Budget RC ULD
By David R. Vaught
Photos: Dawn L. Vaught
The RC aircraft model industry continues to push the envelope not only in design, but also with the material used to make planes, how those materials are incorporated and most notably, the distribution created to support the demand for these wonderful planes. BudgetRC.com is an example of a small company utilizing EPP foam in their newest creation: the ULD aerobatic trainer biplane.
I’ve probably grown complacent with the number of RTF planes I fly. Building is something I truly enjoy, but for some reason I don’t do enough. Having grown up with balsa and silk span, I’ve come a long way to now building and flying foamies. My first BudgetRC plane was one of their combat fighters and after building and flying that plane, I had to have another.
The ULD or “U Like Dat” is completely built with CNC-cut EPP and a small amount of Depron. EPP foam is extremely durable, bends and flexes with incredible resilience and it’s both CA-safe and paintable. For any pilot wanting to enhance his or her aerobatic skills and eventually transition to 3D flying, the ULD is a great beginner to intermediate 3D choice. The ARF kit requires glue, paint, hinge tape, three servos, brushless motor and ESC.
As we marvel over the shear variety of plane designs, the standard of incorporating instructions into products being shipped is being changed by companies like BudgetRC. Sold as a plane in a plastic bag, the instructions are downloadable. The benefits of this method are many and include the ability to make changes and updates to the instructions when necessary, lowered cost for the kit, multiple photographs and increased clarity.
Without too much detail, the ULD build is going to take you a couple of evenings. Don’t be in a hurry. One little item I have discovered is Ultimate Glue. While you may be used to using CA and accelerator, consider using this glue on EPP because when it dries it’s still flexible. As a trainer, accept the fact you’ll be connecting with the ground from time to time, so allowing the EPP wing, tail and fuselage to flex through the glue is important. It will extend your build time and remember that the glue will not set well in an anaerobic state. However, in the end, your build will survive more crashes with less damage.
Almost all of the surfaces are reinforced with carbon strips. These strips are lightweight and when sandwiched within the EPP material, they create just the right amount of stiffness. One of the many well-designed features of the ULD is the reinforced nose and motor mount. The design includes fuselage doublers on both sides that support the lite-ply motor mount. Side stiffeners of Depron firm up the fuselage as the first line of reinforcement. Installed on the underside of the fuselage stiffener are additional angled stiffeners that make the fuselage as rigid as necessary.
With the wings, tail and fuselage components completed, you need to paint the foam. Any cheap enamel will do fine. The EPP accepts paint very well and dries quickly. Protect the Depron or spray very light coats of paint. Use Derm blend tape to hinge the control surfaces after you paint. There should be careful consideration given to keeping everything flat and square. Lateral stability is provided by carbon rods passing through the cabane center and between the fuselage and wingtips. The landing gear is also carbon and optional. I don’t recommend it if you’re flying outdoors off grass.
The placement of the electronics is pretty much as shown, but I found the need to get my battery further forward than shown for the correct CG. Use Velcro to attach your components. Mount your motor so the wire leads exit on the right side of the plane.
Carbon linkages are provided and as a final step, these must be installed accurately. After mounting your servos with hot glue, prepare the servo arms with heat shrink and route the linkages to the control surfaces. A lite-ply control horn is used on the tail components and carbon shafts are placed in the ailerons. I thought the latest update for installing the linkage to the control horn proved too stiff, but in flight it was never a problem.
At first, the build may seem extensive, but the ULD comes together quickly. Once the painting is done and the final components are installed, you’re on the down stroke. That being said, it’s a long down stroke that requires you pay careful attention to centering your transmitter trims, the servos and control surfaces before you finally lock the linkages down with hot glue and CA. The ailerons present the most concern as they need to center exactly. I can assure you being diligent here will pay dividends in your flying quality.
In the air
I did not install the landing gear as I knew hand-launching would be easy and without a smooth surface to land on, the gear would be damaged. As an indoor flyer, you’ll have no problems with the landing gear.
Within the first seconds of your first flight, you’ll know your rudder skills. If you’ve been flying without using the rudder, you’ll notice the ailerons roll the ULD, but do not completely turn the plane. The rudder has a huge amount of authority. In fact, on high rates, the ULD will pivot 360 degrees on its tail. It might take you a few minutes to coordinate your thumbs, but once you do, you are truly on your way to learning aerobatics.
