Preliminary design of an ultralight aircraft BESTA
12-2013 Alejandro GarcĂa Soto Universidad Europea de Madrid Aerospace Engineering
Index Similar aircraft ‌................................................................3 Similar aircraft Cl estimations.............................................5 Fist calculations for area and Cl ..........................................6 Flap systems .......................................................................6 Aerodynamic surfaces .........................................................6 Structure .............................................................................8 Fuel and range ....................................................................9 Drag estimation ..................................................................9 Motor structure ..................................................................10 General views....................................................................11
Similar aircraft Cl estimations Cl maximun at landing is calculated for each similar aircraft in order to get an idea of what can be done with flaps in an ultralight airplane. Cruise Cl is also calculated.
Landing with flaps Pilot and fuel (N) Esqual Black Shape Sting S4 Bambi Vl3 Evolution Tecnam P2002 Da 20 katana Lancair Legacy
Empty weight (N) 800 800 800 800 800 800 800 800
Velocity (km/h) 2750 2965 2970 2359 2850 3310 5290 6800
62 65 65 65 55 65 78 105
Velocity (m/s) Wing area (m²) 17,2 18,1 18,1 18,1 15,3 18,1 21,7 29,2
Cl 9,0 9,9 11,1 7,5 9,8 11,5 11,6 7,7
2,17 1,90 1,70 2,11 2,61 1,79 1,82 1,90
Cruise Weight (N) Esqual Black Shape Sting S4 Bambi Vl3 Evolution Tecnam P2002 Da 20 katana Lancair Legacy
Velocity (km/h) 4500 4725 4725 4500 4730 6000 7500 9980
Velocity (m/s) 265 275 250 250 270 225 256 444
73,6 76,4 69,4 69,4 75,0 62,5 71,1 123,3
Wing area (m²) 9,0 9,9 11,1 7,5 9,8 11,5 11,6 7,7
Cl 0,15 0,13 0,14 0,20 0,14 0,22 0,21 0,14
Fist calculations for area and Cl
The only unknown values in the lift equation are Cl and Area. Asuming a maximung Cl of 2,5 with slotted flaps, a wing area of about 4,5m² is needed. This leads to a cruise Cl of 0,12. This values are coherent with the competence. Flap systems The technical implementation of the slotted flap will be something like this.
Aerodynamic surfaces Keeping the area constant, the following initial shape is defined.
horizontal tail surface 0,45
MAC distace (Wing and horizontal tail)
4
Uh(volume coeficient) 0,5
Wing surface 4,5
Vertical tail surface
MAC distace (Wing and vertical tail)
Uv(volume coeficient)
Wing surface
Wing spam
0,405
4
0,03
4,5
12
Wing MAC 0,8
The following distribution of surfaces is defined. Actual surfaces (shown in general view) are a bit greater (better to have more surface than not enought) in order to compensate for fuselage interference. VTP was chosen to have some surface below the HTP to allow control in the case of stall.
The lines of the fuselage go surrounding people and motor. Landing gear is located wide on the wing so that in case of penetration, it does not hit the pilot
Structure Whole structure will be made out of CFRP. It will be manufacture using a mold to ensure outside surface and reinforced in the inside where it is needed.
Wing structure is composed by 2 semiwings that are joined using an eliptical rod to push and secure the union, making one single beam. Fuselage is attached to 4 points near the front and leading edge of each wing.
Fuel and range Even if more fuel could be stored, normally 100 litres go for about 5-6 hours in similar planes. No more than 2-3 hours are hardly ever flown by normal pilots, so there is no point in adding more fuel space and complexity. Fuel is stored in the front part to help center of gravity allocation.
MTOW
passengers passenger weight Payload (kg)(kg) fuel capacityfuel (l) density (kg/m3) fuel weight (kg) W no fuel (kg) empty weight 450 2 90 180 100 800 80 370 190
BSFC (kg/W*h) Propulsive efficiency g (m/s2) W1 0,000285 0,8 9,8
W2 450
ln(w1/w2) L/D 370 0,19574458
range 20 1121,3438
BSFC of the Rotax UL 912 285g/KW*h Propulsive efficiency assumed to be 0,8 L/D assumed to be 20 Using these values a range of about 10000km is achieved. It's in the same order of magnitude as the competence, so the L/D assumtion is valid.
Drag estimation Cruising at Cl 0,12, Cd would be 0,006. Aspect ratio 10,8888888889
oswald factor Cl 0,85
Cd induced 0,12 0,0004952
Calculating Cd induced to be 0,0005, we can gess a parasitic Cd0 of 0,0055
Motor structure
From the Rotax manual of instalation, the points for instalation are defined. Using the maximung distance allowed by the area of the firewall ( the fist part of the propper structure of the aircraft) a rod structure will be designed.
General views