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Thread: Wood Prop For a 65HP J3

  1. #1
    Grant's Avatar
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    Wood Prop For a 65HP J3

    I have a friend with a J3 who needs a new prop...

    What is the best and totally legal prop for a 65 HP J3 for take off performance?


    We were interested in the Catto but it seems it's not "quite" legal even though it is a wood prop. I'd really like to hear if anyone has had any trouble dealing with an install (A-691 says "fixed pitch wood propeller) I'd like to know if anyone has gotten this done with the FAA or if peope are just reading this and making a judgment call on the Catto being a wood propeller.

    Also Sensenich has the composite ground adjustable props. Has anyone been sucessful in installing one of these on a 65HP J3?


    And finally if anyone has a standard wood prop they are trying to sell just let me know.

    Thanks!

  2. #2

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    CAR 4 allows uncertified propellers on “light airplanes”. CAR4 also defines “light Airplane as being under 1000 lbs gross weight. So, given that, CAR 4 would require a certified prop on a J3.


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    W72CK42 - Sensenich. There is a Floptrop equivalent.

    Some IAs have been known to authorize uncertified props. Find a different IA - dga is correct.

  4. #4
    Grant's Avatar
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    Quote Originally Posted by bob turner View Post
    W72CK42 - Sensenich. There is a Floptrop equivalent.

    Some IAs have been known to authorize uncertified props. Find a different IA - dga is correct.

    I am the IA and DGA is the author of the refrences that I tend to agree with both here and other sites. I can easily find the refrence to the "wood propellers need not be certified" but I am having trouble finding where CAR 4a defines "light airplanes" though. Could you point me to the paragraph number that defines this or a previous CAR that would have defined this? I'm not trying to be obtuse, I just know I am going to be asked the same question.

    Thanks!
    Last edited by Grant; 06-27-2020 at 02:13 PM.

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    Quote Originally Posted by Grant View Post
    I am the IA and DGA is the author of the refrences that I tend to agree with both here and other sites. I can easily find the refrence to the "wood propellers need not be certified" but I am having trouble finding where CAR 4a defines "light airplanes" though. Could you point me to the paragraph number that defines this or a previous CAR that would have defined this? I'm not trying to be obtuse, I just know I am going to be asked the same question.

    Thanks!
    The problem here is that the Type Certificate Data sheet for the J3 is incorrect where it specifies CAR4A as the certification basis. A691 was originally issued in 1938, and CAR 4A wasn’t issued until 1947. It’s kind of hard to design an airplane to a set of regulations that aren’t published until 9 years after the airplane is built! The correct certification basis would be the 1937 version of CAR4, not the 1947 CAR4A. In both the 1937 and 1938 version of CAR 4, 4.01(b) provides the definition of light airplane.


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    Grant's Avatar
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    I found the refrence and have included it below for the next person who has the question.

    Click image for larger version. 

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    Also, some may not know how to find the original cert basis and ammendments. If you ever want to find this stuff go to rgl.faa.gov
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    I think 72/40 would be the climb prop. When I owned a J3 it had a 72/42 on it and performed fine. The new owners put a 72/40 on it for better climb. I didn’t think it needed it, but it’s their airplane.

  8. #8
    Grant's Avatar
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    It's an airplane that I am lucky enough to get to fly so I have my opinions on what "I" want but it's not my airplane either so I want to help him make the best choice. We use it for just bouncing around. We take our kids in it and we will likely never fly it "Heavy". It's a solid airplane with plenty of "Character" so it will see its share of gravel bars and camp outs. There are a few "Shorter" gravel bars and we want to have the best margins and are not concerned with speed.

    The 72/40 is what I was looking for, but is that the Sensenich Wood Prop? If so, I could not seem to find it anywhere...

    Thanks again - This has been a good discussion.

  9. #9
    Richgj3's Avatar
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    Yes, it’s a Sensenich wood prop. Looks just like the 72/42 that was on it, except for the pitch. I guess they got it a couple of years ago.

    Rich.

