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General control line discussion => Open Forum => Topic started by: Claudio Chacon on November 20, 2012, 10:40:26 AM
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Hello guys,
We ALL know -and this have been proven and sufficiently demostrated through the years- that properly sealed hinge lines is a must in order to get the most out of our planes in terms of flying performance.
Again, I'm sure that EVERYONE agrees with this fact.
Now, can anyone please explain me HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!! ??? ??? ???
Many of you in this forum know very well Sergey, and you know that he ain't no rookie!
Please, check out the pics attached (and enlight me!)
Thanks!
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Could it possibly be that the pilot's ability is far more important than the gap?
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Unsealed hinges...seem to work wonders waaaay back in 1968 when "The Bear" won the nats with his GGopler' and ol' Fox 35 Hummm? But by today's standards ::) but again------------we were then "judged by a different set of NAVY standards?"
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From the explanations of why one seals hinge gaps, those gaps look to be engineered specifically to work without sealing.
Those gaps are large (which means that small changes in gap spacing won't make a big difference), and pivot is buried in the elevator, meaning that the elevator leading edge sticks up above the stab, which should cause some turbulation effect (I don't know if it'll work, but that looks to be the intent).
Fellows with a less casual acquaintance with aerodynamics than me may have something to add, but it looks like he's found a good alternative.
And who knows? Maybe he would have taken first place if he'd used conventional hinges and sealed the gaps?
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Often, aileron hinge points on full size aircraft are located ahead of the gap. Aileron deflection causes the leading edge to move in the opposite direction of the main flap area deflection. The resulting "scoop" actually enhances aileron lift.
Floyd
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Might be the reason he finished 14th instead of higher?
Full scale acro aircraft use sealed hinge lines. There is no reason that the model wouldn't fly and do the pattern, and there might be some quirky exception to the laws of physics for this, but I kinda doubt it.
Dan McEntee
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What is the best clear tape to use to seal hinges? I can't get any to stick to my Bearcat
Ed
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Often, aileron hinge points on full size aircraft are located ahead of the gap. Aileron deflection causes the leading edge to move in the opposite direction of the main flap area deflection. The resulting "scoop" actually enhances aileron lift.
Floyd
A minor point, that works if the hinge axis is BEHIND the LE
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I notice there are flies. It's the inexplicable boost from the flies.
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What is the best clear tape to use to seal hinges? I can't get any to stick to my Bearcat
Ed
What's on my bench is Scotch "Gloss Multitask" tape, and it seems to work for me. Just about anything that's from 3M and is clear will probably work.
Did you make sure that the surfaces you were taping to were clean? This stuff isn't going to stick well to an oil-soaked surface.
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Hello guys,
We ALL know -and this have been proven and sufficiently demostrated through the years- that properly sealed hinge lines is a must in order to get the most out of our planes in terms of flying performance.
Again, I'm sure that EVERYONE agrees with this fact.
Now, can anyone please explain me HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!! ??? ??? ???
Many of you in this forum know very well Sergey, and you know that he ain't no rookie!
Please, check out the pics attached (and enlight me!)
Thanks!
YES we are sure !!!! ;D ;D ;D
Use thin sealing tape, or packaging tape, you can buy this tape that is thin or thick, the thin tape is easy to find.
It makes the stuntships turn , stable and consistent. This is the biggest problem when conditions change, The turn rate will change with light of heavy winds, and slower or faster speeds some times, or most times.
The KEY word here is "consistent" ie mainly the same in all conditions, plane turn feels the same in winds, and the trim stays .
Randy
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The best tape we have found is called "Moores' Crystal Clear." It is a mylar
type and goes on smooth and comes off clean when you need to replace it.
Sealing the hingelines is just as important as putting a bellcrank in to move
the surfaces. If you don't tape it up it is not worth flying. It will never fly as
well as it could and is impossible to trim out. RJ
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Look up 'slotted flaps' on full size aircraft, the slot is designed to accelerate air over the flaps leading edge and thus it sticks better to its surface.
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I have used Moores in the past. Good stuff. I tried it on my last two planes with no noticeable difference. So when it wore and needed to come off I didn’t replace it.
I have had planes in the past where sealed lines made a huge difference right off the bat! It is something to try and trim with on every model.
Let me see if I can get this out of my head and onto the screen correctly.
When you try to make the gap as tight as possible there will still be a small gap there bigger than an air molecule. When the flap is deflected there is a pressure along that side of the wing and flap. The air will find the open spot in gap and break through causing a small "spout" of air going through the gap to the back side of the deflected surface. This in turn snaps the air off the back of the flap or disrupts it. In some cases it isn’t noticeable. In others the plane won’t be consistent and you can’t trim it out and you go crazy trying. Seal the lines and BOOM all is well as the air stays on the sides it is supposed to stay on during deflection.
Now the larger gapped on purpose surfaces is doing something different all together. When this is deflected the air flows through the gap on purpose and over the back of the flap and the front of the flap at the same time. It is almost as if the surface is receiving its own airflow top and bottom separate from the wing. Talking with Frank Williams at the Nats he said his "Slot Machine" using slotted flaps similar to what you see here was a beast over head and in the hourglass. Smooth tension and characteristics like nothing he had ever tried before. Certainly something to revisit!
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When you tape a hinge line do you tape both sides or just one, do you tape just the flaps or the elevator too?
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Hello guys,
We ALL know -and this have been proven and sufficiently demostrated through the years- that properly sealed hinge lines is a must in order to get the most out of our planes in terms of flying performance.
Again, I'm sure that EVERYONE agrees with this fact.
Now, can anyone please explain me HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!! ??? ??? ???
Many of you in this forum know very well Sergey, and you know that he ain't no rookie!
Of course sealing the hinge lines is not mandatory to make the airplane fly. If you very carefully control the way the gaps change as the surfaces move, any ill trim effects will be minimized, and then you adjust around whatever non-linear effects you get from having flow through the gap. People flew that way for decades.
People also had mysterious and unresolvable trim issues that varied wildly from day to day and from airplane to airplane for decades, too. Usually, through dint of perseverance, lots of trim adjustments and lots of flights to "get used" to the airplane, they came to grips with it. As far as I can see, there isn't a lot of value in doing it that way if there is an alternative.
