MODEL SPECS and Selection of Brushless Motors.. July 2012
Models built prior to July 2006 were powered with nicad battery packs. The weight and wing loading shown was with the original nicad batteries. With the Li-Po batteries now available, the wing loading will be lighter and flight time longer. Most of the models were designed to fly on one, or sometimes two nine-cell packs of Nicads. A 3S pack of Li-Po cells can be used in place of a nine-cell pack of nicads and will give a slight increase in power. The added power, along with a significant weight reduction, will result in a considerable improvement in performance. Even great increases in performance and flight time are achieved now with brushless motors. When choosing a motor, try to match the propeller size and power to the prototype. More notes on motor selection are added at the end of this list.
Seagull, (1994) Non scale flying boat with pylon mounted motor. Span 60 ins. Wing area 550 sq ins. Length 48 ins. Weight with nine N-1900 SCR nicads, 55ozs. Wing loading: 14.5 oz/sq.ft. Motor, Magnetic Mayhem with 2½:1 ratio gear reduction, driving 10 x 8 folding prop. Static thrust 32 oz at 7,800 RPM drawing 23 amps. Selig 3021 airfoil gives glider like performance. Is capable of doing 15 minute flights with 25 to 30 "Splash and Go" circuits.
Update: 2007 The Seagull now flies on a 3S Li-Po battery and has over 500 flights logged off water. With usually doing about 15 “splash-and-go’s” per flight, that is a lot of take offs and landings. It is still a great “fun” machine to have at the lake.
2011. Now has an Astro Flight 020 geared inrunner brushless motor. Coming up on 700 flights. What a performer!
July 2003: Recommendation.
In 1999 the can motors were replaced with lighter racing car motors rewired into a series parallel configuration and the model flown with eighteen cells. The weight saving resulted in a flying weight of 183 oz and wing loading of 20.3 oz/sq. ft. For future builders, the 22 turn Magnetic Mayhem car motor is recommended, with the four motors being wired series parallel from 18 cells. The Magnetic Mayhem motors have a slightly longer armature and are significantly more efficient than regular car motors. They are also available with timing for reverse rotation, and these should be used if a simple single stage gear reduction is employed. When the original model was built, it was necessary to make the three blade props from blades that were cut from regular two blade wood props. Master airscrew now makes plastic 3 blade 13x8 props, so these are made to order for the Lancaster. A gear reduction of 5:1 should be used. The superbox available from MEC in Seattle is suitable. Static load is 34 amps to the batteries, resulting in 17 amps to each motor with series parallel wiring. This is very light loading for these motors, coming within their efficiency range. This results in good flight endurance and long motor life.
2006: With Li-Po batteries, this model would fly very well on Speed 480 motors.
2011. Now has an Astro Flight Geared 25 inrunner brushless with 13x10 prop. On 4S will about go vertical. Not quite “Auster like,” but huge fun.
Bristol Freighter. (June 2000) 1/12 scale Span 108 ins Wing area 1480 sq.
ins Airfoil Eppler 197 with NACA leading edge cuff outboard. Length 71 ins. Weight with sixteen N-1900 SCR nicadsc is 157 ozs giving wing loading of 15.2 oz/sq. ft. Motors are Kyosho 17 turn Atomic Force car motors running in series drivng four blade 15 x 10 Zinger wood props through 7.2:1 ratio super box. Current is 25 amps static, and props turn 3,200 RPM giving static thrust 86 ozs. Slotted flaps to Andy Lenon formulae are very effective. Wing is built in three sections for ease of transportation. Sturdy fixed undercarriage is good for rough grass strips.
Shoestring “58.” (2001) 1/4.8 scale Span 58 ins. Wing area 500 sq ins.
Length 46 ins. Weight 56 oz with nine N-1900 SCR nicads. Wing loading: 16.1 oz/sq.ft. Eppler 374 airfoil. Magnetic Mayhem 22 turn motor with 3.0:1 ratio gearbox driving 12 x 10 APC-E prop at 5,000 RPM draws 28 amps static. Very fast and aerobatic, especially on a 3S Li-Po battery.
