Recommended, Commonly Available Motors for use with 3 (aka 3S or 3 cells in series) "A123" 2300mAh Cells for Sport and Sport Scale Planes
Ken Myers
September 2010

Why use 3S "A123" 2300mAh packs?

     The vast majority of RC electric fliers today are using Lithium Polymer (Li-Poly) battery packs in their aircraft. Single Li-Poly cells are bing used in very small planes. The Li-Poly packs are lighter for the same capacity and therefore have a higher energy density. Lo-Poly packs are easy to obtain and can be cheaper to initially purchase than 3S "A123" 2300mAh packs. There are some applications where Li-Poly packs are the only viable solution, period! Typical sport and sport scale planes weighing from just over two pounds and up is not one of them though. For some suggestions for appropriate aircraft selections see Some Examples of Appropriate Airframe Selections.

In December of 2007 I wrote an article titled, "One Way of Selecting a Brushless Outrunner Electric Motor for a Radio Controlled (RC or R/C) Sport Plane or Sport Scale Plane Using ANR26650M1 (A123 Systems NanophospateTM lithium ion) 2300mAh Cells ". It has been updated and contains a lot more information about these cells and selecting motors for use with them.

A Quick Review of the Advantages of 3S "A123" 2300mAh Packs

1. They do not require a charger when used in a 3-cell configuration, only a power meter (aka watt meter/Whattmeter), some lamp cord, appropriate connectors and a 12-volt source like a deep cycle Marine/RV battery as they can be Zip charged. Every electric flier should have a power meter and a charging battery.
2. Only one pack is required for each plane.
     a. They can be charged in 8 to 9 minutes or less using the Zip Charge technique. The turn around time is very fast!
     b. They can be safely charged in the plane. It is highly suggested that Li-Poly batteries be removed from the aircraft and placed in a fireproof container for charging.
3. Because the "A123" cells are in a metal cylinder, they are less prone to crash damage and accidental piercing.
4. They do not puff from abuse and seem to handle abuse extremely well and come back for more. Yes, they can be 'killed', but it is much harder to do than with Li-Poly packs which seem to 'die' easily from over-discharge, storage under the wrong conditions or storage for extended periods of time at the wrong state of charge.
5. They can be stored with the same care and precautions that would be taken for other batteries in the household and even left in the plane, while Li-Poly packs should be removed from the aircraft and stored individually in fireproof containers away from other combustibles.
     Here are a couple of links to a couple of ways to MAYBE store and transport individual Li-Poly packs safely. One is the Lipo Safe Roll - Multi-Pocket Charging/Storage Bag from Common Sense RC. The other is the LipoSack Storage Products. I have NO personal knowledge about either of these products, but they look useful, if they perform as advertised.
     There are many reports on RC Groups of problems relating to the volatility of Li-Poly packs. This one was posted by a long time Li-Poly user, and I found it especially interesting. There is also a 'sticky' thread in the Batteries and Chargers section of RC Groups about Li-Poly pack fires.

The Motor and Prop Recommendations

     The following motor and prop combinations are recommended for use with sport and sport scale planes that fly "on the wing", as opposed to hovering 3D-type flight where thrust is more important than the pitch speed to stall speed ratio. The recommendations do not include "square props" (i.e. 9x9, 10x10, etc.) or "over-square" props (i.e. 9x10, 10x12, etc.) that are usually used on models designed for high speed. Props where the pitch is half the diameter (i.e. 9x4.5, 10x5, etc.) or less are not included in the prop recommendations as they are typically used on slow fly and 3-D type aircraft. "A123" 2300mAh cells are not the best choice for high-speed aircraft or 3-D type aircraft where the power to weight ratio is extremely important for the "ultimate" performance!

     The following suggestions were created using Drive Calculator and SHOULD Be Verified using a power meter Before actual use! I used my elevation of about 287m/940 ft. and an ambient temperature of 15-deg C/60-deg F for the suggestions. If your elevation is higher and/or your ambient temperature higher, you will see lower amp draws than suggested below. If your elevation is lower than 287m/940 ft. or the ambient temperature lower than 15-deg C/60-deg F, you will see higher amp draws when measured with a power meter. It is essential to keep in mind that the following are only estimates based on Drive Calculator predictions and must be verified using a power meter to measure the amp draw of your power system. Attempting to uses this data without a power meter to verify the actual amp draw could possibly destroy the electronic speed contol or the motor!
     When selecting a propeller for your aircraft, it is best to choose the largest diameter prop that your plane can easily handle allowing for ground clearance.

