself. So it has its uses...

Mar 20, 2016, 04:53 PM
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Strut bolts

I replaced all the strut Cross Head Screws/bolts with Allen Head Bolts. Allen Heads are a MUCH more robust head that will never 'round' like a Cross head can - especially cheap Chinese screws!

I also wanted them a bit longer so that more thread comes through the bolt and that will allow putting a smear of CA onto the thread so that the nut cannot undo itself ever.
I am actually looking to get some 2mm Lock Nuts to use instead... if they exist. (eBay)

I really like the ROBUST strut system! After being burnt by the weak plastic setup of the UniqueModels PT-17. Mind you it just means that the PT-17 should ONLY ever have been flown to a sedate scale manner!! The full scale one would probably break and crash if they flew it like I had flown my PT-17!! LOL

Last edited by PeterVRC; Mar 22, 2016 at 08:03 AM.
Mar 22, 2016, 08:10 AM
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Battery velcro straps

I expoxied in some 2.5mm plywood plates to screw down the velcro battery straps onto.
The straps don't really hold down the battery totally, that is really done by the underside velcro of the battery, attaching to the floor velcro. The main function of the strap is to KEEP the battery against that velcro, and that also stops the battery being able to move laterally, or longitudinally. But it does also add some of its own help in restraining the battery in the vertical direction too.

I also made an 'arch' in the Battery Hatch Cover, where the front and rear hatches are joined together, to allow battery leads to run over the alloy Strut piece.

Mar 22, 2016, 08:15 AM
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Canopy attachment method

I wanted the Canopy to be easily removable, yet have it stay in place totally reliably. After some thinking over it, I decided to use Self Tapping Screws to attach it to the Fuselage. It only needs two strategically placed screw per side to keep it attached fully.

Mar 22, 2016, 05:19 PM
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Bit & Pieces

I put the CA smears onto all the struts bolt/nuts.
I did order 50 x 2mm lock nuts from eBay, but they will be weeks away. I will change those later.

I 'screwed in' four small self tappers, into the Top Wing underside, to mark the 85mm and 90mm CofG points on each Wing. This allows you to easily FEEL those locations, and any value nearby those (eg 82mm, 93mm etc), when balancing the plane upright.

I put silicone fuel tubing 'rings' onto all clevises.
This high-lighted, and reminded me, of some reasonably serious tail control issues the Pitts will, and must, have really!
Anyone with a truly decent 3D plane would cringe/laugh at the stock Pitts control system! It is pretty woeful really....
I will work out what to do about that soon....

Mar 22, 2016, 05:22 PM
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Tail control surfaces and drive systems

Elevator bridge, Rudder strip and plate:

When I went to install the stock Elevator and Rudder control horns I winced!! What a terrible system, prone to failure over time and not even truly adequate in the first place.
Not the just flimsy and brittle control horns themselves, but just mounting them onto 'foam'!

And the wire Elevator Bridge was a joke too!

Sure, they will 'work' as they come, but they are sub-standard and also asking for trouble to unfold one day!

Firstly I added a 3x1 Carbon Fiber strip into the lower area of the Rudder, to assure it will stay STRAIGHT at all times. Another bonus spin off from doing this is how it will allow the Rudder Control Horn to be fitted much stronger to the new Alloy 'surface' that I will make using some flat alloy plates... so as a whole the Rudder becomes a strong item, not just to have a a Control Horn on a "small rectangle area on foam"!
I got out some different, stronger control horns, and another bonus of these is that there stock holes are dead equal to the Dynam Clevis pin size! Zero freeplay now!

I made up a pair of 0.8mm Alloy plates, 25mm x 30mm, to have one one each side of the Rudder and the Control Horn bolts through those. Because these plates are over the CF strip, and also the tail wheel wire/leg, it makes a grand total very solid attachment to the Rudder, plus strengthens that Tail Wheel leg in the Rudder at that same time! (see pics)
All very easy to do, and makes a massive difference... an almost 'must have' proper Rudder setup!

The the Elevator was a similar thing. That sub-standard wire "U" Bridge! Seeing the Control Horn is on one Elevator and it then passes that drive through to the other Elevator via that wire, it allows twist down the length of the wire! That is another inadequate system!

