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Old Nov 02, 2006, 06:01 PM
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FlightAddict's Avatar
Raleigh, NC
Joined Feb 2005
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Question
Maximizing speed - lipo weight, mah, or C rating?

I'm currently flying my second pylon racer - a Sokol with a Mega 16/15/3 and a TP2100 3S1P. First was a Sunracer with the same setup, which lasted for about 15 flights. The Sokol is very new, with 5 flights so far. Both are amazing planes.

I don't fly full throttle very much, but when I do, I'm a bit dissapointed in the speed of my Sokol. It may be that my motor and lipo are not in top shape, from a performance standpoint. Or, it may be that I'm getting used to the speed. But, I would like to experiment with a new lipo pack, and maybe a motor down the road.

There are so many amazing choices in lipo's now, I'm a bit confused which way to go. Of course, it's got to fit in the fuse.

Question to those who have experience with lipos of different weight, mah, and C rating in the same pylon plane ...

Does mah, say 1800 versus 2100 versus 2150 versus 2200 or whatever, if they would fit, impact speed in the first 3 minutes of flight?

Does C rating, say 12C versus 15C versus 20C versus ??C, impact speed during the first 3 minutes of flight?

How about weight? Seems like it can go from 145g to 190g for 3S1P packs that might fit. Is extra mah or C rating negated by extra weight?

Thanks, Scott
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Old Nov 02, 2006, 11:49 PM
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United States, CA, Los Angeles
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Hi,

Some very general lipo experience of mine may assist you. Hopefully by "connecting the dots" you can make something of this to translate into a better purchase descision.

For the same given manufacturer and cell chemistry, more mah will translate into more initial power due to less strain on the batt and higher voltage available under load. Say you have a NeuEnergy 3s 2500 mah, and compare the same plane using a NeuEnergy 3s 4900 mah pack, the 4900 pack will make more power.

As for the 12C, 15C, 20C ratings, generally, the higher the rating, the more voltage available in the same given setup.

Are all 20C packs created equal? No.

I have a 20C Kokam 3200 and a 20C Hyperion 2500 and guess what? The 2500 Hyperion is "faster". I assume its just better chemistry.

In your position and looking to buy some new packs, I would no doubt go for the NeuEnergy, Hyperion or PolyQuest 20C packs.

As for the weight. that's a tuffy. My inclination to to just get the biggest and highest C rated pack in there and haul as*. Plan a little extra speed for the approach and langing, and consider the plane's wing strength. My guess is that the Sokol can take, may even beg for, the "abuse".

Hope this helps.

Eric
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Old Nov 03, 2006, 12:21 AM
Deletedfor proving Nauga wrong
Joined Mar 2005
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Generally:

If all else is equal, lighter is faster.

With LiPos, higher C rating means it will hold voltage better at the terminals when loaded at the same current as the lower C rated pack. That means higher motor RPM which means higher speed. (but less durration if the same capacity)

Extra capacity will gove some better voltage holding (at the same C rating and current demand) thus improving power... but almost always adding weight... so its dependant on the model if that will help speed, break even or slow it down.

Its all trade-offs... and the only way to get a DEFINITIVE answer is to experiment. I have a little foamie "Superflea" which is more sensitive to weiight than the difference in power by use of different batteries. Best performance is with a 800 mah 2 cell. 850 mah and 900 add weight and a bit more rpm... but the performance drops. Smaller than the 800 mah also reduces performance. (all 15 C rated cells... getting 12 to 15 min per charge from the 800 mah, so higher C rating shouldn't help much if at all)
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Old Nov 03, 2006, 12:36 AM
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Vancouver WA
Joined Jul 2006
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Quote:
Originally Posted by epwierman
Hi,

As for the 12C, 15C, 20C ratings, generally, the higher the rating, the more voltage available in the same given setup.


Eric
It's actually more amperage isn't it?

Good luck
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Old Nov 03, 2006, 01:32 AM
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Quote:
Originally Posted by radralph
It's actually more amperage isn't it?

Good luck
A higher C rated cell will hold higher voltage at the terminals for any given current. the result is more voltage AND more current supplied to the motor. But the voltage is what gives the RPM (motor kv * terminal voltage )
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Old Nov 03, 2006, 02:13 AM
dessertracer's Avatar
Joined May 2006
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Quote:
Originally Posted by FlightAddict
I'm currently flying my second pylon racer - a Sokol with a Mega 16/15/3 and a TP2100 3S1P. First was a Sunracer with the same setup, which lasted for about 15 flights. The Sokol is very new, with 5 flights so far. Both are amazing planes.
Thanks, Scott
Out of curiosity, what happened to the Sunracer? Hope itís not in multiple pieces.

