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Thread: Supercub Thrust Line

  1. #1
    skukum12's Avatar
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    Supercub Thrust Line

    Can anyone tell me for certain that the thrustline of the cub engine is truly angled several degrees down from the centerline of the fuselage? In other words, it sounds as if the plane is fighting itself at take off and thoughout the entire envelope. Is there a workable cure out there? Does this also appear on stock 12s?

    thanks

  2. #2
    SJ's Avatar
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    Interesting you should bring that up. There has been some work done in this area very recently. If you look at these pictures you will see some of that work.

    http://www.supercub.org/gallery/view...percubs&id=cxe

    http://www.supercub.org/gallery/view...percubs&id=cxf

    I'll let somebody else spill the full beans...

    sj
    "Often Mistaken, but Never in Doubt"
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  3. #3
    Steve Pierce's Avatar
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    I had a long phone conversation with Mark the other day on this very subject. Seems he has been very busy zeroing the thrust line. I believe he said it is negative 4 degrees stock. He has an STC in the works that will replace the engine swing out lugs and extend the bottom two cowl "U" channels. He said they decreased take-off roll by 30% on one A/C just by changing the thrust line. The J-3 has the zero thrust line while the PA11 has the 4 degree negitive. Now I know why an 11 won't land like the 3. Penn Yann is going to incorporate it into their new 180 hp engine mounts.

    OK Mark, lets hear the rest of the details.
    Steve Pierce

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    Likes bush4 liked this post

  4. #4
    cubpilot2's Avatar
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    I was told by one "old timer" that he put spacer washers under the lower engine mount bushings to correct the thrust angle on his PA-11. He said it then performed with the J-3. Must be something to it.

    What would this do to cruise speed?
    Ed

  5. #5
    Steve Pierce's Avatar
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    Mark told me Jerry Burr and Denny (can't remember his last name but has the souped up short take-off Super Cub on nitrious) were both impressed. can't wait to try it.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  6. #6
    AkPA/18's Avatar
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    Hi All

    Yes we are working on the ThrustLine change with some pretty suprising results. What Steve P relayed per our conversation is accurate. Denny Martel first used this Mod last summer and took thirty percent off his TO roll and gained 6-8 mph cruise. Jerry will be able to elaborate on this a bit. In our other testing in Stock Cubs it also showed a thirty percent reduction in TO roll. This is a short field--dump the flaps--get off the ground TO. One person full fuel. Everyone wants to take off short but this is not why this mod was developed. It was developed for landing. The pilots who have flown this mod in fact generally don't even talk about the TO performance after they have flown. It is the landings that are so impressive that you don't do much talking about the TO. We have 180 hp Penn Yan conversions landing better than J3s. I can tell you that we found out that it has never been the weight up front that that spoils the landings on a cub. It has always been that negative ThrustLine. By the way--Penn Yan has been instrumental in the development of this ThrustLine and STC. ( Please do not call Penn Yan on Monday---I have been trying to get a hold of them but they are at Sun and Fun. I will see if they will post some info on the boards for us) The trim characteristics are much improved. The following is right from the FAA test flight. We put 46lbs of dive wts on the main bolt that attaches the TW to the tail spring. 25 lbs of wt in the extreme aft Atlee baggage. Two people(400lbs) and full fuel and 10 lbs in the std baggage. The AC was around 1900lbs bouncing off the aft 20 inch line. The stock cub with full flaps could not be trimmed hands off until about 40 mph indicated. As the airspeed increased above 40 --nose down stick pressure needed to be increased. On the modified cub----it was able to be trimmed at full flaps up to 60 mph hands off. You cub pilots that work your cubs with the heavy loads have recognized this common characteristic. The plane just runs out of nose down trim in the landing config. Not with the modified ThrustLine. In the 180hp Penn Yan tests--we trimmed the AC for level flight at a 3000 ft press alt. At 66 and 70 mph--clean--it took 100 to 150 rpm less in the modified AC to perform the manuever. Other tests in cruise have shown a 4-10 percent increase in cruise. The 180 test showed an 8 percent increase at full power level flight. Pages can be written on this and pages will be. I am not much of a salesman nor will I try to be. I have asked Steve if we could start a thread when needed on before mod and after mod test results from the people who end up flying these cubs. I think this will be simple to do and will relay some good info--unbiased--for all to judge. The FAA considered this a substantial change to the AC in so many ways. We have jumped though so many hoops but in the end, the only way this ThrustLine project was approved was on its own merits. In trying to figure out why Piper settled on the current ThrustLine, I had a couple of conversations with Clyde Smith Jr. He said it came right out of engineering and this was the only ThrustLine on the SC ever flown by Piper. There has been speculation as to why Piper did this. We can only imagine they did this for increased visibility over the nose. Usually when you make a performance mod it is a tradeoff. I think Piper might have traded visibility for performance and we are just trading back. That is why the modified ThrustLine performs better in all phases of flight. Wayne Mackey is the only person on the site that has flown this mod in a mostly stock 180 hp cub. His computer is blown up at the present time but I am sure he will be reporting in as soon as he can. I just wanted to get this out in the open now that all our engineering data and the test flights have been approved. The ACO has indicated the STC will be issued within two weeks. My hats off to those folks as they are trying to issue this so we can have the mod at the Valdez show. There is a possibility I hear that Denny will be there but unfortunately no Jerry. The machinist on the project is also expediting the machining of the parts to make the Valdez show. Not saying we will make it but we will do our best. The machinist is Mark Zueger at Polaris Machining. It has been quite a pleasure working with him. He is the same machinist that Bill at BushWheels uses. The best of the best in my book. For the skeptics of this modification---I appreciate your opinion. This ThrustLine has been on the SC for over fifty years. It is hard to believe what this does for perfomance. I can tell you that we can talk about it all we want and until you feel it for yourself you will not believe it. That is why I hope the people will post solid before and after test numbers for you to judge. I know this is a long post but as I write I realize how much I am leaving out. Bear with me on this as we are up to our necks in the last push on paperwork. More info will follow. Just a quick thanks also to Steve and Dana for this opportunity to use this forum.

