|Wing area:||576 sq in|
|Weight:||19.5 – 23 oz (20.5 oz as tested)|
|Wing loading:||5 oz/sq ft|
|ESC:||Hacker Master 18P|
|Prop:||11x4.7 (see “flying” section)|
|Batteries:||3s 2100 Thunder Power lithium polymer|
|Receiver:||Circus 7 full sized caseless|
|Servos:||4x Hitec HS55|
|Manuf. & distr. by:||FlyingHobbies|
Throughout the past few years, parkflyer aircraft have been exploding in popularity. This is largely due to advances in technology, both in the area of electronics and kit design. Despite these advancements, one niche has remained open – a full house aerobatic parkflyer biplane. In what started as an entrant into an RCGroups design contest, the Jitterbug has grown to fill this gap. Along with combining the grace and aerobatic prowess of the pre-war designs such as the Bucker Jungmann, the Jitterbug also incorporates rather simple construction and a forgiving nature.
As always, I first laid out the entire kit contents to take inventory. I was surprised and impressed to find music wire items such as landing gear and pushrod ends pre-bent for me. Also included are all carbon rods and tubes, additional music wire, tubing, hinge material and various other assortment of hardware required for kit construction and completion. Even the wheels come with the complete kit – a nice touch as they are the appropriate size for the kit’s wheel pants. One unique feature to this kit is an included CDROM which contains the entire construction manual, various construction photos, and other added features. Laying out the wood seemed daunting in terms of the number of sheets. However, most of the laser-cut parts are rather large, keeping parts count to a minimum.
A quick scan of the construction manual showed a great attention to detail, especially considering the fact that the introduction says: “This is not a first time builder’s kit”. The entire construction process is fantastically documented with many pictures along the way to alleviate confusion. Everything is taken into account, right down to servo count affecting BEC considerations. In addition, there are notes about the quality of laser cut kits and working with carbon fiber. Despite the warnings about laser cut parts varying ever-so-slightly from the plans, I found the parts fit and match to the plans to be excellent. To keep from getting confused over similar parts, all pieces are clearly labeled as well.
Let’s get started!
Construction itself starts with the tail feathers, as they are the easiest to build. The outlines of the tail feathers are all laser cut, leaving the builder to cut supplied balsa stock to length to form the spars and keels. In any location a laser cut part is almost (but not quite) symmetrical, there are indicators on the parts and in the instructions to keep you from putting the part in place incorrectly. With regards to the few stringers that overhang the outside edges of the tail feathers, I recommend leaving them a little long and sanding to shape after assembly is done. Tail feather construction itself went quickly and smoothly, giving a tangible early indication as to the size of the airplane (aside from the plans, of course).
Next in order is to build the wings. As the top wing tapers with no dihedral but the bottom wing has no taper with some dihedral, there are a few different techniques to achieve each end result. This is all laid out very clearly in the instructions, of course.
Wing construction is started by building the interplanar struts. These are glued to the appropriate top wing ribs early on and become permanent to the assembly. In talking with the designer and kitter, it’s been generally agreed that these struts should be made bolt-removable per the bottom attach points. This will be done in future kits but at this point the struts are permanent. Just be careful when handling the top wing while it’s not on the plane, or you could break these struts off.
Wing spar construction precludes any major assembly. This is done over the plans. The spars themselves are joined in the center by a third piece, ensuring a fairly strong joint even before any added structure.
To ensure proper alignment and keep the wings warp free, there are breakaway tabs on each rib. The ribs get laid into place. Rather uniquely, the ribs and shear webbing alternate order in placement. First you place a rib, then shear webbing, then a rib, etc. The shear webbing itself is sandwiched between the fore and aft spars both on the top and bottom of each wing, making for an amazingly strong I-beam structure once complete.
Through construction of both the top and bottom wing, plywood mounts are integrated to allow for the wing bolts. Alignment of the pre-cut holes in these pieces is automatic. Indeed, these plates become integral parts of not only the wing hold-down structure but also of the spar itself. I took a moment to check out the center section of the top wing once complete and was surprised at how solid the box fore/aft/sub-spar assembly is.
