Hobby Lobby Challenger II Scale ARF Pusher

Mike Llewellyn explores the new KMP - Challenger II Scale ARF Pusher Plane available from Hobby Lobby! This large 80" span bird fits the "highly unique" category and is sure to catch a great deal of attention at the field.

Splash

Introduction


Wingspan:80”
Wing Area:881 sq”
Wing type:Built up balsa flat bottom
AUW weight:Advertised – 8.5 lbs., Actual - 8 lbs.
Length:43”
Wing loading:20.9 oz/sq. ft.
Servos:4 – Hitec 422's
Transmitter:Spektrum DX7
Receiver:Spektrum AR6200
Battery:2 - Poly-Quest 5000mAh 2s LiPoly (wired in series to make 4s)
Motor:AXI 2826/12 Brushless Motor
ESC:Jeti Spin 44 Amp
Available from:Hobby Lobby
Cost:$288 Challenger II ARF / Short Combo - $848 / Full Combo - $1,189

Hobby Lobby has added a beautiful plane to their ARF line: the KMP/Experimental Aircraft Models Challenger II. This is a scale model of the Ultra-Light aircraft produced by Quad City. The full scale aircraft has the unique reputation of being in the marketplace for over 20 years and having sold over 3,500. In fact there is no question why the Challenger was called the "Ultra-Light Leader" by Kitplanes magazine.

The full scale bird tips the scales at just over 300 lbs. - light for a two seater by any standards. Stall is under 30 mph yet it will cruise at over 90 mph. It can carry 500 lbs of payload all with little over 300 foot take off roll. Those are impressive numbers considering they are attained using a 50-52HP engine! I am laying out these impressive statistics out in hopes that I can talk my wife in letting me try the full scale ship out. I will let you know how that goes - it should not take her long to make up her mind.

This Challenger II ARF has a fully glassed fuselage, and I would add that the fiberglass work is impeccable. The paint is immaculate, and the balsa covered built up wing and tail feathers were expertly covered with genuine Oracover. My review model is all white but it is available with blue/yellow trim applied as well. The electric conversion actually saves weight over the glow version and is very easy to do!

Kit Contents

The 1/5 scale Challenger II review package shipped from Hobby Lobby in perfect shape. It was well packaged, with a thick walled box, and the contents were very well protected. All parts were individually protected with plastic wrap.

Kit includes:

  • Painted fiberglass fuselage
  • Built up balsa wing covered in Oracover
  • Pre-covered struts using EZ type connectors
  • Wheels and fiberglass wheel pants
  • Hardware (pushrods, horns, wing tube, CA hinges, etc.)
  • Assembly guide with text instructions

Kit requires:

  • Motor
  • Propeller
  • 4s LiPoly battery
  • 4 - 40+ in./oz. full size servos
  • Receiver
  • 4 channel minimum transmitter

Included for this review:

  • AXI 2826/12 brushless Motor
  • Jeti Spin 44amp ESC with switching BEC regulator for use in up to 6s packs!
  • 2-Poly-Quest 5000 2s battery packs wired in series for 4s voltage
  • 4 - Hitec HS-411 Deluxe servos
  • Aluminum motor standoffs (1.5" used)
  • AeroNaut CAM folding propeller and 3 blade yoke (prop clearance limited) 10x6x3 and spinner

These components are straight from the Hobby Lobby recommended list of equipment for this aircraft.

Assembly

The KMP Challenger II is nearly assembled for you. While instructions do not contain information about conversion to electric, do not shy away from considering it! It is very straightforward and makes an excellent first e-conversion.

Done by the factory:

  • Fiberglass fuselage is joined, sanded and painted all ready for equipment
  • Wing is covered and includes pre-mounted strut connections
  • Surfaces are factory slotted and ready for the included CA hinges
  • Ailerons and tail surfaces are covered and ready to install

The builder needs to:

  • Install the horizontal stabilizer and elevator
  • Install the rudder and fin
  • Install radio system and servos
  • Install the power system
  • Create a battery tray
  • Install the landing gear and wheel pants
  • Install the wing and tail struts

Wing

The wing is balsa built up "D" structure, and it uses a short wing tube for attachment to the fuselage. Each wing half has a servo for aileron control. Hatches secure to a recessed wood frame in the wing.

