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Next Catto Prop

AX-O

Well Known Member
All,
I put a few pics on my fastback thread regarding the next Catto prop. Figured that I would place this under the "prop" section of the forum so people could discuss it if need be. Pics of the new prop came in this morning.

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For comparison; below are the previous versions.

Prop 3 (all black) and Prop 4 (black/orange)
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Prop 2
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prop 1
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To reduce spanwise flow. Will post a pic later of the actual flow on the prop.
 
Any idea why the fence? Never seen that on a prop before.
craig discussed this at some length in his forum at OSH in 2015. He was excited that it could keep the airflow attached to the "wing". Think of those Cessna wings that have them and what effect they provide. The prop blade is just another airfoil just like the wing.

Hey Axel,
I sent you a PM the other day but haven't seen a reply. Did you see it?
 
Spectacular, I'm looking forward to seeing the performance specs...can you add the Nickel Leading Edge to the propeller?
 
I took these pics after flying home from OSH. I ran into some rain. on the first pic you can see a dirt line originating at the trailing edge of the nickel edge. About the center of the picture. The line shows what the span wise flow is doing as the prop moves through the air. On the second pic (not as good) you can also see it. I am pointing at it with my finger.

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A more dramatic view of it.
oil.jpg
 
Jack Norris

Responding to your build thread and Jack Norris contact. One for your personal history book. He is quite the guy, isn't he. I ordered his book a few years back and said I was at Conti during the Voyager flight. I didn't do anything on it, but Jack was an instant friend. He annotated the book and put some reference comments though out. He called (I was shocked and amazed) and we talked for an hour. Always thinking.
 
Is that evidence of spanwise airflow, or spanwise water flow from centripetal force?

Those pictures don't show what the airflow is like in cruise flight. At the tips, the spanwise flow on the front surface of the propellers
should be directed somewhat towards the prop hub (relative to the flow on the aft surface). At the prop hub, the flow on the top
surface will be directed somewhat towards the tip. Near the center of the blade, the flow on top and bottom will be aligned.

The pictures are interesting, thought. The one with oil looks like it was actually taken in flight. Centrifugal forces are dominant in
creating the "streamlines" in the oil. The airfoil is clearly interacting with the oil and it may be possible to tell certain characteristics
(stall,etc) of the airfoil, but to assume that the airflow is aligned with the streamlines is incorrect.

This is also true for the dirt streaks on the propeller.

I understand that it is possible to use tufts, but care must be taken to size the tufts such that the aerodynamic forces on the tufts
are much greater than the centrifugal ones.
 
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Those pictures don't show what the airflow is like in cruise flight.

There was a video awhile back from someone------Paul Lipps, or Craig Catto or?? who mounted a camera in the spinner and took actual in flight photos of a tufted prop.

Anybody know where to find that??? I looked but no joy...
 
Mike,
The video was taken by craig. He has it in his shop.

Gammaxy,
I have studied that video with craig. What i show on my pics are almost identical angles and behavior to his video.
 
Mike,
The video was taken by craig. He has it in his shop.

Gammaxy,
I have studied that video with craig. What i show on my pics are almost identical angles and behavior to his video.

Which is stronger at 2500 RPM (or whatever): Airflow effects or centripetal force? I don't know, but I'd bet on centripetal force.
 
Am I understanding the claim correctly that airflow over a significant portion of the propeller is almost completely spanwise? What is the airflow on the back side of the propeller like?

For this to be true, the air in front of the propeller would have to be accelerated from rest to the same rotational speed of the propeller and drug around with it while being directed outwards laterally. This would cause an amazing amount of drag along with all sorts of conservation of mass violations (what is the airflow on the back side of the propeller doing to compensate?).

There may be some super thin (microscopic?) boundary layer that due to the viscosity of air DOES behave like the oil (due to centrifugal forces), but it's not the effect that would be controlled with propeller fences nor is it the behavior of the vast majority of the air around the propeller.
 
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re: Jack Norris

Responding to your build thread and Jack Norris contact. One for your personal history book. He is quite the guy, isn't he. I ordered his book a few years back and said I was at Conti during the Voyager flight. I didn't do anything on it, but Jack was an instant friend. He annotated the book and put some reference comments though out. He called (I was shocked and amazed) and we talked for an hour. Always thinking.

I second that. Jack is always interested in chatting with fellow aviators. I just sent him an email and a voice mail to draw his attention to this thread. He was at AirVenture this year and still intends to be there next year, too.

