The Ampeer ON-LINE!
July 2008
The Club Newsletter of the Electric Flyers Only, Inc
AMA Charter 2354
Walled Lake, MI, USA
Editor: Ken Myers

Fly the Future - Fly Electric!

Not really. The 0.5 is purely cosmetic. Odd for a math formula isn't it? The tables above show the PF with the cosmetic form factor of 0.5 in the top set of data and without it in the bottom set of data. You should be able to see that it doesn't make a bit of difference when arraigning my planes from least to greatest performance.

     My PF theory does not take the number of blades into account at all. The vast majority of the data that I have collected is for two bladed props.

     I hate to be a pest but these things matter to me. Could you please explain? Thanks as always for doing such a great job with the Ampeer. It is my favorite read every month.

Never a pest, and boy, do I wish more people would ask such great questions! Hopefully, I've explained it above, and the tables should also make it clearer. It is always great to know that at least some folks are reading my stuff. :-)

     By the way, I was not sure of what conclusion was to be made of the data table of PF levels at various CWL levels presented at the end of page 6.

I believe you are referring to the table where I show the Performance Factors I've found over a large range of electric and glow powered models. I've put the table below, so you can look at the data.

     Looking at the spreadsheet, available at metricnewtheory.xls should also help.
     In the table, the first column shows the Cubic Wing Loading Level. Looking at the table you can see that there are no internal combustion powered planes, which I have found, in CWL Level 1. They are, for the most part, indoor types.
     When you look at the level two planes, you should see that I have recorded 3 internal combustion engine types and 30 electrically powered types. This indicates that there are a lot more electrically powered types! The Range indicates the PF low to the PF high for the CWL level. With only three examples for "glow", it should not be considered very reliable, but when you look at the average or median PF, the "glow" versions have a PF over 1.5 times that of the electrically powered versions. In other words, they have considerably "better" performance.
     The "glow" powered versions continue to have higher average and median performance through CWL Level 5 and then the electrically powered planes have a higher PF factor. Of course Level 7 isn't very valid because of a lack of data.
     CWL Level 5 (advanced sport) has about the same number of examples; 39/38. The range indicates that the best performing internal combustion powered plane has almost three times the performance of the best performing electrically powered model at this CWL level, while they average is only slightly better than 1.5 times for the internal combustion type.
     If youÕve not already downloaded this spreadsheet homepage.mac.com/kmyersefo/performancefactor.xls you should. It will allow you to play around with your own planes and see some that I have figured for comparison.
     Thanks again for your great and thoughtful questions. KM

     Last month I gave some links to see video of these planes. I asked Don for more information, so here it is. KM

     Sorry for the delay. My shop has been busy. The P-51 is a Top Flight ARF using an AXI 5345 on 12 Li-Po cells and swinging a 22x12 prop. The same power system is in the Midwest Texan too. The FW 190 is not mine but my friend Denny's. It has a 5330/24 on 10 cells and swings a 20-inch prop, The Stinson Reliant is a built up and spans100". It uses the AXI 5330/24 and swings a 22x12 prop. It flies like a trainer. The P-47 also uses the AXI 5330/24 on 10 cells but I am going to run mine on a AXI 5345 with 12 cells to speed things up some. It is a Hanger 9 ARF. The Pawnee is a nice flying plane. I over powered it with a 5320 and 10 cells to help out with the balance. On 10 cells and a 17x12 prop I can fly about 3, 7 minute flights with throttle control.

P-51 www.youtube.com/watch?v=KWs8ZfS7xbg

AT-6 www.youtube.com/watch?v=RNTAhicEtBU

Stinson Reliant www.youtube.com/watch?v=8x0mFuR_Nz8

The other video links are:

