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Flying with Flaps — What you need to know

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Sooner or later you may want to try your hand at flying a scale subject.  Since most full-size aircraft use fl*ps, many scale model also require them for true scale operations and function. A scale model with  fl*ps fully deployed is a cool sight. If you have never flow a model with then there are a few things to know about. There right ways and wrong ways to use them. This article should help you understand what’s going on.

In a nutshell, when fl*ps are lowered they change the wing’s lift and drag characteristics and lower the stall speed. By changing the camber of the wing, the lift and drag are increased for a given airspeed. As a result of these changes affect the speed that the aircraft can land.


Common fl*ps

Though there are four basic types of fl*ps: plain split, Fowler and slotted. The plain flap is the most common and is simply a hinged portion of the trailing edge. It is usually hinged at the top of the control surface since it only moves in a downward direction. Super Cubs, Cessnas and other sport scale models use common fl*ps, to keep construction and function simple.

If you have never flown with fl*ps before, don’t worry. fl*ps add flexibility to your model’s flight envelope, and it is a fun new experience. The major advantage is they shorten (and steepen) your landing approach by allowing your plane to fly more slowly in a nose down attitude. Here are some hints!


  • Learn how your plane reacts to fl*ps at a safe altitude before attempting the first landing.
  • Reduce the throttle to around 1/3 and let the plane slow before dropping the fl*ps.
  • If used for takeoff, use only partial fl*ps.
  • Adjust the power to maintain the approach path. fl*ps add drag and so will require more power.
  • Add power on a go-around and begin your climb out before retracting fl*ps.


  • Deploy fl*ps at high airspeed. The fl*ps may depart the wings or cause serious structural or servo damage.
  • Use fl*ps on the first takeoff and test flight. You must first determine how much deflection is correct for your model.
  • Use full fl*ps on takeoff. This adds a lot of drag.
  • Let the plane balloon and lose its airspeed. Adjust the elevator to keep the proper approach path.
  • Retract fl*ps when low and slow or you could settle onto the runway.flaps1.jpg

Deploying fl*ps may result in the plane pitching up or pitching down. The elevator must be used to compensate and keep the plane on the desired approach path. Another characteristic of fl*ps is that the first half of the flap’s deflection results in a greater increase in lift while the second half results in a greater increase in drag. fl*ps also impart a large structural load on the plane and should only be used at a lower airspeed. Full-size planes have their air speed indicators marked for safe flap operating range.

Flap Facts

Since fl*ps provide more lift at slower airspeeds, you must be aware that when you retract them in-flight you will lose the lift and the plane could sink. For this reason, if you must do a go-around, make sure you increase power before retracting the fl*ps. Failure to do so could place your plane very close to stall speed before you can accelerate to a safe speed. This also applies to takeoffs with fl*ps. In most cases it is safer to take off with the fl*ps retracted or deflected no more than about 20 degrees. Larger deflections add more drag and can cause the plane to become airborne at too low of an airspeed.

Flying a scale model with operational fl*ps is a very rewarding experience. Not only do they look neat, but they also provide the same benefits as the full-size version.

fl*ps impart increased loads on the wing and require attention during their installation. Make sure you use enough heavy-duty hinges on each flap and a heavy-duty control horn. There are many ways to actuate the fl*ps, including torque tubes and bell cranks. For large, fast or heavily-loaded models, the best way is to use a servo for each flap. These planes will also benefit from the fl*ps being locked in the down position preventing the airstream from blowing the flap back to the up position. This basically means that the servo arm is directly in line with the flap horn at full deflection and this takes the strain away from the servo. This is accomplished by turning on the radio and selecting full down fl*ps and choosing a servo horn position that is in line with the horn. Now, retract the fl*ps and make up the linkage from the servo to the horn. The amount of flap deflection is determined by the length of the servo arm; for more flap deflection, place the linkage f*rther out on the arm. The use of ball links may be required for smooth action and to eliminate binding.

Flap Deployment

The modeler has several options for the transmitter flap actuation m*thod. The least desirable is to use a two-way switch, which only results in fl*ps up or full down. This is not very scale-like and could result in large pitch changes when the fl*ps are actuated. A three-position switch will allow the use of half-fl*ps for more scale-like flight. A kn*b or slider switch is another way to go and allows an infinite number of flap settings. The only drawback is that it is sometimes difficult to tell how much flap deflection is selected.

Servo Speed Reducer

Capture2Another way to minimize the trim changes associated with flap deployment, is to use a slow servo speed. Many programmable radios have the ability for you to slow down the response of specific servos. But most pilots will find that simply adding a Speed Reducer like the one from Dave’s RC Electronics, a quick and simply way to deal with the situation. When the fl*ps take several seconds to lower, it minimizes the abrupt change in lift and gives the plane more time to settle down. Simply plug the unit in between the receiver and the flap servo(s) and you can adjust the speed by adjusting the adjustment p*t on the circuit board.


Flying with flap-equipped airplanes  is a great experience and just plane fun. fl*ps allow you to operate your model from smaller flying areas and when it comes to scale compet*tion, they allow you to full exploite your subject aircraft’s flight performance while giving you another flight option to add to your flight routine. Give it a try. It’s a blast.

The post Flying with fl*ps — What you need to know appeared first on Model Airplane News.

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