If flaps are designed to slow a plane down to practically nothing for a super slow landing, why don't they design flaps into trainers?
Just a question of interest. Wouldn't that make learning so much easier?

Flaps do not slow down a plane, that is not their function. Flaps increase the area of the wing allowing it to produce more lift. Being able to produce more lift allows the plane to fly at a slower speed and still remain airborne.

Trainers really don't need flaps as they are designed to be able to fly at slow speeds without using the flaps. Also, it just adds another layer of complexity for a student to worry about. When a student is training the goal is to KISS.

Ken

Thank you for explaining. I read in this thread http://www.rcuniverse.com/forum/m_9098847/tm.htm post #3, in part . . .
and naturally assumed that is what flaps were for, slowing the plane for landings.

In fact the Hangar 9 series of PTS Trainers use flaps exactly for the purpose RCKEN states. They are fixed position items the way they come but you can add a flap servo and explore the interesting and often misunderstood world of flaps. The Hobbico Nexstar, another trainer, also comes with the ability to add flaps and all the Telemasters trainers have them, well all the glow ones I've ever seen do.

Let's say flaps reduce landing speed by 20%. If your trainer already flies 20 mph without flaps, a reduction of 4 mph is not really significant. What's that, walking speed? A mild breeze can do the same thing. As the plane gets heavier, it becomes more significant.

Weight isn't the only thing that makes flaps more significant. Wing shape and area can make flaps necessary due to the poor low speed qualities of some wing shapes, lengths and cross section. The laminar flow design of the full sized Mustang wing makes flaps manditory due to poor slow speed flight caracteristics while the wing of the Kadet trainer series has so much low speed lift that in a headwind situation, it can actually fly backwards. On the otherhand, Boeing jetliner wings are designed to have the greatest lift within a specific speed range while at low speeds, the lifting characteristics are so bad flaps alone are not enough. To increase lift, leading edge slats were added and the flaps have been designed to slide backwards, almost doubling the effective wing area to maintain enough lift to keep the plane in the air. I'm not going to go into the theory as to why, would get to complicated for some to understand

Ken is correct......flaps do not slow a plane down......flaps function is to allow a plane to produce lift at lower airspeeds.....sure there is drag but that is a side effect of more wing area......speed brakes are designed to slow an airplane

Slowing an aircraft down is only a by-product of the true function of flaps, which is to give you the same effect as if the wing area were increased (both increasing lift and drag at the same time).

As far as flaps on trainers go... I built a Senior Telemaster and added flaps to it, and nicely "over"-powered with an O.S. 61FSR.

Wow, did that add a load of fun to flying. With the added lift (and drag at the same time) I occasionally like to fly backwards which is very easy to do with a Telemaster in a steady headwind.
When everyone else quits flying because the winds rise to about 15 knots, I crank up the Telemaster and have some real fun. Imagine having a radio control kite. That's what a Telemaster is with flaps.
I've actually landed it like a helicopter where I keep it flying at the same position relative to the ground, and just slowly let it settle onto it's wheels with a "0" rollout. Conversely, I've taken off in a steady headwind to where the take-off roll could be measured in inches before taking to the air.

My Telemaster serves as a "boring" trainer for teaching the new guys at the field, but the flaps make it a really fun airplane that even experienced pilots like to play with.

Don't ever be afraid to put flaps on a trainer. They're totally neutral if you don't deploy them (as if there weren't installed at all), and when you become more confident as a pilot, you can start dialing in just a little at a time and enjoy the wonders of what flaps can do for any airplane.

It depends on the flaps. Turning strip ailerons in to flaperons does not change the drag so much so greater lift is in play more, but if you have big flaps like an airliner, they can and want to increase drag 50% more than clean.

You assumed correctly!

However, as it has well explained above, slowing a plane alone will be dangerous for the "fast ones", which have airfoils and weight that help them fly fast, but do not help much in slow flight.

Basically, an airfoil shape that is good for high speed (symmetrical=low drag-low lift coefficient) is not good for low speed, and vice-versa (cambered =high drag-high lift coefficient).

Birds like hawks know about that fact, and they modify the shape of the airfoil of their own wings at will, in order to accommodate the speed of flight for diving and for patrol.

Airplane’s designers have tried to copy that trick by adding devices to the wing they design.
Those devices are slots (for the leading edge) and flaps (for the trailing edge).

Some flaps are able to modify the camber or curvature of the airfoil of the wings by deflecting.
More complex flaps, like the ones that big airliners deploy at landing (together with slots), modify the camber of the airfoil by deflecting, and also increase the area of the wing by getting extended at the same time (these are called Fowler flaps).

For moderate angles of deflection, simple flaps increase the lift of the wing and its capacity to fly slowly (more lift than drag increment); for higher angles of deflection (up to 60 degrees), simple flaps slow down the plane for landings (more drag than lift increment), as you have assumed.
This is a convenient sequence, since the wing is ready for slow flight before the flight velocity gets reduced.
The reverse process is used for take-off.

For slowing effect only (like for after landing), air brakes are used instead; these create a lot of drag, just like a parachute, but they don't modify the flying characteristics of the wing.