A pre-installed 2mm allen screw activates a clamp in the wing allowing it to grip and hold the wing tube. I found this to be a clever way to ensure the wing will not inadvertently work off the tube.

With the relatively short wing tube, I am confident the wing struts are functional - do not omit them. The pre-covered and built struts come with ~1/16" music wire attached at both ends. These ends secure to pre-installed posts with EZ type connectors on both the fuselage and wings. These posts have a small allen set screw in them to secure the wire on the struts in the desired position.

Fuselage

I must say the fiberglass fuselage is a true work of art. The glass work is impeccable, and with the curved lines of the Challenger it looks fantastic. It has an area that is recessed so that the canopy windows are flush with the outer fuselage. Very impressive.

Motor and ESC installation

This was the easiest glow conversion I have ever done. The firewall comes factory installed and preset with the left thrust angles. This molded thrust angle requires that the motor be mounted off center on the right side of the firewall. Mounting it this way allows the motor and shaft to be near the aircraft centerline.

Using the AXI "X" mount as a guide, I marked the areas for the screw holes. If you have not drilled fiberglass before I have a great trick: use a sharp hobby knife to start a small hole in the glass to keep the drill bit tip from wandering on the smooth fiberglass surface.

The motor was mounted to allow clearance for a 11" propeller. Do not mount the motor too high as that will interfere with other internal structures. The higher you mount the motor, the more it will "push" the nose of the aircraft down upon power application.

The motor requires 1.5" offsets to keep the propeller from striking the fuselage. You will need a stand-off kit to move the motor back from the firewall. The recommended Hobby Lobby stand-off kit worked perfectly, but it was necessary to enlarge the holes in the "X" mount slightly to accept the bolts used in the kit.

Horizontal Stabilizer and Elevator

The vertical stabilizer fits in a pre-cut slot in the rear of the glass fuselage. It is important this joint is well glued with 15-30 minute epoxy for a good bond, since the fin also supports the horizontal stabilizer and elevator.

For additional support (and per the full scale design) there is a strut that is added from the fuselage to the horizontal stabilizer. This adds a great deal of strength to the entire empennage.

The elevator and rudder servos are set into a pre-installed servo tray. Installation is completely standard, including the nose gear steering.

Push rod installation is also standard with welcome exit openings in the rear of the fuselage for the push rod wires. The included push rods use wire on each end of a wooden rod.

(not included). I prefer solid wire push rods. Use of these aftermarket push rods allowed the battery placement with no interference worries.

If you use the included wood/wire push rods be sure you use epoxy only to secure the metal to wood bond. Shrinkwrap makes the metal to wood connection even more secure and is highly recommended.

Landing gear and nose gear

While the ARF includes wheels, I used slightly larger 2.5" tires to allow for my rough field conditions. While the landing gear setup was very typical - I should note that I did use a longer nose gear wire to allow for a positive incidence for the wing. While this is not normally recommended, I knew that the high thrust line would push down the nose allowing the plane to lift off easier. The ARF includes three beautiful glass wheel pants. They are perfect, but grass is rough on them, I will use them for paved surfaces.

In order to decrease the takeoff roll, I also splayed the main landing gear to allow more positive wing incidence. This will work well for those using grass fields.

Battery tray addition

A quick bit of work, and I had a battery tray formed in the Challenger II. Balsa and epoxy were used to secure the tray to the LG mount in the rear and a balsa block in the forward. The raised tray allows for a battery seatbelt to be used - important for large packs.

Access to the batteries is complicated by the fact that the single formed and factory trimmed window has 6 retaining screws. My 15 year old son actually came up with a winner idea - "Hey why don't you just cut out the rear window for an access". Remember on the full scale variant the rear doors are an option, so this might actually be considered a "scale" modification!

