Fixed Wing - Setting up a second-hand Plane

Introduction

We all may have to do this at some time, so how do you go about it if you have no information available ?

The same applies to a new design.

You cannot assume anything so start with the basics ;

1) CG

The CG should be checked without the fuel's weight.

1a) Parallel Wing

Aim for a starting point of 25% of chord which is mild. I usually start at 27.5%, then move the battery backwards to suit (for a stable design only). My unstable designs are usually around 15%.

1b) Swept or Tapered Wings or Bi-Plane

Use the Calculator (Excel spreadsheet "Design Calc") to determine the CG.

Download here : 

2) Lateral Balance

It's important to balance the plane's wing laterally, otherwise the plane will not fly straight when the engine stops.

If really unbalanced, it will drop a wing and spiral in. (ask me how I know !)

3) Aileron throws

Keep the mechanical movement low for the first flight, especially if it's in a wind.

Depending on the characteristics of the plane, these can be adjusted later.

4) Elevator throws

Keep the elevator throws mechanically at maximum in case a flaired landing is needed or a dead stick - rates on full for take-off or landing. Set up switchable 1/2 rates in case the CG is too far back and elevator is sensitive. Use full elevator for take-off and landing, and 1/2 rates for flying if too sensitive.

5) Power to weight ratio

There is more confusion about this than anything else.

Basically, if you cannot achieve enough speed to lift off, the plane will attempt to go for the easiest alternative ie) sideways.

Into a wind, you need even more power.

This also depends on whether the wing is large enough to support the weight (lift) and the engine power to maintain the forward speed - this is even more critical taking-off into wind.

Weigh the plane in lbs/ozs.

As a rough guide the following weight / engine sizes have been determined in practise ;

Suggested AUWeights Guide

6) Engine testing

Engine must be running properly (full and tick-over) and nose-up tested prior to first flight.

7) Test Pilot Choice

1) Get one who is used to flying sensitive fast hot planes.

2) Experience of the same plane type is useful.

3) Get a test pilot who usually flys with a Manual Tx , so you know his reactions are fast. Or, Computer Tx and fast hot plane types.

The problem with Computer Tx's is they can insulate and de-sensitise the Flyer (blame rates,expo,and mixes), so it is then more difficult to acclimatise to a Manual Tx.

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