Electric help

Hi,
Where I will be living from July I could have the space to fly a classic size plane. The neighbors may object to the noise, even a 4 stroke. I will try a Saito 30.

Can any one advise on an electric motor that would run at full power for 3 minutes. Land after 3 minutes change batteries and fly the second half of the pattern.

It would need to swing an 11X5, 10X6 kind of prop. Fly 60 feet lines, pull a plane that (with an OS 40 and tank) would be around 45 ounces.

Be up at about 6,000 feet.

Thank you
Percy Attfield

Percy - I'm not too sure where you are but a few people come to mind: Paul Van Dort from Belgium and Mike Palko in the USA. Both have worked with electric C/L and should offer good advice. Also, Bob Hunt (USA) had fitted electric power to a C/L plane.
Hope this helps,
Bob

My own take on this is that it doesn't exist. You are talking a motor that would spin that size prop at 10,000 rpm consistently for 3 minutes and then quit. Electric motors slow down towards the end. They don't just quit. So you would need an even bigger battery and a timed shut off before it started running down. I don't know of a motor that would spin it that fast. I don't know of a battery that would spin it that long (car battery?) and you certainly aren't going to get one in that weight.

Electrics, at this point, are still very much experimental and very much low power.

However, we used to fly in the cul-de-sac of a housing development with a 35 powered plane and no complaints from the neighbors. Have you checked to see how much noise riding lawn mowers make these days? Asice from the fact that the airplane takes the noise above roof-top level, its noise with a good muffler really isn't all that objectionable.

I ve seen a 3D Rc plane fly for 17 min with vertical power for the whole time. It can be done . MM Big dollar brushless and the latest bats.

I agree. If you use the latest high discharge lithium polymer batteries and a brushless motor, it can be done. But it will not be cheap. The batteries will cost probably $150+ per set and the motor about the same or a little more. Then the speed control wil be close to $100. FMA Direct has the batteries. Motors are available from a number of companies like Hacker, Jeti, Mega, and others. Check out www.nesail.com for a quick look at motors and speed controls. The quick and dirty way to control the motor would be with a 1/2 oz. $28 Parkflyer R/C receiver and the cheapest FM transmitter you could find.

Remember, he wants to turn an 11 x 5 prop on 60 foot lines with what will require about 4.7 second lap times (maybe faster if it gets heavier) in a 45 ounce airplane. If there is something that will turn his requested prop at these rpm's, what will the weight penalty be, and will he be able to put it in his 45 ounce airplane?

>Electrics, at this point, are still very much experimental
>and very much low power.

I might disagree with this. Power in and of itself is no issue at all - the FAI R/C electric motor systems will blow any stunt engine right out of the water when it comes to power.

The FAI electric models run at remarkably high power levels, but only in bursts.

The problem is sufficient power for 6+ minutes. This requires an energy density in the battery that can't be acheived with batteries you and I can get on the open market for a reasonable price. Additionally, there's a problem with cooling. If it puts out .4 hp, like stunt motors, but there's no fuel running through it, there's a heat issue. And of course, depending on the energy density of the batteries, there's a weight issue.

All this having been said, I seem to recall that Hunt's eletric experiment (using the original RD-1) use pretty low-tech motors and low-tech nicad batteries - maybe even a standard 6-cell car pack with "400" can motor. The flight profile was similar to the one described - stop at about halfway, with marginal but sufficient performance. A higher-tech system would provide more margin, but even this was sufficient to play with.

Forget powering it through the lines in any but the most minimal conditions. Either you run low voltage for safety and the current drives you to huge lines to carry it, or you run high voltage at low current but take a chanve on electrocuting yourself or others. There's too much power required to make either viable for stunt levels of power with full-size airplanes.

40V - 7.5 amps for stunt power (.4 HP), 33x750 mAH cells for 6 minutes
7.2 v - 41 amps, 6x 4100 mAH cells

7.2V pack, 6x1200 mAH cells for 3 minutes = 24 amps, .23 hp (marginal but OK for "35-sized model")

>

.23 hp (marginal but OK for "35-sized model")
>
> Brett

Terrific, if unconscious pun...

Because that is about the HP of an OK Cub .35. Sad as it was...

Expecting more of the same...

