1/2a electric - Ring Rat by Stevens Aeromodel

Two weeks ago I visited a local hobby store that I visit on occasion. I usually just purchase hardware or odds and ends. This time however an old friend was working behind the counter and has apparently been a catalyst for these folks with fine products to venture into control line. They have specifically been involved in Electric RC. They do that extremely well and their first offering that is now publicly available as of yesterday should be a good one. It is a charicature if you will of a Ring Master named the Ring Rat. Numerous prototypes were being tested and I was given the tour of the built examples. I asked that they contact me as soon as they were ready to sell one. That was yesterday and I bought the first one. What I can tell you is that for a simple beginner plane it has the most thorough set of instructions that anyone would want. Step by Step with photos. There are even photos of the parts so that you can lay everything out before you start to make sure it matches.  While I wont give up my Nitro interests I can tell you that I look forward to finishing this plane!

Take a look at their site. It was updated last week with information on this plane.

http://www.stevensaero.com/StevensAero-RingRat-CL-100-Nostalgic-Electric-Control-Line-Sport-SAK-RRAT100-p-20213.html

Looks like a good introduction into control line electric power.

Here is the story of our, Black Hawk Models, electric experiments:
     For a couple years we had kicked around the idea of electric 1/2A modeling. What we wanted was set down in a list of goals:
1 low cost
2 able to fly from soft and hard sites
3 multiple fliers so clubs could use it
4 safety
Hmmm that doesn't seem to hard.
     Last year we brought in two designers and two engineers to make it all happen.They were given a open budget with the understanding that if it became evident that it would not work we would pull the plug. Six planes were tested with three different motors and two different wires. There was some success but they needed to hit the mark on all points. Earlier we had been contacted by Buzz Flight in England with their electric plane. It was to hard to build and to heavy to fly well. We redesigned the plane for them and helped to cut their cost but success for them was not good enough for us.
     In the end we were using a brush type motor to cut expense and a battery on the pilot to allow for more flying time between charging. If a club has 10 kids to fly and a 30 min. charging time it will take 5 hours for each kit to fly once and they will be bored. For the most part the plane needed to be dragged off of the soft ground field and taxied a full circle on the hard surface. When in the air it was hard to control as there was almost not line tension and the lack of noise was a danger. When testing a model at an air show, there was several old timers watching. These guys were all control liners and even after I told each that we were about to fly an electric plane and to stay clear of the circle several wondered out to ask the pilot questions ... mid flight!!! Adding a noise maker was another goal. In our final success was a plane that flew like a trainer, self destructed like a stick and tissue plane, was a danger to both the pilot and the launcher, flew only from a hard surface and could fly all day long.  Well 1 out of 4 goals isn't so bad.
     Oh yea, the cost. With the less expensive motor we needed very expensive wires to fly on added to the cost of the switches, prop adapters and so on we reached the 100 dollar mark ... to much.
Larry

The high dollar mark won't stop a few adventuresome folks from wanting to give it a shot and also to face the price challenge trying to equip it for flying.

I say, for the time being, firm up the fuse a little, slap a Black widow or similar on it and go flying!

Robert

Well as much of a proponent as I am for electric, to me the major issue isn't cost, but durability given our typical stunt plane designs. The electric motor is relatively fragile compared to a Cox motor. A couple of hard dings and the motor shaft will easily be bent.

So if you want a beginner electric, you need to design a pusher plane, so that the motor isn't the first thing to touch terra firma in a typical beginner "landing". Then to get balance, the battery will probably need to be located near the nose--not so great for the battery in case of a crash.

I am sure we could make a pusher design--maybe a jet-like plane with the motor mounted aft. One downside of a pusher setup is takeoff. Over grass (the nice and soft landing surface, pusher setups are a bit tricky to launch.

Finally there is the cost---but here the cost issue is the charger in my opinion. You want something that can charge the battery in ~15 min minimum, so that you don't need more than 2 or 3 packs. Also if you are a kid, how do you field charge?

So yes there are still cost questions, but it is pretty clear that RC has solved those issues.

A 1/2A is a piston engine with a swept volume of .050 cubic inches or less. 
There is no such thing as an "electric 1/2A".

There is an electric forum for electric stuff, small,or large.

I see someone stirring the pot again.  So it is electric, but it flies a 1/2A size plane.  Granted the 8 inch prop will not work on most 1/2A engines.  So how can we rate electric to IC engines?  If this had been posted on the electric forum I would not have seen it.  I want to thank them for posting this.  Also from the time I have seen electric when it started years ago in RC the prices have come down.  When the control liners start really working on keeping flying sites and getting people flying, electric may take the stage.  Those of us still with IC engines will still have to drive 50 miles round trip to put up a couple of flights.  Another thing the quiet of the electric motor may not scare the real young people so much.

I'll enter the fray here. To get an electric equivilent to gas 1/2A engines look at the power curves for Cox 1/2 A engines below.

The reed valve Black Widow produces about 60 watts max at the prop shaft. Just to keep things simple you can say that an electric with 60 watts at the prop shaft is equivalent. But the comparison has more to it. It has to do with motor/engine raction to prop loading/deloading in flight.  

The TD puts out 80 watts so the equivalent would be an electric with 80 watts at the prop shaft.

Electric motors are known to be about 75% efficient so the equivalent input electric powers would be 80 watts for the Black Widow and  107 watts for the TD.