Brett
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When you tape a hinge line do you tape both sides or just one, do you tape just the flaps or the elevator too?
Sealing one side is all that is necessary – most seal the bottom for cosmetic reasons. Seal flaps and elevator.
Something not stated is that sealing the hinge lines eliminates potential asymmetry due to variation in the gaps.
Jim Hoffman
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If you hinge like Keith Trostle you won't have to use unsightly tape. They're sealed already. His 1960's Focke Wulf is a good example.
Looks like the model in the picture was trying an old fashioned way of boost, or just trying to excite flow by sticking the balance into the boundary layer aft of the hingeline. His hinges are around 10 to 20% of the flap chord, little less on the elevator. It works on real acro airplanes to an extent.
Chris...
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This was done in my garage wind tunnel back in the late 80's. The section was a 3" stab and 3" elevator run at ~50mph. The blue line is with a gap that was "Concours quality", barely the width of a sheet of paper. The redline was with tape sealing the joint. Past about 15 deg of elevator deflection, the difference is very significant.
It looks to me like Belko is after an effect of "bumping" the leading edge of the elevator up above the nominal position to help promote an attachment of flow over the top of the surface.
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This was done in my garage wind tunnel back in the late 80's. The section was a 3" stab and 3" elevator run at ~50mph. The blue line is with a gap that was "Concours quality", barely the width of a sheet of paper. The redline was with tape sealing the joint. Past about 15 deg of elevator deflection, the difference is very significant.
It looks to me like Belko is after an effect of "bumping" the leading edge of the elevator up above the nominal position to help promote an attachment of flow over the top of the surface.
Forgive my naivety here Frank, but is not the lower 'concourse' curve on your graph less drastic and more predictable in practice?
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If you hinge like Keith Trostle you won't have to use unsightly tape. They're sealed already. His 1960's Focke Wulf is a good example.
Looks like the model in the picture was trying an old fashioned way of boost, or just trying to excite flow by sticking the balance into the boundary layer aft of the hingeline. His hinges are around 10 to 20% of the flap chord, little less on the elevator. It works on real acro airplanes to an extent.
Chris...
Although I would not discount Al Rabe's "car hood" airfoil testing with regard to these sorts of airfoils/hinges.
What concerns me most about the various intentional or inevitable gap deals is the non-linearity of the control response. Getting enough lift is a complete non-issue with any reasonable LE radius and modern powerplant/props, so I think designing it for most consistent and linear response is a lot more important. In full-scale acrobatic airplanes you want it to be non-linear and/or stall abruptly, I think, but we certainly don't want that.
Brett
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Yes! We even do this on Old Timers, using 'over-and-under' cloth (or polyester) hinges placed next to each other, full-span. Makes a world of difference.
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Mike,
Really nice looking Ringmaster, yours?
Increased stab/elevator area?
Charles
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If you hinge like Keith Trostle you won't have to use unsightly tape. They're sealed already. His 1960's Focke Wulf is a good example.
Looks like the model in the picture was trying an old fashioned way of boost, or just trying to excite flow by sticking the balance into the boundary layer aft of the hingeline. His hinges are around 10 to 20% of the flap chord, little less on the elevator. It works on real acro airplanes to an extent.
Chris...
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Mike,
Really nice looking Ringmaster, yours?
Increased stab/elevator area?
Charles
Yes, mine....from 2005/2006. Long gone now. And yes, stock stab/elev area. Camera angle probably makes it look larger.
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Forgive my naivety here Frank, but is not the lower 'concourse' curve on your graph less drastic and more predictable in practice?
Chris
Yes it might appear that way because I didn't focus in with alot of measurements around the zero elevator deflection, for either configuration. I was really looking at the linearity of the curve and the maximum force produced. So you're correct that maybe this chart isn't totally germaine to the discussion at hand. I found interesting that there was 20% more force produced by the stab/elev section at an elevator deflection of 25 degrees.
What we really need to see, is how the curves vary with different gap widths, around a zero elevator deflection. I stopped when I saw that the sealed curve was very linear and had a significant increase in maximum lift.
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OK Gentlemen! Thank you VERY much for all your enlightening contributions!
Mr. Frank Williams graphic was a real eye opener!
Thanks again,
Claudio.
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Often, aileron hinge points on full size aircraft are located ahead of the gap. Aileron deflection causes the leading edge to move in the opposite direction of the main flap area deflection. The resulting "scoop" actually enhances aileron lift.
Floyd
Floyd, that's not quite true. We do that to balance the forces and reduce the moment, this lowering the control forces. Notice that it was prevalent on older aircraft with cable controls, after hydraulic actuators connected to servo valves came alone, the balance area disappears.
The balance area creates a lot of drag (and can lend themselves to flutter problems). Sealed gaps increase efficiency and reduce moments, so it's win-win.
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The real question to be asked is:
What harm can it do if the hinge tape is properly applied?
Ted Fancher
p.s. The whole stunt world discussion of sealed hinge lines started many years ago after I brought it up in one of my old Model Aviation columns.
That is "NOT", however, an attempt to take credit for it. The credit goes to Denny Adamisin who brought up the fact that he routinellysealed his hinge lines during a chance "chow time" get together. It was more or less like getting slapped in the face! Why would anyone interested in using lift to make a dog do tricks not do everything possible to maximize and insure the consistency of that prime factor in doing so. I went home, sealed hinge lines on a couple of semi dogs and never looked back.
The fact that an individual airplane might ultimately prove to have not been noticeably improved does not negate the wisdom of the question above. The question itself out to be juxtaposed with a second question, by the way. That would be: "What sort of potential problems can I erase from my trimming list as a result of sealing them as the last step of bench trimming...before the motor is ever started? The answer to that question would take a lot more words than the answer to the first question.
Why leave a easily closed door open in hopes that it might not freeze tonight? Shut the dang door, go to bed and sleep peacefully!
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The real question to be asked is:
What harm can it do if the hinge tape is properly applied?
Well, if your plane is built like Mr. Belko's, then your surfaces won't move any more.