Relative Rating of Props

     We have used watts in per pound of the RTF (ready to fly) plane weight to rate expected performance between various power systems for decades.
     Watts in per pound works reasonably well, but props with the same given diameter and pitch from various manufacturers can behave quite differently in the air. I've tried various methods to rate the props on the same motor/ESC/battery combination. I have not found one that works perfectly, and since I do not have all the various brands and sizes of props to do empirical testing, I am, at this point, using the Drive Calculator derived thrust plus the pitch speed to give a relative prop rating number. While I was trying various methods, I also tried the Drive Calculator estimated thrust times the pitch speed. When thrust and pitch speed are used as factors, thrust dominates the result. When thrust and pitch speed are used as addends, pitch speed dominates the results. For my purposes, I've decided to go with the higher pitch speed being "more relevant". The tables below illustrate the point.

Prop data for the tables using Scorpion SII-3008-1220 with 3S "A123" 2300mAh pack generated by Drive Calculator

Thurst times pitch speed Thrust plus pitch speed

     The original GWS HD prop calculations were inaccurate because of faulty prop data entry into Drive Calclator. I have now tested and redone the numbers for the GWS HD 10x8 prop. Others will be tested soon and corrected. The GWS HD prop data, other than for the HD 10x8, is to be considered suspect until this text is updated.
     Only actually flying the plane with various props will demonstrate which one gives the best all around performance. This theory does suggest which props the modeler might wish to try first.
     I have used various 10-inch diameter props with my 3S "A123" 2300mAh powered planes. Over the last two years (all with different motors) I've only used the Master Airscrew 10x8 G/F 3 Series props. I currently have that prop on my Son of Swallow, Fusion 380 and my parkzone T-28 Trojan. This data was not available to me at the time of selecting the prop, but now I can see why I like this prop so much for this application.

     IMPORTANT NOTICE! - Please read and heed --- The following are possible recommendations only. It is up to the modeler to determine whether any of these suggestions may actually work. A power meter/watt meter/Whattmeter is an ESSENTIAL TOOL when modifying any power system. Do NOT attempt any modification to any power system without a power meter to verify the actual amp draw!!! Be absolutely sure that your ESC with 4 servos and the motor can handle the amp draw shown on the power meter.

The Motors, Electronic Speed Controls (ESCs), and Props

Turnigy SK35-30 1100, weight: 90g Kv: 1100 max amps on 3S: 31.8 (max I would use 31.8 amps * 0.80 = 25 amps) - Price $16.95
Notes: The ESC should be rated for at least 31.3 amps based on a maximum 25 amp draw. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
MA std. wood
10x7
242207750365187
parkzone
9.5x7.5
222007970315788
APC sport
11x6
252257690444488
Aeronaut E
10.5x7
222047930365389
MA G/F 3 Series
10x8
232087890326092
APC sport
10x8
242187770335992
Aeronaut E
10.5x8
242187780355994

Scorpion SII-3008-1220, weight: 95g Kv: 1220 max amps on 3S: 33.6 (max I would use 33.6 amps * 0.80 = 27 amps) - Price $56.69
Notes: The ESC should be rated for at least 36 amps. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
Aeronaut E
10x6
242158680354984
APC sport
10x6
252298400364884
Aeronaut E
10.5x6
272458070394685
Aeronaut E
9.5x7
242198600315788
APC sport
10x7
272458080345488
GWS HD
10x6
232078830395089
APC sport
9x8
252268450276491
APC E
9x7.5
252298400316091
APC E
10x7
272428140385492
Aeronaut E
10x7
272408190395493

Turnigy 3632, weight: 99g Kv: 1200 max amps on 3S: 35 (max I would use 35 amps * 0.80 = 28 amps) - Price $17.84
Notes: The ESC should be rated for at least 36 amps. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
APC sport
10x6
232068320354782
Aeronaut E
10.5x6
252238060394685
APC sport
10x7
252238070345387
MA std. wood
10x7
272457740365187
parkzone
9.5x7.5
252268010315788
APC sport
11x6
282507660444488
Aeronaut E
10.5x7
262297960375390
APC E
10x7
242198120375491
Aeronaut E
10x7
242178150385492
APC sport
10x8
272447760335992
MA G/F 3 Series
10x8
262337900336093
Aeronaut E
10.5x8
272437770355994
GWS HD
11x7
???????????????

