The graph shows the median pitch speeds for electrically powered prop planes in WCL Levels 1 through 7. Median indicates that half the planes are faster and half slower, but it gives a reference point.
     The trend is quite clear. As the wing cube loading (WCL) level increases, the median pitch speed also increases. Most of the electric planes at the flying field, WCL Level 4, are flying at a median pitch speed of about 50 mph. Most twins are found in levels 5 through 7 where the median pitch speeds are between 58 mph and 62 mph.

     The third factor is wing planform and overall design. As demonstrated by the photo of the crashing DH-88 near the beginning of the article, a highly double-tapered wing planform can sometimes provide unwanted consequences, even worse than when used on a single engine aircraft.

     There is little help online regarding the selection and tips for a twin project. There are two articles online that provide some tips for glow powered planes. They are "So You Want To Fly Twin Engine RC Planes" author unknown and "twin tips - 1/21/2012" by Ed Moorman.
     Both articles stress the importance of having a reliable power system, which using an electric power system provides.

     Both authors are vague about wing loading.

Author Fly Twin, "Wing loading is higher than standard airplanes and so landing speeds are faster... Do not try to slow down and risk a stall..."

Ed Moorman, "5. Twins are heavy... and have a higher wing loading.
6. Twins land faster. Since they are heavier, a twin tends to land a little bit faster..."

     For the 'typical' sport pilot, it is a good idea to select a plane with a lower WCL than a typical twin.
     As with most things in life, there are exceptions. Twins are no different.

     According to Model Aviation, Feb. 2012, page 97, Jeff Weisend's DC-3 has an astoundingly low WCL of 3.74 oz./cu.ft. and flies like a backyard flier. With a wing area of approximately 1420 sq.in. and a weight of only 7.25 lb./116 oz. it is truly amazing. This is not something a typical modeler would be able to create, not that they might want to.
     As noted in the text, "... the model looks better in the air from a distance, as one can see the effect on the plane of the slightest breath of wind."

     The Multiplex TwinStar II is a good place to start a 'twin experience'. It has the WCL of a park flier, although it is too heavy to fit the AMA definition of a Park Flyer, but it flies like one.

Click on photo to open the link to the builder's site

     A biplane twin like the de Havilland DH-84 Dragon-2 or the DH-89 Rapide are good choices.
     The biplane configuration lowers the WCL. With no retracts, the weight is kept down and construction kept simple.

     The New 310-Scale 90 - 92.5" Twin Engine Nitro Power Radio Controlled Plane ARF is a glow powered plane but has what appears to be an extremely low WCL, based on their specifications.
     None of the data that I've collected on RC planes ranging from 1000 sq.in. and up suggests the advertised flying weight of 11 lb. is possible.
     Dick Pettit Associate Editor of R/C REPORT Magazine reviewed this plane.
     His weighed 16.5 lb. WCL at 16.5 lb. is 9.5 oz./cu.ft. Although powering this plane would be very expensive, it could make a good first twin electric.

     A twin the size and weight of Keith Shaw's "Black Magic" is best left to the master. The empty fuselage weighs just 4 oz. Can you do that?

     The Dynam Grand Cruiser Twin flies like a sport plane. Anyone who is comfortable flying sport planes should be successful with it.

     The SIG Do 217 provides one more clue to producing a successful twin. It has a WCL on the high side of sport or low side of advanced sport, which indicates that folks who generally fly planes in the Level 4 category shouldn't have a problem flying it. The designer used several "tricks" to make this a twin that can be flown by the 'masses'.
     One reason that it flies like a sport plane is because the designer enlarged the wing. Using the fuselage length to scale the model from the full-size plane, it is about 1/19-scale. At 1/19 scale the wing area should be 242 sq.in. With a 242 sq.in. wing the model would have a WCL expected of a typical twin, ~16 oz./cu.ft. Using the wingspan, the plane scales to about 1/16-scale. At 1/16 scale the wing area would be about 349 sq.in. The given wing area for the model is 335 sq.in. By enlarging the wing the designer moved the WCL to just about 10 oz./cu.ft, which makes it a bit easier to fly for most RC pilots.
     Also, by having the rudder and the landing gear as "optional", the designer cut down on the ready to fly (RTF) weight.

