Need help with prop for C-90 in J3

[a3holerman]

Hi,
Finally we have completed majoring my C90-8 for my 46 J3C landplane. I bought a new McCauley Cm 7443 for the 65 that is in it last Fall, and it has about 40 hours on it. I was led to believe it would be a simple matter to have my AI do a 337 form to use it on the C90. Seems that ain't so. That prop is certified on a C90 in several aircraft at a length not to exceed 73". The plan was to have New England Propeller cut it down an inch and use it on the C90. The problem is that while the prop is certified on several aircraft with a C90 it is not certified on the J3C with a C90. My AI doesn't think the FAA will buy a 337 field approval.

So I am kinda stuck. I would like to use as long a prop as possible as I have been told that a longer prop will get you up and out better. The only legal prop I see is a McCauley CM 7148. Sensenich doesn't even list a prop for a J3c with a C90.

Any suggestions.......

Thanks for any help..

Tom
Cape Cod

 

[Charlie Aileron]

A friend of mine is running a Sensenich 76AK-2-42 on his J-3 with a 90. He performs real good with it. I believe the Sensenich 76AK-2 prop is approved for the C90 on the Piper type certificate.

 

[Jim Mizer]

J-3 Propellor

Well guy's, I run a McCauley CM7148 on my 46 J-3 with a C90-8. The other day I left the farmstead in under 650 ft at 5500' MSL, 87' F, Two men onboard and 17 gallons of fuel. In cruse it seems to pull it along real nice burinng 4.5gph. This is the only prop I have ran on this plane, maybe there is somehing better, however in my opion this would be a hard one to beat.

 

[a3holerman]

Charlie,
Thanks for the reply. As I read the Univair catalog the Sensenich prop is only certified on a PA-11 with a C90 not a J3. That would probably be a good prop but not quite legal as I see it...could be wrong as I am kinda new to this.

Tom

 

[a3holerman]

Jim,
Thank you for the reply...Can you tell me what rpm you get at Takeoff and what you cruise with?

Thanks

Tom

 

[Jim Mizer]

I cruise at 2150 and I think I'm Truing/indicating around 80 mph, the throttle is not at the 1/2 point of travel, just on the closed side of 1/2 travel. Take off rpm is almost 2300. I have never verified my tach with a electronic one, so I think its accurate.

 

[JimC]

Item 311(C)(10) of the J3 Type Certificate (A-691) allows the following props on a C90-8 engine When mounted on a J3C (a C90-12F is not allowed on the J3C under the Type Certificate -- you'd have to go a 337 or STC for that.):

Propeller Item 5, allows a McCauley 1B90 CM or 1A90 CF or CH prop in lengths between 69 & 71 inches.

Propeller Item 6, allows a McCauley 1A90 CF or CH prop to a 1B90 prop in lengths between 69 & 71 inches.

You fall under Item 5, and your 1B90 CM 7443 prop can be cut, repitched, and restamped to a 1B90 CM71 and repitched as desired, so long as the repitch allows the static rpm limits of A-691 to be met and you also meet the requirements of P-842 (see below). This alteration is compatible with A-691, and you should be able to accomplish the change with only a log book entry, without requiring a 337.

Note that the McCauley Type Certificate (P-842) further restricts you not to go below 69.5 inches in diameter, so you are really limited to diameters between 69.5 and 71 inches in diameter.

I run a 1B90 CM7142 on a J3C powered by an O-200 (approved by 337) and think you would find cutting and repitching your 1B90 CM7443 to a IB90 CM7142 or a 7141 would be an almost perfect match for your engine on a J3. As an aside, my 1B90 CM7142 started its life as a 1B90 CM7443 just like yours did. I don't know where you are located, but I've always gotten good results with Memphis Propeller in Olive Branch, Mississippi (800-844-7767). Price varies from roughly $150 to maybe about $450, depending on whether you just repitch, cut & repitch, or overhaul. Caution -- if you tell them to overhaul, be sure to mention that you may be handpropping and don't want the trailing edge to be too sharp.

Note that McCauley also has a Service Letter out (I don't remember the designation number) that makes several different props functional replacements for conversions, and a copy of that letter can be used as supporting information and might help if you elect to go a 337 route. Also check with Joel at the Cub Club for previously approved 337's if you go that route.

