Flap to Elevator ratio, again

[Fred Underwood]

Ever the last couple of years that I've been reading and active I've seen several reference to having flap to elevator ratio of 1/1 or less flap than elevator, never more.  I also see suggestions that we probably don't need more than 25-30° of elevator, perhaps 20ish°.

I see that the Logarithmic System has more flap than elevator to about 25 - 27° of elevator where it crosses over to more elevator, if it really gets to 27°.  If not, then there is more flap then elevator, albeit not a linear amount, the whole time.

http://www.netax.sk/hexoft/stunt/the_max_ii.htm

So, if I have a logarithmic system similar to above in ratios and I do a square corner and only hit 25° elevator, I have more flap than elevator the whole time. Will my plane know that it has violated the standards?  If I can only get 22° elevator throw for a hard square, does the logarithmic device need different ratios so that the crossover occurs before the square corner? 

If all that actually works, what happens if I fly with a fixed ratio of 1.1/l flap to elevator? 

[Paul Walker]

Well, I don't know who the experts are telling you to never have the flaps move more than the elevators. In fact, in 2012 my WC's plane had smaller than usual (for me) flaps and as a result they moved more than the elevators.

That is the idea behind the logarithmic flaps, they move more than the elevators at lower defections, and less at higher deflections. Smoother rounds, and sharper corners.

Linear control systens are still just fine for most pilots. The exact ratio between the flap and elevator is dependent on the aircraft geometry, and the pilots preferences.


So, saying all this, what really is your question?

[Fred Underwood]

My real question was about the correctness of statements about flap to elevator throw, no ulterior motive or underlying question.  My question came up now because the idea was just restated in another thread that the correct throw is usually in 3/4 to 1 up to 1 to 1 flap to elevator, and more flap than elevator is not usually, suggested ever, used.  That sentiment has been noted several times in threads I read. Rather than single any one person out for saying it.  I just wondered about the statement, and what would likely happen in corners.

I haven't seen it suggested otherwise before, so thanks for the comment and adding your experience.

[Howard Rush]

There is no aerodynamic significance to flap-to-elevator ratio. 

[Tim Wescott]

There is no aerodynamic significance to flap-to-elevator ratio. 

More or less.  The clue is in Paul's comment about "smaller than usual" flaps.  If you're cutting your stunter out with the same cookie-cutter as everyone else, then the recommended ratios are right.

Still, if you have your surfaces sized close to everyone else's, then you may expect their "happy" throws to be the same as everyone else's, with due attention paid to whether your plane is light as a feather or as heavy as something I might have built.

[Ted Fancher]

There is no aerodynamic significance to flap-to-elevator ratio.  

Which is why Howard's Impact flies just as well and responds just the same with fixed flaps.  

[John Park]

There is no aerodynamic significance to flap-to-elevator ratio. 

There is, however, a considerable difference in response to control inputs and the general 'feel' of the model.  With a flapped profile model (actually an own-design with the 'numbers' of Al Rabe's Mustunt 1), I have flown successive flights with a 1:2 ratio, then 1:1 and finally back to the model's standard 2:3.  I found it very interesting and informative!

[Ted Fancher]

More or less.  The clue is in Paul's comment about "smaller than usual" flaps.  snip

Very similar results were discussed at length and experimented with sometime back in the Neanderthal stunt era of the late '70s in the Imitation article...which included spanwise segmented flaps to intentionally pursue the wisdom of Bob Gialdini's 1963 Olympic article/plans (published on a parchment scroll) in which he stated (as best as I can recall): [The Olympic has] flaps sized to produce a "snappy class" corner class corner like the T-Bird and the Shark .45. ...a lot of flyers that prefer the slower, smoother corner of the Argus, Ares, Nobler school can rework the Olympic by enlarging the flaps [a picture showed the altered flaps as full span and of greater chord versus the plans which showed roughly 2/3 span length with greater taper, significantly reducing their area] and will have a ship that turns, like, slower." 

As with most of my "great" ideas, I stole those words (almost memorized them as I did with a lot of what Bob had to say), resulting in the experimental segmented flaps of the Imitation which allowed three different span options, full span, about three inches shorter total span and roughly 2/3 span.

My results mirrored Bob's comments, notwithstanding the fact that there was probably no more aerodynamic significance to changing the size of the flaps than of varying the flap/elevator ratio.  What I did find interesting was that the optional Olympic example actually increased the wing area slightly (thus reducing the wing loading) while also increasing the size of the lift enhancing flaps yet, counter intuitively, results in bigger, smoother corners then the lift challenged smaller wing with less high lift device?  That sounds like stunt heresy to me and might actually be considered profane on a CLPA web site.  If so, Sparky can censor it and I will consider myself properly chastened--no hard feelings.

Although--while fine tuning the trim of a new stunter, I've frequently altered the flap/elevator ratio--for apparently insignificant reasons-- yet I've thus far not gone so far as to  experiment with 30 degrees of flap deflection coupled to zero degrees of elevator.  Having generally retired I'll leave that experiment to those more into exploring the unknown.

