Author Topic: Full Span Flaps or Not (Read 4041 times)

Dave Wenzel · « **on:** December 16, 2010, 10:08:31 PM »

Hi Yall. Am working on a Banshee right now, and am a returnee to C/L. My question is what's the difference between full span flaps and flaps that end short of the tips. I understand wings like the Smoothie would have hugh flaps if they were full span, but take the SV-11, the flaps end short of the tips. Also wonder about flap area being larger near the body and taper smaller towards the tip???
Thanks.
DAVE

39847

Howard Rush · « **Reply #1 on:** December 16, 2010, 11:08:36 PM »

Some planes have one, and some have the other. Dave Fitzgerald's world champion airplane has one of each. My flaps go all the way to the end of the wing: I don't want the aerodynamic discontinuity of a gap opening and closing while I'm trying to fly level. I'd expect the fraction of the wing chord that's flap should be about constant, although it's standard practice to have the tip chord of one flap to be larger than that of the other. This a a trim thing too subtle for me to feel or even to remember which one is bigger.

If you take a design made for one and use the other, your elevator won't be the size the designer would have recommended.

You will get some bogus advice about tip vortices

PJ Rowland · « **Reply #2 on:** December 16, 2010, 11:11:35 PM »

This question came up on Stuka stunt forum.
( I trust im not stepping on toes simply making the information avaliable to others. )

I asked the same question ; trim tabs or full span flaps.

Here is Paul walkers response to that exact question ;

Anyway, to your question. For years, I have been unhappy with tweaking flaps by bending the flap horn. So, on this plane, I made the outer 3 inches of the flaps trim tabs for leveling the plane. It did that job, however another problem turned up. It became inconsistent in its trim adjustments. It simply would not turn consistent corners no matter what I did. My coach thought I was simply whining, until he saw it first hand, and agreed that something was wrong. It would take a different "set" through each corner. In this case "set" means that the angle the wing makes with respect to the lines (roll) was not consistent. I checked all the linkages and they were all tight, and the tabs were not moveable in any fashion. They were sealed as were the flaps. I could find no reason for the change in roll attitude.

During that flying session with Don, I finally tried an experiment. I removed the linkages to the tabs, and taped the tabs to the flaps, and the issue of inconsistent roll attitude completely went away. Why, I not sure, but I clearly could see and feel the difference, as well as Don.

Before the Nats, I simply glued the two together and painted a black line at the joint to cover. I haven't made separate trim tabs since.

------

This was ted Fanchers Chime in also :

The Imitation experiment backed up Bob's comments to a "T".

The reason is pretty straight forward. When the flaps are deflected the change our symmetrical airfoil to a cambered airfoil. cambered airfoils have "pitching moments" which result in such a wing wanting to rotate in the direction of the camber and that tendency must be countered by download from the tail. Many fliers have experienced this phenomenon when the pushrod from the flap to the elevator failed and when they attempted to put in up control as the nose dropped the airplane, instead, pitched more down and crashed. Don't ask me how I know this.

When we put flaps on a wing we invite negative pitching moments to our party and must deal with the unintended party crasher they bring with them.

In order to "turn" our airplane in the desired direction (let's say "up" for an inside corner) we must apply enough up control to allow the tail to not only make the airplane pitch up but also to first overcome the negative pitching moment of the cambered wing that shows up as the flaps deflect down to camber the wing and help to produce the lift to support the airplane in the corner.

If full span flaps are employed the entire wing span will be producing this negative pitching moment and more tail download will be required to overcome the effect. As the span of the flaps relative to the wings is reduced less of the wing is cambered and the negative pitching moment is reduced and a given amount of pilot input will result in a more rapid rate of pitch change as more of the tail download is used to "pitch" the airplane in the desired direction and less to merely overcome the pitching moment of the wing.

This is the underlying reason for my firm belief that what we are looking for in a "perfect" stunt machine isn't "maximum" lift but "enough" lift to support the thing for the rate of turn we desire. Making flaps bigger or longer span will make the wing to which they are attached produce more lift for a given total area but that additional lift carries the excess baggage discussed above if the lift produced is significantly more than is necessary to support the airplane in the desired rate of pitch change (remember, we're talking about significant amounts of lift due to the high "G" forces produced in a tight stunt corner).

Sometime try jury rigging a profile stunter so that you can fly it with or without the flaps moving and you will be shocked by the increased response rate with the flaps fixed in place. I learned this lesson in revers when (several decades ago when I was just starting to compete in California) I decided that my unflapped Dick Mathis Coyote could be "improved" by adding "stunt" flaps...who could argue with adding "stunt" flaps to an airplane you want to compete with in a "stunt" event?

Well, I added the flaps to this already pretty darn good airplane, took it to the field and almost crashed on the wingover because the darn thing just didn't want to turn...and these were very modest chord, full span flaps. Because this was long before the advent of adjustable handle spacing I was compelled to add tail weight to regain the lost turn rate. In retrospect, after a lifetime of diddling with these things, I came to realize that doing so was the right fix...as opposed to widening the handle line spacing and trying to force the airplane to turn while overcoming all the negative pitching moment that came to the party with the flaps.

IOW, P.J., the change in turn rate you experienced is "normal".

Ted Fancher

p.s. This is also the reason that flapped stunters work best with larger tails and aft CGs.

RandySmith · « **Reply #3 on:** December 17, 2010, 12:47:20 PM »

"I don't want the aerodynamic discontinuity of a gap opening and closing while I'm trying to fly level. "

WOW NEVER use fillets at the end of the flap where it meetsthe fuse.....