It's certainly an interesting approach, and if I had a lot more time on my hands and flying skills in them, I might even feel motivated to build an airplane or three and see if there was a noticeable difference. It's definitely not something that lends itself well to an A vs. B comparison.
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Again, look at slotted flaps on full size aircraft.
Its been well proven since the 1920's that properly designed and executed slots between the main wing and the movable control surfaces does increase lift further than attached ones.
(And I quote from a NACA source "While in the case of an ordinary trailing end flap any leakage through a gap between the main wing and the flap seems to be highly detrimental, a combination of a flap and a properly shaped slot proves to be very efficient." NACA Tech report 554 1936.)
The issue is promoting the air acceleration evenly between upright and inverted as most known setups are asymmetrical and complicated to build.
Models will not easily promote that level of complexity thus we 'do what we can when we can' and call it consistency.
All of this seems like a bit of a one sided argument without the author of the model in the original post being present to put his case forward to the jury.
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Well, this might not be 100% on topic, but I have decided to use "cloth" hinges on all my newly built stunters so as to not have to worry about sealing the hinge lines with tape.
BIG Bear
RNMM/AMM
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The real question to be asked is:
What harm can it do if the hinge tape is properly applied?
Well I would have to disagree somewhat Ted.
I consider it to be "HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!!"
The subject is the deliberate use of a pronounced gap, his successful use of it (more than evidenced by the obvious photos and his placement in serious competition) and never is there any mention of sealing it, tape or otherwise.
Clearly some fliers consider there is work to be done in this area, and for that I applaud him (and for his outstanding range of F2B engines that again ..... are different.)
Thanks.
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Full-scale airplanes that have surfaces that deflect both ways (elevators, rudders) typically have hinge lines behind the surface and sealed hinge gaps. Sealing the gap of a surface hinged behind the LE is hard to do with our size planes without too much friction. So we choose between sealed hinges at the surface LE or unsealed hinges behind the LE. The latter has two appealing features: less hinge moment and easy surface removal. It may be worth doing some experiments or looking up old NACA data to see if we can make surfaces with gapped hinge lines get as much lift and as consistent lift as we get just by sealing our simple hinges. Theoretically, there's extra lift to be had from properly shaped gaps. Frank Williams and Wes Dick have done some experimenting and may know how. Sergey and the Yatsenkos know more than most of us, but from what I've seen and flown, they don't have anything significantly better than our crude sealed flaps.
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In aircraft design, the rule is that the change in lift coefficient as a function of flap deflection increases 15 percent for a seal gap over an unsealed one. A good reference is Aircraft Design:A Conceptual Approach by Dan Raymer which by the way, is the one book you should own if you are into the engineering aspects of aircraft design.
Mr. Raymer sets out the first chapters showing why and how, and then in the following chapters actually designs a sport aircraft working through the design process. It's the standard text used for aspiring designers.
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In aircraft design, the rule is that the change in lift coefficient as a function of flap deflection increases 15 percent for a seal gap over an unsealed one. A good reference is Aircraft Design:A Conceptual Approach by Dan Raymer which by the way, is the one book you should own if you are into the engineering aspects of aircraft design.
Mr. Raymer sets out the first chapters showing why and how, and then in the following chapters actually designs a sport aircraft working through the design process. It's the standard text used for aspiring designers. Yes, it's an engineering text and the math may beyond the scope of the casual reader, but he does great job with the qualitative analysis as well.
It's fascinating, and I refer to it constantly.
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There is no need to seal the elevator hinge gap. You don't need all the tailplane lift you can get - only enough to steer the plane.
It might help to seal the wing flap gap so as to create the maximum possible lift.
In real planes it is seldom if ever necessary to create all the lift you can possibly get.
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I just went down and checked out the Norm Whittle designed and built Eagle I flew most of last season. There are no seals on either flaps or elevators. The wing TE is squared off and the flap LE is triangular, pretty much as normal practise. The hinges are Robart "Hinge Points", and are notched back into the flaps/elevators much like Mr. Belko's. At neutral, the hinge gap is about the same as the thickness of the cardboard of a line clip pack. The outboard flap has a little more clearance. The interesting thing is that as the surfaces articulate, the hinge gap does not change noticeably. I would have thought a radius would be better. The disadvantage, IMO, is that you can't make the surfaces removeable...which I happen to think is very important.
Norm says it's 638 sq. in., and it weighs 67 oz here on the coast (with 1 oz. of added nose weight to comp for the 2 oz of moisture it absorbed), piped .46VF. Flies pretty darned good, IMO, tho I'm not saying it's wonderful or needing some trim changes. The prop change and nose weight (late Sept.) were big improvements. I'd like to get PW or Howard to fly it, sometime, but their ears are very sensitive now, ya know. S?P Steve
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Full-scale airplanes that have surfaces that deflect both ways (elevators, rudders) typically have hinge lines behind the surface and sealed hinge gaps. Sealing the gap of a surface hinged behind the LE is hard to do with our size planes without too much friction. So we choose between sealed hinges at the surface LE or unsealed hinges behind the LE. The latter has two appealing features: less hinge moment and easy surface removal. It may be worth doing some experiments or looking up old NACA data to see if we can make surfaces with gapped hinge lines get as much lift and as consistent lift as we get just by sealing our simple hinges. Theoretically, there's extra lift to be had from properly shaped gaps. Frank Williams and Wes Dick have done some experimenting and may know how. Sergey and the Yatsenkos know more than most of us, but from what I've seen and flown, they don't have anything significantly better than our crude sealed flaps.
Just an observation, but when Sergey came to Tucson a few years ago to fly in a contest here, He took a neat little box out of his rented car, began removing airplane parts from the box, assembled his airplane, to include installing the flaps and elevators onto the flying surfaces, aligned everything and flew the thing without needing to actually trim anything.
The flaps and elevators had fairly large gaps (maybe 3/32 inch) and were hinged behind the flap and elevator leading edges. I was curious about it but really couldn't quite understand his complete answer, but the best I understood the situation was that the gaps made the flaps less efficient but they were still adequate and because they (the gaps) were fairly large they were easy to make consistent. With a take apart that has removable flaps etc it would be a lot of trouble to seal the flaps and elevators each time the airplane is taken apart and reassembled.
