4 bladed prop suggestion

[Andre Bouchard]

Here are my observations using APC 4B's (14.5x12 and 15x11) with YS-140 4-strokes on two different airframes:

Better braking than a 2B, but not materially better than a lower pitch, higher diameter 2B.

Less vertical than a standard 2B configuration because of the smaller diameter and the reduced efficiency that more blades induce.

The foregoing can be probably be accomodated for, however, the biggest downside I have found to 4B v. 2B props were: 1.) mass-induced effects such as slower acceleration, and changes in pitch reaction (see Troy's comments below about snaps), and 2.) considerable yaw variation v. RPM/airspeed due to spiral airflow (or mass) effects.

Regards,

Andre' 
  ----- Original Message ----- 
  From: Troy Newman 
  To: discussion at nsrca.org 
  Sent: Monday, August 09, 2004 3:12 PM
  Subject: Re: 4 bladed prop suggestion


  Mike,

  14.5-12 works on the 140...also a 15-11 will load it a bit more but will work. Central has them or can get them.

  I'm not totally sold on the 3-4B props...But I have been playing with one on  the 160DZ turns the 17-12 std APC at 8600-8800...Yesterday I was turning the 15.5-12 4B at 8800 in PHX in the heat of the day(4pm) at 113degs...and it had good power and performance....

  Brakes are nice but it does some other things both good and bad....It seems to keep the model from coasting through things....But on the other hand spool up time is not as good....This has always been my complaint with the 3B and 4B props...Those I have seen fly the 3B successfully like Dave Lockhart...the horizontal snap-roll combos needed a different technique....Dave was throttling up during the last rotation of the snap...so that when the rotations stopped the motor was pulling and then he was pulling the power back a little in the following roll combo... I was never as good as he was at throttling during the snap. I just found the 2B props better for me in this case....I found the problem to be even worse when running the 2 strokes...But Dave to his credit made it work. However,  in the current Prelim and Finals sequences we don't have any of these horizontal snap-roll combos....A roll then snap will not be as bad....but the snap then roll was tougher with these props.

  After flying with Quique at the NATS I wanted to do some more experimenting...I had the prop already getting dusty...Besides I moved it from CO-CA-GA-NC-AZ all in the last year or 2 and I was looking at playing a little....Besides Quique made it work very well....His model was a softer sound and quieter than the Electric.....so we are playing with it. The OS 140(EFI) on 30% nitro turns the same prop at about 7800 and still has good power for the Prelim sequence...I did not fly my friends model through the finals pattern with it....I know that my light Supreme (10.3oz) doesn't care....The overall speed management of the props are different and takes some getting used to.

  Not sold yet but playing

  Troy
    ----- Original Message ----- 
    From: mike mueller 
    To: discussion at nsrca.org 
    Sent: Monday, August 09, 2004 3:46 PM
    Subject: 4 bladed prop suggestion


     I want to experiment with a 4 bladed on a YS DZ 140. I have a Temptation. Does anyone know what size to start with? Also who stocks them? thanks, Mike


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