6S Kv range: 320 - 355
7S Kv range: 275 - 300
8S Kv range: 235 - 265
     Changing the prop diameter and/or pitch changes the suggested Kv range.
     I've put some possible motors on the motor notes sheet in the attached workbook. I looked them up on a site called RC Book. I did not fill in the price or possible Web site address for purchase. You can copy the name into Google and find suppliers.

Hope this helps with your project,
Ken

     For more on glow to electric conversions

and the Excel workbook

The specific workbook for this plane is here.

     Fall in Michigan is a great time to be at the flying field. Both the September and October EFO Flying Meetings were blessed with great weather.

     EFO vice-president, Richard Utkan prepares his Mustang in September.

     Rich Sawicki returns from a successful flight of his P-38. The grass was short enough for the provided retracts in this Banana Hobby P-38 to work well on this day.

     The weather was even better at the October meeting. It was a great day for flying and sharing.

     It just doesn't get any better than this. Blue skies and low winds provided the perfect weather.

     A great 'field lunch' was provided to the fliers. A HUGE hit of the day was Arthur Deane's potato soup.

     A plane can be seen landing as the folks chow down.
     It will be quite awhile before we see these beautiful days again!

Ken,

     I'm not sure if it's "your" spreadsheet, but it's the one you used and referenced when you showed me how to select a motor for my Venus 40. I'm doing the same thing with my Sig Kadet LT-40.

KM: Spreadsheet @ http://www.rcgroups.com/forums/showthread.php?t=1472442

     My question is about the Wing Cube Loading level determination. I'm concerned about the fact that the Kadet 40 comes in as a level 3 Park. I just have a hard time using the term "park" and 40-sized trainer in the same sentence.

     KM: Yes, it is my spreadsheet.
     Like the more commonly used wing area loading (oz./sq.ft.), the WCL (oz./cu.ft.) is used to describe how the plane will most likely fly and the pilot's ability required to fly it. It does NOT describe the mission. My flying buddy, Keith Shaw, has a super flying Super Stearman of just over 1200 sq.in. It is NO PARK FLYER!!! It is relatively easy to fly compared to his famous Czechmate or Bugatti which have much higher wing cube loadings.
     Be sure to check out the articles on the EFO Web site about WCL, also known as CWL (cubic wing loading).
     There are four articles and two calculators located not too far down the page.

     So from there, 2 questions arise:

1. Is it ok to use the next level (level 4 Sport/Trainer) and use the numbers from there?

     KM: You can change the targeted power by either changing the "Desired watts in per pound" or the WCL level watts in per cubic foot, as you indicated.
     The Sig LT-40 really doesn't need to have that done though. Because of it's design, flat-bottom wing and relatively high wing angle of incidence, changing it is really not that necessary, as the plane doesn't need to fly much more than 50 mph. The second table on the spreadsheet shows this speed for a Level 4 Sport/Trainer. More speed with this type of plane only results in it climbing like a homesick angel or even going into a loop when full power is applied.

2. If I do use the Sport/Trainer numbers, does that drastically change the flying characteristics of the plane?

     KM: Using the Sport/Trainer numbers does not drastically change the flying characteristics of the plane. The plane will still 'fly' the same. What will change is that, believe it or not, it will be 'over-powered' and harder to trim because of the wide variation between the stall speed and top pitch speed.

     In more of a fuel engine type question terms, would it be like the difference between a 40 and a 60-sized motor, or more like the difference between an OS 40AX versus some other brand's 40 size? Would that be a major difference versus slight difference as far as weight, pull, etc.?

     KM: It would be more like the .40 to .60 comparisons with quite a large difference. I've posted a screen capture of the spreadsheet for the LT-40 using an APC 13x6.5E in your 'Show us your Sig LT-40 Conversions' thread on RC Groups.

     You can compare it to what you've been playing with. I also did a motor search for you as well.

