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Thread: Daydreaming About Flaps

  1. #1
    stewartb's Avatar
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    Daydreaming About Flaps

    Long Performance STOL flaps are known to require strong pull, high cable tensions, and sometimes blow back at flight speeds. With linear actuators a guy could make electric flaps driven by push rods pretty easily. Maybe hydraulics would work, too, especially for guys who want the ability to dump flaps quickly. It could be a fun project for somebody who hasn't already spent all his money and energy on a project.
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    Change the next to seat handle to an overhead and allot of the issue is reduced. I expect a good portion of blowback is in how the flaps are mounted aft of the spar. I for one am not impressed with the original flap mounting being utilized with larger or longer flaps without a full rework aft of the spar itself. The original structure is just not able to handle the higher loads without flexing.
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    If it's hard to pull the flaps then you don't need them yet.
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    I couldn't detect any flexing or warping of any wing structure when demonstrating how easily I could push my own flaps back when deployed. All the give was in the cable and pulleys.

    Obviously flap pull effort is related to airspeed. 9' plus split flaps add more area and more resistance than what a Cub flap control system was designed for. Improving the controls has lagged behind improving the flaps. Rethinking the controls and control geometry seems like common sense.
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    PerryB's Avatar
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    Quote Originally Posted by 46 Cub View Post
    If it's hard to pull the flaps then you don't need them yet.
    First post and post of the day.
    After Monday and Tuesday, even the calendar says WTF !

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    Quote Originally Posted by CharlieN View Post
    I expect a good portion of blowback is in how the flaps are mounted aft of the spar. I for one am not impressed with the original flap mounting being utilized with larger or longer flaps without a full rework aft of the spar itself. The original structure is just not able to handle the higher loads without flexing.
    This higher load spar twisting issue can be addressed by utilizing two sets of bellcranks and push rods dividing the loads between two separate compression ribs. The extra pulling effort can be reduced by lengthening the flap handle.
    N1PA
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    Quote Originally Posted by skywagon8a View Post
    The extra pulling effort can be reduced by lengthening the flap handle.
    Or by slowing down till the full flaps are needed.
    If the pulley mounts and other parts are flexing in the system I would surly analyze all the parts involved to make sure they are sufficient for the loading they need to sustain.

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    skywagon8a's Avatar
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    Quote Originally Posted by CharlieN View Post
    Or by slowing down till the full flaps are needed.
    Charlie there is more to it than this. When at minimum flying speed the load on the latch which is on the flap handle can be too high to even push the release button. This is a result of using a shortened handle. The longer handle provides the leverage to take the friction load off of the latch.
    N1PA

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    Add a 180* return pulley ahead of the flap handle and another in the wing to make a full loop flap control. The flap ratchet gets square notches since now the flaps lock solidly in each notch. Cable tension is high and will be higher with flight loads on the flaps so all the pulleys get reinforced to eliminate flex. My flaps don't droop and I don't need bungee springs, although currently we left one small spring in place on each side. We think this system will allow using the long armed bell crank that Back Country supplied to get 70* flaps without experiencing the blow back that others are seeing. This isn't an intellectual exercise for me or some others with big split flaps. This is real. If I was starting my plane today I'd like to explore an overhead flap handle with push rods. That got me thinking about a linear actuator instead of a manual handle. A small diameter hydraulic ram would do the same thing. If the actuator was strong enough the bell crank could be configured to provide fairly rapid flap travel, unlike the sluggish electric flaps that many of us have used in the past. Like I said, day dreaming.



    [IMG

    ][/IMG][IMG][IMG][/IMG][IMG][/IMG][IMG][/IMG][IMG][/IMG][IMG][/IMG][/IMG][IMG][/IMG]

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    Interesting. In the RANS S-7S world, we have been using teleflex cables for some time, with great results, for flap deployment. They can be routed to wheverever needed, (simple) and no support along the way is needed, just for chafing on something else protection. They are somewhat heavy is the only con I can think about, these are the high quality types, like used in marine use.
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    Quote Originally Posted by courierguy View Post
    Interesting. In the RANS S-7S world, we have been using teleflex cables for some time, with great results, for flap deployment. They can be routed to wheverever needed, (simple) and no support along the way is needed, just for chafing on something else protection. They are somewhat heavy is the only con I can think about, these are the high quality types, like used in marine use.
    Using teleflex cables is an interesting idea. It would really simplify moving a flap handle from the floor to overhead. Thinking about it beings a couples of questions to mind.

