The engine displacement inputs were adjusted to reflect the reported 978 watts in in the Suggested Power: cell.

     The performance section of the worksheet shows that the plane is "okay", but not stellar.
     The pitch speed to stall speed ratio of 2.83:1 is a bit low for an advanced WWII trainer, in my opinion.
     With 6 Li-Poly cells (Number of Li-Poly cells:) the Kv suggestion falls between 226 (Kv (RPM/v) Range Low:) and 251 (Kv (RPM/v) Range High:). The AT-6 used a 245Kv motor. With an estimated amp draw of 46.6 (Anticipated Amp Draw:) the suggested cell capacity was 4658mAh (Approx. Li-Poly capacity:). A 5000mAh pack was used in the AT-6 yielding the expected 7 minute to 8 minute flight time.

     Using the Excel worksheet, shown above, the engine displacement inputs were adjusted to reflect about 1400 watts in in the Suggested Power: cell. The 1400 watts in is used to provide 100 watts in per pound for the anticipated 14 lb. Spitfire.
     When an APC 20x13E prop is used, the performance section looks good. The Target RPM:, Pitch Speed:, Stall Speed:, and Pitch Speed to Stall Speed: indicated good performance.
     When the Number of Li-Poly cells: is 6, the suggested Kv is between 271 and 301. Scott's motor has a 290Kv. His motor weighs 632g and falls within the suggested weight range of 561g (Lightest Motor:) to 876g (Heaviest Motor). The suggested amp draw (Anticipated Amp Draw:) is about 66.8 amps. That suggests an 83-amp ESC (ESC amp rating = or greater). Scott's is an 80-amp ESC, so that's not a real problem. The problem comes with the suggested battery capacity of 6677mAh (Approx. Battery capacity:). Li-Poly cells with a capacity in this range are difficult or impossible to locate.

Solution 1:
     Accept a shorter flight time. A GENS ACE 5500mah 6S1P could be used.
www.hobbypartz.com/98p-25c-5500-6s1p.html
     It weighs 890g and is rated at 25C. A 5500mAh battery has a usable capacity of 4400mAh, which is 80% of 5500mAh. Using only 80% of the battery's rated capacity is recommended for longer battery life. The expected flight time would be 4.4Ah * 60 minutes = 264 amp minutes / 66.8 amps (anticipated amp draw) = 3.95 minutes * 1.75 (a factor that works for my flying style) = 6.91 minutes - let's call it 7 minutes.
     This would require Scott to purchase a new charger, since he indicated that he can only charge up to a 4S pack.
     He could also use two 3S packs in series, and then use his 4-cell charger to charge each pack.
www.hobbypartz.com/98p-25c-5500-3s1p.html
A 3S pack of this type weighs 468g. The total battery weight would be 936g/33 oz.

     The flight time could be increased by using parallel battery packs.
     Two GENS ACE 3300mah 6S1P could be combined in parallel to form a 6S2P pack with a 6600mAh capacity.
www.hobbypartz.com/98p-25c-3300-6s1p.html
The weight for the 6600mAh battery would be 1065g, which is very close to the weight suggested by the worksheet.
     The usable capacity of this battery would be 6600mAh * 0.8 or 5280mAh. 5.28Ah * 60 minutes = 316.8 amp minutes / 66.8 amps = 4.74 minutes * 1.75 (my factor) = 8.3 minutes.
     Scott could also, but I would not recommend, use a total of four 3S 3300mAh packs and combine 2 packs in series to become a 6S and then combine the two 6S packs in parallel to become a 6S2P 6600mAh pack.
     If the battery consisted of four GENS ACE 3300mah 3S1P, then it should weigh about 1462g.
www.hobbypartz.com/98p-25c-3300-3s1p.html
     Besides being a 'wiring nightmare', this battery and its associated wiring would be at least 14 oz. heavier than the 6S2P 6600mAh battery.
     The flying time multiplying factor (1.75) that I use is based on my flying style. I've learned, what I believe, is quite good throttle management over the decades of flying electrically powered planes. I seldom fly 'wide open' when doing level flight and go to full power for vertical maneuvers and ease off the throttle on the down side of the vertical. Each person's flying time factor will very, but still be proportional to the estimates given.

     After completing the calculations for the 290Kv motor, I received the following email from Scott.
     Scott writes, "Just so you know, I had trouble with my Hobby King order and did get the 245Kv motor instead."
     Okay, Geez! Time to rework the workbook page.