Adam Lough

And a follow-up from Adam

Ken,

     I finally got a Watts Up meter. I put it on the Kadet with a 12x8 and here are the numbers I got:
680 Watts
50.93 Amps
     The Kadet has the Scorpion II-3026-710 and a 60 Amp speed controller. I run a separate receiver battery. I was using a 30C 5000 mAh 4S Li-poly fresh off the charger.
     I then changed the prop to a 13x6.5 and got similar numbers:
680 Watts
49.2 Amps

     I'm close to finishing the Venus now.
     All I have left is to mount the battery to balance the plane. The Venus ended up with a power system from Grayson Hobby.
     I'll start with the 14x7 prop. My plan is to use the 4S 5000mAh battery (30C). Do you see any issues with the numbers from your chart versus the numbers on the Grayson website for the motor specs?

Thanks for your time, opinions, and consideration.
Adam

     KM: I used Drive Calculator and it looks like similar motors to the Grayson Hobby motor, which I believe to be a Suppo, when using an APC 14x7E, are about 600 to 650 watts in pulling about 40 to 45 amps on a 4S Li-Poly.
     You might want to consider an APC 14x8.5 for the Venus, as it is a pretty clean airframe. On 4S and that motor it should move the watts in somewhere into the 650ish range and the amps should move up to about 45 to 50.
     Be sure to use that new Watts Up meter to verify that.

Hope that is helpful.

     Skymasters R/C of Michigan would like to welcome your club to join us when the Winter Indoor Flying returns on Tuesdays starting November 1st!
     Gold Card Season passes are on sale now, at our Skymasters' meetings, or on the Web via Paypal (www.skymastersrc.org).
     The price remains at $100 this for the season, but now includes the 2 four hour Holiday Sessions - for 25 sessions - 54 hours of flying! Hope to see you at the arena.
     Click here to signup now!
     5 session punch cards remain $30 and will be on sale at the arena on event days. Each 2-hour session is one punch. (Punch cards may also be used for the holiday flying sessions this season - 2 punches for each 4-hour session.)
     The sessions are at 11:00 a.m. to 1 p.m. on Tuesdays through the winter at the Ultimate Soccer Arena, 867 South Blvd, Pontiac, MI. The Ultimate Soccer Arena is located just west of Opdyke, on the north side of South Blvd. The flying area is 365 ft. by 260 ft. with ceilings from 45 to 75 ft. The facility is temperature controlled and well lit.
     Remember that the season starts on Tuesday, November 1st! Buy your season pass now via Paypal!!

Event Flyer

Hello Ken,

     Another great issue of the Ampeer. (Referring to the November issue where his Magic conversion was featured. KM)
     Here is a bit more on the motor 'fix'. I had to take all the magnets out of the Turnigy motor and re-glue them. I did it with 5-minute glue and filled between the magnet gaps with 5-minute epoxy. Then I balanced the bell housing.
     I flew the Magic on Sunday and it flew well. Another lesson learned. This electric flying is exciting.

Take care,
Willie McMath

Hi Ken,

     Venus 40 Power System Recommendations Adam's RC Groups Thread

     Adam picked a motor with a Kv of 650. As discussed earlier. He might have to drop the prop pitch to 8.5" or possibly even the diameter to 13" to keep the amp draw in a decent range from his ESC and motor combination.

     The worksheet shows that for a 4S Li-Poly and an APC 14x10E prop, a motor weighing between 220g and 330g with a Kv of about 575 would have been a good choice.

Motors for Venus 40 and 14x10 prop.

     Ed Anderson's EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT and Ken Myers' Electric Power Basics now have a new format available on the EFO site. KM

     I read about Ed's book in this month's Model Aviation, and found a copy on your website. I downloaded it along with your book.
     In case you're interested, I used a little script of mine to convert them to a PDF that's easier to read on small-screen devices (like my Kindle). Results attached - essentially converts to four pages per page and strips most margins to maximize use of the screen.

     Thanks very much for sharing!