    Any idea of the force required to deploy flaps? That would dictate the size \ weight of push-pull cable required.

    Why push-pull cables? They have load limits in 100s of pounds. Plain pull cables(i.e. brake cables) are rated in 1000s of pounds, are lighter than push-pull cables and would still get rid of the Y splice and flexing pulley issues.

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    Gordon Misch's Avatar
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    How do you link the flaps together? Dual cables, or??
    Gordon

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    This is very preliminary but, I was thinking an overhead flap assembly with a "torque tube" running the width of the fuselage. The ends of the "torque tube" (wish I could think of a better name) would have tear drop shaped arms that would pull the cable to extend there flaps. To keep large bend radius on the cables the left cable would go to the right flap, etc.

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    Quote Originally Posted by KelvinG View Post
    This is very preliminary but, I was thinking an overhead flap assembly with a "torque tube" running the width of the fuselage. The ends of the "torque tube" (wish I could think of a better name) would have tear drop shaped arms that would pull the cable to extend there flaps. To keep large bend radius on the cables the left cable would go to the right flap, etc.
    Take a look at the system in a Citabria 7GCBC. There is a torque tube which crosses the fuselage actuated by a pull cable from the flap handle. The torque tube has bellcrank arms connected to push rods to the flaps.
    N1PA
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    We had the horizontal part of the stock lever disintegrate. I am almost sure that was due to flap extension at speeds over 60. Some think airplanes climb better with flaps extended, even at 80 mph climb speeds.

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    A plus or the y cable is in the majority of single point failures, both flaps will dump. So no asymmetrical flaps.


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    Quote Originally Posted by Todd long View Post
    A plus or the y cable is in the majority of single point failures, both flaps will dump. So no asymmetrical flaps.


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    I'm kind of new at this, but don't the return springs hold the flaps up? So if the y cable fails both flaps would stay up, not dump?

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    Quote Originally Posted by KelvinG View Post
    I'm kind of new at this, but don't the return springs hold the flaps up? So if the y cable fails both flaps would stay up, not dump?
    The cable is more apt to fail when the flaps are down since that is when the highest load is on the cable.
    N1PA

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    The teleflex cables I’m familiar with are bulky and stiff. That’d make routing difficult, but it is an interesting idea. How the anchor the cable sheath at the top would require imagination. Terminating the cable to a central bell crank the used push rods to extend and retract flaps would be fun to play with. Retracted flaps wouldn’t need a bungee spring and no more flopping flaps in a tail breeze. An overhead handle could do the same thing and eliminate the cable.
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    KelvinG's Avatar
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    Quote Originally Posted by skywagon8a View Post
    The cable is more apt to fail when the flaps are down since that is when the highest load is on the cable.
    Ah! When you say dump I was thinking drop, not retract. My mistake.

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    Quote Originally Posted by stewartb View Post
    The teleflex cables I’m familiar with are bulky and stiff. That’d make routing difficult, but it is an interesting idea. How the anchor the cable sheath at the top would require imagination. Terminating the cable to a central bell crank the used push rods to extend and retract flaps would be fun to play with. Retracted flaps wouldn’t need a bungee spring and no more flopping flaps in a tail breeze. An overhead handle could do the same thing and eliminate the cable.
    Mine exit the wing root at the TE, into the cabin, then down along side the rear baggage bay and then forward into the front of the cabin. I think the tightest radius they need to curve is about 24" or so. The inner push rod is 3/16" stainless I'm pretty sure. I seem to recall they are 14' long.....by the time they make their journey through the wing, cabin, and to the flap handle. that's 1 180 degree change of direction, and 3 90's. Still smooth and not too high of internal drag. One mod some are playing with for my bird is moving the flap handle to the upper left side of cabin, and using a bell crank, making the routing of the cable shorter and saving weight. 14' of high quality teleflex cable, per side, maybe one is shorter, can't remember, they are at least 12') isn't particularly light, though they work great.

