Well, my bench has been empty (besides the mess) for a while and I felt like I needed a new project! I wanted something to fly at electric-only events, and I've always really wanted a bipe. I also had a few batteries for my smaller Osiris pattern plane that I realized I could use in series.

So, I settled on the awesome PAU Pitts Challenger. I went with the Challenger over the Bulldog because the all-red covering is a perfect canvas for a custom scheme. I talked to Herve and he was very excited about seeing the Challenger electrified.

This is my set-up:

Power:

Scorpion 5525-225KV motor
Scorpion 130A HV ESC
Xoar 22x10 Electric prop
Sky LiPo 5S 5000 mah batteries, 2 in series for 10S 5000

Radio:

Hitec 7955TG on rudder
Hitec 7955TG on elevator, only one servo mounted forward in pull-pull configuration for CG reasons
Hitec 7775MG on ailerons (these are low-profile so I can save a few ounces, but they have plenty of torque and they are lightning fast)
Hyperion 2100 mah Life battery into Smart-Fly SuperSwitch

My weight goal is 14 pounds. Having weighed all of my components, I think I can achieve this without too much trouble. I plan on replacing some of the hardware, modifying the motor box, using carbon landing gear, and of course I won't need a throttle servo, ignition battery, fuel tank, etc. I also plan on building a removable hatch in the top of the fuselage for battery access.

It's a bit different than a normal 50cc electric set-up. Usually, for a 50cc electric, 12S 5000 mah batteries are used, for about 3500-4000 watts. However, I already have a bunch of 5S 5000 mah batteries, and the Challenger is a bit smaller and lighter than most 50cc airplanes. The Scorpion 5525-225 motor is rated for 2975 watts continuous. For good 3D power, you want at least 150 watts per pound, with 200 being a real sweet spot. Even if I come out a pound overweight I should still have good performance with this set-up.

This build is going to take some time, as there is a lot of work to do and I am still in the middle of the flying season. Hopefully I will have some pictures up on Wednesday night or so.

Nice going Cody. I've been contemplating an electric my self.
Looking forward to this one.

Any update with this as Im planning one two ! I will be using the same motor. mine produces 2850 watts in my MX2 73 ( 26% )

Unfortunately I have been pretty busy with work and a few other projects so I haven't had any time to do much work on the Challenger. I am also still waiting on some servos.

However, I did complete the design of a new motor box.



The stock motor box is a bit overbuilt for electric, and would have required the use of some extremely long standoffs (about 4.4 inches). By designing a new motor box, I will only need 1/2" standoffs (I didn't design it to have the motor mount flush to the box in case I want to use a larger motor later), and I save between 2 and 2.5 ounces in wood alone.

Hopefully I will have the pieces laser cut soon.

Cool project! I'm looking forward to seeing how it turns out!

I had a lot of fun with mine... I remember needing to locate the batteries up front to get final CG. I did have elevator sevos in rear and throttle and choke servo just aft of CG. I only thing I didn't like was haveing to flip her over at the field to attach the bottom wing, would rather have CF tube with bolts. Good luck will be watching.

if anyone is wanting to add a scale pilot to ther Challanger I have some real nice 25% scale mosel pilots of Sean D Tucker that is spot on and would fit nice in this plane . to see more of my pilots check out my facebook photos http://www.facebook.com/media/set/?s...7245097&type=3 or contact me by e-mail at flyjay77@yahoo.com .

jason,

Originally Posted by Wojcigitty

Unfortunately I have been pretty busy with work and a few other projects so I haven't had any time to do much work on the Challenger. I am also still waiting on some servos.

However, I did complete the design of a new motor box.



The stock motor box is a bit overbuilt for electric, and would have required the use of some extremely long standoffs (about 4.4 inches). By designing a new motor box, I will only need 1/2" standoffs (I didn't design it to have the motor mount flush to the box in case I want to use a larger motor later), and I save between 2 and 2.5 ounces in wood alone.

Hopefully I will have the pieces laser cut soon.

If it wouldn't be much trouble, would you mind posting the dimensions on the stock motor box? I just picked up a used Challenger and am probably going to have to rebuild the motor box which has already been "liberally modified!" Thanks for any help you might provide.

Originally Posted by F-16Wpnstech

If it wouldn't be much trouble, would you mind posting the dimensions on the stock motor box? I just picked up a used Challenger and am probably going to have to rebuild the motor box which has already been "liberally modified!" Thanks for any help you might provide.