As you continue to fly the ULD, you’ll also become aware that throttle management not only moves the plane forward, but it also increases the airflow over the control surfaces. EPP is not a slick surface and because of that unique characteristic, your flights are not at high speeds. You’ll certainly appreciate this as you learn to coordinate maneuvers. You’ll also appreciate the quick response of the ULD for vertical pull-outs. Overall, the components suggested by BudgetRC are well thought out and have gone through considerable testing. That effort is evidenced in the ULD.
If you’re someone wanting to learn aerobatics, I just can’t say enough for the controllability of the ULD’s slow flight. Once I had the plane trimmed and settled on the battery location, I could fly into a light wind with almost no forward movement. The harriers are incredible and with little effort, I could drag the tail on the ground either upright or inverted. Slow rolls are just that and because of the speed, you can learn when to dial in and out the rudder in coordination with the elevator. Knife-edges are almost automatic. The ULD made me look good through every maneuver.
If the ULD has a fault, it becomes evident outdoors. On a calm day, you’re fine, but when you’re over five miles per hour, you’ll notice the lightweight plane buffeting and really struggling as the wind catches the wide body. On a couple of early fligh
ts, I thought I might not get it back. Because of wind limitations, the ULD is a perfect indoor flyer. The slow flight lets you keep it close and under control at all times. The only change recommended indoors is to use a smaller battery.
+ 20 degrees, 20% expo (low)
+ 40 degrees, 40% expo (high)
+ 20 degrees, 20% expo (low)
+ 40–45 degrees, 40% expo (high)
+ 30 degrees, 20% expo (low)
+ 60 degrees (maxed), 40% expo (high)
General Flight Performance
You really get a great-flying plane in the ULD and much of that is attributed to stability at slow speeds. Here it shines and thrives on getting as slow as possible without stalling.
Tracking is heavily influenced by the rudder. Even a little movement will start the roll. This is not to be perceived as a negative, just information provided as to rudder authority. Hands off, the ULD follows the GWS 9×5 prop without hesitation.
Get ready for some fun, all while the ULD is within a few arms length. It can slow roll, knife-edge, harrier, fly inverted and hover with ease. Through practice, your hovers will become rock solid. I noticed the deeper I got into the hover and the more vertical it became, the less wing rock I experienced. This is a testament to BudgetRC’s mathematically matched fuselage, wings and control surfaces.
>Glide and stall performance
Because the ULD weighs in at 12.7 ounces (360 grams), little momentum is available for a forward-glide slope. It can settle almost straight down, and in spite of the fact there are no true airfoils, it does glide pretty well as long as some incidence is applied. Stalls don’t really occur in the sense you may be used to them. When they do happen a quick throttle bump pulls the nose forward so quickly it never has a chance to drop. Generally, in a full, really slow-speed harrier, I could land on a dime.
I am a big fan of EPP. Learning to fly aerobatics at a comfortable, if not aerodynamically unreal, airspeed is so beneficial. I can lead with my thumbs, see the motion and prepare rather than react to the next maneuver. The durability is incredible and while I tanked it more than once, I just picked it up and launched it again. The flex in the EPP is something you learn to appreciate, but because the ULD is well-designed, that flex only becomes notable with ground contact. In the air, the ULD is rigid and predictable. You can play with the CG, but a rearward CG is not necessary for a good hover. As you move the CG back, the pitch sensitivity increases. It’s capable of flying on up to a 1200mAh 11.1V LiPo, which does help if some winds are present.
· Slow flight controllability
Radio: Futaba 9cap Super, Corona RS610II 6 channel FM (futaba-rc.com)
Engine/motor: TowerPro 2408-21T-3A
Battery: 900mAh, 11.1V LiPo, 20C
Prop:GWS 9 x 5
ESC: 12-18amp brushless
Servos: 1-9 gram TowerPro SG-9 (ailerons), 2–5 gram TowerPro SG-5
Type: EPP Biplane
Wingspan: 29 in. (736mm)
Wing area:460 sq. in.
Length: 35 in. (890mm)
Weight: 10.6 ounces (300 grams) w/o battery, 12.7 ounces (360 grams) w/ battery
Wing loading: 3.98 oz./sq. ft.
Radio req’d: 4-channel