I have flown many of my designs with both full span and recalculated partial span flaps. The partial spans flaps worked better, track just as well, went thru the corners cleaner, and "felt better as far as control goes

Regards
Randy

Peter Hess · « **Reply #4 on:** December 17, 2010, 03:28:51 PM »

Randy:

Is the Vector 40 one of your designs that you think benefits from partial span flaps? If so, how do you configure them? Do you leave the stab and elevators the same or would you modify them as well?

Thanks in advance for your thoughts and suggestions.

PJ Rowland · « **Reply #5 on:** December 17, 2010, 06:42:51 PM »

Im with you on that one Randy I prefer the feel also..... But its hard to argue against Paul..

RandySmith · « **Reply #6 on:** December 17, 2010, 07:56:43 PM »

Quote from: PJ Rowland on December 17, 2010, 06:42:51 PM

Im with you on that one Randy I prefer the feel also..... But its hard to argue against Paul..

Hi PJ

No Not really, Paul did NOT do what I did, he used 2 differant sized flaps, PAUL did not recaculate the area of the flaps and use them he just simply glued the stationary parts back to the movable part...that is NOT the way to do it. What Paul did was to "add" more area to the flaps, this is a huge differance just in itself. And not at all the same as using the same area flap to do both test. If I hooked up the stationary parts of my KATANA it would fly and turn much differant with the extra increased area.

Randy

RandySmith · « **Reply #7 on:** December 17, 2010, 08:01:36 PM »

Quote from: Peter Hess on December 17, 2010, 03:28:51 PM

Randy:

Is the Vector 40 one of your designs that you think benefits from partial span flaps? If so, how do you configure them? Do you leave the stab and elevators the same or would you modify them as well?

Thanks in advance for your thoughts and suggestions.

HI Peter

The plane was designed with the Partial span flaps, they are shown on the plan, so just built is as the plan shows. It is a wonderful flying airplane, and is a World class stuntship, built just as shown

Regards
randy

Brett Buck · « **Reply #8 on:** December 17, 2010, 11:43:19 PM »

Quote from: RandySmith on December 17, 2010, 12:47:20 PM

"I don't want the aerodynamic discontinuity of a gap opening and closing while I'm trying to fly level. "

WOW NEVER use fillets at the end of the flap where it meetsthe fuse.....

That makes absolutely no difference - the flow around the very inner edge of the flaps is turbulent and slow, and doesn't have any significant capability to generate roll torque. The end of a partial-span flap is a different story - the flow is full-speed and relatively clean, and it has abundant moment arm with with to roll the airplane if it's even a teeny bit different from inside to outside.

After Paul's experience, I changed my airplane to have full-span flaps. The area was identical to the previous airplane. This airplane flies almost exactly the same as the previous airplane with the exception that it doesn't have a little "hitch" right around neutral that I could never trim out of the other one.

By all means, do it however you want, but I want full-span flaps for exactly the reason Paul found.

Brett

RandySmith · « **Reply #9 on:** December 17, 2010, 11:56:18 PM »

"After Paul's experience, I changed my airplane to have full-span flaps. The area was identical to the previous airplane. This airplane flies almost exactly the same as the previous airplane with the exception that it doesn't have a little "hitch" right around neutral that I could never trim out of the other one. "

Brett,happily my planes, so far, do not have the hitch around neutral that yours had, and when I changed flaps design from full to partial and back, the Flaps are "not" the same size, they are calculated to be the same "area " that is moving, My planes also have very differant tips than yours or Paul's, that maybe another difference,
and Your right I agree, i also encourage peopletry it and see which way it works best for you. This doesn't discount what Paul says or found on his plane, like wise your findings, however It doesn't seem to be the same on mine, or other people's ships.
In addition I don't have to work the flaps up and down trying to fly level, The ships groove very well, and the amount the flaps move in level flight is very tiny

Regards
Randy

Dennis Adamisin · « **Reply #10 on:** December 18, 2010, 09:29:42 AM »

I'm gonna shock Randy and AGREE with him completely!

Partial span works better for me - however....

* There have been LOTS of very successful designs with partial span, and lots with full span - either can be made to work, suggesting there are different solutions to the strengths & weaknesses of each approach. Everyone's mileage will vary, we'll all use what we feel comfortable with.

* Ted's "Imitation" article remains the single best back-to-back-to-back empirical study of the issue, we are lucky he shared his results. Close second would be Bob Gialdini's Olympic article which detailed his recommendations (note: Oly's evolved from full span to partial span flaps)

* I have flown several full span airplanes that ALWAYS achieved better corner when the outer ends of the flaps were clipped - as predicted by Ted's Imitation experiments and Bob G's recommendation. It has improved performance every time it has been tried.

* The above is counter-intuitive - I think it is a question of (reduced) control efforts winning out over theortical aerodynamic advantage of 100% flapped span. Right or wrong the wingtip vortex theory "fits" the observed results, I am not aware of an alternate explanation for the observations. Misunderstandings occur in whether the vortex generated by the deflected flap tip will be added to the total-airplane vortex shed at the wingtip (like full span flaps) or separated (like partial span flaps) from the wingtip vortex ?

* I am only aware of one designer (Ron Adams) who ALSO used fixed tips on horizontal tails for the same reason he used partial span flaps. This is the same gentleman who introduced me to the flap vortex/wingtip vortex idea. Ron was campaigning very large (70"+ wingspans) very heavy (95 oz+) airplanes in the era were 35 sized birds ruled, Ron was very much into reducing control loads.

* Full span flaps are easier to build & finish. Would be nice not having to deal with the fixed portion of the flap.

* I have never observed a "hitch" around neutral setting, could be I have hands of stone...

I have grown used to partial span & do not even fuss over it anymore. No doubt full span flap guys feel the same about what they do!