    Mark
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory

  7. #7

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    Mark, I Have the engine off for rebuild right now and would like to try this mod, please post info on purchaseing STC and assocated parts.
    Thanks,
    John

  8. #8
    PA12driver's Avatar
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    Ok Mark,

    I guess we can talk about what I have known about for over a year! As you know there are several (not mentioning any names) that have experimented with the "washer under the mount" approach for quite a while. I aplaud you in going for the STC and for all of you guys that knew about it and kept it under wraps till the testing was done with the FEDS.

    As for the 12 I know you are working on that next. (Ain't that always the case) Can't wait to build an experimental for just that reason.

    See ya soon and best of success.

    Tim

  9. #9

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    On the second picture posted I can't see the thickness of the spacer placed on the lower engine mount. I assume that spacer is the extent of the modification. I am certain you will have great sucess with this mod. My two questions are: Is there anything more to the mod than the lower spacer? How did you arrive at the proper thickness ( I assume you tested all different thickness and found one to be the most efficient, can you describe what you found when testing various thicknesses or angles?)?

  10. #10
    Wayne Mackey's Avatar
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    Thrust line

    Hi folks,
    New puter just fired up, hope I don't total this one. Been wating for
    this thred to be in the open so it could be disscussed. I was a little
    sceptical of the claims on perfomance when I first heard them, but
    everyone had the same story so there had to be somthing to it. I
    contacted Mark about 10 months ago and was let inside the circle
    and made part of the project. As Mark have stated the improvements
    are in every flight envelope. But by far the biggest is in the landing
    mode. When you slow a cub down under power and have it all out
    hanging on the edge it is quite a dance to keep it under control. With
    the thrustline change it's simply a walk in the park. I personaly think
    it is the best single mod a cub could have. It works well with all other
    mods as well as the slats. My hats off to Mark, he has worked long
    and hard to make this happen. That also goes to his lady for putting
    up with him though this project. Wayne

  11. #11
    Gunny's Avatar
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    Really interesting stuff Mark. Looking forward to it. I'm assuming slots and slats are similar - so what't the net result there? Less (or no) nose up trim to get the AOA right for the descent rate? Seems like it would make the slots behave more like a stock wing. Curious to hear if anyone has flown them with slots or slats. Congrats and best of luck with it.
    "You are the Gray Rider who would not make peace with the Blue Coats, you may go in Peace." - Ten Bears

    Gunny

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    Seems like what this mod is doing is about the same as changing the wings angle of incidence....the wing is now flying at an angle closer to the thrust line (less drag). Isn't that one of the reasons always given as to why the PA-12 is faster in cruise than the 18? Am I seeing this correctly or not?

    Frank

  13. #13
    Wayne Mackey's Avatar
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    thustline

    Gunny,
    Yes it is being flown with the slats and it does work well. Denny has
    the new thrustline and has more elevator control at the low speeds
    and it is easer to hold the nose up without a lot of power.
    As far as the 12 goes I think you are right, with the lower AOA it
    would have a 1.5 degree less spred between the thrustline and the
    eng. maybe helping the cruise. Wayne

  14. #14
    T.J.'s Avatar
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    Pretty good article on high lift devices in the March issue of the EAA Magazine.