Suppo 2814-08 aka BP A2814-8, weight: 103g Kv: 1100 max amps on 3S: 36.4 (max I would use 36.4 amps * 0.80 = 29 amps) Price: $26.95/$29.95
Notes: The ESC should be rated for at least 36 amps. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
MA std. wood
10x7
222037300324880
APC sport
11x6
232097250404181
MA std. wood
11x7
262356810384583
APC sport
11x7
262386770384583
Aeronaut E
10x8
232127160305484
APC sport
10x8
222017320305585
GWS HD
10x8
242147120315485
MA std. wood
10x8
242187080315485
APC E
11x7
242187070394786
Aeronaut E
10.5x8
222017330315687
MA std. wood
11x8
282506570375087
APC sport
11x8
272436680365187
APC sport
12x7
292566540444387
APC E
11x8
272406730375188
APC sport
10x9
252237000296089
GWS HD
11x7
???????????????
APC E
11x8.5
262326850375592
APC E
12x8
292566490464995
GWS HD
12x8
???????????????

Hacker A30 16M, weight: 104.5g Kv: 1060 max amps on 3S: 36.9 (max I would use 36.9 amps * 0.80 = 29 amps) - Price $59.99
Notes: The ESC should be rated for at least 35 amps. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
GWS HD
11x7
???????????????
parkzone
9.5x7.5
222017920305686
MA std. wood
10x7
242217700355186
APC sport
11x6
252267640444387
Aeronaut E
10.5x7
232057880365288
APC E
11x8.5
292607260425890
MA G/F 3 Series
10x8
232087840325991
APC sport
10x8
242197720335891
Aeronaut E
10x8
262327580345791
MA std. wood
11x7
292617260434891
GWS HD
10x8
272397500355792
MA std. wood
10x8
272397500355792
Aeronaut E
10.5x8
242197720355893
APC E
11x7
272407490445094
APC E
10x9
272467430336396

AXI 2814/16, weight: 106g Kv: 1035 max amps on 3S: 37.5 (max I would use 37.5 amps * 0.80 = 30 amps) - Price $94.99
Notes: The ESC should be rated for at least 35/36 amps. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
Aeronaut E
10.5x6
232088030394685
APC sport
10x7
232088040345387
MA std. wood
10x7
262317750365187
parkzone
9.5x7.5
232118000315788
APC sport
11x6
272367690444488
Aeronaut E
10.5x7
242157950375390
APC E
10x7
222048080375491
Aeronaut E
10x7
222028120385492
MA G/F 3 Series
10x8
242187910326092
APC sport
10x8
252307770335992
Aeronaut E
10x8
272427620345892
MA std. wood
10x8
282497530355792
GWS HD
10x8
282497530355792
Aeronaut E
10.5x8
252297780355994
APC E
11x7
282507520445094
APC sport
10x9
292567460336497
GWS HD
11x7
???????????????

Turnigy TR 35-36C, weight: 106g Kv: 1100 max amps: 37.5 (max I would use 37.5 amps * 0.80 = 30 amps) - Price $25.20
Notes: The ESC should be rated for at least 35/36 amps. A 36 amp rated ESC like the Castle Creations Thunderbird 36 ($33.99) might be a good choice.

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
Aeronaut E
10.5x6
242137860374582
APC sport
10x7
232137870325284
MA std. wood
10x7
262337530345084
APC sport
11x6
262377450424284
parkzone
9.5x7.5
242167820305686
Aeronaut E
10.5x7
242197760355186
MA std. wood
11x7
302666950404686
APC sport
11x7
302696900404686
MA std. wood
10x8
282487260325587
APC E
10x7
232107930355388
APC sport
10x8
262327550315788
Aeronaut E
10x8
272427360325688
GWS HD
10x8
282467290335588
Aeronaut E
10x7
232087960365389
MA G/F 3 Series
10x8
252227710315889
APC E
11x7
282497250414889
Aeronaut E
10.5x8
262317560335790
APC sport
10x9
282537170316192
APC E
11x8.5
302646990385694
GWS HD
11x7
???????????????

