Advice from Eric Brownbill on how to set up the steerable nosewheels on ARTF Trainers. This article discusses the common problems with steerable nosewheels and may save you a wasted trip to Aston Down.
Steerable nosewheels :
The current 40 size ARTF Trainers are all designed on very similar lines and fitted with a steerable nosewheel. It’s easy to see why the manufacturers include this; it’s an extra feature they can add at minimal cost, and the novice can dream of taxiing out onto the runway for his first takeoff, then triumphantly taxiing back after his first super smooth landing!
Sadly, the steerable undercarriage isn’t going to be at all effective unless you have the benefit of a smooth tarmac runway. But even on the tarmac of Aston Down, there are several almost inevitable problems with the steerable nosewheel. On at least one occasion, the result of these problems was that it was impossible for anyone to get the model airborne.
Nosewheel movement :
If you hook up the nosewheel to the servo in the obvious manner, say middle hole on the servo arm to middle hole on the nosewheel arm, you get far too much movement. Most people are used to the sort of movement you see in the front wheels of cars which can move 30-40 degrees each way, so this is the sort of movement they put on a steerable nosewheel. If you've this sort of movement, a slight touch on the rudder stick, even while taxiing slowly, will cause the model to roll on it’s side. At high speed on a takeoff run, or after a landing, touching the steering becomes an excellent way of destroying the model.
To be effective and controllable, you need minimal movement. This means that the link attached to the servo needs to be on the innermost hole of the servo arm and the link attached to the nosewheel on the outermost hole. Practical experience has shown that sorting the link attachments out on the flying field is almost impossible, it’s really a workshop job, so the advice is to do it before you go flying. It will save you disappointment and a wasted journey.
Nosewheel alignment :
Every owner of an ARTF Trainer has told me that the nosewheel is aligned correctly, but none of them ever are. The only way to find out if it is, is to test it. The way to do this is to sit the model on a flat bit of runway, or it could be your drive at home, hold it by the tail fin and give it a smart push forward. It soon becomes clear which way the model wants to run and you can make adjustments to the linkage until it goes straight.
You may find that making adjustments to the nose linkage on the field is difficult, it’s really another workshop job so the quick fix is to use the rudder trim to get the nosewheel straight. The rudder may go out of alignment in the process but you can then adjust the linkage to the rudder because it’s usually quite easy to make adjustments to the external clevis with attaches the linkage to the rudder horn.
Keeping the nosewheel alignment correct :
You will need to check the alignment regularly. If you do a heavy landing, the bit that will hit the ground is the nosewheel, and even if it doesn’t look bent it easily gets knocked out of alignment.
Advice on steering the model on the ground :
The basic advice is use care and finesse at all times.
On a take off run, try and anticipate if the model is going to run off course and apply a little correction (stick pressure rather than movement) before it does. Once it has veered off course it becomes very difficult to get it straight again, and you usually finish up with a series of over corrections which cause the model to zigzag all over the runway. Once this happens, the only course is to kill the engine and start again.
The other thing is not to get too hung up about steering the model; if you want to do model cars you need to join a different club! The purpose of the take off run is to get up enough speed to get airborne, so if you have enough speed get airborne, get into the air even if you are pointing 45 degrees the wrong way (subject, of course, to considerations of safety). I’ve seen several members so concerned about steering that they’ve run off the far side of the runway even though they had flying speed.
Finally, be very careful what you do following touchdown. You spoil the effect of a super smooth landing if you hit the rudder stick too hard and the model rolls on its side!!