Swappable Pitts Special S1S - an aerobatic classic

by ultramicrobe | January 11, 2014 | (41) Posted in Projects

Swappable Pitts Special S1S

In the summer of 1973, when the Rolling Stones and Tony, Orlando & Dawn were topping the charts, my mother and her flying partner Bert scratch-built a Pitts Special S-1S based on plans from Aviat Aircraft. Bert was an excellent mechanic and designer, and even my aunt was enlisted as  a pro-seamstress. The project took 2500 man- and woman-hours of work, and some of my earliest memories are linked to the build - sewing and doping the canvass, the wood and steel skeleton, and the smell of oil and engine parts. 

Their Pitts was serial number 427 and was tagged CF-BRT. They flew it in local airshows and trained in basic maneuvers. The S-1S is a one seater, so no rides for the kids unfortunately, but we spent a lot of time around the plane on the ground and watching it fly. In 1978 the plane was involved in a major crash - a bungee in the landing gear broke and the gear failed. My mother flew it around for a while to use up fuel, and belly landed on the grass rather than bailing out and ditching it, but unfortunately BRT pitched end-over-end. She walked away with minor injuries, but BRT was an almost total wreck. They re-built it through 1978 and got it back in the air, and it is still flying today. 

 

 

 

The Pitts S-1S is a classic, and I am partial to it over some of the newer performance aerobatics planes, probably because I spent so much of my childhood at aerobatics competitions (we even got to the Worlds in 1980 and saw Leo Loudenslager win the Aresti cup with his Laser 200 that is now in the Smithsonian) where the Pitts featured so prominently.

So I came at this project from two points of view. One, I wanted to have a good, tough, aerobatics plane and have been unhappy with a couple that I have bought commercially, since they seem to require too much speed on account of their weight. I wanted a light plane that could fly at more scale speed but still have the power to do the moves. On the other hand, I thought it would be fun to take on the Pitts, a challenging plane from a design perspective and see if we could make one for the swappable series with excellent flying characteristics with foamboard. So I set about making a swappable CF-BRT, as close to the original in form as possible, with no real idea how it would perform. 

The results were WAY past my wildest expectations. This is one of the most fun planes I have ever flown. It’s as gentle as a kitten if you want, but when you open it up it’s amazingly agile in the air. It takes off in a shot, even from grass (which surprised me because the wheels are scale), and lands on grass well too. Initially I had the throws dialed way down, but I quickly went to high rates and now that’s all I use - in a word, if flies great. 

Below, I provide build instructions, and plans at the end. Above and below are some videos of it in the air. Flying videos of tiny planes too far away are not the most interesting, so I focused on low passes etc. just so you can see it flies smoothly. I also have some wing-cam clips of basic moves, rolls, loops, hammerheads, again to show the plane works. My friend Ed did the other video (below), complete with music, as usual - Thanks Ed! 

The movies are mostly from the maiden flight day and the next day. As I said, the flight characteristics were beyond my expectations - the plane is light and virtually floats and is easily able with a modest power set to do any of the basic moves a real Pitts would do. You might notice some differences in the plane in different clips - I made some cosmetic modifications to the cockpit and rear deck after construction to make it more realistic (noted below), and put the stripes on it after the maiden (Ed's movie below is all from the first day). 

 

 

Build instructions:

This plane is a bit tricky to build because the two wings are different, the top is flat and swept back, the bottom has dihedral but is not swept. This gives most of the characteristic looks of the Pitts, especially from head on. I used tape for the colour as I went, but that adds a lot of work. If you don’t want to have a sun-burst on the wing, painting would simplify it. I don’t recommend this for a first time build. Compared to my other designs like the Messerschmitt and Mustang, this is harder, even harder than the B25 bomber (though WAY easier to fly). But if you have built a couple planes, make this one since it flies great. 