The airplane had one of his 75's in it and it flew very well. He won the contest and here in Tucson that's not cherry picking.
Personally I always seal flaps and elevator hinge lines because I had serious trim problems with unsealed hinge lines a long, long time ago, and being primarily a combat flier then, my Stunt Guru at that time (Mr Hoffman) said to always seal them and it works. However I've never built
wide hinge lines and tried to make them consistent because I always seal them.
Randy Cuberly
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No point in having gaps unless: a) you do some science to make sure they're blowing the flaps right, or 2) you hinge the flap aft of the LE, or iii) both. You can remove the wing and flap together if you use a slot for the control horn to slide into. The slot only needs to bear a load at its end, when it's in the flying configuration.
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There is no need to seal the elevator hinge gap. You don't need all the tailplane lift you can get - only enough to steer the plane.
It might help to seal the wing flap gap so as to create the maximum possible lift.
But, again - getting more lift is not a critical issue. We have had enough lift (in the wing) to do as hard a corner as we want since about 1988.
The important part about sealing the hinge lines has only peripherally to do with enhancing the lift. A far more important effect is that it tends to remove variability in the lift over the range of control motion. The result is that the airplane is far more consistent in trim, many of the previous problems that people had with "inside/outside" turn differences go away or are significantly reduced, and that the airplane is far more honest over time and over other variations.
Brett
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So Belko's model has inconsistent trim?
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So Belko's model has inconsistent trim?
I have no idea. Please read above.
Brett
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I have no idea. Please read above.
Brett
Mate, I have no idea also.
The more I read here the less I know. :-[
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I presume Brett's observation pertains to the flap configuration we use: hinged at the flap LE with only a small gap betwixt flap and wing.
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Here's a very objective account of Sergei's appearance at the Meet & Meat a few years ago. Brett made him some parts to fix his plane. http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=316105&mesg_id=316105&listing_type=search
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Hi Claudio
Since I started using sealed hinge gaps I cannot think of a reason to stop - no scenario where the seal might be CAUSING a problem. I am also pretty sure that sealing the gaps preempt those gaps from causing problems on their own.
I am also very impressed by the plot Frank Williams posted a few posts ago - it provides a solid justification for using seals.
So to answer your question YES I am sure and I always (since 1980) use them.
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Does anybody here read what anybody else writes?
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No.
I mean, yes.
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Are the Yatsenko models like the Shark equipped with sealed hinge lines? I can't remember checking this myself. Maybe Orestes seals his models so someone in the USA will know for sure. I do know however, that they do pretty well all over the globe in competitions. I enjoyed watching Sergei's huge model in Bulgaria. It was an impressive sight and also sounds wonderful. It could be that in the windy and gusty conditions that such a big model is difficult to fly. Either way, Sergei is a very good pilot and such a nice guy as well. Besides Igor's electric Max Bee, I watched Sergei's model the most.
Keith R
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Hi.
One thing to consider is that Sergey's model has fully take-apart construction, also flaps & elevators come off.
It's a big model, weights around 80oz. if I remember right.
I have taped hinges in my Yatsenko models (Shark). In good weather it allows me to fly with more forward c.g., but in strong wind and especially turbulent wind I like it more without tapes. Recently I haven't taped anymore.
Besides, as the hinge geometry is what it is (hinge pivot point in the center of Flap l.e. radius), you must make kind of a lip seal. This increases friction and causes some kind of hysteresis in control, especially in landing glide. For that reason I had to remove the tapes from stab hinge lines.
Also the chinese use to have huge hinge gaps without tape, plus their flaps look very flimsy.
Maybe the point is, that those molded planes are close to ideal weight, plus the accuracy of construction is better than average. Also, the eastern design filosophy is slightly differend (light weight, front c.g.), it makes taping less important. L
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Hi Claudio
Since I started using sealed hinge gaps I cannot think of a reason to stop - no scenario where the seal might be CAUSING a problem. I am also pretty sure that sealing the gaps preempt those gaps from causing problems on their own.
I am also very impressed by the plot Frank Williams posted a few posts ago - it provides a solid justification for using seals.
So to answer your question YES I am sure and I always (since 1980) use them.
Hi Dennis! Me neither! I seal my hinge lines too as a standard practice since 1984. But when I saw the pics you see in my original post, I began to scratch my head! I'm a mere mortal!
This "gap thing" seems to be a common russian way for hinge line treatment (with particular emphasis on the word SEEMS...I don't wanna cause an international conflict here ;D)
In the following picture (Anatoly Koleshnikov, 1986 WCH winner, Hungary) -although much less evident than in Mr. Belko's plane- you can still see the light coming through the flap hinge line.
Thanks for your input, pal H^^
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Does anybody here read what anybody else writes?
Yes, I read most of the stuff on this forum and a few others. Some parts I don't go to as they get too technical. Also some I don't respond to for the same reason. I love to build, can't finish worth a darn and fly worse than most beginners.
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Years back, most the pattern guys in R/C would use tape.
Some said it made no difference, others would swear by it.
Outstanding!
Charles
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Does anybody here read what anybody else writes?
Sometimes I wonder that myself??
The way I heard the story of how sealing came about, was that Bill Werwage built a classic model of one of his designs, Ares or one of his other designs, and was having a bit of a trim issue and was analyzing the problem by comparing the new one with the old one. He realized that the original was built with full span cloth hinges, and the new model wasn't, so he taped up the hinge lines and that corrected the problem. Don't remember who told me that but it is plausible.
As for comparing slotted flaps for fulls scale aircraft with flaps for a stunt model, they are the same but different in my opinion, with the slotted flaps doing a completely different, more complicated job. As I recall, there were some designs featured in the magazines years ago that had strange articulated flaps that could resemble slotted flaps, but they didn't go anywhere.
HAPPY THANKSGIVING!
Dan McEntee
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Does anybody here read what anybody else writes?
Well, except for that guy who's avatar is wearing a clown suit, yes.
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Does anybody here read what anybody else writes?
Not very many?
Chris...
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Does anybody here read what anybody else writes?