Hangar 9 Pawnee www.youtube.com/watch?v=mQ0WnGHkEdY

FW 190 www.youtube.com/watch?v=m3pRFtBAWVE

     Last year, at the Midwest 5 Mile Rd. flying field I had a chance to help a young man and his father with the boy's first R/C plane. The plane was the HobbyZone Firebird Freedom. They had just picked it up at Joe's Hobby and came out to the field for some instruction. That was a very wise move on their part. The plane is billed by HobbyZone and its distributor, Horizon Hobby, as a "3-channel Teach-Yourself-to-Fly RTF with Anti-Crash Technology".
     I went over the plane to check it out, and then had one of my flying buddies give it a good hand launch. The initial flight was short, as the pack had not received a full charge. That was okay, as it proved to be somewhat tail-heavy and out of trim. A novice would have probably crashed the plane, even with the ACT turned on and never known the reason why.
     The battery was charged and I added some weight to the nose and adjusted a push rod. I took a short flight to set the trims and get a feel for the plane.
     I had already "ground schooled" the young pilot on how to move the controls and what to expect.
     I once again flew the plane after a hand launch, having the student pilot watch my inputs. I handed over the controls and we flew together for a while. The ACT was not on, so he did a bit of over controlling at first, but we did okay. There is a bit of a lag between the transmitter input and the plane's response, so that took some getting used to. I landed the plane again, noting that it tends to "come in hot.&quqot;
     We did one more flight, and then the winds picked up to an uncomfortable level for training. He and his father thanked me for their experience, left, and I never saw them again. I do not know whether he ever successfully flew the plane.
     I hadn't given that experience too much thought until I received the August 2008 issue of FlyRC. Scott and Andrew Stoops' review of this plane can be found starting on p. 100. I give Scott credit for making this "toy" sound like what it is, but still not laying it all out for the beginner.

1.) The wing loading/CWL is too high to be an effective trainer; 13.8 oz./sq.ft or 10.9 oz./cu.ft. (advance sport CWL). With this type of loading the plane needs to be flown relatively "fast" to keep it from wallowing and stalling in the turns. It also lands at a higher speed than desirable for a "trainer." This type of loading also requires a forceful, correct hand launch to get it "moving", and a beginner would not know how to do that successfully.
2.) It uses a 7-cell 900mAh NiMH pack as its flight power source. Small NiMH cells, like used in this pack, are possibly the worst cells ever chosen to power an R/C aircraft. They have high internal impedance, which reduces the power available, and they have a very, very short useful life.
3.) The radio system components are not transferable to other standard R/C planes.
4.) The landing gear is ineffective and unnecessary. On grass, the gear tends to flip the plane on every landing. If take offs are attempted from a paved or dirt surface, the plane is not steerable with its "V" tail configuration. It can be clearly seen in photos accompanying the Stoops' review that they've removed the landing gear.

     The plane is marketed directly to young fliers looking for "playability." It has the ability to carry X-Port modules aloft with a "bomb" or parachutist drop, lights for night flying or a "combat" module. It is marketed directly to the young flier's parents with a price point under $150 for everything, except the X-Port modules.
     This plane is a throwback to 25 or 30 years ago, when RTF beginner planes first hit the market. It is just one example of the many out there designed to separate a potential R/C pilot from their money.
     I strongly urge you to discourage the purchase of this type of plane and recommend a decent, true beginner plane like the Multiplex EasyStar RTF.
     Unfortunately, the reality is that there is very little we can actually do about these types of planes with their mass marketing techniques and "positive&qot; reviews in the modeling magazines. When folks show up at the field, we just have to show them our enthusiasm for the hobby and try and help them the best that we can.
     My review of the EasyStar RTF is at: homepage.mac.com/kmyersefo/easystar.htm

     I recently received an email from Walt regarding balancing these cells. Part of that email and my response has been reproduced here. KM

WT: I've had some problems recently with my A123s going way out of balance. I was under the impression that if a pack was closely matched they didn't require as frequent balancing as Li-Pos.

KM: I've found this to be true. I went downstairs and measured my three packs of these cells. All three packs have been left uncharged since their last flights. The CellMeter-8 was used to read all of the individual cell voltages at the same time.

Pack in Fusion: 3.262, 3.268, 3.265, 3.255, 3.274, 3.266 (pack has set for at least 3 weeks since last use)
Pack in Flite 40: 3.159, 3.178, 3.164, 3.187, 3.167, 3.177 (pack has set for at least 3 weeks since last use)
Pack in Son of Swallow: 2.895, 2.947, 2.897 (last used 5 days ago and flown to the "cliff")

     I charged all three packs. Using the CellMeter-8 I took the individual cell voltage readings about 5 minutes after charge. From my previous experience with these cells, I already knew they would be "all over the place."

Pack in Fusion: 3.773, 3.684, 3.730, 3.663, 3.927, 3.942
Pack in Flite 40: 3.695, 3.685, 3.665, 3.676, 3.669, 3.705
Pack in SOS: 3.513, 3.532, 3.497

     About 22 hours later, after a nice long rest for the cells to "settle down", I once again read the voltages. I was quite sure they would all be between 3.4v and 3.5v, as this is what I've usually found them to be, but I got a surprise.

