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Thread: Thrustline, Real world

  1. #1

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    Thrustline, Real world

    So, I think I've read every thread on this site about the thrust line mod, seems like its all positives, but a lot of the threads I'm reading are 15 years old, I'm looking for some updated experience with guys that have ran it long term, plane will be on floats 70% of the time, skis the rest, maybe the odd couple weeks of low snow and thick ice when its on wheels.

    I haven't been able to find a cost for this mod? install time? any other changes that need to be made to the plane, such as cowling angle and location.

    Anything else I should know?

    EDIT: I also like the idea of having more prop clearance while on skis, is it unrealistic to expect an extra couple inches of prop clearance?
    Last edited by fishingh; 10-25-2020 at 05:34 PM.
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    RaisedByWolves's Avatar
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    It really depends on your fuselage. If it measures out good it works great. Give mark a call and he can get you set up. I didnít think you could have your pie and eat it too. I thought no way would it shorten takeoff and landing and cruise faster. But it sure did. I had a lot of time in that particular airplane before putting it on.


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  3. #3

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    Also puts the prop a bit higher off the ground for ski work. I second my cubs faster and gets off the ground quicker.

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    Fish,

    Congratulations on your new cub! beautiful plane.
    Well rigged cubs fly pretty good right out of the box, id suggest you get a few hundred hours in it before you start thinking about performance mods.
    Thrustline, like P-stol flaps dont start to earn their worth till youre comfortable playing at the edge of the envelope. Spend the money on gas and go out, have fun, and get to know your bird. With skiis, wheels AND floats, like getting to know three birds. Lucky dog! Once you've got them all figured out, then look forward to tweaking on it a bit.

    Damn, I've been opinionated lately. Old age settin in?

    Doug

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    Quote Originally Posted by Oliver View Post
    Fish,

    Congratulations on your new cub! beautiful plane.
    Well rigged cubs fly pretty good right out of the box, id suggest you get a few hundred hours in it before you start thinking about performance mods.
    Thrustline, like P-stol flaps dont start to earn their worth till youre comfortable playing at the edge of the envelope. Spend the money on gas and go out, have fun, and get to know your bird. With skiis, wheels AND floats, like getting to know three birds. Lucky dog! Once you've got them all figured out, then look forward to tweaking on it a bit.

    Damn, I've been opinionated lately. Old age settin in?

    Doug
    yep, totally agree, don’t plan on doing anything till next spring at the earliest, during the thaw most likely.... will see what happens over this winter, I imagine I’ll have at least 100 hours on skis by spring, at least that’s My goal.
    1967 Piper PA18 Super Cub
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    I guess you answered my question.....if you are going to fly it 25 hrs a yr I wouldn’t do thing. If you are going to fly it 250 hrs a yr put it all on. If your cub is a good candidate, thrustline may get you out of a bind or two.

  7. #7

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    Quote Originally Posted by KevinJ View Post
    I guess you answered my question.....if you are going to fly it 25 hrs a yr I wouldnít do thing. If you are going to fly it 250 hrs a yr put it all on. If your cub is a good candidate, thrustline may get you out of a bind or two.
    pretty quiet recently with the whole Covid thing, Iíve done 300 hours since may, planning to keep up the pace haha.
    1967 Piper PA18 Super Cub
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  8. #8
    Steve Pierce's Avatar
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    Nothng has changed in my experience if you have read the other threads.
    Steve Pierce

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    Quote Originally Posted by Steve Pierce View Post
    Nothng has changed in my experience if you have read the other threads.
    seems like a lot of guys really like it, but a few that still donít think itís something that should be altered due to the stall characteristics, is that pretty close? Lol
    1967 Piper PA18 Super Cub
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  10. #10
    Steve Pierce's Avatar
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    Never heard or seen that posted. See no change in stall characteristic just in the speed at which it stalls.
    Steve Pierce

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  11. #11

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    Quote Originally Posted by Steve Pierce View Post
    Never heard or seen that posted. See no change in stall characteristic just in the speed at which it stalls.
    I found a post from a long time ago talking about it, Iím going to go with the other 99% of the population, lol
    1967 Piper PA18 Super Cub
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  12. #12
    S2D's Avatar
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    Best thing I like about it is the come about speed !!

