45/45 or 30/45 seem to be the number of degrees movement up and down on flap/elevator that people go for. There are reasons for choosing one or the other or somewhere in between, but there are others better equipped to explain that to you after they get back from Tuscon.

Start with 30/45 with room to adjust and you won't be far wrong.

It depends mostly on the weight/wing loading of the plane.  I haven't figured out any kind of exact graph, but a 38 oz. Smoothie has plenty of flap with the flaps travelling 2/3 of the elevator.  A 44 oz. Cardinal needs the flaps to move about the same, or trim the width a third.   Something like a 45 oz. Nobler is usually fine with 1:1 travel. Like Rich says, if at all possible, make the travel ratio adjustable.

Too much flap makes the plane stagger in turns, possibly because the excess lift and drag slow it down before the elevator can get enough lift to turn the plane.

As has already been suggested several times, the best flap/elevator movement ratio for ANY model is dependent on many factors including but not necessarily limited to:

wing loading
size of the flaps
size of the elevators
tail moment
the power train
effectiveness of elevator gap and flap gap seals

The optimum flap/elevator ratio may be different for two models of the same design that might have slightly different weights and power trains.

If you are building an existing design, use what the designer used as a starting place as that was something that worked for that designer (but may not necessarily best for your particular model).

If you are building a model to do serious stunt flying, even a proven design, it is imperative to make provisions to be able to adjust the flap/elevator ratio.  For "typical" configurations, you will likely find that a flap/elevator ratio from around 2:3 (or 0.67:1) to 1:1 will get you in the right range.  I can tell a difference in turn performance by changing the ratio, for example, from 0.7:1 to 0.8:1. 

I had two Chizlers, same power plant, different props, different weights, and they trimmed out with different flap/elevator ratios.

Keith Trostle

As a starting point, is there a  rule of thumb for the throw ratio between the flap and elevator on a newly constructed C/L aircraft?

You've gotten some good generalized input so far.  Any chance you can give us specifics as to what design you're talking about, what power plant and how much it is going to weigh?

With that info we can probably give you a good starting place.

FWIW, my Vice President's column in the next issue of Stunt News will discuss my trimming experience with the brand new unflown Ruffy I took to VSC last week.  It will include some discussion of ratio changes, what I did, why I did it and the results.

As a teaser, first flights were just awful in terms of response to control inputs and the last flight before leaving for home was the highest scoring flight of the last round of Classic.  A lot ... once again, a lot ... of the reason for that improvement was from finding the right flap elevator ratio and getting the CG and leadouts in the right position.

You might find it interesting reading.

In the meantime, give us some info on the ship.

Ted Fancher

Hi Jim,

No, so far I haven't put a "wart" on the Ruffy.  I thought about it a bit at VSC but there were other problems in greater need of "fixing" and it kind of got lost in the noise.

It is possible that, if I ever get serious about refining the trim, I might experiment with one but, since I usually only fly my classic ships at contests it probably won't happen any time soon.

Now, a thought about flap movement for those who believe that tight corners are solely the result of wing loading.  Why would anyone choose to use less flap movement than they can mechanically obtain?  After all, flaps add lift, so moving them as much as possible short of stalling the wing should always make the plane turn tighter shouldn't it?

(Hint, I don't really believe that's a good idea myself!)
 

Ted

Bill,

The answer to that is actually kind of simple.  We need enough lift to support the weight of the airplane in the corner (weight X G force for the radius of turn).  th eproper amount of lift will result in the CG of the aircraft pretty much following the desired radius.

Too little lift and the airplane will stall because the wing can't support the weight in the corner. The flight path will open up (nose down) as a result ... and, of course, if the stall happens in the wrong place you might break something!

Too much lift and the ship will accelerate perpendicular (roughly) to the desired flight path and the track of the CG will tend to be inside the desired radius (the appearance of turning aft of the wing and "leaping" into corners).

The results you mention (one to one with a heavy ship, 2/3 for a lighter ship, etc) fall neatly in line with that concept and are generally a pretty good place to start.  then you use the slider horn to fine tune the response and flight track.

It does, of course, get a little more complex the deeper you delve into the issue.  One of the consequences of cambering an airfoil (what happens when we deflect the flaps) is the airfoil produces a pitching moment in the direction the flaps are deflected; i.e. when the flaps go down the ship wants to pitch nose down (a negative pitching moment).