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    KelvinG's Avatar
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    Quote Originally Posted by courierguy View Post
    Mine exit the wing root at the TE, into the cabin, then down along side the rear baggage bay and then forward into the front of the cabin. I think the tightest radius they need to curve is about 24" or so. The inner push rod is 3/16" stainless I'm pretty sure. I seem to recall they are 14' long.....by the time they make their journey through the wing, cabin, and to the flap handle. that's 1 180 degree change of direction, and 3 90's. Still smooth and not too high of internal drag. One mod some are playing with for my bird is moving the flap handle to the upper left side of cabin, and using a bell crank, making the routing of the cable shorter and saving weight. 14' of high quality teleflex cable, per side, maybe one is shorter, can't remember, they are at least 12') isn't particularly light, though they work great.
    Would you have some pictures or drawings your could share?

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    RVBottomly's Avatar
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    Quote Originally Posted by stewartb View Post
    Stewart, I'm trying to learn some of your fabrication techniques. The pulley looks like it is supported in compression, so I was trying to see how it was braced.

    Also, as my annotation of your picture asks, what's the carbon fiber looking material doing?


    IMG_2520-M.annot.jpg

    Thanks,
    Vic

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    Since we're just daydreaming here, what about using Amsteel rope in place of cable? 3/16" amsteel would be stout enough, and a fraction of the weight.... Thoughts?

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    stewartb's Avatar
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    Vic,

    The flap return necessitated a third pulley and added strain on the pulley stud/post. That post is simply a stud welded to a tube. We used tabs on the airframe to support the reinforcement in the picture, which serves to stabilize the post to prevent flex. No flex, no fatigue cracks is the idea. The carbon fiber scrap serves as a spacer to represent the final carbon fiber interior panel.

    SB
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    Todd long's Avatar
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    Quote Originally Posted by KelvinG View Post
    I'm kind of new at this, but don't the return springs hold the flaps up? So if the y cable fails both flaps would stay up, not dump?

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    “Dumping” the flaps is retracting them.


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    Quote Originally Posted by Todd long View Post
    “Dumping” the flaps is retracting them.


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    Yes, in post #20 I acknowledged my mistake. I should never post before coffee!

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    Todd long's Avatar
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    Quote Originally Posted by KelvinG View Post
    Yes, in post #20 I acknowledged my mistake. I should never post before coffee!

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    Saw that after. Tapatalk has locked up.

    An overhead flap handle with a push pull control rod and a bell crank seems way easier. A single positive unlock detent and ratchet for the down detents.


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    Quote Originally Posted by KelvinG View Post
    Would you have some pictures or drawings your could share?

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    I don't have my build manuals handy, but I know RANS has them on their website. They have been using the tele flex method of flap control for over 20 years now on hundreds of kitplanes, and i have never heard of any issues with that method. The obviously important part is the proper "teleflex retainer bracket" on either end, which locks in the cable housing to the airframe. they are very simple and are available via the parts department at RANS, just a crimped and stamped metal bracket that locks into a notch in the cable housing when two AN-3 bolts are tightened, any source for the teleflex cable itself probably has them also.

    In my wing anyway, once the cable starts it's journey through the inside of the wing to the actuator from the flap bracket, it's just a matter of finding the most direct routing while avoiding too sharp of bends, and not interfering of course with any thing else in the wing, it's simply zip tied to various compression struts etc. as you go. It being a self contained kind of deal, the cable housing with it's internal cable/rod, it's kind of hard to screw it up, at least as compared to routing aircraft control cable, pullies, etc. It's one of those beautifully simple quick and dirty way to get the job done, KISS applies here, RANS is pretty good at keeping things simple for their builders and cost effective for them to supply, and between myself and a few other S-7 pilots I personally know, with well over 10K fleet hours, there are zero issues with this system. Once properly setup, they don't stretch, move, or seem to require any attention.

