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Old Oct 18, 2012, 07:37 AM
looking up down under
scruffy1's Avatar
Australia, NSW, Fairlight
Joined Feb 2008
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pitts epp from hobbyking

fresh from my blog over here, a cut 'n' pasta to commence a discussion somewhere more public

i wondered if this belonged in 3d foamies , but here's where i lobbed it

ah, hobbyking, you've done it again

i killed my spitfire it has a fierce tip stall just like the big one... or more correctly it had one, and too low for me to save it, as i was distracted fiddling with the trim at rather slow speed

still, i did get the opportunity to extract the servos and esc, and that's all that was needed for the pitts epp

so, while i am close to finishing the durafly slick 360 v2 and only need to mount the hardware and hook up the controls in my cuckoo, i have started another plane

i guess i always enjoyed building rather than flying, and foam is ridiculously easy to start

so, presently i am agonising over substituting carbon fibre spars in place of the supplied fibreglass rods, and i have already added carbon fibre tissue with finish-cure epoxy to the struts because i am learning the technique and it weighs ziltch for the strength it gives

i have also dragged out a really ancient hitec hs100 for the paired ailerons; it was my most micro servo way back when i scratch built a thermal glider last century; at 25gm it is a monster compared to my current (largest) 9gm from the spitfire

i've taken some education from here and a huge dose of inspiration from this video

Pitts-EPP from Hobbyking 1/2 (6 min 39 sec)


anyways, there are 3 x 1300mah batteries here without any other appropriate plane now, and i am eyeing off the belated spittie's plastic battery cage and rear wheel steering mount too

pictures as i progess to follow, but here's a teaser of the contents of the well packed (double boxed) contents for starters
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Old Oct 19, 2012, 12:32 AM
looking up down under
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Australia, NSW, Fairlight
Joined Feb 2008
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the carbon fibre "tissue" did a good job on the struts and fuselage upright - as shown in the attached pic #7

i used the master airscrew balsa stripper to great effect for cutting the slots as required in the fuselage; the instructions specify one only, but i spared no expense and put one on each side, only after gluing them with cyanoacrylate and kicker did i realise one side got carbon fibre, but as it ended up really stiff all is good

the method i devised worked really well - i pressed down a small phillips head screwdriver and pulled towards me with the rod held within the X while opening the slot on one side with simple traction near the cut - popped straight in and any "curl" under was easily teased out with a #11 blade or traction on the trapped side of the cut

dunno if that's standard way to do it, but it will be my method in such situations

the screwdriver incidentally also came with the spitfire i crashed - so the instructions for the pitts should have as a prologue - "buy the hobbyking spitfire and then crash it to obtain the necessary parts and equipment to complete the pitts"

cyano and kicker for the motor mount which was previously glued with titebond and clamped, and then filled for support with a mix of 5 minute epoxy and microballoons, to seal the gaps and conveniently match the colour of the fuselage

some hotglue to the wire junction on the motor, carefully avoiding gluing the motor parts because that's the bit i usually kill myself without flying being involved

i am still vacillating on the servos, but given the size of the 4 ailerons, the hitec seems a good choice for that control, despite the weight; the rudder and elevator spots pre-cut in the cockpit area fit the 9gm servos perfectly, and i can likely hide all the connections and the receiver (+/- removing the case) in a slot in the same area

the esc and battery mounts are still problematical - i have the ready-to-go spitfire 20 amp esc with the correct connectors, but the "blue" 20 amp one is smaller but lacks the proper connectors (as yet)

and last but not least, the very bright wheels supplied are okay, but i have the slightly larger 40mm ones that will suit the airfield better - no urgency on the choice, as the supplied wheel collars can work with either - not sure on the tail skid too - i have the means from the spitfire to have a small steerable tail wheel

all fun so far
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Old Oct 19, 2012, 08:04 PM
looking up down under
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Australia, NSW, Fairlight
Joined Feb 2008
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i really need to just build things to the design, but tinkering is hard to avoid once i get started

strikes me that if i have 2 aileron servos and plug them individually then with the dx8 i immediately add the possibility of adding mixed aileron "droop" as flaps for low speed, and also for coupled flaps to enhance aerobatics

this plane presents a dangerous opportunity to teach myself how to use the dx8 to greater effect than i have so far, and it's cheap enough to be a little less than devastated should i exceed airframe (or pilot) capabilities

does anyone know if the hxt500's would have enough grunt for the elevator and rudder ? because if so that would free the pair of 9g for the aileron duties

the next bit of the build will require me to make firm decisions on fitting servos

and does the blue series esc have any advantage over the other one shown ? easier to hide in the fuselage i expect

thanks for any thoughts
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Old Oct 31, 2012, 08:36 PM
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Australia, NSW, Fairlight
Joined Feb 2008
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back to business

spent some of the time working, and more of it thinking

in my usual stream of consciousness style, thoughts and suggestions for other builders

i noted that most people seem to have their servo arms out in the wind, but the situation lends itself to my arrangement where all can be hidden out of the airstream - the photos are self explanatory, but details to note are :
  • make the back (elevator) servo lower so the control rod from the rudder servo can pass unimpeded over it

