RCU Forums - View Single Post - TF GS P47 Build - yeah another bloody one!!
Old 08-11-2014, 04:26 PM
  #10435  
Peter_OZ
Banned
My Feedback: (1)
 
Join Date: Jun 2002
Location: Brisbane, Queensland, AUSTRALIA
Posts: 7,744
Likes: 0
Received 2 Likes on 2 Posts
Default

Dave,

doing some basic calcs using good old ohms law and ignoring things such as resistence losses va the cable and connectors, we will assume they are 0 ohms. We also assume it is running at max power consumption.

Motor specs: rpm/v 1550 kv

Motor voltage: 22v

motor power consumption at max rating: 2400W

P=IE

Therefore;

I=P/E

I=2400/22

I=109A

The ESC that comes with the kit is 100AQ but assume some efficiency losses in cables, motor etc of around 10% hence the 100A supplied ESC is just within parameters.


Lipos are 5000mA/h 6S 40C.


so . . . 5000mA/h x 40C = 200 mA/h discharge rate, Therefore 200mA/h / 1000 = 200A constant dischrage rate at max.


Calculating flight time and assume average of say 50% throttle setting throughout the flight....

(5000mA/h / 1000) / 50A=0.1

0.1 x 60 = 6 mins flight time @ 50%.

So will need to keep my throttle settings moderate so as to a) not run out of battery; and b) not burn out the ESC!!

Appling the 80% rule will give a 5 min flight which should be ample.

QED

Now as for thrust and flying weight. Let's assume the model comes in at correct AUP of 3.6kg, or 8 lbs. From the research I have found the fan unit fitted should develop about 3.45kg of thrust. Or 7.6 lbs.

That is a thrust to weight ratio of 1:0.96 - almost 1:1 so should really get up and get going. Of course the crappy inlets are going to restrict that. If I can get around 1:0.75 I'd be quite happy. I'll fabricate some sort of ductings and open up the inlets to help with that inlet flow.

cheers
Peter

Last edited by Peter_OZ; 08-11-2014 at 05:08 PM.