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Scale Build Off - 1/4 scale (55") Pitts Challenger III

wilmracer

I build things that fly (sometimes)
Mentor
#1
Scale Build Off - 1/4 scale(58") Pitts Challenger III

So I'll be getting an earlier start on this year's build-off build. I'll be doing a 1/4 scale Pitts Challenger III in the ORACLE scheme as flown by Sean Tucker

This one has been on my build list for a while. A few years back a VERY lucky break scored me a chance to go on a ride-along with the Collaborators - The aerobatic team sponsored by Oracle (and by a friend of the family's company) and lead by Sean Tucker in this beautiful biplane. I got to do a long formation aerobatic flight with the team and even got to fly the Oracle Extra 300L for a bit.

The day after the ride along my father and I went out to Andrews Airforce base for an airshow and got to go on the field during Sean's solo routine. My father and I got to hold one of the poles for Sean's famous ribbon cut. If you're not familiar this is when Sean comes in low and cuts 3 ribbons at 20' off the ground. He cuts the first in knife edge, the second in opposite knife edge, and cuts the third ribbon inverted. Truly amazing to have this aircraft blast within feet of you at 200mph UPSIDE DOWN!


I've wanted to tackle this build ever since that weekend but have been on a warbird kick lately. I've decided that I'm ready from a break from retracts and gear doors so this one got bumped to the top of the list :cool:

A few shots I got of the Pitts Challenger. In the first few you can actually see me in the Oracle Extra 300L. The last two pictures are ones I took of Sean's routine just before we hoisted the poles.

So enough backstory... On to the build.

Specs:

Wing Span: 55" Top,
Length: 51.5"
Power: TBD
Weight: TBD

Extras: Have a few things in mind but also TBD
 

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wilmracer

I build things that fly (sometimes)
Mentor
#2
One last thing to share before diving into the build... Here is the flight video from the ride along
 

AkimboGlueGuns

Biplane Guy
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#4
That's a good build. I met Sean a few years back at Oshkosh and got to find out lots of stuff about the plane. Will you be doing all 8 ailerons?
 

willsonman

Builder Extraordinare
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#5
What a great subject. I would highly recommend Callie Graphics for your finish work. Should make it much less painful for you. Also, Check with Keith Sparks at Park Flyer Plastics. He may have a canopy that would be suitable for your needs. Some fantastic opportunity to demonstrate many different build techniques. For the size, I would recommend a .46 or .32 size motor on 4S with a 12x6 or 10x5 prop. Should be doable in less than 5 pounds if you are building with foam.
 

wilmracer

I build things that fly (sometimes)
Mentor
#6
That's a good build. I met Sean a few years back at Oshkosh and got to find out lots of stuff about the plane. Will you be doing all 8 ailerons?
Probably. I need to do a bit more research to be honest. Need to find out more about any special mixing that might be going on. If there isn't anything more complicated than a DX9 can handle then I'll do it for sure. Maybe a low, mid, high rate with 4 ailerons and a low, mid, HOLY-$H!77 with 8.

Do you have any details on how the inboard ailerons are mixed? Are they essentially slaved to the outboard ailerons or does he also use them independent to the outboard for extra yaw authority and maneuverability? To be honest I'm not a 3D pilot, or even that good with complex aerobatics, so for my flying style it would be overkill.
 

wilmracer

I build things that fly (sometimes)
Mentor
#7
What a great subject. I would highly recommend Callie Graphics for your finish work. Should make it much less painful for you. Also, Check with Keith Sparks at Park Flyer Plastics. He may have a canopy that would be suitable for your needs. Some fantastic opportunity to demonstrate many different build techniques. For the size, I would recommend a .46 or .32 size motor on 4S with a 12x6 or 10x5 prop. Should be doable in less than 5 pounds if you are building with foam.
I'll probably be hitting Callie up for the graphics... there are a LOT of sponsors on there.

