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Old Nov 18, 2007, 11:02 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Build Log
** The Pitts Challenger ** more Plans, Pics and FUN!

The Pitts Challenger

At the request of several RC’Groupers and my flying buddy, Airplane Ed, I was asked to design an aerobatic biplane. After scouring the web for a suitable subject, I came upon the Pitts Challenger biplane. The full-scale aircraft, flown by the amazing Sean Tucker, has delighted air show audiences across North America for Team Oracle.

I started with photos of Sean Tucker’s aircraft and a three view of the Challenger. Wanting to create a solid aircraft that could withstand the knocks of aerobatic flight and was simple to build, I utilized the same proven construction techniques pioneered in the Blu-Baby Primary Trainer. If you can build a Blu-Baby, you can build this semi-scale aircraft.

I also utilized the proven KFm2 airfoil for the top wing and the KFm1 airfoil for the bottom wing. That way, the plane doesn’t know if it is upside down or right side up, it still has the same great lift characteristics.

Rigging is set a 0 degrees for both the stabilizer and the motor mount, also allowing exceptional inverted flight. Control surfaces are large, enabling the aircraft to perform all standard aerobatic manoeuvres with ease.

The aircraft was designed to fly on the inexpensive BP-21 motor, so any brushless motor that produces similar or greater thrust will capably fly it.

As work commitments did not permit me to develop the beta model of this plane, RC’Groups members Tuppertn and Skotman volunteered to do the beta builds. Both of these fine gentlemen rose to the occasion and built the Pitts Challenger. Both have been waiting for weather to clear but at 6:00 am this morning, Tuppertn was able to maiden version 1.1 of the aircraft.

The results are contained in his video and fight report, which will follow this posting. To say the aircraft flew exceptionally well is an understatement. It performs the entire pantheon of classic aerobatics with ease and grace (no doubt due in large measure to Tuppertn’s flying skill) and does it at a speed that most pilots would find comfortable in a park.

This is an exceptional aircraft, combining strength, good looks, manoeuvrability and building ease into a tight package. A word of caution however; Although easy to build, this aircraft is NOT for the beginner or the faint of heart. THIS IS NOT A TRAINER!

Many thanks to Kendall and Scott for participating in the Beta Build. I owe you guys.

Specs
Overall Length: 32.9”
Overall Height: 12.08”
Wingspan: 30”
Weight: 18-19 oz
Power: BP-21 or greater
Battery: 3S
CG: 1” to 1.25” back from the leading edge of the bottom wing.
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Old Nov 18, 2007, 11:04 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
I don’t know about the “flying skill” thing. Anybody can edit 20 minutes of video into something that makes it look like they know what they’re doing.
Quote:
Originally Posted by Tony65x55
Many thanks to Kendall and Scott for participating in the Beta Build. I owe you guys.
We accept cash, visa and free beer.

Beta version 1.1 is my second complete build of this plane and represents Tony’s latest fine tuning of the airframe.

At 0600 this morning I had a window of calm after two days of high winds since completing the new version. I took her out to the local ball field and did the usual pre-flight routine. Besides the structural changes to the lower wing I had also paid more attention to the motor mount and gave it a more appropriate thrust angle at zero degrees to the h-stab. Throws were set to 45 degrees max on all surfaces with low rates at 40% with 40% expo. High rates were set to 100% with 60% expo. The maiden jitters weren't quite as bad as with v1.0 since I knew the design was good and would certainly fly. Still, it was an entirely fresh build and there's always that moment of trepidation as you first ease up the throttle.

Ground roll was straight and true. Once it was evident that she wasn't going to do anything crazy on rollout I headed up to a safe altitude to trim her out. With the proper thrust angle this time she was level at half throttle with just one click of up elevator. A slight torque roll was eliminated with a couple clicks of right aileron. Rudder was dead on.

I made several slow circles gradually tightening the radius until I'd reached the limits of the low rate throws. On low rates loops were 50-60 feet tall and nice and round with no discernible wing flex. Aileron low rates yielded very scale-looking, crisp, axial rolls. Inverted flight was a snap with just a passing thought of down elevator. The stall was more pronounced than with the other KF wings I've flown. Powering down with full up elevator resulted in a gentle drop of the nose to just under the horizontal and a slight dip of one wing. She kept flying though, repeating the move if I held onto the elevator. She never got any more aggravated than that.

On high rates she got frisky. Aileron rolls were quick, but controllable. Her snap rolls were so quick that at 30fps the NogginCam couldn't smoothly capture the flurry of movement. She has an incredible amount of rudder authority. Stall turns on high rates were a quick, tight flip around within a fuse length. WOT was dangerously addictive (dangerous for my lipos, addictive for me, that is).

