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Thread: Static pull test results

  1. #1

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    Static pull test results

    Static pull Data

    Husky
    Roller Cam O360 with 3 blade MT
    Pulled 732 LBS. at 2700 RPM, 55F, 125 MSL

    Exp. Super Cub
    O320 E2D with 9:1’s, Avstar Carb, Prop is a 74DM6 0 56 , 1 Surefly E mag, 1 Slick standard on other
    Pulled 484 LBS. at 2350 55F, 125 MSL

    PA 12 with Kenmore 160HP
    O320 A1B Prop is a 74DM6 0 56
    Pulled 450 LBS. at 2350 55F, 125 MSL

    * PA 12 Kenmore with 150 HP, 1 Surefly E mag, 1 Slick standard on other
    O320 A1B Prop is a 74DM6 0 56
    Pulled 498 at 2350 55F, 125 MSL

    * What is puzzling is the 150 HP PA 12 pulled the highest of the O 320's. I would be interested to hear what others have achieved. We used a fairly standard electric digital scale bolted to concrete tarmac. All airplanes went to full throttle for 10 seconds.
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  2. #2
    behindpropellers's Avatar
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    I have always thought static pull tests were pointless based on the fact that propeller efficiency is lowest in a static condition. A better test would be the time to accelerate to XX speed, which is basically integrating the pull test over a unit time.

    Tim

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    Quote Originally Posted by behindpropellers View Post
    propeller efficiency is lowest in a static condition.
    Tim
    I respectfully disagree.

    Static tests may not be perfect because propellers are not perfect, but they are practical and they truly compare apples to apples.

    Acceleration time calculations are hard or impossible to do correctly. All of the planes have to be tested under identical atmospheric conditions at the same time in the same place, on a windless day. It requires 100% accurate knowledge of each plane's weight at the time of the test. It does not take into account the fact that the characteristic wind resistance of the planes is different for each one and the wind resistance of each model is also non-linear in a different way. Wind resistance goes from zero at the start to very significant values as a plane speeds up, so it can't be neglected in the acceleration calculation.
    Last edited by Tennessee; 04-06-2021 at 01:09 PM.

  4. #4
    Crash, Jr.'s Avatar
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    You should pull test the O-320 planes with a borer prop instead of a Sensenich cruise prop. They should be pulling harder than that but the props are the limiting factor.

    I'm also kind of confused why all 3 of the O-320 powered planes pulled different numbers but are using the same prop at the same pitch and doing the exact same RPM. Either the RPM's differ between them or the props are different pitches. If one of the engines are making more power than the others (and the 9-1 engine should be) you would see increased RPM on that plane if it's using the same prop as the others.
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  5. #5

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    Does anybody in that bunch have a borer or catto to compare? 74/56 is a boat anchor but at least it was consistent

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    mvivion's Avatar
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    Were all those pull tests on the 320s done with the SAME PROPELLER, or just with same MODEL propeller?

    Frankly, go to any prop shop and they'll tell you there's worlds of differences in same model, same (alleged) pitch props. Have them show you how they "adjust" pitch on a fixed pitch prop sometime.

    If these were just "identical" props, I'd bet the props were not in fact, identical, just marked the same.

    MTV
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  7. #7

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    I question if the three different O-320 readings are statistically significant. Your average is 477, and not a lot of deviation between them. Like others have said, were they really all at the same RPM? Did you use a digital tach? Remember HP= (RPM* Torque)/5252. If you are running the same RPM, and the same torque (same prop load), you will have the same HP.

    For a more statistically significant test, 1. use a quality digital tach for each run (the same tach in each airplane). 2. do at least 3 runs with each engine/prop combination. 3. Run each engine with each of the 3 props (total of 9 runs per engine).

