Balsacutter

My Feedback: (3)

Computer radios makes it easy to build full-span flaperons, but are they a good idea in a power plane?

Seems like drooping the ailerons would cause a snap stall or loss of control if you got clumsy trying to lift a low wing on a slow final approach...

Is this one of those theoretical problems that doesn't really show up in real life?

Or should I continue to dream about building separate slotted flaps?

- Norm

Tall Paul

The flaperon induced tip-stall is a reality in models.
Seperate flaps are to be preferred.

mesae

Ditto Tall Paul: Tried'em, don't like'em. At least not with constant-chord flaps on a strongly tapered wing.

The tippy-stall effect can be mitigated if the flaps are tapered so they are always constant percentage of chord, but this configuration is unusual. More often, the flaps are constant-chord, but the wing is tapered, so the percentage of chord increases with span. This is bad for flaperons.

They can be fun on a fun-fly, fat, constant-chord type wing.

The full-scale kitplane Kitfox has full-span, offset flaperons, and they seem to work well (Constant-chord wings and flaperons).

jlkonn

My Feedback: (1)

Norm,
I think moderation is the key.
If you put them down to the max then I have experienced the effects everyone is talking about.
However, if you use only a slight amount I think they can have a desirable effect.
I have flapperons/elevator mixed on a UCD 60.
Not a whole bunch just a little.
I like it for looping and landing.
Don't like it for rolling...think it messes them up.
Try 'em...you might like 'em.
JLK

rmh

If you are into aerobatic stuff -with a large model - you can use the full span flap setups for some corrective stuff -such as -- setting flaps to decrease effective wing angle when flying around at very high angles .
Frankly I think they are not worth the effort -tho they can reduce wing rocking .
actually -- to get a far better rocking control-- a set of small mid span fences on the ailerons ala the H9 Showtime model - will reduce spanwise flow and the result is absolutely remarkable .
This is from actually doing it -- not from theory---
Back to the flap/aileron combo in actual use - the model can be expected to turn loops more quickly - --in some cases but in actual practice - unless the model has extremely low wing loading - this is also --a bust - again having tried this setup on various models
back in 1950-- I started flying control line stunt -and any decent model had coupled flaps - so I have had a fair exposure to them . When I tried flying competitive stunt again in the late 60's -I did a model with no flaps -just a larger plane and very light - the difference in performance without flaps was minor but the old die hard stunt guys ,still use em today
On smaller models with higher wing loadings -the coupled aileron flaps are just added weight and effectively -will cause more problems than they will solve
Bottom line - large very lightly loaded models such as a Sig Cadet - can use em nicely and they allow for nice level slow controlled landings .

mesae

I thought those were called spoilerons - up flaps with up elevator & vice versa. They can effectively reflex the airfloil when deflected.

BMatthews

Coupling some flaperon with elevator can help generate extra wing lift for doing various maneuvers but you'll find that for a typical model if you use them for landing then things get ugly quickly. Try if you want but don't go beyond about 20 degrees droop angle or adverse yaw will come on big time.

And this only applies to strip ailerons. If you have conventional outboard style ailerons then forget about using them. They are a tip stall waiting to happen.

Up to 20 degrees they can be fine with no tendency to tip stall on full span strip types. Beyond 20 things get bad with the effect coming on a little at a time until with wide enough ailerons at more than about 70 degrees the aileron action is actually reversed due to the severe adverse yaw effect.

Ed_Moorman

My Feedback: (1)

Norm,

Despite all the "no" answers you got, I disagree. I use a Flaperon wing type on nearly every model. Notice I didn't say I used the ailerons as flaps, but I don't want you to get the wrong impression since there is a good reason for a Flaperon wing type.

With this wing type, you can individually adjust the center and end points of each aileron separately. I find this really helps especially on planes with wide ailerons. You set the servo arm as close as square to the servo as possible, then use subtrim to get it exactly on.

For end points, I set the flaperons to move 100%, then hold full control and adjust the end points at full deflection the same. Do this at full up and full down. You can see that they are the same movement when they are moving in the same direction, whereas when I try to do it by measuring the ailerons on opposite sides, I never seem to get it exact. After adjustment, you can zero out your flaperons.

I usually also set up spoilerons, some percentage movement in the same direction as the elevator for some 3D work. Seems to help flips on some planes.

