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Thread: Help with static RPM

  1. #1
    Kahle76's Avatar
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    Default Help with static RPM

    I have a IV Classic with a 582 gray head, B gear box 2.58:1, Warp 2 blade 70” w/ tapered tips pitched at 10.7 degrees. Static is 5950 RPM short of 6200 RPM. Talking with a few local friends, they seem to think that the engine isn’t producing the HP that it should. History of the engine it had a previous prop strike, rebuilt 7 years ago by a guy in FL who didn’t replace the crank. I assumed he inspected the crank? It then sat in a conditioned room for 5 years. After a few run ups, checked the plugs and it appears that it’s burning rich. Running cool. EGTs 950-1000. Rebuilt carbs replacing all jets and needles with the factory recommended jetting. Did some run ups with no change in RPM. Started stepping down in the main jet size followed by run ups. No change. Did the main jet sep down 4 times with no RPM increase. EGTs did rise to 1100. Did a compression check and it’s OK. Does anyone with this set up run the prop any flatter? Trying to decide what to do next.
    Mike Kahle
    Jackson, MO
    IV Classic 582
    RV-12is building

  2. #2
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    Default Re: Help with static RPM

    Static rpm may not give the exact EGTs or rpms for that matter when you are climbing out. When the prop unloads a bit, and revs go up, EGTs will likely go up some as well. If you have Rotax recomended jets for temp and altitude, you may have to go a bit flatter on the prop pitch. Verify that you are not getting any leakage past the primer if you have one, and that your float setting is not to high. Both of those could cause a richer mixture. I had the same engine and prop on my Kitfox 1 and it really performed. Can't remember what I had the prop set for on static rpm now though. Another thing, make sure your tach is accurate. Tiny tachs are good. The round 2 1/4" tachs are often not very accurate. Here is a link to a temp and altitude correction chart. And it's better to take it for a quick trip around the patch and find that yes it's to rich, then to find out it's to lean as you glide back to a landing with a cooked engine. JImChuk
    Carb_Jet_Cht-2.jpg (847×1053) (challengers101.com)

  3. #3

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    Default Re: Help with static RPM

    My 582 would load up and die on extended idles. Like on final approach! Plugs would foul.

    Cure was to change from #55 to #45 idle jets.

    Changing to fine wire iridium plugs helped as well.
    Building a KF IV Classic

  4. #4
    Kahle76's Avatar
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    Default Re: Help with static RPM

    i have cleaned and replaced the old jets and needles with the factory recommended jets and needles ,except for the main jets which I went one size leaner. Float level was checked. Using the enrichener and not the primer. I have the analog tach and a tiny tach. Both were checked by using a prop tach. When o first picked up the prop from Darryl at Warp, he recommended the starting pitch of 11-12 degrees. I started at 11.5, then 11 and currently at 10.7. Readings were taken at the prop tips as instructed by Warp. I called Warp and talked with a tech guy about flattening the prop more than 10.7 to get the 6200 static and he commented that the pitch should be around 12 degrees and that is the reason I’m hesitant to go flatter than 10.7 and started questioning the strength of my engine and gearbox. Should I just keep flattening the prop until I get 6200?
    Mike Kahle
    Jackson, MO
    IV Classic 582
    RV-12is building

  5. #5
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    Default Re: Help with static RPM

    I never really worry about what the pitch angle is, I just set the prop up for the correct rpm. If it was mine and the engine was running smooth and I had confidence it was going to stay running in the air, I think I would take it around the patch and see how much it unloads in flight. Or if you have a longer runway, you could lift off with the intention of landing further down the runway if you don't like what rpms or egts are doing. Just my random thoughts of what I would do, and in the end, you have to do what you think is right. JImChuk

  6. #6
    Kahle76's Avatar
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    Default Re: Help with static RPM

    Static is 5950. Was able to get a test flight this morning and climb out at 60mpr was 5200-5400 rpm WOT.
    Mike Kahle
    Jackson, MO
    IV Classic 582
    RV-12is building

  7. #7
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    Default Re: Help with static RPM

    In that case, I would flatten the prop till you are at 6250 and see what it does.

  8. #8
    Senior Member 109JB's Avatar
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    Default Re: Help with static RPM

    If you are sure your tach is correct, I would pitch it for proper static and go fly it and see how it does. Just know that when you decrease pitch your EGTs are going to go up.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  9. #9
    Kahle76's Avatar
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    Default Re: Help with static RPM

    Quote Originally Posted by avidflyer View Post
    In that case, I would flatten the prop till you are at 6250 and see what it does.
    Flattening the prop pitch from 10.7 to 9.5-9.7 will be my next step. Flew today and collected some more data. WOT on climb out at 60mpr was 5400rpm. That’s less than static by almost 500rpm. EGTs and coolant temps OK.
    Mike Kahle
    Jackson, MO
    IV Classic 582
    RV-12is building

  10. #10
    Kahle76's Avatar
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    Default Re: Help with static RPM

    Quote Originally Posted by 109JB View Post
    If you are sure your tach is correct, I would pitch it for proper static and go fly it and see how it does. Just know that when you decrease pitch your EGTs are going to go up.
    I’m running a dial tach and a tiny tach. Both read the same and checked against a prop tach.
    Mike Kahle
    Jackson, MO
    IV Classic 582
    RV-12is building

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