Run-up at 1700 vs. 2000rpm

Discussion in 'Maintenance Bay' started by Ryanb, Feb 16, 2020.

  1. Ryanb

    Ryanb Touchdown! Greaser! PoA Supporter

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    In the Cessna’s we run the engine up to 1700rpm for the mag check. Even in the 180hp 172’s the check list advises 1800rpm for run up.

    In the Archer, the checklist says 2000rpm. Why is this?
     
  2. Velocity173

    Velocity173 Touchdown! Greaser!

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    Same engines? My IO-320 shows 2,000 RPM while the IO-360 says 1,800. Generally my brakes don’t hold well so I do 1,800 in both.:D
     
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  3. Snowmass

    Snowmass Pre-takeoff checklist

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    Since I operate out of dirt strips regularly I might just run up at 1200. You can learn a lot at this RPM as roughness will be detected.
     
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  4. Ryanb

    Ryanb Touchdown! Greaser! PoA Supporter

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    Heh... the brakes don’t hold well in the Archer at 2000rpm either, which was partially the basis for my question. Are there any implications for doing the run-up at 1700 instead of the check list 2000rpm? I can’t imagine there would be...

    The 172S has the IO-360-L2A, this Archer has the O-360-A4M. The M and N model 172’s were both O320’s.
     
  5. Tantalum

    Tantalum Final Approach

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    I've wondered the same.. I've also seen people "to hell with the checklist" and do a full power run up, lean it until it starts to get rough, then go to 1,700 and do the mag check there. The drops were substantial, but within tolerance, and per at least two CFIs this was done to more closely emulate what a real mag failure in flight would be like, and to burn off any gunk

    If you ask me.. follow the checklist. There could be reasons outside the checklist for the different RPM.. maybe Cessna figured 1,700 was "high enough" and would blow less sand and grit onto the tail.. and the Piper dudes figures 2K was closer to flight RPM, or close to the upper end of the what brakes will hold on the ground
     
  6. GRG55

    GRG55 Final Approach

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    Lousy brakes seems a poor excuse for not following the manufacturer's instructions for the runup mag check RPM.

    Different engine models of the same displacement are likely to have different models of magnetos as well. Just because one type says XX RPM doesn't mean it applies to every single engine Lycoming or Continental ever built of the same displacement.
     
  7. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    I recent came across something interesting. Someone did their runup below manufacturer recommended rpm based in a recommendation by their seller. Had a problem with detonation in cruise.

    Punch line. The prior owner did the runup at lower rpm because the detonation would show up at the manufacturer recommended runup rpm.

    sigh
     
    Last edited: Feb 16, 2020
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  8. Tantalum

    Tantalum Final Approach

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    ^unfortunately stuff like that is pretty common in the ga world I've found.. "yeah that's what the checklist / poh says but my plane likes it done like X"
     
  9. MauleSkinner

    MauleSkinner Final Approach

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    When I got my ASES rating, I was taught to do mag checks at idle.

    My guess is that any rpm will work for a functional check, but the max mag drops specified are only an accurate indicator at the rpm specified.
     
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  10. Bill Jennings

    Bill Jennings Touchdown! Greaser! PoA Supporter

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    Because the poh says so?
     
  11. Ryanb

    Ryanb Touchdown! Greaser! PoA Supporter

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    I DO follow the manufacturers instructions, I was just asking why there’s a difference between the two for the same type engine.
     
  12. Velocity173

    Velocity173 Touchdown! Greaser!

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    You’re not gonna see a difference in drop between 1,800 or 2,000 rpm. I get the same drop at both throttle settings.
     
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  13. Dave Theisen

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    Seems like every Cirrus pilot starts the engine at 2200 rpm. What’s up with that? :)
     
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  14. mondtster

    mondtster En-Route

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    I don’t have time to go looking for the reference but I recall Lycoming recommending doing the runup at a certain percentage of total power. I suspect the engine/prop/airframe combination differences may lead to requiring slightly different engine speeds to get the requisite power.
     
  15. Bell206

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    I believe that was for controllable props and was 50-60% based on manifold pressure. Fixed pitch was 1800-2000.
    I seem to recall airframe OEMs also used braking efficiency, etc. with their AFM/POH requirements. From strictly the engine OEMs, Lycoming used the above recommendation and I believe Continental was 1700 across the board.
     
  16. KA550

    KA550 Pre-takeoff checklist

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    That rpm is required to arm all the crutches these drivers need active to be able to fly the airplane.
     