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    Just looked at my trusty North Land CD drawing of the PA-18 engine mount. It shows the thrust line canted down 4 degrees from the fuselage level line. Until now I always assumed the thrust line and the fuselage level line were the same.

    With the thrust line canted down 4 degrees from the level line, isn't the PA-18 wing actually flying at an angle of incidence of +5.843 degrees instead of 1.843 degrees? No wonder this mod picks up so much cruise speed!

    Frank
    Thanks Cramer907 thanked for this post

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    diggler

  17. #17
    Wayne Mackey's Avatar
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    nose

    Diggler, thats pretty simple math but you have a point. You do loose
    some sight over the nose. Most peaple can't see directly over the nose
    with big tires and longer gear anyhow. I havn't heard anyone complain
    and it gave me no problem, but I did notice the differance. Wayne

  18. #18
    PA12driver's Avatar
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    Will it help a Husky??? (just had to throw that in)

    Wayne and Mark,

    What is the thrust line angle on a 12?? I would suspect that it wouldn't help a 12 and you damn sure don't want the nose any higher! That is my only complaint with a 12 is there is a second or two that you are blinded. the fuselage is too wide to see out both corners of the window without moving your whole upper body, (no time for that) as some of you know in tight rough places.

    Can't wait to put a set of slats and speed brakes on my experimental and 35" tires! I would already be building if the meat head from NY didn't back out of the purchase of my 12 on the last minute after stringing me along till for a week! (Oh well I did get the maintenance and repairs done and now it is licensed and flying again! (I even passed a Bi-Annual) what is Class A, B, C airspace anyhow??? I know I don't want to go there cause they have only that tar stuff and cement!

    Tim

  19. #19
    skukum12's Avatar
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    To solve the 12 high nose low visiblilty problem, I've come up with a solution. I intend to spend all my wife's money on developing a "Concorde" stc. A simple design really, pivot the cowling and engine down for take off and landing. How hard could it possibly be to convince the FAA to sign off on the idea?
    "Always looking up"
    Likes pfm liked this post

  20. #20
    Bill Rusk's Avatar
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    This sounds great. What kind of cowling mods have to be made?. Do you have to completely redo the boot cowl and the forward cowl, or just the forward part? Does it affect the exhaust system etc?
    Thanks for doing all the work. I hope it turns out to be profitable for you.

    Bill

  21. #21
    Steve Pierce's Avatar
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    The Husky already has a zero thrust line so I guess you could say Mark is copying a Husky rather than the other way around.

    The only thing changed is the engine mount lugs at the firewall and the bottom "U" channel cowl braces are lengthened.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    I was wondering if the engine mount were laid down on a flat and perfectly level surface could a digital level be laid on the engine mount end with the fuselage attach end down and be able to tell what degree positive or negative a mount is. heres some part numbers to start with, maybe some of you allready know. 12351-15 pa18, 12351-11 pa18, 12351-12 pa18, 12209-00 pa18-90, 10576-00 pa11, 71163-00 j3, 10070-00 pa12. with access to blueprints im sure it would be easy to figure out. and how thick of a washer does it take to change 1 degree of angle. one more quick question here not to get off topic, but is there a sure fire way to get a wife to like aviation, or maybe theres a thread on this. thanks doug

  23. #23
    AkPA/18's Avatar
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    Just checking in and will try to answer a few questions

    Ground Loop---yes we tested various ThrustLines and came up with what we found to be the optimum for the Cub. Look close at the pic and you can see the reflection of the upper and lower SS lugs. I will get around to posting some more pics in the future.

    Gunny--I just don't have the answers to that question. I suspect Jerry and Wayne are the guys for slots and slats.

    Diggler-- a couple of inches--no firm measurement here but it does make a difference while taxiing.

    Steve addressed the lower cowl changes and lugs.

    Yes the Husky already has similar TL. Look at the pics and compare the Blue Cub to stock cubs and Husky's

    The increased cruise is probably the easiest to explain. Thrust also has direction. In level flight you are controling the negative thrust direction by increasing AOA---this increases lift which increases drag= lower cruise than the modified cub.

    Hope to have testing done for the 12 by the Airmans trade show. If it does work on the 12---which has a similar stock ThrustLine---you should get away from having to carry substantial power with the high nose up attitude and still be able to land at a reasonable airspeed. We won't know until we test.

    Thanks guys--Back to the paperwork

    Mark
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory

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    Anyone know what the angle of incidence is on the Husky?

    Frank

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    Why did you need to add the upper bushing?

  26. #26
    AkPA/18's Avatar
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    Evening Ground Loop

    I assume you mean the lugs. As you cant the mtr mount the attach fittings of the mtr mount are no longer square to the firewall lugs. These lugs(all four) have been machined to incorporate that angle change.