Hi Guys,
Thank you all for all the information, this is what I needed.

Thanks for the names Bob Z, I will contact them.

Leonard you are right the battery runs down over a period of time. Provided I have full power for 3 minutes it can then take another few minutes before I land for the battery replacement. Since it is not a contest there is no time limit in which the flight must be done.

Thanks to all.

Percy Attfield

Mike Palko has occasionally been seen on the "Electric Control Line" forum which I moderate over on www.rcgroups.com I believe he's currently having some success with brushless motors and a Z-Tron infra red system to control the throttle.

One simpler approach which I'm playing with is an infra-red switch so you can just switch off and land when the power drop as the batteries run down becomes noticeable. It also allows you to fly alone without messing with a stooge, if you're trusting enough. Walk out to the handle, switch the motor on and you're away.

Steve

LAST EDITED ON Apr-24-03 AT 06:04 AM (CDT)
 
I wonder if one might not take an "ultra-lightweight" approach to this. Build something like a RC Unlimited Fun Fly plane rather than a CL Stunt plane. Skeletal frame, clear mylar covering, carbon fiber boom. You won't get precision CLPA flight, and it sure won't get any appearance points, but it'd do all the stunts recognizably.

Maybe this might change the outlook somewhat in terms of achievable weights.

The power and the duration to fly a C/L PA model through an entire stunt pattern is out there right now - for a price! Dig out your January 2003 issue of Flying Models and check out page 64. You'll see .46-size, 6 lb. models taking off vertically.

This is the current leading edge of electric power for models. The bad news is the price. For instance, a Hacker Brushless B50-S series motor goes for $250.00 to $300.00!

No doubt the price will come down in the next few years, once this type of power is "old technology".

Other issues, like shutting the motor off as the batteries run down can be worked out (a low voltage cutoff, or a Z-tron throttle control as suggested by Steve Lewin, are good options).

I've seen RC planes that had home made can mufflers in addition to the torpedo muffler on the engine. They were made from small aluminum muse cans and connected with silicon tubing. Quieter than any lawn mower.

The technology to do what you want exists right now, without exotic, or expensive, motors and batteries. I have a 42 ounce electric helicopter that flies for 7 - 8 minutes on a 540 ferrite motor and 8 sub-C cells. However, I agree with Iskander. Why not take an R/C aerobatic park flyer and convert it to C/L? All easily available technology and fairly cheap. My problem relates to that 6000 feet. I don't think it's possible at any price.
One other point. Are you trying to tell me that 4-strokes are QUIET?

>Hi,
>Where I will be living from July I could have the space to
>fly a classic size plane. The neighbors may object to the
>noise, even a 4 stroke. I will try a Saito 30.
>
>Can any one advise on an electric motor that would run at
>full power for 3 minutes. Land after 3 minutes change
>batteries and fly the second half of the pattern.
>
>It would need to swing an 11X5, 10X6 kind of prop. Fly 60
>feet lines, pull a plane that (with an OS 40 and tank) would
>be around 45 ounces.
>
>Be up at about 6,000 feet.
>
>Thank you
>Percy Attfield

I'd like to put in my $.02 also since I've been sttruggling with the noise issue here too... You have two sources of noise to address: the engine exhaust and the prop. To keep the prop noise down you need to keep the RPM down and to keep the exhaust noise down you need a good muffler. Both of which seem to be more easily within reach than the battery issues. I've been playing with a diesel and a second muffler. I suspect that the second expansion muffler would work on a glow engine as well as it does on the diesel. Diesels (I think) have a lower exhaust temperature and so have a lower exhaust note that is less irritating. Diesels also seem to be less affected by mufflers than the glow engines. Our models may not make any more noise than a Weed Eater but people are a lot less tolerant of models.

One thought that I haven't tried yet is putting an expansion muffler on after a tuned pipe. It might not upset the tunning too much??? Carbon fiber pipes would help keep the weight down... You'd get the benefits of the pipe and lower noise, too.

Electric motors draw more current as they slow down and less current as they speed up (right?). If you had essentially (theoretically)unlimited current potential and regulated the voltage to be constant, would the RPM be constant? i.e. current and power (constant voltage) increasing as the engine is loaded and power decreasing with increasing RPM? and, wouldn't this be a good thing for a c/l stunter?