Pitty - Pitts inspired 24 inch bipe, with plans! - RC Groups
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Jun 10, 2011, 04:28 AM
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slebetman's Avatar
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Pitty - Pitts inspired 24 inch bipe, with plans!

About a month ago someone flew a Pitts Special above my house. The real thing, not RC. I loved the way she looked in the sky. It's the first time I've seen a real life biplane. About two weeks ago she made another appearance and this time she did loops and rolls. It was then that I decided that I had to have a biplane in my fleet.

So roughly two weeks ago I built a profile bipe and crashed it several times before I got all the proportions right. This is a full fuse version of that final configuration. It is inspired by the Pitts but is not a Pitts. I didn't like the looks of the tail section on a real Pitts so I made my own. Then I had to redesign the wing tips to match the tail.


There are two versions of plans: the full plan and the half plan. They are identical except that the half plan requires you to manually mirror the templates. Both plans are available tiled to A4 and US Letter.

Target weight for the build should be around 200g to 250g. Recommended motor is the AX 1806N 2100kv brushless. But any 20g brushless motor should do fine. Recommended battery for the target weight should be around 600mAh 2S or 400mAh-500mAh 3S.
Last edited by slebetman; Jun 21, 2011 at 09:56 PM.
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Jun 10, 2011, 05:42 AM
It's Just Foam!!!
EZglider's Avatar
Looks good! Got any pics/videos of the finished plane? Also specs and what pwr system you're using would be helpful. Nice looking plans, this one is going on the Bipe-To-Do list.
Jun 10, 2011, 07:58 AM
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Originally Posted by EZglider
Looks good! Got any pics/videos of the finished plane? Also specs and what pwr system you're using would be helpful.
Thanks. I don't have a picture of the finished plane because I'm in the middle of the build . Don't worry though, this is going to be a quick build. I'm hoping to maiden it on Sunday.

Here are some pictures of the build progress:
Jun 10, 2011, 08:12 AM
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OK, got the depron pieces cut. I decided to try dry fitting them before gluing. Good thing I did because I realised the slots for the cabane struts are too narrow.

What happened was that I originally designed the fuse to be very narrow, to help when knife edging. Then I thought it looked too much like a profile plane with the narrow fuse so I broadened it a little. But I forgot to also broaden the center section of the wings. So now the cabane won't fit.

I don't really feel like making another set of wings so I'll either have to revert back to the narrow fuse or modify the current set of wings. Whatever I decide, I'll have to correct the plans. So I'm removing the plans for now until I've made the correction.
Jun 10, 2011, 09:52 AM
Foam Av8r
RogueTitan's Avatar
looks pretty good IMO
Jun 10, 2011, 10:08 AM
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nice looking plane so far, think i'll have to build one when you are done.
Jun 10, 2011, 11:04 AM
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slebetman's Avatar
OK, I've decided to go with the narrower fuse since that requires the least amount of modifications to the current plans and it doesn't look too different.

I've also updated the rudder to look a little more roundish. I think it looks better now.

So plans are updated. I still think the plans need a little tweaking as I have found attaching the tail landing skid to be a little difficult. But basically I'm satisfied with the design overall.

Next is to do the hinges and install the control horns.
Jun 10, 2011, 03:06 PM
Aero Andy's Avatar
Good looking Pitts, great job on the build so far.
Jun 10, 2011, 03:15 PM
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Looks good. I cant wait to see the maiden video. I will be building this for sure. Keep up the good work and please keep us posted

Jun 11, 2011, 05:45 AM
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slebetman's Avatar
Thanks for the words of encouragement guys. Means a lot to me.

So, the last thing I did last night was to hinge the control surfaces. I use tape hinges but done slightly differently than how I see others do it.

One problem I've had in the past with tape hinges is that the tape tends to come off the depron after some time. My solution to that is to cut a grove for the hinges but not all the way through. That leaves the shiny 'skin' of the depron uncut which protects the tape from becoming unstuck. I then tape the inside of the grove with masking tape to protect it. I find masking tape sticks better to cut or sanded depron.

Of course if you have glass tape then maybe all the above isn't necessary but I'm a cheapskate and packing tape is cheaper :P

I've tried hot glue hinges but the quality of the hinge depends on the glue. When I use the bendy, more rubbery glue then the hinge works well but when I use the harder, more brittle glue then it tends to break. The problem for me is that around here the glue are typically sold unbranded and even from the same store you sometimes get one type and sometimes the other. I just can't depend on the quality of the glue sticks around here and I don't like depending on luck.

Anyway, here are some progress pics:
Jun 11, 2011, 06:25 AM
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This morning I started some work on the internal structure of the fuse. Some of the bits in this part of the build isn't on the plans at the moment because I find it easier for me to design and solve problems when I have the actual 3D structure in my hands. Don't worry though, I'll update the plans later to include them.

The structure is basically similar to a monoblock but is built-up instead of carved out. The internal structure is really minimal and I depend mostly on the skin to provide most of the support. Basically a monocoque construction. At this size 3mm depron is strong enough but any larger and we'd need more structure.

Currently the AUW is around 172g. That's just 28g shy of my target weight of 200g. I'm still hopeful that I'd be able to reach that target.

Now I'll have to install the control horns. Have to do it now if I want to maiden this tomorrow morning since the epoxy takes 12 hours to cure.
Jun 11, 2011, 09:39 AM
tree scavenger

oh very Nice!

...been wanting to do a semi-Pitts too,,
i think i have everything....cept the skills!? hehe
how'd you make the lightening holes?
...really liking the looks of her so far
Jun 11, 2011, 10:40 AM
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slebetman's Avatar
Originally Posted by silentsurfer
...been wanting to do a semi-Pitts too,,
i think i have everything....cept the skills!? hehe
how'd you make the lightening holes?
...really liking the looks of her so far
Thanks. The holes were simply cut out with an x-acto knife and then smoothed out using a round file.

Unfortunately I made a mistake with the servo placement. The casing of the higher servo blocks the movement of the sunken servo. The good news is that it isn't too much work to redo the whole thing. The bad news is the setback may mean that I wouldn't finish her by tomorrow morning and will have to wait for next weekend to maiden her.

Still, not a big deal but I'm not good at waiting.
Jun 12, 2011, 01:39 AM
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slebetman's Avatar
OK so it's official, I wouldn't be able to maiden her this weekend. Which means a week of waiting for me. On the plus side, this means that I have more time to build. I'm already sort of regretting rushing through the rebuild of the internal framework - it caused too many imperfections.

The servos are now installed inline. Looking at it now it looks like the most obvious way to do it. But it actually took me a while to figure it out.

Forgot to mention this before: for this build I'm using mostly hotglue except for the installation of the control horns which I used epoxy.

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