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Design => Stunt design => Topic started by: Howard Rush on May 10, 2021, 02:17:48 AM
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Some flap experiments that I'm to lazy to do, but that you may find interesting:
1. You could attach some leading edge flaps fixed in place at a given deflection. This allows you easily to see what LE devices could do. You wouldn't have to worry about mechanisms or hinge moment to do the experiment.
2. You could experimentally fix the TE flaps at a given deflection. This could tell you what the flaps do without the confounding effect of hinge moment. You could see what flap deflection gives the tightest loop, how much drag the flaps have at various deflections, and, by setting neutral at the handle and seeing how much elevator it takes to fly level, how flap pitching moment varies with deflection. I once did this with an experimental aircraft named The Cow. The Cow had fixed split flaps (say that three times fast) set at 60 degrees deflection. The Cow was a proof-of-concept article for the rather unsuccessful slow combat plane shown here.
3. Brett proposed flaps driven in multiple places along the span. I scoffed at this idea, carbon torque tubes having been invented, but how about if the flaps are divided into independently moving segments, each with its own control horn? For one thing, this would be the mother of all lucky boxes. You want to tweak a flap to level the wing in roll? Just adjust pushrod length of one segment. You could have some segments move more than others: symmetrically, asymmetrically (Palmer differential flaps-- same sign as Palmer's or opposite)), or just the outboard outside segment for trim like Igor's or Ted's tab. Independently moving segments would allow a lighter wing structure. The wing could deflect without binding the flap hinge.
One caution is that you'd probably want to mass balance the pushrod that runs out the wing. Hang a weight on the other side of the bellcrank.
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I mentioned
EddyR
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The issue that I have with 'fixed flaps' is that it actually changes the wing section and won't show transition between ' normal', as in flight without lift devices, and flight with enhancements.
In other words you will have changed normal and lose your base reference.
Chris.
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The issue that I have with 'fixed flaps' is that it actually changes the wing section and won't show transition between ' normal', as in flight without lift devices, and flight with enhancements.
In other words you will have changed normal and lose your base reference.
The "transition", IOW any nonlinearities around neutral, are important, but that's not what Howard's test is intended to explore.
Note that the wing section changes in normal conditions, too. It is changing all the time. It's deflected in level flight, just not very much. Howard's test gets one data point and a known condition. which more-or-less how wind tunnel tests work. Do a lot of them, and you have a full picture.
Brett
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Agreed Brett, but 60 degrees fixed flap seems like a heck of a lot and would have to be more of an air brake than anything else.
But kudos to Howard for trying.
Chris.
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Agreed Brett, but 60 degrees fixed flap seems like a heck of a lot and would have to be more of an air brake than anything else.
I did the experiment, and I know the result. Chris made the conclusion. It might be fun to play poker with Chris.
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I had forgotten that the Boeing-NASA QSRA (Quiet Short-something Research Aircraft) had fixed LE devices. Its test conditions were low speed near the airport. Laura Nicol, who introduced me to my lovely wife, suggested that they not bother with LE device actuation, so they didn’t.
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I did the experiment, and I know the result. Chris made the conclusion. It might be fun to play poker with Chris.
I fear that if I played poker with you Howard there would be too many jokers in the pack. n~
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Agreed Brett, but 60 degrees fixed flap seems like a heck of a lot and would have to be more of an air brake than anything else.
But kudos to Howard for trying.
Chris.
I tried something similar on a profile carrier- a 9inch straight wing with 2.5in. wide full span flaps. They had an adjustable fixed travel, and a great big stab/elevator.
The weirdest thing, which I should have thought of, was that at 30deg flap deflection the plane would fly with the nose pointed down about 30 degrees. It could easily fly at about 1mph, but under contest conditions you couldn't do that. The slightest breeze would over power it.
Couldn't get the motor to run slow enough to get the plane anywhere near level flight attitude.
