D

Dmadd

Well Known Member
RV-4 Drivers,
Specifically guys with the O-320 and fixed pitch props. (160 HP) What RPM represents (approximately of course) 75% power at sea level? Not that I ever pull it back to that, but it could happen... ;-)
Thanks,
Dennis
I have a Warnke prop and need a guess on this...
 
% Power=48

Percent power is based on temperature and pressure however...the cockpit selectable answer is a sum of two numbers (MP and RPM) to equal 48. 24" MP and (24)00 RPM would be 75% power at SL.
I tested seven different props on my RV4 over the years (including a Bernie and Margie Warnke prop) and found it to be very accurate.

Smokey
HR2

I raced a 180C/S RV6 back in the day and beat him soundly with my garage-built, home brew balanced and blueprinted 150HP 0-320A. He asked how I did it. I gave him the Steve Wittman answer, RPM my brother, 3200 RPM!
 
Last edited:
Best Prop..

Sid,
Out of my "Magnificent Seven" props, my favorite was my Margie Warnke Claw(Bernie's Daughter) which now graces our mantle after I found cracks in the tip. I also tested the first 2 blade Catto for RV's on my RV4, I liked it too. I also really liked my Gary Hertzler prop (Long EZ prop maker) which was the absolute fastest. Ed Sterba's props are a bargain and perform well too. OK, I liked ALL of them...:)

I sold it with a MT fixed pitch which also performed very well, had factory support, leading edge protection and a nearby repair shop. I tried a Sensy metal and didn't like it, too heavy, flywheel effect and the RPM restriction. I do alot of acro and it just didn't fit my requirements. Since I only had 150 HP at rated 2700 RPM, why restrict myself?

All of that testing and 1500 hours showed me the optimum 0-320 RV4 prop length was 69" with a equivalent 72" pitch. This equalled the best overall performance. 69X69 though is great for Racing...the greatest speed increases came not from James Cowlings and cool wheelpants, but the right propeller bolted to a very well tuned engine.

Smokey
HR2
 
Last edited:
Opportune time to chime in....

.....since my buddy Brian is replacing his Ed Sterba with a Catto. He damaged the Sterba and has been wanting a Catto. Craig told him that another gent had also recently replaced his Sterba prop with a Catto two-blade and picked up 17 MPH:eek: ....hard to believe but he did tell Brian to expect a 10-12 MPH increase at 2700 revs.

BTW, the F-1 racers turn over 4000 RPM's racing and some ferry turning 3000 or better.

Regards,
 
Catto vs Hertzler...

Pierre,

First, thanks again for the great hospitality when we visited your fly-in last month! Back in 99' I visited Craig's Cabin/shop by landing my RV4 on a nearby mountain airstrip. Several notable items were a computer designing the blade lengths and HP requirements, another was the number of glass layups on each blade and the quality of the finish. Very strong and pretty! I have heard he outsources the painting to a professional now and they are even better. Craig even offered to make me a Racing composite FP prop for my Rocket....hmmmmm.
Craig has a 3 blade Vari-EZ prop on the wall that had an exhaust stack go through it over the Rockies and flew home! I ran the Catto 2 blade on my -4 for 1000 hours, longest of any prop. When I changed the engine to a wide deck 0-320 Airboat Racing modified 0-320, I ran a Gary Hertzler composite which even outperformed the Catto slightly. Gary only makes props on a limited basis for the EZ group, but they are awesome!

Smokey
HR2

http://www.cattoprops.com/
[email protected]
 
Last edited:
Smokey,
Did you find the MP and RPM went up at about the same rate (at sea level) IE, 2400 rpm was about 24 inches? 23/23 22/22 etc etc.?
Don't have an MP gage, so I'm trying to get a rough idea. Anyone that has fixed pitch AND an MP gage, I'd be interested to know what you see in this regard.
I've been accused of having only two power settings when chasing around with the rest of the fellas... One of them is idle... ;-) (I have the smallest engine, you do the math.. ) <BG> But I might want to actually go somewhere one of these days, and the info would be useful.
I always figured (in this A/C) that anything above 8500 ft would be 75% or less, at WOT. But, this engine prop combo will still over rev (above 2700 rpm) until I get above 10K. Any help the brain trust can shed on this, I'm listening...
Thanks,
Dennis




smokyray said:
Percent power is based on temperature and pressure however...the cockpit selectable answer is a sum of two numbers (MP and RPM) to equal 48. 24" MP and (24)00 RPM would be 75% power at SL.
I tested seven different props on my RV4 over the years (including a Bernie and Margie Warnke prop) and found it to be very accurate.