Scorpion SII-3014-1220, weight: 129g Kv: 1220 max amps on 3S: 46 (max I would use 46 amps * 0.80 = 36.8 amps) - Price $61.41
Notes: The ESC should be rated for at least 45 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
Aeronaut E
9x5
252289710384684
Aeronaut E
9.5x5
232079960384785
Aeronaut
9.5x6
242209750395594
APC E
9x6
242169800395695
APC sport
10x6
302659210435295
Aeronaut E
10x6
282509460425496
GWS HD
10x6
272389540455499
Aeronaut
9.5x7
282529370376299
Aeronaut E
10.5x6
332888930485199
APC sport
10x7
3328789404259101
MA std. wood
10x7
3731685904457101
APC E
9x7.5
3127091503765102
parkzone
9.5x7.5
3429588503963102
APC sport
9x8
2926192503370103
Aeronaut E
10.5x7
3429688304559104
APC sport
11x6
3832785405549104
APC E
10x7
3228489804660106
MA G/F 3 Series
10x8
3530087804067107
Aeronaut E
10x7
3228090404760107
APC sport
10x8
3631486204165107
Aeronaut E
10.5x8
3631386204365108
GWS HD
11x7
????????????????

Scorpion SII-3014-1040, weight: 129g Kv: 1040 max amps on 3S: 46 (max I would use 46 amps * 0.80 = 36.8 amps) - Price $61.41
Notes: The ESC should be rated for at least 40 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
APC sport
10x6
222008440364884
Aeronaut E
10.5x6
242178210404787
APC sport
10x7
242168220355489
parkzone
9.5x7.5
242218170325890
MA std. wood
10x7
272417940385391
APC sport
11x6
282477870464591
Aeronaut E
10.5x7
252248130385492
APC E
10x7
232138250395594
Aeronaut E
10x7
232108290405595
MA G/F 3 Series
10x8
252288090346195
APC sport
10x8
272407960356095
Aeronaut E
10x8
282537800365995
GWS HD
10x8
302627700375895
MA std. wood
10x8
292617720375895
MA std. wood
11x7
322847460464995
APC sport
11x7
332887420464995
Aeronaut E
10.5x8
272397960376097
APC E
11x7
302627710475198
APC sport
10x9
3026876403565100
APC E
11x8
3429473504456100
APC sport
11x8
3429673304456100
MA std. wood
11x8
3530772004555100
APC sport
12x7
3630971805348101
GWS HD
11x7
????????????????
APC E
11x8.5
3228574504460104
GWS HD
12x8
????????????????

Turnigy TR 35-42C, weight: 132g Kv: 1100 max amps: 46.7 (max I would use 46.7 amps * 0.80 = 37.3 amps) - Price $21.00
Notes: The ESC should be rated for at least 45 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
APC sport
9x8
232128490276481
Aeronaut E
10x6
222008650354984
APC sport
10x6
242158450364884
Aeronaut E
10.5x6
262348200404787
Aeronaut E
9.5x7
222048600315788
APC sport
10x7
262338200355489
MA std. wood
10x7
292567880375289
parkzone
9.5x7.5
262378150325890
APC sport
11x6
292607810464490
APC E
9x7.5
242168440316091
Aeronaut E
10.5x7
272408100385492
MA std. wood
11x7
342947330444993
APC sport
11x7
342987280454893
Aeronaut E
10x7
252278290395594
APC E
10x7
262308250395594
APC sport
10x8
292547900346094
Aeronaut E
10x8
302677730355994
GWS HD
10x8
312747620365894
MA std. wood
10x8
312747630365894
MA G/F 3 Series
10x8
272448060346195
Aeronaut E
10x7
252308300405595
APC sport
11x8
353057180425496
MA std. wood
11x8
363147040435396
Aeronaut E
10.5x8
292547910376097
APC E
11x7
312757620465197
APC E
11x8
353027220425597
APC sport
10x9
322807540346498
APC sport
12x7
373167020514798
APC E
11x8.5
3429473404359102
GWS HD
11x7
????????????????
APC E
12x8
3732169405353106
GWS HD
12x8
????????????????