 

Step 1 - top wing. The overall construction is much like the wings on other builds I have done with a few exceptions. There is no dihedral, but it’s swept back, so the spar is different as is the joint between the two halves. The bottom panel ends in a line parallel to the fuselage and correspond to where the struts will connect. Glue the short spar into place so it ends where the bottom panel ends, and I always glue skewers into the folds of the upper panel for added strength (see picture). Fold and glue wings as usual. To join the two halves and get the right sweep-back angle, short joining-spars are first inserted and glued in to each wing at an angle so they meet face to face when the wing halves are joined. In addition, two popsicle sticks are inserted tight to the front and back of the inside space and glued into one wing. Now join the wings with lots of glue on both spars, sticks, and the joint itself, and tape once the glue hardens. A semi-circle is cut away from the trailing edge joint to suit your taste (I re-cut because the first was not big enough). Cut ailerons. 

Top Wing Halves

Join halves with short joiner spars and popsicle sticks (for sunburst instructions see below).

 Cut out wing above cockpit.

 

Step 2 - bottom wing. Again the overall form is similar to the top wing, but with  a few degrees of dihedral (guided by spar in plans), and here the bottom panel ends where the servos are installed. Join as usual and cut ailerons. 

 Bottom wing set up and joining.

 

Step 3 - make the fuselage. This is a standard box fuselage, short and stubby.

Fuselage and two wings. 

 

Step 4 - assemble the tail. The horizontal and vertical stabilizers are straightforward, and give the Pitts a lot of its look too, as well as huge control surfaces. The elevator is forward of the rudder, so I cut a pie slice out of the horizontal stablizer above, and the fuselage below to allow a popsicle stick to be added to join the two halves of the elevator, for extra strength (see pictures). Glue the two stabilizers together at 90 degrees, then join them at the tabs on the top of the fuselage, and again make sure they are true as the glue hardens. Once assembled, trim the bottom of the fuselage or rudder (whichever extends beyond the other so the line of the rudder and fuselage are the same (see picture). Servos are installed under the horizontal stabilizer and connected to the controls, nothing unusual here. 

 

Notch fuselage for elevator movement.

Join stabilizers and check mobility.

 Once tail joined to fuselage, trim the bottom of the fuselage to match the sweeping line of the rudder. 

 

Step 4 - Install lower wing, and layout the wing struts. Insert the lower wing into the slots in the fuselage and glue into place once the wing is centred and 90 degrees to the fuselage. The wings are joined with two “I”-struts. I reinforced these with 0.5mm CF (just cut out with scissors using the same pattern, then hot glued to the foam). They would probably function without it, but I suspect in a crash the reinforcement will be useful. Now dry-fit your I-struts to the top wing as shown, so they close up the openings at the end of the bottom panel, and hold them in place with some tape. place the top wing on the bottom wing so that the bottom surface of the strut comes just to the leading edge of the wing and check the alignment. The bottom curve of the I-struts should be close to the curve of the wing - you can trim a bit if it is way off, but make sure the wings stay parallel - measure the inter-wing distance on both sides at the struts, and make sure it is about the same. The wing tips should be at about the same position on either side, and the centre of the top wing should be a few cm forward of the bottom wing. If that all looks good, then outline where the struts contact the bottom wing, when you have everything centred and lined up perfectly. At the same time, measure the distance from the top of the fuselage box to the bottom of the top wing and bend yourself some piano wire struts as shown, and glue this down to the fuselage box, as shown. These will eventually be taped in place to the wing for extra strength. 

Lower wing install.

Bend wires and install the fuselage struts. Position at front most short former.

 

Step 5 - Install fuselage decks. Now its time to cover up the top of the fuselage. First, glue all the formers into place. These are fairly standard, except that there are several in the front, to support the change in shape at the cowling, and these extend over the sides of the fuselage to create the whole front shape - this is an important part of the way a Pitts looks - the front cowling flairs. Leave the front-most former unglued until later (see below). 

Test fit formers (note that the back formers of your's will look a little different because I moved the cockpit forward and raised the back deck height of mine later - a big improvement)

 

When the formers are done, dry fit the three paperboard deck pieces and make sure they fit. In the centre piece, you will need to trim out a little notch on either side for the wire struts to pass though. Leave some extra room here, you will hardly see it, but you don’t want it too tight when you are rushing to get it in place before the glue sets. When you are happy, start with the middle deck, which forms the cockpit. I glue first, tape later, so all formers that join this deck are glued, and the paperboard centred and then held down into place until the glue hardens, then tape down the two sides. Then do the rear deck in the same way. Before you do the front-most former and cowling, make sure you fit your powerpod. I also insert a velcro strap through the top of the fuselage that will wrap around the battery, for extra support (see picture).