Smokey
HR2

I raced a 180C/S RV6 back in the day and beat him soundly with my garage-built, home brew balanced and blueprinted 150HP 0-320A. He asked how I did it. I gave him the Steve Wittman answer, RPM my brother, 3200 RPM!
Click to expand...
 
smokyray said:
Percent power is based on temperature and pressure however...the cockpit selectable answer is a sum of two numbers (MP and RPM) to equal 48. 24" MP and (24)00 RPM would be 75% power at SL.
I tested seven different props on my RV4 over the years (including a Bernie and Margie Warnke prop) and found it to be very accurate.

Smokey
HR2

I raced a 180C/S RV6 back in the day and beat him soundly with my garage-built, home brew balanced and blueprinted 150HP 0-320A. He asked how I did it. I gave him the Steve Wittman answer, RPM my brother, 3200 RPM!
Click to expand...


How does that work with altitude? Is there any easy way to calculate % power as the altitude increases? Thanks Smokey.
 
I think as you go higher and the air decreases in density, the MP will decrease in parallel.

24" MP and 2400 RPM will be 75% at SL and 10k MSL. Although 75% at 10k MSL with a fixed pitch will more than likely be something like 23" and 2500 RPM. (if it can make that)

I was just introduced to this theory a few weeks ago so I may be wrong.
 
Negative, Sid.......

.....since we lose an inch of MP per thousand feet. All you can reasonably expect at 10,000 MSL is around 20" at WOT, maybe 50% power. Remember what Smoky said...the MP and the revs should add up to 48 for 75%. So, at 10K, 20" + 25(00)RPM is only 45.

Regards,
 
OK, I get it, I was just doing a poor job of explaining it. I put the "(if it can make that)" after because I didn't think 23" could be obtained at that altitude. But if it could that would be 75%.

So is there a cheat sheet for what the % is if it's not 48? Like 45?
 
I use the following with my
O-360,Sen. fixed prop:

For every MP+RPM sum drop
of 3, I figure a 10% drop in HP
Also, my fuel burn drops about
one gal/hr.

IE:
48 = 75% = 10Gal/Hr
45 = 65% = 09G/H
42 = 55% = 08G/H

This seems to be close enough
for me under 12,000 ft. of altitude.
You can check these numbers against
the power charts for more accuracy.
Tom
 
Last edited:
By the numbers...

Sid,
The RV4 is a much cleaner airframe and way more efficient than the other RV's, especially the nose draggers, only the -3 and Rocket compare or better it. Since this is the RV4 site I can brag on the design a bit. I normally operated my RV4 anywhere between the surface and 12.5 but did take it up to 20.5 once (nearly froze). I had a Ram Air setup with a diverter for filtered air on the ground. I found that the 48 number worked well up to 12K and after that the air became too thin for propeller performance. The mark of a good FP prop I found was 2700 RPM at full throttle at SL. This gave the best overall performance at all altitudes. A balanced engine with a climb prop running 2800-3000 at SL, slowed down up high as the climb prop "lost efficiency" above 10K.
Amazingly, I have found my 285 HP Rocket equals my 150HP RV4 in fuel economy over a given distance. I normally fly the Rocket (and my -4) at 8500 or 9500 ft unless I'm in the hills. At full throttle my RV4 would get 21" and 2625 RPM at 8500' burning 8.8 GPH at 160 Knots True. My Rocket does 180 Knots True at 10.5 GPH 20"/2350 RPM with GAMI injectors at LOP, 200 True at 12.0 GPH 21"/2450. Sea Level all levers forward is 28"/2750 at 22GPH/215 Knots indicated...It really is just a big RV4.

Speed=$$$/Time...:)

Smokey
 
Last edited:
You must log in or register to reply here.