Side thrust or rudder trim?

I'd like to make my Wot4 into the supreme flying machine it promises to be, and learn something about aerodynamics while I'm at it.

I've notice on vertical climbs it needs a bit of right rudder to to keep it straight. So this might mean I need some rudder trim, or that the side thrust of the motor needs adjusting. But how do I know when it's a side thrust issue and when is it a rudder trim issue?

Any advice would be gratefully received,

Chris

You might have already read Jon's atricle . Reading between the lines, the rudder needs to be centred and if it veers off-line it is a side-thrust issue. This assumed the model is straight and true. If it's banana-shaped you may never get it right.

Thanks Mike,

It's been Jon's article I've been looking though, and what you say makes perfect sense, just checking the rudder is actually trimmed centrally...

Okay, just discovered a bow in the rudder control surface, can this be straightened by using an iron on the convex side to increase the tension of the covering film and bringing it straight?

If the warp is covering-induced, then yes, it is possible to straighten it. I heat gun can shrink the covering a lot more than an iron, BTW. But if the surface is warped due to the wood or construction, it will be difficult and possibly impossible to straighten it.

The iron has improved things a bit, enough that I'm happier it's centered,(ish) the vertical stab is a consistent thickness but the control surface is tapered so it's a case of trying to judge the gap is consistent either side with a piece of wood referencing off the vertical stab.

I was within a click or two of center on my trim so suspect I have a bit of a side thrust angle issue as well, and have now tweaked it with a couple of washers... hopefully the weather will be obliging tomorrow evening and I can see what difference it has made

Hi Chris

Good to know someone is actually reading my article!

You should be able to tell if your model is straight by taking measurements on both sides, nose to tail tips, fin post to wing tips etc. Also in flight if your rudder is not centred the model will come down verticals (power off) with some yaw and will also tend to pull out of the vertical dive off line. So trim the rudder for down lines first then when happy see what it does on vertical full power uplines.

When doing this with any wind, make sure you do it dead into or downwind, so there is no cross wind element to affect things. Best to do it on a calm day if possible but you might have to wait for weeks for the chance.

If you are at Cashmoor on Saturday I would be happy to help you with it. Always up for a chance to fly a Wot 4 as you know