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Old Nov 10, 2012, 03:53 AM
looking up down under
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Australia, NSW, Fairlight
Joined Feb 2008
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no luck with the bolts, but i pressed on anyway, managing to intersperse the afternoon's entertainment with 2 separate trips to the park to fly the bonsai, plus shopping for a cook-top and oven; but i digress...

i measured up the lower wing using the centre line for reference, and made the slots for the struts symmetrical, 29cm out from the midline starting 45mm from the hinge line and extending perpendicularly forward the right distance measured against the struts - the marks provided on the wing in texta were pretty much at this spot, hence my choice to use that as a "standard"

i cut the slot again using the balsa stripper set to depth, but mostly for the square drop it creates; the width of the slot was a tight fit for the struts
you can remove the waste with a haemostat , or a very fine screwdriver - both work fine

struck me that the length of the strut peg is the same as the wing depth and i wanted in hidden, so i trimmed ~1/8" from both ends to keep it under the surface skin on the outside of both wings; that also allows it to lock on the lower wing carbon 3x1mm spar, but i neglected to put epoxy in the hole - simple cyanoacrylate and kicker using the jig as shown; in retrospect i might have put epoxy in the base before i did the c.a., but too late now

note that the struts are not rotationally symmetrical ! i chose to have the slight bevel at the top front - look at the stock you received and you'll get what i am on about

hollowed out the slot for the baldachin between the two upper wing halves, again leaving the top surface intact due to the shorter plug i had modified
the upper slots for the struts were again 29cm out perpendicular to the midline, and 35mm from the hinge line - the marks provided in texta on the kit are ~3mm inboard of the appropriate spot to keep the struts square to the lower wing - dunno if that was on purpose by the manufacturer, but i doubt it, and did my own thing

glued the top wing halves together, and still need to inset the 3x1mm carbon spar i intend to use - the baldachin will be glued square and upright (and with epoxy in the base), and then dry fitted to mark the slot on the forward fuselage accurately to cut the necessary hole

then i'll finalise gluing the bottom wing in squared and true, and use it to key in the top wing with epoxy before measuring every diagonal i can access to confirm alignment ; the strut locations and centre of rear fuselage will act as my reference points, given i know they are symmetrical

then the diagonal bracing and measuring up for fitting the 1300mah battery to balance it 10mm behind the lower wing leading edge - i can add a small bit of tail weight if i get the urge to make it twitchy

more building as it happens, but i have to do 12h hours of paid work tomorrow, so i suspect it will be wednesday when i get back to it
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Old Nov 10, 2012, 05:54 AM
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Australia, QLD, Mountain Creek
Joined May 2012
151 Posts
Scruffy, mate, the virtual blog you you have running here is invaluable. Thanks so much for the info. Helping my son buy a car today but will be following in your foamsteps ( sic) tomorrow. Thanks again.
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Old Nov 10, 2012, 03:29 PM
Proud of Brushless Sprouts
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Belgium, Flanders, Antwerp
Joined Feb 2007
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Quote:
Originally Posted by scruffy1 View Post
really fast, and with so much flex the wingtips would clap hands in the death dive
One tiny carbon rod and adding ailerons would make it an awesome low wing racer.


Quote:
Originally Posted by scruffy1 View Post
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
I know what you mean. I built several balsa planes back in the day but I was happy to switch to foam because of its resilience.
First things I learned: it's flexible so keep it flexible; you only need some carbon rods/strips to keep the fuselage and wings rigid, anything not flexible will break while crash landing.
Basically, nowadays I build them with crashing in mind, and I fly accordingly


Off to read your binary 900 thread now...
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Old Nov 11, 2012, 08:37 AM
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Australia, QLD, Mountain Creek
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Hi Scruffy One,
I got through the build painlessly till fitting the top wing. If I place the baldachin on their mark the wing struts marks are directly above one another. Then i noticed the front of my baldachin is 35mm from the black stripe across the fuse. This is a lot further back than the photos in the guide appear. What distance is yours?
I also just noticed my mark for the lower wing strut is halfway between second and third stars in from the tip. Pics in guide show strut fitted on third star. Im begining to think these marks are random guesses by bored factory workers
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Old Nov 11, 2012, 09:00 AM
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Australia, QLD, Mountain Creek
Joined May 2012
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Ok so if i have reread your build again correctly you are working top wing/ baldachin position from the bottom wing mark as your baseline. Makes sense. Wish i hadn't hot-glued the baldachin to the fuse already. Im just too trusting sometimes...........
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Old Nov 11, 2012, 01:29 PM
Proud of Brushless Sprouts
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You can melt the hot-glue by holding the hot-glue gun against it. Even a hairdryer seems to work from what I've heard.
Test the melting point of your EPP first!