Power system

This 1/5 scale Challenger II uses the powerful AXI 2826/12 brushless outrunner motor. I have used many AXI motors, and all have given tireless, flawless service. The 12 turn Kv is 760, and it will handily replace the intended .40 size glow motor.

The Jeti Spin 44 AMP ESC has a built in switch mode BEC that enables it to provide power for your receiver and up to 8 standard servos on 6s voltage. The ultra efficient switch mode BEC makes this possible. The typical inefficient linear BECs found in most ESCs are simply unable to get rid of the excess heat of dropping the higher voltages. There is no need to use an separate battery or separate BEC with this controller.

Amp draw

The motor produced the following results:

Motor statistics
Props Amps Watts Voltage
10x6x3 CAM CF 25.6 400 15.6
11x7x3 MAS 34.3 537 15.47
11x7x3 Graupner 44.7 692 15.3
11x7x2 APCe 32.7 504 15.42

The recommended 10x6x3 CAM CF propeller is a very light load for the AXI motor and for the large Challenger II. This was especially true since I use a grass runway. With clearance for 11" propellers, I opted for more load on the motor.

The APC-e 11x7x2 propeller gave the Challenger 63w/lb performance - and most flights were at less than 3/4 power settings. This really was plenty of power for this high wing plane. Considering most aerobatics are out, the additional power is simply not needed. As you can see from the video it does not lack power.

Jeti Spin 44 amp ESC

Jeti 20 AMP ESC

  • Size – 2" x 1" x 7/16"
  • Weight – 40g
  • Operating Voltage - 6-18 NiMH/NiCd, 2-6 Li-Poly, 6-26V
  • Switching BEC produces 5.5V BEC w/max. current 5A up to 8 servos

I have long been using Jeti ESCs and they performed very well. The Spin controller is able to handle the 4s voltage and still provide power for the all the servos and receiver - highly recommended.

Batteries

I used two Poly-Quest 2s 5000 mAh packs wired in series to provide the electrons. The use of Sermos/Anderson Power poles made the serial connection easy as they are genderless and thus interchangeable. I have many of the Poly-Quest 20c batteries and have never been disappointed with any of them. The 5000 mAh capacity and relatively low AMP draw would allow long 15+ minute flights!

Completion

KMP has expertly painted the beautiful fiberglass fuselage. Since my model was all white I used some spray paint and imagination for my own scheme. After studying a number of full scale color schemes I went out on a limb and did a design of my own selection. I used 600 grit sandpaper roughed up the covering on the wings, surfaces and the fuselage to aid in paint adhesion.

Flying

The Challenger II comes "pre-ballasted" with nose weight installed in the nose of the fuselage. I debated attempting to remove some but I knew that the gang at Hobby Lobby flew theirs with all the ballast, and they have had great results. Placement of the batteries just aft of the servo tray works well anyway.

Flight testing revealed the 73mm CG required a great deal of up trim. I found that a CG of 82mm was much better, and in fact, I would not hesitate in moving it back further.

I used the Spektrum DX7 transmitter and AR6200 full range receiver for this plane. Rates were set as recommended in the manual with ailerons at 16mm and elevator at 12mm. Rudder was set to 18mm. No high rates were mentioned, so I set those for about 20% more throw.

Flight testing showed the 12mm elevator was not sufficient. I settled on 18mm for low and 22mm high. No exponential rates were mentioned so I used 15% for all primary flight controls and these settings worked well for me in flight, however rates are a very personal preference.

I set the flight timer to count down from 10 minutes. This gives an audible warning long before the 5000mAh battery is depleted.

As you can see, the Challenger II is a very attractive model. I really like the fact that the model is not commonly modeled.

Takeoff and Landing

Although I had slightly extended the nose gear it was clear on my first takeoff roll that it was not enough positive incidence for rotation. I further extended the nose gear giving more positive wing incidence, and I splayed out the main gear so that it would sit much lower. Both of those helped and allowed the Challenger to lift off and climb out. These were both due to the high thrust line.