Update: June 2006. The Mars now flies on four Jamara 480 HS BB motors with MP Jet 4.1:1 ratio gearboxes and 10 x 7 APC electric props. The landing speed is slower because of the weight saving, and flights are longer.
Richard Pearse Monoplane 370. Park Flyer. 2002. Span 36 ins. Wing area 432 sq. ins. Length 20 ins. Weight 14 oz. Wing loading 6.2 oz / sq.ft (75% equivalent for flying wing.) Motor, GWS EPS-300C-AS (Speed 370) with 3.75:1 reduction, driving 8 x 6 APC slow flyer prop. 8-720 NiMH cells give 5,000 RPM static at 7.5 amps. Aerobatic park flyer. Model of first plane built by Pearse, and claimed by historians to have flown in New Zealand in March, 1903.
Richard Pearse Monoplane 600. ¼ Scale. Jan 2003. Span 60 ins. Chord 20 ins. Wing area 1,200 sq. ins. Length, 35 ins. Weight with nine Sanyo CP-1700 SCR cells is 60 ozs. Wing loading, allowing for 75% efficiency of flying wing, is 9.6 ozs/sq.ft. Motor is Magnetic Mayhem – reverse timing. Master Airscrew gearbox 2½:1. Prop is 12 x 8 APC-E turning 6,700 RPM at 27 amps, giving a static thrust of 38 ozs. General. Construction of all models is basically very traditional with Balsa (lots of 3/16" stick) and moderate amount of Basswood. Very little ply and epoxy. Covering mostly low temperature film with Mica film on lower surfaces of wing for weight saving and added strength. Weights given are with Sanyo RC-1700 nicads.
SHORT SOLENT 400. March 2004. Scale 1/16.5. Span 82 in. Wing area 905 sq.in. Length 65 in. Airfoil, Selig 7055 with NACA leading edge cuff on outboard sections. Weight with eight N1900 nicads, 83 ounces. Wing loading 13.2 oz/sq.ft. Four GWS Speed 400 geared drive motors, “E” series with gear ratio 3.4:1 driving GWS 9x7 three blade props (EP9070x3) and GWS 35mm three blade spinners. Motors are wired parallel, static current 35 amps at battery, 8.25 amps to each motor. Static thrust 48 ounces at 4,900 RPM. Construction and covering as for Sealand. Flies for 9 minutes on eight 1900 mAH nicads or 15 minutes on nine 3,000 NiMH cells . Alternate power would be “F” series gear drives with 3.9:1 reduction from nine nicads. This should give the same power for a 12% reduction in current, resulting in longer flight duration. If difficulty is encountered in finding the GWS three blade props, two blade 9x6 APC slow flyer props can be used. This may sound smaller than what would be expected, but it is because of the difference in loading from different manufacturers. The APC slow flyer props give the same performance on less amps that that required for the GWS three blade props, so the flights are longer.
Upgrade 2006. This model flies very well on Speed 480 or Cobalt 400 motors, especially with a 3S Li-Po battery. It is the easiest of the twin motor models to build and is recommended for anyone building their first electric twin.
GRUMMAN ALBATROSS. December 2004. Scale 1/12. Span 84 in. Wing area: 945 sq. in. Length 62 in. Airfoil: Selig 7055. NACA leading edge cuff on outboard sections. Can fly on eight to ten cells. Weight with nine N1900 SCR nicads, 93 ounces. Wing loading 14.2 oz/sq.ft. Two Magnetic Mayhem 22 turn motors, reverse timing, wired parallel. Great Planes “GD-600” 3:1 reduction, driving 11 x 7 APC electric props. Static current with nine cells is 32 amps at battery, 16 amps to each motor, giving a static thrust of 52 ounces at 6,000 RPM. Fuselage is stick construction, sheeted below water line and on top. Covering below the water line is silkspan applied with nitrate dope and painted with lacquer. Upper fuselage, tail surfaces and wing are covered with film. The Albatross is slightly larger in size than the Sealand, has a lower wing loading and flies a little slower.