BEFORE THE ELEVATORS CAN DRIVE THE NOSE IN THE DESIRED DIRECTION (UP IN THIS EXAMPLE) THEY MUST FIRST PRODUCE ENOUGH DOWN FORCE TO OVERCOME THE NEGATIVE PITCHING MOMENT!  THIS CAN BE A VERY BIG DEAL.

Thus, if you increase the flap movement on a given ship you will do two things. 

First, you will increase the amount of lift from a given amount of control input at the handle.

Second, you will reduce the rate of pitch change because the pitching moment of the wing has increased (see the above).

The net result?  More lift, less turn!  Sheesh, who made up these rules anyhow?

No problem, if you need the lift (your airplane is heavy and may stall once in a while in hard corners) you can simply increase the spacing on the handle to regain the rate of pitch change you want and the wing will produce the additional lift necessary to avoid the dropsies.  (I may just have had some experience with this phenomenom over the years).

It's even a bit more complicated than that.  Let's look at another aspect of the lift/pitch conundrum.

The down load the tail produces to overcome pitching moments is exactly the same thing as adding weight to the airplane itself.  Anything you do to the airplane that produces a negative pitching moment is precisely the same thing as making the airplane heavier.  It's even worse because it compounds itself in corners. 

(It is worth mentioning here that there is one more very real source of negative pitching moment that is very important in our stunters.  That's right, Ted's favorite subject, the relationship between the Center of Gravity and the Center of Lift of the wing.  The farther forward the CG is from the center of lift the more download is required by the tail to keep the nose from falling.

Every little bit of added G force (whenever we maneuver) accelerates that moment and, given enough Gs and enough distance between the CG and the CL and it is entirely possible that your stunter will not be able to stunt worth a darn ... if at all)  So, if you combine excesses of these sources of negative pitching moments you can easily reduce the performance capability of the ship.

Lift in and of itself will not generate a tighter loop.  The more lift you are capable of producing, however, the tighter the corner the airplane will be capable of flying given the necessary tail authority to drive the wing to the resulting G loads.

As others have said here, however, the ability of the wing to produce enough lift is seldom a problem on a sound stunter at a "reasonable" weight.  The limiting factor has always been more the degree to which the pilot is capable of utilizing the performance he can build into the airplane and still present a pattern which will impress the judges.

The discussion on another forum regarding our eye/brain's ability to process visual data was a real eye opener.  From my reading following a google search I can see that even if we could produce five foot corners we would have great difficulty in processing the result visually.

Fascinating stuff.

Ted


EDIT for HTML

Hi Ted,

This goes with the overall trend towards bigger tails and longer effective tail moments, I guess. 

Looking at the evolution of a series of "like designs" over the years, it appears that airfoils got fatter when more power became available.  With that came bigger planes and the bigger tails, etc.

One design that I have flown in Classic, the "Spacehound" is a wierd one.  Longish wing, thin airfoil and tiny tail surfaces.  Since I didn't really build it too light, I inserted a ST 46.  This plane "presents well" as I am told, but it sure is hard to get a "corner" that "I" like.    It is now retired!!

This stuff is beginning to get my attention.  In the past, I took the lead from y'all, and just built proven designs, or slight cosmetic differences to suit my taste.  That has worked well.  But, I now have an URGE to "design" one myself.  Is this a sign of senility setting in??? 

Hi Bill,

No, I don't think so.  Or else I've been senile for many a year.

You're exactly right about the longer, bigger tails.  The first step was the bigger tails used by the New York/New Jersey guys like Jimmy Casale, Bobby Hunt.  Later came the longer tails and then a bit later yet the thicker wings for the heavier power trains.  They've all kind of come together the last 10 years or so and are more or less the standard for US designs.  Billy's stuff seems to be the primary exception and, as I'm sure you're aware, we have some differing ideas on wing loadings, etc.  Different strokes and all that.  I sure haven't beat him much lately ... although he beats me just as bad when I fly skinny winged Noblers, Tuckers and Ruffys as when I fly T.P. sort of stuff.  Maybe the airplane isn't everything, ya think?