Cheers,
Patrick

     Thank you Patrick for sharing them with us! KM

Ken,

     Could you give me a brief/quick/down n dirty explanation as to why when the number of cells goes up, the amp rate of the ESC goes down?
     Also, I have a Sig Kadet LT-40 with an OS 52 4 stroke. Same thing with it, would it be a good candidate for conversion? And it is setup as a tricycle gear.
     Again Ken, I appreciate your time & effort to help me.

Adam

     There are a lot of variables when selecting a successful power system for a glow to electric conversion. Some decisions need to be made to limit the number of variables.
     Tom Hunt, in his Electro-Active column starting on page 52 of the August 2011 Fly RC, noted some very important considerations in his article titled "Glow to electric conversion tips - Part 1, Theory". He lays out a ten-step method, which is very similar to what I've used over the years.
     He put a very important concept into a few words that I'd not been able to do, up until now.

p. 54 "ASK YOURSELF THESE THREE QUESTIONS
The next step is all up to you. I cannot help you with answers. How was the model intended to be flown? How do I want to fly it? What is my skill level? Answering these questions (honestly) will help us choose an "appropriate" power system for the model."

     You'll note that I set a target power in for the Venus at about 660 watts in using the glow to electric spreadsheet as a 'guide'.

     That input power could be higher or lower and the plane still considered a successful conversion, as demonstrated by Tom's questions. To make it easier for most folks interested in this type of conversion, I just let the formulas on the spreadsheet do their work.

     For this explanation, we will assume that a Li-Poly cell can supply approximately 3.7v under load at some point in time when we might be measuring it with a power meter. This is only done to make comparing what is going on with the different number of cells easier. It absolutely does not happen in 'real life' for many various factors. Using 3.7v per cell -
4S 14.8v
5S 18.5v
6S 22.2v

660 watts in / 14.8v = about 45 amps required
660 watts in / 18.5v = about 36 amps required
660 watts in / 22.5v = about 30 amps required

     See this post by Lucien Miller. The 80% 'Rule' is discussed as the second item in his reply.

     Some folks, including myself, use this 'RULE', while others don't. Like all rules of thumb, only the user can determine if it is useful for their purposes.
     The inverse of 80% (0.80) is 1/0.8 or 1.25. That means that if you multiply a number by 1.25, 80% of the new number will give you the original number.

4S 45 amps * 1.25 = 56.25 amps (56.25 * 0.8 [80%] = [tah dah] 45) A 55 amp or greater ESC would be appropriate, if you want to follow the 80% 'rule'.
5S 36 amps * 1.25 = 45 amps or greater for the ESC
6S 30 amps * 1.25 = 37.5 amps or greater for the ESC

     Keep in mind that the 'target' power in is ALWAYS 660 watts in for this example.

     Selecting the battery. I use a simple method of multiplying the 'target' amp draw by 100.

4S 45 amps x 100 = 4500mAh or slightly greater or less to get a real world capacity
5S 36 amps x 100 = 3600mAh or slightly greater or less to get a real world capacity
6S 30 amps x 100 = 3000mAh or slightly greater or less to get a real world capacity

     As I previously noted, the weights of similar cells in the given packs will be very close to the same, even though the cell count changes. As the cell count goes up, the capacity, and therefore the weight goes down.
     Flight times will all be relatively the same. Again using the 80% 'RULE', 80% of a 4500mAh pack (4.5Ah) is 3600mAh (3.6Ah). 3.6Ah * 60 minutes = 216 amp minutes. 216 amp minutes / 45 amps = 4.8 minutes of wide open throttle flying, which generally translates to 7.5 to 9 minutes of flight time depending on the airframe, pilot's throttle management ability and how 'aggressive' the pilot chooses to be during the flight.