Ted Fancher · « **Reply #11 on:** December 19, 2010, 03:12:30 PM »

Quote from: Dennis Adamisin on December 18, 2010, 09:29:42 AM

I'm gonna shock Randy and AGREE with him completely!

Partial span works better for me - however....

* There have been LOTS of very successful designs with partial span, and lots with full span - either can be made to work, suggesting there are different solutions to the strengths & weaknesses of each approach. Everyone's mileage will vary, we'll all use what we feel comfortable with.

* Ted's "Imitation" article remains the single best back-to-back-to-back empirical study of the issue, we are lucky he shared his results. Close second would be Bob Gialdini's Olympic article which detailed his recommendations (note: Oly's evolved from full span to partial span flaps)

* I have flown several full span airplanes that ALWAYS achieved better corner when the outer ends of the flaps were clipped - as predicted by Ted's Imitation experiments and Bob G's recommendation. It has improved performance every time it has been tried.

* The above is counter-intuitive - I think it is a question of (reduced) control efforts winning out over theortical aerodynamic advantage of 100% flapped span. Right or wrong the wingtip vortex theory "fits" the observed results, I am not aware of an alternate explanation for the observations. Misunderstandings occur in whether the vortex generated by the deflected flap tip will be added to the total-airplane vortex shed at the wingtip (like full span flaps) or separated (like partial span flaps) from the wingtip vortex ?

* I am only aware of one designer (Ron Adams) who ALSO used fixed tips on horizontal tails for the same reason he used partial span flaps. This is the same gentleman who introduced me to the flap vortex/wingtip vortex idea. Ron was campaigning very large (70"+ wingspans) very heavy (95 oz+) airplanes in the era were 35 sized birds ruled, Ron was very much into reducing control loads.

* Full span flaps are easier to build & finish. Would be nice not having to deal with the fixed portion of the flap.

* I have never observed a "hitch" around neutral setting, could be I have hands of stone...

I have grown used to partial span & do not even fuss over it anymore. No doubt full span flap guys feel the same about what they do!

Denny,

Thanks for the nice words.

Proving, however, that nothing is new under the Sun I've got to go back to Bob G's Olympic article for full disclosure regarding the Imitation flap experiments. I pulled out my copy of that article to find the exact quote that drove me to do the tests. On the three dimensional cutaway drawing Bob included a window with a drawing of the Oly wing showing both the partial span flaps as per the plans and an "alternate" full span flap. Here are Bob's comments verbatim: "The flaps used on my Olympic are sized and moved per the NACA idealized flap formula which produces maximum lift at 30 degrees and doesn't increase the drag radically. Thus the model turns a SNAPPY CLASS square corner like the T-Bird and the Shark .45. There are a lot of fliers that prefer the slower, smoother corner of the Argus, Ares, Nobler school. The Olympic can be simply reworked to do this also. Enlarge the flaps per sketch. Do not Change the linkages, and you will have a ship which turns like SLOWER." (emphasis mine)

IMHO, the underlying reason for the change in response from resizing the flaps (and leaving everything else--especially the CG--the same) was the increased pitching moment from flapping the entire span of the wing. Because the tendency of the wing to pitch opposite the desired pitch change of the airplane increased due to the extended flap span, the rate of turn in the corner for a given control input is reduced (Because the tail has to overcome the increased negative pitching moment before it can change the pitch attitude of the entire airplane.) Doing so also increased the amount of lift produced by the wing in that "SLOWER" corner...which raises the question of "why" is it worthwhile to produce that extra lift if you don't need it?

If the airplane with shorter flaps turned a "snappier" corner (by definition pulling higher G's and requiring "more" lift to avoid stalling) why does it need "more" lift to fly the lower G corner with full span flaps?

The answer, of course, is that it didn't need more lift. Nonetheless, again by definition, if the control linkages stay the same and the negative pitching moments increase, more elevator deflection is going to be required to fly a corner which will mindlessly drive the flaps to a greater deflection thus increasing the lift. The question once again is "why"? I have strong feelings about "why" and I follow those feelings with an even stronger opinion of "why we shouldn't". I'm getting off track here so will abandon that extra added attraction.

Bob's quote; plus that "why" question above ; plus a bunch of stuff gleaned from Bill Netzeband's classic "CL Aerobatics Made Painless" series were the catalysts for the entire Imitation exercise. From that exercise flowed everything I've written since about my personal view of stunt model design and my conviction that lighter wing loadings and "MORE" lift aren't necessarily synonymous with optimum stunt design. Those philosophies have proven extremely successful influencing not only my subsequent designs but those of other National Champions such as Brett Buck and David Fitzgerald.

FWIW, I'll be adding some comments to one of Randy Smith's earlier posts addressing the aspects of Wild Bill's articles which struck me as germane to both this thread and the Imitation article.

Ted

FLOYD CARTER · « **Reply #12 on:** December 19, 2010, 04:00:57 PM »

It seems to be typical to "tweak" the flaps for whatever reason--mostly to level the wings. If a wing flies high, the best solution is to remove the warp in the wing panels instead of bending the flaps or adding a trim tab.

F.C.

Ted Fancher · « **Reply #13 on:** December 19, 2010, 05:01:45 PM »

Quote from: RandySmith on December 17, 2010, 11:56:18 PM

[snip]

... when I changed flaps design from full to partial and back, the Flaps are "not" the same size, they are calculated to be the same "area " that is moving, My planes also have very differant tips than yours or Paul's, that maybe another difference,
and Your right I agree, i also encourage people try it and see which way it works best for you. [snip]

Regards
Randy

Hi Randy,

Have to make a comment about the above. I'm sure you're more than aware of the following but just in case others try to make that simple assumption...