On a related subject, I have some pics somewhere of airflow tracks on a Prince prop that I was testing. The tracks are in the inboard 1/3 of the span. They clearly show that the airflow over the chord is at a significant angle, maybe 30 degrees. I chatted with Craig Catto about this last year. I am of the (inexpert) opinion that most prop designers are not taking this into account because if the flow is at such an angle then the airfoil is a different shape than if it were straight on. Craig seemed to agree and didn't find it very surprising. I think he was way ahead of me. That was the year when he discussed the fence research for the first time, I think.
 
Which is stronger at 2500 RPM (or whatever): Airflow effects or centripetal force? I don't know, but I'd bet on centripetal force.
So would I. Tufts, oil streaks, etc. will all "show" a significant outward spanwise flow because of the centripetal force. It's misleading, and doesn't represent the airflow over the propeller.

When you look at the tip, there should be airflow back towards the center along the top of the blade, due to the tip vortex. Just like you'd see on a wing. But the oil streak photo above shows no tip vortex effects, and that suggests to me that you have centripetal forces grossly exceeding the effects of the airflow.
 
So would I. Tufts, oil streaks, etc. will all "show" a significant outward spanwise flow because of the centripetal force. It's misleading, and doesn't represent the airflow over the propeller.

When you look at the tip, there should be airflow back towards the center along the top of the blade, due to the tip vortex. Just like you'd see on a wing. But the oil streak photo above shows no tip vortex effects, and that suggests to me that you have centripetal forces grossly exceeding the effects of the airflow.
Forgive the question since I am not an aerodynamic engineer. Heck, I didn't even sleep in a Holiday Inn last night. But whether it is centripetal force or airflow that is moving the air, does that really matter in terms of HOW the prop blade is moving the air? Isn't the fact the air is moving in a particular manner the important issue? Not what is making it move in that manner. Please educate me if this is not true.
 
But whether it is centripetal force or airflow that is moving the air, does that really matter in terms of HOW the prop blade is moving the air? Isn't the fact the air is moving in a particular manner the important issue?

For a starter, folks need to get centripetal and centrifugal force correct. Different forces that act in opposition to each other.

http://www.livescience.com/52488-centrifugal-centripetal-forces.html

And, yes I agree that the reason is not the issue, controlling the flow is.
 
For a starter, folks need to get centripetal and centrifugal force correct. Different forces that act in opposition to each other.

http://www.livescience.com/52488-centrifugal-centripetal-forces.html

And, yes I agree that the reason is not the issue, controlling the flow is.
Well see, there you go. I am not an engineer, nor sleeping in a Holiday Inn, but I most certainly was thinking in terms of centrifugal force when reading posts and viewing Axel's photos. I was actually wondering why people were posting about centripetal force. It was mighty confusing to me, but hey, I just figured there were a lot smarter people than me discussing the issue so they must know more than me.
 
does that really matter in terms of HOW the prop blade is moving the air? Isn't the fact the air is moving in a particular manner the important issue? Not what is making it move in that manner.

I think we are attempting to point out that the patterns in the oil (or dirt trails) do not show how the air is moving.

Think about watching rain streaks on your car windows. If you travel slow enough, gravity moves the rain drops straight down the window. As you pick up speed they get angled back, but you wouldn't assume the air flow is angled in the direction of the streaks until you are going reasonably fast.

Now consider that the oil on the propeller blade is subject to > ~4,000 G's outwards from the prop hub (rather than 1G for the water on your window). Also assume that the air flow (what we actually care about) over the propeller is more-or-less aligned with the chord of the propeller and interacts with the oil film through skin friction drag.

Any reasonable set of numbers I try has the centrifugal forces dominating by such an extreme amount (30-100x) that to draw any conclusion that the airflow doesn't travel approximately in the direction predicted by over a century of propeller theory would be premature from the presented evidence.

Here's the equation I derived for anyone who cares to criticize my math. It's probably impossible to calculate an exact answer, but showing that there's really no contest between the two forces is not difficult.

Centrifugal force magnitude at propeller tip relative to aerodynamic force =
4*(oil film thickness)*(density of oil)/((skin friction drag coefficient)*(density of air)*(diameter of propeller))

I estimated .0041 for the skin friction drag coefficient. There's a lot of small numbers in the denominator and only one small number in the numerator (oil film thickness).
 