Why yes, Brother Howard, I do read all the posts in a thread........ ;D
BIG Bear
RNMM/AMM
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Define 'anybody.'
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Why?
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I do not have taped hinges on any of my planes and I use a rounded flap line in both wing and flaps. I think the main thing is to have a vry good fit and accurate hinge line so most of the air doesn't get by the flap hinge line. I think using a pointed flap on the leading edge that is harder to seal than a rounded one works better. I have used both but can tell very little difference in performance of a sealed hing line and one that isn't sealed. I never used sealed hinges on any of my designs. and the performance of the plane was better than I can fly. y1 y1
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Does sealing gaps helps to reduce flexibility of control surface besides of incrising lift ?
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No, if it is done correctly. RJ
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Well I would have to disagree somewhat Ted.
I consider it to be "HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!!"
The subject is the deliberate use of a pronounced gap, his successful use of it (more than evidenced by the obvious photos and his placement in serious competition) and never is there any mention of sealing it, tape or otherwise.
Clearly some fliers consider there is work to be done in this area, and for that I applaud him (and for his outstanding range of F2B engines that again ..... are different.)
Thanks.
Chris,
What Sergey proves--more than anything else-- is that sufficient "lift" isn't a huge problem in CL stunt. The probable advantage of a large gap is that it minimizes any effects of changes in the size of the gaps and the resultant differential in lift that results. I'd remind that perfectly competitive stunt flights can be performed by a well trimmed and powered stunt ship with no flaps at all. Properly powered, for instance, Dave Fitzgerald has regularly been competitive flying a Ringmaster with a consistent running Veco .19BB and a low pitch prop in any number of Classic events. Flaps are an advantage in a number of respects but aren't necessary to produce quality stunt patterns.
The debate over sealed versus non-sealed hinge lines really has more to do with consistent response of the airplane without undesirable pitch and roll issues exacerbated by differences in lift per unit of deflection of flaps and elevators: up versus down, roll left and right, etc.
I stand by my comment. There is nothing bad that can result from properly sealed hinge lines and a lot of trimming problems can be eliminated by doing so.
Have a great holiday.
Ted Fancher
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Pay attention!! Ted is also exactly right! RJ
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Dare I say there is not one of you out there that can build a stunt model with
flaps and elevators, myself included, that do not leak at the hingelines, period.
Since that is fact then it only stands to reason that they should be sealed or
taped up so as to preclude any leakage and therefore lessen the performance
of said model. An example would be a high performance sailplane, full size. I would
never fly one without the hingelines taped. The performance enhancement is
significant. Sure, you can fly the plane without it but again what's the point?
Try it, you'll like it and never look back. RJ
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Dare I say there is not one of you out there that can build a stunt model with
flaps and elevators, myself included, that do not leak at the hingelines, period.
Since that is fact then it only stands to reason that they should be sealed or
taped up so as to preclude any leakage and therefore lessen the performance
of said model. An example would be a high performance sailplane, full size. I would
never fly one without the hingelines taped. The performance enhancement is
significant. Sure, you can fly the plane without it but again what's the point?
Try it, you'll like it and never look back. RJ
No matter how small you make the gap, it's still smaller bigger than an air molecule.
As a point in fact (noted above) the larger the gap the less effect a variation in the gap will have. If the basic gap is .020" a difference of .005" is a 25% change. IF the gap is .100", a .005 change is only 5%. Sergey is doing what we all used to do, in additional to making it large, he is *very carefully controlling the gap". After I realized what was going on I would install the flaps with a .020 gap and futzed with it for hours to get it to be as constant as I could. Making it bigger would have lost a lot of performance (which, at the time, we needed, unlike now) but made it less touchy to the gap shape.
Brett
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In regards to the relative merits/demerits of large hinge gaps on stunt ships.
The biggest reason the "amount of lift produced per unit of flap/elevator deflection" is important is that the more deflection that is necessary to produce the lift required, the greater the line tension must be to allow the greater deflection to be accessible to the pilot, i.e. there must be enough line tension available to allow the flaps/elevators to be driven to the necessary deflection angle to produce the lift required.
Lift in stunt is required for only two reasons: First, so the wing can support the airplane under the full spectrum of G conditions encountered in a competitive stunt pattern without stalling and; second, to allow the tail to generate the "force" necessary to drive the wing to the Angle of attack required to produce that lift, plus enough additional lift to rotate the airplane to which the wing is attached to direct the thrust generated by the prop to the direction necessary to point the airplane in the desired direction.
The amount of tension required to accomplish these tasks can be minimized by reducing the amount of flap/elevator deflection necessary to achieve the lift required to accomplish these tasks. To the extent that more deflection is necessary to produce the required lift, the greater will be the line tension necessary to deflect the surfaces against the air loads. Any "system or configuration" that minimizes the amount of deflection necessary to achieve those ends will reduce the line tension necessary to do so. Sealed hinge lines are an obvious and easily achievable method of doing so.
Another effective source of minimizing the force necessary to deflect the control surfaces to the angle necessary is increasing the aspect ratio of the flaps/elevators. The "modern" split of stabilizer/elevator to less than 50/50 is a good demonstration of this. Too often people tend to think only the "elevator" or only the "flaps" produce lift and, thus, they need to be large to do so. Simply not true. What flaps/elevators do is alter the "airfoil configuration" of the "wing/flap" and/or the "stabilizer/elevator" to "cambered" sections that increases the lift potential of the total surface. The reality is that there is "modest" advantage from a lift perspective to "low aspect ratio (long chord per unit of span)" movable surfaces and a large disadvantage in that the greater the relative chord of the moving surface to its fixed surface the greater the "hinge moment", i.e. the force required to deflect it. Thus many "modern" designs, have narrower chord flaps/elevators relative to the chord of their fixed surfaces. As a result, such control surfaces require substantially less force to deflect, yet suffer only modestly versus movable surfaces of greater chord percentage. A net plus, IMHO.
One more "modern" approach to minimizing the control deflection required to perform competitive tricks with modest control inputs is the trend to more aft CGs. Modern era large tails allow stability to be maintained with CGs near the neutral point of the wing (~25% of the MAC [Mean Aerodynamic Chord]). Stable configurations with aft CGs require much less control deflection to provide the tail authority to achieve competitive corners. It also reduces the lift required of the wing because the download required of the tail to drive the pitch attitude to that desired is reduced.
