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I am new to the Kitfox / Rotax world.  I have not been able to find the answer to this question.  Kitfox SB #17 references  that a Rotax engineer says that the Kitfox III side rail engine mount for a LC582 should only be used with a type C gearbox with 3 to 1  gear ratio and not a higher ratio of 3.47 or 4 to 1.  Unfortunately there is no justification declared in the SB. '

Is it acceptable to use a type B gearbox with 2.58 to 1 ?

I am aware of the torque loading difference between the type B and C gearboxes but cannot figure out why a 582 with a type B gearbox is ok on one mount and not the other.

Can someone clarify that for me ?

Much thanks,

Avmech

 

 

 

 

  • Re: Rotax 582 Kitfox SB#17 Type B Gearbox

    by » 5 months ago


    Hello Michael

    i have worked on many 2 stroke Kitfox aircraft in my time.  This information is not from an SB of Rotax and I have never seen the Kitfox one you refer of.  When I search the Kitfox SBs it will not download.  Perhaps you can post it here. 

    It would appear this was in regards, based on your comments,  to be a prop matching issue to the model 3.  (3 to 1 ratio only) At that time Kitfox supplied CGS props with the kits and they were a custom profile then for Kitfox.  It may also be related to different position hole placement for the Kitfox mount to the mounts found on the gearbox.  I would contact John McBean at Kitfox and see if he can recall what that referred to. You can get their contact information online. 

    Cheers


  • Re: Rotax 582 Kitfox SB#17 Type B Gearbox

    by » 5 months ago


    Here you go.

    37714_2_Kitfox M3 SB-17.pdf (You do not have access to download this file.)

  • Re: Rotax 582 Kitfox SB#17 Type B Gearbox

    by » 5 months ago


    Thank you Eric

    I did also contact the folks at Kitfox and they sent copy as well.  In short the recommendation for the 582 C gearbox with 3 to 1 ratio was the best match for that prop at the time, As I recall they used a 68* GSC prop back then.   The factory never did supply any C boxes with the other ratios.  i am sure with the available props in the market now something better might be found, it has been a long time since this was ever reviewed I think.

    If you use a B gearbox with 2.58 ratio you will need to do some prop matching for sure. i think the issue was the big round cowl needed the larger diameter to work correctly to drive the air.  The 2.58 with the smaller diameter prop would not be as efficient.  A 68 inch might work, depends on the prop type and profile. 

    Cheers


  • Re: Rotax 582 Kitfox SB#17 Type B Gearbox

    by » 5 months ago


    I'm not sure the cowling profile is the issue.  The bottom support engine mount uses the same cowling and is not mentioned in the SB, only the side rail type mount.

    The only thing I can assume is the 3 to 1 and above gear ratios are swinging much larger props and require the higher torque gearboxes with the internal dampers to relief stress on the engine mount isolators.

    I have the GSC with the 66 inch 3 blade wooden prop. It is my understanding that the torque loading is within the rating of the B type 2.58 to 1  gearbox.

    Kitox was unable to provide me with the justification the engineer was using to support his recommendation.  That information seems to have died with Denney Aero Craft Co.

    I think I will be ok but I would like to upgrade to a type C or E but that seems to be an issue of availability these days.

    Thanks for all the help.

    Avmech

     

     

     


  • Re: Rotax 582 Kitfox SB#17 Type B Gearbox

    by » 5 months ago


    I think the requirement for a C box with the sidemount bearer better centralises the prop hub in the round cowl aperture...the earlier Mk2 kitfoxes with 532 engines mounted on a bottom mount was not centered well in the cowl

    I have read that the 3:1 ratio prevents amplification of natural frequency of vibration of combined crank, transmission, and prop...Earlier Models were also lacking the vibe damper "doughnut" from the drivetrain.


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