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STUDIES ON THE BOW WING

1. Basic information
2. Delka geometrical analysis
3. Known models
4. Structure interpretations and notes


1. Basic information

Longbow details article by Brett Snellgrove in Skysailor:

http://www.hgfa.asn.au/skysailor/Issues/0409/theparanglider.htm

and in Rigid Wing Web Site: http://midtoad.homelinux.org/midwinter.ca/RigidWings/Longbow.html

Didier Favre merci video (Delka in the Dune of Pyla and Sonchaux)

01
Laurent holding the bow wing		 02
Laurent jumping on the dune
03
Didier running to take off
 04
Didier flying on the dune



2. Delka geometrical analysis
Delka analysis



3. Known models:

Model
 Longbow
 Delka
Area (m2)
13,7
Span (m)
10,5
Weight (kg)
25 kg (including harness)
Folded length (m)
 2,4
 2,5
Glide
 9:1
Bow radius (m)
 14,8?
 7,88?
Profile
 reflex
 reflex (80% of span)
Bow preload (kg)
 180 ?
Frame
 HT30TF aluminum (6082-T6).
Five sections
2 5/8", 2 1/2", 60 mm x 1mm wall
 Five sections,
and two fiber glass tips                                          
Year
 1992
 1994
Pitch load test
 +400 kg/ -150 kg
Observations
 Spiral dive tendency


4. Structure interpretations and notes:

I have an article about the Delka, appeared in the Spanish magazine "Parapente Vuelo libre" No. 18 & 19 (August-September 94). I assume that similar articles appeared in other journals in 1994, "Vol Libre" and others. The photos show a short large-diameter tubes (3 "?) And probably aluminum, like Longbow. I do not know whether or not the wing used indoor sprogs. On the picture of Delka in flight over Lake Leman, is clear the reflexed and autoestable profile, and it also seems that the wing has diedral also induced by the weight in flight. The structure of Delka, is hidden under his yellow cloth ... but the video in the Dune of Pyla and Sonchaux provides lots of information.

Certainly, the leading edge is working on a complex combination of compression, bending, twisting and cutting efforts...

The concept Longbow-Delka could be very "radical" in 1992, but not in 2009, with many cantilever rigid wings structure, flying around the world.  But I think that the study of the project "bow hang glider" must be continued, since it has potential.

An important question to consider (I do not know if properly explain in English): The string of the bow, which connects the tip of the edges of attack with the keel (the tightening of the wing), could bend slightly down in the event of negative charges, making it less effective profile autoestable, hence the need for sprogs, it must be analyzed in detail.

Once analyzed the structure, we have to analyze the aerodynamics. The Delka is handled as the Fledge or Icarus V: weight shift to control pitch, and tip rudders for roll and yaw. Dual deflection of the tip rudders was assumed also to induce pitch change. The use of elevons as in the Millennium, could improve control...

Notes-1:
bow1

Notes-2:
bow2

Notes-3
bow3

Notes-4:
Notes-1

The rigid wing in an arc Structure is very curious...

We can imagine a continuous evolution from a wing with a simple beam structure, to a wing arc as follows:

1) One wing of simple beam, consists of a beam straight and guidelines section on "I", square circular, since virtually only must resist bending moments on a vertical plane (in the opposite direction to gravity). The axis of the beam would be coincident with the center of pressure profiles that make up the entire wing.

2) A simple evolution would be double the previous beam at its center. Bending the beam at an internal angle of 140 º and changing the section of the same to a "D" section gives the structure Millennium / Atos...

3) The choice of the Longbow / Delka to form the wing is to bend the beam in an arc. The advantage is a one-dimensional structure (a line formed by tubes spliced) easy to disassemble keep, and transport, which can be converted by bending in a two-dimensional structure (the plane's wing). The disadvantage is that the section of the main beam worked under tension (especially in the central section corresponding to the nose). It is therefore very important to select the proper way for the section of the main beam, their variation along the wingspan, and his material.

Brooks and Kalbermatten's solutions used simple circular aluminum tubes linked together, but can still be much development in this field... There's a lot of structural research to be done, but it is conventional problems ..., then come the aerodynamics research, profiles, and control mechanisms (tip rudders? or elevons + V tail?)...

Notes-5:
Notes-2

Variation: DHERCA (HERnandez CAsellas :-) ! )
Drawing from 1994
DHERCA

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