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Pitts style biplane scratch build.

RacerX

New member
#1
Winter is here! And the "here" is Ohio! Insert appropriate cuss word. I prefer flibbatteefloo.

I started on this last Saturday morning. Drew up the plans a week before that and I finished the build last night.

I really like the styling of the Pitts biplane, so I thought I'd try to make something similar. I also like the 750mm wingspan size which is right around 30". It makes for a nice size to transport but still gives a decent scale for keeping orientation in the air.

I named this plane Fitts. I'm hoping it doesn't give me fits when flying.

(added the plans in PDF format)
View attachment FittsPlans1.pdf
View attachment FittsPlans2.pdf

One thing I'm not sure about is that I only put the ailerons on the lower wing. I didn't do corresponding ailerons on the upper. I did make the ailerons oversize to hopefully gain some authority. If it doesn't fly well, I could always cut in upper ailerons and link them together.

One other change, to the original scale design, is a larger rudder. I also made two changes (one was a mistake) during the build process. First, I mounted the landing gear farther back than the scale location. It seemed like a good idea to have it mounted right at the front of the lower wing for good support. The landing gear location might make it tend to nose-over during landings. The bigger mistake was when I mounted the upper wing. I centered it on the upright struts which shifts it more forward than an actual Pitts. Will the accentuated "stagger" make it fly worse? I'll have to find out when I maiden it.

I don't try to build as "swappable." I've decided that for my purposes, I would rather dedicate the electronics to each plane I build. That and it makes it a tiny bit lighter because I don't have the extra foam board for the power pod.

I made this out of standard Dollar Tree foam board and wrap all of the parts with clear shipping tape for durability.

Notes on the design:
- 3/16" wood dowels in the wings for spars
- barbecue skewers shoved through the foam board upright wing struts
- bottom of fuselage left open to reduce weight
- CG is a bit tricky and I'll have to see how it flies
- had to mount the battery right behind the firewall to get where I think CG should be
- I didn't separate the aileron servos for flaperons (might do that later)
- I laminated a second layer of foam board on each wing to create a KF airfoil
- the fuselage is a bit wider than scale - I wanted it to be pudgy, go figure
- I may put a smaller prop on it, once I maiden it, just to get longer flight time
- no plan for a canopy - easy access to everything

Here's the CAD view of the profile and the Pitts photo that I used to trace the basic shape.
Fitts-0DWG.jpg


Here's the printed full size plans for all of the parts.
Fitts-0prt copy.jpg


Here are some photos at different stages of the build.
Fitts-1.jpg
Fitts-2.jpg
Fitts-3.jpg
Fitts-4.jpg
Fitts-5.jpg
Fitts-6.jpg
Fitts-7.jpg
Fitts-8.jpg
Fitts-9.jpg


Here's the completed plane.
Fitts-10.jpg
Fitts11.jpg
Fitts-12.jpg
Fitts-13.jpg

Added a couple of closeups of the fuselage showing the upper wing attachment and the placement of the elevator and rudder servos.
Fitts-clup-1.jpg
Fitts-clup-2.jpg


And here's why I won't be showing a maiden flight video for a while. (taken about an hour before I posted this thread)
NoFlyFly.jpg


I used fishing line for the wire reinforcing between the wings. The firewall is a plastic tray from a 2.5" SSD - I get a lot of those from work.

Here's the specs:
- 30" wingspan (approximately)
- 671 grams flying weight with revised landing gear (measured)
- EMax CF2215 1200kv brushless
- HobbyWing 30A ESC
- 1300mah 3s LiPo
- LemonRX DSMX receiver with stabilizer
- 10x4.5 GWS style slow fly prop
- EMax 9g analog servos
- 21.2A draw at WOT (measured)
- 823 grams thrust (measured)

Here's a photo of what the AUW (flying weight) is now that I revised the landing gear location. Thanks to jamboree1 for the advice on that.
Fitts-weight.jpg
 
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jamboree1

Active member
#2
Thats a sweet design, I really like it. It is almost guarnteed you will pitch forward on takeoffs and landings where you have the gear placed. I also just went thru a bipe build and faced the same issues with top wing placement. My bipe is based off the nnMoth Minor, pics in his build forum. I will be doing my maiden tomorrow in a balmy forcasted 88 degree temps:cool:
 

RacerX

New member
#3
Thanks!

I'm hoping it doesn't nose-over on takeoffs. I think the wheels spin free enough and it has the power to pull it into the air with a little elevator. But I am nervous for the landings. If it starts eating props, I may just have to move the landing gear forward.

Enjoy the weather! We hit -2F last night.
 