     A 3S 5500mAh and 4S 5500mAh can be connected in series to create a 7S pack.
A 4S GENS ACE 5500mAh weighs 612g.
(www.hobbypartz.com/98p-25c-5500-4s1p.html)
A 3S GENS ACE 5500mAh weighs 468g.
(www.hobbypartz.com/98p-25c-5500-3s1p.html) The battery weight is then 1080g/38 oz. and is very close to the Approx. Battery weight: on the worksheet.
     Flight time should be about 5500mAh * 0.80 (80% of the rated capacity for longevity) = 4400mAh or 4.4Ah * 60 minutes = 264 amp minutes / 57.7 amps = 4.58 minutes * 1.75 [flight time factor] = 8 minutes.
     Scott's 4-cell charger can charge each pack separately. That is probably not the best solution, as 4-cell chargers tend to have low charge rates. A higher capacity charger would allow faster charging at home and especially at the field. A charger that can charge a 4S Li-Poly at about 3C (15 to 16.5 amps) would be good. That would be at least a 300 watt charger.
     The CellPro 10XP (www.progressiverc.com/fma-cellpro-10xp.html) with the appropriate adapter boards and plugs could charge both the 3S and the 4S pack at the same time.
     Receiving the 245Kv motor should work to Scott's advantage as he can 'play' with props without having to 'worry' too much about his 80-amp ESC. If a 20x13 draws more than about 60-amps, and he wants longer flight time, he can try a 20x11. If the 20x13 isn't drawing in the high 50s or close to 60 amps, he can try a 20x15, or if a bit less flight time is acceptable, he might like the way the 20x15 flies the plane better.
     No matter which power system Scott uses, a power meter is a MUST, to check the amp draw of the power system to see that the amps and watts in are indeed in the intended range!
     Scott might also want to do a Kv check on the motor that he has in hand. What Kv is and how to check it is found at www.theampeer.org/Kv/kv.html. There is also a link to a handy spreadsheet there for doing the math, once the measurements are taken.
     Good luck with the conversion!

     The February EFO was held at Ken's house.

     Richard Utkan, EFO vice-president, lead off the meeting with his two-day project, a FuglyJet. It is an EDF design constructed from Dollar Tree foamboard and colored packing tape.
www.rcgroups.com/forums/showthread.php?t=1577312
     Richard's version uses a 3500Kv outrunner in an EDF fan unit from the E-Flite Airliner. Power is provided by a 3S1P 1300mAh Li-Poly pack. The all-up-weight (AUW) is 17 oz. It features LEDs around the exhaust outlet. There are more pictures of Richard's plane in the RC Groups thread noted above.
     The foamboard construction technique is discussed in this RC Groups thread - www.rcgroups.com/forums/showthread.php?t=1587275

     Denny Sumner shared his gorgeous Pou-du-Ciel. It was built from Traplet plans.
shop.traplet.com/product.aspx?c=3221
     It's flying weight is 13 oz. Everyone was intrigued with the design, especially the "wing tilting" and many folks had some interesting stories about what they had read about the full-scale Pou-du-Ciel.
     Some barebones photos of this model are here:
www.rcgroups.com/forums/showpost.php?p=20432671&postcount=154

     Bill Brown is building a Wright Model B from plans that Jim Young drew up for him. He rolled out the plans and explained a problem he was having on strut attachment.

     Soon, everyone was involved in trying to give useful suggestions to Bill.
     Ken Myers let the members know that Keith Shaw's surgery on his spinal column went well on February 14 and that he was now home.
     Ken also noted that Thayer Syme is no longer the editor of Fly RC. Ken had received an email about this and confirmed it with Thayer.
     Ken showed two segments from the Modern Marvels episodes "Tiny Weapons (2012)" and "Extreme Aircraft II (2007)" that had interesting information on sUVA type, military aircraft.
     Ken then presented a power point presentation based on "P-40 Warhawk" by Keith Sparks in the February 2012 issue of Model Aviation. It was noted that Mr. Sparks' model had a 123.5 watts in per pound power ratio, yet it did not fly very well, according to Mr. Sparks on p. 57; Flying. Rick Sawicki came up with what the problem was; lack of pitch speed due to under-pitching the prop.
     Ken presented data and suggested that an 18x9 2-bladeÊprop might have been a better choice since it allowed a pitch speed to stall speed ratio over 3:1. Mr. Sparks' version had a ratio of only just slightly over 2:1.
     Here is what Keith Shaw said in his Electric Sport Scale article in the July 1987 Model Builder.

     "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."