Matching "area" of the movable part of the wing (the flaps) when shortening or lengthening the span of the flaps is not a one for one exercise. Much more changes when (for instance) you shorten the flaps from full span to (for instance) two thirds span and simply increase the chord of the movable part of the flap to match the "moving area" of the full span version.

First, it isn't the "flap area" in and of itself that increases the lift coefficient of the total wing. The moving flap is nothing more than a part of the wing that moves so as to change the part of the wing to which it is hinged from a symmetrical to a cambered (higher co-efficient of lift) airfoil. Thus, if you shorten the flaps on a sixty inch span wing (ignore the fuse for simplicity of illustration) by one third you have reduced the "enhanced" part of the entire wing by 20". A full one third of the wing has lost its ability to change camber and, thus, create more lift than it is capable of doing as a simple symmetrical section. The overall lift of which the wing is capable will suffer as a result.

Increasing the chord of the 40 remaining inches of movable flap will recoup a percentage of what is lost by the unflapped 20 but not remotely as effectively as having the entire span flapped with the same amount of longer but narrower flap. If you don't need the lift (and most ships don't) that's not a big deal, But......

The only way to retain the same amount of area in that shorter span is to increase the chord of the movable flap (probably by one third) so that instead of a three inch chord for 40 inches you'll have a four inch chord (this is, I understand, a distorted example but is done so purposely to make the effect of increasing the chord more obvious). Increasing the chord of a movable surface exponentially impacts the hinge load (torque) required to deflect the surface. Increasing the chord of a flap by one third will increased the force necessary to deflect the same amount of area as the longer flap by much more than 1/3. (Howard or Igor or Brett can do the math). In addition, after a point, the effectiveness of the longer chord flap to increase lift versus the drag it produces to do so becomes much less efficient.

Let's make the example really extreme and say we'll make the flaps only 1/3 span but retain the same area as a "conventional aspect ratio" full span flap. Now the span of the flap will only be twenty inches but the original three inch chord will have extended to eight inches. The torque required to deflect such flaps will likely exceed the line tension available to apply it enough to generate the pitch change necessary to fly a stunt pattern. In addition, the amount of lift generated by a wing which only has 1/3 span flaps that are very hard to deflect will be significantly less than the same wing with "conventional" aspect ratio, full span flaps (less "high lift" flapped span and a less efficient spread of fixed vice movable chord for the 20 inches of flapped wing).

Again, without going into a classic "Fancher marathon meltdown", the bottom line to this discussion is determining how best to achieve the lift that is "necessary" to support the airplane flying corners as tight as the pilot is capable of flying them competitively. A large part of this equation, IMHO, is reducing necessary control forces as much as possible to allow the airplane to be flown precisely with a preponderance of small muscle inputs using a firm but light grip on the handle.

Bill Netzeband in his CL Aerodynamics Made Painless articles 40 or so years ago addressed the phenomenon of hinge loading and it is the primary source of the now infamous "Netzeband Wall" which most of us know is the point at which inadequate line tension exists for the control system to overcome the airloads on the movable surfaces. I encourage every who is interested in Stunt Design to get their hands on Wild Bill's priceless exposition on how these things (stunt ships) work. There is maybe 10% of it that I don't think is gospel and even that 10% would be primarily argument over details. They can be found in the Jul/Aug, Sept/Oct 1966 and the Dec 1967 American Modeler magazines (the AMA publication of the era and, thus available at the Museum library in Muncie). The math is pretty heavy reading and the nomographs a bit clumsy to use but the text can be read carefully, pulling theory and effect from between all the numbers, to make the reader a pretty informed individual.

Ted

RandySmith · « **Reply #14 on:** December 19, 2010, 05:36:10 PM »

Quote from: Ted Fancher on December 19, 2010, 05:01:45 PM

Hi Randy,

Have to make a comment about the above. I'm sure you're more than aware of the following but just in case others try to make that simple assumption...

Matching "area" of the movable part of the wing (the flaps) when shortening or lengthening the span of the flaps is not a one for one exercise. Much more changes when (for instance) you shorten the flaps from full span to (for instance) two thirds span and simply increase the chord of the movable part of the flap to match the "moving area" of the full span version.

First, it isn't the "flap area" in and of itself that increases the lift coefficient of the total wing. The moving flap is nothing more than a part of the wing that moves so as to change the part of the wing to which it is hinged from a symmetrical to a cambered (higher co-efficient of lift) airfoil. Thus, if you shorten the flaps on a sixty inch span wing (ignore the fuse for simplicity of illustration) by one third you have reduced the "enhanced" part of the entire wing by 20". A full one third of the wing has lost its ability to change camber and, thus, create more lift than it is capable of doing as a simple symmetrical section. The overall lift of which the wing is capable will suffer as a result.

Increasing the chord of the 40 remaining inches of movable flap will recoup a percentage of what is lost by the unflapped 20 but not remotely as effectively as having the entire span flapped with the same amount of longer but narrower flap. If you don't need the lift (and most ships don't) that's not a big deal, But......

The only way to retain the same amount of area in that shorter span is to increase the chord of the movable flap (probably by one third) so that instead of a three inch chord for 40 inches you'll have a four inch chord (this is, I understand, a distorted example but is done so purposely to make the effect of increasing the chord more obvious). Increasing the chord of a movable surface exponentially impacts the hinge load (torque) required to deflect the surface. Increasing the chord of a flap by one third will increased the force necessary to deflect the same amount of area as the longer flap by much more than 1/3. (Howard or Igor or Brett can do the math). In addition, after a point, the effectiveness of the longer chord flap to increase lift versus the drag it produces to do so becomes much less efficient.

