MotOpinion - Sig LT-25 Twin
1300ft above Sea Level, 101.3kPa, 20°C
|| Kyosho Atomic Force 17T; 3531rpm/V; 2.94A no-load; 0.035 Ohms.|
|| Sanyo RC2000; 14 cells; 2000mAh @ 1.2V; 0.0035 Ohms/cell.|
|| Castle Creations Griffin 50; 0.0011 Ohms; High rate.|
|| Master Airscrew 3.0:1 Gearbox w/APC Prop; 2 motors (series); 10x7 (Pconst=1.11; Tconst=0.95) geared 3:1 (Eff=92%).|
|| Sig LT-25; 724sq.in; 104.2oz RTF; 20.7oz/sq.ft; Cd=0.063; Cl=0.52; Clopt=0.69; Clmax=1.2.|
|| 60 W/lb in; 42 W/lb out; 22mph stall; 29mph opt @ 68% (15:15, 41°C); 33mph level @ 75% (12:48, 44°C); 591ft/min @ 13.4°; -289ft/min @ -6.5°.|
Power System Notes:
- The full-throttle motor current at the best lift-to-drag ratio airspeed (24.5A) falls approximately between the motor's maximum efficiency current (25.6A) and its current at theoretical maximum output (112.7A), thus making effective use of the motor.
- The voltage (15.5V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.
Possible Aerodynamic Problems:
- The static pitch speed (52mph) is less than 2.5 times the stall speed (22mph), which may result in reduced performance at typical flying speeds and a low maximum speed. This situation is usually acceptable for an electric sailplane or other slow-flying model.
- Pitch speed can be increased by using a higher pitched and/or smaller diameter propeller, a lower gear ratio, a higher cell count, or some combination of these methods.
- With a wing loading of 20.7oz/sq.ft, a model of this size will have trainer-like flying characteristics. It would make an ideal trainer, for use in calm to light wind conditions.
- The static thrust (51.1oz) to weight (104.2oz) ratio is 0.49:1, which will result in medium length take-off runs, and no difficulty taking off from grass surfaces (assuming sufficiently large wheels).
- At the best lift-to-drag ratio airspeed, the excess-thrust (26.1oz) to weight (104.2oz) ratio is 0.25:1, which will give strong climbs and rapid acceleration. This model will most likely readily loop from level flight, and have sufficient in-flight thrust for many aerobatic maneuvers.
- This analysis is based on calculations that take motor heating effects into account.
- These calculations are based on mathematical models that may not account for all limitations of the components used. Always consult the power system component manufacturers to ensure that no limits (current, rpm, etc.) are being exceeded.
Generated by MotoCalc 8.00, 2005-12-18 17:11.