Hey guys, I think we're re-hashing old ground here but I have a bit of a conundrum with on of my ships..

I have a modified Imitation which has been my workshorse for the last year or two.

I've been running a middle of the road setup, reasonably high rpm, and reasonably low pitch  10x5. I'm finding that I'm nearly killing a 3100mah 4S pack each flight.

This has me thinking about things, I'm now thinking of slightly repitching up so as not to hurt the packs so much each flight, by reducing RPM a little.

The next logical step is increasing pitch even more, and reducing the pack size and hence overall weight. I can do this with the current setup as increasing pitch doesn't increase amps nearly as much as a change in diameter.

Seeing as most of the modern IC ships are running big props with low pitch for speed regulation, should I actually be going the other way, bigger pack again, and more diameter, lower pitch, more rpm? the obvious thing here is bigger motor, bigger ESC more weight etc.


Whats more important, power or all up weight?

Somethings not right, need more info. I think your prop's too small and you're making up for it with rpm? Some 5 pitch props measure 4 pitch but if your plane is bigger than 500 Sq. In. you need an 11" dia for a 2 blade. Try an APC 11x5.5 EP with the rpm around 9200 and trim from there. Need more info.

MM

The efficiency of Motor/ESC vs. prop size should not vary dramatically IMO (unless you turn prop extremely fast which assuming not the case here).  The biggest factor might be the air speed of the plane.  Meaning if you use a longer line than needed, you have to maintain the line tension by flying faster which will take lots of juice from the battery.  Also, longer line means longer traveling (factor of 2pi).  Cutting couples of feet and flying slower makes a big difference if you can afford to do it.


Regards,

Sean

Guys, I was talking in hypothetical terms, whats more important:

Power and speed regulation, or weight?

So the five paragraphs about things to do to your prop to change power consumption (which may not have the results you expect) were just a red herring, and the one line at the bottom is what you really care about?

I'm not sure exactly what you're asking, but given a fixed airframe weight I think you want to have adequate power for that weight.  Reducing weight by reducing power is not, I believe, going to lead you to joy and happiness.  Of course, if the airframe is just too damned heavy then you'll be chasing an ever-receding goal, which is what motivated my comments about huge engines and bricks.

More pitch means lower RPM and thus less power. But it also means lower speed stability (more slippage under the same load = brake - for example in vertical climbing or divig) ... so it works pretty weel the same like diameter, while larger prop needs more power and keeps speed better, also lower pitch does the same.

However there is small detail. The prop with higher P/D ratio, has usually better efficiency (yes it is question of that ratio, not the diameter itself), so it is nice thing for cruising, lower P/D has good static thrust. So while we have lot of power on IC engines, we can trade efficiency for good thrust. Electric need better efficiency, but we will never use props with P/D = 1 like we see on constant load applications. So P/D equal or little lower then 1/2 is way to go.

Hi Greg,
In all this, I did not hear what the plane in question weighs.
If it much over 56 ounces, you are cutting things too close. (I figure 0.65 Watt/hours of battery capacity per ounce all-up-weight to fly the schedule.)
The battery you have is ideal for 52 ounces or less.
It is also possible to run too high an RPM, in combination with low pitch, so that you can't effectively use the battery capacity you have.
Regards,
 Dean P.