Comparing props

[hcccs]

How do you compare propellers with different lengths? I have a copy of a Ted Hendricks 68" x 76" propeller for my RV4 and it is a 'climb' prop. With 2350 RPM I have a speed of 125 kts which isn't enough. I've seen props with diameter of 72" but with pitch around 40-44. I know that a prop with greater diameter can have a lower pitch and still have the same performance. Is there a way to compare prop?

 

[Taltruda]

Are you saying you only get 125 knots at 2350 rpm? Indicated or true? What altitude? What engine?

What’s your static RPM full throttle with the brakes locked?

Pitch around 40-44 must be a typo..

 

[hcccs]

Are you saying you only get 125 knots at 2350 rpm? Indicated or true? What altitude? What engine?

What’s your static RPM full throttle with the brakes locked?

Pitch around 40-44 must be a typo..

TAS 130 @ 2400 RPM at 1000 ft. Static is 2300 RPM Lycoming O-320-E3D. That flight was without wheel pants.
Yes, the 44" pitch prop must have been for some other engine.

 

[Taltruda]

So you are throttling back to 2400rpm? I assume you don’t have a Manifold pressure gage on your fixed pitch engine.. you can’t really compare power settings without one.. I do feel that RPM static is a little high, I get 2200 static, yet I can overspeed to 2850 WOT.
What kind of speed do you get at 2700rpm?

 

[hcccs]

So you are throttling back to 2400rpm? I assume you don’t have a Manifold pressure gage on your fixed pitch engine.. you can’t really compare power settings without one.. I do feel that RPM static is a little high, I get 2200 static, yet I can overspeed to 2850 WOT.
What kind of speed do you get at 2700rpm?

Yes, I have Skyview and upload flight to SavvyAnalysis. I get 130 kts with 2400 rpm and MAP 23. I will test full throttle at next flight but I still think I need another prop.

 

[jclark]

TAS 130 @ 2400 RPM at 1000 ft. Static is 2300 RPM Lycoming O-320-E3D. That flight was without wheel pants.
Yes, the 44" pitch prop must have been for some other engine.

Add wheel pants and associated fairings.
Push the throttle "all in" at the 1000' you mentioned.

You should see much better.

I used to run an O-320 (160 HP carbureted) on an RV6 (more drag), using an Ed Sterba fixed pitch wood prop, with dimension similar to what you have and got over 150kts.

Maybe "fixnflyguy" will weigh in as he has an RV4 with fixed pitch wood prop as well.

Comparing dimensions on different props can be like comparing "apples to watermelons", so a baseline with all other variables (HP, fairings, altitude, etc. ) becomes very important.

I wouldn't make any changes before having all that info locked down for comparison. Now, on the other hand, if there is a prop, on a similar plane, with the same HP, that you can borrow and do some test runs, that might be helpful.

 

[Roadjunkie1]

Prop length and pitch

Add wheel pants and associated fairings.
Push the throttle "all in" at the 1000' you mentioned. You should see much better.

I used to run an O-320 (160 HP carbureted) on an RV6 (more drag), using an Ed Sterba fixed pitch wood prop, with dimension similar to what you have and got over 150kts.

I have a Bernie Warnke 68 X 74 (BEAUTIFUL) wood prop on SuzieQ with O-320 160 hp and easily consistently get (for example) 152 kts cruise at 2400/19.5 @ 7500 msl

Comparing dimensions on different props can be like comparing "apples to watermelons", so a baseline with all other variables (HP, fairings, altitude, etc. ) becomes very important.

Good point. Just because I cruise at that speed......

I wouldn't make any changes before having all that info locked down for comparison. Now, on the other hand, if there is a prop, on a similar plane, with the same HP, that you can borrow and do some test runs, that might be helpful.

That would be an ideal way to compare what you have and what other people are running.

 

[fixnflyguy]

My RV-4 with Sterba 68X74

I have a Sterba 68X74 , 160HP Lyco on my RV-4, and get about 150kts at 8K, but that's turning 2600 RPM..its definitely a climb prop and I can easily hit 2800 RPM or more. I have Jclarks "old" tried and trued Sterba ,68X76 I'm going to put on to settle my RPMs down at cruise. You will likely see a lot of variance in different brand props with the same diameter/pitch, and I recommend flying your plane for a while and see what your mission is, and go from there. I haven't met many RV folks with FP props that haven't tried at least 2 different ones to find their sweet spot in performance vs efficiency. I flew an RV-4 160HP delivery flight for a friend from Fla to NC with a Sterba 68X76 that couldn't get to 2350 RPM at full throttle yet cruise was around 150Kts. Variations in tach indication, AS indicator accuracy and other factors may hide the truth. Go fly awhile and use calm day GPS ground speeds to give you some comparison.