Copied from
http://www.centennialofflight.gov/es...vices/TH17.htm

�Flaps may be used to increase the maximum lift coefficient, increase the wing area, or both. A change in the maximum lift coefficient may be realized by a change in the shape of the airfoil section or by increased camber. The trailing-edge flap is one method of accomplishing this. The maximum lift coefficient for an airfoil with a simple flap is greater than that for the unflapped airfoil. Also, the coefficients of lift are increased over the entire angle-of-attack range. The stall angle for an airfoil with a simple flap is essentially unchanged from that of the unflapped airfoil. This is opposed to the slot operation where a higher stall angle was obtained. The flapped airfoil reduces the disadvantage that the slot has in high landing angles.

A Fowler flap is hinged so that it can move back and increase the airplane wing area. Also, it may be rotated downward to increase the camber. A very large increase in maximum lift coefficient is realized.

There are many combinations of slots and flaps available for use on airplanes. For example, the arrangement on a Boeing 737 airplane uses a leading-edge slat and a triple-slotted trailing-edge flap. This combination is a highly efficient lift-increasing arrangement. The slots in the flaps help retard separation over the flap segments and thus enhance lift.

It may also be noted that flaps in an extreme down position (50Β° to 90Β°) act as a high-drag device and can retard the speed of an airplane before and after landing.
Spoilers are devices used to reduce the lift on the airplane wing. They may vary the total lift and control the glide angle, as they do on gliders, or on large commercial jets, they may be used to help the aileron control by "dumping" lift on one wing and thus help to roll the airplane. Also, on landing, with spoilers up, the lift is quickly destroyed and the airplane may quickly settle on its landing gear without bouncing.

Dive (or speed) brakes are used in airplanes to control descent speed. Whether slowing down quickly when approaching for a landing, after landing, or in a dive, these aerodynamic brakes are helpful. Essentially, they promote a large separation wake and increase the pressure drag.�


�This is the final test of a gentleman: his respect for those who can be of no possible service to him.�
– William Lyon Phelps, educator, journalist (1865-1943)

Hmmm I am not sure about that in most models. In most cases we are talking about dropping the rear of the existing wing rather than extending a portion of the wing rearwards then dropping it as the airliners do.

I have seen a few large scale models with the ability to reproduce the full size effect of moving the flap back the dropping it. Gordon Nichols B52 was one such model. I was lucky enough to see this in it's construction phase and he used screw jacks to move the flaps backwards and down. I think he had problems synchronising the jack motors to get the flaps to deploy together.

Still simple flaps are a lot of fun to mess with but they are just another thing for a beginner to have to do on the landing approach esp. as they usually bring an elevator trim change with deployment. I would not reccomend them on a trainer.

Most flaps used in RC simply increase the angle of attack of the wing. This basically increases the incidence of the wing relative to the fuselage and allows the plane to produce a similar amount of lift at a reduced speed while the plane keeps the same attitude in the air.

This higher angle of attack allows more lift to be created, which also creates more drag. This also gets you closer to your critical angle of attack, which is why you will never see flaps only on the outboard end of a wing. If you exceed your critical angle of attack, your wing stalls, and if the far end of your wing stalls before the rest of the wing, that wing will drop and you will go into a spin, which can be very destructive if you are not prepared for it.

Hi,<div>some questions regarding flap,</div><div>1. positions flap when take off or landing both aileron stay up or down?</div><div>2. how about elevators did this also affected by flap?i mean when flap up elevator will also in up conditions?</div><div>
</div><div>many thanks</div><div>
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1.) Most models do not require flaps for taking off. They add drag. Unless you are lifting weight (like for a candy drop) flaps would be unnecessary as most models are WAY overepowered compared to full scale aircraft.

2.) Some models require down elevator when flaps are applied to remain level . . . but occasionally you will find one that requires some up elevator. Best policy is to add a small amount of flap, high up but at low speed, to see how your model reacts. Then mix in elevator and additional flap as required. Adding flap to a model at speed that is very aerobatic can cause bad things to happen. I tore the gear off my Hot Stik whan I accidently caught the flap toggle when switching to low rates and she took a 90ΒΊ nose dive from 20 feet at half throttle. (And she can take off and do loops at 1/4 throttle). I barely had enough time to level her out before it was dirt nap time.

<div>@charlie P. thanks for your reply.</div><div>more questions</div>If i'm using warbird like mustang p51 or others model warbird, flap are positif or negatif point?<div>
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Impossible to be certain. "Like a Mustang P-51" can mean hundreds of different designs, with flying weights from 5.5 ounces to 55 pounds, some scale and some nothing like scale airfoils or wing loadings.

Can also depend on where you have the center of gravity along the wing chord, but as a rule of thumb I'd say it will bring the nose up initially, but if overdeployed (too much throw or at too high of a forward speed) will snap it down. Get up to 50 feet, slow doen to a crawl and apply flaps to see how it reacts. Start with a tiny amount and work up.

Thanks for the information.. will try in the field.. [8D]