Botmite

Construction
Details &
Photos

Camera
Transmitter
Hacks & Mods

Basic

Aerodynamics

Mods from Botmite 1 to 1.1

Repair
Repair 2
Vacuum 3
Repair 4
Repair 5
Repair 6

Botmite2 tools
B2-calcs1
 

wings -

 Airfoil

 Lift

 Drag

Moment

Wings - Botmite Development

Power

Range

 Re

   Botmite 1 has thin high performance wings ready for fast flight. Calculations show, however, this first sleek (Eppler - 374) 8 foot wingspan, 510 square inch area wing requires a different (read larger and stronger) airfoil and wing for long distance and heavy flight. The point is to provide a wider speed envelope while maintaining a low drag and power efficient wing.  

   So, Botmite 1A is a redesign of the initial set of wings.  After testing the new wings will be shown here.  The 1A wing consists of a higher lift airfoil, a 10 inch root chord and a 10 foot wingspan with approximately triple the plan area of the original wing. To keep it simple, this wing has a hershey bar or rectangle shape geometry. Further, this wing should not require struts and can function fully in 10g aerobatic flying.

   A shorter Botmite 1.1 six foot wingspan yet wider twelve inch chord in a rectangle planform is desiged to fly in  a flight envelope from human powered bicycle speeds to the 100 mph plus area further providing an introductory 20 g force dynamic range of mobility.  Wingspan for this version presently stands in the 6 foot length, aspect ratio 6. While the rectangle wing geometry and chord ratios are not optimum, it presents a useful and practical testing platform for further study.  Successful airfoils for this experimentation include Clark-Y and E-205.  So while tail geometry and wing area ratios (typically range from .09 to .2 of the wing area) for proven designs, this approach does not consider expanding dynamic range beyond human endurance.   

   As a result, the botmite 1.1 version aircraft turn helix now targeted begins at 720 degrees per second at top speed.   To attain this goal, testing of lightweight carbon fiber mixed with various cores (balsa, birch, foams and flexible structures) to form a lightweight composite sandwich to improve  airfoil resilient qualities and then to incorporate this into a new design.  Further enhancements include increasing tensile skin strength materials and structural design epoxy fused to core structures which serve to limit wing flex.   Boundary layer airfoil drag enhancements are being considered and evaluated along with control surfaces and mechanisms. 

                           Botmite 1.1 New Wings

     One pound foam core, Clark-Y and E-205, initiate the testing program to enhance the performance of Botmite.

 

 Note: increasing wingspan from 6 feet to 8 feet results in 40% additional lift, all else constant; Wing loading decreases, glide ratio increases. A larger wingspan also means at low power climb the attainable ceiling is higher with a slight increase of drag.

   Thrust from propeller must be greater than minimum drag to fly at 40 mph; typically if airplane weight is 9 pounds, then thrust should be minimum of 3 pounds or 33% of airplane weight. 

   What this equation means: either increasing aircraft weight or how fast it flies requires a multiplier effect on the amount of energy spent in performing that task.  And that is without additional considerations of aerodynamics.             See: Isaac Newton, Principia Mathematica.

Above Graphs (CL)(CD)
E-205 Green and Clark-Y Blue

Alpha or AoA, the pitch up or down of the aircraft and how the lift (left) and drag (right) is affected by change of pitch, meaning rate of climb or descent in altitude, the rate of climb increases as alpha increases and stops at stall.  A stall precedes a rapid descent of the aircraft.

Botmite 1.1A

  New 8 foot wing, half shown here, under the original 8 foot Botmite 1.  Botmite 1.1A features more than double the original 510 sq.inch area.

New wing area: 1,080 square inches. Concurrent with this development is the internal strengthening to manage high centrifugal force or Gs while stiffening the wing structure.  New wing more than double the thickness of original but under 14% of chord.  Only styrafoam is shown here - wing is contained within it.

             BOTMITE 1.1A 8 foot wingspan
                           General Specifications

 Wing area: 7.5 sq. ft. or 1,080 square inches
  Wing root chord 1 foot
  Wing tip chord 0.5 ft.
  Wing span 8 ft. or 96 inches
   Aspect ratio: 8.53
   minimum sink rate: 143.85 ft./min.
   maximum Lift to Drag ratio: 15.4
   effective span loading: 1.53 pounds /sq.ft.
   calculated stall speed: 21 mph (no flaps)
   maximum speed: 85 mph
   maximum dive speed: 170 mph
   Power / mass: 0.102 Bhp/lb. or ( 170 W/ kg. )
   Rate of climb:  3,600 ft/minute @ 11 pounds gross
 

                               The Take-a-way

   New 8 foot tapered wings increase the lift over the original while adding slight more drag from the original wings. Yet the wings weigh about the same.  More range, able to carry a couple pounds cargo with a range of about 40 miles with a larger flight envelop - slower and faster. Service ceiling is increased here along with glide ratio.  Turns can be more steeply banked; larger ailerons mean nible performance; larger flaps mean steeper glide slope availability to very short runways and lower landing or takeoff speed.  Flying stalls are gentler, predictable and more manageable; tip stalls are avoided.

   Botmite 1.1A has wing loading cut in roughly a quarter from version 1. Carbon fiber composite construction covers with surface area; its reinforced internally make for stiffer, stronger, lighter per unit area at a higher price for a more stable and powerful platform.
   One could argue maintaining the first planform would be better, perhaps, but for what?  Enhanced stability means a better imaging platform scaled for lower Reynolds numbers,  this coupled with agile performance yield additional opportunities. 
 

Span Efficiency  vs. Stall Character

  Above chart demonstrates wing form performance is a maximum using an ellipse tapering somewhat with a trapezoid - botmite 1.1A wing form. An ellipse wing form is a sudden stall across the wing. Trapezoid stall character, according to experiment, is proved to begin at the wing tip and progress to the wing root as turbulence over wing increases from speed loss and higher alpha.  Given design goals, the opportunity cost of this form has lower cost and better performance.

Lifting Line Theory

   F. W. Lanchester, and L. Prandtl (published in 1918) bring forth lifting line theory, a mathematical model predicting lift over a three dimensional wing based on its geometry,this air circulation theory gives rise to wing efficiency concepts.  Part of fluid mechanics (an engineering specialty): how  vortex strength reduces along a wingspan in particular across the trailing edge of a wing is explained.  Hence, carefully engineered, designed and built wings with a aspect ratio 10 prove more efficient for gliders but require more attention to flying.   
   Supersonic shock waves and theories of flow came from Prandtl and Theodor Meyer in 1908.
  Nearing 250 mph, air begins to compress on the leading edge, moving faster through air the wing efficiency changes. 

The Tail

  At 22 % of wing, the tail area would be 238.6 square inches without consideration of moment or how far from the wing this vector force upon the pitch of this aircraft. 
  Presently, the tail is at .09 or 9 percent of wing area.  So, testing and further evaluation of stability versus dynamic performance along with the related structural considerations.  

How to derive aspect ratio or AR

  Aspect Ratio is also expressed as the ratio of wing span to wing chord.

Wing Structure - Internal Reinforcement

Wing - Fuselage :: Redesign and New Construction - See: Repair4.asp

[Photos] [Aircraft] [Electronics] [Sensors]

.