October 2007

October 2007 Issue Electric Flight Column by Greg Gimlick

A Short Break:

I’m going to stray off topic a bit this month to cover some things from a recent trip to Joe Nall and touch on a couple of interesting items. Jet’s, big planes, cool chargers, and not enough space this month already!

A Gift to Me from Iraq

Soldiers Sean Hayes and Larry Mulholland must have known this was my birthday because they sent this old retired Army helicopter pilot the coolest photos I’ve seen in a long time. Larry shot the photos while Sean flew his T-rex under the crossed sabers marking the entrance to the main parade field

in Baghdad.

Sean saw the photo of Hayes Hobbies in the June issue and knew the shop well. I look forward to meeting him there upon his return. I doubt the former “leader of Iraq” would have approved of this great usage. Thanks a million guys.

Electric Jets Top Joe Nall for Me:

I love Joe Nall and make no bones about it. It’s big planes and more and more electrics are showing up and doing more than holding their own. I’ll toss in some others over the next few columns, but I could spend a whole article just covering the new Electra Jet from Bob Violett (http://www.bvmjets.com/) If you’ve followed model aviation for any time at all you know the name Bob Violett as one of the great innovators in jets. With the introduction of his new electric line, I can say for the first time in my life I have jet fever. These are simply the finest jets I’ve seen since electric jets starting showing up at the fly ins.

I also want to thank Bob Fiorenze (http://www.rcaviation.com/fiorenze/) for taking the time to take apart his jet so I could get shots of the inside and all the components. His is a real work of art and a lesson in perfect finishing techniques. More on that later…….

The Electra Jet Kit:

The plane spans 60 inches and has an area of 710 sq inches. The length is 67 inches and weighs between 13 and 15 pounds when complete. Everything is made in the US at their plant in Florida and the fuselage, vertical fin and cockpit components are all beautifully molded fiberglass with carbon fiber and Kevlar reinforcements. The wing and stab are built up from laser cut balsa and ply with one-piece wing skins. To help absorb landing and flight loads the wing spars are extruded carbon fiber and all the braces, landing gear plates and special parts are injection molded carbon fiber. Jet designers are the kings of access panels and the BVM guys are no different. Everywhere you need to access something or even think you might need to in the future; there is a hatch that molds perfectly into the body.

The Electric Vio Fan:

The specially designed EVM power units are a combination of BVM fan units matched to specifically designed Neu motors and come in 10S and 12S versions. Both units are listed as 4000-watt systems and with 37 and 44 volts respectively under load, you can do the math and see these are sucking some current. Bob was using a Castle HV-110 controller in his to do the work. For more information on the EVM system, check out their website.

One of the interesting things about the BVM system is the saddle cells they use to slide in the sides of the jet along the fan unit. These are nicely made and make the most of the design of the fuselage to get cooling air.

The price of the jet, power system, and retracts aren’t for the faint of heart, but neither is flying a 160 mph jet! The performance is on par with the small turbines and actually cheaper. For the first time since getting into electrics, I can see myself wanting a jet.

Bob’s Finishing Techniques:

My hat is off to one of the masters of finishing. I overheard arguments among spectators about how it was done and how many coats of clear coat were on it. Guess what – NO clear coat was used. Bob used ¾ ounce glass cloth and Z-Poxy to cover the jet and then two coats of primer being wet-sanded each time. Once that was complete, he used PPG Single Stage Automotive paint with each coat being sanded. For the final finish he sanded in stages all the way down to a 4500 grit paper and finished it up with compound. I would have bet it had several layers of clear over the paint if he hadn’t told me the process. By doing it this way the entire jet only gained 7 ounces and you could see your reflection in the finish. The weight of Bob’s Navy jet is 11 pounds without the batteries.

The “Animal” and Hacker:

Andrew “the animal” Jesky was there with his Hacker powered Radio Wave Extra 300 at 35% scale. Hacker’s new A-150 outrunner on Thunder Power 14S2P 9600 mah lipos powered this 104-inch monster. Spinning a Mejzlik 27-12 prop producing 7400 watts, this machine pulls a whopping 180 amps static at full throttle.