    Now you have sufficient data to determine which engine/ prop combination is best. Keep in mind that even the same model prop with the same pitch will pull differently based on diameter (while it may be an M74DM, is it really 74"?), actual pitch (Prop pitch will change over time, and if it was repitched, the theoretical pitch will be different for a prop originally set to 56" vs. one repitched to 56"), prop condition (nicks in the leading edge, smoothness of the paint on the face, actual conformance to the airfoil shape), and engine condition (compression, spark plugs, cam condition (lift and duration), volumetric efficiency based on induction system and exhaust system, spark advance) will all have an impact on HP output.
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  8. #8

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    The digital tach is a great idea so I guess at our next Idaho Mountain Planning session we will tighten up
    All 3 engines slightly different O 320's without getting into dash numbers,etc.
    All engines had the same propeller as far as we could document - 56 inch twist.
    As noted, 150 hp , 160HP, and my E2D with 9:1's call it what you will for HP.
    1st and 2nd O320s had Surefly mags
    the 160 had standard slicks with 800TT on the mags
    This exercise was all just for fun but does give an indication as to the potential engine health problems.

    Statistically plus or minus 48 pounds. I thought I would pull the most with my E2D 9:1 set up but much of my surprise the narrow deck pulled the hardest. I will investigate the prop logs of the other aircraft.

    We all have Sutton exhaust.

    I think its worth noting too that the Surefly mags have spark advance that gets MP from one cylinder. Both of us with SureFly mags have this option connected. and we were only 16 pounds apart.
    Last edited by Fortysix12; 04-06-2021 at 04:14 PM.

  9. #9

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    Swap the lowest performing 56 pitch prop with the highest performing prop. You might see a trend.
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  10. #10
    DJ's Avatar
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    What about tires, tire pressure, head wind etc. Seems really odd the 150 horse can turn the same pitch prop the same rpm as a 160+ hp engine.
    I just went from 9.5:1 pistons up to 11:1. I used to see ~2300-2320 static consistantly at 10,500 ft DA. With the 11:1s its up to ~2430 with the same prop same conditions. More horsepower equals more static rpm.

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  11. #11

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    We are checking propeller log book entries now just to make sure. A lot of great points for sure.

    Side note, How do you handle the heat with the 11:1's seems like it would be an issue?

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    BC12D-4-85's Avatar
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    As altitude increases the compression ratio of air and fuel stays the same...but effective cylinder pressure is reduced due to lower available air pressure. Heat produced should decline but so will the ability of thinner air to cool the cylinders at the same outdoor temps. Usually it's cooler at altitude so that helps cool the engine. Something like that, maybe.

    Gary

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    mvivion's Avatar
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    Quote Originally Posted by Fortysix12 View Post
    All engines had the same propeller as far as we could document - 56 inch twist.
    I will investigate the prop logs of the other aircraft.
    Actually, "the same propeller" is in fact ONE distinct propeller, NOT the same model prop. Believe me, different props can have an inch or more difference in twist. You can measure all you like, but the twist may be different. So, you would need to measure each prop twist at a bunch of different stations to be able to say that the propellers were "Actually" similar. And, even then, as noted above, there are a dozen other things that can affect propeller efficiency.

    As noted before, without using the exact same prop, your results are probably within the same range, statistically.

    MTV
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  14. #14

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    And not just twist, but condition!

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    Quote Originally Posted by Fortysix12 View Post
    We are checking propeller log book entries now just to make sure. A lot of great points for sure.

    Side note, How do you handle the heat with the 11:1's seems like it would be an issue?
    Still waiting for permission for the first flight with the new pistons. There is plenty of fuel available for cooling The real question is whether I will be able to actually climb better or if extra speed and fuel to keep it cool will negate the extra potential.

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    A few years ago i got together with a couple buddies and spent a morning pull testing. Catto vs Borer, Our goal was to see which pulled harder.
    kind of comparing apples and oranges.
    Both props will flex a bit and go flatter during a static pull. A conversation with Craig at Catto indicated composite prop will flex a bit more turning higher rpm but not pulling as hard. Untether the plane and things change. Numbers are kind of meaningless due to the different composition of props, and will even differ between metal props for reasons already mentioned.
    I guess you could compare engine performance between planes by turning static rpm by swapping out the same prop under identical conditions and digital tach.
    The whole static pull thing is a little too nerve wracking with questionable results.
    Id rather spent the day out flying
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  17. #17
    n40ff's Avatar
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    Waste of time. Does not significantly relate to anything actually meaningful. OTOH my reply is also a waste of time. Oh well. Thanks anyway.

