Catto Vs Borer floatplane

[Smith PA12]

I have a Smith PA 12. Ew 1385#, 31's, Atlee3" extended, 0-360, currently running a Mac A200-8244 prop, looking to go to a Catto 8638. With the Mac I cruise at 2350rmp and 103mph. Anyone out there with same configuation that might know what I should expect with a Catto 8638 for cruise and TO?

 

[Bill Rusk]

I have a PA-18 (Javron Experimental) Ew 1052, 31's, 3" extended, 0-360, currently running a Cato 84-43. With the Cato I cruise at 2350rpm and right at 100mph

Hope this helps

Bill

 

[mvivion]

As far as the Cessnas. All the 172S that I have seen have identical mags on both sides. We have 125 of them at least; 20-25 in Mesa alone. The Seminoles have O-360 L2A and they use 4 different mags. PITA to stock 4 different mags for one airplane and all the rest use only one mag.

Lycoming provides accessories as spec'd by the aircraft manufacturer. Cessna apparently decided to make life simpler on these aircraft.

Nonetheless, the long time convention on Lycoming engines was for one impulse coupling, on the left mag. If I'm hand propping any Lycoming, it's left mag only to start......if it has two impulse couplings, no big deal. Hand propping is the most critical time to have the impulse "right".

MTV

 

[JimParker256]

I have a Smith PA 12. Ew 1385#, 31's, Atlee3" extended, 0-360, currently running a Mac A200-8244 prop, looking to go to a Catto 8638. With the Mac I cruise at 2350rmp and 103mph. Anyone out there with same configuation that might know what I should expect with a Catto 8638 for cruise and TO?

Cruise Airspeed calculation based on 100% prop efficiency (slightly optimistic):

Prop pitch (in inches) X RPM X 60 (min per hour) / 12 (inches per foot) / 5280 (ft per mile) = Speed (in MPH)

38" X 2350 RPM X 60 / 12 / 5280 = 84.5 mph
38" X 2550 RPM X 60 / 12 / 5280 = 91.8 mph
38" X 2700 RPM X 60 / 12 / 5280 = 97.3 mph

(By the way, those same calculations indicate that your tach may be reporting a bit on the low side, since it would take 2472 RPM to get 103 mph out of a 44" prop. And that's at 100% efficiency, which is a wee bit optimistic...)

Takeoff distances and climb rates are much more challenging to calculate, and well beyond my simple skills...

 

[cub12]

I have a Smith PA 12. Ew 1385#, 31's, Atlee3" extended, 0-360, currently running a Mac A200-8244 prop, looking to go to a Catto 8638. With the Mac I cruise at 2350rmp and 103mph. Anyone out there with same configuation that might know what I should expect with a Catto 8638 for cruise and TO?

my TCOW pa-12 on bush wheels with the catto 86/38 and 2475 rpm cruise was 95-97mph with the 86/40 same rpm 105-108 mph

 

[Smith PA12]

Cub12, did you see much difference in TO run. I would assume you spooled up to 2600+rpm much sooner with the 38. What is your empty weight on you 12?

 

[cub12]

I never ran a Mac on mine so i can't compare, the T/O run diff on wheels wasn't much between the 38 and 40, that said 95% of my flying was heavy on floats so i stuck with the 38 but i think the 40 would have been fine. my ew on wheels was mid 1200's( i can't remember exactly as i sold the plane last year) with the 38 climbing at 2600-2650 rpm at 75 mph i had a fairly steep deck angle and had to throttle back almost immediately upon starting to leval off to not over speed the engine

 

[roxiedog13]

Cruise Airspeed calculation based on 100% prop efficiency (slightly optimistic):

Prop pitch (in inches) X RPM X 60 (min per hour) / 12 (inches per foot) / 5280 (ft per mile) = Speed (in MPH)

38" X 2350 RPM X 60 / 12 / 5280 = 84.5 mph
38" X 2550 RPM X 60 / 12 / 5280 = 91.8 mph
38" X 2700 RPM X 60 / 12 / 5280 = 97.3 mph

(By the way, those same calculations indicate that your tach may be reporting a bit on the low side, since it would take 2472 RPM to get 103 mph out of a 44" prop. And that's at 100% efficiency, which is a wee bit optimistic...)

