Cloud Whisper - ePowered Plank

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A 1500mm size thermal ePowered plank wing. Composite construction

Medium AR, low WL .. Elevons moved outboard to enable inboard wing generate max lift during slow thermalling. 



 Dimension Sketch







Airfoil BW050209
Wing area 39.43 sq dm
CG @ 10% SM = 100 mm, @ 15% SM = 87




The wing was hotwired out of high density EPS (thermocole).


Built-up full length CF spar. Tow width on top 18mm, bottom 24mm. The spar has a 5 x 3 mm vertical balsa compression webbing buried below the CF tow (full length).. The built-up spart is at 33% of cord. The routed 5mm groove for the vertical compression webbing visible. Also you can see the shallow trough which has been sanded for the CF tow cap of the spar.




A picture of the wing core with the CF tow for the spar caps.

A view of the laid out built-up spar


This one shows the vertical webbing



Built up spar ..all elements in position and weighed down …. awaiting for the epoxy to cure


the wing with the spars in place.. is is not covered yet




Wing glassing in progress.. I am using @80gsm cloth at 45 degree baise. Also near the root there is an addition layer 10cm wide to reinforce the wing joining tubes



drilling for the the wing joining tubes. I am using 10mm Al tube for the main (front) tube and a thin brass tube for  the alignment (rear) tube. The rear tube was actually a jotter ball pen refill cut and cleaned  

The main hole is drilled using a jig based on a channel slider. The edges of the Al tube is sharpened and clamped as a bit in the drill. A guide edge is set on the table to align the root of the wing and the incidence  and the wing is held firmly to the guide edge, thus ensuring alignment of the hole being drilled. The drill was run at medium speed so as to not tear the foam. The bit tube had to be cleared of foam inside at shot internals so that it cut and move ahead. This was done till the right depth of the hole was achieved.

note: the drilling of the was done after the wing was fiberglass covered and a balsa root rib was epoxied to the root.



Once the holed were dilled, the tubes were inserted (without adhesive) to check both the wings mated properly. The very minor alignment changes were done by inserting a long screwdriver in the tube and applying pressure appropriately to adjust and align the tube. Once properly aligned, very small amount of adhesive was applied to the walls of the tube and they were fixed in place.. once again checking for alignment before the adhesive set. 

here is a view of the finished root 


The fuselage is simple 3mm balsa. It is designed to have curvature in one dimension only. This keeps the construction easy without much compromise on the aerodynamics. The wing joiners double up as topside former. The whole fuselage is covered with 80 gsm fiberglass. The vertical tail is built up and covered with monokote. It slots through a slot in the top fuselage and is hot glued. There is a latch on top which locks the battery compartment in the front and the wing joiner portion in the center


the wing joining setup,,, notice locking tabs with the holes 


the wings locked in place with the nylon bolt




here is pic of how it looks from top.. note the wing TE fairing  where it joins the fuselage. Also the elevon horns and the control link. They barely jut out are quite streamlined






Some changes were made after the initial test flights 
- changes in the paint job for better visibility at distance
- 4gms weight had to glued onto the left wing tip
-  power setup wads changed 2212 980kv motor and 1500 mAh bty... this was more, because I found this to be minimum adequate (the bigger motor was required for different plane)
- CG was set at 100mm from LE  @ 10%SM
- added vortex generators on the outer wing 
- the vertical tail area was reduced
- a cooling air intake was made in the motor mount firewall 
- AUW was brought down to 900gms



a very stable flyer .. it flies hands-off ... with  a great glide glide ratio... 

Here is a flight video
https://www.youtube.com/watch?v=jUjI9yWp7Cc







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