  • note the orientation of the front (rudder) servo - the wire they supply will be ever so fractionally short for the task if you put it in the other way round (don't ask me when i discovered that; the scratches on the servo were from my surgical removal of the first learning experience)

  • remember to thread the pushrods through their surface control horns and their guide rods before you glue on the tail feathers (see educational point above )

  • the given pushrod connectors bind very badly if you install them per instructions - some careful reaming of the servo arm hole will allow them to be firm but rotationally mobile by simply screwing them into the hole after expanding the diameter carefully; the nuts to lock them are pointless as the rotation in use is only ~90 degrees at max

  • bury the control guides, but it helps to make the slot at the cockpit end of things a bit large and not glue it near the exit, allowing some movement to maximise available throws without binding

other things i learnt : cyano kicker is great, but the colour scheme isn't very agreeable with whatever chemical it contains, so try not to soak the decoration, as it bleaches the "paint"


off to lunch now, more later today
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Old Nov 01, 2012, 12:42 AM
looking up down under
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Australia, NSW, Fairlight
Joined Feb 2008
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back from lunch; a few more words of wisdom on my choices...

i am definitely going 2 servos for the ailerons, and will plug them to allow mixing (at a later time, once i have mastered simple full-house) this choice was somewhat influenced by finding the last of the four spitfire 9gm servos that had disappeared down the side of my desk and hidden under the scanner i have stored in a box there, so it requires no purchases, nor do i need to pilfer the big hitec servo from my old glider

current plan is to have one servo each lower wing, on the top surface, with the wiring in a groove in the wing, and then a groove up the fuselage sides to the cockpit, with a small step over the carbon rod reinforcements in the fuselage; possible rod stiffeners in the ailerons but still thinking on that

i will sand the hinges to loosen the action, but sadly was a little enthusiastic with the elevator and hence the tape reinforcement... i may add tape to the wing leading edges too, although the (also epp) bonsai does fine without

the wiring will all plug in as shown already, but i will probably gouge a slot behind the receiver to house the excess wires once the aileron leads and throttle leads need homes

i had thought of adding a secondary receiver in the gap between the pushrods behind the cockpit, but taking a hint from albert einstein, i have elected presently to "make things as simple as possible, and no simpler" - can always plug it later without needing to do any major alterations to the plan

the supplied canopy needs to be hollowed out, and it is possible i may either find a suitable plastic container to replace it with, or table saw the top centimetre or so off and add depron sheet sides leaving the hollow area for the servo and receiver; magnets at the back and front for ease of access

undercarriage - probably the bigger wheels; steerable tail wheel - uncertain

1300mah 3s placed for balance when i get that far, probably simple slot and velcro

more action as it happens, folks...
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Old Nov 07, 2012, 01:23 AM
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Australia, NSW, Fairlight
Joined Feb 2008
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a little progress

wimp that i am with cutting into foam for the servos in the wing, i decided the fuselage is good for practice

armed with trusty #11 x-acto i managed to cut a tidy hole for the esc, and then ran a groove to the cockpit, which i widened internally at the deep end to accept the throttle wires to the receiver; i also made a bevel for the motor wires so all sits nicely

i then gently glued the throttle slot closed with minimum line of cyanoacrylate and kicker - hope i don't need to rejig the connection for the esc, but i tested the 20amp esc and it stays cool at peak revs, and there's a space for a little bit of ventilation as the pic of the other side shows

per the specs it's good to go for 30amp burst so i have some leeway

now i just need to get brave with the wing excavation...
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Old Nov 07, 2012, 05:34 AM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
12,668 Posts
The landing gear slot is a weak spot, so I put 1/32 aircraft plywood triangular plates over the sides to stiffen it up. On a bit of a sideways touchdown, it will pull out of the foam. I built a Pitts for a buddy and put them on. My own Pitts is still in the box but I do the same on any fuselages of this type. This is on my 6 yr. old beat up Zoombi. Your Pitts looks great otherwise.

Gord.
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Old Nov 07, 2012, 07:03 AM
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spurred on by my gouging at foam, i reneged on my plan to modify the canopy greatly, and instead set to what they provided with the #11 and hollowed it out considerably

this unsurprisingly made it rather flimsy, so i broke out the 0.4mm ply and beefed up the edges a bit; the photos of my excavations and the reinforcements are pretty much self-explanatory

thanks for the landing gear tip fly, but the mounting on mine seems uber-tough with some effort to prove otherwise, so i'm leaving it unmolested until it proves me foolish

the canopy will need some small magnets i think... with it attached the servos and links and receiver are completely enclosed

i must say i'm getting braver with hacking into foam, which augers well for me finally braving the binary 900 build
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Old Nov 07, 2012, 07:08 PM
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Joined Feb 2008
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minor further work, but essential details

use 2 neodynium button magnets - one inset in the cockpit floor, and the other glued under the 0.4mm ply front reinforcement