I also like to mix throttle-master and spoilers-slave as landing spoilers. This helps a light plane on windy days to sit down and not float all over the place.

I hope you can see that the use of the Flaperon program, or Elevator-Flap mix, is for more than just CL stunt flaps.

acemcduck

My Feedback: (17)

So aerobatic wonderment aside, I've been planning to set up my old, slightly heavier than it used to be, Lion models FW-190 with flaperons. I used to fly it from 300 ft paved runway with no major issues but now I'm flying from a shorter strip with tighter approaches and thought this modification would help me come in a bit steeper and slower if need be. Is this worth while?

Dave

rmh

for that particular application- it sounds a bit spooky
here is a sad truth
flaps do not add lift - (this is a matter of semantics)
whoa buckaroos - before you trot out the flying manuals -
the flap reconfigures the wing and makes it work more effectively at a lower speed but we are still working with the same area and weight - and a lot more drag..
It can tho - allow at a lower overall wing and fuselage angle-- at a higher angle of approach to the ground- and--
That improves control of the plane at lower speeds
so - if you could rig your FW190 with inboard flaps - it MAY help . as long as you don't get into a really high sink .

mesae

Right. The flying manuals agree with you, Dick. And it's not just semantics. They increase the lift available at a given AOA or speed, but an overall increase in lift will result in a reduction in sink rate, or a climb.

B.L.E.

Flaperons essentially give you a variable camber wing. I understand that they are used a lot on the higher tech sailplanes, not so much to maximize the plane's L/D but to give the plane a larger range of airspeeds where the L/D does not suck. With the flaperons down a little, you have a cambered airfoil that can fly slowly while circling in a thermal with a minimum sink rate and with the flaperons reflexed up a few degrees, the plane can blast through sink or penetrate a headwind at speeds approaching 100 mph without the drag, and thus the sink rate, going through the roof.
By controlling lift with wing camber instead of angle of attack, the fusilage is always aligned with the airflow for minimum drag.

stek79

Sorry guys, it seems I can't figure out the whole picture...

IF the lift doesn't increase with flaps, how can the stall speed be slower?

mesae, you say that the CL actually is greater, so the total lift increases too, or I'm wrong?

Other question, if I can: how reflex should reduce wing rocking? I thought the opposite, as Dick said, i.e. the flaps can help.

Good info guys!

mesae

CL is not the same as total lift. It is a dimensionless coefficient. Increasing camber increases (to a point) the amount of lift a wing can generate at a given speed (CL), meaning it can fly slower. Again, increasing total lift means a decrease in descent rate, or a climb, which is not what we want when landing. We want to generate 1 g of lift (using the small angle approximation), at a lower speed, hence flaps.

I have found spoilerons (reflexerons?) to be of little value (not necessarily no value) in reducing wing rocking. Leading-edge shape (sharper is better, but this is not the only factor) and pilot technique are more important.

Balsacutter

My Feedback: (3)

What a great discussion.

Andy Lennon pushed the edge of envelope for this stuff during the '80's with designs that featured full span slotted flaps for variable CL/CD, and slot-lip spoilers at the tips for roll control. He claimed his designs (Crane, Crow) had a wide speed range, and effective roll control even at low speeds.

I was always intrigured by the idea, the spoiler-roll control would have no adverse yaw (all up, no down). But Andy is a builder's builder and you'd have to dedicate a lot of time to scratch-build one of his complex machines to try out the idea.

- Norm

stek79

Sorry but I don't understand.

Cl is a factor in the lift equation, so how can Lift remain constant with an increase in Cl? And after all, the Lift is the think to look at (I'm asking), since it is the Lift that keeps up the plane - so, if the speed is lower there must be a greater Lift, right?

B.L.E.