I also found the elevator response to be a bit light. I still regularly use full up elevator for rotation. Do not be reluctant to apply the needed force for liftoff!

The thrust line on this model will cause the nose to dip with power application indicating the need for a bit of motor upthrust. I simply added washers to the motor mount for about 2 degrees of up thrust, and that has helped the power on nose down tendencies.

I found the AXI brushless system and the large wing gave a good climb rate using the APC-e 11x7x2 propeller. I used 60-70% throttle settings for scale flight characteristics. This is not a highly aerobatic airplane so additional power is simply not needed. Hobby Lobby uses the 10x6x3 Aeronaut CAM propeller, and you can see the Challenger is perfectly happy with it.

Certainly the 44amp ESC and motor are both capable of producing higher power output if you desire just a bit more but one note about power: the more you use, the stronger the nose down at power up tendency will be. I recommend 500w for great scale flight characteristics.

Landing with positive wing incidence allows for lazy, slow nose high setups with the nose gear left hanging in the air. The Challenger slows very well and settles in effortlessly. Even with the rearward CG and positive wing incidence the plane lands fine.

Special Flight Characteristics

Any aircraft with a high power thrust line needs some special consideration in flight. Power application will reward you with a slight nose down push. Not a big deal, but it does warrant your attention on landing approach. If you need to apply more power - apply power slowly.

This plane stalls very predictably for a model with this wing loading. When pushed to a stall, you get a gentle nose drop. The Challenger II slowed very significantly before stall, and it remained fully controllable right down to the last second.

Stall recovery was quick, with smooth throttle application. As with many high wing airplanes you will find adverse yaw is present, so be sure to follow the directions regarding setup of the aileron servo. If you adjust the servo arm so that it is off one or two splines off of 90 degrees the servo will mechanically give more throw in one direction - up. Co-ordinated turns using rudder, aileron and elevator look the best and are certainly appropriate. If that is not your thing, using the transmitter to mix rudder with the aileron works well also.

Aerobatics are not the strong suit of the Challenger II. Rolls were not totally axial, just as expected with this high wing plane. I found the recommended 16mm aileron throws are responsive, but it takes a while to swing that large wing around! No question that aerobatics are not part of the full scale flight pattern!

Thanks to Dawnron1 for these excellent flying shots:

Is this plane for a beginner?

While definitely not for the first time pilot, the Challenger II is well behaved in flight. But the high thrust line does require thought and attention in flight, so the Challenger is best suited for seasoned pilots.

Flight Video

Downloads

Conclusion

The Hobby Lobby recommended AXI brushless motor system provides abundant power for this 8 pound scale bird. The Challenger II is has unique looks and is large with an 80" span. That is 1/5 scale! Assembly and conversion to electric was easy and completely straightforward. In fact, I think the electric conversion was easier than the glow engine setup would have been.

I always look for scale planes that are not commonly modeled, and the Challenger II certainly fits that category. For something unique, check out the KMB Challenger II!

Pluses:

  • Unique looks
  • Looks fantastic in the air
  • Short assembly time
  • Fiberglass fuse and wheel pants are a work of art
  • Easy glow to electric conversion
  • Electric version actually saves weight
  • Flies well even at lower power levels

Minuses:

  • Upthrust needed but not molded into the firewall
  • Included nose gear is too short, longer gear is needed for proper takeoff rotation
  • Pre-ballasted nose for electric conversion not fully needed
Last edited by Angela H; Sep 11, 2007 at 10:23 PM..
Thread Tools
Sep 12, 2007, 08:02 PM
Registered User
lake flyer's Avatar
A neighbor of mine has a full size one of these on floats , unfortunately he hasn't finished it yet.
Sep 12, 2007, 08:42 PM
Fokker Ace's Avatar
Well done review of a nice, big model.