If you haven't downloaded the PDF's for A-691 and P-842, you should probably consider doing so (they are free).
All the best, and good luck with your conversion.
JimC

 

[a3holerman]

JimC

Thank you very much for the reply. It was very helpful and did give me a bit of optimism. The problem I see is that according to my Univair catalog the CM 7443 can only be cut down to 72.5 inches. The 7146 can be cut to 69.5. Maybe there is more to this but that is where I see a problem.

Thanks again
Tom
Cape Cod

 

[a3holerman]

I just called McCauley and I stand corrected. The blank is the same. The length limit is for that particular aircraft so yes a 7443 could be cut to 71".
Now I just need to determine the proper pitch for using it on a C90

Tom

 

[bob turner]

This is a J3? With a few exceptions like Jim C, they are used for fun, not for serious stuff. They are wonderful flying aircraft, and other than plain old fun, are really only suited for primary instruction. Even a C 65 with a wood prop gives you enough performance for a safe flight if you don't overload the thing. The heavy duty mods belong on the Super Cubs that work for a living.

I believe that any wood prop within diameter restrictions is legal, and I also believe that one could get away with almost anything within reason in any case. The only possible hangup might be hull insurance, which in some states might be voided by an incorrect part, but at 25 grand, who needs hull insurance anyway?

 

[JimC]

I agree with Bob about most things and have the utmost respect for him, but differ about this. For about 17 years I flew search and rescue with a J3, mostly along the Mississippi and White Rivers. I found the J3 to be ideal for the work when adequately powered. Much better than the SuperCub, because the J3 will get off over a hundred feet shorter than the 18 and can land and park on softer surfaces when both are using 8.00x4 tires. The 3 can be the ideal working plane. It was for me, for quite a few years. I no longer do search and rescue work, but because of it still have more landings and takeoffs off-airport than on, most of it on soft sand. Nothing could beat an adequately powered 3 for that work. The 65 J3 was inadequate in that role and quite dangerous. An 85 with a flat prop (7438) worked quite well, and a 90 or O-200 would be even better.

Bob, you'll never convince me that a 65 powered J3 would have been adequate for that job. I've tried it. And you'll never convince me that an 85 powered J3 would have been inadequate -- I've tried that too.....
JimC

 

[JimC]

>I just called McCauley and I stand corrected. The blank is the same. The length limit is for that particular aircraft so yes a 7443 could be cut to 71".<

I know. I've done it. It is legal.

>Now I just need to determine the proper pitch for using it on a C90<

If you want the prop to be biased slightly toward climb, go the 7141. If you want it to be biased slighly toward cruise, go the 7142. If you are happy with crappy climb, pitch it greater than 42. If you are willing to risk engine overspeed, make it flatter than 41.

If you don't like it the first time, you can always repitch again it for another $150.
JimC

 

[bob turner]

Jim - you really aren't disagreeing with me - note that I mentioned the work you are doing as an exception to my statement.

If you are in Alaska, hauling tourists and hunters in and out of the bush, may I suggest that an O-200 J3 would be somewhat inadequate? And the man who asked the question is not going to be doing the kind of work you have done; he is simply going to enjoy a superb aircraft. My advice to him is to quit worrying so much, and fly once a day.

I am not a bush pilot. My off-airport landings can be numbered on my hands (all successful). I really like going straight up, but I don't think a 38" pitch is in the cards for me. I admire your work, and your skills as an aerodynamicist. Most of us ought to stay away from sand and gravel bars on the river.

Where I expect disagreement is in my hint that you can probably get away with a transgression now and then. I fly with my door closed once in a while, and that is strictly forbidden. My "bear" is 150% of the regulation Piper bear. And once, a long time ago, I flew with a disc on one side and a drum on the other. I like the discs.

 

[a3holerman]

Thank you all again for the input. JimC, thank you for the advice. I have a question. The McCauley specs call for a 7148 on a J3 with a C90- is that too much pitch? I will be doing a bit of beach work here on the Cape, but yes it is for fun only. I would like to keep the same speed without too much of a fuel burn penalty. It would seem that if a 7148 was called for in the specs that a 42 pitch could cause a bit of overspeed.....