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These turning vanes are on the underside of the Feiseler Storch tail. The tail needs maximum downforce at low speed during landing, especially on the Storch with its high lift wing, slats, and flaps. These vanes are very effective in increasing the downforce of the tail, almost doubling it, by "jetting" a force of air onto the stabilizer at high deflections. The F4 flying tail has mods to the underside of the leading edge to accomplish the same thing, namely keeping the flow attached to the surface at higher incidence angles to make more downforce for landing conditions. I've done it on stunt ships and it works. I wish someone else would try it.
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Has anyone tried straight square edged flaps? Seems with this shape rather than the normal tapper the flap would engage faster, might need less throw?
Best, DennisT
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Yes, this is the fashionable shape now. There is some actual aero reason why they work. I still have tapered flaps because I think they are prettier.
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Has anyone tried straight square edged flaps? Seems with this shape rather than the normal tapper the flap would engage faster, might need less throw?
Best, DennisT
Do you mean something like this?
Dennis
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Do you mean something like this?
Dennis
Wow. Nice plane! Who made it?
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Has anyone tried straight square edged flaps? Seems with this shape rather than the normal tapper the flap would engage faster, might need less throw?
Best, DennisT
Some random guy named Paul Walker advocates for it.
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Wow. Nice plane! Who made it?
Thanks Tim. It's my plane. You can read all about it on the Flying Lines website at http://flyinglines.org/nunes.circulas46lle.html (http://flyinglines.org/nunes.circulas46lle.html). ;D
Dennis
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These turning vanes are on the underside of the Feiseler Storch tail. The tail needs maximum downforce at low speed during landing, especially on the Storch with its high lift wing, slats, and flaps. These vanes are very effective in increasing the downforce of the tail, almost doubling it, by "jetting" a force of air onto the stabilizer at high deflections. The F4 flying tail has mods to the underside of the leading edge to accomplish the same thing, namely keeping the flow attached to the surface at higher incidence angles to make more downforce for landing conditions. I've done it on stunt ships and it works. I wish someone else would try it.
Pretty interesting concept to consider. I imagine the drag component could be significant depending on the size and height.
I made this little drawing showing flat and airfoiled vane types attached to pylons.
Does this seem like an arrangement that would be used?
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Brent
You've got the right idea .... but redraw it with the slats attached to the elevator ..... at least thats the way I did it ....
Frank
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These turning vanes are on the underside of the Feiseler Storch tail. The tail needs maximum downforce at low speed during landing, especially on the Storch with its high lift wing, slats, and flaps. These vanes are very effective in increasing the downforce of the tail, almost doubling it, by "jetting" a force of air onto the stabilizer at high deflections. The F4 flying tail has mods to the underside of the leading edge to accomplish the same thing, namely keeping the flow attached to the surface at higher incidence angles to make more downforce for landing conditions. I've done it on stunt ships and it works. I wish someone else would try it.
That's an interesting idea Frank. Can you point me to the NACA report you found it in? Cessna did a whole bunch of work on their Citation jets to achieve this kind of performance without a significant drag increase. They used a combination of flap leading edge shape and cove shape to guide the airflow though a channel from bottom to top to "blow" the surface invigorating the boundary layer. One of the guys that came up with this is a friend of mine and is very bright. The auxiliary foil surely increases the raw Clmax better than the "ducting" approach. Like spades, I would worrying about handling damage.
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Something i learned with the RC hydro race boats is you have to have a shape the edge on the sponsons which i think would apply to control surfaces trailing edges so the air can exit the surface and not try to stick like a rounded edge would do.we rounded off the edges on the sposons of the boat and it had a hard time getting up on plane because the water would stick to the sponson instead of releasing which caused drag.
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Brent
You've got the right idea .... but redraw it with the slats attached to the elevator ..... at least thats the way I did it ....
Frank
How did you mount them Frank? I’d be interested in trying them and have a really good test bed airplane to try them on!