I think we are attempting to point out that the patterns in the oil (or dirt trails) do not show how the air is moving.

Think about watching rain streaks on your car windows. If you travel slow enough, gravity moves the rain drops straight down the window. As you pick up speed they get angled back, but you wouldn't assume the air flow is angled in the direction of the streaks until you are going reasonably fast.

Now consider that the oil on the propeller blade is subject to > ~4,000 G's outwards from the prop hub (rather than 1G for the water on your window). Also assume that the air flow (what we actually care about) over the propeller is more-or-less aligned with the chord of the propeller and interacts with the oil film through skin friction drag.

Any reasonable set of numbers I try has the centrifugal forces dominating by such an extreme amount (30-100x) that to draw any conclusion that the airflow doesn't travel approximately in the direction predicted by over a century of propeller theory would be premature from the presented evidence.

Here's the equation I derived for anyone who cares to criticize my math. It's probably impossible to calculate an exact answer, but showing that there's really no contest between the two forces is not difficult.

Centrifugal force magnitude at propeller tip relative to aerodynamic force =
4*(oil film thickness)*(density of oil)/((skin friction drag coefficient)*(density of air)*(diameter of propeller))

I estimated .0041 for the skin friction drag coefficient. There's a lot of small numbers in the denominator and only one small number in the numerator (oil film thickness).
Well, the way my practical mind sees this is that given the facts you describe does it still really matter? That is, does it really matter that the air is acting in that particular fashion BECAUSE there is a huge force (centrifugal) that is overpowering another force (natural air flow)? If that centrifugal force is there in the majority of times in which we wish to determine the effects of a particular blade design does it really matter that this huge centrifugal force is what is sending that air in that direction? No matter what is making the air behave in that way, we still want to design a prop blade to take advantage of that air movement. Do we not?
 
Well, the way my practical mind sees this is that given the facts you describe does it still really matter? That is, does it really matter that the air is acting in that particular fashion BECAUSE there is a huge force (centrifugal) that is overpowering another force (natural air flow)? If that centrifugal force is there in the majority of times in which we wish to determine the effects of a particular blade design does it really matter that this huge centrifugal force is what is sending that air in that direction? No matter what is making the air behave in that way, we still want to design a prop blade to take advantage of that air movement. Do we not?

I think the point is it is likely water is moving in that direction, not air.
 
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Forgive the question since I am not an aerodynamic engineer. Heck, I didn't even sleep in a Holiday Inn last night. But whether it is centripetal force or airflow that is moving the air, does that really matter in terms of HOW the prop blade is moving the air? Isn't the fact the air is moving in a particular manner the important issue? Not what is making it move in that manner. Please educate me if this is not true.
That's a valid question, and I agree this might not be intuitive. What's happening is that the air is flowing over the top of the propeller blade from the leading edge of the prop to the trailing edge of the prop. That's how the lift is generated on each blade that acts as thrust.

The oil, however, is much more viscous and is stuck to the prop. Due to centripetal force it is being thrown out towards the tip of each blade, as shown in the photo with the really oily prop. The oil is moving to the tip, but the airflow is definitely not flowing with the oil.
 
That's a valid question, and I agree this might not be intuitive. What's happening is that the air is flowing over the top of the propeller blade from the leading edge of the prop to the trailing edge of the prop. That's how the lift is generated on each blade that acts as thrust.

The oil, however, is much more viscous and is stuck to the prop. Due to centripetal force it is being thrown out towards the tip of each blade, as shown in the photo with the really oily prop. The oil is moving to the tip, but the airflow is definitely not flowing with the oil.
Of course, makes perfect sense now. Thanks.

So then my next question: HOW would one ever be able to measure what exactly the air is doing over a prop with such a huge force obscuring any attempts to observe that flow? Is it now just a matter of entrusting the analysis to some group of physicists who have a string of mathematical equations to plug numbers into? Is there not a practical observational method that would account for this powerful obscuring force?

Ok, so that was more than just one question. :)
 
HOW would one ever be able to measure what exactly the air is doing over a prop with such a huge force obscuring any attempts to observe that flow?
That, my friend, is a question they've been trying to answer for ages.

Near as I can tell, the only way is theoretical calculation. Any physical method of observation would involve something that had mass... Oil drops, water, even tufts have mass that would be "thrown" to the outside of the propeller disc.