Bottom wing dihedral is precisely acquired by the use of angles drawn on the plans over which you build your spars and an angled plywood shear web/spar joiner. Through the leading edge of the bottom wing are a pair of carbon tubes which plug into the fuselage when installing the wing. The trailing edge is held in place against the fuselage by a pair of nylon bolts. The center sections of the wings are sheeted with pre-cut balsa which is integral to the structure around the bolts. As no large washers are used, this trailing edge area is also re-enforced strategically with plywood.
As the Jitterbug was originally designed for one aileron servo per wing driving both the left and right aileron on their own wing, in the middle of the wing construction you are to take some time to do aileron assembly. However, I got approved by Flyinghobbies to change things slightly. My preference was to mount both aileron servos on the bottom wing and link each aileron to the top wing. This would allow for flaperon/spoileron mixing for a variety of flying goofiness.
I moved these servos simply by adding two rails of 1/8 by ¼ balsa as shown in the picture. These rails ride underneath the wing center sheeting, leaving a gap between the top of the rails and the surface of the wing. I capped the empty space with 3/32 balsa which was later sanded down to match the contour of the wing surface. This mating of the 3/32 to 1/8 makes a strong location to mount your servos. In addition, I cut a small (1/2” square) hole in the upper center section of the bottom wing to allow for routing the servo wires.
Fuselage construction is a combination of laser cut parts and balsa stock as per the tail feathers. However, this differs from many other “stick” fuselage builds in that the sides are held together with true formers as opposed to more sticks. This makes for a very solid and true fuselage. As a start, the formers are all strategically re-enforced to strengthen key areas. Fuselage sides are constructed over the plans (right side being strategically shorter than the left to allow for right thrust) and then fuselage formers are added. In this process, the landing gear wire is also installed. The former this wire goes into is designed such that the wire is automatically level and perfectly aligned. Turtle-decking formers are also integral to the structure, aiding in keeping the tail of the fuselage straight and true.
A few features to the fuselage were new to me and are very noteworthy – first off, the entire decking behind the motor and forward of the wing is removable as a large access hatch. This allows quick and easy checks of motor temps after flying or for a motor change-out. Second, the battery hatch is also used as the battery tray. That is, the battery velcros to the hatch and the hatch is slid into position. The hatch itself slides along rails and clips into position using a small plywood piece glued to a T-shaped brace in behind the tray. Thus, the battery tray/hatch takes all of about 10 seconds to remove, allowing access to your connector, the backs of your servos, and even the receiver.
The only possible mod to the fuselage is to modify the balsa tail skid if you’re planning on flying from a harder surface than grass. The instructions mention this and I opted to re-enforce the tail skid with music wire to keep it from getting sanded down on the gravel ball diamonds I frequent.
The completed bare structure is quite strong and remarkably light. She weighs in at a mere 5.8 oz before covering and hardware. Yes, that’s only 5.8 oz for 4 square feet of wing area! My covering of choice is Nelson’s Litefilm (aka Solite), the standard in iron on lightweight covering. Using a single color would require two rolls of Solite but, as you can see, I opted for a few more colors. Covering added 2 oz to the total weight of the airplane.
CA hinges are the material of choice and are provided with the kit. As a good portion of the rudder is hinged to the back of the fuselage, fin alignment is automatic. After a quick measurement or two to align the stab, the tail feathers were glued into place.
My servos of choice are four Hitec HS-55s, mostly because that’s what I had on hand. Any micro servo will work, from GWS Picos and Naros to HS55s or any competitor. The servos simply get screwed into place on balsa sticks. Control rods are supplied in the form of carbon rods and pre-bent music wire. Just sand down the music wire and glue it to the carbon! I also wrapped the joint in thread and CA saturated it, though that’s likely not necessary if medium or thick CA is used.
My receiver of choice is an older Circus 7 full sized PCM with the case removed. Yes, this does weigh more than any of the micro receivers out nowadays but the Jitterbug can’t tell the difference either in weight or size. The receiver tray is plenty big enough to accommodate any receiver. Also, the tray sits directly over the CG so adding a heavier receiver doesn’t affect balance in the slightest.