     The fourth factor is pilot experience.
     To learn what your pilot experience is, inventory the planes that you fly day in and day out and calculate their wing cube loadings.

WCL = RTF weight in ounces / ((wing area/144)^1.5)

     The highest WCL of your regularly flown fleet indicates the level that you are comfortable flying at.

     For me, it would be my Bill Griggs Rocket and my self-designed E-250. The Rocket has a CWL of 16 oz./cu.ft and the Lightening (yes, I meant Lightening not Lightning) E-250 14.9 oz./cu.ft. Both are CWL Level 6 types. Personally, I would choose a twin like those listed in the Level 5 table to start with and then move up through each progressive level to reach my 'ultimate scale twin'.

     Whenever possible, follow the recommendation of the manufacture, designer, supplier or what was used on similar types and sizes found in the modeling press or online.
     If that is not possible, selecting a power system for a twin propeller type plane depends on ground and fuselage clearance. The largest diameter prop should be chosen that provides sufficient clearances.
     There are many ways to select an electric power system, if one is not recommended. If you are unsure of how to do that, please drop me an email, and we will discuss it here in the Ampeer, or give me a call. Also, see the February 2012 Ampeer. I describe how to select a power system for an 80" PBY and that information may be applied to other twins as well. Also, the first article in this issue should help as well.

1.) For your first twin, choose a subject with a WCL similar to or just below the WCL level you are comfortable flying at now. There is a lot to learn about twin engine operation. Learning to fly with a WCL greater than you are comfortable with should not be one of them.

2.) Before flying your twin, put in a lot of practice time on your highest WCL plane(s) and consider acquiring a single-engine type with an even higher WCL or even adding weight at the CG to a plane you already have.

3.) If you 'roll your own' designs, consider going through a series of steps to get to your ultimate twin. Remember that the more options* that are added to the airframe the heavier it becomes with a resulting higher WCL and the more difficult it becomes to fly.
(options* - anything that is added to the airframe that has nothing to do with controlling the airplane. Keep the Sig DO-217 design in mind; start with only the necessary flight controls, keep the landing gear simple, if used, and/or fudge the wing area of the early prototype.)

     Information about wiring brushless twins:

Video:
www.youtube.com/watch?v=aADN7iCx9E4

Web Links:
www.electricflyermagazine.com/page17.html
www.electricflyermagazine.com/page16.html
www.electricflyermagazine.com/page18.html

Magazine:
November 2004, Fly RC, Tom Hunt's article on multi-motor brushless power systems.

Hi Ken,

     Here's my 2012 Project. It is a 1/4-scale Piper Tri-Pacer from Calvin's Classic Plans. I'll keep you posted on the Tri-Pacer!

Ken,

     Many of the better indoor 3D type flyers are using aircraft from Western Michigan Parkflyers. We fly in a smaller size church space. Web address wmparkflyers.com/default.aspx

Bill

Ken,

     Have enjoyed the Cube Wing Loading pieces.
     I have two electric sailplanes and a pure sailplane that have low sink and yet are clean and penetrate fairly well. Modern composite and balsa construction permits thin wing sections that still have good strength.
     The 2 meter Electron F5J (571" sq., 21.5 oz.) has a loading of 2.72 oz./cu. ft.
     The Ava electric (1100" sq., 54 oz .) has a loading of 2.56 oz./cu. ft. The AVA sailplane (37 oz.) has a loading of 1.75 oz./cu. ft.
     These are all in the "indoor" category as far as wing loading. No wonder they have low sink and are easy to fly.
     Sadly Kennedy Composites no longer sells the Ava series. They have the Electron F5J and a new Ava Pro series but it is harder to electrify than the Ava.
     My Electron F5J has 200W/lb. input and the Ava 300W/lb., so they climb well. A friend thinks he can build an Ava electric for altitude limited electric soaring (ALES) competition down to 44 oz. which would give a loading of 2.08. For ALES you need only enough power to get to 660' in 30 sec so the battery and motor can be fairly light.
     Bob Livin and I are looking forward to the Mid-Am and Keith's Birthday Party next season.