    When I run into a cloud I can be out of it in a heartbeat now.

    Eaton said he can be outta there before anybody knows he was there !!!
    (doing whatever Eaton does)
    I may be wrong but that probably won't stop me from arguing about it.
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  13. #13
    Utah-Jay's Avatar
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    I looked at the Thrustline website, and I really don’t understand what it is.

    Is it an engine mount that changes the angle?

    Sorry for the newbie questions

  14. #14
    Steve Pierce's Avatar
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    Yes, look at these engine mount lugs on the firewall.
    Click image for larger version. 

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    Now look at the engine mount lugs of the thrustline modification.
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    Steve Pierce

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  15. #15

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    Its a good idea to fly as is before you install the T-L mod

    Steve Pierce installed mine at New Holstein years ago. Mark can tell you if your cub will benefit after measurements. My cub was a bit faster and just felt lighter which makes sense, since it reduces the thrust line vs chord line of the wing which increases efficiency.


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    There is a lot of technical bs answers why it works, but it has sure saved my butt a couple of times. Flew when it shouldnít have, like a bumble bee. Not sure I know anyone that bought one that wasnít happy. But then again I only have two friends, Tim and Glenn.


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  17. #17

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    Quote Originally Posted by Utah-Jay View Post
    I looked at the Thrustline website, and I really donít understand what it is.

    Is it an engine mount that changes the angle?

    Sorry for the newbie questions
    Looking at Steve's pictures the lower engine mount is longer, extended to raise the angle of the centerline or thrustline of the engine more in line with the chord of the wing.
    The factory setup has the engine pulling down while the wing is pulling up...supposedly for the sake of stability. The thrustline mod aligns the thrust of the engine more inline with the chord of the wing making a more efficient arrangement with power/thrust.
    Some Cubs vary in the stock angle between the engine and wing and this is why some Cubs benefit and others, not so much. Measurements need to be made and Mark will be able to advise....he is a super nice guy and will be the first to tell ya if the mod will or won't benefit your cub.
    \

  18. #18
    supercrow's Avatar
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    Mark called me years ago and we talked about his thrustline mod. He, of course, was much more knowledgeable about the theory than I was. He was interested in mine because I had been flying my homemade mod for a long time at the Greenville competitions and it was an improvement over the original mount setup. I had installed my homemade setup in 97. We talked about the degree that I had been running mine at and what would be the best overall for the average s. cub. I appreciated his input and have been flying his setup now for some time. Give him a call with questions. He knows his stuff. I would never go back to the piper stats, at least on my machine.
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  19. #19

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    How is the TL going to help me takeoff/climb and approach/land that I am not doing now? Otherwords can I approach more slowly or climb steeper or at a lower airspeed or what? It has nothing to do with the angle of attack of the wing and it's stalling characteristics. I am not against it I just would like to understand how it can help me fly more on the edge than I would be flying without it. It most likely helps but I don't understand how exactly?

  20. #20
    Steve Pierce's Avatar
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    You should read the Thrustline thread. The wing and engine are in line instead of having a 4 degree difference. I flew my Super Cub for several years prior to installing the mod and was pretty intimate with it in slow flight and short field ops. It surprised me the difference in when it was ready to fly both light and loaded as well as my slower approach speed. I kept floating past my touchdown spot until I got use to it.
    Steve Pierce

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  21. #21
    Steve Pierce's Avatar
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    Better yet, people need to call Jim Richmond and Pat Horgan at Cub Crafters, Darin Hart at Legend Aircraft, Jay DeRosier at Javron and Bruce Reed at Backcountry Super Cubs and ask them why they use the thrustline modification on their airplanes and kits. If I am not mistaken the Husky has it as well.
    Steve Pierce

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  22. #22

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    Yes, I know it's very popular but I want to know the specifics of why or how it does what it does. Then I will understand how to better fly it or put it to it's potential use. I am no aeronautical engineer but I suspect that because it's more in line with the wing it tends to pull the wing through the air more horizontally vs more down (without it). Horizontally is more likely not to stall where down is more likely to stall because of how the air meets the wing. But what about when the power is backed way off; then what?

