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How to get started with electric planes

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Old 04-17-2006, 12:35 PM
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coolbean
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Default How to get started with electric planes

This is basically all the information I WISH I had before I started blindly into electrics. Hopefully I can keep someone from going through what I had to.

My FRIST suggestion is to get a copy of MotoCalc. It is extremely valuable and lets you virtually setup an aircraft before you spend the money on the hardware. On the downside, it is $40. It does have a free trial period though. At the vary least use the trial period and play around with different setups to get an idea of how all this works.

Now for the easy stuff; pick an airframe based on your experience and preference, then get the recommended size servos and receiver for it.

Now the fun/confusing stuff. You need a power train.

Lets start with the motor. Your plane probably came with a motor, but don’t fool yourself; it might fly with it, but your not going to be happy. You are going to want a brushless motor. There are two kinds, outrunners and inrunners. Outrunners are generally slower but make more torque so you can swing a bigger prop directly. They also usually come with handy brackets that make them easy to attach to a firewall. Inrunners are usually very fast and work great for spinning small props for speed applications. They can also come with geared drives (some with multiple gears) so you can swing bigger props more slowly just like an outrunner. They are a little bit more difficult to mount unless it uses the almost standard GWS stick mount. Himax and a few others make inrunners (and outrnners) that are directly compatible with this mount. A good source for comparing motors is the Great Electric Motor Test. [link=http://www.flyingmodels.org/index_en.htm]http://www.flyingmodels.org/index_en.htm[/link]

Now that you have a motor, you need a speed controller.
The first thing you have to do is figure out how many amps your motor is going to pull at what voltage using what prop. The easiest way to do this is in MotoCalc. If for whatever reason you don’t have/can’t get MotoCalc, try this calculator from Diversity Model Aircraft. [link=http://brantuas.com/ezcalc/dma1.asp]http://brantuas.com/ezcalc/dma1.asp[/link] It has the most preset batteries and motors of any free tools I have found. You can also check out the Great Electric Motor test again, if your motor is listed there. You need to have an idea of how many volts you are going to use before you get started.Standard now days is Lithium Polymer (LiPo) in either two cell (referred to as 2s or 2s1p) which runs at 7.4 volts or three cell (referred to as 3s or 3s1p) which runs at 11.1 volts. But we’ll get into that a later. Ok back to the calculator. Basically what you are trying to do is get the highest amount of thrust and/or pitchspeed with the lowest amp draw. You do this by changing the prop length, pitch, and motor gearing (if available with your motor). Make sure to check your motor to see what its limits are as far as voltage and amperage so that you don’t exceed it. Now that you know how many amps you are going to draw at what volts, you can start looking at speed controllers. First you either need a brushed or brushless controller based on your motor. Second it needs to be able to handle the volts and amps you plan on running. Remember to calculate in 1 amp for powering the servos and receiver if you are running mini servos, more if using standard servos. Allow yourself for some headroom here, no sense frying your speed controller and crashing your plane because you wanted to save a couple of bucks. Finally look at features. The most important of which, especially if you are going to be using LiPo batteries, is voltage cutoff. Make sure it has an adjustable cutoff. I’ll explain more later when we get into the batteries. Also make sure it has a battery eliminating circuit (BEC) so you don’t have to use a separate battery to power the receiver/servos. A few other noteworthy features are electronic break, adjustable timing, and soft start/cutoff.

