saotome

Brushless motors on helis and planes' power consumption are calculated the same way.

Flight time is typically between 2.5 minutes to 6 minutes for EDF planes.

For example, an EDF that draws 30A in average, paired with a 40A or 50A ESC (speed controller) and a 25oomah lipo, the theoretical max flight time you can get is:

2.5A / 30A = 0.0625 hour = 5 minutes

However, you shouldn't drain lipo all the way to the bottom as it will bloat and then burn if the voltage stays below 3v per cell. Thus you should start landing at the 3 minute-ish mark.

I just fly my planes / helis at a local park in Richmond. The closing flying clubs are in North Delta and Burnaby - way too far for me.

My favorite only online stores are rctimer and hobbyking, what's yours?

saotome

如果要襟撞既話，EPP 機會係你最好既選擇，例如以下既 EPP SU-31：


不過可以既話，最好都係唔好撞啦。你有冇玩 sim 架？用邊款？
不如開過個 thread 貼下你 d 愛機，我都響度識左 d 機友，一齊搞個 LYK 機聚分享下都好喎。

ACC-HE

yo!




http://www.hobbyking.com/hobbyki ... asp?idProduct=14509

and...

$0.01 is all you pay from the US warehouse!
Any product sold from our US warehouse can now be shipped for just 1cent when you choose USPS Parcel Post (ground shipping) and spend over $100.
Planes, cars, batteries and more. On sale or not, its still just 1cent shipping when you order more than $100 from our US warehouse!

saotome

haha ya I know this package. But I am too cheap to fork out $300 ;)
And as I said before, flight time is just too short for EDFs, especially you need 4 of those in the A380

Guy

flight time is just too short for EDFs,
saotome 發表於 2011-1-19 15:17

How long to you have I have 8 min from my 30C battery

saotome

Ok here we go again with the math:

The A380 selling at HobbyKing uses 4x EDFs, with 4x 25A EDF. Let's assume that we can keep the plane up in the air at around 60%-70% throttle level which is normal for EDF planes. That makes it around 15A per EDF and thus 60A for all 4 EDFs.

The recommended battery for this plane is 3000mah 20C, that means the capacity is 3A and the battery max discharge rate is 3A x 20 = 60A, which is barely enough to keep up with the 4 EDFs usage up there.

The estimated maximum flight time would be:
3A / 60A = 0.05 hr = 3 minutes. As I said before you should never completely drain your lipo battery thus 3 minutes x 2/3 = 2 minutes.

My DIY A380 uses 2x props drawing 33A at maximum throttle, and I can cruise at 1/3 throttle which is at around 15-16A with a 2200mah 20C 3s lipo. That means I can theoretically fly for almost 15 minutes, and in reality I can still fly for 10 minutes and I still have juice left in the pack.

ACC-HE

but the EDF looks cooler.
why do they suck up so much juice?  weight?

saotome

Don't worry, props aren't visible when they spin.

EDF is very inefficient in terms of thrust by its nature. To make up for the lack of thrust (per rotation), they would use a high kv motor that spins very fast to build up speed. Thus EDF planes fly faster than proped ones. At the same time, a high kv motor would consume more current from the battery and thus the flight time reduces.

In addition, since EDFs draw much higher current than prop, you would need to put a larger battery to feed them. Keep in mind that the battery is the heaviest component in a plane and it would increase the wing loading. Then we need more thrust to move the plane...

In essence, the objective in EDF planes is to pick a battery that would provide enough "ceiling" for the current draw, yet it doesn't add too much weight to the plane. Thus they would use higher "C" rating packs and yet lower capacity to reduce weight. As a result, the only thing that needs to be scarified is flight time.

This above explains why EDF planes have shorter flight time than proped one in general.