High flight time RC aircraft

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Building a high flight time RC aircraft, which is easy to carry and fly, made out of easily available materials (foam), and reusing my existing electronics

After deliberations, decided on a  simple dihedral (rudder and elevator) tractor of 40" span..  Wing chord was kept at 7" (below that airflow disruption due to low Re number)  It would be flying at low Reynolds numbers (around 80000),accordingly a thin and slightly  under-cambered (4 degree) plate airfoil section was chosen. The dimensions / parameters were calculated based on the design requirements and based on RC aircraft parameters.

This aircraft regularly flies + 45 minutes flights on a 1000 mah bty..and is super easy to fly. Many a times after reaching a good altitude & trimming the aircraft I have taken a short break. She can hold bearing even in windy conditions. Just by pointing her into a decent wind and with very minimal ground speed (zero or sometimes negative)she can gain altitude.

DIMENSIONS
  1. Wing Span= 40"
  2. Wing Root Chord =7"
  3. Wing Tip Chord =4"
  4. Dihedral panels=8" each .. so 24" center section, and 2 X 8" outer sections at a dihedral
  5. Dihedral =3"
  6. H stabilizer span =14"
  7. H stabilizer root chord = 5" (including elevator)
  8. H stabilizer tip chord=4
  9. Elevator  = 1.5" constant chord full length
  10. Sweepback =1" for leading edge
  11. Distance from wing trailing edge to tail leading edge =14" ......which is 2X wing cord
  12. V tail span =5"(including rudder)
  13. V tail hight =6"
  14. Rudder  =1.5" constant chord full length
  15. Prop is 7" ahead of the LE of wing...... which is 1X wing chord
Power and Electronics
The power setup and electronics was based purely on what was available with me
2217 1780 kv motor, 7X3.8 prop, 20amp esc , 2X 5gm servos, 1000mah 3S bty

AUW= 300 gms or 10.6 oz

The dimensions were iterated a couple to times and frozen to achieve the the below mentioned vital parameters
a. Re  at wing tips 80850
b. Wing loading =5.9 oz /sq feet.. note it is a outdoor flyer
c.Spiral stability factor=9.38 (4-6)
d. H tail vol(pitch stability)=0.79 (0.3-0.6)
e. V tail vol =0.053 (0.02-0.04)
f. equi dihedral angle - 11.28 (12)
g. Dihedral sizing =0.49


Build (5mm foamboard was the primary material)
The fuse and tailplane and tailfin are straight forward builds from 5mm foam board. The fuse is a square xsection with a slight taper in the rear. Tailplane and tailfins are flat sections with LE rounded. Servos are mounted on top of the fuse





The wing is interesting. to achieve the desired undercamber the cord section consist of 3 sections glued together. The leading edge consist of a triangular balsa TE with the sharp side forward. This is slightly angled down (drooping) and glued  to a 5 mm flat middle section . The rear section is again a 5 mm foam which is slightly tapered and  glued with a slight down angle.. the overall effect is a very slightly drooping LE, a flat middle section and a downward canted TE.. which overall produces a camber.. the balsa LE acts as a spar and other than that there is only a full length fiber tape to strength the wing...






the complete aircraft .. notice the long tail arm for gentle movements in pitch and yaw control


Comments

  1. Chloe Masel11 October 2018 at 08:04

    Great blog, thank you for the detailed parameters and specific tutorials, RC enthusiasts really like this post

    ReplyDelete

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