Let's make the example really extreme and say we'll make the flaps only 1/3 span but retain the same area as a "conventional aspect ratio" full span flap. Now the span of the flap will only be twenty inches but the original three inch chord will have extended to eight inches. The torque required to deflect such flaps will likely exceed the line tension available to apply it enough to generate the pitch change necessary to fly a stunt pattern. In addition, the amount of lift generated by a wing which only has 1/3 span flaps that are very hard to deflect will be significantly less than the same wing with "conventional" aspect ratio, full span flaps (less "high lift" flapped span and a less efficient spread of fixed vice movable chord for the 20 inches of flapped wing).

Again, without going into a classic "Fancher marathon meltdown", the bottom line to this discussion is determining how best to achieve the lift that is "necessary" to support the airplane flying corners as tight as the pilot is capable of flying them competitively. A large part of this equation, IMHO, is reducing necessary control forces as much as possible to allow the airplane to be flown precisely with a preponderance of small muscle inputs using a firm but light grip on the handle.

Bill Netzeband in his CL Aerodynamics Made Painless articles 40 or so years ago addressed the phenomenon of hinge loading and it is the primary source of the now infamous "Netzeband Wall" which most of us know is the point at which inadequate line tension exists for the control system to overcome the airloads on the movable surfaces. I encourage every who is interested in Stunt Design to get their hands on Wild Bill's priceless exposition on how these things (stunt ships) work. There is maybe 10% of it that I don't think is gospel and even that 10% would be primarily argument over details. They can be found in the Jul/Aug, Sept/Oct 1966 and the Dec 1967 American Modeler magazines (the AMA publication of the era and, thus available at the Museum library in Muncie). The math is pretty heavy reading and the nomographs a bit clumsy to use but the text can be read carefully, pulling theory and effect from between all the numbers, to make the reader a pretty informed individual.

Ted

Ted

I am very aware of what you stated above, but..To start with, I did not shorten my flaps by 1/3, my point on what i said was that what Paul did was NOT what I did, My designs have the flaps short by 1 3/4 to 4 inches, Many of my wings also have swept back tips that make the trailing edge 3 to 10 inches longer than some planes of the same span, Thus my flaps if Full span would be as long or much longer anyway.
However it does NOT work as well to just cut off part of the flaps, and make that part stationary as it does to increase the area and re cut new flaps....When you are speaking of just the tips, At least it never did on my test or on my ships. I may have came to the same conclusions as Paul had I simply did that.
I also never suggested to anyone that you can make a flap at 1/3 span then increase chord to make it up, My less than full span.. PARTIAL.. flaps are as long or ...LONGER.... than many ships of the same wingspan.
I do not think anyone should try to just add area on flaps as short as you are stating and that was never my intention to suggest that.

Regards
Randy

Dave Wenzel · « **Reply #15 on:** December 19, 2010, 07:34:47 PM »

I REALLY enjoyed this information. Seems like I've gotten a different outlook on how flaps work. But why the flaps themselves taper from the body to the tips is still out there. Is there any tip stall to be thrown in here also, or is airspeed and/or the fact we have control wires on the plane cancel any chance of tip stall.

DAVE

Oh. On the Banshee. Moved wing 1" forward and increased horizontal stab and elevator area. Will go with full span flaps. Hope it works out OK.

You guys are GREAT.

Ted Fancher · « **Reply #16 on:** December 20, 2010, 09:41:16 AM »

Randy said:
"Ted

I am very aware of what you stated above, but..To start with, I did not shorten my flaps by 1/3, my point on what i said was that what Paul did was NOT what I did, My designs have the flaps short by 1 3/4 to 4 inches, Many of my wings also have swept back tips that make the trailing edge 3 to 10 inches longer than some planes of the same span, Thus my flaps if Full span would be as long or much longer anyway.
However it does NOT work as well to just cut off part of the flaps, and make that part stationary as it does to increase the area and re cut new flaps....When you are speaking of just the tips, At least it never did on my test or on my ships. I may have came to the same conclusions as Paul had I simply did that.
I also never suggested to anyone that you can make a flap at 1/3 span then increase chord to make it up, My less than full span.. PARTIAL.. flaps are as long or ...LONGER.... than many ships of the same wingspan.
I do not think anyone should try to just add area on flaps as short as you are stating and that was never my intention to suggest that.

Regards
Randy"

Easy Randy!

I never said that you suggested anything like that. I use "extreme" examples of aerodynamic concepts strictly to make the more modest but predictable results of "lesser" such changes obvious. I've done this for years because I had experienced examples of fliers taking popular trim "suggestions" too literally and going too far with them...almost always a very bad thing to do. I tried (apparently unsuccessfully) to make that clear when I stated: "The only way to retain the same amount of area in that shorter span is to increase the chord of the movable flap (probably by one third) so that instead of a three inch chord for 40 inches you'll have a four inch chord (this is, I understand, a distorted example but is done so purposely to make the effect of increasing the chord more obvious)".

I encourage people to look at suggested changes in extremes such as the 1/3 span flaps of the same area as full span flaps (the only way to do so being to increase the chord of the flaps). It is easy to for the layperson to recognize that flaps that are almost as long in chord as they are in span will be much harder to deflect--and therefore require greater line tension and pilot muscle to apply; even to the point that there may not be enough line tension available to do so.

From that clear and unambiguous illustration the flier can then extrapolate that only a reasonable amount of such "tit for tat" flap area (in this particular instance) can be useful and that if he/she takes the suggestion to an extreme the outcome will almost certainly be a worse airplane rather than the better one hoped for.

In this case I felt it was important to let fliers consider the effects of flap/elevator chord on the torque required to deflect them against the airloads they must overcome.

A secondary consideration was to possibly whet someone's interest in the subject of a mindless search for "more" lift and why somebody who has been pretty successful at this stuff doesn't believe that the zero wing loading stunt ship is a goal to be pursued at the expense of all others.