I wonder if a smoke trail, streamed into the propellor, and photographed from a rotating camera mounted at the hub, would work... No contact with the blade, you might be able to observe the air flow pattern?
 
The prop showed up today.

At this point, I am not sure I should post results since the reason for the design of the prop apparently is not valid.
 
Test on

G'day Axel,

I like the way you are continuously testing and adjusting your plane to get the optimum performance for your mission. I don't think there is any harm testing the prop and letting folks know the results. If it performs better great, if not try prop number 4 or 5. Its all knowledge, even if it only helps us not try it again. We could argue all day about the theory, why it will or wont work, but flight test is the answer in the back of the book.

Cheers

Nige
 
Huh? Not sure I know what you mean by this statement.

Methinks it is a sideways reference to all the armchair engineers out there who have been explaining how "centripetal" force acts on the prop-------and many of the other comments too.

Or something like that;)
 
The prop showed up today.

At this point, I am not sure I should post results since the reason for the design of the prop apparently is not valid.

Awesome (the first part, hah). Looking forward to seeing that bad boy perform! And I still hope you haven't painted the tail. :)
 
Huh? Not sure I know what you mean by this statement.

What mike said below.
reference to all the armchair engineers out there who have been explaining how "centripetal" force acts on the prop-------and many of the other comments too.

G'day Axel,
We could argue all day about the theory, why it will or wont work, but flight test is the answer in the back of the book.

Cheers

Nige

Ding ding, we have a winner.

And I still hope you haven't painted the tail. :)
there was an update to the primer. different color primmer.
 
The prop showed up today.

At this point, I am not sure I should post results since the reason for the design of the prop apparently is not valid.
I hope you do post results. While the oil-streaks don't show the streamlines the air follow, the air most definitely *does* move spanwise. The fences will help with that, and I would not be surprised to see a performance benefit.

but i'm just an aeronautical engineer sitting in an armchair... :)
 
but i'm just an aeronautical engineer sitting in an armchair... :)

That should give you excellent resources to also perform some tests and report back. Best wishes if you choose to advance the Experimental aircraft community with your skillset.

Break

I looked at the blade profile yesterday and it is a much wider cord than the current prop. This blade looks similar to the all black prop shown on the previous pics. I hope that does not mean that I will loose the 3 kts I gained with the current prop. Flight test will determine that. As much as I want to put that thing on and go. I plan on collecting more data in the current config for RPM-MP-TAS-IAS at different DA/PA in order to compare apples to apples.
 
As i am on the way to Reno i wont tell you the actual TAS but will report this. The new prop is a win! It is more in line with other Catto props for slowing down and taking a bite out of the air on take off.

Ground static went from 2380-2400 rpms to 2180-2200 rpms.

Wide open leaned out rpms went from 2940 to 2860.

The prop slows the plane down as soon as you pull power. I am extremely happy to have this back. It is extremely helpful when flying form.

So now for the actual gains. I flew the plane in the morning at 8000 ft DA landed then swapped the props. Went back to 8000 ft DA. OAT was off by 2 deg f on the second flight. Close enough...

2 kts increase in TAS. More like 2.5 kts as it kept bouncing up and down 1 kt. I called craig and told him to start selling the blade. The plane has never felt this balanced. Will do a prop/engine balance this weekend.
 
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As i am on the way to Reno i wont tell you the actual TAS but will report this. The new prop is a win! It is more in line with other Catto props for slowing down and taking a bite out of the air on take off.

Ground static went from 2380-2400 rpms to 2180-2200 rpms


Hi Axel curious how your takeoff distance and climb rate were afected seeing you had a 200-280rpm decrease in static rpm?


Thanks
Bill
 
Bill, i have to do more testing. I was not targeting takeoffs specifically as i had chts on my mind. I was comparing the cooling. The previous prop raised my chts about 12 deg.

This one put my chts back in line to what i was seing 2 props ago. The nice thing was that i was also able to close my cowl flap all the way vice 1 inch open (adding 18 inch sq to the exit area).

I got off at the same place i always do, right before the captain's bars at 60kts. My tail came up almost imediately after the start of the roll. I was not expecting that.

Although the previous prop could turn faster on the ground, the engine did not feel like it had the same power. Specially during the mag check portion.

Will do more performance testing but for now the priority is max speed and chts/oil temp.
 
This one put my chts back in line to what i was seing 2 props ago. The nice thing was that i was also able to close my cowl flap all the way vice 1 inch open (adding 18 inch sq to the exit area).

