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New electric tug added to Tug models (Read 1342 times)
james_h
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Re: New electric tug added to Tug models
Reply #15 - 03/11/10 at 10:44:45
 
I've plumbed the numbers for the e-flite 160 in my spreadsheet and you should get 4 minutes of full power out (60A) of the Lipos so as I'm reminded to control throttle for a more scale tow I should get 8-10 tows out of my lipos ?

I guess I'm always conservative as to taking too much out of the batteries especially as the price of replacements is 3 times what I originally paid for them !

I'd be interested for you to take a look at my spreadsheet to see if it accords with your testing data
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flyingseale
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Re: New electric tug added to Tug models
Reply #16 - 03/11/10 at 11:43:34
 
james_h wrote on 03/11/10 at 10:44:45:
I should get 8-10 tows out of my lipos ?

I guess I'm always conservative as to taking too much out of the batteries


Your conservative approach is probably a good one because most of the 'damage' suffered by lipos occurs as you discharge the last 30% of available energy.  Another way of looking at it is that five tows followed by a charge of, say, 30 minutes and then another 5 tows is just as good as ten tows followed by a charge of one hour but with the advantage that you're not stressing your cells as much.

Mike
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james_h
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Re: New electric tug added to Tug models
Reply #17 - 03/11/10 at 17:24:51
 
I'm afriad that glider pilots don't see it that way, expecially when the thermal actiivity is good !!!!!

A friend over in China has got a lipo manufacturer making me up some large packs to test so should be good for two sets this summer, I must get out to some of the organised aero-tows to get some tips for the pro's Smiley
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John Greenfield
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Re: New electric tug added to Tug models
Reply #18 - 03/12/10 at 08:11:57
 
James

I am not a great fan of calc spreadsheets once past the "general pointer" stage. I prefer to get out and do some real testing. With the help of Ivan Goodchild we optimised our set up by fine tuning on the flying field. I have lost count of the number of different props we tried but you will be amazed at the difference just changing the make of prop makes. (A big thank you to Dave Wilshire at Motors and Rotors for lending us a box of props). Both the Ampley and the 1/4 scale Cub that we have  now run a similar set up drawing 60 amps at takeoff but as soon as the combination is off the ground we have found we can "throttle back" to 55 amps on the tow up without any loss of performance. With this set up we get the 5 tows to 1000 ft at a climb rate of 1000ft per min towing a glider not exceeding 12 kg. The Cub does not quite match the Ampley climb rate due to its inbuilt drag and the fact that it is a little bigger so we tend to use it more for scale towing and towing low and slow in circuits and figure eights. Great practice for both the tug and glider pilot when there are no thermals.

John
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flyingseale
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Re: New electric tug added to Tug models
Reply #19 - 03/12/10 at 09:31:11
 
John Greenfield wrote on 03/12/10 at 08:11:57:
I have lost count of the number of different props we tried but you will be amazed at the difference just changing the make of prop makes. (A big thank you to Dave Wilshire at Motors and Rotors for lending us a box of props).


And did you find that the same brand/size prop worked best on both planes?  In theory they would need different props according to their weight and drag, but in reality you only have a small number of manufacturers and sizes to play with and I'd imagine that what works well for towing on the E-Flite 160 will work no matter what model it's in.  If that's the case then knowing that the Graupner G-Sonic 20x10 is well suited to the E-Flite 160 could save a lot of time and money experimenting.

Mike
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John Greenfield
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Re: New electric tug added to Tug models
Reply #20 - 03/15/10 at 08:00:11
 
Mike

you are right re the props hgaving to be optomised for eachmodel but after all the testing we have ended up with the G sonic 20 x 10 on both the Cub and Ampley. This may be more due to the wide paddle type blade on the prop working well whilst towing. A lot of the other props we tried were APC types which have a thin blade which "may" not move the air so well with the weight and drag of the glider on the back.

John
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flyingseale
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Re: New electric tug added to Tug models
Reply #21 - 03/15/10 at 09:13:04
 
Thanks, John.  Very useful info.

Mike
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