My bet on the Spacehound is that you found the response rate to change pretty dramatically from start to finish of a flight.  Tiny tails don't take well to CG changes and the response on a ship with a 15 or 16% tail can go from sluggish at the start of the flight to twitchy after three or four oz are burned out of the nose.  Ships with bigger tail volumes retain their stability through a much wider useable range of CG locations.

At least that's my opinion and I'm stuck with it!


Thanks for the questions.
Ted

Hi Bill,

No, I don't think so.  Or else I've been senile for many a year.

You're exactly right about the longer, bigger tails.  The first step was the bigger tails used by the New York/New Jersey guys like Jimmy Casale, Bobby Hunt.  Later came the longer tails and then a bit later yet the thicker wings for the heavier power trains.  They've all kind of come together the last 10 years or so and are more or less the standard for US designs.  Billy's stuff seems to be the primary exception and, as I'm sure you're aware, we have some differing ideas on wing loadings, etc.  Different strokes and all that.  I sure haven't beat him much lately ... although he beats me just as bad when I fly skinny winged Noblers, Tuckers and Ruffys as when I fly T.P. sort of stuff.  Maybe the airplane isn't everything, ya think?

My bet on the Spacehound is that you found the response rate to change pretty dramatically from start to finish of a flight.  Tiny tails don't take well to CG changes and the response on a ship with a 15 or 16% tail can go from sluggish at the start of the flight to twitchy after three or four oz are burned out of the nose.  Ships with bigger tail volumes retain their stability through a much wider useable range of CG locations.

At least that's my opinion and I'm stuck with it!


Thanks for the questions.
Ted

           

Hi Ted,

I am finding this stuff is starting to "get to me"!  I have looked over your designs from the Citation, Excitation through the Trivial Pursuit, and see slight changes as you went.. 

I see much the same in Billy's USA-1 through the Geo Xl, which all carry pretty much the same wing 

A *little* something here, and a *little* something there.  Refinements and revisions as different engines, power trains and all were developed.

But, you know, it's weird that a Ruffy, Nobler, Skylark, Ares, Tucker Special, Caprice,et. al., can be pretty darn good airplanes especially since we add in the adjustable trim features and a modern powerplant.  I still convince myself that the "new" stuff is really much better, but I sometimes wonder just HOW much better.  Especially in the hands of us that are not up to the level of the World Class flyers, yourself included, naturally!

Ted,

There was lots of Baron influence no doubt in Bill's 35/40 Average Stunter Concept, but it did have flaps!  I forget what date that came out in Bill's Round and Round article but I seem to remember sometime in 1969 or maybe 1970.  Bill sometimes - or maybe a lot of times shadows these boards and if he sees this he might remember the date of that aritcle and chime in or e-mail you the date, or even a copy of the R&R in question here?

Jim Pollock     

Just to keep this thread active here's another thought to consider.

Almost by definition, the less flap travel required to perform the desired pattern  means the wing is larger than necessary to do so.  IOW, the same amount of lift could be produced by a smaller wing with the flaps deflected further.

This is clearly obvious.  What's the matter with that?

Possibly that the bigger the wing or the lighter the wing loading the more the airplane will simulate a stunt kite in high winds.  We can never lose sight of the fact that our airplanes are tethered and will quite literally react to winds exactly like a kite.  This is preciselly how Marvin and others manage to do all those dead engined figure eights, etc.  The are essentially flying kites.  the wind is supplying the motive force which drives the stunter/kite forward, thus allowing the wing to do its thing in supporting pitch responses.

The case could be made that the smaller the wing area required to provide the lift necessary for the desired pattern the better in terms of flying in the wind.  This is really brought home to yours truly flying the Doctor in high winds.  Zero flap, very low wing loading and serious kiting effects.

Not a no brainer, however, since all the "downsides" of pitching moments, etc. discussed previously remain to be dealt with.  The less you deflect flaps the less of those you get.  Hate all these trade offs....


Ted

I've only stumpled over this thread today.
I fully agree with what has been said so far. I have always built my airplanes with a 3/4 ( flap to elevator ) deflection ratio, and I still do it today, but I have fully adjustable controls, so after trimming I really don't know what exact ratio I finally have.
But my ( 41 ounces !) Smoothie has more flap than elevator travel now !!!
Regards,  claus

HI Claus,

Just saw this post.

Worth pointing out that the Smoothie is quite a bit different from the standard full flapped stunter.  It's flaps are only about 2/3 span and have a pretty narrow chord.