In the great scheme of things, all the foregoing is just slightly above the "noise" factor and can be routinely overcome by superior piloting skills. The problem is, piloting skills at the very top are so high that the "noise" factor becomes relevant and, under competitive conditions, might well be one of the factors that makes the difference between 14th place and the top half dozen or less.
At least that's the way this over the hill, but once competitive, stunt flier sees it.
Ted Fancher
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I found the plot from MA.
Keith - I don't think the Sharks have any seals ... really free moving hinges though.
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At least that's the way this over the hill, but once competitive, stunt flier sees it.
And this over-the-hill, not quite competitive stunt flier, too.
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No matter how small you make the gap, it's still smaller than an air molecule.
Whoa! Those Californian air molecules are big.
(Sorry. I know what you meant. Couldn't resist. :) )
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I was wondering the same thing as Howard, as I read through the early part of this thread just now. The non-contradictory answers had already been given early on, but were not logically handled by all. I was then ready to chime in with Ted's later (thus far unread) points and in full agreement with Brett. I'm not sure how comparable RC pattern ships are to CL stunt here, due to vast differences in Reynolds numbers.
Still, it's just slotted flaps vs plain flaps and how to handle and employ each. To me there's no conflict here in the first place. As Ted and Brett have said here and so often before, sufficient lift is all that's needed - not too much. There are otherwise penalties to overcome. If a plane with sealed flaps is inordinately affected by gusts, then its lift curve is probably too steep, like that for a high-aspect-ratio wing in gusts. It probably needs less flap deflection. The point seems to be consistency, which most attribute to sealing, for the reasons given several times and initially, at least, ignored.
I finally saw Wes Dick's bi-directional, double-slotted flaps at our contest this year. Of course I was happy and fascinated to see them, while doubting that they'd prove advantageous, for reasons given on this thread. We were all fortunate to hear Wes' own impressions and to get a flight report from Bill Werwage, who checked it out. Both agreed that the plane was maneuverable and pretty consistent. However, both remarked on how much elevator and handle force were necessary in corners. Wes even warned Bill ahead of time to watch out for that near the ground. What I then felt was that more stab/elevator and/or tail arm was needed. Another way to look at this might be to say that the flaps seemed to further reduce the amount of wing needed in comparison to the other flight/control surfaces, while needlessly increasing the control forces (Edit: I probably should have noted more explicitly the expected increase in opposing pitching moment from such flaps). 'sounds a lot like what has been said here. Incidentally, Wes' flaps seemed to produce that lift pretty consistently, even though they flexed.
SO... the slotted Belco flaps serve their purposes in consistency and ease of assembling and trimming a take-apart model. Sealed plain flaps are preferable to unsealed plain flaps for reasons of consistency. They apparently increase efficiency (as should be expected), and the flap deflection and area should be adjusted to suit. Unsealed plain flaps may or may not function well, and as Ted says, why not just eliminate the variance by sealing? I can't imagine anyone thinking that anyone here actually meant to suggest sealing slotted flaps! Oh, FWIW, even my SkyRay liked the elevator hinge-line seal.
Here are some pictures of Wes Dick's cool double slotted flaps...
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I found the plot from MA.
Keith - I don't think the Sharks have any seals ... really free moving hinges though.
Thanks very much Frank. That's a most interesting chart.......especially the bump at higher deflections angles.
Keith R
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Hi Genlemen,
I was in reading your threads and want to say that Mr. Fencher is very corect in what he
is telling us. Still remember his 'doctor' post some time ago /pampa/.Everything comes from
the type of airplane you have/build. Do we remember Netzeband.
The rest is flying, flying @ trimming. Mr.Malila also pointed out and I agree with him..there are
major differences in how Eastern country modelers are building and the rest.
Thank you.
Valentin Apostolov
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Still, it's just slotted flaps vs plain flaps and how to handle and employ each. To me there's no conflict here in the first place. As Ted and Brett have said here and so often before, sufficient lift is all that's needed - not too much. There are otherwise penalties to overcome. If a plane with sealed flaps is inordinately affected by gusts, then its lift curve is probably too steep, like that for a high-aspect-ratio wing in gusts. It probably needs less flap deflection.
Wow, there's a lot here, and plenty of stunt score available to he who unravels it.
As Ted and Brett have said here and so often before, sufficient lift is all that's needed - not too much.
Ted has said this in his previous writings, but he was not using the standard aeronautical definition of lift. He may have been describing the evil effect of the rate of change of pitching moment with angle of attack petering out at high lift.
Brett's comment about lift above was to emphasize the benefit of flap taping on consistency, rather than on max CL. I think you are on the right track regarding gust sensitivity, but I think you are looking only at section characteristics, rather than those of the whole plane d CL / d alpha, rather than (d L / d alpha) / m. A good way to reduce gust sensitivity for a given turn radius capability is by having a high CL max and a hefty wing loading. A 747 in approach configuration doesn't get blown around on a blustery day as much as a Cub with the same stall margin. Deliberately unsealing the flaps to get better gust response puts you on the nether parts of the lift curve. I think this is an idea worth pursuing, but for the airfoils we use, most folks high-scoring stunt fliers elect to operate in the linear part of the lift curve, where the airplane's response is dependable.
However, both remarked on how much elevator and handle force were necessary in corners. Wes even warned Bill ahead of time to watch out for that near the ground. What I then felt was that more stab/elevator and/or tail arm was needed.
That's what the clown on the left thought about the airplane he is holding in the picture. He didn't understand the problem he was having, and more elevator made it a lot worse.
I can't imagine anyone thinking that anyone here actually meant to suggest sealing slotted flaps!
Without sealed elevator gaps, a 707 would be almost impossible to fly. There is a heap of stunt score available to whoever figures out a frictionless way to seal stunt flaps hinged behind their leading edge.
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There is a heap of stunt score available to whoever figures out a frictionless way to seal stunt flaps hinged behind their leading edge.
Hello Howard.
