2cell lipo 3dx and eastern model supply

[barrett]

Just have to give thanks to eastern model supply for supplying me with more lipo's, small gws stuff, and carbon rods, all for unbeatable prices.


however my 2 cell pack just isnt doing it. i am using a 12x6 prop for my 3 cell pack and the power is great, should i be going down to a 10x4.7 for my 2 cell pack?
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thanks

[can773]

A 2 cell LiPO with a 12x6 should be fine on a 3Dx......

What motor/gearbox are you running, also what is the weight of you 3Dx?

[barrett]

its the d gearing.

im not sure of wight, i wouldnt think much more then 15 oz though.

i think it may be the -15ish weather im flying in. it seems to hover inside the house around 3/4 thottle, but once its outside, it can barely hold a hover.

[can773]

15 oz!!!!

I am doing mine down at 10 oz flying.....with that setup I dont think you will get much more than 17 oz thrust on 2 cells, so if you are that heavy combined with the cold it wouldnt surprise me that you dont find the performance all that steller.

I think you will find a 10x4.7 to be less thrust yet.

[barrett]

10oz?? hmm maybe 15oz was a bad guess. i dont know how you could build a 40in ws pane with 2 carbone rods for much less. Tim (the creator of the 3dx) always said to shoot for around 14. i think, ithink, i think. i dont know now though, 10oz REALLY has me wondering. is that will all electronics and batteries? cause thats what im talking about

[can773]

I ended up designing my own (cause I didnt thing Tim had a good design) but I actually have more wing area and a bigger fuse than Tims design, and both of them have been 10-105 oz with a 2 cell Lipo. That is flying weight, 3 servos, receiver, esc, battery everything. I am real careful on the glue, scotch tape for hinges, .039 wire for pushrods, no wheels, no decoration.

I thnk 14 oz is way too much, especially for indoor flying....outdoors its probably better being a little heavier to deal with wind.

[barrett]

ya i painted this one, that maight be teh reason for the weight issues.

[Flypaper]

Seems like cold really effects LI Poli batts. Was out flying the other day at about 25 F. first 30 seconds OK then power dropped a bit. About 25% of normal run time. Same batts work fine indoors.

[barrett]

i did a knife edge into a gaurd rail today, looks like more glue time, and even more weight. however, i put the cg forward a bit, i was running it about 1 inch behind the carbon rod, and i noticed with it up more, it flew way better and way more responsive in hover. incase anyone is following the "set the cg as far back as possible" rule with this bird, i dont think its the best idea.

[can773]

i did a knife edge into a gaurd rail today, looks like more glue time, and even more weight. however, i put the cg forward a bit, i was running it about 1 inch behind the carbon rod, and i noticed with it up more, it flew way better and way more responsive in hover. incase anyone is following the "set the cg as far back as possible" rule with this bird, i dont think its the best idea.

That will end your day quickly :)

As for CG, I think a lot of guys run then that far back to have the elevator trimmed to neutral instead of carrying up trim. This also will allow more or less hands off inverted (which is too tail heavy IMO)

A better solution is to build the model with just a slight positive incidence on the wing, maybe like a 1/16" at the LE. This will allow you to fly around with a close to neutral trim and still have the CG in a spot more suitable for stable flying.

Or you could just ignore the elevator trim position altogether :) My design is a bit different than the standard 3dx, but I have the CG at around 3" from the LE. Plenty responsive yet easy to fly at that point.

[barrett]

well the only REAL difference i noticed is that in hover, my tail response is much better with the cg more forward. (on point for what the plans call for)

although the changing in incidence makes sense.

it was a great flying day here to today, -3 weath, about 2kmh winds. perfect. hopefully another nice one tommorow, the bird is glued back up, couple more grams, and a straightened out prop shaft that isnt perfectly straight :x