5S 3600mAh (3.6Ah) @ 36 amps - 3.6Ah * 0.8 = 2.88Ah * 60 minutes = 172.8 amp minutes / 36 amps = 4.8 minutes

6S 3000mAh (3.0Ah) @ 30 amps - 3.0Ah * 0.8 = 2.4Ah * 60 minutes = 144 amp minutes / 30 amps = 4.8 minutes

     The original calculation for the Venus 40 and recommendations were based on using an APC 14x10E prop. Prop selection is a key to all electric power system's success, as well as for glow to electric conversions. Tom Hunt explains why on page 52 of his article and notes, "The biggest advantage to electric flight is to choose a motor/prop combination that swings a large prop that better matches not only the way you want to fly, but the ability of the model to fly in the manner intended." That is why I chose to do the original calculations with a 14x10 prop.
     Tom's first step, as well is mine, is to get an approximate required power in. The spreadsheet does that using several formulas or the simple watts in per pound can be used with experience. The second step for both of us is to select the prop. He says to use the largest diameter possible based on the pilot's experience.
     After leveling the plane on a flat surface and measuring from the flat surface that the airframe is sitting on to the center of the glow prop shaft the beginning prop radius can be determined. p. 53 "A "skilled" pilot can subtract one inch or so. A less skilled pilot might subtract 1.5-2 inches. If you fly off a very rough field, even a skilled pilot may choose a higher number to avoid prop breakage." Once that number is determined, multiply it by 2 for the largest diameter prop.
     The spreadsheet uses a slightly different method, but pretty much ends up with the same results.
     The "How to Guide" explains my method.
     If the actual measurements for the Venus and your experience indicate that a 15" diameter is appropriate, the spreadsheet allows for this. Note that the only numbers that change are the motor Kv (RPM/v) numbers. Even the recommended motor weights remain the same. A 12" pitch, as suggested by the pitch area of the spreadsheet, would be good. New possible motors would need to be chosen based on the new Kv numbers for a 15x12. Conversely, if a 13" diameter is more appropriate to the real world measurements and your ability, new motors, based on the new recommended Kv would need to be considered.
     Appropriate pitches are noted on the spreadsheet as well.
     The use of RC Book is a great resource for finding the data on a lot of motors without having to go to the suppliers' sites and look up each motor.
     If you have downloaded the spreadsheet, fill in this data for the Sig Kadet Senior from the Sig Web site.

2-stroke 0.40
4-stroke 0.45 (even though you are using a 0.52)
Weight 6 lb.
Wing area 1150 sq.in.

     The spreadsheet has been updated and the numbers for the average and median watts-in per the cubic wing loading are automatically displayed.
     You will note that everything concerning the power system recommendations comes out about the same as for the Venus 40 when using the 14x10. Of course the two planes, even with identical power systems, will fly extremely differently, as they have very different 'missions'.
     If a 15" diameter prop is appropriate for the Senior Kadet and your flying ability, it might be a better choice to haul the 1150 sq.in. 'trainer' around. An APC 15x10E might just be a tad more 'appropriate' to the mission, yet the APC 14x10E would certainly work.
     Again, if the 15x10 could be used, then an outrunner with the appropriate Kv for the number cells chosen would need to be located.

And from Adam:

     I have been using the "magic spreadsheet" to gather parts for my Sig LT40 conversion from fuel to electric. I have a 710kv Scorpion motor. The battery comes out to be a 4 cell, 4500maAh that I have not purchased yet. My question today is, can I use a 5 cell, or even 6 cells with similar/more/less capacity? My speed controller is in the 65-amp range. I'm using the 13x8 prop.

Adam's build thread with the maiden info on RC Groups

     Ken Myers was awarded the Carl Goldberg Vital People Award in a surprise presentation during the annual Midwest R/C Society Swap Shop in Northville, MI USA on Sunday November 6, 2011. Over 200 modelers were in attendance. Through special arrangements, Ken's wife was there for the award as well.
     Ken was recognized for his decades long work in promoting electric flight, in all of its many forms, through the AMPEER newsletter and the MID-AM Electric Flies. Keith Shaw probably said it best, "Ken provided the vehicle, through the AMPEER and his technical expertise, to help electric flight grow into the remarkable form it is today". Ken's unselfish willingness to help modelers around the world be successful has been appropriately recognized. The award application can be found elsewhere in this issue of the AMPEER. It was very difficult to compress all of Ken's contributions into the limited space available on the form. Imagine writing and, for many years printing and mailing, a monthly newsletter for over 20 years! Ken did it without hesitation.
     After it was confirmed that Ken was the winner, work went in to high gear. The event director Rudy Reinhart, officers of the Midwest Club and members of the EFO where all contacted. Last years Goldberg Award winner Gary Weaks from the Skymasters R/C Club and past AMA Hall of Fame winners Keith Shaw and Pete Waters were present. Erin Dobbs at AMA headquarters expedited getting the award created and delivered to chief instigator Joe Hass as there were only a few days from the initial confirmation of Ken's award and the swap shop. Arrangements were made for the application to be framed with a large mat so that those in attendance could add their personal wishes to Ken.

