Difference between similar sized electric and glow models - RC Groups
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Dec 05, 2006, 05:09 AM
super_nova's Avatar

Difference between similar sized electric and glow models

I've been flying parkflyer sized and smaller electrics for awhile now and I've really gotten the electric bug. But I've always wanted to get back to flying some larger sized glow models (.40 +) like what I originally started out on. I'm at university and keeping a large glow plane with me is not feasible, which is why I've been flying the electrics and putting off getting anything bigger. However, now I'm getting close to finishing and looking to move up.

I'd love to get into some larger electrics but the cost of large lipols is something I don't want to deal with since in order to be able to fly for any decent length of time you need at least a couple packs. I'd rather put the money into a good glow setup, so I haven't payed much attention to models above 20oz in size. Recently though I've been reading up on the new A123 cells and they have really sparked my interest because of their low cost and fast charge times. With some of the other low cost alternatives to the big name brand electric motors and speed controls, its now possible to actually set up a low cost electric conversion. One of the planes I have had my eye on is the Funtana .40. I really like the design of the plane and I've heard alot of good things about it and I was considering eventually putting the money into a good 4 stroke setup on it. But now I've been thinking along the lines of a cheaper electric conversion. Then I stumbled on this : https://www.rcgroups.com/forums/showthread.php?t=605510, the new KatanaS 30E. Its the same basic design as the funtana (both designed by the same guy) but designed specifically for electrics. Its a similar size to the Funtana .40, roughly 5 inch shorter wingspan and length. However it wieghs less than half the wieght of the Funtana .40(~2.2lbs as opposed to ~5)!

So now after that short background I finally get to the topic of this thread . What is the fundamental difference between these two planes that accounts for the huge weight difference. Obviously the smaller size of the KatanaS is a factor, but still there is a 3lb weight difference between the listed weights of the model. I am ofcourse assuming the weight listed for the Katana is the ready to fly weight, but I am pretty sure I read that elsewhere.

I actually like the look of the KatanaS more than the Funtana so now I'm considering it. With its lighter weight it could be setup with a smaller motor and thus less in terms of battery power. But then, seeing as these planes are so close in size, how does the much lighter weight affect the plane in terms of handling and flight performance? Would you be able to double your batteries, running them in parallel for even more flight time and not suffer as much from the weight gain? I'm assuming these planes must have pretty different flight characteristics due to the weight difference even tho they are so similiar.

I know in indoor flying the planes just fly so much better the lighter they are, but from what I have gathered the funtana .40 is already a light and good flying plane, so I would assume the KatanaS would just be that much better...however, I also know the lighter the plane gets the more the wind affects it and I'm looking forward to flying some planes again that can actually handle a bit of wind.

Anyways I have dumped out a bunch of thoughts here and probably rambled on a bit, but my main question is just what is the fundamental difference between 2 models like the Funtana .40 and KatanaS 30E which are similar in size and design but have such differences in flying weights.
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Dec 05, 2006, 09:23 AM
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Ryguy's Avatar
Electric power setups are generally lighter in this size. The glow engine weighs about 10-16oz more than an electric, and the fuel tank and servo for the engine also adds nearly the weight of the lipo. So just in the power setup you're saving about a pound or so. In addition, electric planes can be built lighter. No vibration from the motor, so less need for reinforcement, and the lighter weight of the power system adds to the weight reduction in the construction of the airframe.
Dec 05, 2006, 02:40 PM
I Wish I Was Flying...
sdueck's Avatar
What he said^^^

Also, something to think about is that if you double the size of a plane, you don't double the weight. Take into account Bill Hempel's 52% Edge 540. I believe it weighs like 75 pounds. The full size Edge weighs 1527 pounds. Definitely not twice the weight, just twice the size. In the same way, when you stop in a car from 60 to zero, say you can do it in 100 feet (pretty darn fast). Well if you cut your speed down to half, then you will be going 30 mph and will not stop in 50 feet. Everyone knows it is less, and according to physics, ceterus paribus (all things equal), you will stop in 10 feet. Exactly the suare root of the first distance. I'm not sure it is exact as far asa weight, but I could imagine that as you double the size of a plane, you would add closer to the square of the weight than twice the weight. Just my $0.02, but the engine setup really does have the most to do with it IMO.
Dec 05, 2006, 03:29 PM
Deletedfor proving Nauga wrong
You won't necessarilly up lighter with e-power at .40 size.... we tend to put on a bit more power for the weight though.

You can end up lighter using marginal LiPos trying to save weight, but overall you are better off carrying the added battery capacity to match the glow power version weight. The added capacity will give longer flight times and improve average battery life (number of cycles)

The electric motor will be turning a larger diameter prop at a bit slower rpm, which is more efficient at low airspeeds, and you'll match or exceed the glow power version's 3D performance.

E-power setups for .40 size are getting to be very competitive in cost compared to glow. Just a couple of "gallons worth" (at $15 to $25 per gallon) of flying and the electric starts being cheaper than the glow power. Careful selection of your power system components and taking care of the batteries correctly... the electric version will save you a lot of money vs glow powered flight in the long run. (as long as you don't crash and destroy the LiPos...)

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