TowerPro 3015-7, weight: 134g Kv: 1000 max amps on 3S: 47.4 (max I would use 47.4 amps * 0.80 = 37.9 amps) Price: $15.95
Notes: The ESC should be rated for at least 45 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).
I measured the Kv of mine at 1065 not the advertised 1000

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
Aeronaut E
10.5x6
232077890384583
MA std. wood
10x7
252287600345084
APC sport
10x7
232067900335285
parkzone
9.5x7.5
232097860305686
APC sport
11x6
262337540434386
Aeronaut E
10.5x7
232137800355287
APC E
10x7
222027950365389
MA std. wood
11x7
302657120424789
APC sport
11x7
302697070424789
Aeronaut E
10x7
222007970375390
MA G/F 3 Series
10x8
242167760315990
APC sport
10x8
252277630325890
Aeronaut E
10x8
272397470335790
GWS HD
10x8
272447400345690
MA std. wood
10x8
272457380345690
APC E
11x7
282467370424991
Aeronaut E
10.5x8
252267630345892
MA std. wood
11x8
322856860405292
APC E
11x10
312727030405393
APC sport
11x8
312766990405393
APC sport
12x7
332876830484593
APC sport
10x9
282517300326294
APC sport
12x8
373216390474895
APC E
11x8.5
302647140405797
GWS HD
11x7
???????????????
APC pattern
12x9
3630865604456100
APC E
12x8
3329167805151102
GWS HD
12x8
????????????????
APC sport
13x8
3631564705549104

Hacker A30 10L, weight: 144.6g Kv: 1185 max amps: 50 Price: $67.99
Notes: The ESC should be rated for at least 50 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust+
pitch speed
APC sport
10x6
252228650384987
Aeronaut E
9.5x7
232118780325890
Aeronaut E
10.5x6
272438410434891
APC E
9x7.5
252248630326193
APC sport
10x7
272428430375693
parkzone
9.5x7.5
282488370345993
MA std. wood
10x7
302698130405494
APC sport
9x8
242198680296695
Aeronaut E
10.5x7
282518330405595
APC sport
11x6
312758060494695
APC E
10x7
272398460415697
Aeronaut E
10x7
262368500425698
GWS HD
10x8
332927870395998
MA G/F 3 Series
10x8
292548290366399
APC sport
10x8
302678150376299
Aeronaut E
10x8
322817990386199
MA std. wood
10x8
332897900396099
MA std. wood
11x7
363137630485199
APC sport
11x7
373177590495099
Aeronaut E
10.5x8
3026681603962101
APC E
11x7
3329078904952101
APC E
11x8
3832475104657103
APC sport
10x9
3429678203767104
APC E
11x8.5
3731576104661107
GWS HD
11x7
3026981305454108

AXI 2820/10, weight: 151g Kv: 1200 max amps: 42 Price $99.99
Notes: The ESC should be rated for at least 42 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
GWS HD
10x6
242189260335386
Aeronaut E
9.5x6
222019439375491
APC sport
11x6
343018380434891
APC sport
10x6
272448990415192
Aeronaut E
9.5x7
262319120356095
Aeronaut E
10.5x6
302678750465096
APC sport
10x7
302668760405898
APC sport
9x8
272419020316899
APC E
9x7.5
282488950356499
parkzone
9.5x7.5
312738680376299
MA std. wood
10x7
342958450435699
Aeronaut E
10.5x7
3127586604457101
APC E
10x7
3026387904458102
MA G/F 3 Series
10x8
3127685903865103
Aeronaut E
10x7
2925988304559104
APC sport
10x8
3329384704064104
Aeronaut E
10x8
3530883004163104
GWS HD
10x8
3731881204262104
MA std. wood
10x8
3631782104262104
Aeronaut E
10.5x8
3329984804264108
APC E
11x7
3731882005454108
GWS HD
11x7
3429584505856114

KD A36-12L, weight: 152g Kv: 1000 max amps: 37 Price: $29.95
Notes: The ESC should be rated for at least 37 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
APC sport
9x8
222058420276481
APC sport
10x6
232078380364884
APC E
9x7.5
232088380305686
Aeronaut E
10.5x6
252268140404686
APC sport
10x7
252258150355489
MA std. wood
10x7
282497840375289
APC sport
11x6
282547780454489
parkzone
9.5x7.5
252298100325890
Aeronaut E
10.5x7
262338050385391
APC E
10x7
242228200385492
Aeronaut E
10x8
292607700355893
GWS HD
10x8
302647580365793
MA std. wood
11x7
332887320444993
APC sport
11x7
332927280454893
Aeronaut E
10x7
242198230395594
MA G/F 3 Series
10x8
272407960346094
APC sport
10x8
282477870346094
APC E
11x7
302687600455095
Aeronaut E
10.5x8
272477870366096
APC sport
11x8
342997180425496
APC E
11x8
342967210425597
MA std. wood
10x8
302677600365898
APC sport
10x9
312737520346498
APC sport
12x7
363117020514798
MA std. wood
11x8
3731776604951100
GWS HD
11x7
2824978505052102
APC E
11x8.5
3328873204359102
APC E
12x8
3631669505453107
GWS HD
12x8
3530770705954113