Pack in Fusion: 3.649, 3.471, 3.492, 3.550, 3.799, 3.813
Pack in Flite 40: 3.464, 3.457, 3.461, 3.461, 3.452, 3.460
Pack in SOS: 3.420, 3.421, 3.402

     As you can see, the "little surprise" was the voltage differences in the 6S1P pack used in my Fusion. The other two were exactly what I expected.
     I plugged the Fusion pack in and ran the motor up to full throttle and back and then got the following:

Pack in Fusion after run up: 3.496, 3.409, 3.423, 3.458, 3.597, 3.610

     This is the biggest variation between cells that I've ever seen. The pack was balanced using the Astro Flight Blinky for A123 cells.
     Most of the time, when these cells are fully charged and left to rest, the resting voltage is between 3.4 and 3.5, and most usually 3.45ish, although I've seen them resting at about 3.6v after a recent Zip charge of my SOS pack.
     Once they have rested, the cell voltages will all be very close once again. I've found that the individual cell voltage readings are best taken 24 hours after charge, or the freshly charged battery can be put into the system, motor run up quickly to full throttle and shut down and then the cell readings taken. They'll be close, like the 24 hour later readings.

     K2 Energy provides a Lithium Iron Phosphate type cell. www.peakbattery.com
     Steve Hill, of Robotic Power Solutions (AKA www.battlepack.com), provided some of these cells for me to compare directly against the 26650 A123 Systems, Inc. 2300mAh cells. The K2 cells are described as; LFP26650P Hi Power Rechargeable 3.2V 2500mAh. There is a thread on RC Groups about these cells. Everydayflyer is also testing them and has reported his results in the thread. www.rcgroups.com/forums/showthread.php?t=868243

     Here is what K2 Energy says about their 26650 cell:
"...This cell can handle 42 Amps continuous discharge with over 50 Amps 30 second pulses. The cell is rated at 3.2 nominal volts and 2500mAhrs. (snip) The internal impedance is less than 9 milliohms. This battery is 26.2mm D x 65.2mm H and weights 82.5 grams (with a card board sleeve)."

K2 diameter 27mm, length 65.1mm
A123 diameter 26.5mm, length 65.6mm
K2 individual cell weights with tan cardboard-like sleeve: (I have four cells.)
#1 82.7g, #2 82.2g, #3 82.8g, #4 82.8g
Resting voltages as delivered:
#1 3.28v, #2 3.28v, #3 3.28v, #4 3.27v

Note: The button end is positive on the K2 Energy cells, which is the reverse of the 26650 from A123 Systems, Inc.

3S1P Pack weights:

     Cells #1, #2, and #3 were made into a pack using 2 APP connectors, power leads, node/balance leads, tape and hook and loop fastener strips. Everything was done to duplicate, as closely as possible, the A123 pack I've been using.
A123 240.5g (8.48338 oz.)
K2 267.85g (9.44813 oz.)
Difference: 27.35g (0.964742 oz.)

     The new K2 Energy pack was first charged at 2.5 amps (1C) using an unmodified AF109 charger with termination done manually with the resting cell voltages being 3.732, 3.738, 3.719 about an hour and a half after the initial charge. The pack was discharge using the AF 109. The pack was then charged at 5 amps (2C) and 2.526AH was returned to the pack in 32 minutes, again terminating manually. The pack was discharged using the AF 109. The pack was then charged at 7.5 amps (3C) in 21 minutes with 2.492Ah returned to the pack. The pack sat overnight. In the morning, I was very surprised to see the Cellmeter-8 read all three cells' voltages exactly the same at 3.334v!
     I noted one thing, while charging on the AF 109. The K2 pack gets warmer, much warmer, than my A123 pack when it is Zip charged. This indicates higher cell impedance.
     Comparative testing was done using the Son of Swallow power system; Hyperion Z3019-10, Master Airscrew standard wood 10x7 prop and a Castle Creations Phoenix-45 with low timing.
     My Hyperion Emeter can store 5 data points at a time. For each static motor run, at full throttle, I collected data every 5 seconds with shut downs and run-ups between each one. I did three data gathering runs for each pack so that 15 data points were gathered, recording the data to a spreadsheet for each 5 gatherings, and then I captured the next 5 data points. The graphs show the behavior of the packs with the slight resting between each 5-point collection. When viewing the graphs, it is easy to spot the "break" between the data collection runs.
     RPM is not on the graph because, when RPM is changed to RPM/1000, the KRPM is approximately the same as the voltage and does not present well.
     I did a second test after doing several cycles and some prop testing. That data is presented in the graph.