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Old Dec 07, 2011, 06:49 AM
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Lightest / Best 3s Lipo for AEO 27mm

What is the lightest option for a 3s in my micro AEO 27mm powered project Hawk ?

My thoughts were to link three 160Mah 1s lipo's which at around 4.5grams each would come to around 15 grams with connectors and wiring .
Been advised there might be a big voltage drop linking the three but can't see why .
What is the lightest off the shelf option ? Anything under 20grams would be OK , I'm aiming for AUW of 50 grams .
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Old Dec 07, 2011, 07:50 AM
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FANtastic,

On 3S the 27 mm EDF is going to draw about 5.5a at WOT. TP has a 250mAh 25C 3S and Hyperion has a 240mAh 25C 3S bat. Either will do and weigh in at approximately 24g.

Here's a 27 mm EDF flying with a TP 250mAh 20C 3S and a TP 320mAh 30C. http://www.rcgroups.com/forums/showthread.php?t=1527311.

Ksqm
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Old Dec 11, 2011, 04:46 AM
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I really want to keep the wing loading down , at around 24g even these batteries will weigh nearly half my AUW taget !
Are these two lipos the only option in 3s ?
My Hawk project will be 1/32 scale , just under 12" span , whilst it might fly at 75 - 80g I'd really like it nearer to 50g .
I'm using injection molded foam for fuselage and wings with balsa bracing .
Hope to be around 15g - 20g for the complete airframe .
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Old Dec 11, 2011, 05:14 AM
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50 grams seems very light for an edf27 jet. With my jet I'm aiming for 80-100 grams, including a 2s lipo. Is your hawk made out of foam? what is the wingspan? I think that it will fly pretty well on 75 grams, but that is just my 2 cents.
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Old Dec 11, 2011, 06:07 AM
we can take off without that
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as Ksqm said you really have to watch the max amp draw of the battery.
For example a 160mah 25c battery has max amp draw of 0.16 x 25 = 4A
Even then, dont go up to the full quoted draw of 4A because the voltage will drop so much it will trigger LVC cut off possibly for both the ESC and the Rx. I have had this happen to me on another project with a 350mah 18c battery (6A max) to such an extent I couldnt even go to full throttle during bench testing without hitting LVC and that was with a freshly charged battery.
After reading posts by more experienced people I learned the max current you should draw is 80% of the stated capability. So for a 160mah 25c that would be 4A x 0.8 = 3.2A
If you are pulling 5.5A at full throttle, The minimum capacity battery you should use at 25c is 275mah. If you can find higher discharge rating batteries, 45c for example, then you could go down to 150mah.
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Old Dec 12, 2011, 04:00 PM
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Trying to find some 160 MAh 1s lipos with 50c and above or a light 3s pack with similar numbers , any ideas ?

It seems the battery is still the one component that needs development . We have come a very long way since NiCads but hope we don't stop where we are now ! Only a matter of time before technolgy catches up again !
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Old Dec 12, 2011, 04:15 PM
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None, as you said about battery technology, you are asking too much from such a small size. The smallest 35C+ battery is the TP 325mah 65C.
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Old Dec 15, 2011, 06:48 AM
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Think my best option to keep weight down is to go 2s and use two 300Mah
1s Nano Tech in series . Rated at 35c they should deliver the amps but best of all only weigh 7 grams each .
If I can reach my target weight of 50 grams RTF then I should still have enough thrust from the 27mm unit. Anything above 40grams thrust should be enough .
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Old Dec 15, 2011, 08:04 AM
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Nano techs are crap. Or at least 4/5 of my 25c 160s were. My hyperion 25c 100s outperform them.
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Old Dec 15, 2011, 09:56 AM
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FANtastic,

Let's take a different approach. You're building a plane with a 12" WS. You plan on AUW of 50g. What kind of thrust are you shooting for at WOT and or say 3/4 throttle? Have you considered a 1220/30 or 1015 motor. Using a 22mm or 25mm shroud will put you in the 3a - 4a range. Depending on 2S or 3s used. Thrust can get upwards to 60g, again depending on configuration.

Now, what's the important points for this build? You want a light wing loading right. Well, what do you consider light? I built a 10" WS plane, that was 58g AUW. I was running a B.I.M 22mm shroud, Turnigy 1015 motor, and Hyperion 180mAh 3S 25C bat. To launch was a LIGHT toss at 3/4 throttle. Now, up 'til I did my build, a plane with it's specs was considered a porker weight wise. So, if you're doing a build that's been done, check out the build thread.

You're running an AEO 27mm EDF in a 12" WS plane. If you go 2S, you'll get approx 60g thrust, but you need to power it with a decent 25C bat at the least. If you go 3S, you'll be pushing 85g+. Again, you will need a decent 25C bat. At 12" WS, your wing loading will be just fine. Check the forum for my builds, the proof is in the flying. For the Hawk, you have to check out NitroCharged's build. Just go for it!!!

Ksqm
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Old Dec 18, 2011, 10:35 AM
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I want to use stock parts hence the choice of an AEO 27mm edf .

I want a model that will fly well at lower speeds rather than just flat out !

If I can get 50g thrust on 2s and stay at 50g RFT then that would be ideal , no need to go 3s .
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Old Dec 18, 2011, 12:23 PM
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Well, hobbyking claims that their edf27 can produce 75 grams of thrust on a 2 cells lipo. I'm not sure if that is true, but I think it will produce plenty of thrust for my jet (should stay below 100 grams).
Adding a good exhaust tube also helps improving the thrust.

Lets say that 75 grams is realistic, then it isn't that hard to build plane with a 1:1 thrust to weight ratio. Especially when made out of foam and with light equipment...

In my jet, a big part of the weight is caused by the battery, I'm aiming for ''long'' flight times, so I use a 2 cells 370 mAh lipo.
Hanzie.
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Old Dec 18, 2011, 12:59 PM
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Never follow the specs posted by HK.
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Old Dec 18, 2011, 02:28 PM
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Yep, that's why I try to keep the weight down as much as possible. It's, as always, a good example of the good old Chinese accuracy...
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Old Dec 18, 2011, 02:41 PM
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Quote:
Originally Posted by boredom.is.me View Post
Never follow the specs posted by HK.
I have seen the AEO 27mm EDF listed by some ebay sellers at over 100g thrust !
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