I designed and built a light plane (similar in proportion to a quickie 500, but flat bottomed airfoil and lighter). I had planned on using a 19 turn speed 600 motor with 7-SC cells. What prop/gear box should I use? Will I be able to get enough power to make the plane fly well? What size plane and box are speed 600 (550) motors used on?

I appreciate any help.

Mark

Car motors on 7 cells are what gave E-flight a bad name all those years. What makes a car go does not necessarily make an airplane go.

Take a look at the Gary Wright Model Products Kwik-E (http://www.gwmp.net, though it may be .com. I know one is Gary's site, and the other is a porno site or something...) That runs on a car motor and 6-7 cells. It might give you an idea of what you can do.

For sleek, fast, light airplanes, you don't need a gearbox. I'd say if the plane is under 2lb and very aerodynamically clean, you have a winner.

A bigger, floaty airplane would do well with a 2.5:1 or 3:1 gearbox and a 12x8 propeller. I have a Hobby Shack "Flying Start" converted to electric that weighs 3lbs, and floats around well on a Speed 500, 7 CP1300 cells a 3:1 gearbox and 12x8 Master Airscrew folding propeller.

The plane is 46 oz. It's sleek and has 480in^2 of area. I expect it will fly good. I'm trying to find out more about the speed 600 motors. Some people tell me that you just cant get them to do anything but consume power and wear out. Many people say that I should use a brushless motor. How does a brushless work better?

46 ounces will work Ok with 7 cells, not great,.. assuming that's the weight WITH the motor and battery pack, ready to go. An endoplasma (kyosho car motor, has large comm and brushes), with a 13X8 prop , geared 4.6 to 1 will pull it, even with a 12X8 it should be OK, not stellar performance, but should takeoff nicely from grass and fly. With that small wing, you might want to go a bit higher pitch speed and sacrifice some thrust, so a 12X10 might be in order. This is all assuming your weight (46 ounces) is with everything on board. If that is without power system, then you'll be at about 4.5 lbs ready to fly, which is gonna be very difficult to make "go" on just 7 cells. Possible, but not what I'd want to fly. For a "reality check" on weight,.. my E3D kit is 600 square inches, 52 inches long, and built and covered they end up in the 16 to 18 ounce range, with equipment about 22 or so, with motor/gearbox/prop, just no batteries, 32~34 ounces. If you want to see how an endoplasma works, the E3D video on my site (www.gwmp.net) is an E3D, stock, 56 ounces flying weight (that's with 10 sub-c cells) and an endoplasma. It has flown well on 6 cells, going up to a 15X10 prop, but speed is low on that plane anyway, not exactly what it sounds like you have. It's very very easy to get TONS of thrust from relatively low power input on an electric motor, just gear high and swing a really big prop. It becomes much more difficult when a fair amount of speed is required. Power requirements go up exponentially with speed requirements.

Thanks for your input. The weight at 48 oz is ready to fly. Should I use more cells if I want more performance? How many cells? I have room for 10 (believe it or not). Will my speed 600 burn up?

depends on exactly which speed600 you have. speed600 is a pretty generic term, there are literally hundreds of motors that are called that. Mabuchi makes dozens, if not hundreds, of motors that physical size, with different windings, so does johnson and sagami. Most of the motors sold in the hobby industry as "speed 600's" will take 10 cells fine as long as you prop/gear them to draw about 25 amps maximum.

The watts (amps x volts) is the power limiting factor. How efficiently the power is converted into thrust and how much load is created by weight and drag are the two largest factors that determine performance. The lighter the plane, the more efficient the motor, prop and speed controller, the faster and longer the flight. The number of cells should depend on the maximum amperage sustainable by the motor windings without over-heating the motor or the batteries. A direct drive is more efficient than a gear box. Choosing the right size and pitch prop for a given motor is the key to achieving optimum performance from a given motor battery combination. The weight should always be minimized and the drag as low as possible to achieve the fastest airspeed. The power can be increased by adding cells, but this also adds weight. Choosing the right voltage motor (different number of amp turns and wire guage) allows the power to be varied. Since the batteries have a fixed amount of stored energy, i.e. 1.5 Amphours (1500 maH) at 8.4 Volts = 12.6 watts for 1 hour,
this means that your flight time will be shorter the more watts you use to fly the plane. For example, if you are drawing 15 amps in flight, the batteries will last for 60 min x 1.5 AH/15A = 6 minutes. Also, the batteries will get quite hot at that 10X discharge rate. Adding cells will increase the volts and amps and therefore the watts, but could result in overcurrent conditions for both the motor and the batteries. The power is battery limited. Using larger cells 3300maH will reduce the heat and battery overcurrent heating. As always, everything is related to everything else. If a given motor is twice as efficient at converting the input power to thrust, the plane can fly twice as fast, or twice as long with the same batteries.

something just struck me the wrong way when reading the above. The direct drive being more efficient thing. Yes, a gearbox requires some watts , but it's a fixed amount, not a percentage of the input power as many people seem to think, so the more power you're making, the less the issue of "gearbox losses" becomes. I'm a huge proponent of gearing ans swinging a very large prop. Yes, you "waste" a few watts in the gearbox (far less than many people want to believe, however), but the aerodynamic efficiency gained by the larger prop, in the majority of instances, far outweighs the socalled "gearbox loss". I've flown 3lb airplanes on 300 watts direct drive, then geared the motor to turn a larger prop, reduced the current (input power) and taken them from "mild sport performance", to very close to hovering power, without losing any visible level flight speed,.. on only 200 watts. Makes you wonder which is the better solution,..eh?
On a side note, regarding the above, I've converted several quickie-500's to electric, powering them with everything from 280 watts (10 cells, mag mayhem, geared for a 12X10 prop, weight 60 ounces) up to 800 watts with a brushless (geared hacker, 20 cells), and they all flew very very well. The best setup I had in one for a "cheapie" motor, was an endoplasma, 10 cells, 4.6 ratio, with an 11X10 apc "E" prop. Right at 7000 rpms on that prop, so pitch speed was in the mid 60's, and it was as fast as most any 46 size sport plane at the field. That was a very good setup. Brush wear on that setup is about 35 or so flights between brush changes, but hey,..it's only a $25 motor so the cost to get in the air initially is very low.