No disrespect was ever intended, my friend.

Merry Christmas

Ted

p.s. BTW, you can check out the tips on my designs all the way back to the early '60s. With one (startlingly unsuccessful) exception, all of my original designs had the "swept" tips typical also of all of the Smith designs.

Only once that I recall did any of these designs have flaps that extended "into" the tips and most were somewhat shorter than the "basic" wing sans tips. This was when I modified and partially repainted the Purple Pond Scum (this is really embarrassing. I can remember Bobby's "funny" name for the airplane but don't remember what name was on the wing!) At that time I extended the flaps all the way to the tips (primarily because David Fitz who was flying a very "similar" design with full span flaps was regularly kicking my butt). Although the airplane was still competitive after the change (it won the Walker Cup one year...for get which) it never "felt" as good cornering and took more effort to do so. I didn't "like" flying it as much. For the record, this was the same airplane that had previously won the Cup in 1995 as the Great Expectations. At this time it had the partial span flaps and a Red, White and Blue paint job which pretty much squelches any argument that lengthening the flaps improved the performance.

RandySmith · « **Reply #17 on:** December 20, 2010, 09:54:30 AM »

Hi Ted

I didn't take any offense in reading your post, my point was to make my postion perfectly clear, so there was no chance of someone thinking I was suggesting..shall we say less than optimun changes in wing/flap design. Too many times some will read things into a post that was not said. I wanted to make my statements Clear.
There are many ways to skin cats, Some people like one way, others like another, some times both work well
As I had stated earlier, some of my shorter span flaps are longer than others full span at the same wing span, others are not, they all work and work well. So ya pays your money and take your chances

Merry Christmas

Randy

Randy Powell · « **Reply #18 on:** December 20, 2010, 12:06:26 PM »

RAndy,

Good point. My rule of thumb is, if it works for me, I keep doing it. If it doesn't, I try something else.

Clint Ormosen · « **Reply #19 on:** December 20, 2010, 08:51:26 PM »

Quote from: Randy Powell on December 20, 2010, 12:06:26 PM

RAndy,

Good point. My rule of thumb is, if it works for me, I keep doing it. If it doesn't, I try something else.

......which is much better than my rule of thumb of, If it works for me I keep doing it. If it doesn't, I keep doing it anyway.

RandySmith · « **Reply #20 on:** December 21, 2010, 10:36:46 AM »

"" With one (startlingly unsuccessful) exception, all of my original designs had the "swept" tips typical also of all of the Smith designs.""

Well... not really ,many of my designs have eliptical wings. :-)

Happy Holidays !

Randy

RandySmith · « **Reply #21 on:** December 21, 2010, 12:26:15 PM »

"The end of a partial-span flap is a different story - the flow is full-speed and relatively clean, and it has abundant moment arm with with to roll the airplane if it's even a teeny bit different from inside to outside. "

Hi Brett

Correct, and i would point out that the ends of full span flaps have even more or an abundant moment arm in which to roll the airplane with, than the ends of the partial span...if they are even a tiny bit differant

Regards

Randy

RandySmith · « **Reply #22 on:** December 21, 2010, 01:53:14 PM »

Quote from: RandySmith on December 21, 2010, 12:26:15 PM

"The end of a partial-span flap is a different story - the flow is full-speed and relatively clean, and it has abundant moment arm with with to roll the airplane if it's even a teeny bit different from inside to outside. "

Hi Brett

Correct, and i would point out that the ends of full span flaps have even more or an abundant moment arm in which to roll the airplane with, than the ends of the partial span...if they are even a tiny bit differant

Regards

Randy

ps I wasn't arguing Pauls findings and some assumed, what I was trying to get across is that Paul's findings were right for Paul, not right for every other application, airplane, or person, and Paul did an entirely differant "test study" than I and maybe others did. sort of like comparing apples to limes

Chris Wilson · « **Reply #23 on:** December 21, 2010, 02:11:20 PM »

Quote from: OLDPATFLYER on December 16, 2010, 10:08:31 PM

My question is what's the difference between full span flaps and flaps that end short of the tips.

Something not touched upon here I believe (unless I have skimmed over it) is how the flap terminates (length only being a part of this) and that really is the topic at hand.

I personally like zero chord on flaps at the wing tips (as in tapered to nothing) but like them full span as I believe that the tip stays away from a possible stall zone all the better.

In other words, I do not want a camber change at the tips at any time but still want full length flaps to effect as much of the wing as possible. This seems to me to be the most efficient use of wing.

Cheers.

Ted Fancher · « **Reply #24 on:** December 21, 2010, 05:30:12 PM »

Quote from: RandySmith on December 21, 2010, 10:36:46 AM

"" With one (startlingly unsuccessful) exception, all of my original designs had the "swept" tips typical also of all of the Smith designs.""

Well... not really ,many of my designs have eliptical wings. :-)

Happy Holidays !

Randy

Good point, Randy. I stand corrected.

Ted

p.s. I thought sure you were going to ask me about my "startlingly unsuccessful" exception. I built an original take-apart ship for the 1974 Nats when Bill Fitz, Gary McClellan and I started our long series of consecutive trips. It was (strangely enough) a clipped tip true elliptical design that was pretty good looking and had the first of my earlier version of the R.W. and B paint jobs. It crashed on the second trip to the field for trimming sessions when the take apart pushrod design proved not up to the task. The wing, however, survived intact. I subsequently installed the wing permanently into the ship I took to the 1975 Nats.

On my first practice flight in Lake Charles Shareen let go of the ship; it rolled about 25 or so feet and the outboard gear hit a tie down hole in the ramp; the prop hit and apparently threw a blade while the engine continued to run; the nose came apart in about a thousand pieces within the next half lap...the ST .46 bouncing down the tarmac as the airplane--from the leading edge aft rolled to a pleasant stop.

