saotome

Thanks guys. It was a great relief to have it finally in the air.
Does any of you know where to get cheap and good spray gun?

saotome

星期日 flight gathering 既相，有個有靚相機既朋友真係冇得頂！

saotome

Ducted Fan would definitely make it more scale, but it has the following shortcomings:

1. I would need to install 4x Ducts in order to have enough thrust to fly
2. 4x ducts, assuming each duct takes 25A, that's 100A of current and it would require a much bigger battery
3. The extra weight of speed controllers (4x), ducts (4x) and heavy battery would make the load per wing area (sq inch) a lot higher. That means the plane will need to fly a lot faster to maintain level flight
4. The extra speed in flight and landing makes it a lot riskier to fly in park and windy situations

EDF (Electric Ducted Fan) works best in light models; or in very large scale models where modelers can use the extra wing area and large ducts (90mm+) to compensate. Alway remember EDFs' efficiency is a lot worst than props; where EDFs excel in nothing but pure speed and scale look. Props has been serving me well for my uses (so far). I may consider EDFs in the future but not in this plane.

saotome

Sounds like you've never dealt with modern brushless motors that drive EDFs nowadays

A typical 64mm EDF can max out at 45A easily if you go full throttle, which is often required during launches and bad situations. 25A is pretty conservative even for the smaller 55mm EDF units.

As a responsible modeler I must track all the numbers to ensure smooth and safe operation of my equipment. I use a watt meter to measure the amp drawn on all my gears and I use a thrust stand to make sure my motors are adequate for the sizes of the planes I fly.

Many EDF planes fly at 2/3 or even at full throttle most of the time and yes it is normal because of the nature of EDFs - they are inefficient at lower RPM. Motors should perform well with carefully selected duct sizes, ESC and batteries regardless of the throttle level. Of course flight time will suffer if full throttle is needed all the time.

FYI my current proped A380 uses two 30A ESCs and the static amp drawn of the two motors at full throttle is 34A in total. That's 17A per motor and I know it will not touch the ceiling of my 30A ESC.

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。

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

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.

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.

saotome

What you have said is true in ideal conditions.
Don't forget that extra battery has the same effect as using a larger battery - weight penalty. So far I have not seen any mainstream EDF jets in the 2-3' wingspan that carry multiple battery packs.

FYI I don't use a separate Rx battery, instead I use an UBEC so that I don't rely on the BEC on the ESC. Rx battery only make sense for larger models, such has 6' wingspan and up.

Sir, could you post some pics of your masterpieces so we can all learn from your techniques?