Now you need a battery. This is probably the most important, and most overlooked part of going electric. First decision is what battery chemistry to use. NiCd, NiMh, or LiPo. NiCd and NiMh are a little bit heavier and bigger for around the same voltage and capacity. LiPo’s are more expensive, the chargers for them are more expensive, and they are more prone to damage and explosions/fire. There are several posts and discussions on which is better, proper charging, battery safety, battery maintenance, etc… so I won’t cover any of that here. By this point you have probably decided on what voltage you are going to run, so the next choice is capacity. Capacity is measured in milliamps per hour (mAh) This will determine how long you can fly on a charge. MotoCalc and the tool from Diversity Model Aircraft will tell you approximately how long you can fly with a given capacity. The next and OH SO VERY IMPORTAT thing to consider, especially if you are using LiPo batteries, is discharge rate. This is measured in a multiple of capacity. For example if you have a battery measured at 1200 milliamp and a discharge rate of 10C (1.2 amps X 10) you can safely draw 12 amps. Most batteries have two ratings, a continuous and a max or burst rating. With a continuous rating, you can draw that many amps from beginning to end and be perfectly fine. The max/burst rating is the maximum number of amps that can be drawn for a short period (somewhere between 10 and 30 seconds depending on the battery) Depending on your flying style, find a battery that suits your needs. If you are a full throttle from beginning to end type flyer, or if you just want to be safe, then the continuous rating needs to be higher than your predicted maximum draw for your motor/prop/gearing combo. If you fly at ½ to ¾ throttle with only short busts for vertical flight, take both numbers into consideration. If you draw too many amps from your battery, voltage will drop, you will hit the voltage cutoff on your esc, assuming it has one, and your motor will stop. You will also permanently damage and/or destroy your battery, possibly with explosions and fire. Finally, for LiPo batteries, there is a concern about cell balancing. If one cell doesn’t charge properly, the other cells over charge to make up for lost voltage. Looking at the pack as a complete unit, you can’t tell the difference, but it will damage and destroy your battery. Some cheap LiPos only have a single power lead with no way to balance the pack. Some cells have a small built in circuit and a separate charging lead that helps keep the cell in balance. And finally some cells have a tap into each cell in the pack so they can be charged and balanced separately. I don’t suggest buying a pack that doesn’t have any sort of cell balancing protection. The ones with the built in circuit are OK, but you don’t have any way to confirm that it is working. Separate taps are the only way to know for sure that all cells in your pack are healthy and happy.

Now you need a battery charger. If you are using NiCd or NiMh, then any charger that can charge at the voltage you need at the mAh you need is fine. They get as simple or complex as you want. If you are using LiPo, there are a few cheap chargers, but I don’t suggest them. If you are really in this, then you need a good hobby charger. The one I suggest is the ProPeak Prodigy II. (This is also available in several clones that are exactly the same except the sticker on the outside of the box, any of them are fine.) You can pick one of these up for around $70. It will charge, discharge, and cycle 1-3 cell LiPos, 1-14 Cell NiMh/NiCd, and 3 to 12V Lead Acid (Pb). Unless you get into BIG electrics with some higher voltages, it is the last charger you will ever need. (well.. at least until the next battery chemistry comes out) If you are using LiPos, you might also want to consider getting a cell balancer, there are several models out there for around $20.

Finally I suggest checking out the R/C Battery Clinic, [link=http://www.rcbatteryclinic.com/]http://www.rcbatteryclinic.com/[/link] , It has a lot of great information, including a great article on how to build a 12V power source out of an old computer power supply. Also I suggest searching through the RCU forums about LiPo fires. What you will find are some great videos. I suggest you do this so you will respect the power of these batteries and learn proper care and use of them.

EDIT 5/3/06 One note about picking a motor to fit your plane. The general rule is 100 watts or more to 1lb for 3d flight. Around 75 watts to lb for aerobatic flight, and around 60 watts per lb for leisure flight. To calculate watts multiply volts by amps. The calculator at Diversity gives you the watts, and some manufactures will tell you how many watts their motor is good for. A plane may fly on as little as 50 watts per lb, but will be VARY sluggish.

Now go fly something already.
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Old 04-21-2006, 10:14 AM
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Default RE: How to get started with electric planes

Did anyone find this useful or think that it would be useful to a new person?
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Old 04-21-2006, 03:35 PM
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Default RE: How to get started with electric planes

ORIGINAL: coolbean
Did anyone find this useful or think that it would be useful to a new person?
Yes. Kudos to you coolbean.
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Old 04-25-2006, 03:06 PM
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Default RE: How to get started with electric planes

Yes, me too. Thanks for putting all that good information in one place. Nice job.
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Old 04-28-2006, 11:20 PM
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Default RE: How to get started with electric planes