May 2005 update. The same motors can be used with 12 x 8 APC electric props and Master Airscrew 3.5:1 gearboxes, or Great Planes GD-600 gear drives. Static current draw with nine cells and 3.5: ratio is 30 amps (15A to each motor), giving a static thrust of 54 oz at 5,100 RPM. Flight time on an eight cell 3,000 NiMH battery is 17 minutes. Alternate props are Master 11x8 three bladers, but flight time is shorter.
September 2005. Because of the Magnetic Mayhem motors no longer being available, the Albatross was used to test a pair of Multiplex Permax 7.2 volt Speed 480 motors, flying on eight or nine cells. It can fly and land considerably slower because of the weight saving. 12 x 8 APC electric props were used with 4.1:1 ratio gearboxes. With a nine cell pack of CP-1700 SCR nicads the flying weight is 81 ounces for a wing loading of 12.2 ounces/sq.ft. On an eight cell 3,000 NiMH battery the flight time is 28 minutes.
DHC-6 Twin Otter 600. May 2005. Scale 1/9.3 Span 84 inches. Wing area 956 sq.in. Length 65 in. Airfoil: Selig 7055. NACA leading edge cuff on outboard sections. Flies on eight to ten cells. Weight with nine N1900 SCR nicads is 100 ounces giving a wing loading of 15.0 oz/sq.ft. Two Magnetic Mayhem 22 turn motors, reverse timing, wired parallel. Master Airscrew 3.5:1 gearbox, or Great Planes GD-600 gear drive, 3,8:1 ratio. 12x8 APC electric props. Static current draw with nine cells and 3.5:1 ratio is 30 amps (15A to each motor), giving a static thrust of 54 oz at 5,100 RPM. Has optional slotted flaps. Can be flown with 11x8 three blade MasterAirscrew props.
SHORT SEALAND 480. August 2005. A scaled down version of the Sealand 600. (July 2002) Scale 1/10. Span 74 ½ inches. Wing area 695 sq. in. Length 53 in. Airfoil: Selig 7055. NACA leading edge cuff on outboard sections. Flies on eight or nine cells. Weight with eight CP-1700 SCR nicads is 61 ounces for a wing loading of 12.6 oz/sq.ft. Two Jamara Pro 480 HS BB motors wired parallel. MP-Jet Speed 400 gear boxes, 4.1:1 ratio drive 10 x 7 APC electric props. Static current draw with eight cells is 23 amps (11.5A each motor) giving 30 ounces thrust at 5,900 RPM. Has flown 32 minutes on an eight cell 3,000 NiMH battery. Very lively performer. Handles wind and rough water extremely well for a model of this size. The Sealand 480 can also be flown with Multiplex Permax 7.2 volt plain bushing Speed 480 (long can Speed 400) motors with MP-Jet Speed 400 gearboxes, 4.1:1 ratio, and 11 x 7 APC electric props. Pitch speed is not as high with these motors as with the Jamaras. The Sealand 480 is 5.5 inches shorter than the Sealand 600 and the wing area is 135 sq. inches less. However, the span is almost the same as the larger Sealand, but the chord is narrower and the aspect ratio higher, more in keeping with that of the full scale plane.
DHC-6. Twin Otter 480. December 2005. Scale 1/12 Span 67.5 inches. Wing area 612 sq.in. Length 52 in. Airfoil: Selig 7055 with leading edge cuff on outboard sections. Flies on eight to ten cells. Weight with eight CP-1700 SCR nicads is 60 ounces giving a wing loading of 14.1 oz/sq.ft. Two Jamara Speed 480 HS BB motors, wired parallel. MP-Jet 4.1:1 gearboxes with 10 x 7 APC electric props. Static current draw is 23 amps (11.5A to each motor), giving a static thrust of 30 oz at 5,900 RPM. Weight given is without optional flaps. Flying weight and wing loading will be considerably lower with brushless motors and LiPo battery.