#5
Thats sweet :),me n my mate were discussing an Ultimate Biplane build today while flying one on Realflight sim :)
will look out for the maiden......sometime soon yeah :p

cheers
 

RacerX

New member
#6
Thanks!

beautiful design. do you plan to release plans? I would love to build this.
I'm not trying to discourage you but I haven't flown this design yet, it's completely unproven except that it is loosely based on the Pitts proportions. If the maiden goes well, I can release the plans but they are very basic. And it might be a month or so until the weather is good enough for a quick flight.

I didn't take a whole lot of pictures along the way and this is the first biplane I've ever built. I don't do A folds, B folds, or keyed tabs or anything fancy. My simple cutouts work for me because it's quick and easy but they might not work for anyone else.

With any of the planes I draw up, I only have a general idea for where/how the servos, ESC, and battery will be mounted. I make sure there is enough space for them but then I wait until I have the frame together to place them.

If you don't mind not having perfectly clear plans or instructions and you like to improvise, you'd probably be OK.

I'll edit the post, with a maiden video, as soon as I make sure this baby can fly. :) Ummm, if the maiden doesn't go well, you might not see the video. :-(
 
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RacerX

New member
#7
Thats sweet :),me n my mate were discussing an Ultimate Biplane build today while flying one on Realflight sim :)
will look out for the maiden......sometime soon yeah :p

cheers
If we can hit 40F outside and the wind isn't too bad, I'll try to get her in the air.
 
#9
Thanks!

With any of the planes I draw up, I only have a general idea for where/how the servos, ESC, and battery will be mounted. I make sure there is enough space for them but then I wait until I have the frame together to place them.

(
Now that sounds like spot on scratch building to me :applause:
pardon the pun but 'winging it' :p

It does look good tho and I'm sure you will dial it in fine ;)

cheers
 
#10
It is almost guarnteed you will pitch forward on takeoffs and landings where you have the gear placed.
Darnit! You nailed it right on the money! I tested it here in my basement. When I was on the smooth concrete, it taxied fine. But on the carpet, nose-over, nose-over, nose-over. So, I moved the gear forward. I had to make new fairings but it was pretty easy. Thanks for the advice! Now I can taxi it on the carpet perfectly.

Fitts-mod1.jpg
Fitts-mod2.jpg
 
#11
Now that sounds like spot on scratch building to me :applause:
pardon the pun but 'winging it' :p

It does look good tho and I'm sure you will dial it in fine ;)

cheers
Ah yes! Winging it. I have used that expression a few times and my friend rolled his eyes each time.

Thanks for the encouragement. I've checked out your F4 Phantom thread and that thing is awesome! The detail you are creating is amazing.
 

jamboree1

Active member
#12
Bipes are one of my passion planes. even those set with perfect COG and good diameter wheels are susceptible to nose overs, seems a lot of tail traggers share this trait also when taking off or landing on grass. Taller wheels do help as this shifts weight to the rear of the plane when on the ground. There will be some that will argue that this is not true but i have checked this on a postal scale and find it to be true. Just think of the old drag car gassers that had nose bleed ride height in the front, this was to put more unsprung weight on the rear.
 
#13
Funny,my mate does the same lol...I cant help myself...winging it...such a cliche :)
Yeah the F4 is the ultimate 'winging it' build I've done so far, I'm sure your maiden will be far more successful than mine tho ;)

Cheers
 
#14
Funny,my mate does the same lol...I cant help myself...winging it...such a cliche :)
Yeah the F4 is the ultimate 'winging it' build I've done so far, I'm sure your maiden will be far more successful than mine tho ;)

Cheers
I'm not very familiar with EDFs, I've only flown one. Good luck with the F4!

I'm still trying to make sure what the CG wants to be for this biplane. I'm using some calculations I found online. I really want it to be slightly nose heavy for the maiden.
 
#20
yes plans would be great! i need a bipe in the fleet
You got it! I will work on that. I'll label all of the parts and try to show where I ended up installing the wing spars. My designs/plans don't use fold-over joints. I just butt the foamboard together with hot melt. The nice thing is that you can scale the plans however you want without worrying about the thickness of the foamboard foldover grooves. I know nerdnic has done scaling on the grooves for the foldover joints on the FliteTest plans. The joints on my planes are probably not as strong but wrapping them with shipping tape probably makes up for most of the loss in strength.


Glad to hear that great looking plane flies great too. And holy crap, someone finally gave me credit on a design tip!
No problem. You called it and I heeded your advice. Thank you.

Also, I'm not used to flying biplanes and a friend of mine warned me how they need to have coordinated turns in order to keep the tail from "dipping" during banking turns. He was right! At one point during the maiden, I had a hard time turning it in the breeze and he reminded me to use the rudder. That instantly let me get it turned around. Now I just need to remember that. Ha!

I really need to work on my landings. This one ended WITHOUT any damage but it wasn't pretty. You'll see it when the video gets done processing on youtube. (it's taking a long time to process...meh)