Tom

 

[Alex Clark]

I use a Sench 76AK-6 (74 inches long) with a little flatter than a 40 pitch for float plane work. But mine has been converted to a PA-11 , which while still a J3C on paper has all PA-ll balance points, performance numbers and prop installation.under 311D5

FROM ATC-691
ENGINE item number 311 C-10(10) C-90-8F (landplane, skiplane and seaplane) Use actual weight change
Engine Limits: Takeoff, 2475 r.p.m. (90 hp)
All other operations, 2375 r.p.m. (80 hp)
Fuel: 80 minimum octane aviation gasoline
Oil Capacity 5 qts.
Propeller Limits:
Static r.p.m. (with Item 101, 5 or 6 propellers) at maximum permissible throttle setting:
Not over 2300; not under 1950 for land and skiplane, and and not under 2100 for seaplane.
No additional tolerance permitted.
Diameter:
(a) With Item 5 or 6 propellers:
Not over 71 inches, not under 69.5 inches.
(b) With Item 101 propeller:
Not over 76 inches, not under 70 inches.
Carburetor heat system must be modified to provide required heat rise.
Approved modification made by M. Mullis, York, South Carolina.

PROPS

Propellers and Propeller Accessories
1. Propeller - Beech (Roby) R-002-205 blades +15 lb. (-51)
Eligible on Models J3C-65 (L-4J - See NOTE 5) and J3C-65S
(a) Pitch setting at 27 in. station: Low 13°, High 18.5°
with Items 311C(1), (2) or (3) engines
(b) Pitch setting at 27 in. station: Low 9.5°, High 16.5°
with Item 311C(5) engines
2. Propeller - McCauley 1A90CF or 1B90CM +26 lb. (-51)
Eligible with Item 311C (1 through 6) or Item 311D (1 through 3) engine
Limits:
Static r.p.m. at maximum permissible throttle setting:
(a) Landplane and skiplane:
Not over 2250, not under 1950.
No additional tolerance permitted.
(b) Seaplane:
Not over 2250, not under 2050.
No additional tolerance permitted.
Diameter: Not over 74 inches, not under 72.5 inches
Page 9 of 21 A-691
Propellers and Propeller Accessories (cont.)
3. Propeller - McCauley 1A90CF or 1B90CM. Eligible with Item 311D(4) or 311C(9) engine +21 lb. (-53)
Static r.p.m. at maximum permissible throttle setting:
Not over 2550, not under 1950.
No additional tolerance permitted.
Diameter: Not over 71 inches, not under 68.5 inches.
4. Propeller - Hartzell ground adjustable hub HA12U, blades 7414 to 6814 or 7214M to 6814M. +18 lb. (-51)
Eligible on all models and all engines at diameter and static r.p.m. limits shown on specification
for fixed pitch wood propellers. Where no limits are specified use those of the propeller being
replaced.
NOTE: 7414 blades not eligible on Item 311C(5) for takeoff rating or on Item 311C(8).
5. Propeller - McCauley 1B90 or 1A90. +21 lb. (-53)
Eligible with Item 311C(10) and Item 311D(5) engines.
6. Propeller - McCauley 1A90 to 1B90. +21 lb. (-53)
Eligible with Item 311C(7), 311C(8), 311C(10) or 311D(5) engines.
7. Propeller - Koppers F200/00-73E +30 lb. (-51)
Eligible with Item 311D(5) engine on landplane or seaplane.
Parts List Assembly No 4348.
Low pitch setting 12.5° measured at 24 in. station.
Static r.p.m. at maximum permissible throttle setting:
Not over 2425, not under 2375.
No additional tolerance permitted.
Diameter: Not over 73 inches, not under 71.5 inches.
Installation and operation must be accomplished in accordance with Koppers'
"Installation Procedure and Operating Limitation" No. 33.
8. Propeller - Koppers F200/00-72D +30 lb. (-51)
Eligible with Item 311C(9) or 311D(4) engine on landplane or skiplane only.
Parts List Assembly No. 4369.
Low pitch setting 12.7° measured at 24 in. station.
Static r.p.m. at maximum permissible throttle setting:
Not over 2525, not under 2475.
No additional tolerance permitted.
Diameter: Not over 72 inches, not under 70.5 inches.
Installation and operation must be accomplished in accordance with Koppers' "Installation
Procedure and Operating Limitation" No. 29.