Turnigy TR 35-48-A, weight: 163g Kv: 1100 max amps: 47 Price: $23.80
Notes: The ESC should be rated for at least 47 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
Aeronaut E
10x6
232108810365086
APC sport
10x6
252268640384987
GWS HD
10x6
222018900395190
Aeronaut E
9.5x7
242148760325891
Aeronaut E
10.5x6
272478420434891
APC E
9x7.5
252288620326193
APC sport
10x7
272468430375693
parkzone
9.5x7.5
282518370345993
APC sport
9x8
252238670296695
Aeronaut E
10.5x7
282548340405595
APC sport
11x6
312788080494695
MA std. wood
10x7
312728140425496
APC E
10x7
272438460415697
Aeronaut E
10x7
272398500425698
MA G/F 3 Series
10x8
302628250366399
APC sport
10x8
302708160376299
Aeronaut E
10x8
322848000386199
GWS HD
10x8
332917860396099
MA std. wood
10x8
332927920396099
MA std. wood
11x7
373167650485199
APC sport
11x7
373207610495099
Aeronaut E
10.5x8
3027081703962101
APC E
11x7
3329379105052102
APC sport
10x9
3429978403767104
GWS HD
11x7
3127281405454108
APC E
11x8.5
3731876304761108

Scorpion SII-3020-1110, weight: 166g Kv: 1110 max amps: 60
Notes: The ESC should be rated for at least 50 amps. A 54 amp rated ESC like the Castle Creations Thunderbird 54 would be a good idea. ($40.99).

PropAmpsWatts
In
RPMThrust
oz.
Pitch
Speed
MPH
thrust +
pitch speed
APC sport
9x8
272419100326991
APC sport
10x6
272449060425193
GWS HD
10x6
242179340435396
Aeronaut E
9.5x7
252319200356196
Aeronaut E
10.5x6
302678830475097
APC E
9x7.5
2824990203664100
APC sport
10x7
3026688404159100
parkzone
9.5x7.5
3127387603862100
MA std. wood
10x7
3429685304457101
Aeronaut E
10.5x7
3127687404458102
APC sport
11x6
3530684805448102
APC E
10x7
3026388704559104
GWS HD
10x8
3832382004262104
Aeronaut E
10x7
2925989104659105
Aeronaut E
10x8
3631083804263105
MA std. wood
10x8
3731782704263105
MA G/F 3 Series
10x8
3328886604066106
APC sport
10x8
3429785704165106
MA std. wood
10x8
3732283004363106
Aeronaut E
10.5x8
3329385604365108
APC E
11x7
3732382905555110
GWS HD
11x7
3429585105956115

Pitch Speed to Stall Speed Ratio

Wing Loading Formula
Weight in ounces (oz.) divided by (/) the wing area in square feet (sq.ft.)
One sq.ft. is 144 sq.in.
Wing area in sq.in. / 144 = wing area in sq.ft.

Stall Speed Formula
square root (SQRT) of the wing loading (square feet divided by (/) the weight in ounces (oz.)) times (*) 3.7

Pitch Speed Formula
Pitch times revolutions per minute (RPM) divided by 1056

Pitch Speed to Stall Speed Ratio Formula
Pitch Speed divided by (/) Stall Speed

Example 1: parkzone T-28 with stock motor, 9.5x7.5 prop and 3S 1800mAh Li-Poly Battery

Ready to Fly (RTF) weight: 30.62 oz.
Wing area: 315 sq.in. (315 sq.in. / 144 sq.in. (1 sq.ft.) = 2.1875 sq.ft.)
Prop: parkzone 9.5x7.5 (pitch 7.5 inches)
Measured RPM: 7,740

Wing loading:
30.62 oz. / 2.1875 sq.ft. = 13.997714 oz./sq.ft

Pitch Speed:
(7.5 * 7740) / 1056 = 58050 / 1056 = 54.971591 mph
Note: The Pitch Speed is NOT the speed that the aircraft attains in level flight at wide-open throttle (WOT). The flying speed in level flight will almost always be less than the Pitch Speed. The flying speed, known as Vopt (velocity optimum) in Drive Calculator, is usually 60% to 80% of the pitch speed.

