PROP DIAMETER?

[EDMO 1078]

On certified planes and engines, you only have certain choices for a prop.   We have almost unlimited choices for our birds.   I was always told to "Use the biggest prop available."

With the Subaru EA-81, the 72" Warp Drive prop has to be set for a very small angle in order for the engine to turn static rpm.  This cuts down on cruise speed.

I am wondering about the possibility of using a shorter prop, say a 68", like the 912 uses, and set it for more angle to get better cruise.  I have mostly long runways to fly from.

WD told me that there would be almost no difference between the 72 and 70" props.

I am also considering an IVO since it is lighter.

Any opinions ?

EDMO

[akflyer 1427]

I think Randy has well documented his likes for the IVO IFA ummm, I mean electrically ground adjustable prop.  you get take off and cruise.  I would think its well worth the saving a few more pennies for it.

 

[EDMO 1078]

I think Randy has well documented his likes for the IVO IFA ummm, I mean electrically ground adjustable prop.  you get take off and cruise.  I would think its well worth the saving a few more pennies for it.

 

Alaska Flyers live in a different world - We just cant get away with some of the things you do.  The IFA would be heavier than the WD, and I am trying to cut nose weight if possible.

EdMO

How many ramp checks did you go thru last year?  We had 2 with the C-90 Cub!  They may not know much about what they are looking at, but they sure want to know what us "Old Codgers" are driving without a medical.

Edited 14 Jan 2015 by Ed In Missouri

[Dusty 126]

My experience is with a 582 with a 3 :1 box.I was looking for a better cruise without too much loss on take off.

The smaller prop with more pitch gave a better cruise (8 kts) ,and as a bonus a slightly better take off performance.

Static rpm set the same but jumps 200rpm on take off

A 4stroke may behave differently but worth a try!

[Av8r3400 1178]

Going to a two blade prop may cut the drag as well, but they don't run as smoothly.

[EDMO 1078]

I agree Larry, sometimes a 2-fer will outperform a 3,  But I have never seen a Soob with a 2-blade.  Just imagine the Vibes would be bad.

I am looking at weight and size for performance.

EDMO

[Av8r3400 1178]

I think that vibration has more to do with the redrive ratio than anything.

[EDMO 1078]

I think that vibration has more to do with the redrive ratio than anything.

All I know is that my only info from Rotary Wing writer, says 3 blade for Soob.  I have 1.84:1 belt drive.

Stratus may recommend 3-blades, as far as I have seen.   They have 2.2:1 mostly.

EdMO

Edited 14 Jan 2015 by Ed In Missouri

[dav8or 20]

I am flying a 2 stroke on a speedwing so this may not apply. I just increased my diameter on a 532 with 2.58:1 A-box from 64" to 68" last summer by changing blades. In theory my climb should have been better with slightly less pitch and more disk area pulling me. The climb remained about the same but I seemed to lose cruise/top end speed. A couple of months ago I got fed up with point setting and swapped to a 582 with B-box and still 2.58:1. At first I put a 71" Culver fixed pitch prop on while waiting for the correct bolts and drive pins for the GSC. I had more power from the engine and the climb was a little better than I saw with the 68" GSC but static was well below Rotax recommended. I think I was getting 5600-5700 on the Culver instead of 6250. I switched back to the GSC as soon as the bolts came in and with a few other minor adjustments/corrections that come with a new to me engine I am back to testing. At first I pitched the prop for 6250 static. Climb was incredible but it would run way over max RPM in level flight at a relatively slow for me 100mph indicated. I have re-pitched a couple of times now until it would run around max RPM at WOT in level flight. With that setting I now get 5800 static. I am climbing at 6100-6200 rpm which still gives me 1100-1200 fpm at 75-80 mph. Cruise at 6000 is now a little over 100mph and 6500 rpm gets me over 110 mph.

 

I do not expect to be going back to the recommended static RPM setting as it seems to wasting available power when it is set that way. I do watch EGT and water temp closely at all times.

 

Not sure if this helps at all but what I noticed is a widening range between static and max RPM as the prop diameter went up. After I have some more time on the 582 I may try the 64" blades again just to see what happens. BTW both props used are 2 blade.

 

Dan