In this next article in my Discus Launch Glider (DLG) project I was going to have a look at the different types of DLG out there and what I can learn from them.
Dr Mark Drela
Dr Mark Drela
Aeronautical Engineer – MIT
Before we get into this all we should probably mention Dr Mark Drela. Dr Drela is an Aeronautical Engineer and Professor of Fluid Dynamics at MIT. He is widely regarded as the Godfather of RC gliding having spent many years researching and developing aerodynamic principles for low Reynolds number airfoils. His own DLG design, the Apogee, is something of a benchmark for early DLG design and construction.
Variations on a theme
As with any arm of RC flight, there are many different variants on the theme of Discus Launch Gliders, but they mostly fall into three categories:
- One-meter class gliders
- F3K competition gliders
- Experimental and plank style gliders
One-meter and micro-class gliders
Popular due to their simple construction and relatively low cost, micro class gliders have a wingspan of one meter or smaller. Construction tends to be balsa or foam, steering away from expensive composite constructions.
Micro gliders are almost exclusively rudder/elevator only with increased dihedral for stability. As a result the performance envelope is nowhere near as wide as the larger F3K machines with full house controls.
Probably the most popular micro DLG at the moment is the UMX Whipit from Horizon Hobbies. This tiny foam glider comes almost ready to fly at a very attractive price. It’s small size and reasonable performance make it easy to fly in small spaces in calm conditions.
F3K competition gliders
F3K machines are more tightly regulated than the other classes. With a span of 1500mm and target weight of 250g, full composite construction is preferred in order to survive the high-energy launches of competition flying.
From what I have read there are a number of different designers working on the leading edge of F3K design. All models tend to follow the same pattern with a pod and boom fuselage, offset tail surfaces and either skinned foam or hollow carbon wings.
The DreamFlight Libelle stands out as an exception to the rule. At 1.2m span it is nearly up there with the F3K ships and has full house controls. With all foam construction and a price of only just over $100 for the kit, the Libelle offers a taste of competition flying without the cost.
Experimental and plank style gliders
This is where things get weird! There are a number of smaller slope gliders that are easily adapted for a discus launch. A popular model is the all foam DreamFlight Alula. Of course, moulded EPP wings will never have the same performance as a composite machine but the ruggedness of foam “planks” is popular with sport flyers who don’t want to build.
Other, more complex tailless and flying wing designs crop up from time to time. I think the only thing that stops them from being truly competitive DLG models is the inability to use flaps to modify airfoil camber and lift profiles.
So, I’d love to be able to stroll out into the workshop and begin laying up carbon wings but that just isn’t going to happen just yet! I may well play with the plank designs in due course but I think I am going to follow a process of exploring the micro class format first and then scaling up as I go.
Until next time…