     "Ken also presented what he thought was a reasonable power system for the plane using the same 2100 watts in. He suggested a 11S1P 5500mAh Li-Poly and a motor weighing between 840g and 1313g with a Kv between 160 and 180 turing an APC 20x15E. It would give a pitch speed of about 75 mph and a pitch speed to stall speed ratio of over 4:1. The example motor he used was a Turnigy Aerodrive SK3 - 6374-168kv Brushless Outrunner with a weight of 840g.
     There was one question that the group was left with. Is the Turnigy a bigger motor? The Turnigy motor is 190g heavier and there was one cell added to the battery, but the suggested watts in were maintained at about 2100, so is it a "bigger" motor?
     The group closed the meeting by sharing lots of 'goodies' and talking about planes, RC, you name it! It was another great EFO meeting. Remember that anyone with an interest is always welcome!

Good afternoon Ken,

     I just settled down in front of the computer after a happy hour of removing about 4" of wet snow from my driveway. Lo and behold, the December issue of the AmPeer was posted. It was just what I needed to take away the "I'm feeling sorry for myself, there's no flying until spring" attitude.
     Another really interesting issue, particularly your explanations regarding power system selections.
     Congratulations or your award, it is richly deserved!
     I've attached a couple of photos of my latest project. Unfortunately, I ran out of decent flying weather, so will have to wait until spring for the test flights.
     It is a 1/5th scale Tiger Moth from Gordon Whitehead's plans that were published in RCM around 2003. I sat on the project until I came in contact with a gent by the name of Bob Laserve, of Lased Design Service. Long story short, I e-mailed him a scan of the plans, and about two weeks later, a short kit arrived. Talk about service! Anyhow, two building seasons later, here she is, a representation of the third Tiger built, and the oldest one still flying regularly in England at the "Tiger Club" field.
     WorldTex on the wings and tail, polyester dress lining and dope on the fuselage. It weighs 9 pounds, 10 ounces with the 20 cells, power is from a MaxCim geared 4.5-1, and I'll start off with 20 3300mAh NiMH cells, as Gordon did, as she balances just about right on with that battery.
     I cranked it up in my garage, and it blew crap all over the place, and dragged the vice that was holding it back across the floor, so power is there. Not very scientific, but I loaned my Wattmeter out, and it hasn't come back. I will probably move on to 8 A123's after it flies.
     I'm still hoping to get to the Mid-Am one of these days, but in the meantime, thanks again for all your hard work in getting the AmPeer out every month. I really look forward to it!

Cheers, and with best regards,
Ross

Hi Ken,

     Just a further update on my return to electric flight.
     A geared neodym motor in one of my sport models objected to being awoken after many years and showed its disgust by throwing a magnet in flight. After considering simply hanging the plane up until after Santa delivered me a new brushless motor and ESC my 'experimental compulsion disorder' took over.Ê The motor mount had been sized to accept something as big as the Speed 700 and there was one (9.6V plain bearing) lying forlorn in the junk box. The motor was attached with Velcro and a tie wrap (as designed) and the 4S 2300mAh A123 pack was moved around in the battery box until the plane was balanced to my satisfaction. After some trials I settled on an 8x6 Taipan prop. The flight time exceeded 12 minutes with quite satisfactory performance in the air.
     While I am aware this power system is very inefficient, I asked myself just how efficient did it need to be? I find a 12 minute flight time quite OK for this type of model. I have lost the short takeoff ability that I had with the geared neo driving an 11" prop but once in the air the plane is quite pleasant to fly making use of speed rather than torque to perform vertical manoeuvres. It may well be that the new brushless will have to wait until I have worn this motor out. Without the reduced weight and increased capacity of the A123's the performance would have been unacceptable using my previous 10 cell NiCad packs. So with that success in mind I may have to rethink the retirement of the geared Speed 400s also thrown in said junk box.
     On another note, after ground testing my planes to determine how the radio control gear responded to depleted 4S 2300mAH A123 packs I have ceased to be concerned about having no suitable autocut in my existing 35A brushed ESCs.
     Use of a timer is now more of an indication that I should cease low level flying and stay up high. I have deliberately run the battery down in flight several times now and have found no issues except for having to make a dead stick landing. Given most of my landings are performed this way this is not really an issue. This has worked with both my JR FM receivers and Orange DSM receivers operating a variety of servos. I normally use a separate receiver pack for planes that spend most of their flight soaring with the motor shut off (gliders and old timers) and will continue to do so.
     I am now considering a 2S pack of smaller Lithium Phosphates with a diode in series to drop the voltage and a separate charge lead (without diode) to replace my aging nicad receiver pack. Perhaps others have already done this?
     Keep warm.

Regards
Bob Comerford