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Flying High With Electric Power!
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| President: | Vice-President: | Secretary/Treasurer: |
| Ken Myers | Richard Utkan | Rick Sawicki |
| 1911 Bradshaw Ct. | 240 Cabinet | 5089 Ledgewood Ct. W. |
| Commerce Twp., MI 48390 | Milford, MI 48381 | Commerce Twp., MI 48382 |
| (248) 669-8124 | (248) 685-1705 | 248.685.7056 |
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| Board of Directors: | Board of Directors: | Ampeer Editor |
| David Stacer | Arthur Deane | Ken Myers |
| 16575 Brookland Blvd. | 21690 Bedford Dr. | 1911 Bradshaw Ct. |
| Northville, MI 48167 | Northville, MI 48167 | Commerce Twp., MI 48390 |
| 248.924.2324 | 248.348.2058 | 248.669.8124 |
| Mailed Ampeer printed subscriptions are no longer available.
The Ampeer is FREE on-line in Acrobat .pdf format and HTML with active links! | ||
| The Next Flying Meeting:
Date: Saturday, Nov. 1 Time: 10 a.m. Place: Midwest RC Society 7 Mi. Rd. Flying Field | ||
| What's In This Issue? | ||||
| Upcoming AMA District 7 Town Hall Meeting Meeting Announcement | Upcoming November 2 Swap Shop Info Upcoming Midwest RC Society Swap Shop info | |||
| Skymasters' Indoor Flying Starts Soon Winter Indoor flying starts at the Ultimate Soccer Arenas in Pontiac, MI. | Indoor Flying in Brighton Fall/Winter 2014/2015 info for winter season flying in Brighton, MI | |||
| Follow-up from Owen Morgan via email regarding his planes at the March EFO meeting Owen shares more details on the planes he shared at the March EFO meeting. | Min-E Mambo May 2014 Follow-up Ken describes some of his first flights with the Min-E Mambo. | |||
| LiPo Puffing Question Ken Myers tries to explain the causes of LiPo puffing to an Ampeer reader. | Can Adding a Cell to an A123 Pack Increase Flight Time? Ken explains how the answer can be yes or no. Huh? | |||
| Thinking About Going LiPo Ken thinks about it a bit. | ||||
|
From Joe Hass Sunday, October 26, 2014
Ultimate Soccer Arenas
FEATURING AMA DISTRICT 7 VP
FREE INDOOR FLYING
HEADQUARTERS GUEST SPEAKERS PROGRAMS AND SURPRISES From Rudi Reinhard, Swap Meet Chairman Midwest RC Society
Sunday, November 2, 2014
location
admission charge
vendor table cost
For Information
directions
Return to "What's In This Issue" Skymasters' Indoor Flying Starts Soon
The Winds of November are approaching fast. Fear not, you can enjoy a full winter season of indoor flying at Ultimate Soccer Arenas beginning Tuesday, Nov. 4. There are 26 flying days this winter for a total of 57 hours of flying fun from November through March. Skymasters has reduced the cost of the Season Pass to $100. It's a great deal. How great you ask? It is $100 for 57 hours of flying time that comes to $1.75 per hour. Less per hour than a Starbucks coffee. That's a Great Deal. Soon we will have online registration available, I will keep you posted. Indoor Flying in Brighton Fall/Winter 2014/2015
Here is the information on Indoor flying at the Legacy Center in Brighton MI for the Fall/Winter 2014/2015 season. When: Thursdays 12:00 noon to 2:00 pm
More information: info@legacycentermichigan.com It starts on November 6th, 2014, and runs through April 30th, 2015. Follow-up from Owen Morgan via email regarding his planes at the March EFO meeting The planes are shown in the October 2014 Ampeer. Hi Ken, The bipe is a Sopwith Camel (Snoopy's plane). It's the Great Planes Electrifly version. I maidened her on April 19th and she flew pretty tail heavy, so I'll have to add some ballast before I fly her again. The recommended CG in the manual is NOT good! The wood prop seems to work fine and flight time was around 12 minutes. The battery only just fits and with the short nose, most of the weight of the battery is around the CG, so one thing I might try is to use a smaller/shorter battery and place it as far forwards as possible so I can balance her better without adding more weight. The Spitfire is a foamboard build using plans from www.flitetest.com. If you're not aware of FliteTest, you really should have a look at their site. A couple of young guys having an insane amount of fun with RC and getting paid for it. One of the videos they did was a speed challenge. The winner was a Spitfire like mine (one of the prototypes) where they'd cut off the wing tips and used a bigger motor. They clocked her at 116 mph airspeed. Mine is thankfully nowhere near that fast. For the wing area calculations I use a scale that reads max 100g. If using a scale with lower resolution, you'd need a heavier reference material. Here is the one I have, only $12: I had a little oops the other day. I use a FlySky TH9X transmitter with a Orange RX DSM2/DSMX transmitter module and Lemon RX 6 channel (3 gram) receivers. The other day I