I almost do that on my Bearcat. What I do is not totally without friction, but it is close and it works. My stab/elevators are 1/2" thick. The elevators have a 1/4" radius LE. The hinge line is 7/32" behind the elevator hinge line and the hinge line is sealed. By some accounts, this Bearcat has a "respectable" corner. And I have some interesting obsevations on the way this sealing process works.
Keith
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According to Pete Peterson, the Bearcat flies splendidly. I never noticed the hinges. My mind was so boggled by the rudder mechanism that I never got that far forward. Bring it out one more time so I can look at the hinges.
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There is quite a bit to chew on here, so I will simply say how I have seen all of this played out In Australia.
Blunt diamond shaped flap/elevator leading edge pushed up hard against the trailing edge of the wing, no seal added and the parameters are the control surfaces must droop under their own weight without lines attached.
As the flap angles towards its maximum usable deflection any gap on the high pressure side will naturally approach zero and virtually close anyway.
I too worry about the fact that any simple seal will give friction and any complicated seal could be prone to failure.
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I'll have a couple words to add tomorrow. - SK
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I too worry about the fact that any simple seal will give friction and any complicated seal could be prone to failure.
A simple tape seal as shown in any number of posts on here and SSW will cross the gap right in line with the hinges and add no detectable friction or resistance. When done right the tape will simply bend and that has absolutely negligible effect. What will screw it up is any sort of accordion or rolling motion of the tape.
Pushing it tight up against the TE is likely to lead to the worst of all conditions, a small or zero gap at some points in the travel, and a substantially wider gap at other points. If you are going to do it that way make sure that you put the hinges very close to each other, so when there is load on the flap, it won't ballon out between the hinges. Almost the entire point of sealing it is to make sure the leakage is the same (i.e. zero) throughout the travel.
Brett
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Pushing it tight up against the TE is likely to lead to the worst of all conditions, a small or zero gap at some points in the travel, and a substantially wider gap at other points. If you are going to do it that way make sure that you put the hinges very close to each other, so when there is load on the flap, it won't ballon out between the hinges. Almost the entire point of sealing it is to make sure the leakage is the same (i.e. zero) throughout the travel.
Brett
Hi Brett,
I probably did not explain myself well enough back there.
When the flaps are pushed hard up against the trailing edge, that is exactly where the hinge line is - the flap rotates around its sharp leading edge and at no point during rotation does the gap vary. In other words the contact edge IS the the pivot edge.
I would assume that suffering any gap inflight would mean flap flex and most of better fliers here would be well on top of that problem.
Very informative thread so far, thanks.
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I'll have a couple words to add tomorrow. - SK
I falsely accused you of not considering the whole airplane. I fixed my post above. You considered aspect ratio, but I don't think that's the biggest player. Gust response in normal acceleration per unit alpha is proportional to q S dCL/dα / m, where q is dynamic pressure, CL is lift coefficient, α is angle of attack, S is wing area, and m is airplane mass. If there's no wind, turn radius is proportional to m / (S CL). m/S is wing loading, so the more CL you can get, the higher the wing loading you can have for a given turn radius. Wing loading is the first thing that comes to mind for gust response. You can change lift curve slope by changing aspect ratio, but other considerations are probably more important in picking aspect ratio.
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Interesting thread. I don't have a dog in this yard, however I well remember the BIG MAN in RC that was a definite proponent of sealing ailerons - like CL flaps - and he was RIGHT. Sealing ailerons or flaps is very important if one wishes to lessen wing wobble as much as one can do.
Don Lowe was the BIG MAN and while there were differences in certain politics, Mr. Lowe was the best of the best when it came to the "How does we do it? " stuff. I never questioned him as he always knew exactly what needed to be done with a toy airplane. y1
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HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!! ??? ??? ???
good question Claudio, but I see it little bit different ... I am sure top 3 had tape sealed hinges ... I cannot speak for Paul and Dave, but I expect the same ... so top 5 has sealed hinges and only then come guys from ukraine with such construction of composite models with large gaps ... and it looks relatively consistent if we consider guys building but also developing their models, which are good flyers and I am sure they know what they do ... so for me sealing looks like good way :- ))
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good question Claudio, but I see it little bit different ... I am sure top 3 had tape sealed hinges ... I cannot speak for Paul and Dave, but I expect the same ... so top 5 has sealed hinges and only then come guys from ukraine with such construction of composite models with large gaps ... and it looks relatively consistent if we consider guys building but also developing their models, which are good flyers and I am sure they know what they do ... so for me sealing looks like good way :- ))
Yes, Igor. I agree completely that a properly sealed hinge line is the way to go. That was precisely the reason of my original post.
Thanks! H^^
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Just a few comments. I didn't mean to oversimplify things earlier, but this was started on the general forum.
Ted has said this in his previous writings, but he was not using the standard aeronautical definition of lift. He may have been describing the evil effect of the rate of change of pitching moment with angle of attack petering out at high lift.
I was talking about the lift curve slope and consequent actual lift force at some alpha for a given weight model, as I presumed Ted was. I think that for any given model, there can be too little mass and/or too steep a slope, making planes jumpy and devoid of enough inertia to deal well with gusts. With a constant theoretical slope for flapless planes, the flap progression ought to be the major determiner of that slope (right??). I also didn’t mention the possible role of span-wise a.c. position in encounters with side gusts. I agree with what you have said.
Brett's comment about lift above was to emphasize the benefit of flap taping on consistency, rather than on max CL. I think you are on the right track regarding gust sensitivity, but I think you are looking at d CL / d alpha, rather than (d L / d alpha) / m. A good way to reduce gust sensitivity for a given turn radius capability is by having a high CL max and a hefty wing loading..
‘understand and agree. I tend to think of the two affects (slope of either curve and mass) separately, but see that your second expression is a nice overall measure. I thought that's what I said about consistency. Of course, I know that for level flight, the lift equals the plane's weight, regardless of the wing mechanisms. I do think though that for any particular model, there can be too much lift at other aoa’s (alphas), so that too little input is needed and there is too much gust sensitivity (increase in lift per change in air speed relative to weight – which is what I think you’ve said). ‘guess I’m being redundant, but...for reasons akin to what you’ve posted, I’d then diminish the flap deflection or area – or add that mass - to deal with gusts. Elevator/flap ratios enter here. The post from the member who did not seal flaps because of gust sensitivity seemed to suggest that gusts were creating too much sudden extra lift; I took him to mean that he’d left the flaps unsealed to prevent the plane's reacting too much. So I’d have chosen those more potent and consistent sealed flaps, but with less deflection or area.