Thanks coolbean,
I found that very helpful, I was afraid electric flight would be complicated. I enjoy building from plans so chances are I'd have to do my own research. I wish they could just list motor/esc/batt. packages that would replace a .15 or .25 size engine. Then I could jump right into it.
Bernie
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Old 04-29-2006, 11:21 PM
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Default RE: How to get started with electric planes

I wish they could just list motor/esc/batt. packages that would replace a .15 or .25 size engine. Then I could jump right into it.
That's exactly what's holding me off. I have been dropping into this forum to get an idea of how to do this. I plan to just get the parts and experiment, but not for a while (I have glow planes to fly )
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Old 05-01-2006, 03:50 PM
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Default RE: How to get started with electric planes

If you are still confused on how to pick a power system, just search on the boards for somone flying the model you want and ask them what they are using in it and buy it... That's how I finally got my first electric to fly
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Old 05-02-2006, 01:37 PM
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Default RE: How to get started with electric planes

I just bought a aon 3kv thrust motor,a phoenix 60 amp controller and a 3 cell lipo for a BD-5(aeroworks).The hitec os5 receiver has 5 channels. Where do I connect the elevtaor,rudder,thorttle and elerons? Does it matter? also, where does the esc(battery) plug into?

thanks for the answer
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Old 05-02-2006, 09:19 PM
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Default RE: How to get started with electric planes

The BD-5 is a pretty hot little pusher... I havn't heard of aon motors. Do you have a link to it? Also what are the specs for your battery (mAh and C rating) Hopefully it isn't taking FULL advange of that pheonix 60, becuase if it is, then you have way to much motor for that plane.
It also sounds like you are new not only to electronics, but to rc aircraft in general.. if that is true I highly suggest you DO NOT START WITH THIS PLANE!..
But I'm going to answer your question anyway.
They do it differntly in Europe and Japan, but here in the states most everyone uses mode 2.
That is ailerons on ch 1, Elevator on channel 2, Throttle on channel 3 and Rudder on channel 4. The system gets power through the speed controller.
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Old 05-03-2006, 07:19 AM
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Default RE: How to get started with electric planes

Thanks for the answer,worked perfectly. nice drawing!
I am using a 3 cell li-po 2100mah.a phoenix 60 controller and a aon thrust series 3000kv motor and a 5x5 carbon prop.their website is "aonelectric.com"

thanks again for your help.........
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Old 05-03-2006, 08:38 AM
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Default RE: How to get started with electric planes

Ok, that should be a pretty good setup for that plane as long as your battery is rated at around 10C continuous to 15C max. You should max out at around 25 amps with a static thrust of 34oz and a pitchspeed of 112 mph [X(]. This plane will be pretty fast. Again if this is your first plane I highly suggest you try something else first...
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Old 05-03-2006, 01:08 PM
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Default RE: How to get started with electric planes

Excellent summary, Coolbean--your post is now in my "Electrics" file. I have been looking for this kind of info--especially on motors and speed controllers. I am a lifetime glow aircraft person, and the idea of getting into electric is very appealing--but as a newbie, it is also a little overwelming--there is so much new information to learn. Thanks!
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Old 05-04-2006, 09:16 PM
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Default RE: How to get started with electric planes

I edited and added a few things that might clear up motor selection a little.
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Old 05-23-2006, 10:49 AM
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Default RE: How to get started with electric planes

I am so new to this that I am just researching how to get started. I do want to stick to electric (too many toys with gas motors). My neighbor is experienced and will help, as will the local flying club (paved strip with mowed grass alongside). I appreciate your info but want to "keep it real simple, stupid" (me, not you)

I have narrowed it to (I think) the Toytronix T-Hawk or Megatech Freedom Flyer RTF but cannot decide between them. The T-Hawk has rave user reviews, great company support reputation, and comes with a complete spares package. Downside only seems to be 3 channel receiver and no easy upgrade for ailerons. The Megatech looks more pleasing to me, has a 4 channel radio, and spares and aileron upgrades are readily available, BUT the company's former reputation seems spotty.

