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Thread: Spinner Bulkheads - Again!

  1. #1

    Spinner Bulkheads - Again!

    Haven't seen another response to this yet, so I'll toss out three cents.

    I have not read an authoritative analysis of all of the causes of spinner and backplate cracking. On the assumption that the parts are correct for the application and are properly made, I suspect three primary factors, in this order:
    (A) Badly unbalanced prop (includes an unbalanced spinner)
    (B) Improperly fitted/installed prop and spinner combo
    (C) Internal engine imbalance

    My belief is that Beech requires replacement of spinners and bulkheads as a balanced assembly; a practice that is apparently widely ignored. There is normally a set of index marks (or index labels) inside the spinner and on the bulkheads, showing how to orient them during assembly to retain balance. I don't know whether a spinner shop like ASEI (link on BAC; more info at bottom of this note) performs rebalancing following repairs, but I suspect that they do. You can check with them before buying new parts. They may also be able to aid diagnosis.

    If the prop has been field-dressed repeatedly for nick repair, and has never been re-balanced, it is almost certainly out of balance. It doesn't need frequent re-balancing; but metal removal during dressing, despite efforts to stay consistent on both blades, eventually leads to the need. While the spinner assembly should first be balanced "standalone", the final prop balancing will include the backplate. The final check may or may not include the spinner itself, depending on the equipment being used.

    The spinner is (normally) supposed to be a snug fit over the bulkheads. It should almost require some hand-slapping to get the holes to line up. This is also true of spinners on Hartzell constant-speed props, where the prop dome serves as the front bulkhead pilot. Heavy-duty Mylar packing tape (like the premium 3M brand) can be used for shimming out clearances. Don't bother trying to get by with the usually thin junk Mylar tape that tears easily; it will rapidly chafe away. If you can easily slip your spinner on and off, it is probably too loose on the bulkheads. In addition to this factor, many of the spinners are supposed to have Nylon washers under the heads of the spinner screws. This allows stresses to equalize, rather than concentrating them at a tight screw. Very seldom do I find the Nylon washers on the spinner screws. The parts book must be checked for your application. I am out of town without my books. I don't see a reference to Nylon washers for the 1963 spinners, in the poor images in the BAC 1963 IPC download. You might want to verify that the bulkheads have the proper high-strength AN525 washer-head screws. Also that the spinner screws are correct; if they have been replaced with stainless-steel screws, they should be the proper heat-treated aircraft-grade SS, not the cheaper commercial-grade access panel SS screws. Contrary to popular belief, not all SS hardware is created equally. For that reason, not all of it is equally legal for aircraft applications. Probably half or more of the SS hardware you see on planes is technically illegal for the application, as it is not a MilSpec hardware grade.

    And finally, if the engine has dynamic counterweights and they become de-tuned (too long a story to explain here), they can produce vibrations that lead to cracks, thrown alternator belt/broken alternator brackets, etc. That doesn't apply to a 1963. You can look up your engine suffix letters and decode them, to see whether your engine has this form of internal balancing.

    ASEI is located just 1/4 mile south of Hartsfield Atlanta International Airport. Phone: 404-559-1946, Fax: 404-559-1975 Hours 9:00am - 6:00pm EST Monday through Friday




    ---------- Original Message ----------------------------------
    From: "Paul Edwards and Sheril Kolenda" <sparknco@velocity.net>
    Reply-To: Sparknco@velocity.net
    Date: Mon, 26 Dec 2005 15:34:44 -0500 (EST)

    This note is aimed primarily at the IA-guru types, Bob and Mike, but
    obviously, anyone else with insight or suggestions is welcome to jump in.

    As some of you may remember from a couple of my posting a little over 2
    years ago, we jumped through quite a few hoops to replace the spinner and both spinner assembly bulkheads on 2388Z. Well, you can imagine Don Eddey's (my local IA) and my surprise (and fear!) late last week when we pulled the spinner as part of the annual and discovered several cracks around the bolt holes, particularly on the forward bulkhead. The cracks are severe enough that they must be "addressed" before 88Z flies again. That said, here are the questions?

    Question 1: Can a '63 A-23 be flown without a spinner? Is it required
    for engine cooling?

    Question b: I'm surprised that such a new (installed late '64 <Ed. 94?>) and low time (certainly less than 200 hrs) bulkhead should have any cracks! Might there be something else wrong that is caused these stresses? How might we go about diagnosing the situation?

    Question iii: Anyone out there just happen to have spare forward and rear spinner assembly bulkheads for a '63 sitting around their hangar? Or know of anyone who might? I'm pretty sure I got this set through Arrell Aircraft, so I'll be contacting them ASAP.

    Just think folks, the days are getting longer now, so spring can't be far behind! (WINK!)

    Paul Edwards and Sheril Kolenda
    2388Z at ERI



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  2. #2

    Spinner Bulkheads - Again!

    > Haven't seen another response to this yet, so I'll toss out three cents.
    >
    > I have not read an authoritative analysis of all of the causes of spinner
    > and backplate cracking. On the assumption that the parts are correct for
    > the application and are properly made, I suspect three primary factors, in
    > this order:
    > (A) Badly unbalanced prop (includes an unbalanced spinner)
    > (B) Improperly fitted/installed prop and spinner combo
    > (C) Internal engine imbalance
    >
    > My belief is that Beech requires replacement of spinners and bulkheads as
    > a balanced assembly; a practice that is apparently widely ignored.

    *** And indeed, Beech does list individual parts.

    There
    > is normally a set of index marks (or index labels) inside the spinner and
    > on the bulkheads, showing how to orient them during assembly to retain
    > balance. I don't know whether a spinner shop like ASEI

    *** I just got my spinner back from ASEI. The original marks and painting
    on the inside of the spinner seem to be intact.

    > The spinner is (normally) supposed to be a snug fit over the bulkheads.
    > It should almost require some hand-slapping to get the holes to line up.
    > This is also true of spinners on Hartzell constant-speed props, where the
    > prop dome serves as the front bulkhead pilot. Heavy-duty Mylar packing
    > tape (like the premium 3M brand) can be used for shimming out clearances.

    *** How about teflon anti-chafe tape? I just happen to have a roll of this.

    many of the spinners are supposed to have Nylon washers under the heads
    of the spinner screws.

    *** My understanding is that the washers are actually fiber. I just went
    across the street to the Cessna store and asked for 22 "#10 Spinner
    Washers". I would have ordered the Beech part, but there is none in the
    parts list.

    - Jerry Kaidor ( jerry@tr2.com )


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