News:



  • May 13, 2024, 03:01:45 AM

Login with username, password and session length

« previous next »
Pages: [1]   Go Down

Author Topic: Propeller Pitch Question  (Read 532 times)

Offline Chris Gilbert IRL-1638

  • EI-1638
  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 111
Propeller Pitch Question
« on: September 15, 2010, 06:44:07 AM »
I made the decision a few weeks back that my next stunt model will be electric.

I've spent a deal of time reading through the 'list your setup' topic, and even more time spreadsheeting through it to assist in my learning.
I'm puzzled about the choice of prop pitches though for EP.

It seems (to me anyway) that 6 inch pitch is pretty much the norm in most of the listed EP packages.
But if I read up on tuned pipe setups I see that 4 and 4.5 inch pitch are more usual (ok, in exotic Carbon Fiber 3 blade propellers).

Why aren't finer pitch props more common in EP setups?

Surely all that is required to make one work is a suitable motor with appropriate KV?

Logged
IRL-1638

Offline TDM

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 844
Re: Propeller Pitch Question
« Reply #1 on: September 15, 2010, 06:55:06 AM »
They both work. Just buy a 7$ prop made for electric you do not need the big bucks CF props but sure you can make the work. The heaviest penalty on an electric setup is the battery weight. The more efficient the prop the less Amps you need to go through the flight and the smaller the battery you need to carry. Go to list your setup in this forum and pick whatever you like. Also you can get many ideas from there.
Logged
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Dean Pappas

  • Moderator
  • Trade Count: (0)
  • Admiral
  • *****
  • Posts: 1195
  • Welcome to the Stunt Hanger.
Re: Propeller Pitch Question
« Reply #2 on: September 15, 2010, 06:58:14 AM »
Hi ... (what is your name anyway?)
Yes, it is simply a matter of getting the battery voltage, Kv and pitch harmonized so that there is between 15 and 25% more voltage available than what is needed to maintain the desired lap time.
Propellor efficiencies suffer and noise  n1 gets ugly above about 10,000 RPM on a 13" diameter prop as the tips start to go transsonic. A 10" diameter prop could easily run as high as 13,000 RPM without getting noisy.

It looks like we are, in fact, evolving toward the 4-1/2" pitch as a norm, with exceptions for those who are still running short landing gear and smaller diameters with more pitch at lower RPM in order to absorb the necessary horsepower.

Regards,
 Dean P.
Logged
Dean Pappas

Offline Dean Pappas

  • Moderator
  • Trade Count: (0)
  • Admiral
  • *****
  • Posts: 1195
  • Welcome to the Stunt Hanger.
Re: Propeller Pitch Question
« Reply #3 on: September 15, 2010, 08:19:24 PM »
I almost forgot the gratuitous mention ... reverse pitch prop!
Genuflect in Dennis' direction when you bolt it onto the motor.

later,
Dean P.
Logged
Dean Pappas

Offline Dennis Adamisin

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4343
Re: Propeller Pitch Question
« Reply #4 on: September 15, 2010, 09:18:31 PM »
Hi E1638

Welcome to ECL, here's to your pending succes, hope you also post your build thread and certainly post to the "List your Set-ups thread.

No doubt the APC 12x6-E has shown up on more ECL apps than any other prop.  Also significant is that it was one of the only props available as a pusher when we all started changing over.  However in the past year we go APC to introduce the 13x4.5 E-pusher and the 11x4.5 E Pusher prop.  Each can be clipped down about 1" to cover those sizes. 

Like Dean and Dorin said you just have to have enough kv & cells to generate enough RPM something around kv=850 - 1000 and 4 cells will cover about anything you want to do.

Dean's right about prop tip sped.  Flew the Strega with a 13x4 turning 11k.  Pulled great, howled like a banshee.  Replaced the 13x4 with the 13x4.5 slowed the prop to around 10k and it sounds MUCH better.
Logged
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline Jim Moffatt

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 114
Re: Propeller Pitch Question
« Reply #5 on: September 16, 2010, 05:54:37 AM »
I'll add my 2 cents. A slower turning motor has less windage and iron loss so as far as the motor is concerned slower is better. The iron loss is a fixed amount per revolution and more rpms mean more wattage loss to the iron.

In contrast to a gas engine which develops peak power at some, usually high, rpm an electric motor can reach peak efficiency at any rpm if the Kv is chosen correctly.  I believe this is why electrics have tended to bigger and higher pitch props.

On my 1/2A Baby Clown I did extensive testing for efficiency with several motors of the same design with differing Kv's and ended up with an APC 8x8 prop running at 7000 to 7500 rpm. This was much more efficient than the best motor with an APC 8x6.

I tested 4 motors with Kvs of 950, 1100, 1250 and 1400 with 8x6 and 8x8 props.

I know that 8x8 is a little too much pitch for maximum acceleration but once flying it performs extremely well.
Logged

Advertise Here
Pages: [1]   Go Up
« previous next »
Tags:
 


Advertise Here