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    The Flightstar I retired a few years back had Teleflex on both elevator and ailerons.(2 redundant on the elevator) I didn't like the looks of them at first, but had to admit there wasn't much friction and after 200 hours I quit moaning about them.
    What's a go-around?
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    RVBottomly's Avatar
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    I found this on the Rans website regarding teleflex for flaps.

    rans.jpg


    It comes from the discussion of the S-21 Outbound. Scroll down to 3/29/17 entry:

    https://www.rans.com/21-outbound-progress-page-2

    I notice that flap deployment is in a pull configuration on a bellcrank. I remember the telexflex "Xtreme" cables can handle an 8" bend radius.

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    I was almost going to say RANS was using them (tele cables) on the new 21, but wasn't sure and was too lazy to find out, good catch! And, that picture shows how simple the retaining bracket is for the housing, I'm sure there is some engineering out there saying it is plenty strong for the anticipated loads.

    Using them for ALL flight controls works also, but not as light a feel as cables I'm guessing? Flaps don't matter near as much for primary controls as far as a delicate touch/small break out force.

  33. #33
    Cubus Maximus's Avatar
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    This early 90's Cub Crafters test mule had oversized hydraulic flaps that were infinitely adjustable (and dumpable). Worked pretty good!



    Flap release / dump button (red) was on the control stick.









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    RVBottomly's Avatar
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    Quote Originally Posted by Cubus Maximus View Post
    This early 90's Cub Crafters test mule had oversized hydraulic flaps that were infinitely adjustable (and dumpable). Worked pretty good!
    Thanks for reminding me of that. I love playing with hydraulics, but I always wondered about the weight compared to cables and pulleys.

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    KelvinG's Avatar
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    Quote Originally Posted by RVBottomly View Post
    I found this on the Rans website regarding teleflex for flaps.

    rans.jpg


    It comes from the discussion of the S-21 Outbound. Scroll down to 3/29/17 entry:

    https://www.rans.com/21-outbound-progress-page-2

    I notice that flap deployment is in a pull configuration on a bellcrank. I remember the telexflex "Xtreme" cables can handle an 8" bend radius.
    The teleflex 60X cable is rated for 250lbs pull. And from 250lbs down to 150lbs push depending on length of travel, (1" to 5"). I would need to know what kind of force the Keller flaps are producing before going this route.

    All the talk of addition deployment forces being generated by Keller flaps makes that number critical in my mind. The RANS is a smaller lighter plane which means (I assume) lighter deployment forces.

    Nice idea though! Does anyone have real numbers in regards to the Keller flaps? Seeing how you can get Keller flaps in various lengths it would be a psi per square foot number.

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    Backcountry's about two weeks from flying the new Rev 3 wing. Maybe the long Keller flap pressure thing becomes unimportant to anyone other than those of us with "old iron?"

    Things sure change fast. Lead, follow, or get out of the way!
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    RVBottomly's Avatar
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    Quote Originally Posted by stewartb View Post
    Backcountry's about two weeks from flying the new Rev 3 wing. Maybe the long Keller flap pressure thing becomes unimportant to anyone other than those of us with "old iron?"

    Things sure change fast. Lead, follow, or get out of the way!
    Heh. Looks like by the time I start building wings on my project, I'll have yet another design to consider. I'm intrigued--haven't heard about the Rev 3.

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    I guess it’s okay to share a photo now that Rev 3 flight videos are showing up on Facebook. Cool new flap design. Controlled by an overhead lever and push rods. No more return springs. It appears to perform well in the videos. The ailerons are shorter in span and deeper in chord similar to Mackey’s SQ-12 wing. Back Country Supercubs continues to innovate. Bravo!

    IMG_0076.JPG


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    RVBottomly's Avatar
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    That is very interesting.

    I like apparent simplicity of the mechanism.

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    Where on Facebook are these flight videos of the Rev3? Thanks, Joel.
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