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Thrust-weight ratios - 9/21/2003 8:32 AM   
toy264



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Status: offline 		Has anyone studied the thrust to weight ratio curves of various e power systems compared to glow? There are a lot of reasons to convert to electric, and I'm wondering if there is some point at which a lighter equivilent power is one of them.
Thanks,
John

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RE: Thrust-weight ratios - 9/22/2003 4:44 PM   
Matt Kirsch



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Status: offline 		I think that traditionally, electric has always been heavier based on sheer power to weight, but it makes up for it somewhat in efficiency. Bigger prop spinning slower in cleaner, less turbulent air allows you to get away with about half as much sheer horsepower in an electric system. Comparitively speaking, glow is like driving a tuner Honda Civic down the road with the emergency brake set. Lotsa wheel spinning, lotsa noise, lotsa smoke, lotsa wasted energy.

LiPolys have screwed it all up Now you have a battery that can produce the horsepower, but doesn't weigh much. With a lightened airplane, a super-efficient geared brushless motor, and lightweight lipolys, you can have power-to-weight ratios that glow can only dream of...

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RE: Thrust-weight ratios - 9/25/2003 9:58 AM   
toy264



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Status: offline 		So assuming equal weight airframes, a Li powered electric system could be put together that would afford the same performance (say 5 min. of scale manuvers for a 15 lb, 71" P-51) as a typical .91 with 16 oz of fuel, at a lower all-up weight?

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RE: Thrust-weight ratios - 9/25/2003 11:38 AM   
gwright


 

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Status: offline 		not exactly, but you could get the same or better performance for 15 to 20 minute flight times
For a "warbird" example, Kyle Mashima is flying an 80" span world models ARF Zero. He's using a 10S4P thunder power lithium setup. It's 17.5 lbs, and has superior performance to glow. Flights can go well over 20 minutes with proper throttle usage.
Another example is my 2 meter funtana, which, with lithium polymers is now under 10 lbs, can fly for 15+ minutes of full 3D, and is spinning a 22X12 at just under 6000 revs (not quite the power of a G62 zenoah, but more than a G45, and on a less than 10 lb plane ). thrust to weight is over 2 to 1

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RE: Thrust-weight ratios - 9/25/2003 5:34 PM   
Sprink



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Status: offline 		I'm surprised that the top scale flyers haven't yet leapt on to the electrics yet as it can mean running scale props.

I once worked out that the scale prop for the Top Flight Spitfire (a 60 size plane) is a whopping 18" diameter 4 blade prop! Not possible with glow without destroying the plane (nearest you can get is an RCV 120, which can give you an 18" 2 blade or 15" 4 blade). With electrics it is not a problem.

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RE: Thrust-weight ratios - 9/25/2003 7:35 PM   
toy264



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Status: offline 		Could one of the problems be that without the weight of a G45 and fuel up front, you end up with a tail-heavy model? Having to add lead defeats the idea of gaining an improved wing loading. Nevertheless, not having the hassles of endless mixture tweaking, and the concerns over big engine starting safety issues (search the site on "stitches"), and even a break-even scenario on weight has an e-system looking attractive!

My only electric experience is with a little GWS Moth, but it sure is easy to grab and fly without a 5 lb box of fuel, battery, and starting paraphernalia! Humm, looks like I'd better start getting cozy with ElectriCalc...

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RE: Thrust-weight ratios - 9/27/2003 10:36 PM   
Henke Torphammar



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Status: offline 		toy264,

you can adjust the CG very easy by moveing the battery pack. makes it possible to ballance the plane diffrent depending on if you want to fly perfect pattern or wild 3D.

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RE: Thrust-weight ratios - 9/28/2003 3:07 AM   
toy264



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Status: offline 		Your point is well taken; however, if I have to add heavy batteries to make up for the substitution of, say, a B50 for a OS 91, I haven't gained anything as far as reducing the weight of the powerplant and fuel. Do you suppose mounting the batteries directly under the motor is an option (I've got a huge cowl)? I am really liking the idea of swinging a big prop (21" is the scale size for my project), and not spending as much time tuning as flying!

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RE: Thrust-weight ratios - 9/28/2003 3:13 AM   
Henke Torphammar



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yeah, I put them up under the cowl. as the motor is much lighter then a simmular performing engine you need the battery pack pretty far forward.

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RE: Thrust-weight ratios - 10/2/2003 3:02 AM   
Shawn-Palmer


 

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Status: offline 		Many years ago, I built a CG Superchipmunk for a club friend w/a .60 in it. I flew the holy crap out of that plane before giving it to him ("testing"), and it remained my favorite flying model until I completed my own CG Superchipmunk a while back. Mine is 80oz RTF, and 2:1 thrust to weight, and of course - electric. Ten times the model I built back then, and It's everything I've ever wanted in an R/C plane and more.

Aveox 27/39/2 4.4:1
6S5P LiPo's
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Shawn Palmer
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shawnp@castlecreations.com

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RE: Thrust-weight ratios - 10/2/2003 6:05 PM   
Greg Covey



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Status: offline 		Sprink,

Some of them have discovered electric power and won!

Electrics Win Team Scale at 2003 Masters Competition

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RE: Thrust-weight ratios - 10/3/2003 2:27 AM   
Hannu Vuorinen


 

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Status: offline 		Yeap, Greg,


Took 1st place in Stand of scale cup in Finland, 3rd in F4C, 4th in Scandinavian
Opens at Stockholm. My fleet was Piper J3 ant FW44 Stieglitz bipe, both outrunner and lipo powered. So, competing in same class with glow/gasoline pilots, they are not unbeatable..

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