Takeoff distances and climb rates are much more challenging to calculate, and well beyond my simple skills...

This is why I questioned if the catto pitch numbers were inches or degrees, many are reporting speeds that are beyond 100% efficiency if the numbers quoted are in inches. Apparently there are a lot of broken tachs ,
props are not pitched like the number indicates or something is wrong with the math. I do believe the math is right other variables somehow are sneaking into the equation.

 

[Farmboy]

I don’t have a dog in this race, and so this may just muddy the waters.

The one time I was able to speak to Craig Catto directly because Nicole wasn’t in the office to stop it, I learned a few things.
~ Catto builds different props in the same size, and so unless you call them with the serial numbers of different props, comparing two props of the same size and pitch can mislead you. Same diameter, same pitch, different chord/blade design, but labeled the same.
~ Props labeled as one thing can be slightly different. I pulled a 7638 off a plane to test on mine, and inside the hub was the signature of a fellow at Catto, signing off the prop as a 7637.

Props have a lot of black art in their designs, so I believe the only truths are directly from the guy that makes it, and/or your exact results of the specific prop mounted on your specific engine mounted in your specific airframe.


Sent from my iPad using SuperCub.Org

 

[roxiedog13]

I have a Smith PA 12. Ew 1385#, 31's, Atlee3" extended, 0-360, currently running a Mac A200-8244 prop, looking to go to a Catto 8638. With the Mac I cruise at 2350rmp and 103mph. Anyone out there with same configuation that might know what I should expect with a Catto 8638 for cruise and TO?

The Mac with 44 inches of pitch should not be able to go faster than 98.23 , the Catto with 38 inches 84.83 . You are indicating 103 for the 44, something is not right as no prop is 100% efficient let alone 105% . If the error remains you would expect to see 98 with the Catto at the same RPM.

Errors could come from inaccurate air speed, tachometer, pitch is not what manufacturer says.

At the end of the day you would expect the Catto to be slower in cruise BUT get out of the hole better and climb better. I will save almost 20lb of weight and provide more efficient cooling .

 

[PerryB]

I've never run the numbers on theoretical pitch before, but it's interesting. Based on the numbers alone, my 82-42 Mac is cruising at 98% efficiency and the 82-39 Catto is defying physics. Any fairly modern fixed-pitch prop has a significant amount of twist/washout down its blade, along with a large variation in cross-sectional blade area. The theoretical pitch is an average number. I think the big difference is simply in how the mfgr. chooses to establish this number. Do they measure pitch at 50% span (diam), median blade area, or something else? I don't know. I CAN tell you that the two props mentioned above perform almost identically in rate of climb, and cruise speed vs. RPM, despite there being a 3" difference in claimed/theoretical pitch.

 

[cubdriver2]

I don’t have a dog in this race, and so this may just muddy the waters.

The one time I was able to speak to Craig Catto directly because Nicole wasn’t in the office to stop it, I learned a few things.
~ Catto builds different props in the same size, and so unless you call them with the serial numbers of different props, comparing two props of the same size and pitch can mislead you. Same diameter, same pitch, different chord/blade design, but labeled the same.
~ Props labeled as one thing can be slightly different. I pulled a 7638 off a plane to test on mine, and inside the hub was the signature of a fellow at Catto, signing off the prop as a 7637.

Props have a lot of black art in their designs, so I believe the only truths are directly from the guy that makes it, and/or your exact results of the specific prop mounted on your specific engine mounted in your specific airframe.


Sent from my iPad using SuperCub.Org

Not just Catto. If you buy a Mac or Sen prop for a small Continental they all start as the same blade for each model and then are cut and manually twisted to the pitch up want. What says they are all pitched the same the full length of the blade each time?