Stall Speed:
SQRT(13.997714) * 3.7 = 3.7413519 * 3.7 = 13.843002 mph

Note: there is no reason to use all of the decimal point digits as the numbers are only approximations.

Pitch Speed to Stall Speed Ratio:
55 mph / 13.8 mph = 3.9855072 or about 4:1

     Drive Calculator makes a velocity optimum (Vopt) prediction that suggests 45.26 mph. Using that number divided by the stall speed still gives a ratio of 3.28:1
     The pitch speed to stall speed ratio can be used to compare various power systems and props, but be aware that the Vopt will be a closer prediction of actual expected flight speed in level flight.

What does this ratio mean as it relates to expected performance?

     According to Keith Shaw's article Electric Sport Scale published in Model Builder in July of 1987, "In order to just do a nice inside loop, the plane must enter at twice the stall speed. To do clean inside loops, rolls, and other sport-type aerobatics, three times stall speed is needed. Anything over 4 times the stall speed gives 'fighter-type' performance and extended vertical aerobatics."

Why did you use a Li-Poly battery in Example 1 when this is an article about using 3S "A123" 2300mAh packs?

     I wanted to illustrate, with the next example, that there can actually be an increase in performance with careful selection of motor and prop when a 3S "A123" 2300mAh pack is used in the same application.

Example 2: parkzone T-28 with Scorpion SII-3014-1200 motor, Master Airscrew 10x8 G/F 3 series prop and 3S "A123" 2300mAh Battery

Ready to Fly (RTF) weight: 37 oz.
Wing area: 315 sq.in. (315 sq.in. / 144 sq.in. (1 sq.ft.) = 2.1875 sq.ft.)
Prop: Master Airscrew 10x8 G/F 3 series (pitch 8 inches)
Measured RPM: 9,017

Wing loading:
37 oz. / 2.1875 sq.ft. = 16.914286 oz./sq.ft

Pitch Speed:
(8 * 9017) / 1056 = 72136 / 1056 = 68.310606 mph

Stall Speed:
SQRT(16.914286) * 3.7 = 4.1126981 * 3.7 = 15.216983 mph

Pitch Speed to Stall Speed Ratio:
68.3 mph / 15.2 mph = 4.4934211 or about 4.5:1

Drive Calculator (Vopt) 52.7 mph. 52.7 / 15.2 = 3.5:1

     The math demonstrates that there is better performance available and so does the actual in flight performance!

Return to Introduction

Some Examples of Appropriate Airframe Selections

     The motor/prop tables suggest that the appropriate usage of a 3S "A123" 2300 pack ranges from about 200 watts in to a bit above 300 watts in depending on the motor and prop selected.
     There is really no "one" correct size or weight of airframe to use with the 3S "A123" 2300mAh pack, but some practical examples can be a guide to a successful plane.
     I have four trainer, sport, sport scale planes currently flying using these packs. The data for the parkzone T-28 Trojan as flown with a 3S "A123" 2300mAh pack and stock motor is also included for reference.

PlaneTypeMotorPropWing Area
sq.in.
RTF wt.
oz.
Watts In/
lb.
Wing
Loading
Wing
Cube
Loading
Pitch
Speed
mph
Stall
Speed
mph
Pitch Speed
to
Stall Speed
Model Tech Fledgling Gen-IIShoulder wing trainer/sportTowerPro
3015-7
APC
12x8E
469.540.3111.212.366.8552.513.04.04:1
parkzone T-28 TrojanLow wing Trainer/Scaleparkzone
480
MA std. wood
11x8
31534.6784.515.8510.7246.114.73.14:1
parkzone T-28 TrojanLow wing Trainer/ScaleScorpion
SII-3014-1220
MA 10x8
G/F 3 Series
31537126.316.911.4466.615.24.38:1
Scratch-built Son of SwallowLow wing sportScorpion
S-3020-11Turn
special wind
MA 10x8
G/F 3 Series
41541.34124.614.348.4567.514.04.82:1
Scratch-built Fusion 380Low wing sportHyperion
Z-3019-10
MA 10x8
G/F 3 Series
375.539.78122.615.259.4566.014.454.57:1

     New text here

Return to Introduction