Slow David Wing

Objectives

• very slow flying wing strictly for indoor and absolutely calm outdoor conditions
• as small as possible
• simple build w Depron

Ideas

• 32" version of my David with with same motor and 5x3" prop (i.e. similar weight as David, but 4x wing area --> 0.5x stall speed)

  • but can't cut wings from depron sheets in one piece, would need to glue on centre-line

• KFm6 airfoil (3mm Depron) --> 15/292 = 5.1% thickness

Weight Budget

• AUW = 150g
• airframe = 100g (4x David)
• battery (180mAh 2s) = 13g
• servos - HK251 (2.5g) x 2 + linkages = 8g
• RX 6 ch Orange w.o. case = 6g
• ESC (HK 8A)w.o. heatshrink = 8g
• motor (HK AP05 3000kv 5.4g) + 5x3" prop = 8g

Ideas carried over from David Wing

• as described (one of the options) in http://www.rcgroups.com/forums/showthread.php?t=1173701

• plans attached KFmDavidWing.pdf

• plans measurements (imperial) KFmDavidMeasurements.pdf

• use the 16", 20" or 24" version?
  • want to stick to original 3mm depron and KFm4 airfoil (3 layers)
  • but wing thickness will affect robustness and slowness of flight characteristics

    Wingspan (")	thickness	MAC (mm)	wing area(in2)	loading(oz/ft2)	loading (oz/ft3)
    16	6.2%	146	86	3.9	5.0
    20	4.9%	183	134	2.5	2.6
    24	4.1%	219	194	1.7	1.5

  • original 16" version uses a 5g motor capable of driving a 3x2 prop, but my 5g motor can drive a 5x3 prop, so can drive a bigger wing area?
  • may need to make bigger purely to accommodate the larger propellor (prop space consumes more than 1/3 of wingspan on 16"!)
  • 24" (being 1.5x each dimension) should give 0.66x the stall speed (for same weight)
  • experience of 24" builders is that it still flies well even though only 3x3mm depron thickness airfoil
  • but with 24", three layers of 3mm depron doesn't come close to the required minimum 6% KFm4 airfoil thickness (is 4.9% for 20" wingspan)
  • if 24", maybe need the KFm6 airfoil, which has another 2 layers of depron to get the thickness near LE
  • benchmark against Battlewing: 0.83m (32.7") wingspan, AUW=265g, avg chord 220mm and 13.6% thickness
• modifications
  • consider wing-tip cut-offs similar to Assassin(?) to get increased stability without winglets
  • consider very small winglets to help protect ailerons
  • consider step taper at wingtips towards 100% of chord to provide a winglet effect (and strengthen tip)
• alternatives
  • 24" fold-over full airfoil wing - but this really complicates the build! Maybe as a second version if I like the first
  • single 3mm flat wing with CF spar with electronics glued on top (without KF airfoil this may need winglets!)
• Add top and bottom 3mm balsa reinforcement plates to increase wing thickness at the motor mount (may be more solid than 3mm depron)
• widen elevons to get better control at low speeds (better at high alpha?)
  • would need to shorten fixed wing area, or extend step location to maintain at 50%
• electronics compartment options
  • separate cutouts for battery, ESC, and RX (cut battery last to get CoG)
    • perhaps a larger hole for battery to allow larger battery sometimes (small sideways at front, large lengthways at back)
  • a single large cutout for electronics, Velcro to fix, hatch cover, plastic floor