That's what the clown on the left thought about the airplane he is holding in the picture. He didn't understand the problem he was having, and more elevator made it a lot worse.
I meant more stabilizer area and tail arm, with the appropriate % elevator area. In other words, “stab/elevator” was intended to mean taken together as “horizontal tail (area)”. FWIW, for the same tail, a longer tail arm would actually require a tiny bit more elevator deflection to have the same effect in maneuvers, since the horizontal tail’s aoa increases with distance from the c.g. But, while increasing elevator deflection is the easiest thing to try, I’d expect increasing tail effect as a whole – stabilizing and lift producing - to be the better bet. Keeping the elevator to stab area ratio at a reasonable value seems prudent. That was just my initial take from what I’ve tried and read.
Without sealed elevator gaps, a 707 would be almost impossible to fly. There is a heap of stunt score available to whoever figures out a frictionless way to seal stunt flaps hinged behind their leading edge.
That fortunately doesn’t appear to be so true of our models. Perhaps I’m just not understanding what was meant, but to me, a slotted flap is a slotted flap. When extended/deflected, it has to be open, or there’s no slot. So do you folks mean sealed just at or near neutral? If not, I’m not seeing how deflecting a sealed flap's leading edge above the t.e. surface could help. If it’s better for it to be sealed at zero deflection, that’s fine, but I still cannot imagine anyone wanting to tape a slot on a model, or having the controls even work then.
If I’ve still missed the boat, I’m always willing to learn, but I sense that this part of the discussion has really exceeded the tolerance of some of its general contributors, who like us to play out on the south 40. - SK
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good question Claudio, but I see it little bit different ... I am sure top 3 had tape sealed hinges ... I cannot speak for Paul and Dave, but I expect the same ... so top 5 has sealed hinges and only then come guys from ukraine with such construction of composite models with large gaps ... and it looks relatively consistent if we consider guys building but also developing their models, which are good flyers and I am sure they know what they do ... so for me sealing looks like good way :- ))
Dave's certainly is, we would disown him otherwise. I am pretty sure Paul's airplane is, too. He was the first person to note that there was a difference between sealing it only between the hinges and sealing over the hinges (2005 NATs)
As alluded to earlier, if there was some good way to keep the gaps constant over the travel and eliminate construction differences from airplane to airplane, most of the value of sealing it up would go away. The best way to keep it consistent would be to build it in a mold - which is how the Sharks, "Classic"s , etc, are built. That's probably why a lot of these airplanes get away with it with no impact.
BTW, if you use a continuous hinge pin, it gives you the requisite gap, and a place to attach the tape that holds it solidly in the gap.
Brett
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If not, I’m not seeing how deflecting a sealed flap's leading edge above the t.e. surface could help.
I think it provides an opportunity for the flow over the wing to reattach to the flap. At least, I assume that's what the hullabaloo is about.
Maybe Howard could speak up. And if it's just about flow reattaching, would turbulators around the LE fix things without funky (to us) surface geometry?
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I think that for any given model, there can be too little mass and/or too steep a slope, making planes jumpy and devoid of enough inertia to deal well with gusts. With a constant theoretical slope for flapless planes, the flap progression ought to be the major determiner of that slope (right??).
No. The transfer function from gust to airplane response is different from the transfer function from handle to airplane response. This is a subtlety that I have seen confused by actual S&C engineers-- one of them, anyhow. A gust that increases lift won't increase the flap deflection. If anything, a gust blows the flap down and softens the gust response, so even at the same wing loading, the unflapped wing responds more to gusts. The Beringers have very wimpy flap control horns, maybe for just this gust load alleviation effect.
I meant more stabilizer area and tail arm, with the appropriate % elevator area. In other words, “stab/elevator” was intended to mean taken together as “horizontal tail (area)”. FWIW, for the same tail, a longer tail arm would actually require a tiny bit more elevator deflection to have the same effect in maneuvers, since the horizontal tail’s aoa increases with distance from the c.g. But, while increasing elevator deflection is the easiest thing to try, I’d expect increasing tail effect as a whole – stabilizing and lift producing - to be the better bet. Keeping the elevator to stab area ratio at a reasonable value seems prudent. That was just my initial take from what I’ve tried and read.
The problem the clown had was hinge moment, rather than pitching moment. I suspect Wes would have that problem, too. Ted writes about it above. I am trying to quantify all that stuff and write it up.
That fortunately doesn’t appear to be so true of our models. Perhaps I’m just not understanding what was meant, but to me, a slotted flap is a slotted flap. When extended/deflected, it has to be open, or there’s no slot. So do you folks mean sealed just at or near neutral? If not, I’m not seeing how deflecting a sealed flap's leading edge above the t.e. surface could help. If it’s better for it to be sealed at zero deflection, that’s fine, but I still cannot imagine anyone wanting to tape a slot on a model, or having the controls even work then.
There are a couple of different kinds of slots being discussed. Full-scale airplanes have slots in front of flaps to energize the air in the boundary layer over the flaps to keep the flow stuck down and make more lift. That's what Wes is shooting for. It is hard to mechanize for surfaces that move rapidly in both directions. If you can do it, you wouldn't want to tape them. The flap gaps typical of American stunters hurt, rather than help lift, which is a secondary reason to tape them. I, too, can't see how deflecting a sealed flap's LE above the main wing element's surface helps lift, although maybe it does. The biggest effect of hinging a stunt plane flap aft of the LE is to reduce hinge moment. Primary control surfaces (elevators, rudders, ailerons) on fast full-scale airplanes are usually hinged aft of the LE and are sealed. This is mainly to control hinge moments, particularly for control surfaces without hydraulic boost.
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Does anybody here read what anybody else writes?
Hey Howard I did