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Wooden Spar Citabrias

Discussion in 'AviatorChat.com' started by Chupacabra, Sep 27, 2009.

  1. Chupacabra

    Chupacabra F1 Rookie
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    OK, I understand this topic has caused heated debates among pilots, but...

    What is the general opinion here concerning wood spar Citabrias and aerobatics? I'm using one with the wooden spars right now...about 2,200 TT, spars inspected every 100 hours, no visible cracks or damage as of yet. I'm told the plane was purchased from someone who didn't do any acro with it, but it is a 1970's airframe (I believe from the last year of production for wooden spars), and some of the reading I've been doing lately has me a bit concerned. I'm routinely pulling 3-5Gs in this thing, within limits, but at the top with the +4.5 to 5G maneuvers. I think we all know that bailing out of a citabria is, at best, a 50/50 proposition, especially with no skydiving experience.

    What do you guys think? Should I just trust the inspections or should I can the acro 'til I can afford my own acro machine with metal spars or more G limits?
     
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  3. 2NA

    2NA F1 World Champ
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    #2 2NA, Sep 28, 2009
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  4. Chupacabra

    Chupacabra F1 Rookie
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    OK, there's one vote for "you're going to die"

    ...anyone else?
     
  5. solofast

    solofast Formula 3

    Oct 8, 2007
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    Wood spar Citrabria's are plenty stout, and will live a very long time so long as nobody overstresses them. The only problem is, if it's a rental, you don't know if somebody has and just walked away. Kinda makes me wish there was a telltale on the G meter. If there was I wouldn't worry a bit.
     
  6. James_Woods

    James_Woods F1 World Champ

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    For many years, the Bellanca Viking was just about the only high performance single which had never had a main spar failure.

    As the planes aged, one or two spar failures did occur. The thinking was that wood rot had occurred in planes that spent a lot of time outside. But Bellanca (who made the later Citibrias) certainly knew a lot about wood airframe construction.

    I had the 1969 5190X Citabria 7ECA from about 1980 until 1986 and never gave it any concern. The do have inspection holes to look for rot or moisture and mine was always fine - but I did keep in hangered.

    The only true airframe failure on a Decathlon that I am aware of was due to failure of the horizontal stabilizer - resulting from a failure of the upper bracing on one side. Then the pilot idiotically removed the one on the other side and went ahead and flew an airshow
     
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  8. Chupacabra

    Chupacabra F1 Rookie
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    Woah! Well, I know I certainly won't have that problem. It's true what they say -- can't fix stupid. This plane is always hangared, btw.

    Solofast, the good thing about it being a rental is the fact that I know everyone who does acro in it...everyone being me :) Two acro instructors take it up from time to time, but I've flown with both of them and they are very proficient and don't exceed the structural limits of the airframe. Neither do I, of course...but I just worry (a little) about repeatedly stressing the spars to probably 4G.

    I read somewhere that most of the compression cracks found in wood spar 7KCABs and such were the result of some kind of impact damage during ground loops, etc. I also spoke to an A&P who said he trusts the wood spars more than the metal ones and that the compression failures are kind of an "if you have them, you do and if you don't, you don't" kind of situation. Comments?

    Thanks!
     
  9. Bob Parks

    Bob Parks F1 Veteran
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    Wood does not fatigue, it yields. But unlike metal, it attracts fungi and " rots". A consistently hangared wooden spar'd airplane should be fine if it is regularly inspected and properly designed like the Aeronca and Bellanca airplanes. We flew two Aeroncas that were over 20 years old and both had wooden spars, one built in '42 and one in '46. Both were sound and both were aerobated about.
     
  10. Bob Parks

    Bob Parks F1 Veteran
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    I used the wrong word, " Yield", in this discussion. Wood won't bend or take a "set" as some say. it simply breaks when it reaches the point of failure. I did see a case in a homebuilt where the lift strut bolts had begun to work the wood and enlarged the bolt holes due to inadequate bearing area and the lack of doublers on the spars. It was detected when someone wiggled the wing up and down one day. The owner junked the airplane to everyone's relief. My airplane was destroyed in a mid-air when it was run over by a larger biplane. It was hit in the top center. When I looked at the wreckage I could see where the spar fittings had pulled out a large section of the wooden spar about 18-20 inches in length but the bolts and fittings where okay. The spar was made of 1 inch square laminations of spruce and was in beautiful shape in spite of being 28 years old and having served in the war.
    As long as the spars are inspected regularly and don't sit out in the rain all the time, I WOODEN worry.
    Switches
     
  11. davebdave

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    #9 davebdave, Sep 28, 2009
    Last edited: Sep 28, 2009
    I remember the last time I looped our champ. I was coming out of the bottom of the loop when I heard the unmistakable sound of splintering wood and felt myself drop. In that instant I knew the wing had failed. In the next instant I was sitting low in the seat where the wooden seat strapping had given way. After that I decided not to loop the Champ anymore. I felt like the airplane was trying to tell me something.

    I think most spar cracks/damage are caused by hard landings. Something to think about in a rental.

    You asked for opinions so mine is that I would not exceed 2Gs in a rental Citabria with a wood spar. However, I am probably just getting old. . . like that wooden spar :)

    Dave
     
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  13. snj5

    snj5 F1 World Champ

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    LOL.
    You should see the G meter after a few of my landings. Sink rates can cause some impressive instantaneous G.

    Also, there are also rolling accelerations where pulling while in a roll will generate huge G loads in the wing (lever arm) with low g readings in the cockpit. F-15s have lost a few wingtips to this. I was always taught roll to point the lift vector, stop, then pull.
     
  14. Chupacabra

    Chupacabra F1 Rookie
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    Well, thankfully, this plane is pretty new to the rental fleet. Not many people are flying it without an instructor, too, so I suppose that is a plus. Not a lot of folks interested in tailwheel flying or acro around here (I don't know what is wrong with them :)
     
  15. davebdave

    davebdave Formula 3
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    Interesting, I was also taught to roll then pull for all aerobatic turns. I never considered there might be a purpose other than aesthetics.
     
  16. Chupacabra

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    How about maneuvers like barrel rolls where the roll (obviously) and back pressure are both fairly extreme? Are they likely to cause some additional stress?
     
  17. James_Woods

    James_Woods F1 World Champ

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    The highest number of G that I ever saw on a tell-tale meter was when my friend and I trailered a biplane (wings removed) from one airport to another.

    Just bouncing around on the road built up around + and - 7 Gs.

    We left it that way just for the hanger bragging rights.
     

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