The right prop for climb performance. Reporting my E-flite Apprentice S.

[Strange82]

The right prop for climb performance. Re-powering my E-flite Apprentice S.

Hi folks! I think this may be my first post here. I've been lurking for a while and picked up some good info. Thanks for that!
So the Apprentice is my first plane, I've had a lot of successful flights so far, on wheels and floats. My elevator servo died and went full down deflection in flight on me, needless to say the rate at which the plane met the earth was not optimal. I was flying on floats so it soaked the speed control and damaged the motor as well. Oh well, if we're gonna fly 'em we're gonna crash 'em, right!?
So I plan on re powering with the Turnigy G-25 http://www.hobbyking.com/mobile/viewproduct.asp?idproduct=14401
And a 60amp Plush ESC. I want more STOL performance, as I plan on converting to a conventional gear and adding flaps in the future.What would you folks suggest for a prop? It currently swings an 11x8 blade. I don't really want a larger diameter, although when I convert to the tail dragger I could accommodate a bigger diameter. Is there a advantage to swinging a three blade prop? Other than they look sweet? Again, I'm looking for mostly takeoff and climb performance, not looking for more speed. Is this even the right motor? It's available in two KV ratings, 870 & 710, if I'm looking for torque I want the lower rated one right?
Thanks in advance for your input!

 

[ZoomNBoom]

Converting it to a tail dragger will not really allow a bigger prop, you dont take off with the tail low, you should take off roughly at the same attitude you do now, or at least be able to balance on your gear with tail high without prop strike. To allow a larger prop, you need to increase the gear height.

Adding flaps should be a big help (but will also cause the nose to pitch down further)

As for motor/props, dont know the apprentice, so I cant really give recommendations, but I think you get the right idea, you want low KV for higher static thrust. Just dont overdo it. From what Ive seen, even a stock apprentice doesnt really need much of a take off roll

A three bladed prop is useful if you are limited in prop diameter (which you seem to be). A three or more bladed prop effectively works like a larger, but less efficient 2 bladed prop. More blades= more thrust and less efficiency.

 

[quorneng]

A lower kV motor will indeed generate more torque but also at a lower revs so the prop needs to be able to effectively absorb the power delivered this way which usually means bigger diameter or with a bit less efficiency by using more blades.
As a rough rule of thumb adding a blade is equivalent to increasing the prop diameter by 10% so a 3 blade 11x8 would be equivalent to a 2 blade 12x8 if we assume the motor turns them at the same revs, however as ZoomNBoom points out the 2 blade would be more efficient generating the same thrust but using a bit less amps to do it.
So unless you can go to a significantly larger slower revving prop (which you can't) then it might be better to keep the kV the same but use a slightly more powerful motor (drawing more amps at the same revs) to drive the 3 blade 11x8.
Remember it is the level of excess thrust to weight that creates take off and climb performance. Just be careful that any excess thrust is not simply absorbed by the extra weight needed to generate it.
For aircraft in particular there is a lot to be said for the old saying "To increase performance - add lightness"!

 

[Strange82]

Hey folks!
I just wanted to update what I did with my apprentice. I wound up re-powering with the Turnigy G-15 810kv and a 40a ESC, still turning the stock screw. I gotta say the G-15 is a notable upgrade from the stock apprentice motor! It will almost climb straight up. I don't think I'm going to do any more with it at this point.

 

[pressalltheknobs]

Sounds like you had a lot of fun with it. What's next?

 

[Strange82]

What's next?
I'm picking up a 1/4 scale Cub in three days! It was a deal I couldn't pass on. I'm super thrilled. I never thought I'd get to fly a 1/4 scale let alone own one.

As far as the apprentice, I'd still like to add flaps and convert to tail wheel, but I've got to convert it in a way I can still use my floats.

 

[quorneng]

Lots of full size (and models) tail draggers (eg Super Cub) can and do use use floats.
It just needs appropriate fuselage mounting points.

 

[Strange82]

Sure. But I have the floats from elite for it already. Most people that convert to tail wheel either reverse the battery box, or permanently mount the landing gear. I've got to find a way that keeps the mounting points original and removable so the float / wheel swap can be done easily. I've got an idea but I've got to try it and see how it goes.