 

[hcccs]

Are you saying you only get 125 knots at 2350 rpm? Indicated or true? What altitude? What engine?

What’s your static RPM full throttle with the brakes locked?

Pitch around 40-44 must be a typo..

Sensenich makes a prop with type no 72CK-42. That must be 42" pitch. So far I haven't seen any 72" props with pitch of more than that.

 

[Roadjunkie1]

Wood props...

I have a Sterba 68X74 , 160HP Lyco on my RV-4, and get about 150kts at 8K, but that's turning 2600 RPM..its definitely a climb prop and I can easily hit 2800 RPM or more. I have Jclarks "old" tried and trued Sterba ,68X76 I'm going to put on to settle my RPMs down at cruise. You will likely see a lot of variance in different brand props with the same diameter/pitch, and I recommend flying your plane for a while and see what your mission is, and go from there. I haven't met many RV folks with FP props that haven't tried at least 2 different ones to find their sweet spot in performance vs efficiency. I flew an RV-4 160HP delivery flight for a friend from Fla to NC with a Sterba 68X76 that couldn't get to 2350 RPM at full throttle yet cruise was around 150Kts. Variations in tach indication, AS indicator accuracy and other factors may hide the truth. Go fly awhile and use calm day GPS ground speeds to give you some comparison.

I miss Bernie Warnke! He was a MASTER at carving props and his are still some of the best-looking, if not THE best, of all the props out there. The only problem I had with such a great-looking prop was wanting to hang it on the wall rather than put it on the airplane! RIP, my good man! My fellow aviators miss your amazing talents!

Prop making is a mixture of art, science and a little Grey Magic that few people have mastered. Bernie called his the "Almost Constant Speed Prop" and I can actually feel it start to grab the air better once it spools up. My imagination? Perhaps! But I like it! Add me to your list of those who only tried one prop and were happy! Mine was perfect right out of the box. Bernie said if it wasn't performing the way I wanted, to send it back and he would tweak it if necessary. No need!

I pulled out my travel logs from several years and 2400/18-22 was typical zipping around at an average 152kts sipping 6.5-7.5 gph. Altitude changes the MP but not much else. She will get close to 200kts throttle full forward but that little O-320 is working hard and tickling 2600 while sucking down 10+ gph. Naaaa. I'm was used to a Cub, for crying out loud! Anything faster than 75kts made me a happy man!

I consider myself fortunate to have such a beautiful piece of aviation ART that does a most excellent job of pulling SuzieQ and I around!

 

[Roadjunkie1]

Pitch and length of props

Sensenich makes a prop with type no 72CK-42. That must be 42" pitch. So far I haven't seen any 72" props with pitch of more than that.

I run a 74-45 on my C-90-8 J-3 Cub. It is a good all-around prop that keeps me in STOL competition but gets me to the backwoods in good time! I would NOT put that on an RV.....

 

[hcccs]

I have a Bernie Warnke 68 X 74 (BEAUTIFUL) wood prop on SuzieQ with O-320 160 hp and easily consistently get (for example) 152 kts cruise at 2400/19.5 @ 7500 msl

Good point. Just because I cruise at that speed......

That would be an ideal way to compare what you have and what other people are running.

Where would I be searching for a Sterba prop? Everyone seem to praise it.

 

[jrs14855]

Props

Sterba stopped making props some time ago. Catto, Prince and Performance seem to be the popular props currently. I believe Performance evolved from Warnke.
Pressure recovery wheel pants should give you about 8 m/h gain.
If you don't have a manifold pressure you could measure fuel consumption on a flight of at least two hours at 8'000' pressure altitude. You are probably at 65% power at 2350 r/m.
Get a Whirlwind ground adjustable.

 

[BH1166]

Ed is still making props last i heard.

I have a Whirlwind GA prop … I replaced a Bernie Warnke ACS needing better climb performance. Love my WW GA200 !


Updated August 28, 2021
Anyone interested in contacting Ed Sterba please use his new email address of: [email protected]. His phone number is 941-778-3103

Butch

 

[PropMan]

How do you compare propellers with different lengths? I have a copy of a Ted Hendricks 68" x 76" propeller for my RV4 and it is a 'climb' prop. With 2350 RPM I have a speed of 125 kts which isn't enough. I've seen props with diameter of 72" but with pitch around 40-44. I know that a prop with greater diameter can have a lower pitch and still have the same performance. Is there a way to compare prop?

Diameter is determined most of the time by ground clearance or rpm limitations. Pitch, no matter the diameter sets the speed range. Most RV types are pitched between 68"(climb) to 78"(cruise). This is for most wood props. Lots of other factors, what's your operating field elevation, empty weight of the plane, rpm range you'd like to operate at(I've had customers run an O360 past 3300rpm). So lots of variables to consider. Then, every mfg measures Pitch different. Never apples to apples
My RV6 with O360 would cruise at 200mph at 2600 rpm at 7500ft DA. I don't recall the mp. At 2700 it was 210mph.

