Daryl_y

Although I am a experienced builder and flier of glow powered planes I have never had an electric plane. I have looked at several electric kits /arfs for my first e-flight project, But I think I have a better idea. For about 10 years I flew a World Models Cosmo 25sr It was wonderful flying plane that I lost in a mid air a couple of years ago. Since I still have the plans I would like to scratch build a new one for for e-flight. Since I am new to e-flight I would like your recommendations on battery motor combinations so I can have them on hand before I start the project. The dimensions are as follows:

wingspan 50"
Wing area: 450 sq inches
weight of the old glow version: 3.75-4lbs (could easily be built lighter)
the old version was powered by a OS 40fp which produced right at 1HP and gave the plane good performance

I am look for and electric motor/battery combo: that will give me similar performance along with 10 min or so of flight time.

Greg Covey

Daryl,

Here is some information that will give you added confidence in your choices.

[link=http://www.gregcovey.com/Glow_Conversions_Made_Easy.htm]Glow Conversions Made Easy[/link]

perttime

One of the AXI 2826 motors should do well:
http://www.modelmotors.cz/index.php?id=en&nc=produkty_rada&kategorie=m_neodym_ac&id_rady=axi_28&nazev=Series%20AXI%2028%20GOLD%20LINE&hmotnost=(78%20-%20161%20g)

Then you need an adequate controller (ESC).

Do you want to use LiPo or NiMH batteries?
NiMH gives you good power but they are heavier, at least if you want enough for 10 minutes.
LiPO can easily give you the power and duration at less weight, but they cost more and they do not tolerate abuse (crashing, high temperatures, over-charging, over-discharging)

Building an electric, you do not need to add all the reinforcement that the glow vibration needs. You do need to figure out how to mount the motor and where to put the battery so that it stays put and allows you to get CG right.

Daryl_y

I've done a little home work seems like I found something that might be a good match AXI 2814/12, Jeti 30+ speed control, 8 cell 1700mah nimh, and 11 x 7 e-prop. The 2820 series motor seemed a little over kill for a 4lb or less plane. My mine goal is too have a nice flying plane that can do standard aerobatics from level flight with a run time at or near that of a glow powered plane, The total weight of the power system motor and batteris is right at 14 0z only a couple onces more than a ball bearing .25 glow engine so hopefully I won't have overall weight worries. I would also like some help on estimating run tiime.

analucius

Hi Daryl,

Ive looked over your numbers and allied by MotoCalc I get this info for you:

The question to your answer is highlighted in BOLD and run time is 3 minutes and some... Short! With a brushless you need more capacity - higher mA count on the batt.

MotOpinion - MUH Ripmax Spitfire AXI2820-10
5m above Sea Level, 101,3kPa, 15°C

Motor: Model Motors AXI AC2814/12; 1390rpm/V; 1,8A no-load; 0,053 Ohms.
Battery: Sanyo 1700SCR; 8 cells; 1700mAh @ 1,2V; 0,004 Ohms/cell.
Speed Control: Jeti 40; 0,0035 Ohms; High rate.
Drive System: Generic 11x7in Prop; 11x7 (Pconst=1,25; Tconst=0,956) direct drive.
Airframe: SpitFire Ripmax; 29dm²; 1487g; 51,3g/dm²; Cd=0,048; Cl=0,47; Clopt=0,67; Clmax=1,24.
Stats: 183 W/kg in; 98 W/kg out; 8,4m/s stall; 11,5m/s opt @ 46% (23:48, 32°C); 13,8m/s level @ 53% (18:43, 35°C); 4,11m/s @ 21°; -1,06m/s @ -5,3°.

Possible Power System Problems:

The full-throttle steadty-state motor temperature (204°C) is extremely high, which will likely damage the motor unless full-throttle is used very sparingly (even then, damage is possible).
Current can be decreased by using fewer cells, a smaller diameter or lower pitched propeller, a higher gear ratio, or some combination of these methods.

Power System Notes:

At full-throttle and the best lift-to-drag ratio airspeed, the motor is operating approximately between its maximum efficiency current (17A) and its current at theoretical maximum output (80,8A). However, it is operating at only 57% efficiency, which is significantly less than its theoretical maximum efficiency (80%). Efficiency may improve at reduced throttle settings.

Possible Aerodynamic Problems:

The static pitch speed (19,7m/s) is less than 2,5 times the stall speed (8,4m/s), 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 higher cell count, or some combination of these methods.

Aerodynamic Notes:

With a wing loading of 51,3g/dm², 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 (928g) to weight (1487g) ratio is 0,62:1, which will result in short 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 (555g) to weight (1487g) ratio is 0,37:1, 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.

General Notes:

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.
*********

These are the numbers:
5m above Sea Level, 101,3kPa, 15°C



Motor Model Motors AXI AC2814/12
Motor Constant (rpm/V) 1390
No Load Current (A) 1,8
Armature Resistance (Ohms) 0,053

Battery Sanyo 1700SCR
Series Cell Count 8
Parallel Cell Count 1
Cell Capacity (mAh) 1700
Pack Capacity (mAh) 1700
Cell Voltage (V) 1,2
Pack Voltage (V) 9,6
Cell Resistance (Ohms) 0,004
Pack Resistance (Ohms) 0,032

Speed Control (ESC) Jeti 40
Resistance (Ohms) 0,0035
Maximum Current (A) 40
Number of ESCs 1

Drive System Generic 11x7in Prop
Gear Ratio 1,00:1
Propeller (in x in) 11x7
Series Motors 1
Parallel Motors 1
Number of Propellers 1
Blades per Propeller 2

Airframe SpitFire Ripmax
Wing Span (cm) 127
Wing Area (dm²) 29
Total Weight (g) 1487

Static Predictions
Current (A) 32,2
Motor Voltage (V) 8,5
Input Power (W) 272,6
Input Power Loading (W/kg) 183,1
Power Loss (W) 126,8
Motor/Gearbox Output (W) 145,8
Output Power Loading (W/kg) 98,0
Motor/Gearbox Efficiency (%) 53,5
Shaft Efficiency (%) 47,1
Motor RPM 6659
Propeller RPM 6659
Static Thrust (g) 928
Pitch Speed (m/s) 19,7
Run Time (min:sec) 3:10

Flight Predictions
Stall Speed (m/s) 8,4
Optimal Flight Speed (m/s) 11,5
Throttle for Optimal (%) 46
Duration at Optimal (m:s) 23:48
Motor Temp at Optimal (°C) 32
Hands-off Speed (m/s) 13,8
Throttle for Hands-off (%) 53
Duration Hands-off (m:s) 18:43
Motor Temp Hands-off (°C) 35
Best Rate of Climb (m/s) 4,11
Rate of Sink (m/s) -1,06

Note: Motor performance calculations take ambient temperature and heating effects into account.

Generated by MotoCalc 8.01, 23-01-2006 14:32.