Two thing then happened. First, Shareen retired from launching duties...never touched a running airplane again. Second. Gary and Bill came out and picked up the entire thousand small pieces, bought a lot of five minute epoxy and in one of the great Nats stories glued the jigsaw puzzle back together all the time watching the clock count down to the end of appearance judging (long before the current floor line up. The pilots stood in line for hours on end waiting their turn to have the judges excoriate their craftsmanship.) The ship was eventually in one piece and we had it judged in the nick of time.

Next morning I went out and flew it and it seemed to fly just fine...except the judges in the first round apparently didn't agree with my assessment of the quality of the tricks. My score was sorta sucky and didn't look to be "finals worthy". Foolishly feeling I could learn how to fly better with just a few more practice flights, Bill and I ran off to a practice circle and started to pound in a few. Climbing into top of a vertical eight something went "pop"! the elevator started to buzz and the airplane came straight down and destroyed everything except the wing once again.

Somebody ran to tell Shareen who was, as usual, tabulating at the official circles. She came running over while I was throwing the parts into the trunk of the rental car, ostensibly to commiserate with yours truly. Well, not exactly. She saw the wing leaning intact against the back bumper and glared at it as only she can. In something of a harbinger of things to come she proceeded to say something to the effect that she'd seen enough of that damn wing and promptly helped it join the rest of the airplane on the battle field of broken pieces. Can't say that I blamed her. No way was I going to put that perverted demon wing back into yet another airplane.

Well, you probably assumed that was the end of the story. Nooooooooo, engine man!!

I then threw the last pieces of the wing into the trunk of the rental car. Tossed the big tool box in on top of the whole mess and slammed the trunk lid closed while saying something really clever like "take that you miserable blankety blank". Which made me feel a little better until I remembered that inside the toolbox, now inside the closed trunk lid of the rental car were the keys to that selfsame rental car! Rented in Houston, Texas a bazillion miles from Lake Charles, LA! A pretty little Avis girl drove all the way from Texas with a spare set of keys for the car.

It was really, really dark when Shareen and I left the field that night...and quiet, too.

Tom Niebuhr · « **Reply #25 on:** December 21, 2010, 06:36:57 PM »

Ted,
That is a great story. I have an additional question. Is that how Shareen felt about a certain Nobler too?

Please say hello to her.

Merry Christmas!

Ted Fancher · « **Reply #26 on:** December 21, 2010, 07:54:27 PM »

Quote from: Tom Niebuhr on December 21, 2010, 06:36:57 PM

Ted,
That is a great story. I have an additional question. Is that how Shareen felt about a certain Nobler too?

Please say hello to her.

Merry Christmas!

Naw, the Nobler was a completely original event! She sorta thought "mystical forces" were at work when she saw the video for the first time at VSC. The "repro" really did look pretty darn close to the original.

Merry Christmas to you, my friend.

Ted and Shareen

RandySmith · « **Reply #27 on:** December 21, 2010, 09:19:15 PM »

"Ted
p.s. I thought sure you were going to ask me about my "startlingly unsuccessful" exception. I built an original take-apart ship for the 1974 Nats when Bill Fitz, Gary McClellan and I started our long series of consecutive trips. It was (strangely enough) a clipped tip true elliptical design that was pretty good looking and had the first of my earlier version of the R.W. and B paint jobs. It crashed on the second trip to the field for trimming sessions when the take apart pushrod design proved not up to the task. The wing, however, survived intact. I subsequently installed the wing permanently into the ship I took to the 1975 Nats."

Hi Ted

Well I was afraid to ask.....I was at the 75 NATs flying with you, That was my first NATs, I saw Bob G and Les Mc crash also ?:-( many ships bit the dust at that NATs. I was fortunate to keep mine in 1 piece and finish in the top 18. That was a goal I didn't think I could make but fortunatly did.

I won't even talk about the 1 time my keys locked themselves in the car at the NATs

Regards

Randy

Ted Fancher · « **Reply #28 on:** December 23, 2010, 02:26:51 PM »

Quote from: RandySmith on December 21, 2010, 09:19:15 PM

"snip"

I won't even talk about the 1 time my keys locked themselves in the car at the NATs

Regards

Randy

Don't you just hate it when they do that!

Ted

john e. holliday · « **Reply #29 on:** December 24, 2010, 05:31:02 PM »

Hey Ted, that isn't as bad as some one who shall remain name less went get in his car to go back to the dorms at a NATS. Think how many years ago that has been. Anyway reached in his pocket and no keys. Was on passenger side of car. Tried all the car doors to no avail. Standing there scratching his head, someone else reach in thru drivers door window and took the keys out of the ignition and handed to him. I will never forget the look on his face and the silence around the car. I still wonder to this day how the story stay suppressed.

Ted Fancher · « **Reply #30 on:** December 25, 2010, 04:57:45 PM »

Quote from: RandySmith on December 21, 2010, 09:19:15 PM

"Ted
p.s. I thought sure you were going to ask me about my "startlingly unsuccessful" exception. I built an original take-apart ship for the 1974 Nats when Bill Fitz, Gary McClellan and I started our long series of consecutive trips. It was (strangely enough) a clipped tip true elliptical design that was pretty good looking and had the first of my earlier version of the R.W. and B paint jobs. It crashed on the second trip to the field for trimming sessions when the take apart pushrod design proved not up to the task. The wing, however, survived intact. I subsequently installed the wing permanently into the ship I took to the 1975 Nats."