Do you have any thoughts that would push me one way or the other? Also, while I was able to find how to respond to your posting it is not clear to me how to start out with a posting of my own that is not a response to someone else. I also am unclear if this note is going only to you or the forum in general.

Thanks for any help you can supply
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Old 05-23-2006, 11:58 AM
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Default RE: How to get started with electric planes

- You can get a free flight simulator at http://n.ethz.ch/student/mmoeller/fms/index_e.html You can download a lot of available models into it. Use a two stick analog game controller for $12 from Walmart
-
The cheapest starter is the Air Hogs Aero Ace. It’s $30 RTF including a transmitter. It’s only controlled by thrust of the two motors so you can’t do loops and it will fly different from a rudder and elevator plane, but its’ tough. It only needs the space of a two car garage to fly.
-
With a Slow Stick you will go through a ton of props, a motor and maybe a fuselage before you are competent. A Slow Stick does require only the space of a baseball field to fly. It’s more of a “floater”. A Multiplex Easy star is bigger than a slow stick, much tougher, has a very difficult to break pusher propeller and can handle more wind. It's available RTF for about $180 and as a ARF for $55. The Easy star requires the space of a soccer field to fly. They soar well. See http://www.plawner.net/3/1st_plane/ in which he recommends mainly Multiplex planes for their toughness and ease of construction. They also fly very well. Other options from Multiplex are the Easy Glider and the Twin Star II.
-
- I think the best idea would be to get a http://www.aeromicro.com/Catalog/gw....29.htmreceiver ready Mutliplex Easy Glider Electric, which is all built except the receiver installation and get a JR Spectrum radio and receiver for it. Would make a 4 channel great trainer.

http://www.redrockethobbies.com/Spe...M_p/spm2460.htm

http://www.hobbypeople.net/gallery/240107.asp
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Old 05-27-2006, 03:32 PM
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Default RE: How to get started with electric planes

Excellent info, thanks, this is just what EVERY beginner needs to know, answered all my questions about these issues!
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Old 05-27-2006, 11:39 PM
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Default RE: How to get started with electric planes


ORIGINAL: bgerth

Thanks coolbean,
I found that very helpful, I was afraid electric flight would be complicated. I enjoy building from plans so chances are I'd have to do my own research. I wish they could just list motor/esc/batt. packages that would replace a .15 or .25 size engine. Then I could jump right into it.
Bernie
Well that might be useful for a glow pilot converting to electric power but it wouldn't do an electric pilot much good. This should help:

SIZING POWER SYSTEMS FOR ELECTRIC AIRPLANES
by Ed Anderson
aeajr on the forums

This may get a little technical but I will try to keep it as simple as I
can. I will draw parallels to cars and bicycles in many places as most
people can relate to these and know at least a little about how they work.
I will use round numbers where I can and will use some high level examples.
If you are an engineer you will see that I am taking some liberties here for
the sake of simplicity. I will go through the parts of the power system,
then, toward the end, I will show you how we tie these all together to come
up with a complete power system.


POWER = WATTS

I will be using the terms Volts, Amps and Watts throughout this discussion.
Let me define them.

Volts = the pressure at which the electric energy is being delivered - like
pounds per square inch or PSI in a fuel system or water from a garden hose.
Volts is about pressure, it says nothing about flow. You will see volts
abbreviated as V.

Amps = the quantity or flow of electricity being delivered, like gallons per
minute in a fuel system or that same garden hose. Amps is about flow, it
says nothing about pressure. You will see amps abbreviated as A.

Watts = V X A. This is a measure of the energy or power being delivered.
This is how we measure the ability of that electricity to do work, in our
case the work of turning a propeller to move our airplane through the air.
Watts is about both pressure and flow. This serves the same purpose as
the horsepower rating of your car's engine. In fact 746 watts = 1
horsepower. So if you had an electric car, the strength of its motor could
be reported in either watts or horsepower. You will see watts abbreviated as
W.