KZ-IV March 2006. Scale 1/7.8 Span 80 inches. Wing area 765 sq. in. Length 48 in. Airfoil: Selig 7055 with NACA leading edge cuff on outboard section. Flies on eight or nine cells. Weight with nine CP-1700 SCR nicads is 68 ounces for wing loading of 12.8 oz/sq.ft. Two Jamara Pro 480 HS BB motors wired parallel. MP-Jet Speed 400 gear boxes, 4.1:1 ratio drive 10 x 7 APC electric props. Static current draw with nine cells is 26 amps (13A each motor) giving 38 ounces thrust at 6,200 RPM. The KZ-4 is a lively performer and quite aerobatic.
SHORT SOLENT 480. May 2006. Scale 1/14.5 Span 99 inches. Wing area 1,200 sq. in. Length 73.5 in. Airfoil Selig 7055 with NACA cuff on outboard sections. Weight with ten 2,600 NiMH cells is 124 ounces for a wing loading of 14.9 oz/sq.ft. Four Permax 480 can motors are wired parallel. MP-Jet 4.1:1 gearboxes drive 10 x 7 four blade props 4,600 RPM. Static current is 38 amps (9.5 amps each motor). Static Thrust: 60 ounces. The propellers are regular Master Airscrew two blade nylon props that are notched at the centre where they cross, and bolted together on the shaft.
May 2007 update. The Solent is now flying on 3S Li-Po batteries. It will fly on a single 3S1P 2800 mAH Li-Po, but even with the battery right up in the nose, there is hardly enough weight to bring the C of G forward enough. Instead of using additional ballast in the nose, it is felt better to add an extra 3S Lo-Po battery parallel. This gives the needed ballast as well as increasing the endurance. It also makes it easier on the battery because the load is being divided between the two packs and the discharge rate of each battery is half of what it would be for a single pack.
May 2008. With difficulty in finding a reliable ESC to handle the amperage of all the motors wired parallel, the wiring has been change to series parallel. The motors on each side are wired parallel with each other, and the pair on the port side are in series with the starboard pair. Power is from a 6S pack of LiPos. The voltage is double, but only half of it goes to each motor. The amperage from the battery at 21 amps is now about half of what it was formerly, but each motor is only drawing half of this, 10.5A. The pleasant surprise in this configuration has been the increased efficiency overall. The prop speed is now 5,100 RPM giving 75 ounces of static thrust. For enhanced performance, the model may be powered with 7S LiPos, but check the voltage limit on the ESC. Also check the BEC limit. The BEC in most speed controls is suitable for 3S operation such as used with all the motors parallel, but with series – parallel wiring and 6S operation, it is usually necessary to disconnect the BEC and use a separate receiver battery.
BLACKBURN BEVERLEY. August 2007. Scale 1/15.5 Span 125 inches. Wing Area 1,700 sq.in. Length 77 inches. Airfoil Selig 7055 with NACA leading edge cuff on outboard sections. Slotted flaps. Wing built in three sections. The nose section of the fuselage is removable to give access to the battery and make adjustments to the nose wheel mounting, as well as reducing the size of the fuselage for transportation. The tail plane and main landing gear are all removable for transportation. Weight with a 6S Li-Po 2800 mAH battery is 164 ounces giving wing loading of 13.9 oz/sq.ft. Four “Speed 600” (Mabuchi 550) can motors wired series-parallel, with 3.5:1 Master Airscrew reduction gearboxes, turn 10x6 four blade props at 6,500 RPM. Static thrust is 110 ounces at 32 amps (16 amps to each motor). Each airscrew is made from two regular 10 x 6 Master Airscrew GF nylon props, notched at centre and crossed. These are held in place by bolting together on the propeller shaft. It is not necessary to glue them. The four motors used in the prototype are the same ones that were used in earlier years in the Lancaster and Mars before those models were upgraded to other motors. The Beverley has a lower wing loading than the other models these motors were used in, so it has a better climb rate on similar power. Because the 6S Li-Po batteries being used in this model have a slightly higher voltage than the 18 nicads being used in the older models, the pitch of the propellers was decreased. The previous four-motor models used 10x7 props. The Beverley is flying on 10x6 props. The four blade props are strictly for looks. The performance would be better with regular two blade APC electric props. This model would fly on Speed 480 motors. The wing loading would be lighter and the endurance would be increased. In selecting a speed control, use one that does not have a brake engaged permanently. It makes for smoother landings if a little power is left on, and this is not always possible with a brake on the ESC. The Castle Creation 35 amp Pegasus is one possibility. When using the Pegasus 35 with 6S Lo-Pos, the BEC should be disconnected, and a separate receiver battery used.