With tongue firmly implanted in cheek (knowing full well that Howard will have an arcane definition of aerodynamic significance making me look foolish),

Ted

[Mark Scarborough]

I seem to notice when manipulating the proportion of flap to elevator that the "rotational point" in squares is different and in some extreme cases the airplane just looks strange when turning the squares if the ratio ( and other factors are off)

[Steve Helmick]

But is the snappier corner of smallish flaps (or the snapless corner of largish flaps) due to control loads (i.e., Netzeband's Wall) or is it due to aerodynamic reasons?  Steve

[Howard Rush]

I might elaborate. Flap-to-elevator ratio is something you can measure, but there is nothing special or universal about a given number.  Yes, it usually works out to about 1 for conventional stunt planes, and the same ratio will cause otherwise identical airplanes to fly the same.  Also, changing elevator control horn radius, hence flap-to-elevator ratio, changes flight characteristics in a predictable manner.  What flap-to-elevator ratio works out to be when the airplane is trimmed, though, is dependent on airplane configuration.  Just changing the flap stiffness is enough to make it come out different.  Nothing is magic about a ratio of 1, and certainly nothing abruptly changes at a ratio of 1.

 

[Tim Wescott]

I seem to notice when manipulating the proportion of flap to elevator that the "rotational point" in squares is different and in some extreme cases the airplane just looks strange when turning the squares if the ratio ( and other factors are off)

Way back when I was flying Beginner with a yellow V-tailed thing with flaps, and getting dinged for the flaps (and the V-tail), I stuck with it because an airplane with flaps just looks better in the air -- not enough flaps means that the nose is leading the tail in turns; too much flaps would make the airplane push the canopy through the turns (which would look odd and ugly), just enough looks -- right.

You can make the center of gravity travel through the right path just fine without flaps -- IMHO the biggest thing that flaps do is make the direction that the fuselage is pointing stay more in line with the direction of flight.

[Tim Wescott]

I might elaborate.

Uh oh.  The end times are upon us!!!

[Ted Fancher]

...Snip...

Nothing is magic about a ratio of 1, and certainly nothing abruptly changes at a ratio of 1.

 

At last!  I totally agree with the above statement!  I suspect the whole kerfuffle was due to the missing phrase "...of one." [one to one for the non-cognoscenti among us). un-appended to Howard's "yeah, but... " arousing sentence: "There is no aerodynamic significance to [a] flap to elevator ratio." !

The really good news is the detente appears to have been reached prior to most stunt fliers epoxying their elevator horn access covers in place.  God bless Sparky's Stunthanger!

Ted

[Randy Powell]

I defer to Howard and Paul's obviously superior knowledge. 

[Randy Cuberly]

I on the other hand, being a "risk taker" Will say that the ideal ratio of flaps to elevator depends a good deal on the airplane (probably weight and wing loading dependent) and the wishes, likes, and dislikes of the flier.

With a reasonably light airplane the ratio seems to not be critical and I agree that changes in the ratio seem to be somewhat negligible to how the airplane reacts within reason of course.

However I can tell you with certainty that on my Trivial Pursuit that weighed in at 75 oz using a ratio with more flap than elevator made it both easier to fly and gave significantly better corner.  With a 1 to 1 ratio it had a small tendency to stall on the third corner of the hour glass in less than ideal conditions but with the increased (I don't remember what the final ratio was) flap movement relative to elevator the tendency was not there.

The Trivial Pursuit has relatively small flaps compared to a lot of airplanes and with the extra weight of a nearly 20 oz (don't laugh) finish, it required a lot of power and more flap movement to fly respectable corners.  It also required a somewhat more sensitive (aft) CG location than just about any other TP I had come across.

Taking all of that into consideration it was an excellent flying airplane and worked very well for me once it was trimmed.  I will say that it and Bob Whitely taught me a lot about trimming airplanes!

On the other hand my 53 oz 720 sq in Geo XL with fairly large flap area flew best with a ratio of 2/3 to 1.  Increasing the relative flap movement on it caused a heavy control feeling and a somewhat "dumbing" down of the corner and it became more difficult to fly precisely.  Needless to say, properly trimmed it was a very hard cornering airplane.

I wanted to say this because I began to get the feeling from some of the previous posts that flap to elevator ratio didn't really matter much.  Perhaps on some airplanes with some pilots that's true but I've found it to be like most other trimming tools effective and necessary in a lot of cases.

I'm not, I repeat, not challenging any of the previous posts or trying to start an argument just stating my personal experiences!

Randy Cuberly

PS:  I don't think the Trivial Pursuit ever came close to the Netzeband wall because it pulled like a freight train everywhere.   

[Ted Fancher]

But is the snappier corner of smallish flaps (or the snapless corner of largish flaps) due to control loads (i.e., Netzeband's Wall) or is it due to aerodynamic reasons?  Steve

Steve.  My guess is some of both although less due to the N-wall in recent years thanks to more appropriate leverage over the surface loads with control systems better suited to the demands placed on them.  Aerodynamically the adverse pitching moments of flap deflection is reduced by either less deflection or area...chord in particular which increases both the adverse pitching moment and the hinge loading which simultaneously does battle with the N-wall.

Ted

[Fred Underwood]

Thank you all for the great discussion; questions and concerns well answered.