Glenn

 

[hunt/trapak88]

The Mac with 44 inches of pitch should not be able to go faster than 98.23 , the Catto with 38 inches 84.83 . You are indicating 103 for the 44, something is not right as no prop is 100% efficient let alone 105% . If the error remains you would expect to see 98 with the Catto at the same RPM.

Errors could come from inaccurate air speed, tachometer, pitch is not what manufacturer says.

At the end of the day you would expect the Catto to be slower in cruise BUT get out of the hole better and climb better. I will save almost 20lb of weight and provide more efficient cooling .

360 on 35's with 8638, high 80's at 2350.

 

[cruiser]

Not just Catto. If you buy a Mac or Sen prop for a small Continental they all start as the same blade for each model and then are cut and manually twisted to the pitch up want. What says they are all pitched the same the full length of the blade each time?

Glenn

The design spec under their TSO.

 

[roxiedog13]

360 on 35's with 8638, high 80's at 2350.

Max speed with a 38 pitch is 84.8MPH at 100% efficiency. If you are showing high 80's something is wrong. The pitch is more, the tach is wrong, the airspeed indicator is wrong or induced errors.

Think of propeller pitch as cogs on a pedal bike. At a given pedal crank revolution the bike moves forward a fixed distance based on the number of cogs on the front ring and the back ring. There are two ways to make the bike go faster, speed up the pedal speed(RPM) , or change the gearing rings with different cogs , more or less ( same as increasing the pitch or decreasing) .

For a a bike the cogs and pedal cadence produce a speed/distance that is fixed , a propellers pitch and rpm are identical . If a propellers produces a cruise higher than the advertised pitch then something in the chain( excuse the pun) is wrong. It has more pitch( like the bike more cogs) than advertised or the measuring device is wrong.

I think part of the issue is how pitch is measured. Better designs that are more efficient can get closer to 100% but overall every one of them are not . They can be a little less but not more than 100 percent. More than 100% means simply that something is not accurate, to realistically compare propellers that needs to be figured out .

 

[cubdriver2]

The design spec under their TSO.

Yup, as best they can by hand.

Glenn

 

[hunt/trapak88]

Max speed with a 38 pitch is 84.8MPH at 100% efficiency. If you are showing high 80's something is wrong. The pitch is more, the tach is wrong, the airspeed indicator is wrong or induced errors.

Think of propeller pitch as cogs on a pedal bike. At a given pedal crank revolution the bike moves forward a fixed distance based on the number of cogs on the front ring and the back ring. There are two ways to make the bike go faster, speed up the pedal speed(RPM) , or change the gearing rings with different cogs , more or less ( same as increasing the pitch or decreasing) .

For a a bike the cogs and pedal cadence produce a speed/distance that is fixed , a propellers pitch and rpm are identical . If a propellers produces a cruise higher than the advertised pitch then something in the chain( excuse the pun) is wrong. It has more pitch( like the bike more cogs) than advertised or the measuring device is wrong.

I think part of the issue is how pitch is measured. Better designs that are more efficient can get closer to 100% but overall every one of them are not . They can be a little less but not more than 100 percent. More than 100% means simply that something is not accurate, to realistically compare propellers that needs to be figured out .

no offense but your calculations mean nothing to me. Punching in a few constants does not mean each aircraft is the same. I think it's safe to say Multiple ppl with 8638 will attest high 80's cruise at 2350-2400 in a 'standard' cub. Your telling me my gps is wrong in a nocwind configuration? Have you even flown a catto? Is your cub the exact same as mine? I have more incidence in my wing...does hat make it faster or slower...?? How are the wings rigged?? The tach is not wrong, checked. I don't even look at my ASI. I am going off a garmin 495 gps. Maybe I should call garmin and tell them their sh*t is messed up..?? You keep punching in 'desk engineering' stuff and I'll go off real world numbers. Good day.

 

[Carey Gray]

Delete. Shouldn't have wasted my time.