2mm carbon rod with cyanoacrylate into the posterior cabin wall, after first drilling the ply reinforcement and push fitting it there to align the necessary parts, with slight upward angle to facilitate sliding it into place

locks firmly, and conceals all the radio gear completely

+1 for a tidy build, although i concede my obsessive compulsive attention to detail in a very basic foamie is excessive, but that's my nature

now for the aileron servos
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Old Nov 08, 2012, 04:46 AM
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i'm going for it !

measured out the bits to utilise the pushrods from the spitfire ailerons (so i have some adjustments for throw and fine tuning the neutral) and cut out the outlines for the servos with the master airscrew stripper to depth

hacked away and got frustrated with the angles i needed to adequately dig out the aileron servo recess, then dragged out the dremel clone and fitted what approximated a router blade, set the depth so it was pretty much at the chuck fitting, and went to town

sadly got a bit lax on the second hole after marked success on the first, but the general result was very positive

now i just need to figure out how to get a hole bored through the fuselage up into the receiver recess, but i'll sleep on that

pretty happy with the results so far - i think a dab of hot glue to hold the servos in place will be the way, although the option of using tape over the top of them has a certain appeal if i need to do any repairs is also possible - i am hoping it remains intact for the duration, or totally explodes if there is a major prang, as repairs aren't going to be easy given my approach to burying / channelling things
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Old Nov 08, 2012, 11:18 PM
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Australia, NSW, Fairlight
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further work for the day

i hot glued the servos in place, and then cursed because i thought the port one wasn't centred, but realised that the splines on the mount mean one side is always just not quite where it looks like it should be - i'll fix that with the trim

set to the fuselage to create the aileron wire conduit with the dremel and a simple 1/8" drill, but trying to hold it steady against the edges of the hole to enlarge it was difficult, so after making a vague pilot hole i ditched the power tools

thereafter i hand drilled it further with a large drill bit, and then gave it a ream with the knife sharpener, and vacuumed out the debris, then tried a small rasp on it but the end results were rough as guts - luckily all invisible, and the hole was sufficient for the job

i will need to create a pit behind the receiver to bundle all the excess wires into, but everything should fit under the canopy without cramping the servos; the aileron wires have a groove behind the receiver pit to keep them from being stressed by the receiver

the photos show the current state of play; the wing isn't glued in yet, as i intend to epoxy the struts square and true in the lower wing and attach the baldechin likewise to the top wing as guides for the final fit out before i glue the bottom wing and then fit the top one

pity the tiny but long bolts i need to mount the 1/4a aileron horns through the depth of foam haven't arrived, or i might have got it finished tomorrow


ah well, progress is happening
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Old Nov 09, 2012, 02:34 PM
Registered User
Australia, QLD, Mountain Creek
Joined May 2012
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Dont stop now Scruffy, my kit arrived Tuesday and you have already sorted out a few questions for me. Looks like a wet weekend here so its a race to the finish
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Old Nov 09, 2012, 05:36 PM
looking up down under
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Australia, NSW, Fairlight
Joined Feb 2008
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hi xmod

here's a little more inspiration for you then

all you need is a spirit based marker pen (i used one of the japanese copic markers from my daughter's huge collection - yellow ochre yr23), a pilot cd/dvd marker, and some adhesive label paper

the same paper i used also inside the canopy to reinforce the rather delicate thinness of the foam - much stronger and won't easily gouge with the servo stuff when fitting it

once again, spitfire remains to the fore; the wheels are from the spittie too, and a much better size for the grass at the field, plus they fit the axle length perfectly

the tail wheel i think will get dropped as an idea; i have a perfect plastic skid that looks way more appropriate than the f'ugly half moon ply thing they supplied, and i can always retro-fit a tail wheel if i get the urge later

i'm off to try the local hobby store for the 1/4a bolts (slim chance), so maybe i can beat you to the finish

the photos are self explanatory
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Old Nov 09, 2012, 06:06 PM
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What an attention to detail!

I wonder how it would fly with only the lower wing attached.
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Old Nov 09, 2012, 06:15 PM
looking up down under
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Australia, NSW, Fairlight
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Quote:
Originally Posted by Commander Clumsy View Post
What an attention to detail!

I wonder how it would fly with only the lower wing attached.
really fast, and with so much flex the wingtips would clap hands in the death dive

yeah, as for details, i suspect the reason is that i came from 4 decades of obsessive balsa building and this is my first "put the parts together" foamie, having only had the bonsai (glue on wingtips and landing skid) and spitfire (glue the tail halves together) as prior opportunity to go for foam

i am largely doing all this to improve my confidence to finally get stuck into the binary 900

and the pitts is a great choice for my trips the local park given it is small-ish, relatively slow, and less likely to kill people (and dogs) where i usually fly
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