Needless to say, Andy doesn’t spend much time at full throttle. The plane weighed in at 31 pounds and he really knows how to show it off. The real surprise came at the end of his flight when we were talking in the pits. Andy had been on the ground about 5 minutes and said, “Stick your hand in the cowl and feel that motor”. I figured he was trying to get me to burn my hand as a joke, but then he stuck his hand in. When I felt the motor, it was barely above ambient temperature! I couldn’t believe it was that cool after that aerobatic flight. I am very impressed with the new Hacker A150. At 4.5 pounds and a Kv of 166 it’s meant for big planes and big props and it certainly didn’t disappoint the crowd.

FMA Direct Cellpro 4S Charger:

I mentioned a while back that after talking to Red Scholefield I planned to make the FMA Cellpro 4S charger my next purchase and I’ve made good on that. I wanted a small charger that I could literally toss in my back pocket and it would do the job of balancing and charging the smaller packs for my planes and helicopters. Measuring only about 3 x 4.5 inches and less than ¾ inch thick, it’s the smallest of my chargers and one with incredible features. Since Red has talked about it I won’t repeat it all here, but this one will do both A123 and regular lipo cells. Cut-off is programmable so you can set it for storage levels too.

How easy is it to use? In my haste and excitement to try it, I took it on a trip and forgot to take along the instructions. Most of the problems people write us about could be avoided in the first place if they’d RTM (read the manual) and here I was about to go down that road. Since it was the only charger I took with me I started looking thru the menus and options and tried a couple of changes to see if I was doing it properly. Everything went smoothly and I finally decided I was confident enough to charge a pack. I would never recommend someone risk charging lipos without first reading the instructions for their charger, but with a bit of careful study this wasn’t a problem. This thing is really easy to figure out and it’s doing a great job with my smaller packs. Once again – Red was right!

Back on Track:

Just a short step back into our previous discussion on choosing power systems since we’re running out of space. I talked about big planes and I know you’re thinking you may never use 36 volts, but I hope the idea of volts vs amps was made a bit clearer. Now let’s take a look at what our thought process might be like with a smaller plane.

Let’s say we have a sport plane that’s meant for a glo 40 engine. The wing is about 600 sq inches and the plane is projected to weigh 6 pounds. With lipos and our new equipment, I figure we’ll target that for the final electric weight too. We want it to be aerobatic so we know we want at least 80 watts per pound.

6 pounds at 80 watts per pound = 480 watts

Let’s further decide we don’t want to be in the super high current crowd so we’re going to say our goal is to stay around 30 amps to keep our lipos happy.

480 watts divided by 30 amps = 16 volts

With our lipos delivering about 3.7 volts under load, we can divide that 16 volts by 3.7 and see that we’ll need 4.32 cells. Since they really don’t come in fractions we’ll decide between a 4S pack (14.8v) and a 5S (18.5v) pack.

480 watts / 14.8v = 32.4 amps

480 watts / 18.5v = 25.9 amps

Which is the right choice? Either one if you ask me. Now it may come down to looking at your equipment and seeing if you can support the 5S pack. If you have a charger that only does 4 cell packs then you’ll want to go with the 4S pack unless you’re willing to buy the new charger. Since I have chargers that will go well beyond either pack, my personal choice would be to go with the 5S pack because I like the higher voltage and lower current. Either setup is going to fly your plane nicely and have very similar performance depending on your prop choice.

Final Approach:

That’s it; I’m over on space once again. Next time we’ll look at using the simulation programs to check our plan and see how we can determine the missing motor constants when we only get the Kv from the manufacturer.

Contact Info:

Castle Creations 402 E. Pendleton Avenue, Wellsville, Kansas 66092 USA

Phone: (785) 883-4519 Fax: (785) 883-4571

sales@castlecreations.com

www.castlecreations.com

FMA Direct 5716A Industry Lane, Frederick, MD 21704

800.343.2934 • Fax: 301.668.7619

www.fmadirect.com

Aero Model (Hacker USA) 2122 West 5th Place, Tempe Arizona 85281

Phone: (480)726-7519

info@hackerbrushless.com

http://www.hackerbrushless.com