 Cover the centre section first. Note the notches for the wires at the front. 

Then do the back section (and your's will be higher and further forward). Then fit your powerpod. Note the velcro strap inserted at this stage - do it now before you cover the cowling section. 

 

Lastly, install the front-most former, which is special because it has a piece of paperboard glued to it that makes the front of the cowling. Cut out the former and the paperboard, glue them together and then trim the paperboard to match the former around the top. This leaves enough space to get your powerpod in and out (it has to be a short powerpod, so it can drop down and clear the front former, but it does work - see picture), but covers over much of the front to give it a nice look. Once this is set, glue and tape the front cowling so that it extends forward to be even with the front-most former. It should extend out the rear to past the last former so from behind it looks like there is a space under the cowling. 

Shown with powerpod in place. Not the first former has a paper/tape face. Glue it into place and check the powerpod still goes in and out okay. 

With the cowling installed the motor should be clear of obstructions. 

 Cowling from behind - gives the oval look to the nose, which is a distinctive Pitts Special feature. 

 

A note here: I originally had the back deck about 1cm lower and the cockpit about 2cm further back. It did not look good, and made the fuselage look too long and thin. Some of the pictures of the build are from this version. After a day, I ripped the back deck off and added some height to the back former, then installed a new former further forward to make the back of the cockpit and it totally changed the look of the plane. In the plans, this is all simplified for you - I just wanted to explain why some of the pictures might look a little different. 

 

Step 6 - Install top wing. Now its time to join the two wings. First, remove the temporary tape on the I-struts, and glue them into place on the top wing with hot glue, making sure they stay at 90 degrees to the bottom of the wing. Once both are hardened, re-position the struts to your outlines on the bottom wing, and check everything is still lined up well. If so, glue the bottom of both struts, place them on these marks, and hold into place until the glue hardens. Re-glue the joints on both sides as squeegee away the excess glue. Your wire struts to the fuselage should also be in the right place now, and you can just tape them onto the top wing with packing tape. Your wings should not be REALLY strong, you should feel no wobble between the two wings. 

Tape struts on to re-test fit - should sit on the wires.

Check (and re-check) that wings are parallel and struts conform to shape of both wings fairly well.

When you are happy with the fit, glue struts to top wing.

Re-test, and if all's well glue struts to positions marked on bottom wing, hold them into place and re-glue joints.

 Lastly, tape wire struts to top wing. 

 

Step 6.5 - connecting the ailerons. I wanted dual ailerons, so I had the bottom ones on a servo and connected them to the top wing ailerons. Based on the way it flies, I strongly encourage this since its does not have crazy roll rates, just scale. So, THIS turned out to be WAY harder than I imagined, knowing nothing. Originally I thought I could just put two horns on the top and bottom behind the strut, and hook ‘em up, but its not that easy. First try the top ailerons would go up, but not down, then they would go down and not up. Only then I decided to read up on this and learned you can only connect them where they are directly above one another, so I redid it at the very edge (see pictures). I had a couple pin hinges around, and I used these and taped them together with a skewer. This works brilliantly, although does not look great. A wire would be better and smaller pins, but it's what I happened to have on hand. 

Join the ailerons near the tips - as close as you can to straight up and down. Test to make sure top aileron has full motion in both directions before gluing anything. 

 

Step 7  - Landing gear. A rear wheel is installed on a little length of thick piano wire that is bent in any way you see fit to attach it to the rudder. Tape that on. The front landing gear are made of two pieces of 2mm piano wire as shown. One is much like the ones that Bixler always makes, The second one provides more support out the back, it is a simple squared off U-shape with loops on the ends. Loop these over the wheel axels before you put the wheels on. Now put three skewers in the fuselage as shown below, and use short stiff elastics to attach as shown. I use old bike inner tubes for this - just cut sections like slicing salami and you have great elastic bands that never wear out. This set up looks realistic, but also gives you great stability and some shock absorption. This plane eats up grass take off and landings, even with fairly small wheels. I cut out a piece of paper in a triangle and taped it between the two to finish the look. Over time the tape wears out, just re-tape it.  