PM sent!

F-16. Have you been working on the Pitts? I am thinking about doing the same and was wondering if it has worked out. My concern is getting it to cg.

...

OK, it’s been a while since I’ve had a chance to update this thread. Sorry for the delay! But things are progressing well and I think I should be able to maiden this weekend and then fly this thing at SEFF.



I decided to first tackle the most tedious and time-consuming task: making the new interplane struts. The original struts are very well built and perfectly adequate. However, I knew I could save a little weight here. I also wanted to add a little side area…I’m not sure if that’s necessary (or wise), but I can always change back to the original struts if these don’t work well.



First I traced the original struts on some 6mm depron. I added about 1.5” in width, then cut them out.







Next I sheeted the foam with 1/16” balsa. I added some hardpoints and reinforcements from 1/16” ply where the screws go through. I used Gorilla glue to glue the sheeting on.







I weighed them down and let the glue cure.







Then I trimmed the excess sheeting away and finished the ends with cross-grain 1/16” balsa. Trimming away the excess sheeting was difficult because the glue had oozed out and hardened everything near where I wanted to cut. This was extremely time consuming and I wouldn’t do it again like this. Instead, I would simply sheet a rectangle of foam, then cut it out to shape on a band saw…this would keep everything nice and uniform. After some sanding and filling I covered the struts and they are finally good to go.



I got the pieces for the motorbox cut by a friend of mine. We originally planned to laser cut it, but his laser wasn’t strong enough to deal with the firewall so he used a CNC router. They came out great in any case after a little trimming.







Gluing everything together:











I reinforced the corners with triangle stock as I did it. It came out very nice.



Next step was to cut off the original motorbox.









I left ½” of the material proud of the F1 former. The new motorbox just slips over this material:







Next I put the blind nuts in the back of the firewall.







I took some time at this point to lighten the F1 former. It’s designed around a gas motor, so it’s much stronger than necessary for my application. There was also a can tunnel which I enlarged to simply cut away wood.







I test fit the cowl and motor to make sure nothing was drastically wrong.







Everything seemed to fit well, so I glued the motorbox on. I used Gorilla glue here because it’s light, strong, and as it expands, it forms a fillet that reinforces the joint similar to triangle stock. In fact, if you ever want to strengthen the gear cage on a smaller airplane, just pour some Gorilla glue in the fuse over the gear plate. It will expand and reinforce everything…looks ugly but it works well.







I only used 1/16 ply for the sides, top, and bottom, and 3/16 for the firewall. It was very flimsy before I glued it together but now it’s very stiff. Even so, I don’t totally trust it yet. I think I’m going to reinforce the firewall with some carbon plate, and put some carbon strips on the sides and top of the firewall to tie it to the fuse. Besides, carbon adds bling, so that’s gotta count for something.



I also made room for using ¾” spacers behind the motor’s X-mount. If that Scorpion isn’t enough power, I can trade up to something bigger and remove the spacers.



Next I had to cut the hatch out for the batteries. This is always a challenge on a biplane but I think this will work OK.









The hatch will be in the area just below the cabanes.



Next I decided to do the landing gear. I elected to save some weight and use Graph-Tec carbon landing gear. It’s designed for the Great Planes Ultimate, but the dimensions were pretty close to identical to the stock gear. It has a little rearward rake to it, which looks nice, but if it causes any nose-over issues I’ll shim it or replace it.



Since the gear is not drilled, I needed to make some holes. My favorite way to do this is to first put a piece of masking tape over the gear plate where the gear will bolt.







Poke some holes through the masking tape, then put that over your gear. You now have a perfect pattern for your bolt holes. I also decided to use Azhar’s awesome new Spot-On axles.







I screwed the gear to the fuse, then installed the tailwheel. I used the stock PAU tailwheel assembly but replaced the wheel itself with a Maxx products lightweight electric wheel, because I was a bit worried about getting the CG right on this plane, and every gram I can take off the tail is good.







I’m not sure how well that wheel will hold up, though. If it breaks I’ll find something stronger.



Next I decided to mount the stab and fin. First step here is to remove the excess covering. On the fuse, I trimmed the covering away with a foam cutting wand, available at a craft store for 10-20 bucks. It’s very thin, so you don’t get melted covering all over the place. To cut away the covering on the fin and stab, I used an old soldering iron. I like this because you don’t accidentally cut into/score the wood.