If you want more depth on this, visit this thread.
http://www.wattflyer.com/forums/showthread.php?t=1933


MOTOR EFFICIENCY - Brushed vs. Brushless

Whether brushed or brushless, the motor's job is to convert electricity into
mechanical motion to turn the propeller to move air. Efficiency is how we
measure how much of the power, the watts, that our battery delivers to the
motor is actually turned into useful work and how much is wasted as heat.
A higher efficiency motor delivers more energy to the motor, and wastes
less.

A typical brushed motor, say a speed 400, is only about 40-50% efficient.
Only about half the watts delivered to the motor actually end up as useful
work turning the propeller. The rest is wasted. Motors that have a "speed"
designation, like speed 400, are brushed motors. There are other names for
brushed motors but the "speed" term is a common one. They are inexpensive
and they work. For example, you can buy a speed 400 motor and electronic
speed control, ESC, for $35. A comparable brushless motor/ESC combination
would
typically cost 3 to 4 times that much.

Brushless motors tend to be more efficient. They typically deliver 70-90%
of
that input power to the propeller, Thus you get better performance per watt
with brushless motors. Seen a different way, if you use a brushless motor,
then, for the same flying performance you will use less energy which means
you battery will last longer. Or you can use a similar size and weight
brushless motor and get much higher performance because the motor turns more
of the watts from the battery into useful work of turning the propeller.

So, as with many decisions we make, this is a cost benefit decision. Am I
willing to pay more to get more? That is up to you.


THE BATTERY IS MORE THAN JUST THE FUEL TANK

Think of the battery as the fuel tank plus the fuel pump and a supercharger
all rolled into one. It feeds/pushes energy to the motor. So you have to
look at the battery and the motor as one unit when you are sizing power
systems for electric planes. In many cases we start with the battery when
we
size our systems because the motor can't deliver the power to the prop if
the battery can't deliver the power to the motor.

The higher the voltage rating of the battery, the higher the pressure, like
a supercharger on a car engine. More pressure delivers more air/fuel
mixture to the engine which allows the engine to produce more power to turn
the wheels of the car. Higher voltage pushes more electricity into the
motor
to produce more power.

Using our electric motors, a given motor may take 10 amps ( the quantity of
electricity flowing ) at 8.4 volts ( the pressure at which the electricity
is
being delivered) to spin a certain propeller. We would say that the
battery is delivering, or that the motor is drawing 84 watts, ie: 8.4V x
10A. If you bump up the voltage to 9.6 volts, the battery can ram in more
amps delivering more energy to the motor which will produce more power to
the
propeller. In
this example, if we move from an 8.4V battery pack to a 9.6V battery pack
the motor may now take 12 amps. This will typically spin the motor faster
with any given propeller or allow it to turn a larger propeller at the same
speed.

However, if you bump up the pressure too much, you can break something.
Putting a big supercharger on an engine that is not designed for it will
break parts of the engine. Too much voltage can over power your electric
motor and damage it. So there is a balance that has to be struck.
Different motors can take different amounts of power, watts, volts X amps,
without damage. For example, a speed 400 motor might be fine taking 10 amps
at 9.6 volts or 96 watts. However a speed 280 motor will have a short life
with the same
combination of volts and amps.

If you match the right battery with the right motor, you get good
performance without damage to the motor. In many cases airplane designers
will design planes around a specific motor battery combination so that they
match the size and weight of the plane to the power system for good
performance.


PROPELLERS

Propellers are sized by diameter and pitch.

The diameter of the propeller determines the volume of air the propeller
will move, producing thrust, or pushing force. Roughly speaking the
diameter of the propeller will have the biggest impact on the size and
weight of the plane that we can fly. Larger, heavier planes will typically
fly better with larger diameter propellers.

Pitch refers to the angle of the propeller blade and refers to the distance
the propeller would move forward if there were no slippage in the air. So a
7 inch pitch propeller would move forward 7 inches per rotation, if there
were no slippage in the air. If we combine pitch with the rotational speed
of the propeller we can calculate the pitch "speed" of the propeller. So,
at 10000 revolutions per minute, that prop would move 7000 inches forward
70,000 inches per minute. If we do the math, that comes out to a little
over 66 miles per hour.

