Ideal Propeller Specs?

[henriquerv9]

Hi All,

Does Anyone Here With Technical Knowledge Enough To Help Me With My Issue ?


I Have A Rv9a Running With A Continental Io240 (125hp) Engine. Also Is Installed A Sensenich Propeller 72x59. With This Propeller I Get About 1300fpm And About 115kt Ias Cruise Speed At 2400rpm And 6000?.

I Installed A Wood Propeller With 70x76 But The Performance Iam Not Satisfied With The Results. What Could Be The Best Dimensions To Get At Least 1200fpm And 140kt Ias Cruise?

Henrique
Rv9a Ppxrv

[rv6ejguy]

I don't think you are going to see 140 kts. IAS at 6000 feet MSL and still see a ROC of 1200 fpm with this engine and a fixed pitch prop.

[rv7boy]

Henrique,

I would suggest you contact Mr. Ed Zercher ( email: ez@sensenich.com ) at Sensenich. Since you already have tried one of their props, he would be very interested in you being a satisfied customer. Also, Ed is very knowledgeable about RV's. Their web site is

www.sensenich.com

Also, you might contact Van's for their advice since I believe their first RV-9A demonstrator had an O-235 on it (similar HP to your O-240).

In either case, do not delay your inquiry as they soon will be departing to Oshkosh Airventure 2005.

Good luck,

Don Hull

[Highflight]

Since you're already set up for a Sensenich, I'd suggest that you stay with a Sensenich.
But to offer as a point of discussion, I know exactly what engine I'm going to use and the performance options it will have. I have also decided to use the Catto 3-blade prop.
So I called Craig Catto and he tells me that he, knowing what my engine is going to be and what climb and cruise performance I am looking for, can pitch the prop to match my desired performance (within the usual trade off of a FP prop regarding climb to cruise performance).

Because RV's are so common now, and because there are so many Sensenich props on them, I'll bet that the people at Sensenich will be able to tell exactly which FP prop configuration will give you your best performance (again, within the usual climb vs. cruise performance) probably better than anyone here can do for you based on their singular anecdotal experience.

[gmcjetpilot]

Originally Posted by henriquerv9

Hi All, I Have A Rv9a Running With A Continental Io240 (125hp) Engine. Also Is Installed A Sensenich Propeller 72x59. With This Propeller I Get About 1300fpm And About 115kt Ias Cruise Speed At 2400rpm And 6000?. What Could Be The Best Dimensions To Get At Least 1200fpm And 140kt Ias Cruise?Henrique Rv9a Ppxrv

According to Van's spec a 118 HP RV should cruise around 138kts (TAS) and climb at solo weight of 1,200 fpm, 1,000 fpm gross. Your 125 HP should do this also or a little better. Because your climb rate is about right I suspect a few things: (sorry if they are dumb questions but I have seen this before and some times the obvious gets missed.)

Have to ask, do you have all gear leg and wheel fairings on?
Is the airspeed indicator calabrated?

Some things to measure:
What is the RPM and Speed at full throttle near sea level?
What is the RPM and Speed at full throttle at 8,000 density altitude?
What is the static ground RPM at full throttle (right at the start of takeoff roll)?

If you are indicated 115 kts @ 6,000 (std day 3.1c) your TAS is about 125kts, which is still about 15 kts slow, which is quite a bit.

For the purpose of comparing one RV to another, most people use 8,000 feet density altitude and wide open throttle as a common point for future reference. Also for the record the Sensenich props tend to give very good performance and speed. I agree with the above, call them. Something does not sound right.

Cheers George

[penguin]

Henrique,

You have to be really careful with the pitch number. Most wooden prop makers don't measure it in the same way - so a 76" pitch prop from two makers will often not give the same performance. Jumping 17" of pitch is also a huge change. I have just changed by 2" and really noticed the difference.

As George said, you need to provide more details to get sensible suggestions. Metal props are relatively easy to re-pitch (any good prop shop can do it for around $150), so you could have a few inches added to your Sensenich to improve cruise speed - an inch of pitch will probably drop your full throttle rpm by around 40.

With the Sensenich what is your full throttle rpm at the start of your take off roll and what is it at your normal cruising altitude? Which do you want more - cruise speed or climb rate?

To get 140kt IAS at 6000' I would have thought you would need the engine running close to the red line - my RV-6A with 150 hp would only get to about 140 KIAS at full throttle (2450 rpm). A prop that allowed the engine to rev close to the red line in cruise will also give the best climb rate (highest static rpm). My 6A, now with a 160hp engine, will just get to 150 KIAS (at 2620rpm) at 6000' - which is around 165 KTAS. I would have thought you would be very lucky to see 140 KIAS on 125hp? You are very unlikely to get that cruise speed at 2400rpm.

Fixed pitch props are always a compromise - give us a few more details, we might be able to come up with some suggestions.

Pete