After everything was lined up, I glued in the fin and stab.







Next I decided to join the wings. No drama here…I was a bit worried about setting the dihedral angle angle but the fit is so snug that you don’t have to worry about it. I did add some 5 mil Dave Brown carbon fiber strapping to the top and bottom…I’m sure it’s not necessary but it about doubles the strength for no weight penalty.







I held the top wing together with binder clips.







Next I installed the Spot-On aluminum double truss horns and ball links in the elevator. These things are awesome…super light, look great.







After that I hinged the rudder and elevator. I had to set a bit of a gap to get 3D throw but it looks pretty good to me.







Next I opened up the bottom of the fuselage to allow air to escape. I cut away the covering, leaving about 1/8” behind, then sealed that down with the iron. I was tempted to just burn it away with the wand but I was worried that it would peel up eventually.









Next I decided to do the rudder linkage. I used the stock Rocket City-style horns here….they work very well.







The rudder servo is a Hitec 7955. Overkill but whatever. I used Spot-On arms, with their new specialized cup washers and socket head cap screws. These are so much easier to deal with than the phillips style that come with the servos...highly recommended.







I ran the wires in an X configuration. To keep them from rubbing, I slipped each wire through a piece of inner pushrod, and held the pieces togher with a piece of heatshrink tubing.







I used the Secraft wire tensioners to keep everything snug…these things are awesome. The aluminum piece attaches to the cable, and then that aluminum piece is attached to the ball link or clevis with a small turnbuckle. This means that you can tighten the cables by simply twisting the turnbuckle without twisting the cable or taking a ball link off.







Next I did the elevators. Same thing here…Spot-On arm, screws, and washers, this time with four ball links on the arm. I also used a Spot-On side mount.







I mounted the servo approximately where the pilot would go. The rear of the servo mounted nicely to the rear crossmember of the canopy, and I made a beam to support the front. It’s shaped a little funky to remain strong while taking the loads of the servo and clearing the arm as it swings throuh its movement, but it works well. I was able to stall the servo by hand and nothing broke.







This took a lot of figuring and consumed a lot of time. Next I ran the cables.









The top wires came out the turtledeck sheeting, but unfortunately all I could do with the lower wires was run them through a hole in the covering. It seems OK so far, but I did reinforce the place it comes out with a piece of blenderm. Of course I used Secraft tensioners here as well…gotta keep those elevators tight. This install was a lot of work, but I’m happy with the result. Everything moves smoothly, it’s very tight, and it keeps a lot of weight out of the tail.



Next I did all of the aileron linkage. Again I elected to use Spot-On double truss horns here. They are strong and offer significant weight savings over the stock Rocket City style horns, at the expense of a little adjustability. I first tacked them in place with a little medium CA.







I held them in with 6 stainless #2 wood screws that I found in my hardware bin…drilled the holes, dropped in some thin CA to harden the holes, then drove the screws in. I was a little concerned about how strong this would be but I gave it the ol’ tug test and it’s very secure. Besides, I have four ailerons, it don’t matter if I lose one or two.







Next I opened up the covering and started installing the servos. I decided to use Hitec HS-7775MG low profile servos here.







These things are fantastic. Insanely fast, great resolution, and really good torque. They are a great servo anywhere you have a standard sized opening and you want to save some weight. I installed them with the provided Hangar 9 titanium turnbuckles and some Spot-On 1.5” horns. I wound up using the inner hole; the geometry wasn’t right with the outer one.







Next I installed the cowl. The kit has tabs with blind nuts already installed which makes this cake. I elected not to use the lowermost of the 6 tabs because as an electric I don’t think they are necessary… not as much vibration.











The kit comes with bonded sealing washers which are extremely secure.







Next I trimed and installed the spinner and prop. I used Chris’s tutorial and it worked great…super easy to do.







Next I installed the wheelpants…nothing special here.







The canopy went on next. I lined it up, and taped it in place.







Next I drilled a bunch of holes and used more #2 wood screws to hold it on. Looks pretty slick.







I decided to use wood screws here instead of guing it on in case I ever need to get in and mess around with that elevator servo again.







I still have more to do, but it’s going very well so far. It’s been a fun project for sure.



Here she is put together at our club’s meeting…looks super sleek!

Nice job Cody! I can't wait to see some video. I really like what you did with the elevator servo, good thinking!

Nice going Cody. Nice engineering.

You"re going to bring that to Joe Nall. Right?