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What size motor??

Old 10-21-2003, 02:10 PM
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Squire
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Default What size motor??

I am in the throws of building a Dykes Delta. It calls for a 15 size 2 cycle engine. I would like to convert this to electric.

Question: what size motor should I use (with gearbox if necessary) to power this plane with some authority? I don't want something that will fly just above stall but fast enough for aerobatics.

Is there some chart somewhere that give the electric equivalent of fuel engines?

Thanks, Phil
Old 10-21-2003, 02:36 PM
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Greg Covey
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Default RE: What size motor??

Phil,

What is the wingspan and flying weight of your Dyke Delta wing?

There are many solutions available to make it e-powered. Is a brushless option to costly or would you prefer a canned ferrite magnet motor? Either cost solution can be made direct drive...no gearbox.
Old 10-22-2003, 02:05 PM
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LowAndSlow
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Default RE: What size motor??

There is a program that is a big help in deceiding what motor, battery, prop,etc. works with a given airframe. you can get a trial download at http://motocalc.com
Old 10-22-2003, 02:28 PM
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Matt Kirsch
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Default RE: What size motor??

Be warned that Motocalc will give you hundreds, if not thousands of pretty outlandish combinations, along with a few usable setups, if you don't keep it reined in. A noob with no electric experience and no electric knowledge will be even more lost than before.

Here are a few rules of thumb to help you with MotoCalc:
1. You will want to limit your max current to 40 Amps for sport models.
2. You will want to concentrate on 8-cell systems for a .15 size airplane.
3. You will want a direct drive with maximum pitch speed for a speed-demon, and a geared system with a more reasonable pitch speed, ~40MPH, for a 3D plane.
4. Don't let the numbers confuse you. Read the in-flight summary for english explanations as to the behaviour of the plane with a given power system. You're mostly concerned with Amps, static thrust, and pitch speed.
5. Ideally, static thrust should be at least 25% of the airplane's weight, preferably more. At 1:1, the plane should hover at full throttle, and at greater than 1:1, the plane will climb vertically.
6. Pitch speed is the maximum theoretical speed the plane can go. It's easy to figure out what pitch speed you need for a fast plane: How fast do you want it to go?
Old 10-22-2003, 06:22 PM
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Squire
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Default RE: What size motor??

Thanks people for your replies. I did download Motocalc and tried it. You're correct - I am overwhelmed with information. There's gotta be a way to filter this down a bit. As for the plane that I'm building, I do love to build light but since I have nothing other than the RC Modeler plans to go by I have no idea what the weight will be. I am assurred that a .15 glow engine will do just fine. This being the case, I would assume (i know) that it would weigh with engine about 3 lbs (48 oz.). The wing area is about 500 sq. in. Now I have a Quickie 500 that was designed for a .15 glow. Perhaps I should weigh it since it has neither engine or radio in it right now. (Oh yes, I had a .40 OS in it - a real bear - but my reflexes are not up to that thrill anymore!) I plugged this data into MotoCalc and got, like you all said, hundreds of choices! Much more than I could digest.

I'm currently flying a Combat Wing with a Speed 400 on an 8 cell 1100 Mah pack through a 20 amp ESC. It will haul pretty good but it is also light. Haven't weighed it yet.

Again, thanks for your patience with an electric newbie.

Phil
Old 10-23-2003, 07:35 AM
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Default RE: What size motor??

Yeah, a Speed 400 is a little on the wimpy side for a .15-size plane unless it's really light. I tend to figure 25oz, no matter what the plane is, is about maximum takeoff weight for a Speed 400 model.

Let's see... An important question to ask is how you want this plane to fly? Slow and floaty generally means a large prop and high gear ratio. Fast generally means direct drive. Aerobatic is somewhere in between, geared, but not geared as much as the slow floater.

What are you looking for in a motor? Planes of this size can be still be powered well with inexpensive car motors, or you can go brushless.

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