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Thread: Prop clearance on a Challenger II

  1. #1

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    Prop clearance on a Challenger II

    I just received and installed new Warp Drive prop blades on my Challenger II. The new blades are 2 1/8" longer than the original ones and only clear the tail upper support tube by 3/4". I am not sure if the originals were cut or not as I bought this plane used. I have pulled and tugged on the engine to try to get the tips to contact the airframe in any way and can not. I have run the engine at full throttle and all seems oK.
    My question is, " is there a set or suggested minimum clearance for this configuration? " I can cut the blades but would rather not after spending $600.00 for them.
    I am running a 70 HP 3 cylinder engine with 3 blade hub

  2. #2

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    cut em,, if ya cut em cut in circle, dont cut square! Cutting a inch want hurt. I have 3 blade warp pusher and tractor prop for sell 910-257-7322.

  3. #3

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    For what its worth, the clearance required is a function of how much your engine moves on its mounts. You would be surprised at the amount of motion allowed by the rubber shock mounts. For example, on startup, during the first few cylinder firings, most engines move around. And since the prop functions as a gyroscope at normal operating rpm, when you pitch up or pitch down, the prop yaws left and right (look up the "right hand screw rule") as the force is translated through that gyroscope.

    So I will offer the guess that you want more than 3/4" clearance.

    Most propeller manufacturers like Hartzell spec a minimum and maximum blade length. The maker of your prop can offer advice as to how much trimming is OK and the best method for your winding up with a properly balanced prop. They will likely even do it for you for a fee. And you do NOT want to fly with an out of balance prop. You will need even more clearance to the tubes if you attempt that. And a parachute....

    Best of luck,

    Wes
    N78PS

  4. #4
    Paul Chaplin's Avatar
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    The FAR's require a minimum distance between prop and aircraft. Look it up. Don't cut the tips from your prop. That is considered a major alteration and, if the manufacturer approves it, must be done by an FAA approved facility (FAR 43). Not even an A&P can legally do this job.

  5. #5
    kscessnadriver's Avatar
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    Quote Originally Posted by Paul Chaplin View Post
    The FAR's require a minimum distance between prop and aircraft. Look it up. Don't cut the tips from your prop. That is considered a major alteration and, if the manufacturer approves it, must be done by an FAA approved facility (FAR 43). Not even an A&P can legally do this job.
    Challenger II is not a type certificated aircraft and as such, most, if not all, of what you posted doesn't apply.
    KSCessnaDriver
    ATP MEL, Commercial Lighter Than Air-Airship, SEL, CFI/CFII
    Private SES

  6. #6
    Paul Chaplin's Avatar
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    One of the biggest reasons home builders get into trouble is that they ignore conventional wisdom and invent their own rules and processes. Granted the Challenger II is not type certificated but that is not an excuse to commit acts that endanger the operator and/or passengers. The point of my posting was to inform and educate.

  7. #7

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    Thanks everyone for your input. First I would like to let you know I have seen the FAR's 25.925 minimum clearance requirements which call for a minimun of 1" radial clearance between tips and structure as well as 1/2" longitudinal from blade to stationary parts of the plane which I will correct by cutting 1" off the new blades as I only have 3/4" from tip to tail tube. I also have contacted the prop manufacturer who has informed me that they can be "cut to fit" using a fine tooth saw blade as they are composit and it will not harm them.
    Safety is a number 1 factor with me and as a ELSA repairman/inspection certificated individual I can do the work log it and certify it. FAR 65.87 and FAR 87.107
    My other alternative is to return the blades and have the manufacturer cut them or build new ones to exact length. This is from the prop builder.
    Last edited by danawalker2@gmail.com; 09-01-2012 at 06:03 AM.

  8. #8

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    The C ll needs an airworthness cert.. As far as blades go i took mine to local wood shop and he made a jig , cut blades and did a wonderful job! Cut in a circumfrance circle ( "rounded on the ends like a circle" ) in his simple jig. Your making a mountian out of a mole hill with the 3 warp blades.

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