20 Years of RC Blimp Optimizations

July 19, 2017

Calculating pressure fields on blimp envelope surfaces

To an outsider, and most likely to a consumer making his or her first RC blimp purchase, all blimps look more or less the same. As an engineer, it’s heartbreaking to see people opt for a competitor’s RC blimp based on surface level cost. In reality, a blimp’s performance will generally correlate to its cost. While you may not directly care about a blimp’s performance characteristics, if you care about cost (which you do if you opted for a cheap solution), a lower performance blimp will require more helium and will therefore become more expensive in the long run. And so a cheaper blimp is not only more expensive over time, but it also won’t fly as well and may not even meet your initial needs. Unfortunately for our own clients and our business, it’s a predictable story where clients opt for cheaper solutions only to return with the same requirements and a now smaller budget.

All this said, we compare the current version of our aircraft to our designs from 20 years ago, and while the blimps themselves are nearly indistinguishable on the surface and from a distance, the iterative increases in efficiency have allowed us to produce blimps that are small, fast, reliable, aerodynamically efficient, capable of retaining helium well, and can carry comparitively large payloads.

Blimp Shape

Starting with the most obvious, a blimp’s shape greatly affects it overall performance. Envelope design is actually less intuitive than might initially be expected. Creating an envelope shaped like those from the early 20th century will create a satisfactory design, but subtle changes influence a variety of key metrics. Unique to blimps, the center of gravity is not the same as its center of mass. Moreover, a blimp’s center of buoyancy is a key component in blimp design. And like other aircraft, the center of lift must also be considered. All four components are individual variables that are uniquely influenced by the shape of an envelope. It’s impossible to say that one design is “best” because each component can be maximized through a variation in design. Through trial and error though, we’ve arrived at several blimp shapes that are optimized for different cases.

Other components of our blimps, such as our tail fins and gondola, are designed in fairly predictable manners but are nevertheless optimized for blimp flight. Not all blimp manufacturers make the effort of optimizing all of the low hanging fruit available.

Materials

Ideal blimp materials are an elaborate subject, and we actually discuss ideal RC blimp materials in great detail in another blog post. But the moral of the story, in short, is that we use material that’s optimized for light weight, high helium retention, and reasonable rigidity. The blimp envelope is as thin as possible while still capable of retaining helium and maintaining a resistance to regular wear and tear.

Tail fins are noteworthy components in our blimps. Upon a cursory glance, they appear to be cheap, flimsy, and low quality. And in a sense, they are, but the point here is that those design decisions were deliberate. We use a special styrofoam to produce tail fins, and the material is indeed flimsy, but it’s also incredibly light weight and perfectly capable of creating torque to pitch or yaw the airframe. Moreover, the material is intentionally cheap so that they’re easy to replace, and if and when they get banged up from standard wear and tear, it’s no big loss to replace them. The downside, if we would agree to call it that, is that the fins do not always hold up well in the case of a crash into a tree or fence or any other structure. Some would call this a flaw, but the question becomes whether or not we should even try optimizing for the case of a crash. More rigid materials would introduce weight and cost, and it’s still impossible to guarantee that those materials would survive a crash any better than their cheaper counterparts. To provide an analogy, vehicle manufacturers do not optimize cars for crashing into a tree. While mitigation techniques exist, it is not the primary influence in design decisions.

Our gondolas are also made from molded carbon fiber. This again enables super-lightweight material and high tensile strength all at cheap input costs obtained from economies of scale over time that are eventually passed to the consumer.

Camera gimbals are also optimized either for cost or performance, and we accomodate either case. For the case of high performance, we custom build our gimbals from carbon fiber and typically provide three axes of rotation with two axes of control.

Electrical Components

Probably the most obvious differentiator of our blimps is the electrical components visible from the ground. We run wires inside the blimps for better performance and aesthetics. On the one hand, wires not exposed to the air produce better aerodynamic results, and on the aesthetic front, our blimps simply do not look tacky. In the not so distant future, we’ll also eliminate many of the long wire runs completely with wireless components that further reduce overall weight and improve visual appearance.

Again with a weight optimization, all of our circuitry runs at 12 volts. This enables us to avoid having to add transformers that would detract from the aircraft’s overall carrying capacity.

And finally on the front of electrical components, we are uniquely positioned to sell LED screens. The concept is obvious: string a sheet of LED’s together and slap them on a blimp. But the problem is that LED’s and their corresponding circuitry quickly add up to a heavy aggregate weight to the point that excessively large blimps are required in order to carry the payload. Comparitively smaller blimps would not be capable of carrying a proportionally smaller screen because volume is proportional to the cube of length while surface area is proportional to its square. Therefore the ratio of volume to surface area increases with size, and a heavier LED screen requires a higher break-even point.

The point is: we’ve established the right relationships with the right manufacturers to produce some of the lightest weight LED’s in the world, if not the lightest. Ten of our LED’s and their associated circuitry only have one gram of mass. Manned blimps such as a Goodyear Blimp have LED screens on display, but the implication of our manufacturing process is that we can deliver the exact same capability on a much smaller blimp. It could be said that conventional blimps with LED screens are obviously superior because they have a much bigger screen, but it could be equally argued that that LED screens on manned blimps are actually inferior because they require a large size in order to be feasible. If an apples to apples comparison were made, our LED sreens, scaled to the size of a manned blimp, would be dramatically lighter and would therefore allow the overall blimp payload to be composed of other components.

Control

Finally, our blimps are optimized for better control over other RC blimps on the market. Spend some time perusing RC blimps on YouTube, and you’ll notice some subtle shortcomings. First, not all blimps necessarily have the degree of control that our blimps allow. For example, our tail fins provide a mechanism to yaw while hovering, much like a helicopter.

In other designs you may also notice main motors that are held in a static position. In such a case, the inherent advantages of a blimp are nullified for no good reason. Blimps are capable of operating like a helicopter and a plane at the same time, and if a thrust vector is not present, the blimp is forced to fly like a plane without the capability of vertical take-off and landing. You can also watch the take off of a manned blimp, and conventional designs don’t have thrust control, and as a result the blimp must take off with assisted pitch control from ballonets. Our vectored thrust also allows a blimp to fly in reverse without having to actually reverse the direction of the motors.

One final optimization that is most definitely not obvious is our flight controls embedded in the RC transmitter. Few, if any, of our customers are experts at blimp flight, and the nuances of how to most efficiently fly are not necessarily obvious or even intuitive. We abstract this away for you, and instead the flight controller takes care of these subtle movements for you. If an operator were given complete control of a dumb transmitter, there’s almost no way to fly efficiently at all times. Tail elevator position, thrust vector position, and how they should change in response to forward thrust are among the aforementioned components.

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