Was the 1" difference in cowl flap for climb or your cruise condition.
If cruise, it could be the closed cowl flap that provided teh speed increase instead of the prop.
 
I compared apples to apples. The closed cowl flap, flushed fuel drains, and light covers were independently measured.
 
As i am on the way to Reno i wont tell you the actual TAS but will report this. The new prop is a win! It is more in line with other Catto props for slowing down and taking a bite out of the air on take off.

Ground static went from 2380-2400 rpms to 2180-2200 rpms.
How did the drop in RPM affect your climb rate? Or did it?

The prop slows the plane down as soon as you pull power. I am extremely happy to have this back. It is extremely helpful when flying form.
That would be nice. Although, I remember flying with an RCAF instructor who commented how nice it was to fly behind a propellor vs. in a jet in formation... Pulling the power off on a jet doesn't slow you down until you've already blown through the overshoot... :p

2 kts increase in TAS. More like 2.5 kts as it kept bouncing up and down 1 kt. I called craig and told him to start selling the blade. The plane has never felt this balanced. Will do a prop/engine balance this weekend.
Nice! Catto is definitely at the top of my list when I need to replace a prop.
 
That would be nice. Although, I remember flying with an RCAF instructor who commented how nice it was to fly behind a propellor vs. in a jet in formation... Pulling the power off on a jet doesn't slow you down until you've already blown through the overshoot... :p


So for real excitement, you need to try the Snowbird rejoin: 45 degree angle on Lead, full throttle, then crank the airplane inline at the last second, pull throttle to idle and pop speed brakes. Change underwear following completion of maneuver. My son (RCAF instructor and Standards pilot) has many hours of form in prop (Harvard II) and jet (T-38 and Tutor) aircraft, and he has found the Jets far easier in close form; no compensating for P factor and torque, no prop wash to fight, and the Tutor does have those handy little speed brakes!

My apologies for the thread hijack...back to your regularly scheduled programming.
 
next prop to be tested. Craig wanted to evaluate if the way the blade tip is bent (forward or aft) makes a difference. We were supposed to test today but weather is acting up in CA.

This blade is exactly the same as the one I ran in Reno but with the tips bent aft. We are going to tuff the blade and also use oil flow. I will be using a video camera to record the flow.

break

the current prop did not show any noticeable difference in take off or landing distance over the previous prop. I did pick up 2kts cruising at 2700 rpm at 50 deg LOP. Depending on altitude I can now cruise at 176-178 KTAS burning approx. 7.5 gal/hr.

I climb at 125 KIAS for cooling. At that speed the rate of climb is approx. 1,000 fpm.

Catto does not have the tooling made for the nickel leading edges associated with this blade design. They need to test a few more things before they invest in the tooling. will let you guys know if it made any difference.

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I spent this weekend doing some prop testing with Craig Catto. We evaluated the current prop (with fences) and a new prop/blade (no fences) in flight. We have not had a chance to overlap the video, audio and time stamps yet. We did tuff testing and oil flow testing. The oil/powder made a freaking mess on my plane :( Understand that the inflight pics are at a moment in time and I don't know the test conditions associated yet.

There is a Gopro camera at the end of the crush plate pointing at the blade.

The plan is to continue testing blade designs until he is happy to release. Nicole was telling me that they will release a RV 2017 version based on this testing.

BTW, these are not my props. I bought the one with the nickel edges.

Test set up (current prop, charging camera)
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Test set up (new prop)
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in flight (current prop)
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in flight (new prop)
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Engine start with oil/powder
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after flight
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Nice pics

Is it just me or does the oil flow have centifigal effects as compared to the tufts? I bet the only real comparison would be by the numbers of clean blade prop one to clean blade prop two. Also to me it seems like the tuft and oil test suggest one would want spanwise flow on front side, just saying.
Kudos for doing this testing. Probably hasnt been done in a decade or more; time to push the envelope a little more. I will be buying a Catto prop, if nothing else than to support this grass roots research. Vote with my wallet.
 
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This is superb testing. Thanks for publishing these photos.

Do the tuft positions appear to change consistently with rotation angle? That is, does the prop seem to be strongly influenced by the cowl shape?

Also, if you had a chance to put a spinner on it with a window, I wonder how much of that inboard trailing edge disturbance is related to the lack of spinner.

Dave
 
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