Wheel retention is accomplished simply by the fact that the wheel pants get lightly glued into place. With the mild amount of pre-bent toe-in, the wheels work to keep the pants in place. Small balsa/ply collars inside the pants keep the wheels from rubbing. It’s a simple and effective setup!
To join the top and bottom ailerons, I utilized the plywood control horns which were supplied for the stock aileron torque rods. I made sure to bare the wood on the side of the aileron to ensure a solid glue joint. The horns attach to the inner trailing edge of each aileron and use carbon/music wire pushrods to connect the top wing ailerons to the bottom. At the top wing, I used an EZ connector to retain the pushrods and left a small V in the pushrod itself to allow for precision adjustments.
The Hacker motor is held in place by a pair of ty-wraps around the motor itself and two carbon rods. I substituted a small wrap of Velcro for the ty-wraps but the effect is the same. Also, the gearbox gets screwed into the back of the firewall.
After gluing in a few strips of Velcro for the receiver and battery pack, the Jitterbug was ready for programming!
For initial flights, I opted to activate my dual rates and add in some expo on high rates. Low rates I kept at the manual’s recommended throws and high rates are basically the maximum mechanical with a bit of expo thrown in on rudder and elevator (30% in each case). Total control throw on elevator and rudder on high rates equates to about 45 degrees in either direction. To attain the plans-shown CG location, the 3s 2100 pack was located about 2/3 forward on the Velcro strip under the battery hatch.
With a quick control direction check, it was time for takeoff!
A quick taxi out to the takeoff position showed very positive ground control despite the lack of anything steerable and great stability. She showed no signs of wanting to lift the tail, let alone nose-over.
At this point I should take a minute and explain that a different prop was used for the initial test flight. It was larger than I’d recommend and, as such, led to the motor becoming very hot. Power was naturally better but at too great a cost. The only difference this makes in terms of this review is basic throttle settings. Further flying was done with the listed prop (APC 11x4.7 SF) which has proved to be an excellent prop for the experienced throttle-management flyer. Takeoff rolls and throttle settings are the same with this prop but it requires more throttle for higher speeds, which is natural.
I flicked the rate switches to “low” and pushed the throttle ahead. At 1/3 throttle she was flying! There was no real tail-lift. The Jitterbug pretty much flew off at a 3-point attitude and started a nice aggressive climb. As the takeoff happens in a big hurry, I found no need to do any corrections on rudder which quite surprised me. This tells me that, for takeoff at least, the right thrust built into the kit is the correct amount.
“High speed” is a relative term with the Jitterbug. With a low (5 oz) wing loading, the Jitterbug’s true domain is slower speeds. However, push the left stick ahead and she will get up and move at a good clip. Vertical climbs at speed are pure beauty, particularly combined with rolls on the way up. With the built-in right and down thrust, I’ve noticed little to no trim changes when transitioning from low to high speed, even with drastic throttle changes accompanying rapid acceleration/deceleration.
Now, what would an aerobatic biplane be without some aerobatic prowess? This is the Jitterbug’s forte. The basics are done with grace and style.
Loops on low rates are accomplished in about a 10 foot diameter with full up elevator and need only minor left rudder to keep tracking straight. Outside loops are only slightly larger, owing to the stagger in the wings. I programmed in some flaperon mixing (50% initially and then hopped up to 100% for the second flight) and on high rates a loop can be done in about a 3 foot diameter with mixing and mild rudder correction. A high rate loop without flaperons will induce a wing drop in the last 1/3. However, my preferred loop with a stylish plane like this is not the smallest possible but instead large, round, and precise. Given the inherent stability in all modes of flight, larger loops are stunning and remarkably easy to keep tracking straight. Basically, the Jitterbug shows no signs of falling off or changing trims when transitioning from positive to negative G’s through the second third of the loop which is very, very nice.
Rolls can be done fast or slow, given that there is plenty of fuselage side area and control throw to compensate for slow rolls. On the stock control throws, the maximum roll rate is around ¾ to 1 roll per second depending on flying speed. On high rates the maximum roll rate hops up to 1 to 1.5 rolls per second, again depending on flying speed. Slower rolls require a minimum of rudder correction and, with my conservatively nose-heavy CG per the plans for the test flight, about ¼ down stick when passing inverted. Further flying with the CG moved back about ¼” results in rolls that only require a breath of elevator when passing inverted.