I'll see what Keith has in the way of canopies. Worst case my vacuum former big enough to pull it if necessary. It would be PITA but it is doable.

Still in the early research phase at the moment. May not start building until November. I want to have a solid build plan before I start bashing.
 

wilmracer

I build things that fly (sometimes)
Mentor
#8
Oh, and does anyone have experience with any of the electric smoke systems? I'm thinking of trying to put one on a removable tray so it can be optionally installed to give more presence in the air. Just playing with the thought... not committed yet.
 

AkimboGlueGuns

Biplane Guy
Mentor
#11
Wilmracer, the inboard ailerons move less than the outboard ones do so Sean can control the airplane better in high AOA and hovering maneuvers. I started tinkering with a manual (non electric, non gas) smoke system that uses baby powder as the smoke. I'll probably write an article on it once I finish the valkyrie project I'm working on for Julian.
 

wilmracer

I build things that fly (sometimes)
Mentor
#13
Man... It has been a slow morning here and I've been doing a LOT of research. I have good references on the Challenger II... Challenger III references have been harder to come by but I'm getting most of what I need. The fact that there have been so many version of the Challenger makes it tough when you're looking at images. I'm sure by the time I'm done with this build they will all look completely different to me but right now they bleed together like crazy.

As for construction method... I'm going to be using some techniques I haven't tried before...

  • I'm building a hotwire bow this week and this will be my first foray into cutting wing panels. May be tough as the Challenger III has a newly designed wing that tapers and curves a bit but I think it can be done.
  • I think I'm going to try a different method for fuselage construction. The plan is to build an accurate foam plug and then use that plug to lay up a fiberglass and CF fuse that will then be cut off of the plug. The plug can then be sacrificed to get accurate formers that will reinforce the hollow FG/CF section. I've seen John Morgan and others use this technique with great success and want to give it a shot myself.
 

AkimboGlueGuns

Biplane Guy
Mentor
#14
Using the plug would be a good way to make the plane reproducible. Will you be putting carbon in the wings? I'd imagine you'd need a pretty beefy spar for this one.
 
#15
Hey! Looks like a great project. I actually work for Oracle as a consultant ;) and have always loved that plane. Good Luck, look foward to following along.
 

wilmracer

I build things that fly (sometimes)
Mentor
#17
John Morgan techniques=win
Yup.

AkimboGlueGuns: Yeah. I haven't settled on exactly how I will do the spars. CF arrow shafts are an obvious choice but I will give it some thought. BTW... I've learned that the inner ailerons are apparently setup to move at 50% the rate of the outer ailerons. Should be easy to replicate either mechanically or with 8 individual servos. I'll probably be going with the 8 servo route... so likely it will be 10 servos. Plan to do scale-ish pull/pull mechanisms for the tail surfaces.
 

willsonman

Builder Extraordinare
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#18
If you need a few lessons on hot wire cutting let me know and we can get together. It takes a little practice but given your skill set, you will catch on fast.
 

wilmracer

I build things that fly (sometimes)
Mentor
#19
If you need a few lessons on hot wire cutting let me know and we can get together. It takes a little practice but given your skill set, you will catch on fast.
I may take you up on that. Let me get my materials together and get this bow built and we can look at our schedules.
 

wilmracer

I build things that fly (sometimes)
Mentor
#20
Willsonman:

So I put together the bow... It is made from pine and the arms are supported on both sides. I'm planning to use a bungee cord between the two screw eyes in the back section. Plunge depth is a maximum of 17.5"

My intention is to run the wire between the two posts on the outside of the arms. There is a grove sanded in each of the arms to prevent the wire from slipping.

Two questions (and I'd love any other thoughts/suggestions)... First what gauge wire would you recommend? Second, is there a particular charger or power supply you would recommend? I've read that some of the newer chargers have safety features that keep them from being used like this.

I've got some 10 gauge wire that I think I'll be using to hook everything up. Still working through that part.

On Edit: Forgot to add picture of bow.
 

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