was running ahead of schedule at work, so decided to catch a quick flight with my TLAR camera plane on the way from one job to the next. However, I could not get any contact between the transmitter and plane. If I tried to rebind, it would work for a couple of seconds, then stop working again. I didn't have time to troubleshoot, but when I came home I discovered that the "Change ID" button on the transmitter module had somehow got pushed in and was jammed under the plastic casing on the module, so the transmitter was constantly changing it's ID. Oh, well, now I have to rebind all my planes and some of those receivers are quite well buried... I never use that button and it's recessed in the module, so I have no idea how it got pushed.  The TLAR is a plane I scratch-built to have something to put a camera on where the plane and prop would not be visible in the picture. The name comes from the highly scientific design process. "That looks about right". The wing is from a foamy cub of some sort, the fuselage is central vacuum pipe, the tail booms are arrow shafts from Walmart and the tail feathers are Adams foam board from the Dollar Tree store. I bought that wing a long time ago planning to modify the tips and build a stand off scale (way off) model of the Spirit of St Louis, then I found the Thunder Tiger model of that plane so the project never happened. I used a hair dryer (don't tell the wife) to reduce the dihedral and added ailerons. The plane has no rudders. She flies fine, but does a funny little tail wag at some speeds as if I was alternating a little right and left rudder. It's not a lot, but not great for a camera plane when shooting video. Do you have any ideas what may be causing it and what I might do to reduce or remove it? I haven't flown her in zero wind yet, so don't know whether it's wind induced. I did try giving her a little nose ballast as the CG is a bit aft of where the cub has it on the same wing, but don't think it changed much if anything. The tail booms are pretty stiff, so I don't think they are bending and if they were, I'd expect to see some horizontal tail wag too. One idea is that the vertical stabs may be too far apart, but it would be a royal pain to change that now, particularly as the elevator servo is build into the wing and the linkage runs inside the arrow shaft. Maybe a third vertical stab in the middle of the horizontal one. (And cut down the two others?). I'll try flying with the camera pointing backwards one day and maybe that will give some clues. Launching this plane without loosing fingers is always interesting. I tried a discus launch, but that was a miserable failure. Thankfully, no damage. I have a throttle kill switch on the transmitter, so my method now is to engage the throttle kill, advance the throttle to 3/4, give the plane a hefty toss and then disengage the throttle kill immediately after she leaves my hand to start the motor. It works better in a bit of wind. AUW is about 25oz with battery and camera and wingspan is 48". I'm thinking of trying FPV with this plane and with the thick Clark-Y profile I think she should be able to carry a lot more weight without trouble. I'm using the KEDA KA22.22L 85g 950Kv motor, Saker 30A ESC from www.strongrcmotors.com and an APC 10x4 slowfly prop. Not sure it's the best prop for the job. I'd bought it for the Sopwith Camel, but then found a wood prop for that plane. She has plenty of power and the motor and ESC should manage up to 11x6. I have several motors from Don and they run smooth and have never given me any trouble. I figured out the yaw instability of the TLAR camera plane with the help of a friend. It was caused by the flat nose. I put a rounded nose on it and the plane now tracks like she's on rails. Owen Min-E Mambo May 2014 Follow-up
The CG on the original plans was used for the less than successful first flights. I recalculated the CG using my spreadsheet and adding one ounce of nose weight behind the firewall. That set CG at my calculated ISCG. The 'warps' in the wing and horizontal stabilizer were corrected. On Sunday, May 25, the Min-E Mambo flew perfectly as a throttle and rudder model. I should have paid attention to a note that I had written on my original 1963 plans. The note said that I should lower the trailing edge of the horizontal stab about 1/4". That probably would have worked and no additional nose weight would have been needed. One should never ignore oneself even if oneself was a teenager at the time. LiPo Puffing Question
Preface: I recently exchanged emails regarding this topic with a regular Ampeer reader. Our exchange of emails follows. Both the Reader's and my responses have be edited while keeping both the information exchange and intent intact. The reader's comments appear in blue font.