  10. #10
    Richgj3's Avatar
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    Looks like all 72 inch wood props are special order new from Sensenich. I assume you’re not wanting to spend that much. I guess the 72/42 is going to be the most common used prop for a J3 A65. 72/40 less common.

    Rich

  11. #11
    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    The problem here is that the Type Certificate Data sheet for the J3 is incorrect where it specifies CAR4A as the certification basis. A691 was originally issued in 1938, and CAR 4A wasn’t issued until 1947. It’s kind of hard to design an airplane to a set of regulations that aren’t published until 9 years after the airplane is built! The correct certification basis would be the 1937 version of CAR4, not the 1947 CAR4A. In both the 1937 and 1938 version of CAR 4, 4.01(b) provides the definition of light airplane.
    dga, Is it possible that the CAA amended the Type Certificate for the J-3 after CAR4A was issued to make the "new" CAR4A be applicable to the J-3? If so, the "light airplanes" statement would no longer apply and the "wood propellers need not be certified" would now apply?

    Since the PA-11 is on the same type certificate and was approved on April 30, 1947, it would make sense that the CAA would have upgraded the TC at that time making 4A applicable.
    It is also noted that all of the applicable TCs for the J-3 TCDS #A-691, A-692 and A-698 contain the same note.
    SPECIFICATIONS PERTINENT TO ALL MODELS
    Certification Basis Type Certificate No. 691 (CAR 4a).
    And all TCDS have later revision dates.

    I have nowhere near your expertise in the details of the regulations. It appears to me that there is enough printed/published material which would allow Grant to use the "wood propellers need not be certified" portion of 4A.
    N1PA

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    All the old TCDS are handed down from the old “Inspectors Handbook”, and most only list the TC number as the certification basis without a specific regulatory basis. All the new TCDS list by amendment level what the Cert basis is for each model covered by that specific TCDS. I would love to see an early version of TC 660, 691, 692 and 698 to see if earlier versions call out CAR 4 or 4A.

    It is interesting that the purpose for dividing CAR4 into 4A and 4B was to segregate transport airplanes from small airplanes. It would be nice to see the preamble to 4A to see if it addresses the dropping of the light airplane classification in 4.01.


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    Some more background: The original CAR 4 became effective 11/1/37. The section 4.01 was in all versions of CAR 4 until Amendment 48 on 7/1/1940 when 4.01 became "unassigned". July 1 1942 amendment 4-13 (CAR 4 had been rewriten and the amendment numbers started over again) added 4.01 back in but this time identifying airplane categories Normal, Transport and Acrobatic. CAR 4 was split up into Car 4A and CAR 4B on 11/9/1945.

    I haven't been able to find any reasoning for removing the definition of Light Airplane. I can only thingk that since so few aircraft were certified in the 1000 lb gross weight and under that the CAA decided it wasn't worth keeping that class of aircraft.
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    Another item, from CAM 4 dated July 1, 1938 "
    .01 CLASSIFICATION OF AIRPLANES.
    1. It should be noted that the airworthiness requirements for normal and light airplanes are the same except that in the latter case a rated engine (see 6 CFR 04.60), an unapproved propeller (see 6 CFR 04.61), and light airplane fabric (see ACM 04.415) may be used."

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    Thank you Grant for bring up this topic once again. You are not the only one to have this question of wood props on their mind. I sent a message to my PMI several years ago asking for clarification on this subject. He responded that he would have to research it and get back to me. I'm still waiting.
    I take the lack of response as "I have no idea and don't dare to say anything, so I'll say nothing.". That's telling me to do whatever I feel like, Mr FAA-PMI doesn't know the difference.

    These are the oldest which I have in paper with their revision dates. All of them state certification basis as CAR 4a. This is leading me to believe that it was not an error on the CAA's part to classify the certification basis as CAR 4a. If it was in error, why have ALL of the TCs been changed to CAR 4a?
    A-691 J-3C/PA-11 rev 11/1/77
    A-692 J-3F rev 11/1/77
    A-698 J-3L rev 10/30/53
    A-703 J4 rev 3/21/49
    A-740 J4E rev 2/19/57
    A-725 J-5A rev 10/5/64

    When looking in the aircraft listings at the older TCs, dga is correct as they just list their respective TC number, no particular CAR.
    I respect and thank dga for his analysis of the break down of what reg applies to what. I for one would welcome the opportunity to face my PMI with a copy of CAR 4a and the airplane type certificate with the Propeller - Wood (fixed or adjustable pitch) list as approved. I do not believe that any of my more recent PMIs would be able to refute the use of CAR 4a.