Landing gear held in place by bike inner-tube elastics.

Paper triangle taped to two gear wires.

 

Step 8 - extra decorations. I made mine up to look like a classic Pitts S-1S to match CF-BRT, with the sunburst top wing (made by covering the wing with red tape, then cutting the lines with a very sharp razor blade and peeling the tape triangles off. Do this BEFORE you install the wing - see pictures), and classic double pinstripe with the diamond (this would also be easier to do before you put the wings on, but I did it later and it was no big deal). Stripes were all cut out of white tape, surprisingly simple (you know those things that you could spend twice as long finding it on the internet as it took to just make it up from junk you have?). The windscreen was cut from garbage clamshell packaging, and is just as easy as it looks. I put a couple pieces of back tape on the nose to look like the air intakes. On the tail I put an EAA sticker (classic logo, of course) and the registration tag letters CF-BRT were just printed on my computer on paper, cut out and taped on with packing tape - presto. Done. 

The sunburst is made by lightly cutting the tap with a very sharp blade and a flexible straight edge of some sort (above), then peeling it back (below)

 

A windscreen, of course (cut from clamshell packaging - see plans). Pin-stripes are just white paper tape. One the cowl I just bent it around a bit to make the distinctive stripes (below)

 

Taped some paper letters for the CF-BRT on the tail to finish it off. 

Then I thought I needed a pilot, so I put my “Bixler Doll” in the seat. 

 

The pilot functioned well at basic moves. 


Step 9 - Power setup. This plane takes a standard powerpod, except because it is so short and stubby, you have to cut the end off (at least a couple cm, but why not just cut it in 1/2 to reduce weight). To be honest, I have begun making all my powerpods 1/2 length since they never are the fuselage anymore like in the first FT planes. 

 Anyway, I set mine up with a NTM 2826 1300 kV motor, a 40 amp ESC, and a 9X4 prop. It runs on Nanotech 3S batteries, and either 1300mah, or 1500mah fit into the battery slot fine. I make little foamboard boxes for my batteries, and in this case it helps complete the look too. With this set up the plane can take off in a few feet, can go vertical, and do anything you want, but it is not stupidly overpowered so it looks non-scale, or flies badly because of torque. I balanced it on the spar of the top wing about 5cm from centre (remember because it is swept back, the position of the spar is not constant), and this seemed ideal. 

 The first flight was a dream - it just took off and flew, no trim was even needed. I started with low rates on my ailerons and elevator (like 50%), but quickly went to full 100% because I loved the way it rolled and climbed, and I did not find this made it hard to handle.  In my first flight, the brand new  25amp ESC burned out and I learned it does great landings on grass, and soon learned it takes off well too, so I am really pleased with this plane. Seems like a great trainer for aerobatics - its powerful and agile, but can be slowed right down to soar gently, so it does everything. 

 Of the planes I have designed, or even built from scratch, this is easily the most fun one to fly. I wish I knew what it was like to fly a real Pitts, but I will have to make do with this little one, and imagine they are similar - agile but not twitchy, fast enough to do what you want but not so fast it takes a lot of space, a great glider with soft landings. I hope some of you can work up the energy to make this, because its flight characteristics are excellent. 

 

Here are some pictures of the final product, and the build plans are provided below. Please comment if you build one - I would like to know how it goes and how it flies. 