  23. #23
    Steve Pierce's Avatar
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    When the power is off it has no effect, prop isn't pulling. I haven't found anything that I don't like about it. Some complain about loss of visibility but I didn't notice that, I dropped the nose bowl.
    Steve Pierce

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  24. #24

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    I think maybe my assessment is correct? I gotta tell ya. Today I took off with full PSTOL flaps, and I do have the TL kit on this bad boy that I just got back from a two year rebuild and a 180 hp engine and it climbed like I have NEVER EVER experienced before at just above stall. It was quite steep. I was quite impressed. I also have VGs where before I didn't but had a cuff which I don't have now. So the TL wants power "on" to help out with how the air flow direction over the wing. I need to know these things. Thanks.

  25. #25
    Steve Pierce's Avatar
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    In my head I know the thrustline of engine doesn't have any effect if I am off the power cause the prop isn't pulling therefore the angle of the engine has no effect. You changed a lot of things at once. Probably hard to tell what did what. I have incrementally modified my Super Cub from basically a stock 150 hp with VGs to where it is now. Lots of changes, nothing I want to take back off.
    Steve Pierce

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    I changed out my shock mounts at 1000 hours got back to a stock 4 degree down and gained 3 mph at 2400 RPM. I did not notice any takeoff or landing change. I am temped to due the thrust line mod for STOL comps. However, consideration should be given to normal flight ops!! 4 degrees nose down helps pick the tail up, something to think about if you fly HEAVY!!
    DENNY

  27. #27
    Gordon Misch's Avatar
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    Years ago Mark told me the thrustline change would not be of help on my -12. I'm aware of the wing incidence difference, but for the life of me I don't understand why there would be no effect on a -12. Anybody know for sure why that would be? I'm sure Mark did testing and knows his answer is correct, but I'm baffled as to why.
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    skywagon8a's Avatar
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    Quote Originally Posted by The Kid View Post
    How is the TL going to help me takeoff/climb and approach/land that I am not doing now? Otherwords can I approach more slowly or climb steeper or at a lower airspeed or what? It has nothing to do with the angle of attack of the wing and it's stalling characteristics. I am not against it I just would like to understand how it can help me fly more on the edge than I would be flying without it. It most likely helps but I don't understand how exactly?
    I think you are looking at the wrong end of the airplane. The original 4 degrees of down thrust requires a certain amount of nose up trim on the stabilizer. This is called drag. When the thrust line is raised to zero, much of the trim drag is removed. It is the equivalent of taking several pounds out of the plane since nose up trim adds weight which the wing must lift. This allows the wing to function more efficiently. More efficiency with less drag equals better overall performance and cruise speeds.

    The original nose up trim setting makes the tail heavier also creating more take off run to get to flying speed.
    N1PA
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  29. #29
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    Quote Originally Posted by skywagon8a View Post
    I think you are looking at the wrong end of the airplane. The original 4 degrees of down thrust requires a certain amount of nose up trim on the stabilizer. This is called drag. When the thrust line is raised to zero, much of the trim drag is removed. It is the equivalent of taking several pounds out of the plane since nose up trim adds weight which the wing must lift. This allows the wing to function more efficiently. More efficiency with less drag equals better overall performance and cruise speeds.

    The original nose up trim setting makes the tail heavier also creating more take off run to get to flying speed.
    Hey Pete, your lessons over the years about flying with a little aft c of g have been invaluable. I have been working hard to configure my plane to achieve this. It is very subtle but it works. But one thing this thread has highlighted is something I have been wondering for a long time. I have the thrust line mod. Unless my failing memory is failing me, I also have a 1.5 Deg increase in my wing angle of incidence. Wouldn’t that cancel out the benefits of the the thrust line mod.????
    Javron O-375 wide body extended wing cub
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  30. #30
    skywagon8a's Avatar
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    Quote Originally Posted by cgoldy View Post
    Unless my failing memory is failing me, I also have a 1.5 Deg increase in my wing angle of incidence. Wouldn’t that cancel out the benefits of the the thrust line mod.????
    Was your fuselage specially built with the increased 1.5 degrees? Mine wasn't as far as I know.

