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Thread: Prop Length with 26” tires

  1. #1
    Utah-Jay's Avatar
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    Prop Length with 26” tires

    I am planning on a 82” Sensenich GA prop, will I have enough ground clearance with the 26” tires paired with a 10” tailwheel. I really want the longer prop. I will be doing a lot of dirt and gravel strip landings. If it matters it is a Bearhawk Companion, which is the same fuselage as the Bearhawk 4 Place

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    If it helps you any, the STC to put Borer prop on a PA-12 requires either 3" extending pa-18 gear OR 8:50's , no mention of tailwheel.
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    Utah-Jay's Avatar
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    Quote Originally Posted by MT12 View Post
    If it helps you any, the STC to put Borer prop on a PA-12 requires either 3" extending pa-18 gear OR 8:50's , no mention of tailwheel.
    I believe the 26’s or 4” larger diameter than the 8.50’s, so only 2 inches.

    Hmm, as I thought this is a close call.

    How different is the 80” to the 82” in takeoff performance?

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    Bearhawk Builder's Avatar
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    Your crank center will be at 61-62 inches

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    Utah-Jay's Avatar
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    Quote Originally Posted by Bearhawk Builder View Post
    Your crank center will be at 61-62 inches
    So 20” clearance? Figures you would know. Dave do you think the 82” is ok, or should I play it safe with the 80”? Really only 1” difference ground clearance between the two.

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    Quote Originally Posted by Utah-Jay View Post
    I believe the 26’s or 4” larger diameter than the 8.50’s, so only 2 inches.

    Hmm, as I thought this is a close call.

    How different is the 80” to the 82” in takeoff performance?
    If you’re talking about Goodyear 26 inch tires, they are no more than an inch or maybe two taller than 8.50s.

    MTV

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    Cfr 25.925

    (a) ground clearance. There must be a clearance of at least seven inches (for each airplane with nose wheel landing gear) or nine inches (for each airplane with tail wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level takeoff, or taxiing attitude, whichever is most critical. In addition, there must be positive clearance between the propeller and the ground when in the level takeoff attitude with the critical tire(s) completely deflated and the corresponding landing gear strut bottomed.
    Compressed gear in a level flight attitude is what matters. On certificated planes there’s no wiggle room. I have no idea how part 25 applies to experimentals.

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    Utah-Jay's Avatar
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    Quote Originally Posted by stewartb View Post
    Cfr 25.925



    Compressed gear in a level flight attitude is what matters. On certificated planes there’s no wiggle room. I have no idea how part 25 applies to experimentals.
    Steve Pierce mentioned to me that his Cub buddies love the 82” prop, but they might have 29’s to 35” tires. Certainly I am trying to get it figured out.
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    Probably 31s or 35s on 3” extended gear. When you get a prop that pulls hard you’ll want to increase AOA to take advantage of it. It’s a slippery slooe.
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    When I changed from Goodyear 8.50 to heavy tread 26 inch ABW my FX-3 80 inch prop clearance (3 point, uncompressed gear, normal inflation) increased from 22.75 inch to 25.0 inch.

    CubCrafters requires minimum tire size 29 inch ABW for 83 inch prop on FX-3. Unofficial numbers from CubCrafters show 3.3% increase in static thrust for 83 inch vs 80 inch Trailblazer prop.
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  11. #11
    Gordon Misch's Avatar
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    82" prop on 8.50's is fine. At least some STCs for the 82" Borer prop specify 8.50's or greater. I've run Borer prop on 8.50's for well over 40 years, no problem other than a couple I made all by myself.
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  12. #12
    Bearhawk Builder's Avatar
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    I’m putting an 82” on this latest Patrol for the same reasons. Big pull sacrificing a little cruise With the Bearhawk gear it will be fine Jay You’ll end up with 31s anyway��

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    Steve Pierce's Avatar
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    Here is a starting point of what the FAA requires on a certified airplane.
    There must be a clearance of at least seven inches (for each airplane with nose wheel landing gear) or nine inches (for each airplane with tail wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level takeoff, or taxiing attitude, whichever is most critical.
    Steve Pierce

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    Quote Originally Posted by Bearhawk Builder View Post
    I’m putting an 82” on this latest Patrol for the same reasons. Big pull sacrificing a little cruise With the Bearhawk gear it will be fine Jay You’ll end up with 31s anyway��


    Thanks Dave

    I am willing to give up some cruise for STOL to get in and out of short spots I want to fish. There was an amazing strip in Idaho this week that I could land (morning) but no way I felt comfortable about an afternoon high DA takeoff with only 800’ and a river right at the end of the strip. As for the 31’s, hmmm, not sure as I want to have decent visibility over the cowling and I will only be landing on dirt/gravel/grass strips for my off pavement excursions. Bottom line, as long as I can cruise at 125 mph TAS or higher I am happy.

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    Sounds like you need a 180.
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    Quote Originally Posted by stewartb View Post
    Sounds like you need a 180.
    I am not surprised by this but I want experimental and tube and fabric

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    Quote Originally Posted by Utah-Jay View Post
    Steve Pierce mentioned to me that his Cub buddies love the 82” prop, but they might have 29’s to 35” tires. Certainly I am trying to get it figured out.
    I have that prop on my cub with standard gear and 26 inch goodyears.
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  18. #18

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    Quote Originally Posted by farm_boy252 View Post
    I have that prop on my cub with standard gear and 26 inch goodyears.
    Do you like the prop? Has it stayed clean with the minimal clearance?

  19. #19

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    yes I do. Made a day and night difference in performance (take off/climb). I have 250ish hours in and its still clean yes, about 1/4 of the time on floats. I only recall once when it was a little green from long grass, definitely no issues in terms of big nicks or wear. Hard to tell clearance I guess as prop is not vertical but thats her.

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