Joe Hass (right) presents Ken's Award as former award winner Gary Weaks (left) looks on

     The biggest challenge was to keep the award a surprise. Fortunately Ken had moved to the back of the venue as the final preparations went into place. Jim Young graciously agreed to take pictures. At 10 AM Hass took to the microphone. After a brief explanation of the significance of the Goldberg award Ken's name was announced. As applause rose from the crowd Ken, smiling from ear to ear, made his way to the front of room. Reinhardt, who was standing next to Ken, stated that Ken was totally surprised. As evident by one of the pictures Ken was equally surprised by the check that accompanied the award.
     After the presentation Ken graciously accepted the best wishes and congratulations of all those who appreciated and benefited from his contributions and generosity.
     For those who have been involved in aeromodeling for a while the name Carl Goldberg (1912-1985) is synonymous with prolific free flight, controline and R/C designs that forever changed the landscape of modeling. Carl worked for Comet Models, was one of the founder of American Hobby Specialties (which eventually became Top Flite Models) and founder of Carl Goldberg Models. A consummate gentleman, Carl helped modelers young and old and contributed to AMA during its formative years. Prior to his death he and his wife established the Carl Goldberg Vital People Award to recognize and reward those who make aeromodeling so rewarding. Nominations from the aeromodeling community are accepted by the AMA. A committee reviews those applications and makes the awards in November of each year. Join all of us who know and work with Ken in congratulating him in this well deserved recognition.

Ken and Chris Myers

     Wow, all I can say is thanks to everyone! It was indeed a very pleasant surprise! Special thanks to Joe Hass for the nomination and to the AMA for this recognition. Since only five people a year are awarded this honor, I feel extremely honored and humbled. KM

     There are a precious few individuals who unselfishly contribute to the success of our hobby/sport. To have one who dedicated over 2 decades to the growth and enjoyment of electric flight is truly a gift. For 23 years Ken Myers has created and edited the AMPEER newsletter. With the masthead of "The Future is Electric" Ken's handiwork has been and continues to be the leading source for data on all things related to electric flight. It is read worldwide. Well before successful electric flight was even imagined Ken's work showed how it could be done.
     Ken's skill as a math teacher and his familiarity with computer programs allowed him to develop a variety of analytical tools to help guide us in making successful flight performance and power system decisions.
     Ken is also a gifted speaker willing to make prepared presentations and impromptu talks. The best example occurred to me personally. I was speaking on electric flight at a local hobby shop with Ken in the audience. A question stumped me so I asked Ken if he had any insight. Not only did Ken willingly come to my aid but introduced an entirely new way of matching aircraft to power systems. Using the inventory in the hobby shop he set out example after example of how his techniques could allow a novice to create the perfect power system for any electric airplane.
     If publishing a monthly newsletter wasn't enough Ken created and ran the Mid America Electric Flies in Southeastern, MI. The MID-AM, as it has become known, has been an annual tradition for 27 years. It continues to be one of the premier events where you could see the latest in electric flight actually flying. With the ability to camp on sight flying begins at the first hint of the morning sun and continued into the night. There was always something to surprise and amaze.
     Ken's warm personality, expertise and willingness to unselfishly share epitomize the goals of the Carl Goldberg Vital Persons Award. He deserves to be one of the winners in 2011.