    If it indeed has 1.5 degrees more, it ought to be equivalent to the engine mount being down 1.5 degrees on a stock Cub. The original engine mount is down 4 degrees. So you would still be gaining, though not quite as much. Perhaps not a noticeable difference.
    N1PA
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  31. #31
    cgoldy's Avatar
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    My latest wings from Jay are 1.5 from memory but i measured them to the window/ door sill and didn’t get any difference. I’m a bit confused. I’ll check with jay again. The fuse is standard like yours I think.
    Javron O-375 wide body extended wing cub

  32. #32
    skywagon8a's Avatar
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    Colin,
    I think I know where the confusion is.
    Angle of incidence is the relationship of the chord line to the longitudinal axis.
    The chord line is the imaginary straight line joining the leading and trailing edge of an airfoil.
    On the USA 35B airfoil of the Cub, the chord line relationship to the lower surface of the airfoil is approximately 1.5 degrees.
    So when it is said that a Cub's angle of incidence is 1.5 degrees, that would place the lower camber of the airfoil parallel to the longitudinal axis.


    N1PA

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    Pete’s elevator trim explanation is the first coherent explanation I have seen. Normally it is better to have the prop arc perpendicular to the relative wind for any given operation.
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  34. #34

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    I know I am a bit dense, but the last sentence does not make sense! The lower camber of the airfoil (lower surface of the wing) is not parallel to the chord line. You can see that on the cartoon. What am I missing?

    Quote Originally Posted by skywagon8a View Post
    Colin,
    I think I know where the confusion is.
    Angle of incidence is the relationship of the chord line to the longitudinal axis.
    The chord line is the imaginary straight line joining the leading and trailing edge of an airfoil.
    On the USA 35B airfoil of the Cub, the chord line relationship to the lower surface of the airfoil is approximately 1.5 degrees.
    So when it is said that a Cub's angle of incidence is 1.5 degrees, that would place the lower camber of the airfoil parallel to the longitudinal axis.



  35. #35
    skywagon8a's Avatar
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    Quote Originally Posted by supercub9675 View Post
    I know I am a bit dense, but the last sentence does not make sense! The lower camber of the airfoil (lower surface of the wing) is not parallel to the chord line. You can see that on the cartoon. What am I missing?
    Look again. This is about a Cub not the drawing.
    "So when it is said that a Cub's angle of incidence is 1.5 degrees, that would place the lower camber of the airfoil parallel to the longitudinal axis."
    N1PA

  36. #36
    Steve Pierce's Avatar
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    Thinking about the power off question I can only guess that the mod works the same. I know from changing pitch on a prop on my Clipper I was surprised at the thrust from an idling prop and the difference between the two pitches so it only make sense that it would work at low power as well.

    Bottom line, some of y'all are way smarter and think way more than I do. I listen to the people I trust and luckily I get to fly the mods before and after on other people's airplane. I bolt them on mine which I am intimately familiar with and see what difference it made. The problem is after a while it gets to be the norm and I am always wanting more. Once I get use to it I don't realize what I have until I fly someone else's unmodified Super Cub and then it is like wow again. It is like Crack, I just keep wanting more. I don't always know the science of why something works, I just know it does in the seat of my pants.
    Steve Pierce

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  37. #37
    behindpropellers's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    It is like Crack, I just keep wanting more. I don't always know the science of why something works, I just know it does in the seat of my pants.
    That is very quotable.

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  39. #39
    180TigerCub's Avatar
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    It worked on my Cub. Been flying with it since Mark first started with it.
    You cant have it back, Mark.
    180HP PA-18
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  40. #40

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    Quote Originally Posted by skywagon8a View Post
    Look again. This is about a Cub not the drawing.
    "So when it is said that a Cub's angle of incidence is 1.5 degrees, that would place the lower camber of the airfoil parallel to the longitudinal axis."
    By "lower camber of the airfoil" you mean bottom of the wing. correct?
    DENNY

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