We must remember that flaps only have an effect on the portion of the span that they encompass.  Thus the rather small in area Smoothie has a comparatively high wing loading even at only 41 oz.  When you then install flaps on only a fraction of the 50 inch span the lift capability of the wing at max Lc is even less.

It doesn't surprise me very much that such a ship might fly better with more flap movement than, say, a Chief or Nobler with full span flaps.

My "voluptuous" Trivial Pursuit just earned probably its fourth or fifth Nats second place finish last week.  At at least 68 oz (I'm scared to weigh it any more) on only 660 square inches and with less than full span flaps it is truly on the ragged edge of excessively plump.

You'll probably not be surprised to learn the flaps travel more than the elevators.

I feel the need to stress again; the flaps and the tail (stab/elevator) have two entirely different jobs.  they DO NOT work together to make the ship turn.  The tail makes the it turn.  The wing simply provides the lift to support the "g" increased weight of the ship in the turn.  It's really important to think of them as separate tools even though they work hand in hand.

Ted

Hi Jim,

Hadn't thought of the Citation in some time.  In fact, I need to look up that article because I only have one or two pics of the airplane, none of which are much good.

The airplane is still around, but broken the last time I saw it.  I was flying it at a "mall air show" many years ago (still ST .46 years) and on the take off roll the outboard wing struck a young boy on the ankle.  He had pushed forward against the ropes to get a better view.  Fortunately I was making a long roll and it was just breaking ground when it got to him.

Knocked about six inches off the outboard tip.  I flew out the tank, landed, made sure the boy was OK and left for home.  Stripped the hardware out and stuck the mess up in the attic.

Pete Peterson asked about it a year or two ago while visiting and when he found out it was up there asked if he could take it home and repair it.  Sure, I said, and promptly handed it to him.  As far as I know he still has it at his new home near Tacoma, Wash.

Ted

Attn Ted Fancher,

I enjoyed your analysis of  increase in wing negative pitching moment with flap deflection and its interaction with required force from the stabilizer-elevator.

Imagine that someone has developed a simple, light control means for varying wing incidence. Wouldn't direct lift modulation as the primary pitch control, with the stabilizer (possibly without elevator)  serving to keep the fuselage aligned with the relative wind, offer advantages in CL Stunt?

Will Stewart

Hi Ted,
I found it interesting what you had to say in Stunt news about the flaps on Pauls Cardinal Profile as I have built a couple. Now that you mentioned it, I think there are others also with the same problem. To much flap. It got me to looking at my Nobler also because the flaps are almost the same size as the Cardinal and my Nobler weighs 44 oz. and probably doesn't need large flaps. Your thoughts in general

Guys,
I know this is a very old thread but it has lots of good information and a question comes to mind - is it better to vary the flap travel while keeping the elevator horn length or go the conventional approach by varying the length of the elevator horn and keeping the flap horn length fixed? One could set up the flap horn with a slider and a slider on the elevator horn. Seems this would give less sensitivity on the handle spacing setting.

Best,         DennisT

Hi Dennis,

I in no way can speak for everyone, but i can say what I have witnessed.  The slider horn on the elevator is the easiest set up, so about everyone I have seen simply has used that.  Personally I use the Tom Morris ones all the time now.  Bob McDonald had a movable flap horn a while back in a plane I saw, but I do not know if he still has them available.

Maybe Ted, Brett, Howard, Randy, or one of the designers and are more up on the "What's and wherefores of it will see  this and chime in on what would actually be the "best" way to do it.  I can't go there, I don't know enough of the technical side, really.

But in my experience, a slider elevator horn is sufficient for about all the adjusting usually needed.  The whole trimming process gets involved, so just one thing is hard to pin point for me.  I have moved the elevator horn slider and not had to touch anything else, and have also done it and had to adjust the handle, or even CG, or LOs, .......

Then again, a lot of planes I have built have just gotten everything else trimmed and flown.......


A side note to the previous posts.  Ted mentioned wing size versus lift capability.  That was about 5 years ago, and now models like Dave Fitzgerald's are down in the 630-650 sq. in. range instead of the 670-700 sq in range that was very prevalent 5-6 years go.  And the engines have just gotten bigger in some examples!

Big Bear