Boeing777 scratchbuild twin edf

[Babylon5]

Hi Viper, when and where are you going to maiden the beautiful twin EDF setup.

Cheers and all the sucess.

B5

[dvdykc]

Choosing the right motor

Hi All,

very queries to know how you all calculate and choose motor kv + prop vs all up weight(AUW).

[viper1990]

Hi babylon5!

Most probably and very very likely will be at woodlands this week 13/12/2008, which is tomorrow. No promises i'll granteed 100 % be there, but the chances is i will be. I did countless hours of taxing below my house and test the structure and strength of the landing gear. It only broke off when it run over small pebbles and rocks and small drain covers. On smooth ground i can do Boeing777- drifting! can do donut also haha.

dvdykc-

Motor,prop combination with the weight..., it became a subconcious thing for me already. I just know and how much to get.... But i do apply the following rules such as

1)100watts/pound
2)pitch speed 2.5x faster then plane stalling speed
3)1000kv for 10inch
2000kv for 5-7inch
3000kv for 3-4inch or 68mm edf

and so on..., its just a rough guide.

Pitch speed = Pitch speed = RPM x Pitch x (60/63360)


Then i go buy my stuffs and electronics..., all these are theoritical numbers only. Once i'm home, after the setup i'll test and obtain the true values at home. I also got a weighing scale to test static thrust and plane weight

Ok now if i apply all those to my boeing 777:

My plane weighs 1.8kg AUW or 3.9 pounds , i need approx 390watts. I got myself 2 edf x 12.6v x 28amps each so total i got 705.8 watts... woohoo more then enough.

Stalling speed of my boeing = 4 sqroot(wingloading) = 21mph or 33km/h
So i should get a pitch speed of roughly 2.5x more or 82km/h

So i'll find a reasonable KV for my 68mm edf. Which i choose it to be 3900kv.

Then comes thrust to weight ratio. Snice my plane is not doing any 3D,mild aerobatics, unlimited vertical. I don't need 1:1. I'm finding a thrust to weight ratio roughly 0.5:1 will do.

I on both fans, and place agaist my digital weighing scale, i got 1081 grams of thurst in total. Obtained thrust to weight ratio is : 1081g/1800g = 0.6:1 Pretty reasonable to me.
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And with so many other tons of calculations..., theortically the plane will fly! and the truth will unfold very very soon this year. I'm going to video down this baby rolling down the runway.

[viper1990]

Wooohooo , just to let you guys know my plane flown and landing in one piece..., well not really, the right engine dropped after the touch down hehe.

The plane roll down and took off in a couple of meters, probably 20m. It has too much up elevator so i trimmed it down like 10clicks. Other control surfaces was neutral and tracking straight.

Performance:

1)Glide test- Awesome. It can glide without power for a long distance
2)Low pass full throttle- Once again, awesome, not amazingly fast but it looks like a scale airliner doing a slow flypast.
3)Climb rate- Not really good due to the low thrust-to-weight ratio but still i got reasonably climb rate to quickly get up into comfortable attitude to fly.
4)Landing- shaky, probably i "kan choing" too much, glad it made it up and down in once piece.

Will post my video up soon!

[dvdykc]

boeing 777

Hi Viper,

Thanks for all the advice. Today I saw your Boeing 777 at Woodlands. Its look great. But miss it in action. I just saw it lying on the ground.

Due to pai seh (Afraid that the new plane don't fly), I test fly it on the other side of that area. Well, I consider it another failure.

I’m using 1380kv motor and prop 7x5 and 2 cells batt. It climbs a bit but later was blow by wind, it crash and hit lamp post. Lucky it didn't break apart when it falls down.

Now my confident to fly a plane been shaken when I saw other people fly their plane like eating a piece of cake.

[dvdykc]

digital weighing scale

Hi Viper,

Can post pic of your digital weighing scale. Just wondering how it function.

[SniperWj]

viper~congreat on ur 777maiden!

[viper1990]

viper~congreat on ur 777maiden!

Thanks! Hope some of you saw it flying there. I madiened it quite late. It went up around 6pm if i'm not wrong. Though flying in the evening can't really see much features on the plane, the 777's Silhouette against the sunset was freaking nice like a real commercial airliner.

Hi Viper,


Due to pai seh (Afraid that the new plane don't fly), I test fly it on the other side of that area. Well, I consider it another failure.

Now my confident to fly a plane been shaken when I saw other people fly their plane like eating a piece of cake.

Aiyo..., at least approach the other fliers or my club members, they are all wearing Singapore Poly T-shirts there. If you fly and crash alone will be paiseh. If you come find help, we'll have to trim,adjust ,see when wrong and test fly your plane.Best of all,no paiseh and you get to know us even better. Anyway heres my digital weighing scale.

[viper1990]

Ah whoops, forgot to attach

[jansonfinn]

Ah whoops, forgot to attach

How heavy can this scale takes up to?

[viper1990]

5Kg

[GLENDON]

damn it i should do a roll lol....

[ammo]

3)Climb rate- Not really good due to the low thrust-to-weight ratio but still i got reasonably climb rate to quickly get up into comfortable attitude to fly.

I guess it's a good nice scalish flight

I like r/c planes that take off and like the real thing instead of popping off the ground. I'm prob not the best person to say this, but most people fly powerplants instead of the wings nowadays

[dvdykc]

How about ESC

Hi Viper,

How about ESC? do this play apart on the electronic component.

I always saw people mention that the ESC must be higher than the Motor max amp draw. So if the motor only draw max of 15 amp, is there any different on using 20 amp ESC and 25 amp ESC or even more higher?

Thanks

[viper1990]

Sure do. A 40amp esc used instead of a 20amp esc on the same motor will result in more current drawn. Therefore more power (P= V X I) and more static thurst.

But the increase is barely noticable. I would maybe say 0%-5% increase in static thrust. Depends on the total internal impedence of each ESC circuit. But i wouldn't bother using a big esc for a tiny motor. Just get a ESC 10A higher then the full current drawn by the motor and its good enough. Besides a 40Amp esc could be easily 20grams heavier then a 20amp esc. I could save some weight and space.