11:52 AM Sept. 4
Hi Ken,
Well, I've run into a snag with the big motor and ESC I'm using on my 50" sBach.
I purchased two new 4C (4S - KM) 2200mAh Turnigy LiPos, thinking these would do the trick for the sBach.
After 3 flights on both of the LiPos, I have discovered that they are swollen.
The motor is the Fire Power 46 Sport and is supposed to handle these 4C (4S - KM) LiPos.
The ESC is a 60 amp.
Can you help me? Why did the LiPos swell?
Pictures attached. The photos showed a profile foam 50" sBach and a Turnigy 2200mAh 4S1P 20C LiPo. Sept. 4 Hi, I got the Turnigy 2200mAh 4S1P 20C specifications from the Hobby King Web site. Specs:
For example, the TP2700-4SPP25 lists the following:
44 amps times 14.8V = 651.2 watts in
You didn't note the mission of the plane. I can only assume, and you know what assuming gets you, that because it is a profile model with large control surfaces, the mission is 3D type flying. You also did not state the ready to fly weight. That is very helpful to know. 12:10 PM Sept. 4
Sept. 4 You didn't state which Master Airscrew 13x8 (1380) prop you used, but it was black in the photo, so it was probably not the wood one. My guess is that it was the K-series. If you meant by, "lasted for 5 minutes", that you hit the low voltage cutoff (LVC) of the electronic speed control (ESC), then you flew the pack down too far. That also 'kills/puffs' packs. You should have been using only 1760mAh from the 2200mAh pack. That is 80% of the pack's stated capacity. You can get an idea of about how many mAh you flew from the pack when you recharge the pack. A decent charger will indicate how many mAh was returned to the pack during charging. Even if your charger doesn't indicate the mAh returned to the pack, a power meter can be placed between the charger and the pack and the mAh returned to the pack will be displayed. If the above is true, the average amp draw for 5 minutes was only
That should have been okay, but... It was putting 800 watts in on a static run. 800 watts in divided by 14.8V = 54 amps for a guesstimate. I have found anecdotally, that with typical throttle management, the average amp draw is approximately 1/2 the full throttle static amp draw. This does vary depending on the pilot's throttle management technique and what the pilot expects from the airframe, that's its mission. With an average amp draw of 26.4, previously calculated, that indicates 52.8 amps as the static amp draw. That is right in line with the previous guesstimate of 54 amps.
If you had flown for a timed 4 minutes, MAYBE the pack(s) might not have puffed, but the maximum amp draw was still too high. I just tried a three blade, T1280, again MAS, and the static watts in on this was an alarming 900. 900 watts in divided by 14.8 amps = 64.3 amps. In general, 3-blade props should only be used in situations where there are ground clearance problems relating to prop diameter or if you really, really want to be scale and are willing to accept a prop with less efficiency drawing more current. As for the 4S confusion, I thought this was for four cells, but looking at the LiPo I see 4C as a charging rate? You are correct that 4S means 4 cells wired in series (S). 4C is the maximum charge rate. For this 2.2Ah pack, that would mean charging 8.8 amps and the pack would charged in 15 minutes. You might want to review the LiPo section in "Getting Started in Electric Flight -An Introduction and Some BASICS" Were you able to read the LiPo picture? Is this too small for this setup??
Huh, boy am I stymied, and frustrated, ha ha.
5:24 PM Sept. 4
Sept. 4
While you did add a little resistance, it is really nothing to be concerned with in this instance. It most likely didn't have anything to do with puffing the LiPo battery. 7:20 AM Sept. 6
Sept. 6 Packs do not have amperage. The current drawn depends on the load on the motor. My guess is that he said that it wasn't able to handle the amperage you were asking from it. Looking at a Turnigy 4S 2650mAh 20C LiPo battery. Price: $16.40US (That is actually $1.25US cheaper than the 2200mAh packs.)