 

[roxiedog13]

no offense but your calculations mean nothing to me. Punching in a few constants does not mean each aircraft is the same. I think it's safe to say Murillo ppl with 8638 will attest high 80's cruise at 2350-2400 in a 'standard' cub. Your telling me my gps is wrong in a nocwind configuration? Have you even flown a catto? Is your cub the exact same as mine? I have more incidence in my wing...does hat make it faster or slower...?? How are the wings rigged?? The tach is not wrong, checked. I don't even look at my ASI. I am going off a garmin 495 gps. Maybe I should call garmin and tell them their sh*t is messed up..?? You keep punching in 'desk engineering' stuff and I'll go off real world numbers. Good day.

Problem is you are taking it personally instead of getting to the root of WHY you are showing higher speed than is possible. Comparing props means all variables have to be understood. As with the bike analogy you cannot stretch gears, it is just not possible .
If you are going 88mph with a fixed pitch prop of at 2350 your pitch is actually 40 or if pitch is actually 38 then rpm is 2450 . A more efficient prop will get closer to 100% but not be more .

What needs to happen for members to make proper informed comparison is accurate information. It would appear that since you consider your variables "perfect" then it is obvious that the Catto propeller is actually closer to 40 pitch by design.

 

[hunt/trapak88]

Now my question is how do get rid of the emails when you keep responding your ridiculous engineer method?

 

[JimParker256]

no offense but your calculations mean nothing to me. Punching in a few constants does not mean each aircraft is the same. I think it's safe to say Murillo ppl with 8638 will attest high 80's cruise at 2350-2400 in a 'standard' cub. Your telling me my gps is wrong in a nocwind configuration? Have you even flown a catto? Is your cub the exact same as mine? I have more incidence in my wing...does hat make it faster or slower...?? How are the wings rigged?? The tach is not wrong, checked. I don't even look at my ASI. I am going off a garmin 495 gps. Maybe I should call garmin and tell them their sh*t is messed up..?? You keep punching in 'desk engineering' stuff and I'll go off real world numbers. Good day.

Not to throw gasoline on the fire, but almost all of those issues you bring up would cause the airplane to fly slower than the maximum theoretical speed of the prop. Since the only source of thrust on a single-engine airplane is the prop, there is zero possibility of the plane actually being able to "outfly the prop" unless the airplane is in a slight descent or dive. That's simple physics. But varying angles of incidence for the wing/tail, varying the CG, tachometer errors, ASI errors – all of those can impact the airspeed in flight, but NONE of them can make your plane fly faster than the prop is capable of pulling the plane through the air...

Personally, I'm leaning towards a belief that the prop is pitched somewhat differently than the numbers would indicate. As someone else pointed out, Catto designs his props with a variable camber and angle of incidence, with the intent to maximize the efficiency at each station along the blade's radius. The numbers do mean something when comparing within the Catto prop spectrum, but may not be a valid as a direct comparison to other prop manufacturers.

Congratulations on having a propeller that seems to be very well suited to your airplane!

 

[roxiedog13]

Not to throw gasoline on the fire, but almost all of those issues you bring up would cause the airplane to fly slower than the maximum theoretical speed of the prop. Since the only source of thrust on a single-engine airplane is the prop, there is zero possibility of the plane actually being able to "outfly the prop" unless the airplane is in a slight descent or dive. That's simple physics. But varying angles of incidence for the wing/tail, varying the CG, tachometer errors, ASI errors – all of those can impact the airspeed in flight, but NONE of them can make your plane fly faster than the prop is capable of pulling the plane through the air...

Personally, I'm leaning towards a belief that the prop is pitched somewhat differently than the numbers would indicate. As someone else pointed out, Catto designs his props with a variable camber and angle of incidence, with the intent to maximize the efficiency at each station along the blade's radius. The numbers do mean something when comparing within the Catto prop spectrum, but may not be a valid as a direct comparison to other prop manufacturers.