  18. #18
    courierguy's Avatar
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    It's rather pointless info on how a prop will pull in actual use, granted. BUT, if you pull xx amount static, make a minor adjustment of whatever, (engine related) and and then pull xx PLUS 100 rpm, that has the be a good thing, no?

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    Dave Calkins's Avatar
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    When I am stuck on skis, static thrust becomes important to me.

    Also important getting a floatplane on step and also accelerating a wheelplane.

    Until a dynamic/accelerating thrust test rig is built, static thrust testing is not a waste of time. It is fun to get together and play with airplanes.

  20. #20
    BC12D-4-85's Avatar
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    How about this gadget placed horizontal? Measure max G-force or acceleration for various props during takeoff? There are likely better gadgets available for that.

    Gary
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    RVBottomly's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    How about this gadget placed horizontal? Measure max G-force or acceleration for various props during takeoff? There are likely better gadgets available for that.

    Gary
    I did something like that back in the day in my rebuilt cars. But it was pure analog: Protractor with a pivoting arm and weight.

    You can figure out Gs using a little math and vectors, or a sensitive spring scale if you'd rather be empirical.

    I wonder where I put it. I think it would be fun to set it in a cockpit and with a video camera on it.
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  22. #22
    Crash, Jr.'s Avatar
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    Quote Originally Posted by Dave Calkins View Post
    When I am stuck on skis, static thrust becomes important to me.

    Also important getting a floatplane on step and also accelerating a wheelplane.

    Until a dynamic/accelerating thrust test rig is built, static thrust testing is not a waste of time. It is fun to get together and play with airplanes.
    Currently the best we can do is GPS data to measure acceleration, time to climb tests empty (or close) and time to climb when loaded to gross. At least this is part of the current test regime for new props.

    Static pulls can provide useful data in isolation but when comparing props against each other of different makes it becomes far less useful. An interesting thing to note is that static testing does to a limited extent replicate heavily loaded acceleration performance and that is one area where composite props suffer and aluminum props do well.

  23. #23
    courierguy's Avatar
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    Those modding the 4 stroke Yamaha sled engines are reporting over 700 lbs. FWIW. One is a bit over 1 K.

  24. #24
    Dave Calkins's Avatar
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    Maybe some of you have sample data of exemplary static performance of a prop with piss poor time to climb and acceleration performance.

    I forgot to mention I stand behind my weed wacker testing data also. ��

    I can relate a poor static-performing composite three blade that pulled only 750 lbs while the Pawnee 90’s pulled 950 lbs, and yet the 3 blade would seemingly hover the plane it was on. Yep, been called a liar for that too! By the way....without nitrous.

    Other airplanes were not tested for hover that day

  25. #25
    BC12D-4-85's Avatar
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    My favorite for pull tests are fixed pitch seaplane props (or ski props in deep snow). Listen carefully as some audibly appear to transition from early "stumbling-popping" sounds with throttle application to smoother full engine noise without all the initial racket as speed increases. I assume prop pitch/blade angle, rpm, water-snow-air speed, and engine power contribute at various levels. Can we call that early noise "cavitation", or maybe better yet a stalled portion of the prop blade?

    Assuming static tests duplicate a portion of the early power application for a moving aircraft, then I suggest they should be used only as a comparison for that initial part of flight.

    Gary

  26. #26
    DJ's Avatar
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    I like Mauleguy's idea of timing acceleration over a measured ground run and a climb test. As long as the props are the only variable, this seems like the most useful data for most of us. I plan to compare a Sensenich 76/60 with a Catto 86/38, just for fun while swapping props for break in.

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  27. #27
    Steve Pierce's Avatar
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    I hear you bump the tail a couple of times to get that little extra jolt to beat the other pull test competitors.
    Steve Pierce

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  28. #28
    mvivion's Avatar
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    I wouldn’t say static tests are irrelevant. They certainly don’t tell the whole story of a particular prop/engine combination, but they can be informative. But, to be useful, you need to reduce/control the variables as much as possible.

    But, frankly, propellers are pure magic

    MTV
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