I've never noticed this on RC planes, but I've never flown any with flaps, either. Someone made a comment on another forum that full-size planes actually pitch down with the initial application of flaps. Reportedly, this is due to the center of pressure moving aft when the flaps are dropped. Does this happen in RC aircraft with flaps?

i find it pitches up, need to hold down elevator down,

it pitches up, and full scale too, the ones ive flown would pitch the nose up

All models I've flown or seen, flaps down cause pitch up, thus calling for down elevator to correct. However, competent RC pilots have told me their planes pitch down with flaps down, requiring up elevator to correct. I've never had such a model, never seen it, and can't picture in my mind how that might happen. In U-control stunt flying, very sharp square loop corners are made with wing flaps and elevators moving counter to each other (flaps down & elevator up gives an instantaneous square inside corner).

May need to clarify what flaps mean in full size versus RC/Pattern.

In full size flaps usually go down - and I haven't tried that in RC. In RC -- certainly on pattern planes -- the most usual flap application I have seen (and use) is usually both ailerons up. This certainly lifts the nose and is mixed with down elevator to create a slower, steady glide path on landing approach (useful at tight fields, less error prone than side slipping, and lowers likelihood of tip stalling on higher wing loading -- not an issue in pattern, but is in scale!)

Adding flaps in either direction changes the chord line and therefore the angle of attack of the wing.

Flaps down = change in chord line to a higher angle of attack at the same airspeed, higher angle of attack moves the centre of effort (pressure) forward causing the pitch up. Flaps are used to A, slow the aircraft to enable a lower landing speed and B, give better forward visibilty (in full size) at the lower speed that would otherwise require a high nose attitude to keep the angle of attack in the range the aircraft can fly at the given speed. So left untrimmed the aircraft would initially pitch up but as it slows due to the increased drag of the flap/higher angle of attack the nose attitude would lower again to maintain the same airspeed. In fact youd probably need more power to maintan the same airspeed due to the higher drag.

Flaps up or ailerons up, lowers the angle of attack. With full span ailerons it basically destroys or weakens the lift meaning a higher airspeed is reqd to maintain level flight. High performance gliders use a very slight up or reflex, to allow higher speeds with less induced drag (drag as a by product of creating lift). Half span or tip ailerons with them up, destroys the lift only on the outboard section of the wing. On a any type airplane that is prone to tip stalling this means we can then fly slower with a lot less risk of tip stalling as the outer wing section is at a less angle of attack than the inboard section. You also maintain roll control using this method.

I only have one plane with flaps, a goldberg chipmunk. lowering flaps causes pitch up. I have mixed this out with 20% down elevator mixed in to flaps

Most of the warbirds I've flown, Mustangs, Hurricanes, Sea Fury, T-34 (trainer), FW 190
(both short and long nose) have demonstrated a slightly nose down attitude with flaps
deployed. Most sport planes, especially high wing types have pitched up with flaps
deployed. So, I would surmise it depends on the type of aircraft and it's own
particular configuration.
Jerry

I feel that I have to put in my experience into this thread. Myself are flying full scale and have flown types that do pitch down as well as types that are pitching up when applying flaps.

First of I would like to say that I agree with many of the inputs on this thread regarding this issue.

Basically a high wing aircraft will pitch down and a low wing will pitch up when extending flaps. Opposit will happen when retracting. As the pilot changing the airfoil shape, by extending or retracting flaps, there will be a new point of pressure along the cordline. Thus the distance towards the center of gravity changes. This will call for triming the aircraft in order to maintain level flight. Obviosly, if extending flaps, wich means getting more drag, also more thrust/power is needed to maintain current airspeed.
However, there is no universal rule to high and low wing versus pitch up and pitching down, since every airfoil and aircraft has its own carateristics. It is basically up to the designer of the a/c to put into the design what he/she is looking for. But after been flying 14 different types the past 8 yrs, including high and low wing aircraft with piston turboprop and jet engines being singels and twins, it "usally" turns out that high wing aircraft are pitching down when extending flaps and low wing does the opposit.

Christian

I agree with Christian in that different aircraft react in different ways. I'm a full time flight instructor ( my day job for the last 16 years). The types that we do our elementy training on where I work are the Tobago and the Grob115, both are low wing aircraft and both will have a slight initial pith up as the flaps run out increasing the lift as they do, but both have a stonger nose down pitch once the extra drag takes over.
Where I fly pattern the field lenght can be a bit marginal on those calm days and my Maestro will overshoot most times. As like most pattern models it is not equiped with any flaps so I have the ailerons coming up so it will reduce lift without risking tip stalling and hopefully increase drag. When I first mixed this in and flew with it I thought that I had flicked the wrong switch as there was absolutly NO pitch change. Even the roll was similar(to roll with both ailerons up the radio only allows one to move towards the neutral position.)the glide path is steeper but not by much. I have only just tried this and need to mix in even more up aileron next time. Matthew

Thank you for all of your input. At least for models, and distinguishing true flaps from spoilers, you all seem to confirm my thoughts.

Flaps change the effective AOA of the wing but they also change the downwash angle at the elevator, causing its effective angle (and thus downforce) to change with respect to the incoming airstream. So depending on high wing / low wing and high tail / low tail you'll get different effects. Theres no one "correct answer". --Derek