Congratulations on having a propeller that seems to be very well suited to your airplane!

That the part these guys don't get. You cannot outfly the prop . If a propeller outflys the prop, the pitch is more than advertised . Is it possible the Catto flexes a little for full power and then flattens slightly for cruise ? In this case the flexing would account for the higher pitch in cruise and thus it's a little faster . Life is not magical, if the numbers don't add up there is a reason .

A friend with a prop shop had a 84 37 Catto on a O-320 it pulled 2200 static and under-performed compared to a Borer 82 42 so he had to reimburse his customer , has the 84 37 on the shelf . I will actually get to try this myself later this year
I expect it will likely perform well on my engine which has a little more HP. Catto is a terrific option if you want great climb, it won't outrun a shorter higher pitched borer though, many have both and use the Borer for cruise.

BTW, everyone is not posting speeds that indicate they outrun the prop , their cruise numbers are more consistent with the stupid math funny enough .Go figure.

 

[roxiedog13]

Now my question is how do get rid of the emails when you keep responding your ridiculous engineer method?

How about trying to come up with a reasonable answer rather than just saying, " that's the way it is." Come up with a flexing blade variable pitch hypothesis or other reasonable answer otherwise you are not trying to figure out the reality. The simple math is not ridiculous it is actually dead simple kindergarten level . A prop cannot go faster than the numbers otherwise something else is at play, it obviously is here , you are the one that needs to come to terms with that .

I'm not saying your are wrong, you seem to take this personal, that was never the intention . The catto is a great prop for experimental s for many reasons, and for cubs it makes a wonderful climb prop. As good as it is however, it is not magic , other props do better in their respective areas , great there are choices .

 

[hunt/trapak88]

You said 2x the numbers I posted are impossible due to your math. Are you saying I don't know how to read a gps? I'm not gonna bicker and banter. The price of tea in china means more to me. This started with me asking about how props pull. Not if my cruise speeds were correct or not. Everyone else that has a 38 catto at 86" must be wrong too. The cruise numbers on the ONLY person who posted a pull test AND cruise numbers, matched my cruise exactly when I had a 8436 on a 320 cub. Thank you to those who posted valuable info

 

[C-FIJK]

So with this said would a 84-36 be the best option for a stock 150 hp on a exp pa 12 ?

Thanks

 

[roxiedog13]

You said 2x the numbers I posted are impossible due to your math. Are you saying I don't know how to read a gps? I'm not gonna bicker and banter. The price of tea in china means more to me. This started with me asking about how props pull. Not if my cruise speeds were correct or not. Everyone else that has a 38 catto at 86" must be wrong too. The cruise numbers on the ONLY person who posted a pull test AND cruise numbers, matched my cruise exactly when I had a 8436 on a 320 cub. Thank you to those who posted valuable info

The topic is Catto vs Borer Floatplane . I'm seriously considering replacing my Borer with a Catto as an option . If I'm going to spend a load of money on a new prop I would like to think I am spending my money wisely so I look at the options very carefully to ensure the value is there , I'm sure others are interested too.

I'm sorry you are taking issue with me asking why your 38 inch prop does more than a 38" prop should. I was never saying you are falsifying the information , just trying to get to the bottom of what variables overall in the design of the Catto deviate from what we understand in terms of propeller pitch as it relates to speed and climb performance, in order to make a educated , scientific comparison, ultimately an informed decision .

Your prop is 84" with 38" pitch as we understand the physics and the way props work then at 2350 Rpm IT ABSOLUTELY cannot go faster than 84.84MPH , in fact with slip it WILL be less. To go high 80's as you say is the case then your prop will have to be pitched 40-42 another absolute fact.

I'm interested in learning what are the variables that are different so I can make a appropriate informed decision . Thanks to the many others that I have corresponded with , I do have a better understanding and good feel for what is going on, their approach seems to be more in line with mine and their feedback substantiated with logic , more importantly in a adult like manner .