That is much closer to your 800 watts in for the MA 13x8, so this should have been your first choice, but you didn't know that, or did you? The motor is rated by the supplier, Heads Up RC Hobby shop at 45 amps. 45 amps, give or take a few amps, should have been your target maximum amp draw for this motor in a 3D application. Using the 53 amps math from the previous calculation, it is apparent that you could have figured out that a 2600mAh pack would have been a more appropriate pack capacity, while sill 'over-amping' the motor. |
| The table shows the Turnigy brand 20C LiPo packs available in September 2014.
If the the amp draw noted by capacity in Ah times 20 is used for the maximum target amp draw, i.e. 44 amps for the 2200mAh pack, then the approximate flight time will be just shy of 5 minutes. Actually it is 4.8 minutes if you do the math.
That is true for every pack capacity when that amp draw is the noted C-rate times the Ah capacity. 80% of 5000mAh is 4000mAh or 4Ah 4Ah times 60 minutes = 240 amp minutes 240 amp minutes divided by 100 amps = 2.4 minutes of continuous run time If the amp draw noted in the table as 80% Maximum C-rate Amps is used as the maximum target amps, then the estimated flight time will be 6 minutes.
Approximate flight time for ME, my planes and the way I fly: 3 minutes times 2 = 6 minutes There is a lot of other useful information in the tables, if you look closely. |
| You could also have used a higher C rated battery if you wanted to keep the amp draw in the middle 50's to suit your flying. (See the table above.) The flight time would not increase. The flight time might actually go down a little if the higher C-rated pack allows more current to pass. Most likely though, the LiPo might not have swollen.
If you desire to increase your flight time over 6 minutes, without going to a larger than 3300mAh LiPo, you'll need to change the load, which will decrease the average amp draw. That means a prop that will draw less current but one that will still allow you to fly the plane the way you want it to fly. He also suggested I use a larger prop than the 13/8 that I have on it so picked up a 14/7 APC to try. An APC 14x7 is going in the wrong direction, although it will most likely draw slightly less, or equal, current compared to the Master Airscrew 13x8, it is not a good move. MA props tend to draw more amps than similarly sized APC E props. Even if the APC 14x7E draws about the same amps as the MA 13x8, it would not alleviate the 'puffing problem' or help with extending the flight time of the 2200mAh pack. A profile 3D type plane does not need a lot of pitch speed. An APC 13x6.5E probably draws a few amps less than the Master Airscrew 13x8 that you are using. That's based on my past experience with MA props. The 13x6.5E would only increase your flight time slightly, but it would PROBABLY not puff either the 3000mAh or 3300mAh LiPo battery. I also contacted the HeadsUp RC in Florida, the place were I got the motor originally, he suggested using smaller props, 11" and or 12". That is solid information on reducing the amp draw. Reducing the amp draw is what is needed on the 20C 2.2Ah battery to both increase the flight time and reduce the chance of 'puffing'. Gad, wish I had studied more in my younger days.
Most suppliers of LiPo batteries are in the dark about their use and care. The suppliers tend to 'parrot' any information that was supplied to them by the original equipment manufacturer (OEM). There is really no empirical data to support any of the following statements. The statements are based on anecdotal information from various sources. Some, and or all, of the following might help elevate the puffing of Lithium Polymer type batteries and lengthen their useful lifespan. To Keep the Chance of 'Puffing' to a Minimum:
Could they still 'puff' if you do all that? Maybe, but the chances of 'puffing' will be greatly reduced. Can Adding a Cell to an A123 Pack Increase Flight Time?
Preface: I received an email from Willie McMath requesting some information on going from a 6-cell "A123" pack to a 7-cell "A123". Before responding to Willie, I thought about the obvious; just adding a cell and changing nothing else will increase the amp draw and shorten the flight time. That would change the way the plane flies. Then I thought; adding a cell and dropping the prop size would also change the way the plane flies. Changing the capacity of a LiPo pack can increase the flight time, but "A123" cells, of the type used here, have a 'fixed' capacity. I ended up surprising myself with my answer to Willie. Willie's questions and comments are in blue font.
Hello Ken,
I have a question regarding my Morrisey Bravo that I fly with a Turnigy 42-60-500Kv motor with an APC 14x10E using a 6s A123 battery. It flies really well.
What happens to the performance of the plane if I add one more 2300mAh cell to the pack?
Would it increase the flight time?
