Engine Mount Bolt Size

Discussion in 'Steen Skybolt' started by Chuck, Nov 16, 2017.

  1. Nov 16, 2017 #1

    Chuck

    Chuck

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    I was pondering....

    What analysis was done to require the difference in the bolt size between the fuselage and the engine mount for the 360 or 540 engines? I understand it "feels better" but is there any specific justification?

    On a side note, I understand the Pitts S2B/S2C use 3/8 bolts? Please correct me if I am wrong.

    Chuck
     
  2. Nov 16, 2017 #2

    jrs14855

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    Pitts S2B and S2S use 3/8. No reason for anything larger for parallel valve. Angle valve you're on your own.
     
  3. Nov 16, 2017 #3

    Chuck

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    I am planning for an angle valve. Changing to a NAS bolt gains about 25% in both shear and tensile strength.
     
  4. Nov 16, 2017 #4

    PittsDriver68

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    Check out the bolt size used by Extra on the -300's.

    Best of luck,

    Wes
     
  5. Nov 16, 2017 #5

    Chuck

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    Do you know?
     
  6. Nov 17, 2017 #6

    taildraggerpilot

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    You could draw a free body and derive the loads, comparing the 360 and 540. The CAR 3 aircraft certification guidelines should have the factors to use on an engine mount for a given airframe ultimate load.

    One thing to consider in addition to the bolt size you need to consider the differences in the engine mount tube wall thickness and diameters. You may need to perform some column buckling checks.
     
    Last edited: Nov 17, 2017
  7. Nov 17, 2017 #7

    Lotahp1

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    My Ranger uses 1/2”’bolts to mount the mount to the airframe. Just as a comparison...I’m sure it was done just because it makes since heavier engine equals more load on those bolts.
     
  8. Nov 17, 2017 #8

    lanceav8r

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    My guess is that it is a DIN metric bolt. Good luck buying that.

     
  9. Nov 17, 2017 #9

    PittsDriver68

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    The point is that those bolts are holding on a heavy engine that is being flown to +- a LOT of G. If Extra uses a 12mm bolt you can likely be safe choosing to use a 1/2" AN bolt on your homebuilt ship.

    Best of luck,

    Wes
     
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  10. Nov 18, 2017 #10

    Tcraft

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    Chuck, I think that was a 1990's update to the Hale Wallace plans. Maybe some others will chime in. Are there any pre 1990 builds out there with 0540's?
     
  11. Nov 18, 2017 #11

    Chuck

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    All good points. But the question is what analysis was done to support the increase? The S2B uses a -6 AN bolt for the parallel valve engine. Changing to a NAS bolt is roughly a 25% increase in strength. I know it is more complex than that of course. I have a call into Steen to see if they have any information. And I am talking to some of the structures guys at work for help with the analysis, it’s been awhile...
     
  12. Nov 18, 2017 #12

    EAABipe40FF

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    I wonder if anyone has ever bent or broken their -6 bolts? I recall a mount failure as a result of the loss of a propeller blade and it was the welds that failed rather that broken bolts.

    -8 bolts are certainly stronger than -6's but maybe a case of better is the enemy of good enough?

    Jack
     
  13. Nov 18, 2017 #13

    Chuck

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    That’s rather my point. I am not afraid of swapping to -7 or -8 even but if it’s not needed then it’s excess weight
     
  14. Nov 18, 2017 #14

    bf92

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    Dash-6 AN bolts are good for about 8,200 lbs in single shear (60% of tensile). If you have 500 lbs firewall forward, that's about 16-g if all the load went through one bolt. Times that by four bolts, I doubt you are every going to bend or break one.

    Danny
     
  15. Nov 18, 2017 #15

    Chuck

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    That is more my feeling, but needs to be verified of course. Tubing strength is probably the bigger concern.
     
  16. Dec 15, 2017 #16

    Guillermo

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    Hi Guys, does anyone has an AIRCRAFT MANUAL, OPERATING MANUAL, AEROBATIC SPEED for the STEEN SKYBOLT 200 HP .?

    Thank You!!!!!!!!!!!
     
  17. Dec 15, 2017 #17

    jstreat

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    I used 5/8 bolts on a four point. Doug Dodge built based on his experience. Overkill, but will never fail.

    JST
     
  18. Dec 15, 2017 #18

    Chuck

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    I am still working through Tony analysis and will have it checked by another. So far it looks very clear 3/8 will be more than adequate
     
  19. Dec 15, 2017 #19

    Chuck

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    Through my analysis. Thanks to autocorrect
     

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