 

[roxiedog13]

I had a friend put a 84 37 on a stock O-320 he managed 2150 static went back to his 82 43 borer . For sure go with 84 36 if anything , do your homework first , you money.

Can you actually use a Catto? Are you in the owner maintenance category ? Lastly, what are you using now?

 

[BC12D-4-85]

This is posed as more of a question for consideration than a statement. The fixed propellers I'm familiar with have a variable pitch depending on station from the hub. The metal props may have staged pitch changes (three or ?) versus a continuous change, a visible product of the mechanical bending process after manufacture. Want a different pitch at 75% radius or the tip? Prop shops try to deliver with a bending tool.

But they may also have variable airfoils "blended" along their length and a continuous change in pitch if made from wood or non-metal composites. Machines form the blades by milling and whatever so they can be whatever shape the designer wants.

The question: So even if the prop is spec'd as a pitch in inches at a station (typically 75%?) there is a portion of the prop blades toward the center hub that often has a greater pitch or maybe different airfoil from what I've seen. Could that inboard portion add to airspeed over what formulas that use the 75% portion pitch say is capable of producing?

Gary

 

[roxiedog13]

This is posed as more of a question for consideration than a statement. The fixed propellers I'm familiar with have a variable pitch depending on station from the hub. The metal props may have staged pitch changes (three or ?) versus a continuous change, a visible product of the mechanical bending process after manufacture. Want a different pitch at 75% radius or the tip? Prop shops try to deliver with a bending tool.

But they may also have variable airfoils "blended" along their length and a continuous change in pitch if made from wood or non-metal composites. Machines form the blades by milling and whatever so they can be whatever shape the designer wants.

The question: So even if the prop is spec'd as a pitch in inches at a station (typically 75%?) there is a portion of the prop blades toward the center hub that often has a greater pitch or maybe different airfoil from what I've seen. Could that inboard portion add to airspeed over what formulas that use the 75% portion pitch say is capable of producing?

Gary

View attachment 36019
The diagram above clearly shows how variable and blended most aircraft propellers are from the root to the tip. It's quite obvious that pitch can be variable, question is, how do different designs distribute and how do they determine this number for their published performance specifications .

Well, I couldn't resist, so I called a friend in the business for 50 years, this is what he told me how the process is done with a Mccauley .

The technician explained to me that for the Borer they actually perform a 6-7 station pitch distribution process for the Mccauley propellers. They go by a guide that is supplied by the manufacturer, the pitch given as degrees at each station . In a nut shell the Borer prop is twisted so that each station is precisely the pitch in inches it is supposed to be . Essentially the prop is a constant pitch distributed along the blade at various stations . To me this indicates the certified propellers are likely more honest in terms of true pitch , who knows what others do.

My Borer is 45 pitch at 2400 RPM I cruise around 95MPH, theoretical speed 100% efficiency would be 102.6MPH. I'm running about 93% which is typical for most considering slip and drag. In my case if I were to report a speed higher than 103MPH then I have a greater pitch than is indicated or other variables such as inaccurate instruments or recording errors have been introduced. ALL propellers should run less than the theortical speed if the pitch indicated is accurate throughout the blade length , impossible to outrun the bade.

This is why comparing props of equal length and pitch is not always apples to apples. One manufacturer is more honest to the pitch others probably using a blended average of their own design .

45inches means a prop moves 45 inches in one revolution , if the number is honest that is . The only way around this is variable pitch of some kind be that hydraulic or torsional .

 

[BC12D-4-85]

roxiedog13 thanks for the reply and info. My question was posed to see if it's possible for a prop...composite Catto in this example and discussion...to exceed the theory of advance based solely upon a pitch value. Like are there other factors in design that would allow the plane to go faster than the specified station pitch theory allows? If so that may account for what's being debated. Maybe Catto or Whirlwind or ? would know? If yes then that's info. If no then maybe the pitch info is incorrect or the fixed prop's changing pitch in flight as you mention. Not a big deal but it is worth asking.

Gary