 

Plans:

 

COMMENTS

wizard122 on January 13, 2014
Sweet can I ask where you got your colored tape? Thanks can't wait to build one.
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ultramicrobe on January 13, 2014
Tape Brothers or Hobby King (where it is called "wing tape")
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themajik1 on January 12, 2014
Very nice design and build! That plane looks like such an easy fly. I wish I had the build skills to build this one, I really like the lines of the Pitts and the way this one flies.
Again very nice and great job!!!
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Naloxon3 on January 13, 2014
Awesome build...thank you for the plans... this will diff be my next build... just awesome... fly smooth.
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ray574 on January 12, 2014
So completely AWSOME!!! I love the Pitts, and have eyed it on several rc sites, looking for a manufacturer that had decent scale likeness, but price was the downfall.
Thank you, thank you, thank you, so very much for posting the plans. This is an amazing model that you have completed. The history in your family with this plane is just outstanding. You are also an excellent pilot. I have been downloading plans from flitetest like mad, but have only built the spitfire, bloody wonder, and slinger, and getting ready for the bat wing (such a fan of edf but not flown my f-22 Raptor that I purchased from banana hobby yet since I'm waiting to get used to faster aircraft). My sister is pressuring me to help her build the bat wing, but I think I'll be building the Pitts at the same time - this is just too cool to put off for long!
Again, THANK you for the plans!
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Jaxx on January 12, 2014
This is a beautiful plane! What software do you use to design your planes?
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ultramicrobe on January 12, 2014
Actually, I really only use a pencil and a ruler. Generally all I do is take a picture of the plane I am interested in and measure a few important bits (length, wingspan, etc.), then keep those bits to scale. I draw pieces on the foam board, and when they look good I cut them out. Sometimes something does not work quite right, so you do that bit over (e.g. here I made the cockpit too far back and too low, so I redid it, which only really took 30 minutes to fix). So my advice is just try it and see what happens, because foam board is only $1 a sheet.
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Jaxx on January 17, 2014
That's awesome! How do you transfer those plans to PDF files?
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c.sitas on January 13, 2014
You,my friend are an artist under cover. Back in the 60's I had a glow version similar to yours. About 50" if II recall. That plane was an icon back then.Maybe more so now. There a few copiers around with different titles,but still the same takeoff. Even today , if it even looked like a pitts,they fly like crazy.There was always something about "double winger". Keep up the good work ,your a perfect example of the hobby.
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ttprigg on January 12, 2014
What a great project! and it seems to fly as good as it looks.
Why to think "outside of the box" (literally) with the cowling formers. I am sure that technique will be barrowed on other projects where a curved fuselage is so much a part of the look. I am thinking Corsair... Thanks for sharing.
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mark d on January 14, 2014
Great "little stinker". One of my favorites too.
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Yogenh on February 2, 2014
I love it and will have to build one. You did a great job on it. For something that is as cheep as it is it don't look cheep
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Balsa to Foam on January 12, 2014
Definitely building one already downloaded plans :)
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808aerosquadron on January 13, 2014
Beautiful. The pilot is a great touch.
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Cortes Gary on January 12, 2014
Hi there, Great build article and videos. The plane is a beauty and since I have seen the maiden and a few other flights have to agree that its a fine flyer. A good size for a playground. Its a very pretty plane in the air and on the ground. Keep up the good work.
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wahrhaftig on January 12, 2014
I would start building this minute if I had the plan. How do i download in a tiled version for printing on standard printer paper?
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ultramicrobe on January 13, 2014
You can tile any PDF when you are printing - it does not need to be a special file. You can do this from most graphics software (e.g. I use Illustrator), but if you don't have that you can also do it with free versions of Acrobat Reader. Some old versions don't (e.g the common version 9). Just download a newer version and you should be good to go. I just checked this, and my free Reader tiles these files.
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pintokitkat on January 13, 2014
This looks fantastic. i particularly like the wire work for the undercarriage and top wing fastening. The undercarriage is usually something I struggle with (Or perhaps its heavy landings I struggle with) so alternative ways of building them are always interesting.

Oh, by the way, Tony Orlando was one person not two - comma not required.
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ultramicrobe on January 13, 2014
Huh, you don't say? guess Tie a Yellow Ribbon was not in my own top 10...
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pintokitkat on January 14, 2014
Darn it! Now I've got tie a yellow ribbon going round in my head all the time. Sad thing is, I can remember all the words.
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mark d on January 14, 2014
Bus driver please look for me.... HA !! not I'm stuck too!!
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ftwingnut on January 15, 2014
Awesome job. I have always liked the Pitts, and remember it fondly from airshows when I was a kid. You really captured the essence of it with this model. I too am working on a scale model of a plane that I grew up flying in with my dad. I can't wait to finish it and see how it flies. I will be sure to post the build log and plans here when it's done.
Again, great job. This would also make a great platform if someone wanted to do a Christen Eagle.
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fl_rider on January 12, 2014
What a way to commemorate the plane you grew up with. Thanks for sharing the story, plans and videos. Thank God your mother was able to walk away from the crash. I'm glad they were able to rebuild the plane.