Willie McMath KM: What is your static amp draw now with the APC 14x10E prop? KM: What is your static amp draw now with the APC 14x10E prop? KM: Your numbers do not 'jive'. Ê599.9 watts / 35.1 amps = 17.09 volts. 17.1 volts is exactly the voltage I would expect of A123 cells under a '35' amp load. IF you are drawing 35 amps with either a 6 or 7 cell pack, the flight time will basically be the same. One way to increase flight time would be to use a larger capacity battery, but that is not practical with "A123" cells. The other way to increase flight time is to reduce the amp draw. If you are using 600 watts in with a 6 cell pack, and the power is fine at 600 watts in, then dropping to 29 amps and using a 7 cell pack would still give about 600 watts in. ÊThat would mean using an APC 12x8E with the 7 cell pack and this motor. The 6 cell pack at 35 amps should give a flight time of
That should yield about 5 to 6 minutes of flight time. ÊFor me, my planes and the way I fly them, I actually get 6 to 7 minutes at that 35ish amp maximum static draw.
For the proposed 7 cell pack at 29 amps
120 amp minutes divided by 29 amps = 4.14 minutes of motor run time at full throttle.
The big problem would be going from a 14x10E to a 12x8E prop. The plane would certainly fly very differently, even though both setups would still have about 600 watts in. WM: I have a question on what you mean by fly differently. I used a Turnigy watt meter model# 130 A watt meter and power analyzer. KM: The Volts, Amps and Watts all need to be captured at the same time, like a snapshot. Obviously the 19.88 volts was not captured at the same time as the 600 watts and 35 amps. At first, I believed that your power meter was reading maximums. Obviously, maximum voltage is reached when the power meter is plugged in and there is no load on it. 19.88V divided by 6 cells = 3.31V per cell, so I'm not even sure what that voltage reading means, as 3.31V per cell is almost empty for "A123" cells under no load. That voltage is also too high for "A123" cells with a 35 amp draw. Here is an approximation of what will be happening when going from 6 to 7 "A123" cells and from a 14x10E to a 12x8E
I surprised myself with those numbers. ÊIt looks to me, by the numbers, that the plane should fly similarly. ÊAs I said, I was a little surprised. It looks like you can pick up a couple of minutes of flight time by going to a 7S pack, with the reduced amp draw of the 12x8E prop. ÊOnly flying it will tell if it is really equal in flight performance while increasing the flying time. I had to change the motor in my Hitec Weekender Extra 300. The stock motor was about 610 Kv and the replacement about 810 Kv. The pack is a 4S "A123" 2300mAh. To get the amp draw to where I wanted it with new motor, I had to change to an APC 12x8E. From the July 2014 Ampeer,
From the September 2014 Ampeer,
Both setups give the plane the same perceived performance in the air. The 'speed' and 'vertical height' seemed to be extremely similar. I really didn't understand that at the time, as I expected slightly less performance from the APC 12x8E. I used static thrust data from Drive Calculator (DC) in my comments to Willie. Normally, I pay absolutely NO attention to that bit of info. According to Drive Calculator an APC 14x10E at 5880 RPM produces 66.5 ounces of static thrust and an APC 12x8E at 7810 RPM produces 66.6 ounces of static thrust. Not only is this information useful in changing cell count but also motor Kv. Thinking About Going LiPo
After doing a lot of research to answer the question about LiPo puffing in this issue, and seeing the prices, I was seriously thinking about trying LiPo batteries once again. When thinking of my "A123" packs, I always try to use 100 watts in per cell. That gives a 35 amp draw for estimating purposes. For me, a 4 lb. (64 oz.) sport plane would use a 4S "A123" pack. Using a wing cube loading (WCL) factor of 9, that a typical sport plane would have, yields a wing area of 543.5 sq.in.
The weight savings for approximately the same flight time is about 70g or about 2.5 ounces. The WCL factor for the example plane changes to 8.4 and area loading to 16.28 oz./sq.ft. That is very little weight savings and probably not a perceptible change in how the plane flies. The price savings is approximately $35 per pack. That is significant. With two personal flying buddies with LiPo 'events' while charging and one with an unexplainable 'event' while transporting in a fire safe, I think I'll stick with "A123" packs for a bit longer. |
To Reach Ken Myers, you can land mail to the address at the top of the page. My E-mail address is: KMyersEFO@theampeer.org