Second method is simply cutting through the hot-glu and afterwards, peel/roll away the remnants of the glue.
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Old Nov 11, 2012, 02:38 PM
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Thanks for the tip Commander but the beldachin is a fragile piece of balsa with 10mm glued into a slot cut in the epp foam, its not coming out in a hurry
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Old Nov 11, 2012, 03:21 PM
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http://www.rcgroups.com/forums/attac...mentid=3540208

Looking at this build from another thread the struts are between the second and third stars, same as mine, but the baldachin is level with the stripe. That makes it 35mm foward of mine. Bugga, as they say in the classics.....
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Old Nov 11, 2012, 05:14 PM
looking up down under
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Australia, NSW, Fairlight
Joined Feb 2008
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Quote:
Originally Posted by Xmod View Post
http://www.rcgroups.com/forums/attac...mentid=3540208

Looking at this build from another thread the struts are between the second and third stars, same as mine, but the baldachin is level with the stripe. That makes it 35mm foward of mine. Bugga, as they say in the classics.....
the incidence angle at the top of the baldachin (i had never heard of a baldachin until i got the instruction manual with the pitts ) seems to be pretty much zero, the bottom has a distinct slope down towards he nose - the single hole is at the front, the dual holes at the back
because of the rake on the nose of the fuselage, forward or backward placement might give you a tiny bit of dihedral or anhedral to the top wing, but of no real consequence

i don't think the build is that critical - i am just pernickety

my build order for the parts was just arranged to make it simple for me to fit all the bits as best i could in the right alignment - if you can slot the top wing for the baldachin where it has to go from your work, the net result will be the same, only the cosmetics will change

however, derfnam01 privately mailed me this about his one in the video i posted :
"The weakest point of the Pitts is the wooden linkage fuselage - upper wing: It once broke without a reason after appr. 100 flights - I only noticed a strange flight behavior as if the elevator could not find its neutral position - the upper wing had no connection to the fuselage anymore.
So I reinforced this wooden linkage with epoxy and fiber tissue. No more problems afterwards with the Pitts till now."

i used carbon fibre tissue on the baldachin and struts before i got that info - one reason is for the colour to compliment the wheels and other black detailing, but having added some to my scratch built catalyst i was impressed by the fact that very little weight = almost indestructible
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Old Nov 11, 2012, 09:24 PM
looking up down under
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Australia, NSW, Fairlight
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so, finally slotted the top wing spar, glued in the baldachin, and did a further dry fit for the wings

detail work included inserting a piece of depron sample to hide the redundant servo hole in the bottom wing - still toying with the idea of putting the orangeRx satellite receiver in the hole there and running the connector up with the aileron wires as it will fit nicely with the receiver parallel to the fuselage axis...

i reckon i will do a further balance check and fit the battery hole before i finally glue the wings, and i can floor the slot with depron so it is snug but invisible from the starboard side

maybe tomorrow morning - eating lunch as i type, gotta go to work very soon
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Old Nov 11, 2012, 09:43 PM
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the incidence angle at the top of the baldachin (i had never heard of a baldachin until i got the instruction manual with the pitts ) seems to be pretty much zero, the bottom has a distinct slope down towards he nose - the single hole is at the front, the dual holes at the back
because of the rake on the nose of the fuselage, forward or backward placement might give you a tiny bit of dihedral or anhedral to the top wing, but of no real consequence

i don't think the build is that critical - i am just pernickety

my build order for the parts was just arranged to make it simple for me to fit all the bits as best i could in the right alignment - if you can slot the top wing for the baldachin where it has to go from your work, the net result will be the same, only the cosmetics will change


Not really! The current position of bc(fed up with typing baldachin) in its current position is too far back, the struts would be vertical and not raked foward. If i cut another slot further aft on the top wing to get the angle correct there is not enough even support for the wing.
I probably even have enough room to fit a second scratch built bc in front of the current one....double the support cant hurt! Thoughts?

Where do you get the tissue and epoxy for it? Lhs?
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Old Nov 11, 2012, 09:50 PM
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I reckon a second baldachin might be called for....
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Old Nov 11, 2012, 10:34 PM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
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That baldachin thingy used to be called the cabane strut or struts. On the one I built for a buddy, and got broke, I put a carbon 1mm by 4mm strip down through the top of the wing beside the strut and further down into the fuse. One on the front and one on the back. epoxy'ed in.

Gord.
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Old Nov 12, 2012, 03:54 AM
looking up down under
scruffy1's Avatar
Australia, NSW, Fairlight
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Quote:
Originally Posted by Xmod View Post
Where do you get the tissue and epoxy for it? Lhs?
the lhs barely ever gets a visit - i am a keen shopper from hobbyking, and can thus recommend :
carbon fibre tissue and finishing epoxy

the postage on the tissue is a motza as a single item, but i ordered it with a large amount of carbon fibre rods, spars and tubes, so it wasn't that big an additional cost to the total postage

it is astounding stuff once it sets, adding significant strength and almost no weight - i apply warm finish cure epoxy to the dry tissue, brush it through the matting gently (otherwise it tears the fibre and bunches it), then squeegee off the excess with a card

then i place it wet side down on grease-proof paper on glass, and apply a weight to press it tight, then leave it overnight; the end result is shown in my pics of the struts early in the thread, but on that occasion i used two sheets of glass and sandwiched both sides simultaneously

i also used the technique in my cuckoo build, as shown here

wrt the baldachin - easy enough to cut the remains off flush with the fuselage and then make a new one
the glue might be hard to remove, but it would be simple to hand drill into the balsa instead at the front part, and then extend the groove forward - my one has the back edge of the hole (for the tongue as supplied) at 55mm ahead of the cockpit, measuring from the "lip" of the cockpit... yours might vary depending on how the struts line it up, so you are better off with my dry fit method as already described, with the baldachin glued in the upper wing square and ready to finalise
i used 5 minute epoxy for that bit

hope that helps

if you need a sampler of the carbon tissue, mail me a private message with details and i'll post some up to you it works with normal epoxy too, but you'll need to be impressively brisk to apply / scrape and plate it out for a light and smooth result
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Old Nov 12, 2012, 05:23 AM
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Hi all. (Scruffy and Gord) can anyone give me a distance from front centre of top wing to the front of the fuse(at the front of motor mount)?
I just want to double check position of top wing before things become final.Name: image.jpg
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