The suggested CG at 0.875 from the lower LE is conservative, I think. I eased it back another 1/4-3/8 inch with good results--better glide and noticeably tighter elevator control. She's a very capable ship. It makes me wish I were man enough to handle her like she wants to be handled. I feel bad really that I'm not capable of truly putting her through some real aerobatics. With the CG back a bit I have no doubt she could even pull off some passable 3D action as well. I think she's ready for the big time. I’d like to get her in the hands of someone who can actually fly and see what she's really capable of.

Tony calls it a “snotty little fireball”. That about sums it up.

Now for the vid. It’s not flashy and despite what Tony says I’m not really that much of a pilot, but I think it’s enough to give you the general idea.

BTW - I would normally decorate an aircraft of this caliber, but since it’s a beta tester all she got was some red Sharpie underneath so I could tell the difference between up and down. I call the detailing scheme “Beta Blue with Sharpie”.

kendall

http://video.google.com/videoplay?do...42274735070882
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Old Nov 18, 2007, 11:24 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Build Log 1 - Fuse and monoblock

If you’ve built any of Tony’s planes before then this is all very familiar stuff.

The monoblock design makes assembly quick and easy and assists a great deal in alignment. I cut the the Challenger’s monoblock from 2 pink foam (FWIW, the blue stuff from Lowe’s is better) using a saber/Skil saw locked at 90 degrees. The template shows a tunnel from the battery bay into the optional electronics bay under the canopy. I cut both of these with the saber saw as shown below leaving a thinner wall into the battery bay that was easy to drill through after the fuse was glued together. Also before gluing the fuse sides I removed the canopy section of the block to be hinged later as an access hatch into the electronics bay.

When gluing the fuse sides to the monoblock alignment is of utmost importance. The tail must be able to come together centered with the plane’s longitudinal axis as well as have the h-stab slots aligned perfectly level. It’s best to use a glue with some working time to allow adjustments, I used PU (Gorilla Glue). Glue both sides at the same time and pinch the tail together to test alignment before the glue sets. With the fuse resting on its side the tail joint should be exactly 1.25 above the work surface (monoblock plus 2 FFF sides is 2.5 wide).

There’s no special trick to the tailfeathers. If the fuse sides were properly aligned then they just slide on. As usual, just double check that V-stab is neutral to the midline. Once the sides and tailfeathers are glued on there’s only the “top turtledeck” and “bottom fuse” left to add after the aft control rods are routed to the empennage.

For better access and to aid in balancing with a smaller, lighter battery I located the empennage servos in the monoblock’s electronics bay beneath the canopy. Later on when mounting the motor the thrust line will be zero degrees to the H-stab. I drew a straight line from the middle of the H-stab forward all the way to the nose for later reference when mounting the motor. 4 degrees of right thrust gave good yaw balance and negated the need for any additional rudder trim on my model.
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Old Nov 18, 2007, 11:33 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Build Log 2–Wings

For alignment, strength and weight savings I try to avoid glue joints in my wings when possible. So when cutting out the wings I chose to cut them each as a single piece. This was accomplished by folding the template exactly along its midline after cutting one side to make its mirror image other half.

The Challenger’s Kline-Fogelman wings are a simple fold-over, 6.25% step. KFm2 (top step) on top, KFm1 (bottom step) on the bottom. These can be done by gluing first then sanding the LE, but Tony's tape-fold method adds durability makes a nice, sharp, uniform LE. The bottom wing uses a 2x8" light ply brace beneath its folds at 33% cord.

Start by test fitting the KF strips on either wing. With one-side-skinned fanfold I choose to glue the foam side and tape the skinned side. Mark the outboard edge of the strip at each wingtip. Bevel a 45 degree angle into both the wing LE and the corresponding edge of the KF strip so that the bevels face each other forming a V-notch in the LE. Next lay both pieces flat with the sie to be glued facing down. Using some weight to keep the foam flat against the work surface align the beveled edges together and lay a strip of packing tape over the joint line. Turn the parts over and apply your favorite glue–HG, PU, whatever–I used UH’s “foam glue” contact cement. Here again I used some weight to keep the wing flat against the work surface during folding to avoid unseen warping. Also to avoid warping the KF strip must be folded down as uniformly as possible along its length. I used a piece of flat scrap board (laminate flooring actually) to press the surfaces together as one.

Once all the strips are taped/folded/glued place a strip of packing tape along the joints between the center strip and the ones on each side.

The rest of the wing assembly is simple and self aligning with the cabane tabs and wing slots shown on the plans.
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Last edited by tuppertn; Nov 18, 2007 at 11:39 PM.
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Old Nov 19, 2007, 07:09 AM
Registered HotGlue Addict
chaosMurphy's Avatar
Joined Dec 2006
1,469 Posts
WOW!
My winter build list grows.
Thanks guys.
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Old Nov 19, 2007, 10:07 AM
The Dude Abides
Beemus's Avatar
Brockport
Joined Sep 2005
315 Posts
Right on Tony! I was waiting for the next sweet build!
I actually built one before, but it was underpowered and had flat wings (pre-KFM enlightenment). Will try the new build, but am short on gear. Two of my servos did the twicthy thing on me and broke, and I am down a couple ESC's. The new baby has zapped my RC fund! Ah well, birthday is coming up soon )
Beemus
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Old Nov 19, 2007, 10:38 AM
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Del-Dredd's Avatar
Near Aberystwyth - Wales
Joined Aug 2004
2,119 Posts
Any pics of your battery placement, a vertical shot from the top without the front hatch/cover would show your motor mount as well. Is there any reason for the lower cutout within the monoblock, would not have thought it saved that much weight or is it an alternative battery palcement location (have to put hole in lower wing though).

