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Climb prop C-90

Interesting and thank you for the obs. This is over my job class but I have seen CAR 4 5/1938, Par. 04-61 discussed versus TCDS A-696 Item 1. I suspect those involved weren't as familiar as you with the implications. I know I wasn't as a reader. But that is an excellent point...the question is which Reg pertains? Maybe that has already been answered and any further enlightenment would be appreciated.
This is from the http://www.supercub.org/forum/showthread.php?50672-Best-STC-for-0320-Conversion thread. I suggest that you get in touch with Ben K. (Fat Kid) since he is closer to you than me and likely uses the same FSDO.
PROPELLERS§
4a.597 Propellers. Propellers shall be of a type and design which has been certificated as airworthy in accordance with the requirements of Part 14 of this sub chapter or shall have been approved as airworthy in accordance with previous regulations, except that wood propellers of a conventional type for use in light airplanes need not be certificated. In certain cases maximum engine bore limitations are also assigned to propellers. Propellers may be used on any engine provided that the certified power ratings,speed ratings, and bore of the engine are not in excess of the limitations of the propeller as certificated, and further provided that the vibration characteristics of the combination are satisfactory to the Administrator.

The Catto is a wood prop. Install it and all that is required is a Log Book entry.

Ben K.


As far as PK vs EDO, my intent isn't to imply the PK's aren't without merit in conditions like in the rough marine environment, but...in June 1980 I had the opportunity to fly two similarly equipped C-185's on the job for test purposes. Typical hot and calm Fairbanks day in the low '80's. Both planes were IO-520's with long two blade props that turned tach redline and had similar WFO T/O manifold pressures (logged the info). All-up weight was similar ~60 gallons and one soul. The one with PK 3500's (new in 1979 and latest model as of that date) I'd flown more the previous season than the newer one to me on EDO 3430's. No comparison at partial throttle/high D/A takeoff...the EDO's performed better under those conditions for T/O, and displayed a lesser tendency to pitch nose down on landing on glassy water. The PK's would go about 55 mph max indicated on the water (partial throttle with no flaps); the EDO's accelerated beyond that indicated airspeed if kept on the water. No GPS in those days so the speed may be relative. All history now of course.

GAP
I did a similar comparison test with EDO 3500s and Wipline 3730s. The Wip would not get on the step yet the EDOs flew away, both with the same heavy load.
 
When I was going through this exercise of trying to match a prop to my tweaked 0200 I too was hesitant to purchase a Catto without a comparison. Ms Catto was as helpful as she could be but I still felt like it was a $3000. gamble. With some digging I was put in touch with a guy who is some how affiliated with Catto, he is extremely knowledgeable of cubs and performance, he sent me a Catto 7636 to try, I purchased a 7638 which I'm very pleased with.
I'll leave this up for a spell for those currently interested. Call me and I will pass along his contact info.

Glenn 40M
802-683-7331
 
I had considered getting my 76-36 Catto re-pitched as I am only getting 2500-2550 RPM on takeoff (55mph). Since my O200 is 2750 rpm redline, I assumed I would want to get closer to that number on takeoff….Nicole at Catto told me yesterday that once this prop gets over 2500 rpm thrust falls of rather drastically….I read into this thst they must “cavitate” and although the engine is making closer to rated hp at higher RPM…she said prop performance falls off sharply after 2500. Do any of you have this opinion as well? I’m considering buying a GA Sensenich since I will be on floats next summer. My plane performs well as is, but I will need more umph when I go on floats I think.
 
I had considered getting my 76-36 Catto re-pitched as I am only getting 2500-2550 RPM on takeoff (55mph). Since my O200 is 2750 rpm redline, I assumed I would want to get closer to that number on takeoff….Nicole at Catto told me yesterday that once this prop gets over 2500 rpm thrust falls of rather drastically….I read into this thst they must “cavitate” and although the engine is making closer to rated hp at higher RPM…she said prop performance falls off sharply after 2500. Do any of you have this opinion as well? I’m considering buying a GA Sensenich since I will be on floats next summer. My plane performs well as is, but I will need more umph when I go on floats I think.
Remember, a fixed pitch prop is like driving a car with a standard transmission in just one gear all the time. Whatever pitch you have, it will be a compromise. You have to chose which gear you wish to drive in all the time 1st, 2nd or 3rd.
If you use a 1st gear prop, you will get out of the hole and climb quickly. Then you will go nowhere fast.
If you use a 3rd gear prop, you will get out of the hole and climb slowly. You will cruise faster.
If you use a 2nd gear prop, you will be somewhere between the other two.

A ground adjustable prop will give you the opportunity to choose from one flight to the next which pitch suits your pleasure.
 
But if 2500 rpm is optimum thrust for this prop, and as I approach 2750 (my redline) Nicole says thrust decreases rapidly and results in a net loss of takeoff performance, then how will a ground adjustable help me. This conversation we had yesterday confused my….I understand cavitation….but it seems to me many on here have spun up an O200 to redline with good results. I know she knows props better than me, I’m just looking for a better solution. Does the Sensenich ground adjustable see this same result as rpm goes over 2500? Or is this a Catto only thing? She said she designs the Valdez completion props to optimize around 2500….I said, but I have an O200 which needs to spin up. She said the 2500 still applies. Before I drop another $3k on a prop, I’m trying to see if this translates in real world experience with folks here who have played with props on O200s.
 
Old wives told tales, but they were not always wrong....

Small Continental "C" cases... McCauley 90 aluminum props... From my Champion notebook...

75 hp at 2275 rpm
climb 73x49 102 mph max level
standard 73x51 106 mph max level
cruise 73x53 111 mph max level

85 hp at 2400 rpm
climb 71x48 104 mph max level
standard 71x50 108 mph max level
cruise 71x52 112 mph max level

90 hp at 2350 rpm
climb 71x50 106 mph max level
standard 71x52 110 mph max level
cruise 71x53 114 mph max level

100 hp at 2500 rpm
climb 69x48 103 mph max level
standard 69x50 108 mph max level
cruise 69x52 112 mph max level

Note that in the "real world" the C-90 outperforms the O-200 which equals the C-85's performance. Also, an electron microscope may be needed to differentiate the performance of a C-75 from that of the C-85 or O-200.
 
These are not true necessarily it’s all about the prop…I’ve tried my 76-36 Catto on both my O200 and my C90…the O200 will spin it 100 rpm faster static. And about 150 rpm faster in climb out at 60mph…I talked to Nicole at Catto who schooled me a little when I told her I wanted a re-pitch so I could get closer to 2750 (max rpm) to make 100 hp on my O200….she said the prop loses thrust after about 2500 rpm and you lose climb performance after 2550 rpm…,kinda like cavitation of a boat prop…think slip. Do if my O200 will spin it closer to max thrust than my C90….it stands to reason (all things equal such as weight etc) that The O200 will make more thrust with this prop than my C90. If what Nicole said about their props is true and 2500-2550 rpms is the sweet spot for thrust….she said the curve falls off sharply after that
 
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