    Mark
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory

  27. #27
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    Wayne - Thanks for the reply can't wait to see one and test drive if that's possible. If not I may just have to give it a go on word of mouth. BTW when are you gonna get over this way?


    Mark - understand, as you can see I heard from Wayne. Put me on the short list for notification when its done. Miss Daisy is already sporting the Penn Yan conversion so adding your mod shouldn't be too difficult. Best of luck with the process - and good on you for doing it.
    "You are the Gray Rider who would not make peace with the Blue Coats, you may go in Peace." - Ten Bears

    Gunny

  28. #28
    Wayne Mackey's Avatar
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    thrustline

    Gunny,
    Hope to be over your way in june. last winter weather and timing
    never worked out. All of my slat systems are on planes with large
    flaps and droopy ailerons. Every one flying this way knows there is
    a lot more pitching moment. There is a greater need for elevator
    control and the thrustline change realy improves controlibility at the
    lower speeds. I'm sure you and Mike B will be very impessed with
    the slow speed handling. Wayne

  29. #29
    Tim's Avatar
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    So where is the new thrust line , at the same plane as the bottom of the wing?

    Tim
    2+2

  30. #30
    AkPA/18's Avatar
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    Morning Tim

    If you look at a side view of a stock cub----draw a line from the center of the flange to the intersection of the tailpost and the upper longeron. This is the stock thrust line. Go look at the pics of the Blue Cub(link below). Draw a line from the center of the flange to a couple of inches below the tailpost. This is the Modified ThrustLine. The stock thrust line starts from below the horizontal reference line in front and ends up above the HRL at the tail. The modified Thrustline is approx a couple of inches lower than and approximately parallels the HRL. The modified ThrustLine also comes close to paralleling the horizontal tail plane in the neutral position. It is a substantial change. Hope that helps.
    http://www.supercub.org/gallery/view...percubs&id=cxe

    Mark
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory

  31. #31
    SJ's Avatar
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    Actually, all you have to do is step back from a stock supercub and look at how the spinner points down relative to the lines of the fuselage.

    How come I never noticed this before, but now it sticks out like a sore thumb?
    "Often Mistaken, but Never in Doubt"
    ------------------------------------------

  32. #32
    Crash's Avatar
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    Thrustline

    I've been amazed that Cub guys could keep this under their hats for over a year while Mark worked on his STC. It poped up a couple of time on the board and no one took the bait. I first heard about it in early April 03. Crash

  33. #33
    T.J.'s Avatar
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    delete

  34. #34
    AkPA/18's Avatar
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    Hi folks

    Thanks to you Crash and all the others that helped me keep a lid on it. TJ--I appreciate that. Wayne and Jerry have been great help. They are schooling me!!

    This post is just to get my email contact info out there. We have been overwhelmed with calls and I don't have time to deal with the calls as they come in. If you absolutely need info please email me and I will call you. Include your number, time zone and a good time to call. Our priority right now is to finish the paperwork--and get some before and after info from customers flying this product(VALDEZ). This will help you decide if it is a mod that is right for you. Thanks in advance for having patience with this start up.

    mailto:akcub@mtaonline.net

    Mark
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory

  35. #35

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    Supercub thrustline

    Is this applicable to all engine applications?

  36. #36

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    This might be an interesting read for you engineering type that are interested in thrust line angles:

    http://www.dfrc.nasa.gov/DTRS/2000/PDF/H-2402.pdf

  37. #37
    Bob Breeden's Avatar
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    ThrustLine

    Bob Breeden

  38. #38

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    At full (100 %) power cruise I need to step on the left pedal just a little. Is there a simple fix for this? I am trueing out at 127. Is anyboldy else aware of this with there plane?

  39. #39
    cubpilot2's Avatar
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    Mark:
    Glad to hear what you guys are doing.
    Are you considering creating a replacement engine mount for the standard 150 hp cub as opposed to adding the extended lugs?
    It looks as if a complete mount change would give a bit cleaner looking product and wouldn't have quite the "modified" look to it.
    I am interested in how this works out as I may want to add it to the 18A rebuild that I am doing now.
    Will this be approved for Floats?
    Thanks and Congrats
    Ed

  40. #40
    Crash's Avatar
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    NASA Study

    Quote Originally Posted by ksecub
    This might be an interesting read for you engineering type that are interested in thrust line angles:

    http://www.dfrc.nasa.gov/DTRS/2000/PDF/H-2402.pdf
    Some interesting reading. It looks like 0 degrees works best in some instances and 3.5 degrees worked better in other areas of the flight envelope, but then again this was done on a wide body jet transport. I wonder if that would translate over to a "Widebody" Super Cub??? Crash
    Thanks pfm thanked for this post

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