By changing the diameter and the pitch of the propeller we can have a
similar effect to changing the gears in your car or a bicycle. It will be
harder for your motor to turn a 9X7 propeller than an 8X7 propeller. And
it would be harder to turn a 9X7 propeller than a 9X6 propeller. The
larger, steeper pitched propellers will require more energy, more watts,
more horsepower, to
turn them. Therefore we need to balance the diameter and pitch with the
power or wattage of the motor/battery system. Fortunately we don't actually
have to do this as motor manufacturers will often publish suggested
propellers to use with a given motor/battery combination. We can use these
as our starting point. If we want we can try different propellers that are
near these specifications to see how they work with our airplane.


GEARBOXES

While unusual on glow or gas planes, gearboxes are common on electric
planes. Their primary function is similar to the transmission on a car. The
greater the gear ratio, the higher the numerical value, the slower the
propeller will turn but the larger the propeller we can turn. So you can
use a gearbox to help provide more thrust so you can fly larger planes with
a given motor. However you will be turning the propeller slower so the
plane will not go as fast.

With direct drive, that is when the propeller is directly attached to the
motor shaft, we are running in high gear ( no gear reduction). Like pulling
your car away from the light in high gear. Assuming the motor doesn't stall,
acceleration will be slow, but over time you will hit a high top end!
Typically direct drive propellers on a given motor will have a smaller
diameter.

With the geared motor, it would be like pulling away from the green light in
first gear - tons of low end power and lots of acceleration, but your top
speed is reduced.

So, by matching up the right gear ratios made up of the propeller and,
optionally, a gearbox we can adjust the kind of performance we can get out
of a given battery/motor combination.


NOW WE CAN START TO MATCH UP THE PIECES!

The simplest approach I have seen to figuring power systems in electrics is
input watts per pound of "all up" airplane weight. The following guidelines
were developed before brushless motors were common but it seems to hold
pretty well so we will use it regardless of what kind of motor is being
used.

50 watts per pound = Casual/scale flying

75 watts per pound = Sport flying and sport aerobatics

100 watts per pound = aggressive aerobatics and mild 3D

150 watts per pound = all out performance.

Remember that Watts = Volts X Amps. This is a power measurement.
In case you were wondering, 746 watts equals 1 horsepower, .


AN EXAMPLE!

This should be fun. Let's see where these formulas take us! We will use a
24 ounce, 1.5 pound plane as our example. If we want basic flight you will
need 50 watts per pound or about 75 watts input to your motor for this 1.5
pound plane. That is, 50 watts per pound X 1.5 pounds = 75 watts needed
for basic flying performance. If you want a little more spirited plane, we
could use 75 watts X 1.5 pounds which is about 112.5 watts.

Lets use 100 watts as the total target, just to be simple, shall we? I am
going to use a lot of round numbers here. I hope you can follow.

The Battery:

If we use an 8 cell NiMh battery pack at 9.6 V it will have to deliver 10.4
amps to hit our 100 watts input target ( 100/9.6 = 10.41amps) If my
battery pack cells are NiMh cells that are rated at 10C then I need an 8
cell pack rated at 1100 mah to be able to deliver 11 amps. Sounds about
right.

Now I select a motor that can handle 100 watts or about 10.4 amps at 9.6
Volts. From experience we know this could be a speed 400, a speed 480 or
some kind of a brushless motor.

We now need a propeller that will cause the motor to draw about 100 watts. I
don't know off the top of my head what that would be. I would go to some mfg
chart - GWS has good charts!
http://www.gwsus.com/english/product...tem/edp400.htm

I see that if I use a direct drive speed 400 with a 5X4.3 prop at 9.6V then
the motor will draw about 12.4 amps or about 119 watts. This would be a
good candidate motor/prop for the plane using a 9.6V pack that can put out
12.4 or more amps. This would be a set-up for a fast plane as that motor
will
spin that small prop very fast.

However maybe I don't want such a fast plane but one with a really good
climb and lots of low end pull to help out a new pilot who is in training.