The lift remains constant because we reduce the wing's angle of attack to compensate for the higher coefficient of lift. When you change the flap angle, you have to retrim the plane for level flight. The slower a plane flies, the more nose up it has to be in order for the wings to make the lift nessesary for level flight.

rmh

In laymen speak---
IF the wing is of a fixed size ---the flaps merely reconfigure the wing
You might say
"bending or reconfiguring can produce a more controllable lifting shape at low speed".
this is at the expense of increasing drag.-which can make a controlled steeper angle of flight much easier
for 3Dstuff tho --the tall thingies referred to as side force generators, as used on the Showtime model by H9--are far more effective in controlling wing rock than any flaperon setup
I was amazed at this one --
putting smaller ones on the ailerons ONLY on a foamie -produced the same results -
simply a mazing --

Tall Paul

An example of how Alpha and Cl are related, flap up, flap down.
With no change in weight, the Cl flaps up or down is the same.
With flaps, the Cl changes with lower alphas, so the nose is pushed down...
If the alpha was kept the same, the Cl would be quite different... more "lift"...

mesae

To add to TallPaul's contribution, I have scribbled a little document. I hope it helps.

stek79

mesae:

You say that the lift remains the same since we compensate the higher Cl with smaller alfa... so if we increase alfa we get more lift!? I mean: let's keep alfa to its maximum. All the things equal, let's change only flaps: first case no flaps, second case let's add flaps. For your formula, we can have:

Lift = 1/2 * Cl * c * rho * V^2

Ok? Let's go ahead. IF we change ONLY flaps, with same speed (c and rho don't change obviously) then we can derive:

Flaps => higher Cl => HIGHER LIFT

From the logical point of view, the reasoning seems correct...


Tall Paul, from the polar line it seems that Cl is much higher with flaps, why do you say the opposite?



Thanks for the info guys!

mesae

Alpha and CL vary inversely with the dynamic pressure if lift is constant. If you increase alpha at the same dynamic pressure, then you get more lift (unless we exceed the AOA for CLmax). But if you increase CL (by extending flaps), and reduce dynamic pressure (indicated airspeed), such as is done during a landing approach, lift remains constant (within the small angle approximation).

The above true within your constraint that dynamic pressure and AOA remains the same. However, increasing CL does not necessarily increase lift, unless dynamic pressure is not reduced enough to compensate. When pilots extend flaps, they slow down, and/or decrease AOA. Otherwise they would not lose altitude, which is the whole point of a landing approach.

Think about two identical airplanes making landing approaches under the same conditions. For argument, let's say they are approaching at the same glide angle. The only difference between the two is that one has flaps extended and is flying at a slower speed than the other. Both sets of wings are generating the same amount of total lift; they have to be, since both airplanes weigh the same and are following equivalent flight paths. The one with the flaps extended is operating at a higher CL than the other: It is operating closer to it's stalling AOA, or CLmax.

Think about it yet another way. An airplane that weighs 9000 lbs is generating 9000 pounds-force of net lift with wings level. It is therefore flying straight and level. Do you know how fast it is going? You can figure that out if you know it's CL, or if you know the speed, you can calculate it's CL. It could be flying slowly with a high CL and AOA, or it could be flying fast with a low CL and AOA. The CL can vary while the lift force remains constant. Now if that same airplane starts generating 9100 pounds-force of lift (by increasing speed and/or AOA or increasing camber without reducing AOA), it will accelerate upward.

As long as you don't think increasing CL always means increasing lift, it seems like you get it. A common misconception is that extending flaps increases total lift in practice.

Maybe I'm just beating a dead horse.

stek79

Thanks mesae, finally I got it!


With flaps, the total lift does not increase, it is still equal to weight. But the speed is slower!

Great information here, thanks! I thought that with higher camber we could get an higher AoA... now I know that this is false.

Another question... let's say that we want to reach higher AoA in a wing or a stab (I'm thinking about a STOL airplane), how can that be done?

If we reduce wing aspect ration, greater AoA can be reached, right? But Clmax is lower, right? Here is a very interesting graph about that:


http://adamone.rchomepage.com/index6.htm

BTW, in the first part of the page, there is another extremely interesting graph that shows that with more camber we get a greater Cl, but actually the maximum AoA is lower!

mesae

You're welcome. It does seem like you get it.

As for your other question, with A STOL airplane, the highest possible AOA is not the objective: High lift at low speed is. So a relatively high aspect ratio, highly cambered wing is desirable.

Delta wings can reach very high AOAs without stalling in the conventional sense, but they make lousy STOL planforms.

stek79

What can be an high AR ? 6, or 8?

If it is too high, then at the low Re we fly with our planes the efficiency of the wing would be greatly reduce, isn't it?