Also, this is an interesting thread to read that makes an attempt to explain the differences in the pack brands:

http://www.rcgroups.com/forums/showthread.php?t=482413

I'm not an inside person in the lipo business (just a regular consumer), but it seems like a good number of these are coming straight from overseas. If that's really the case, might as well go with these guys!

unitedhobbies.com

Buy the way--has anyone tried or even heard of that lipo product line? Hope this is somewhat helpful.
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Old Nov 03, 2006, 04:18 AM
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treehog's Avatar
Euroland
Joined Jan 2004
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Banging against the ragged edge

The equipment life and performace will be affected for each flight when you are pushing things to the limit
\
The best thread for most every combo out there is the threads for voodoo as lots of combo especiall mega 3 with lipos were done there


I still stick to nimh for this type of planes as the cycle lifes of lipos at the ragged edge of 20c with 20c type cells can sometimes dictate a low cycle life some makes can sometimes go as low in the thirty cycle regions and this can slow the plane down a lot as the packs start to develop higher resistance

Nimh packs might aso have lowwer cycle fifes at the high amps sometimes low like we thirty cycles but at half the price and able to higher c rates like 30c plus

Also I noticed after some few hundred high speed dives (balliistic dive cycle ratio)most all the fast planes I had seemed to go slowwer and this I attibute to the fact that when I checked wing ridgidy the wings seemed a tad more wobbly or less ridgid which would be consistant with the glass fibre epoxy fatigue from multi flexxing enviorment and more wing wobble will tranlate into slowwer speeds or time to sell of the plane and make it SEP somebody elses problem

Ralf
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Old Nov 03, 2006, 08:57 AM
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Springfield, Missouri, United States
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What size prop are you using?

That will much more of an effect then your lipo C rating which would be about none.

Go here and test out different prop combonation till you get the fastest prop speed at the highest amp your batteries cab take. Smaller prop big pitch

http://www.brantuas.com/ezcalc/dma1.asp

If you really want to have some fun, trim down a 5x5 prop to a 4.75 -4.5 x 5 prop.


Larry
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Old Nov 03, 2006, 09:08 AM
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Raleigh, NC
Joined Feb 2005
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Thanks for some good feedback.

Sounds like fhhuber506771 put it well - it's all trade-offs, and holding higher voltage is the key.

Dessertracer - very interesting thread on who's making the cells and what brand name ends up on them. Thanks.

The Sunracer survived several crashes that would have demolished a lesser plane - from what looked like radio interference, but I think it was due to a certain receiver that reportedly doesn't do well in a hot, tight fuse. It finally bit the dust due to a half-mast antenna (got distracted, hopefully the first and last time I do that).

I've got a very nice grass runway at our club field (Raleigh-Durham R/C), and the Sokol has behaved well landing on it, so the issue about weight and retaining speed while landing isn't a big concern for me (famous last words). So, I think I'll try to determine the max size pack I can fit, and go for max mah and C.

Treehog - I'll check out the voodoo threads as well. Thanks.

Funny how, no matter how good things get, we still want more.
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Old Nov 03, 2006, 09:18 AM
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Larry, I'm using a 4.75 x 4.75 prop, and drawing 24 amps at max throttle. Also didn't mention I'm using a CC35 ESC. I don't recall hearing about anyone using a bigger prop on the small pylon planes, so I assumed I'm pretty much maxed out there.

The TP2100 is the 10C-12C version, and only has fewer than 10 flights on it. A move from southern California to Raleigh grounded me for several months, but I'm back at it now.
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Old Nov 03, 2006, 09:38 AM
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That's a good prop.

Larry
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Old Nov 03, 2006, 12:12 PM
Deletedfor proving Nauga wrong
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What has been found with the larger packs used in E-Powered RC Pattern competition planes is, the LiPos hold voltage under load better if warmed up.

The local "Pattern Guru" makes sure his packs are 110F to 120F when putting them in the plane, and his cooling airflow for the batteries has been limited to allow the packs to stay near 130F through the flight.

I haven't heard of anyone trying the pre-warmed batteries for smaller planes...

I'm not seeking maximum performance from my power systems... I'm usually seeking best longevity for the batteries and motor. Practices that give maximum performance in a sigle flight may be detrimental to overall life of the batteries.

*********

RE the max speed comming out of a dive:

Since drag is a funtion of the aircraft's shape and finish, and "terminal velocity" is a function of drag and weight... all else being equal, heavier models will have higher terminal velocity. The plane can get to where the prop is acting as a brake in a dive, even at full throttle, at which point the plane will go faster if you stop the prop.

If you just want a short, impressive, high speed fly by... heavier batteries will win every time.

If you want to win a pylon race... you won't be too interrested in terminal velocity, and weight becomes your enemy instead of your friend. For level powered flight, the induced drag from producing lift can be reduced simply by making the plane lighter. Keeping the modle's weight under control is very important.

For "ridge racers" (slope gliders) each design will have an ideal weight (with slight variance due to differences in each model), heavier or lighter resulting in a slower plane. But they are trading off lift for airspeed. If you compared the angle of flight to the relative wind, the ridge racers are always in a shallow dive.
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