I can also use a speed 400 with a 2.38 gearbox and run it at 9.6V spinning a
9X7 prop and run at about 12.8 amps for 120 watts. The larger prop will give
this plane a strong climb, but since the prop speed has been reduced by 2.38
times, it won't be as fast. Spinning a bigger prop gives me more thrust but
a lower top speed typically.

Back to battery packs and motors

So if I shop for a 9.6V pack to be able to handle about 15-20 amps, I should
do just fine and not over stress the batteries. In NiMh that would probably
be a 2/3 or 4/5 A pack of about 1100 -1500 mah capacity, depending on the
quality of the cells.

We view the battery and motor as a linked unit with a target power profile,
in this case about 100 watts. We use the prop and gearbox, if any, to
produce the manner in which we want to deliver that power to the air to
pull/push the plane.

If this is a pusher, I may not have clearance to spin that big prop so I
have to go for the smaller but faster prop combo.

If this is a puller, then I can choose my prop by ground clearance or some
other criteria and match a gear box to it.


See, that was easy, right? But we are not done! Oh no!

I could try to do it with a 2 cell lithium pack rated 7.4V. To get 100 watts
I now need a pack that can deliver 13.5 amps and a motor/prop combination
that will draw that much. So if I have 10 C rated lithiums, then the pack
better be at least 1350 mah. Probably use a 1500 mah pack to be safe.

Well, when I look at the chart for the geared speed 400 I see that,
regardless of prop, at 7.4V I am not going to have enough voltage (
pressure) to push
13 amps into this motor. So the 2 cell lithium won't meet my performance
goal of 100 watts+ per pound using this gear box.

If I go back to the charts and look at a different gear boxes I can't hit my
power goals using 7.4V. Maybe we go back to direct drive.
http://www.gwsus.com/english/product...tem/edp400.htm

We see that the best I can get this speed 400 to do is a total of 70 watts
at 7.2V ( close enough ) so I can't hit my power goals using a speed 400 at
this voltage. but 70 watts would be about 48 watts per pound so I could have
a flyable plane, but not an aerobatic plane using this two cell pack.


REALITY CHECK!

Now, in fact that is NOT how I would do this. I would decide on the watt
target, go to the chart, find a combo that meets my goals, then select a
battery that will meet the demand and see if my weight comes up at the
target I set. A little tuning and I come up with a workable combo.

Summary

So, in three posts you have taken in a basic knowledge of how electric power
systems are sized, the factors that are considered an how to predict the
outcome. Simple, right?

Of course there is a lot more to know and time and experience will teach
you plenty, but with this basic understanding you are better prepared to
begin playing with the power systems you put in your planes.

Here are some additional resources that may be helpful.

Good luck e-pilot!

Clear Skies and Safe Flying!
Ed Anderson

Brushed Motors
http://www.hobby-lobby.com/elecmot.htm

Brushless Motors
http://www.hobby-lobby.com/brushless-motors.htm

Battery Packs - NIMH
http://www.cheapbatterypacks.com/mai...=445976&ctype=
http://www.hobby-lobby.com/hydride.htm

Battery Packs - LiPo
http://www.cheapbatterypacks.com/mai...gid=tp&sort=PL
http://www.hobby-lobby.com/lithium-polymer.htm

Gearboxes - Speed 400 & 480 examples
http://www.hobby-lobby.com/gear400.htm
http://www.hobby-lobby.com/gear480.htm

A series of posts on electric power system basics
http://www.wattflyer.com/forums/showthread.php?t=1933
http://www.rcgroups.com/forums/showthread.php?t=417868

Maxx Products has a pretty good tip sheet on coming up
with a glow to electric power comparison. You can find it here:
http://www.maxxprod.com/mpi/tips3.html







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Old 06-14-2006, 05:38 PM
  #18  
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Default RE: How to get started with electric planes

it was a great help mate!!!

Thanks a lot!!