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    Skywagon, I have little faith in the current stock of FAA inspectors and engineers. Each time the ACO assigns me a new advisor, I have to educate them that CAR 4A and CAR 4 predate CAR 3. Since my limitations say CAR 3 and predecessor regulations, they think I’m working outside my delegation when approving stuff that is CAR 3. Very frustrating! Maybe I’ll ask the guy I have now and try and get him to commit to unapproved props for J3s given the strict reading of CAR4A with no definition of light aircraft.


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    I like where this is going . . .
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    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    Maybe I’ll ask the guy I have now and try and get him to commit to unapproved props for J3s given the strict reading of CAR4A with no definition of light aircraft.
    Please do. This is a very obscure regulation in these days when the FAA thinks a small plane is a 737 which the foreign pilots have trouble flying. The question has come up by many of us who do read the TCDS and the old regs. I would not be surprised to learn that most FAA types have no knowledge that airplanes still do use wood props. Every once in a while we come upon a plane which has a McCatto prop on it. So we know that others have the same question.
    N1PA

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    DJ's Avatar
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    This site, with discussions like this one with real experienced and credentialed maintenance guys, is an amazing resource for new IAs working on old airplanes. Thank you so much! Nobody teaches this stuff in A&P school or anywhere else that I've found!

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    Quote Originally Posted by skywagon8a View Post
    Please do. This is a very obscure regulation in these days when the FAA thinks a small plane is a 737 which the foreign pilots have trouble flying. The question has come up by many of us who do read the TCDS and the old regs. I would not be surprised to learn that most FAA types have no knowledge that airplanes still do use wood props. Every once in a while we come upon a plane which has a McCatto prop on it. So we know that others have the same question.
    Email is off to my advisor. I didn’t lead the decision, only referenced CAR 4a, so we will see what he comes back with.


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    Click image for larger version. 

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    Quote Originally Posted by dgapilot View Post
    Another item, from CAM 4 dated July 1, 1938 "
    .01 CLASSIFICATION OF AIRPLANES.
    1. It should be noted that the airworthiness requirements for normal and light airplanes are the same except that in the latter case a rated engine (see 6 CFR 04.60), an unapproved propeller (see 6 CFR 04.61), and light airplane fabric (see ACM 04.415) may be used."
    Not sure how to phrase this question. But, is CAR 4a considered an update to the original CAR 4? If not, then why? If so, then wouldn't it simply supercede CAR 4? Also, since there are several dates on CAR 4, would the latest date take priority if there are discrepencies between two of them?

    Web
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    This question has been asked on other type forums with little consensus. Good to resolve.

    Gary

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    Quote Originally Posted by wireweinie View Post
    Not sure how to phrase this question. But, is CAR 4a considered an update to the original CAR 4? If not, then why? If so, then wouldn't it simply supercede CAR 4? Also, since there are several dates on CAR 4, would the latest date take priority if there are discrepencies between two of them?

    Web
    With aircraft certification, the applicable regulations that apply to a given model are the regulations in effect on the date of application for the Type Certificate, unless the applicant chooses to use a later version of the regulations. Most TC applications are up to 5 years before issuing the Type Certificate. I suspect Piper chose to go with the later CAR 4 in either 1937 or 1938 rather than Aero Bul 7A that was likely in effect when they
    Made application given the TC (691,692 &69 were all originally issued in 1938.

    It all ties back to 21.101 if you want to change something (apply for an STC) imagine if every STC on these airplanes had to meet the current rules? It’s hard enough to show compliance to the old rules, it would be impossible! Imagine, you want to put seat belts in, you would likely need air bag seat belts with current rules!


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