  17. mwagg737

    mwagg737 Pre-takeoff checklist

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    Doing an idle mag check Will yield the same results as doing it at 1700 or 2000. You're not putting enough stress on the engine really truly get an idea of the ignition health.
    Mag xhecks should be done in the air, as close to lop as you can get. This will give you the true health of your ignition system.
    You may find a fouled plug on the ground, but that's about it.


    Sent from my Pixel 2 XL using Tapatalk
     
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  18. Clip4

    Clip4 Final Approach

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    Because the engine manufactures provide a range and the airframe manufacturer selects a value within that range.

    https://www.lycoming.com/sites/default/files/Magneto Drop-Off.pdf

    Fixed pitch propeller). Aircraft that are equipped with fixed pitch propellers, or not equipped with a manifold pressure gage, may check magneto drop-off with the engine operating at approximately 1800 RPM (2000 RPM maximum).
     
    Last edited: Feb 16, 2020
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  19. MauleSkinner

    MauleSkinner Final Approach

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    I’ve been told that with bigger engines, you can mess up the counterbalance if you make rapid power changes.

    (Apparently zero to 2200 rpm in 1.5 seconds isn’t a rapid power change.:rolleyes: )

    Of course, the start that precipitated the comment was a full throttle hot start in a Saratoga, so different airframe manufacturers may have different guidance.
     
  20. Ryanb

    Ryanb Touchdown! Greaser! PoA Supporter

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    Good enough reason for me, just one of those things that make you go “hmmmm....wonder what the reason behind this is?”
     
  21. MooneyDriver78

    MooneyDriver78 En-Route

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    For those with constant speed propellers, it has to be high enough so the prop setting can cause the engine RPMs to vary when we do the prop check.
     
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  22. Southpaw

    Southpaw Pre-takeoff checklist

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    My POH says run up @ 1600 for the 1959 C172, Max Drop 100 RPM.
     
  23. PaulS

    PaulS Final Approach

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    It's tough to hold those FAST airplanes back!
     
  24. Jim K

    Jim K Pre-takeoff checklist

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    Archer & Dakota both get run up at 2000 rpm, brakes hold just fine.... might check your brakes.

    I think the lycoming manual for the o-360 actually calls for 1700, so it must be a piper thing. Kind of like the cessna vs piper lycoming carb heat issue. What's redline on the Cessna?
     
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  25. PaulS

    PaulS Final Approach

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    I just read an article in one of the mags about this. Guy kept getting roughness in the air, but none in the runup. Turns out the POH said 2,200 the guy was doing 1,700 where the issue didn't show up. It was a mag issue. For the Cirrus SR-20, then conti uses 1700, while the Lycoming uses 2200. Don't think the guy in the article was flying a Cirrus though.
     
  26. Ryanb

    Ryanb Touchdown! Greaser! PoA Supporter

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    2700
     
  27. Weekend Warrior

    Weekend Warrior Pre-takeoff checklist

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    I ran up my Warrior at 2000 rpm on a snowy runway today, and the brakes held just fine. I like 2000 especially for winter, as it gives the engine a little more heat before applying full power for takeoff.
     
  28. bluerooster

    bluerooster Pattern Altitude

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    What checklist are you using? My cherokee AFM sez 1800, but the laminated aftermarket one sez 2000. I use 1800, per the book.
     
  29. denverpilot

    denverpilot Tied Down

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    I found a plug wire that fell off. Does that count? :)

    Just so you know, you can turn the Tapatalk signature off in the settings. :)
     
  30. mwagg737

    mwagg737 Pre-takeoff checklist

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    Yes... And, thanks!

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  31. cgrab

    cgrab Pattern Altitude

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    I check my O-320 at 1700 because Orville said so.
     
  32. AKBill

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    I check my O-320 at 1200 mags and carb heat before I taxi, and at 2000 before TO.
     
  33. Doc Holliday

    Doc Holliday Cleared for Takeoff

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    I mag check at 75% according to the checklist, max 7% drop
     
  34. MauleSkinner

    MauleSkinner Final Approach

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    Pops bigger and fluffier that way?
     
  35. Rgbeard

    Rgbeard Cleared for Takeoff

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    The Lance, (TIO-540) is 2,000. I just follow the mfgr's recommendation. If I used 1,700, I doubt the world would end.

    My brakes hold just fine at full takeoff power. (36" manifold, and prop governor is working to prevent overspeed)
     
  36. Velocity173

    Velocity173 Touchdown! Greaser!

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    Did two (IO320/360) separate run ups today, One at 1,800 and one at 2,000. Both resulted in the same rpm drop on both throttle settings.
     
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  37. ktup-flyer

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    Quit skipping leg day and put some muscle on the brake pedals!
     
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  38. NoHeat

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    Maybe a different alternator, that needs to be tested at a different RPM?