DH 86 EXPRESS. August 2008 Scale 1/7.9 Span, 98 inches. Wing area 1,507 square inches. Airfoil Selig 3021 modified towards the tips. Length 71 inches, Weight with 6S 2800 Li-Poly battery, 114 ounces. Wing loading is 13.5 ounces / square foot (allowing for 80% efficiency of biplane wings.) Four Jamara 480 HS BB motors are used, wired series-parallel, driving 10 x 7 APC-E props through 4.1:1 ratio gearboxes. Static Thrust is 76 ounces at 6,200 RPM drawing 26 amps from battery. (13 amps each motor.) The wings have a very high aspect ratio. Efficiency comes from using the thin Selig 3021 airfoil, but as in sailplanes, it makes for a challenge in accurate construction. Wing joiners are optional, but demand good workmanship because of the thin airfoil used. Likewise, the undercarriage is a tight fit in the fairings, but they add to the streamling of the model. The torsion bar suspension used on the main gear gives very good operation on rough fields Flight characteristics are excellent. A safe, easy to fly model.
2009 update. The lowest recommended power weight ratio for electric models used to be 40watts/ pound. Now it seems that the recommended figure is usually 50 watts/lb. This figure however is influenced by wing loading and size. The prototype PBY-5A Catalina with its original can motors flew quite well on 35 watts/pound because of its low wing loading and large size. Larger models with low wing loading fly on surprisingly little power.
2012 update. Motors and batteries continue to improve, so the figures quoted a few years ago seem to be ridiculously low by the standards used today.
Choosing Brushless Motors
In choosing a brushless motor to replace the typical Speed 600 or “05” race car motors used in the older models described above, the list of suitable outrunner motors is endless. Avoid high KV motors that would turn smaller props at very high RPM. Larger course pitch scale-size props turning slower are more efficient than small ones turning very fast, and give more thrust for a better climb rate. They are also quieter and look better. Scale size props are usually the largest diameter that can be used that give adequate ground clearance. Further to what has been written about keeping the propellers diameter on the large size is the matter of pitch. For sport and scale flying, the optimum is to have the propeller pitch about 70% of the diameter. Hence the 10 x 7 inch prop is one of my favorites for many of the “multi motor” models that used the geared Speed 480 brush motors. When it comes to max thrust at slow speed such as in 3D flying, a fine pitch works wonders, but it does not give a good pitch speed for sport and scale models.
A great brushless motor that has been found to be a suitable replacement for the geared brushed motors used in models such as the Mosquito 600, DH Comet, Chipmunk and Auster is the A2820-6; 1,000KV, sold in the USA by BP Hobbies. On three cells it will swing a good size prop. The motor diameter is 35mm and length 47mm. Another good alternative could be the A2814-8 which is the same diameter, a little shorter at 36mm, and an ounce lighter, but has not been tried personally. A smaller motor from BP Hobbies that should be very suitable for the Speed 480 multi motor models like the DH Express, Sealand 480, Solent 480 and Mosquito 480 could be the A2217-8 which comes at 1,100 KV. Diameter is 28mm and length 34mm. All would give more than adequate power on 3S Li-Po batteries.
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