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Brent
You've got the right idea .... but redraw it with the slats attached to the elevator ..... at least thats the way I did it ....
Frank
Frank, do you have a side view sketch of how this works. How much deflection do you have in the elevator, and would this dictate less? Are they sealed, and if not as I expect, how wide should the gap be. Would they work on recessed elevators, I suspect not but the "test bed" I have access to right now has recessed elevators.
Ken
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With the square edge flaps has anyone tried adding a "Gurney flap"? I would imagine it would be something like a strip of 1/64" ply maybe 1/64" above and below the rear edge. From what I have read this vertical strip which you would think would add drag actually reduced drag. It is supposed to keep the boundary layer flow attached all the way to the trailing edge of the airfoil. Interesting idea but how it would work on a movable flap would be the question.
Best, DennisT
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Mark .... Thiis diagram came from a book titled ..."Fluid Dynamic Lift" by S Hoerner. He is famous for his other book "Fluid Dynamic Drag" primarily, and his wing tips. Most of his stuff is from German research during the war years. The implementation you show on the Citation with the "blown flap" does a good job without an increase of too much drag.
Matt, Ken .... they are mounted on little standoffs mounted to the elevator. See pictures The critical points are 1) they have to "Peek" up above the stab surface enough to be above to grab some good air 2) the gap at the jet end has to be small enough to get a "jet" effect of the air and 3) the length of the slat must be sized so that the leading edge of it just touches to stab surface. (not that touching the stab surface is important, but you don't want to inhibit the elevator movement)
I will say that it worked best on elevators and stabs and not so much was felt when put on flaps
Frank
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A diagram and a photo of the bottom of a Fri. Storch and another one of my planes
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Some out of the car window tuft testing
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Some flap experiments that I'm to lazy to do, but that you may find interesting:
1. You could attach some leading edge flaps fixed in place at a given deflection. This allows you easily to see what LE devices could do. You wouldn't have to worry about mechanisms or hinge moment to do the experiment.
2. You could experimentally fix the TE flaps at a given deflection. This could tell you what the flaps do without the confounding effect of hinge moment. You could see what flap deflection gives the tightest loop, how much drag the flaps have at various deflections, and, by setting neutral at the handle and seeing how much elevator it takes to fly level, how flap pitching moment varies with deflection. I once did this with an experimental aircraft named The Cow. The Cow had fixed split flaps (say that three times fast) set at 60 degrees deflection. The Cow was a proof-of-concept article for the rather unsuccessful slow combat plane shown here.
Seems like fixed position flaps, leading or trailing, would have an adverse effect on inverted flight if maximized for upright or vice versa. Or am I missing something here?
3. Brett proposed flaps driven in multiple places along the span. I scoffed at this idea, carbon torque tubes having been invented, but how about if the flaps are divided into independently moving segments, each with its own control horn? For one thing, this would be the mother of all lucky boxes. You want to tweak a flap to level the wing in roll? Just adjust pushrod length of one segment. You could have some segments move more than others: symmetrically, asymmetrically (Palmer differential flaps-- same sign as Palmer's or opposite)), or just the outboard outside segment for trim like Igor's or Ted's tab. Independently moving segments would allow a lighter wing structure. The wing could deflect without binding the flap hinge.
One caution is that you'd probably want to mass balance the pushrod that runs out the wing. Hang a weight on the other side of the bellcrank.
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Seems that fixed position flaps, leading or trailing, would have an adverse effect on inverted flight.
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Dear Dennis,
Look at trailing edge of Wilga' s fin (middle part) :
https://upload.wikimedia.org/wikipedia/commons/thumb/a/a0/PZL_104_Wilga_35A_Taupo_NZ_27.02.92R.jpg/800px-PZL_104_Wilga_35A_Taupo_NZ_27.02.92R.jpg
Nobody could explain amongst pilots, what is it for...
Istvan