Another nice plane from Tony to build, with yourself and GPW cranking them out it will keep me in new designs for ages. Just printed your Pawnee plans for future build. I have a GPW Skyray on the go and 3 view blown up for an A6 Intruder i intend to make as my first complete scratch build (prop at front), maybe an IL2 Sturmovik actually as the proportions are better and its prop driven anyway.

Del
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Old Nov 19, 2007, 11:03 AM
Out the Window
High Flyin''s Avatar
United States, FL, Alachua
Joined Jul 2004
1,294 Posts
WOW!

One of Tony's monoblock designs on steroids. I just wish I had the ability to fly it.

Ray
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Old Nov 19, 2007, 11:04 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by Del-Dredd
Any pics of your battery placement, a vertical shot from the top without the front hatch/cover would show your motor mount as well. Is there any reason for the lower cutout within the monoblock, would not have thought it saved that much weight or is it an alternative battery palcement location (have to put hole in lower wing though).

Another nice plane from Tony to build, with yourself and GPW cranking them out it will keep me in new designs for ages. Just printed your Pawnee plans for future build. I have a GPW Skyray on the go and 3 view blown up for an A6 Intruder i intend to make as my first complete scratch build (prop at front), maybe an IL2 Sturmovik actually as the proportions are better and its prop driven anyway.

Del
Del, the lower cut is an alternative placement for radio gear. The battery goes behind the motor mount.

Tony
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Old Nov 19, 2007, 11:05 AM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by Del-Dredd
Any pics of your battery placement, a vertical shot from the top without the front hatch/cover would show your motor mount as well. Is there any reason for the lower cutout within the monoblock, would not have thought it saved that much weight or is it an alternative battery palcement location (have to put hole in lower wing though).
The 4oz chinese cheapo 3s/1300 balances at the conservative CG when it's right up against the firewall. There's plenty of room to slide aft for heavier bats or a more rearward CG. That cutout in the monblock actually saves almost 1/3oz of pink foam. Although the power is pretty good, my motor is on the light side. I suppose you could mod the wing to use it as a battery compartment if you were going with a heavier powerplant, but keep in mind that there's a very necessary light ply brace across that area. Might be easier and weaken the wing less if you cut the access hatch in the side of the fuse just above one wing. Just a thought.

Quote:
Originally Posted by High Flyin'
One of Tony's monoblock designs on steroids. I just wish I had the ability to fly it.
Me, too.


kendall
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Old Nov 19, 2007, 11:53 AM
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Del-Dredd's Avatar
Near Aberystwyth - Wales
Joined Aug 2004
2,119 Posts
Thanks for the picture, speaks a thousand word as they say.

Ideal place for battery, as you say above wing would be arkward and a heavy motor. I have 2822 as well as others so motor is no problem when i get around to it and not heavy enough to require battery near wing.

Is your motor bulkhead just a piece of ply glued to the fuselage sides and top of monobloc.

Del
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Old Nov 19, 2007, 12:12 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by Del-Dredd
Is your motor bulkhead just a piece of ply glued to the fuselage sides and top of monobloc.

Del
I'm glad you brought that up, Del. I tried something a little different this time. After cutting the monoblock I cut another slot, similar to the LG slot, in the top of the monoblock where the mount was to go. I made it 3/4" deep, 1/8" wide and gave it the 4-degrees right thrust angle. After gluing the fuse sides I put some PU in the slot and slid in a 2" x 2.5" piece of 1/8" ply. I also put a thin bead of PU along the sides of the mount. When the PU foams up it locks the mount in place on all three sides.
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Old Nov 19, 2007, 12:22 PM
Into the Wild Blue Wonder
Jasta_66's Avatar
ATL
Joined Jan 2007
1,018 Posts
Looks like another winner, Tony!

Jasta
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Old Nov 19, 2007, 12:46 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Thanks Jasta, Kendall sure makes it fly nicely.

Tony
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Old Nov 19, 2007, 03:33 PM
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Near Aberystwyth - Wales
Joined Aug 2004
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Thanks for the picture of the slot Kendall, great idea, in built side thrust without the fiddling to get a firewall at the right angle (as long as your slot is cut accurately) a lot easier.

just watched the video, great flying, fast flick rolls, looks like it shifts some.

Del
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