With the CG per the plans, inverted requires about 1/3 forward stick to maintain. Having moved the CG back about ¼”, I’ve found the elevator requirements drop away to less than ¼ stick while inverted. Roll stability is the same inverted as upright (neutral), which is a nice characteristic for a biplane, as they have potential to be top-heavy.
Hammerheads are absolutely stunning with the Jitterbug. With the partial stability in a hover (see below), a very scale looking hammerhead can be neatly accomplished by pausing ever so briefly at the apex before kicking the rudder over. Rudder response at the stall with throttle on is phenomenal, allowing hammerheads to be done literally around the wingtips even on low rates. However, even on high rates I’ve noticed no tail wobble on the way down. This is owing, I’m sure, to the tremendous amount of fuselage side area. The instructions got this into my head, but I can only imagine the sheer beauty of blowing smoke out behind the Jitterbug during that pause and a graceful hammerhead.
Despite the Jitterbug’s low wing loading, she will still very willingly depart a wing when asked. This includes higher speed snaps and tumbles along with a true full-stall spin. I’ve found great pleasure in starting a series of vertical rolls, transitioning into a few vertical snap rolls, finally transitioning into a spin and then flattening it out slightly. Flat spins bring the nose up to about 30 degrees low of the horizon but the rate of descent drops dramatically. Those big wings act as fantastic airbrakes in a flat spin, of course. Spin recovery is as easy as releasing the controls and flying out. With a breath of opposite rudder, the spins immediately halt on any heading you wish with no obscene over-rotation.
As I’m sure you could guess, knife edge is no big challenge for the Jitterbug with all that fuselage side area. With the CG forward per the plans, I found very minor positive pitch coupling. Moving the CG back a touch for flight #2 eliminated this. Knife edge itself requires very little actual rudder input and surprisingly little throttle as well.
Yes, this big parkflyer bipe has a taste for some 3D as well. Though not a dedicated 3D plane, the Jitterbug doesn’t claim to be one either. She just happens to do a few 3D maneuvers quite well. Hovering is remarkably stable, even with a forward CG. The hovering shown in the video below is my first attempt with the Jitterbug and she does quite well. Walls are done quite well, particularly with some spoileron mixing. Adding in a touch of left rudder helps greatly. Harriers are done adequately up to about 30 degrees nose up. Beyond that, there is some wing rock, but that’s to be expected with the thinner airfoil on these wings. Again spoilerons help with this.
You want slow speed? You got it. The Jitterbug, with a 5 oz wing loading, will slow down enough to make a ball diamond infield feel large. A full power-off stall with 3D (high) rates on the elevator produces a forward mush and no predominant nose drop.
The glide with power off and prop stopped is quite good. Granted, there’s added drag from the extra wing but she doesn’t drop like a rock by any means!
Landing roll, even in dead calm, is a few feet at the very most. Landings are done beautifully at a 3-point attitude with no bounce. She tends to come to a stop with no sideways drift, either. This speaks volumes for the design and placement of the landing gear as she has no steerable tailwheel or skid.
Whether you’re looking for a nice flying sport biplane or a full house aerobatic wonder biplane, the Jitterbug is the answer. Though I was expecting a nice flyer, I wasn’t fully prepared for just how nice she can be. The Jitterbug from www.flyinghobbies.com has, in the space of a few flights, grown to “every-flying-session” status and will be a long-time favorite of mine. What better way to accent your parkflyer airforce than to do the Jitterbug?
martins articles are some of the best ive ever seen,,THANKS for the wonderful work.
The jitterbug looks very interesting, and this one really turned out to be a great plane.
i wasnt interested in more biplanes before reading this, but now i am thinking about getting a jitterbug also!
Thanks for the feedback, whitlecj
Peter, sorry for being slow to reply. I'm sure the JB would love that power combo but I've yet to use a 2808. I hope to soon.
Just for the fun of it, here's a new video, only this time it's onboard. I realize at 31 mb it's large but more compression compromised too much of the quality, in my opinion. Enjoy