I wonder, given the subject and cost associated, how many will go for this one.
Sep 12, 2007, 09:18 PM
3DHobbyShop disciple
waltj2k's Avatar
Wow that flys quite well. When I saw the AXI 2826/12 on the back of this large plane I thought it would be slowflyer sluggish. But the video proves that this is a very nice setup.

This is beauty of a plane guys.

Great review Mike.
Sep 13, 2007, 08:42 AM
Registered User
pda4you's Avatar
Thanks guys - the Challenger is a big airplane - 1/5 scale so not small by any means but you can tell the AXI pulls it very well!

Mike
Sep 13, 2007, 11:43 AM
I land with enthusiasm
Arck's Avatar
Quote:
Originally Posted by pda4you
Thanks guys - the Challenger is a big airplane - 1/5 scale so not small by any means but you can tell the AXI pulls it very well!

Mike
Congrats Mike for the review, you confirm that it is a good scale plane to convert to electric,,,,,
werner
Sep 14, 2007, 10:36 AM
3DHobbyShop disciple
waltj2k's Avatar
Quote:
Originally Posted by pda4you
Thanks guys - the Challenger is a big airplane - 1/5 scale so not small by any means but you can tell the AXI pulls it very well!

Mike
You mean pushes it dont you
Sep 14, 2007, 09:40 PM
Registered User
pda4you's Avatar
Quote:
Originally Posted by waltj2k
You mean pushes it dont you
Actually I think I do!!!
Sep 15, 2007, 09:29 AM
Electric Coolhunter
Thomas B's Avatar
hmmmm..it must be a UAV..... or perhaps the Invisible Man is the pilot??..
Latest blog entry: 2014 events and travel
Sep 15, 2007, 11:10 AM
Registered User
pda4you's Avatar
Quote:
Originally Posted by Thomas B
hmmmm..it must be a UAV..... or perhaps the Invisible Man is the pilot??..
That is just what Wendell said........
Sep 15, 2007, 11:23 AM
Electric Coolhunter
Thomas B's Avatar
Quote:
Originally Posted by pda4you
That is just what Wendell said........

then I need to improve my material..
Latest blog entry: 2014 events and travel
Sep 20, 2007, 12:44 AM
Registered User
Gyroflyer's Avatar
Oh man, this isn't fair. What an awesome looking plane. I'm now starting my third real Challenger and the wife would kill me if I bought an rc one.LOL

I've been looking at this little plane for some time. Once I get a few other projects finished, this will be on the top of my list.

Here's the one I sold and building another just like it.

Mark
Last edited by Gyroflyer; Sep 20, 2007 at 12:51 AM.
Sep 20, 2007, 08:16 AM
Registered User
pda4you's Avatar
Too cool Mark - I am trying to talk my wife into the full scale - right now that is not an option! So I would trade you .

So tell us how much you love flying the full scale ship - I am totally jealous!

Mike
Sep 20, 2007, 01:29 PM
Registered User
Gyroflyer's Avatar
Quote:
Originally Posted by pda4you
Too cool Mark - I am trying to talk my wife into the full scale - right now that is not an option! So I would trade you .

So tell us how much you love flying the full scale ship - I am totally jealous!

Mike
LOL!! The nice thing about the full sized Challenger is that you can buy it in sub kits for poor people like me. Oh, By the way, I want to apologize for saying "real" Challenger in my previous reply. The model is real also, just smaller.

Mike, you did a nice job on the review. I really want this plane after seeing you flying it. Ok, let's trade. I've only got the tail section and fuselage so you'll have to buy the rest.LOL!! Do you know if they make floats for this bird? I've never flown floats but it sure would be cool on this bird.

Once again, thanks for the great review and getting me interested in this little model again.

Mark
Sep 20, 2007, 01:56 PM
Registered User
pda4you's Avatar
You are welcome - I may take you up on the trade!

KMP does not make floats but I bet these would work.....

http://www.hobby-lobby.com/floats.htm

Mike


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