Bernie Warnke is where Clark Lydick learned to craft props. Clark taught me

 

[FinnFlyer]

Having a hard time understanding prop pitch (angle), even after reading primer on props.

Have a 76x88 PP prop.

I assume the 88 deg pitch is measured at the 75% point (r/R=0.75).
Tan(88) = 28.6
So 21.5 pitch at tip?
For each rotation the tip covers 76 x 3.14 = 238 inches (6.06m).
Theoretically prop moves forward 238/21.5 = 11 or 238 * 21.5 = 5,100 inches?

EDIT: My misunderstanding was that the 88 in 76x88 was degree pitch or twist. Not so. It's pitch expressed as inches advanced by prop per rotation. This gives about 2,400 RPM for 200 mph.

Let's say airplane is flying at 200 mph. How fast (RPM) should the prop turn assuming 95% efficiency at sea level? At 8,000' feet?

Finn

 

[PropMan]

Finn,
My normal formula is-
Pitch (88) x .000947 x prop rpm (2400) which yields theoretical forward advance of one prop rotation in mph. Now I multiply that by another factor derived from experience, this depends on how clean the airframe is. An RV is somewhere from 1.1 to 1.2. So the math says if you are traveling, mind you this is true airspeed, 200mph with 88" pitch the prop rpm should be around 2200. Lots of variables tho. Is the tach reading properly, are your instruments calibrated , has the prop been repitched but not remarked.
Hope this helps

 

[hcccs]

I'm back with som more questions. Is there a rule of thumb how to exstimate change in static RPM for a change in propeller diameter and pitch. To get my static RPM down and get more cruise speed I was thinking of ordering a new prop with different specs. i have a Ted Hendrickson 68" / 76" and a prop with 70" diameter and 78" or 80" pitch could possibly do the trick. Before ordering I need to be more sure what I'll get. Any ideas?

 

[pazmanyflyer]

I'm back with som more questions. Is there a rule of thumb how to exstimate change in static RPM for a change in propeller diameter and pitch. To get my static RPM down and get more cruise speed I was thinking of ordering a new prop with different specs. i have a Ted Hendrickson 68" / 76" and a prop with 70" diameter and 78" or 80" pitch could possibly do the trick. Before ordering I need to be more sure what I'll get. Any ideas?

Per Tony B. publishing, a rule of thumb has it that when you decrease the propeller diameter by one inch, or decrease the pitch by one inch, the rpm will increase by about 50 to 100 rpm . . . say, on the average, 80 rpm.

Talk with Catto props. Tell them what engine, airframe you have and your expectations and they will tell you exactly what you need in a FP in either 2 or 3 blade versions.

 

[rvbuilder2002]

I'm back with som more questions. Is there a rule of thumb how to exstimate change in static RPM for a change in propeller diameter and pitch. To get my static RPM down and get more cruise speed I was thinking of ordering a new prop with different specs. i have a Ted Hendrickson 68" / 76" and a prop with 70" diameter and 78" or 80" pitch could possibly do the trick. Before ordering I need to be more sure what I'll get. Any ideas?

What you need to do is not try and calculate what you want for a diameter pitch value, but contact someone you want to have make you a prop and talk with them about what you want to focus on performance wise and then let them handle the rest.
The reason this is important is that not all prop makers measure their pitch value the same. I.E., if you order a 70 X 79 prop from three different prop makers and test all three on your airplane, you will likely get different performance #'s from each.
Pretty much any prop maker currently in business is very familiar with all of the different RV models. Knowing your model, engine size, and a few other details, they will make you a prop that does what you want.
I don't see that you have ever mentioned in this thread whether you finally got all of the gear fairings installed. If not, that will have a much bigger effect on performance than most people ever believe. This is particularly true with a fixed pitch prop.

 

[PropMan]

I'm back with som more questions. Is there a rule of thumb how to exstimate change in static RPM for a change in propeller diameter and pitch. To get my static RPM down and get more cruise speed I was thinking of ordering a new prop with different specs. i have a Ted Hendrickson 68" / 76" and a prop with 70" diameter and 78" or 80" pitch could possibly do the trick. Before ordering I need to be more sure what I'll get. Any ideas?

Exactly what Rvbuilder2002 said!
There's too many variables to give you advice. Your best move it to call whoever you plan on getting a prop from and discuss what you want. Every Prop Manufacturer measures differently.
I can tell you what my props performance was, and what changes would effect performance and how, but could only guess what other mfgs would do. For example, a 3 blade Performance Propeller on an RV6(mine) 65" diameter x 74" pitch would static at 2400rpm and occasionally reach 2700 rpm WOT straight and level 210mph true airspeed.