UNDERCARRIAGE WOES AND SOLUTIONS
From the Burglar alias Tom Sparkes
How often at the field have you seen the troublesome model on take off, that
always fishtails all over the field with the occasional ground loop thrown in for
Very often the solution is very simple. It used to be endemic with
the old timer models and is often caused by the wheels being too far forward.
The natural inclination is to think that wheels well forward, will give you a more stable
model on the ground, but nothing could be further from the truth.
The ideal position is just enough in front of the CG to prevent the model from falling
over when the tail is raised to about 10°to 12 above the horizontal.
Think about the landing as well, if the wheels are too far forward then you will get
the bounce upon bounce syndrome, as the wheels touch the first time, being so far
forward of the CG, then it will automatically throw the nose up,the angle of attack
skyrockets (forgive the pun) then the model rears up, then the bouncy bouncy
continues sometimes ending in expensive tears.
Of course with retracts, (my pet hate,) it can be difficult to get your wheels into the
right position, and still get them to retract back into their right place,but there is a
couple of other things that help as well.
A little bit of toe-in goes a long way as well,particularly helping with the old ground
loop as well. With a bit of toe-in set, as the plane veers and more weight is put on
the inside wheel,the toe-in on this wheel tries to turn the model in the opposite
direction,tending to keep it in a straight line. People like the old Henry Ford of old
model T fame discovered this many years ago.
Another rather obtuse thing to help a little bit is to seal the hinge gap on your
rudder,I use spinnaker repair tape from Whitworths Nautical World on all my hinge
gaps, it will increase the effectiveness of the rudder by a good ten percent.
With the current crop of ARF models undercarriage strength always seems to be
less than woeful. Extra area of mounting footprint can be looked into if at all
possible,particularly in a fore and aft direction, and decent mounting plates
reinforced with fibreglass or ply can be tried.
I always, if possible, use nylon bolts to secure the undercarriage to the model to
provide a weak point to shear in case of accident so as not to tear the bottom of the
plane or wing mounting out . Surprisingly the old 1/4” nylon wing mounting bolts
provide just the right amount of strength for models up to about 7 kilos,for my Laird
Turner which weighs in at around 15 kilos I still use just 4 off 8 mm.Nylon bolts, and
they are still OK after many years.
Happy take offs and landings,remember if it goes up it must eventually come down,
the trick is to make sure it does both in the same condition it was when you
THE BURGLAR alias Tom Sparkes.