I made up a new alloy plate "U" Bridge, of a decent surface area. This plate also runs over the stock 'strips' that are embedded in the Elevator undersides - maybe fiber glass strip? By clamping that Bridge down onto the Elevator, using plates from the other Elevator surface side also, it forms a very solid centre section and Bridge, whilst giving a very strong support structure to the narrow middle Elevator area. Plus the stock wire Bridge is still in there and now unable to twist, so it becomes a useful extra link with strength too!
It also means the Control Horn then gets screwed onto the Bridge that effectively gives you a CENTRE drive (even though it is on one Elevator side) which is then feeding equally out into each, well supported, Elevator half!

On top of that, all the tail Control Horns are all on Alloy, not flimsy foam!

It was all quite quick and easy to do, and is MASSIVELY better than the stock junk setup! I had 'imagined' its result when working it all out, but once it was done it was many times better than even hoped! In those many ways, and all so strong in the end result!

Last edited by PeterVRC; May 07, 2018 at 08:36 PM.
Mar 25, 2016, 05:44 AM
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Off to the field....

A dead calm, but grey sky, morning... so off we went with the Pitts! I was expecting/predicting a very straight-forwards maiden flight.....

I took
2x 4S 2200mAH 35C Nanotechs (238g)
2x 4S 2650mAH 35C Nanotechs (278g)
2x 4S 2700mAH 65C Nanotechs (335g)

Even with the 4S 2650mAH 35C at 278g I needed some nose weight added to balance at 85mm!! I stuck down 40g in the nose firewall area!
Then that battery came close to 85mm.... the 4S 2700g 65C was pretty much on the 85mm.... and the 4S 2200mAH was more like 90mm region.

I flew the 2650 first....
The Pitts is awesome! It flies like it is on rails, yet quite nimble with the manuals suggested surface throws - which were my LOW Rate setting (out of Triple Rates).
The Low Rate was very good for just cruising around in a docile scale manner. The first thing I thought was "This is just like flying my 1400m Piper Cub" !!! It is that docile and stable, super forgiving too.

Very soon I switched to Mid Rate so that I could throw it around a bit more... but quite soon after that I went to High Rates and pretty well never used less than that again for any further flights! (5 more).
My High Rate throws are HUGE! What you would tend to see on a fully 3D aerobatic aircraft, but it looked 'psycho' amounts!
I used 50% Expo on all surfaces for High Rate. 40% for mid Rate, and 30% for low Rate. This made ALL Rates very very easy to fly around sedately if you wanted, and then have the huge throws for sharp snappy moves too.
I will probably change the High Rate to be 60% Expo.

It is so forgiving that you can do ANYTHING you want, totally non-aerodynamic/"flight" defying, and just fly straight out of that at any time, or state, in less than a split second! It has so much lift to weight ratio, even with the 335g 2700mAh, that there is nothing that it cannot power up out of!

I would say this would be the BEST of all the MANY foam models I have!! I guess that is a resultant of Mr Pitt's great aerodynamic design mainly!
It has those shortfalls that are best fixed up/ improved.. but it would still fly the same, and fine enough, in pure stock form I am sure. Its main issues would be HOW LONG before something in the tail end fails and causes a crash - or a crash via an error in total control.
So I expect it would be 10/10 in stock form... and then move beyond and up to 11/10 or 12/10 if fully fixed up so that EVERYTHING about it is actually perfect.
I highly recommend this plane.. to ANYONE! Even a beginner could fly it really - with Low Rate dumbed down surfaces. And in aerobatic terms it does them extremely cleanly, safely, easily, and can fly out of any state of issue easily too!

(Videos need editing up)

Mar 25, 2016, 06:50 AM
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Pre-Maiden look

Pitts Model 12S "Python" - 1070mm Dynam - Maiden Flight Preview (4 min 17 sec)
Jul 02, 2016, 09:05 PM
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Lead weights to balance the Pitts

I had forgotten to post that I had to add about 60g of lead weight into the nose area to balance out the Pitts correctly. Some (or all ?) of this would be due to the the tail end strengthening mods, plus the WBPU coats because painting adds 80% of its weight aft of the CofG typically.

I used stick on lead weights, from car tire/rim use. They are nice and 'square' and tidy, plus they stick extremely well! Nice shiny new ones....


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