I have an old Cap231 with a Saito 91 and want to try some 3D. I just purchased a 16x4 wide prop (APC). It seems to produce some strong static thrust, but is this too much prop for this engine? Fully leaned, it turns 8200 rpm and when you let off the throttle, it takes a couple of seconds to slow down due to the interia of the prop. Anyone have experiance with this? Would a 15x4W be better?


Thx


Scot

I haven't tried a 16x4, but i use a 15x4 on my .91 and it works great

Are you using the wide APC prop? What rpm are you getting out of it and on what fuel?

thx


Scot

i have 15x4W apc on wildcat 20/20 fuel and i think it turns around 10,000

1800 rpm difference for 1 inch of prop is pretty extreme. I wonder if my engine is just getting old.


Scot

Can someone check my work for me? This is scary if I am right.

If I can turn a 16x4 wide at only 8000 rpm, then my max speed in level flight is only 30 mph!

(4 inches * 8000 rpm * 60 minutes)/(12 inches * 5280 ft)=30 mph of wind

For a Cap 231, that is kind of slow. I am not sure what stall speed it, but it is not far below 30 mph. Maybe my calculation is worthless.


Scot

I fly the 16x4w on my saito 100 so I would suggest the 15 for the 91.......14x4 works good too.
YardDart is flying a Funtana with a 91 and the 14x4W with 20% fuel...... Its Awesome!!!!

What RPM is YardDart getting on his 91 w/ 14x4W? Would that over-rev this 4-stroke? Saito website posts rpm range up to 11500. I think the 91 will not exceed this rpm w/ the 14x4W on the ground, but would get awefully close in the air. I am getting 9800 w/ 15x4W on the ground. I assume I will get 11000 w/ 14x4W on the ground. I don't know how much it would unwind in the air going full speed. My friend had an Saito 80 swinging MA 12x6, and he has broken his valve in the air twice, I assume it's due to over-reving.

What fuel are you using for that saito 91?

Here is a list of my rpm readings on 10% cool power fuel fully leaned out:
16x4w 8300
14x6 MA 9300
14x6 APC 9700

Do any of these numbers seem out of line?


Scot