Associated Videos:
Causes: Various. E.g.
1. Uncertain how to fly slowly without stalling, hence landing too fast.
2. Over use of elevator on the landing approach, causing a stall on landing.
3. Rates set too high making control on the landing approach difficult.
4. Engine idle speed set too high.
Fix: Learn how to fly slowly, with good control, yet stall free. Learn how to select the optimum elevator trim, so that largely hands off elevator landings become routine.
Comment:
Although much is written about landing model aircraft, the table below seeks to give full understanding, along with some interesting alternatives which, if implemented correctly, should guarantee success time after time.
| What the model pilot needs to know. | Why the knowledge is needed. | Additional detail. |
| The model pilot needs to understand that elevator trim setting equals air speed. | Without understanding, the model pilot will never really believe this fact, as it is counter intuitive. This means the model pilot will still go for elevator control during the landing sequence and thereby risk stalling the model. Close to the ground, during landing, a stall means damage or worse. | The elevator's, (stabiliser's), neutral, hands off trim position dictates the main plane's, (wing's), angle of attack. Increasing up trim lowers the tailplane relative to CG in flight and so increases the angle of attack of the main plane, and vice versa. The greater the angle of attack, the slower the straight and level air speed. Increase the up trim too much however, and the wing will stall continuously, even on the glide. With the up trim adjusted optimally for landing, then provided no additional up elevator is commanded, the stall cannot occur and air speed will be the lowest the aeroplane can manage. See RC Aero Base article: Avoiding the Stall |
| Investigate and know the stall point of the aircraft. | If the model pilot does not know how and when the aeroplane will stall, he can easily get into stall conditions without realising it. | Early during the model aeroplane's history, (often in the maiden flight), the stall should be investigated at height. There are two reasons: 1. The pilot discovers how the aeroplane behaves in the stall, e.g. gently, both wings dip evenly and recovery is easy without significant height loss or perhaps viciously, with one wing, tip stalling, and the aircraft entering a vertical spin, losing much height in recovery. 2. The pilot is able to see how slowly he can fly the aircraft before the stall occurs, by gradually decreasing throttle and increasing up elevator trim until the stall point is reached. |
| Know and record the level of up elevator trim needed for slow safe flight. | This necessary flight data needs to be accessible to the model pilot during flight. | This data can be recorded as trim clicks needed so that they can be dialled in pre flight or stored as a series of flight modes, e.g. 1. Landing Mode. 2. Cruise mode. 3. Full throttle mode. |
| Decide a strategy for accessing the needed elevator trim for slow safe flight. Five alternatives approaches are given below. |
| 1. Do not use elevator trim at all in the process. Instead use elevator control itself. i.e. gradually reduce power on the landing run while increasing elevator at the same time. This works well, but see pros and cons later. |
| 2. For older radios use the elevator trim's analogue slider and arrange the needed landing trim setting to be full up trim so that it can be readily accessed. |
| 3. For digital radios, know the number of up trim clicks needed, and click them in before landing. |
| 4. For modern digital transmitters, use Flight Modes, preferably with voice alerts, so that you can access the needed trim with the flick of a switch, and know by the accompanying voice message, that the correct switch has been used. |
| 5. For the ultra modern pilot with deeper pockets fit and calibrate a model pitot tube to give you additional audible stall warnings. |
When a strategy has been decided, the following additional points should be addressed.
| What to do. | Why. | Additional detail. |
| Whatever strategy is chosen, ensure that it includes a safe stall margin. | If the stall margin is too small, a stall could still occur. | The margin is up to the model pilot, but is easily achieved in the air as follows: In the air fly circuits at the elevator trim slow/safe speed setting. Keep all banks moderate. Do not over control. The safe, slow up trim setting will probably be optimum when no stall tendencies or mushyness of the controls occur. |
| If possible, optimise rates for rudder, elevator and ailerons to match the slow air speed. | This makes control during the landing run easier. | The only way we know of doing this during flight, is with Flight Modes, where with the flick of one switch you can set the elevator landing trim and control surface rates. |
| Do not use elevator once the landing trim is set. Control height with throttle only. Except at the flair. | Use of elevator with landing trims set could easily stall the model. | The landing trim has already put the aeroplane near the stall, but with a safe margin. Any additional use of up elevator will erode the margin and could stall the aeroplane. |
Landing Strategies. Pros and Cons.
| Strategy | Pros | Cons |
| Strategy 1. Above, Elevator only, no trims. | Very easy to set up. Nothing to remember or record. Cannot get confused as there is nothing to change ever. | If your thumb slips on the landing approach, the aircraft will nose in and probably be damaged. |
| If elevator is over controlled on the landing approach, the aircraft will stall and will probably be damaged. | ||
| Strategy 2. Above. Analogue trims with full up set to slow safe flight. | Correct value of up trim instantly accessible. | Fiddly to set up. |
| Need to remember to reset for every flight. If the resets are forgotten, climbouts will be very steep requiring instant correction by the pilot. | ||
| Strategy 3. Above. Digital trims with number of up clicks recorded for the aircraft. | Correct value of up trim quickly accessible. Easier to set up than 2. above. | Need to remember to reset for every flight. If the resets are forgotten, climbouts will be very steep requiring instant correction by the pilot. |
| Strategy 4. Above. Use of Flight Modes with Voice alerts. | Correct value of up trim instantly accessible. Very difficult to get wrong, especially if Voice alerts are used, reassuring the the model pilot that the correct switch has been thrown, so that he does not have to take his eyes off the model. | Need to remember to reset for every flight. If the resets are forgotten, climbouts will be very steep requiring instant correction by the pilot. |
| Strategy 5, above. Use of pitot tubes. | Can be very helpful and reassuring especially with voice alerts. | None. |