9. Propeller - Sensenich fixed pitch metal model M76AK-2. +24 lb. (-53)
Eligible with Items 311D(5) and 311C(9) engines only.
Static r.p.m. at maximum permissible throttle setting:
No additional tolerance permitted.
Item 311D(5): Not over 2425, not under 1950.
Item 311C(9): Not over 2550, not under 1950.
Diameter: Not over 74 inches, not under 72.5 inches.
10. Propeller - Sensenich fixed pitch metal model M76AM-2. +24 lb. (-53)
Eligible with Item 311D(6) engine only.
Diameter: Not over 74 inches, not under 72.5 inches.11. Propeller - McCauley fixed pitch metal model 1C90-LM7249. +23 lb. (-53)
Eligible with Item 311D(6) engine only.
Diameter: Not over 72 inches, not under 70.5 inches.
A-691 Page 10 of 21
Propeller and Propeller Accessories (cont.)
12. Propeller - Sensenich fixed pitch metal model M74CK +21 lb. (-53)
Eligible with Items 311C(1) through 311C(6) engines only
Static r.p.m. at maximum permissible throttle setting:
Landplane and skiplane only:
Not over 2250, not under 2050.
Seaplane only:
Not over 2250, not under 2100.
No additional tolerance permitted.
Diameter: Not over 74 inches, not under 72.5 inches.
13. Propeller - Sensenich fixed pitch metal model M74CK-2. +21 lb. (-51)
Eligible with Item 311C(8) engine only.
Static r.p.m. at maximum permissible throttle setting:
Not over 2440, not under 2340.
No additional tolerance permitted.
Diameter: Not over 72 inches, not under 70 inches.
101. Propeller - Wood (fixed or adjustable pitch). +9 lb. (-51)

 

[a3holerman]

Alex,
I have read through A-691 and although a bit confusing as I read it the prop you have installed under 311D5 is for a PA-11 not a J3 is that correct?

Tom

 

[bob turner]

On the stock C85 I use a 72GK48 for climb, and a 72GK51 for cruise. The 51 is on there now, and I can tell you that climb angle with two guys is about twice as good as that of a similarly loaded Cessna 152. I can also tell you that I swore off flying 152s with two guys on board, unless fuel is way down. Scares me - an engine failure after takeoff at my home airport might not be survivable. With me on board and maybe 12 gallons, I routinely practice engine failure and return to the airport when at the worst possible point. Tower seems to like it. Loaded Super Cub seems to get to the same point, but slightly faster.

 

[Alex Clark]

Tom,
Yeap, it was approved based upon the aircraft being modified to a PA-11 configuration...
The basis being increased saftey while complying with the intent of the modifying STCs.

Oddly enough the same prop (Sench 76AK-2) is approved for the C-85 while installed in the Standard J-3C configuration.... WHAT GIVES....?

There are a couple typos in that Type cert as well, I'll bet you could get an easy field approval on that prop since it is approved in two other instances...

 

[Jim Mizer]

Tom, Cap Cod; and every one else; I learned alot from this post, thanks.
Tom, I'm getting on a soap box here, I could be on it all day about a 90hp J-3.
Here it is;
"The ground and Climb performance is absolutely awesome! What ever prop you go with, you don't have to turn your plane into the CAVITATION CUB to get it!"
Take care and thanks everyone for the input. Jim

 

[JimC]

The 76AK-2 remains approved on the 85's that have been modified with C90/O-200 cranks and pistions (the engine retains it's 85 designation). That engine dynos about 97 hp at 85 rpm limits, so the prop is certainly adequate for the 90. Has anyone checked to see if Joel has any previously approved 337's for it?

Re the 7148, fly it on the 90 first, to see if you like it as is. If you find it anemic, repitch it then. Shipping cost FedEx ground is about $40 to $50, and the repitch cost is about $150, so testing the prop in its original condition first is reasonably economical. If you are comparing the 90/7148 performance to a 65/7443, you will be much impressed with the 48.
JimC

 

[a3holerman]

The prop I have now is the 7443 and my only option as it is now is to cut it to the legal length of 71" and repitch if necessary. Perhaps I cold leave it at 43 and see how it works.

Tom
Cape Cod

 

[JimC]

That's what I'd do. As an aside, I've run both a 7443 and a 7441 with with both a C85 and an O-200 on the J3 while testing, and the 7441 performed better than the 7443. The 7441 did not do quite as well in any aspect of performance as the 7142. However, I'm turning higher rpm, so you will probably need more pitch to keep you from turning up so much. The 7143 is a good reference to start from. I've not run one of those. Please let me know your numbers after you've flown it.
JimC
P.S. I do know that pistons is not spelled pistions (but, apparently my typing fingers don't....)