Please note that these numbers are meant for discussion only. I AM NOT proposing any rules just how someone might put together some.

The Cox power curves are given at this link

http://www.mh-aerotools.de/airfoils/cox_frameset.htm

Allen hit it on the head when he talked about durability. I have been playing around with small electrics for a while now and there is no way they are durable enough for a beginner. Power is fine but the motor shafts are just too small to be able to take a crash or two and not get bent (especially with the added weight they carry in batteries). As a starter plane the electric is just going to be too fragile.

One other comment on power. The concept here is to fly a 1/2A airframe not set a speed or endurance record. The Stevens plane is meant to be a fun flier. That said power really isn't an issue. I agree with Jim on his power calculations and have found the numbers he uses to be about right. The problem is that the energy density vs weight of the "fuel" in electrics is much higher. There is no way to challenge the power to weight of glow fuel with a battery. The electric plane is going to be  heavier than the glow equivalent. For fun flying this may or may not be a problem. The disadvantage is that with added weight any crash tends to be more destructive and you also have the problem of somewhat sensitive battery  packs taking a hit.

My 2 cents worth is that for a beginner electrics are not really a good option based on durability and cost. For someone with some experience though they can be a lot of fun. The Stevens model looks good and probably flies nicely. Good job guys.

Bill
I am really impressed and agree with what you said. Having flown Cox Black Widows 15 years ago and electric 1/2A size now I am convinced that electric is the way to go for beginners. Espeically if they have no experienced flyers to help them.

You have done a real service by developing a plane that flies on only 50 watts or so. My 1/2A size planes use 80 watts and up.

I can attest (from experience) that its easier to change a bent prop shaft on an electric motor at a cost of $2.00 than a bent crankshaft on a Black Widow. Prop Savers also vastly reduce the bent prop shaft problem.

 

If electric is so expensive, how can they sell these complete electric RC outfits for under $100, under $50, etc.?  I still say what we need is what I have seen advertised for RC, "An excellent trainer, everything you need in one box. $79.95."  We need a RTF with modular parts. Replacement parts available at the LHS and on line.  With an available hop up kit which makes the trainer into a stunter. 

If electric is so expensive, how can they sell these complete electric RC outfits for under $100, under $50, etc.?  I still say what we need is what I have seen advertised for RC, "An excellent trainer, everything you need in one box. $79.95."  We need a RTF with modular parts. Replacement parts available at the LHS and on line.  With an available hop up kit which makes the trainer into a stunter. 

I have flown some of the $79 RC.  Most are lame. Very under powered.  Don't forget U-Control takes more power than RC because of line drag.  I have a Grand Son that has a $300 RTF RC that flies great. He bought a second battery at $80 etc etc.  His Pop has spent about $450 to $500 so far.  The days of $15 Fox 35 and a $3.50 Ringmaster kit are gone.

I am confused as to where the signal comes from to operate the speed controller.  Typically a radio does that and with a control line, there is no radio.  Also, what is governor mode.

Thanks,

John

There are low cost alternatives for 1/2A Electric.

I am currently flying a baby clown electric with the equipment shown in the Amped Up page.

Current costs on the BP hobbies web site are;
BP 2212-13 motor, $16.00
BP hobbies 20 amp speed controller, with governor mode., $19.00
APC 8x8 prop $2.50
From Bishop Power Products Hyperion 3G 3S 850 mah battery, $20.00
Typical timer, $30
Battery Charger typically $30

total is $118.

For this you get the ability to fly quietly in your backyard or any small park any time. No noise complaints.
The Hyperion batteries can be recharged in about 20 min so a set of 3 or 4 will allow almost continuous flying.
My baby clown came in at 10.5 oz just an oz or 2 more than with gas. Performance is outstanding on 40' lines and totally acceptable on 50' lines.  "Try it - you'l like it".  

I am confused as to where the signal comes from to operate the speed controller.  Typically a radio does that and with a control line, there is no radio.  Also, what is governor mode.

Thanks,

John

John,
I'd suggest asking electric questions in the electric forum---basically not because we won't answer here, but sometimes we don't see the question.

But John is right. The throttle setting comes from a tiny little chip known as a "timer/throttle", mainly because it provides both functions. It's output is the same electronic signal that a RC-receiver would give to a servo or an Electronic Speed Control (ESC). Here is a link to one I use, the JMP-2, but there are a lot of comparable versions out there that work well too.   http://www.bsdmicrorc.com/index.php?productID=642

Regarding the governor--that is built into the ESC unit. Basically a given throttle setting is mapped into a fixed rpm value. So during the flight, if you want 9000rpm, then the governor will hold 9000 rpm under all load and battery conditions. Of course the rpm setting must be compatible with the load and battery voltage over the range one will see during a flight (the battery voltage drops as the flight progresses).

If your ESC doesn't have a governor mode (most don't), then some timers have a throttle increase function. As the flight progresses, the throttle is slowly ramped up from its start value to a finish value. More or less this tries to compensate the falling battery voltage, so the cruise rpm stays about the same during a flight. Of course when the load increases (like when you pull the nose up and the plane begins to slow down), the rpm will drop a little.

Most of us use governor mode for our "big" PA stunters, but often for the 1/2a stuff just go for a non-governor ESC (they are cheaper) and use the throttle compensation in the timer.

Hope that helps.