Plenny Bates

     I received this reminder from Tom. Check it out. KM

Hi,

     Bob Aberle's "Frequently Asked Questions" column in the February 2012 issue of Model Aviation listed this plan service in the UK. Great source of downloadable pdf plans. Enjoy "hours&quit; of searching and nostalgia.
www.outerzone.co.uk/index.asp

     Ha, did I say your January issue was Fantastic? Well, you've outdone yourself this time. The February issue is a real keeper, even has indoor info. Told ya we'd get you into this. Many thanks Ken. GREAT Job.
     I've ordered a new receiver from Hobby King, for Ultralight indoor models and have pulled out my Lasey to revamp it along with a new heli I got. It is German designed but China made. I have had a ball with this one.
     I've sent some pictures of my latest project and our indoor with the new Parkzone cub and a fellow flyer with his Champ.
     Many thanks for the latest issue. I'll have to print this one off for the other fellows to read.
     I'll send more info on the Lasey as it gets nearer to flying time.

Art

     Thank you so very much Art. Keep us informed on the Lasey. You might be interested to know that your name first appeared in the Ampeer in the July 1988 issue. Scroll to the bottom of the issue and there is your name on the map to the London field.

     You've probably seen this advertised in all the current RC magazines, but here's a little more 'background' on Doug. KM

Hi Kenneth,

     I'm a RC club member from the WRC Club in Gilford, NH. And after years of seeing propeller injuries, we developed the ArmSafe System to help reduce the possibility of propeller strikes. IT IS AN OLD IDEA IN A NEW PACKAGE. The product was developed out of necessity for a small, light, and high amp arming system. The product has gone through several iterations over the many months of development and testing, to make it as small and light as possible. It has been an exhaustingly long (and expensive) process to bring this product to market, but we are finally here!!!ÊÊ
     Our goal was to create a great arming system to add another layer of safety to help keep our electric RC modelers safer. See them at http://www.SharpRC.com.

Thank you and Happy New Year,
Doug Schumacher

     As Doug mentioned, this arming switch has been on the market for quite awhile and has been mentioned in previous Ampeers.
     It is available with both Deans and Anderson Power Poles with 14ga and 12ga wire. Deans are shown in the photo. The arming plug is APP on this style.

Hi Ken,

     First of all, I would like to thank for your monthly information about EFO. I like it very much. Now, since the Winter season is here, the discussions about indoor flying is the number one theme with the club members. I am always looking for mini or micro motors and servos. While looking for parts on the Internet, I came on this page: www.aeorc.com.
     The Chinese people have a lot of micro units, like 15 gram brushless motors and servos, escapements, etc. at very competitive prices. Probably you know this site already or if not, then look once into it.
     I came on this site because I was looking for mini devices for the Mud Bug I am building from Stevens Aeromodel. So maybe you can eventually give this address in one of your newsletters to the EFO fans.
     I take the opportunity to send you all my best seasons greeting for the coming days.

Yours Alex (Oldtimer, only 80 years)!!!!

Hello Ken,

     Enjoyed your latest issue of the Ampeer.
     Here is my latest project with specifications and photos. It is a Brooklyn Dodger old-timer with electric power. It has a 72" wing span. Power comes from four "A123" 2300mAh batteries and two "A123" 1100mAh cells for the Xtreme link 2.4-Futaba 8aup set up. I will fly this in the spring. I canÕt take this cold weather.
     Congrats on your Award. Well done.

Happy Holiday season to You and Family.
Willie McMath

     It is now published and edited by Roland Friestad. Roland took the place of the late, John Worth. (The Cloud 9 Web site should be up and running by the time you receive this issue. KM) We also have plans to place all 38 of my micro designs, that appeared as construction articles in RCMW, on to a single CD which will include access to full size plans and as a bonus will have a copy of my 120 page book/CD on the subject of micro/indoor RC flying.

     I have launched a brand new version of my website, RCadvisor.com. There are two major changes:

1. My model airplane calculator is now 100% free.
2. I'm posting at least one high quality article a day.

     With over 10,000 registered calculator users already, I expect the calculator to be more popular than ever. The feedback on the articles has also been very positive. I hope you like the changes.