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Wednesday, June 29, 2016

A Fresh Look at an Old Flying Wing Project-Future Flight's Klingberg Glider

XFLR5 is an analysis tool for airfoils, wings and planes operating at low Reynolds Numbers. It includes:
  1. XFoil's Direct and Inverse analysis capabilities
  2. Wing design and analysis capabilities based on the Lifting Line Theory, on the Vortex Lattice Method, and on a 3D Panel Method
This tool was used to predict the aerodynamic characteristics of a flying wing 
glider and determine the power required for safe takeoffs and good climb rates.

Future Flight Kit

The bell cranks were removed and micro servos mounted at their locations. 
Control is provided by two 90 micro servos one attached to each of the wing panels control surfaces. The hook-up wires are routed through the outer Ny-rod tubes which were already in place from the old control arrangement.

This aircraft has been flown successfully in the past as a high-start glider and as a geared brush motor powered glider. Pitch and roll control was accomplished by two standard size servos mounted to a mechanical mixing mechanism which was located in the central compartment with the deflections imparted to the control surfaces by ny-rods and bell cranks.The demise of the wing come when one of the bridle rings slipped off during a hi-start launch. Like most of my flying mishaps the damage was not total and the wing was repaired slowly over the next 20 years or so and now we are at that point where a new experiment is taking shape with a few structural improvements and thanks to a new Spektrum dxi 6 transmitter it will use electronic mixing. For power we intend to use a 70 mm EDF or two 55 mm and of course 2500 mah Li-Po batteries.

The earlier flights were conducted with and without the tip fins and as far as we could tell the fins had no noticeable affect on the craft's stability.

Stability Analysis:
The Fins and Stabilizers were removed from the model to see if the model exhibited any  stable flight characteristics. To compensate for the lack of a stabilizer the trailing edge flaps were deflected upwards 5 degrees inboard tapering to 3.5 degrees at the wing tip. These flap angles were a guess based on memory of the values required to trim the wing on those earlier flights.

For initial displacements in the longitudinal and lateral axis the model returns to its normal attitude in a few cycles and the osculations are quickly damped out. This is particularly true for the pitch direction.

We thought we would investigate what would happen to the lateral stability if we were to add tip fins to the model. Check out the mode one lateral stability animation.

Stability Vs C of G Location:

 The effect of C of G location on the stability of the model was investigated by varying the location and re-running the analysis to attempt to establish a stable condition. The model could not be trimmed until the position was moved to 12 inches behind the reference plane. At that point the the results of the analysis predicted a Velocity Never to Exceed (VNE) of 97 mph. The optimum position was established at 12.5 inches  with a VNE value of about 130 mph.

The next plans involve adapting the wing to electric duct ed fan power installation.
I was inspired by this fantastic jet powered wing model.

The original of the plane that inspired this design was never flown. It hangs on the wall of a hangar in the Chino airport in the USA. The original was designed with pusher prop but was intended to have a turbine eventually. It was built in the 1980's and was modelled on the Horten principles. Note no fin and no rudder at all.The plane is scratch built by John Wright from a design by a German modeller Andres Chavarria.The plane has 2m wingspan and weighs 5 Kg The engine is a 60mm diameter turbine that John Wright has designed and made. It is known as the Sprite. It weighs 440 gm and runs at 250,000 rpm Thrust is 3.25 Kg. This is not a commercial project. The design proved to be very strong and very manoeuvrable and has had many flights. Despite the lack of rudders and fin is fully aerobatic.


  1. Hi, really interesting build!
    Just how accurate was XLFR5 in predicting the aircraft's aerodynamic characteristics and behaviour?
    Thank you for your time, have a nice day!

  2. I have not flown the model since doing the calculations but I imagine the predictions are reasonably accurate since the program is based on a tried and true lifting line theory. However the theory does not take into account of: The lifting line theory does not take into account the following:
    Compressible flow
    Viscous flow
    Swept wings
    Low aspect ratio wings
    Unsteady flows