Turbulent Noise And Smoothing The Way

[Capt Kremen]

Many Moons ago whilst I was wearing a 'Blue Suit', required reading was a column entitled "I learnt about flying from that".

This gave aviators insight into the often unusual things that had caught a pilot out in the course of their flying.

 

Whilst not as dramatic as many a full-size exploit, I had been flying a Hangar 9 'Pulse XT 40' low-wing sports, 65" span, 4S electric powered model.

It flew well enough, no major trim issues but made an awful 'rough' sounding noise while doing so.

I'd balanced the prop, the spinner was clear of the blades, (balanced too). The control surfaces were all secure i.e. no obvious cause of flutter.

I suspected a motor bearing although the motor was low time and of reasonable quality (E-Flite Power 46).

Nevertheless, I swapped out the motor for an equivalent, (the same motor only much cheaper 'cos of the branding?), Turnigy G46.

Flight tests continuing, the noise was still there.

Fellow club mates suggested it might be the close fitting cowl resonating against the fuselage nose, much like a 'paper & comb' does when you make a tune through it!

Another flight after removing the cowl, still no change in the 'orrible noise.

Now Hangar 9 models are generally quite attractively trimmed out with 'go-faster' stripes adorning the airframe, including the wings.

It couldn't, could it? 

Sure enough at inflight speeds, a trim strip on the wing was lifting just sufficiently to vibrate and through the built-up wing be amplified sufficient to make the offending sound.

A piece of sticky tape over the trim edges stopped the noise at source and harmonious flight resulted.

I learnt about flying from that!

 

And ....

Smoothing Tip

As a plastic modeller I have had occasion to use a product called 'Johnson Pledge Multi-Surface 5-in-1' , a polish used to assist decal application.

Whilst assembling a ARTF, (you hardly build them do you?), the metal control pushrod was rather stiff and sticking in its fuselage tubing.

It moved but I could see this causing servo, control surface and trim resolution issues as the input deflections wouldn't return to exactly the same position.

I 'Brasso-ed' the wire smooth, better but still not perfect.

Then thought to try the 'Pledge' polish.

Voila, silky smooth pushrod action.

Might be worth a try on your next sticky control run.