Hi Ted

Well I was afraid to ask.....I was at the 75 NATs flying with you, That was my first NATs, I saw Bob G and Les Mc crash also ?:-( many ships bit the dust at that NATs. I was fortunate to keep mine in 1 piece and finish in the top 18. That was a goal I didn't think I could make but fortunatly did.

I won't even talk about the 1 time my keys locked themselves in the car at the NATs

Regards

Randy

Wow, Randy! Do you mean you were actually at the circle when I crashed? or just that you were at that particular nats??? The former would be an amazing coincidence!

Hope you're having a great Christmas. We're about to leave for our son and daughter-in-laws' place for a big family Christmas dinner. Doesn't get much better than that.

Ted and Shareen

RandySmith · « **Reply #31 on:** December 27, 2010, 01:13:50 PM »

Quote from: Ted Fancher on December 25, 2010, 04:57:45 PM

Wow, Randy! Do you mean you were actually at the circle when I crashed? or just that you were at that particular nats??? The former would be an amazing coincidence!

Hope you're having a great Christmas. We're about to leave for our son and daughter-in-laws' place for a big family Christmas dinner. Doesn't get much better than that.

Ted and Shareen

Hi Ted

I vaguely remember you had a broke airplane along with a couple more, I vividly remember Bob G and Les McD crashing..or the handle doing the damage..then that leadout thing... I also remember my first time seeing Wynn P at that NATs, he read a guy the riot act when he was in the pits taking pictures..seems he didn't know about the 60ft plus antenna...ouch He really got an earful. Made a note to "self" don't make Winnie mad!!!
I also have quite a few NATs stories from that one that will live on long after I'm gone

I hope you and Shareen had and have a really Great Holidays,

Regards
Randy
PS i heard from our friend Gary last week, first time in a couple of years, I am glad he still has an interest in the Hobby :-)

Ted Fancher · « **Reply #32 on:** December 27, 2010, 05:58:52 PM »

Quote from: RandySmith on December 27, 2010, 01:13:50 PM

Hi Ted

I vaguely remember you had a broke airplane along with a couple more, I vividly remember Bob G and Les McD crashing..or the handle doing the damage..then that leadout thing... I also remember my first time seeing Wynn P at that NATs, he read a guy the riot act when he was in the pits taking pictures..seems he didn't know about the 60ft plus antenna...ouch He really got an earful. Made a note to "self" don't make Winnie mad!!!
I also have quite a few NATs stories from that one that will live on long after I'm gone

I hope you and Shareen had and have a really Great Holidays,

Regards
Randy
PS i heard from our friend Gary last week, first time in a couple of years, I am glad he still has an interest in the Hobby :-)

Yeah, I sorta remember that Les had an up line fail while in level flight and the ship pancaked pretty flat so it resulted in mostly cosmetic damage. I can recall watching him put some white paint on the wheel pants at some point during the week. I'm less certain about Bob. He's had more than a few nats mishaps and it is kinda hard to keep them all in order. He might be the only guy that has had more "whack jobs" at the nats than me. As I recall, he was able to get back in the air after all of his wrecks...unlike me.

That first (of two) '75 event was the only one from which I recovered to fly again (temporarily). I later totaled that ship (as we've been discussing); then, more or less in order, wiped out the Excitation at a Nats where Lanny Shorts was the event director and then flew the Top Five using my Imitation which Lanny had brought along to warm up the judges (a sidelight to that year was that the Imitation had blown out of his van earlier in the week when the hatchback was open along with the sliding side door in a strong wind...broke the fuse in half and smushed the inboard wingtip but it was repairable enough to fly the finals); whacked the Temptation to smithereens in -91 when the VF flamed out going straight up in a wingover on a practice flight the morning of the top five; and, finally, totalled the Special Edition just before Appearance judging at the 2004 nats right after the WCs in Muncie. I think that's all of them. Unlike most of the "hot shots", I've very few of my competition ships hanging in hobby shops or at home.

Ted

Steve Helmick · « **Reply #33 on:** December 27, 2010, 08:17:25 PM »

Quote from: RandySmith on December 17, 2010, 12:47:20 PM

"I don't want the aerodynamic discontinuity of a gap opening and closing while I'm trying to fly level. "

WOW NEVER use fillets at the end of the flap where it meetsthe fuse.....

I have flown many of my designs with both full span and recalculated partial span flaps. The partial spans flaps worked better, track just as well, went thru the corners cleaner, and "felt better as far as control goes

Regards
Randy

For what it's worth, the IMPACT design does not use fillets at the inboard end of the flaps. Gary Letsinger (retired Boeing aeronautical engineer) pointed this out to me, and said it reduced drag considerably by NOT using fillets there. I just figured they'd be a PITA to get aligned straight, and more trouble to finish well.

Steve

Howard Rush · « **Reply #34 on:** December 27, 2010, 09:06:21 PM »

Could be, but I don't think they're that way to save drag or time. In fact, it's a little bit of bother to keep them close to the fuselage without interference as the years go by.

Steve Helmick · « **Reply #35 on:** December 28, 2010, 07:49:39 PM »

Paint build-up, like on Grampa's house?

Where is the paintbrush icon, when I need one?

Steve

Mark Scarborough · « **Reply #36 on:** December 28, 2010, 09:59:25 PM »

Steve,
its more likely the typicall swelling around the middle and shrinking on the ends that makes it a pain

Dave Wenzel · « **Reply #37 on:** December 31, 2010, 05:34:21 PM »

Flew that Banshee today and it DID seem to fly well. Didn't go too crazy though. One thing I did notice was full up and then full down back to level and I could see the outboard wing above the plane. Is this an indication of too much tip weight? Level flight seemed OK, and it didn't "groove" like my Nobler, but it's not too far away from decent. Am I just dumb or what? The up turn was very crisp and no wobble or stutter.

DAVE