Chris
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sailorJohn on January 12, 2014
Amazing, foam building is progressing at a rapid pace. I like searching the tube with different key words to find other really beautifully done foam projects.
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InTheFade on January 13, 2014
Great design, thank you for posting the plans. I cant wait to build one.
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Kenny G on February 8, 2014
Like the plans, what is the wing span, and scale to print out. Any info will be appreciated. Thank for the great job
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ultramicrobe on February 27, 2014
Don't recall, the wingspan was dictated by the proportions with the fuselage - which was sized to max a single sheet of foam.
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Gantorin on April 1, 2014
1. Props to you with the plane. I LOVE it. I am so going to build me one as soon as I get my Spitfire off the ground. Excellent job!!
2. Props to the person working the ground camera. They also did an excellent job.
I want one of those now very badly... LMAO!!
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ultramicrobe on April 7, 2014
Ed makes nice movies. For my part I have a go pro on a head-strap so it just points wherever I am looking. It actually works pretty well (if you have it set up right - I also have loss of movies with planes just above or below the frame…)
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Wolfee on May 9, 2014
wondering measurement for lower wing spar, no marks on plan? thanks
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ultramicrobe on May 10, 2014
Its the same thickness as the bottom wing spar, but it's in three short pieces as described in the instructions. Each wing half has one, then just make a short one to join them. It does not really matter much hot long they are, just so long as they are the same thickness as the one in the plans for the bottom wing.
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poplton1 on May 26, 2014
Thank you ultramicrobe, I finished my Pitts several months ago with just a little alteration to your plans to accommodate my building style. However l live in Idaho so I've had to wait for the wind to stop blowing so I could try it. I set everything up to your specifications, hand launched and it flew good right out of the box. Just a little kick with the rudder to get into a left turn. Really flew well. I like all of your articles. Keep up the good work. Thanks again. Joe
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ultramicrobe on May 26, 2014
That's excellent to hear. I love hearing that someone had some fun building a plane. And I love flying the pitts too - I also found it was like a rock taking off and flew great.

Maybe someone with more patience for computers than me could start a thread where people post pictures of their builds of some of these planes. I would love to see a pic of your pits. And when people start modifying them then that gets really interesting.
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poplton1 on May 29, 2014
Send me a short email at joepopdragons@gmail and I would be happy to send some pics. Joe
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Flying Fox on September 9, 2014
Beautiful Plane Keep up the good work.
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pressalltheknobs on July 12, 2015
Thanks for sharing this. Love this build and the story behind it. I've been enjoying flying a Pitts Special in my rc flight simulator and if that is to be believed it's a very nice plane to to fly. I'm very curious to try your version. Definitely on the list. Just getting started building planes so I it may be a while yet but I'll let you know when I do.
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bthom84 on December 30, 2015
I'm real excited to build this. I have the plans almost all cut out and the power pod ready. I'm not sure the motor I have is big enough tho (emax cf2822 1200kv). Can you please tell me what the aprox all up weight is so I can do some figuring? Thanks for such an amazing plane!
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ultramicrobe on January 24, 2016
Not too sure, but most of the planes I made are all about the same weight, and I used a 2826 1200 or 1350kv motor most times, so I suspect your set up will not have enough power. With the motors I mention and a 9x4.5 prop it was pretty scale, so not overpowered. with a 9x6 it might be more fun to fly too. But I think your motor is too small.
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macak on September 22, 2019
I love this plane. Can you tell me where the Gravity Center is?
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ultramicrobe on February 11, 2020
right under the top wing spar should do it. It's pretty forgiving.
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Swappable Pitts Special S1S - an aerobatic classic