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Old 06-15-2006, 04:27 AM
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Default RE: How to get started with electric planes

ORIGINAL: tessmar

I am so new to this that I am just researching how to get started. I do want to stick to electric (too many toys with gas motors). My neighbor is experienced and will help, as will the local flying club (paved strip with mowed grass alongside). I appreciate your info but want to "keep it real simple, stupid" (me, not you)

I have narrowed it to (I think) the Toytronix T-Hawk or Megatech Freedom Flyer RTF but cannot decide between them. The T-Hawk has rave user reviews, great company support reputation, and comes with a complete spares package. Downside only seems to be 3 channel receiver and no easy upgrade for ailerons. The Megatech looks more pleasing to me, has a 4 channel radio, and spares and aileron upgrades are readily available, BUT the company's former reputation seems spotty.

Do you have any thoughts that would push me one way or the other? Also, while I was able to find how to respond to your posting it is not clear to me how to start out with a posting of my own that is not a response to someone else. I also am unclear if this note is going only to you or the forum in general.

Thanks for any help you can supply
Get the T-Hawk with the better landing gear and you will be VERY happy. This is an EXCELLENT package. Initally it appears more expensive, but it includes so much. Spare wing, tail, battery, etc. And the plane is very well made. Can't go wrong!
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Old 06-26-2006, 07:09 PM
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Default RE: How to get started with electric planes

AS a newbie to this hobby, toying with the idea of building a Mini Bell and putting an e power out front I will take any and all advice I can get myhands on.

Happy flying
Andrew
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Old 08-30-2006, 10:04 AM
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Default RE: How to get started with electric planes

Thanks a million coolbean. This information is just what I needed. I wish all the vendors for motors, ESCs, LiPos etc. would standardize on how they rate their products. The calculator on the Diversity website was great but it is a bit outdated. I couldn't find any of the current Thunder Power LiPo on their llist. It would be useful if we could plug in our own info.

Anyway, thanks again for the great info. - K01S [8D]
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Old 08-31-2006, 12:28 PM
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Default RE: How to get started with electric planes

Ed:

The links to GWS do not seem to work. Would you, by any chance, have a listing of those prop charts or where to find such a beast?

It seems that my application needs a prop selection to just plain run right, yet I have a limited source (my LHS for now) to get props. I did order a pile of different props from Tower, props ranging from 8x3.8 all the way up to 11x6, all either E or E-Slo Fly. So, I will be able to experiment, but would be nice to have a starting point, and those charts would be grand.

I am beginning to see why one can't simply make a chart of 'Fuel engines vs. Electric motors'. There is more to the electric motor than meets the eye. For instance, with fuel, one buys the plane/engine combination, puts fuel in and flys the plane. More speed, well, add more pitch. More climb, well, less pitch (yeah, within limitations, but the idea works in many cases). Not so with electrics. A lot to consider.. wattage seems to be the biggest issue here, and prop changes can, will, and do change those figures, often dramatically.

Thanks.

DS.
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Old 08-31-2006, 01:21 PM
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Default RE: How to get started with electric planes

One more little item, very confusing. I just ran some numbers into the 'MotoCalc v8' program for the Herr Engineering Little Something Extra.

Here are some numbers for the airplane: Wingspan: 36.5", wing area 344 sq in, flying weight 18 to 22 ounces. Subtract about 5 or so ounces for requirements for the program and go from there.

Using defaults for other items and defining the wing as symetrical with a typical shape, it came up with a motor requirement that drew on the order of over 100 amps. This just does not make sense after reading the above.

Motor/battery requirements were way out of line.

Compare this to my Brio 10. This plane (the Little Something Extra) is a bit smaller than the Brio 10 which has more wing area and span, and I am using a 2200 mah LiPo 20C-30C, Power 10 BL Outrunner, 40 amp ESC with BEC, 4 servo's, and a standard Airtronics RX, and fly it for about 8 minutes.

The motor I want to use on the Little Something Extra is the E-Flite Park 400 brushless inrunner using a 6.6:1 gearbox and a 10x4.7e slowfly prop. From what I can figure out, the motor is capable of right around 200 watts at continuous current operation using a three cell LiPo setup (18 amps continuous at 11.1 volts = 199.8 watts). This should work, wouldn't you think?

That is no way near what the program comes up with. That's what's confusing.

The Herr is somewhat smaller and should fly with a smaller power source. What gives here?

DS
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