Christchurch and District Model Flying Club
 

A lightweight P51 mustang flies!

By mike roach

Some time in 2009 Ivan Pettigrew sent me a free copy of his Shoestring plan and this lovely little model fitted right into my self-improvement class (I really did need to be able to fly better).

While I was at Chilliwack, Ivan very generously let me fly his own Shoestring and while he was giving me tips on flying technique, we both commented on how realistic it looked flying around against the sky and the mountains, and we agreed that a single-engined fighter, built to the same standards, would be just the job. So here's the start of mine: a Mustang drawn up to 1/8th scale (55" span) with a minimum structure and a ladder-type fuselage. The motor is a 3536/1100 from George at 4-Max and the spinner is not quite large enough at 3.25" diameter, from falconsrcss on eBay. (Excellent delivery and service from both, by the way)

The tail surfaces and wing are pretty well as per the Shoestring, as is the basis of the fuselage. It will have to have lots of curved formers, sheet covering and planking round the curvy bits (no, I don't want a profile model thanks) but at first it will have no UC, just a strengthened air scoop for belly landing. There are areas of longer grass at our field that will cushion the arrivals. Later on I might try the new e-flight servo-less retracts, providing it all works!

That’s what I wrote last time. Since then I have finished the model, covered it with Solartex, added a few details (I can never have a fighter without the radio aerial, I really do not know why!) and waited...and waited...until at last a flying day arrived. I worked out a method of solo hand-launching “on the bench” and with heart in mouth gave a large heave-ho on full throttle. You know how I hate doing a maiden flight with an audience, so I sneaked over to our big field a couple of weeks ago and after a few checks and some time-wasting, hand-launched, and away the Mustang went! No pictures of course, but she was stable, nearly trimmed out (just a peck of down and right) and responsive to all controls. The ailerons, despite being quite small, gave at least scale roll speed and probably more. I was surprised how "hands off" she could fly (never having flown a low-winger before) but as you would expect, the speed and responses are similar to the Shoestring.

My two concerns were over the belly landing and the prop/spinner balance. I had two flights and each time the landing was a breeze, she slowed down to perhaps 10 mph a foot off the ground, lots of up elevator and she just flopped onto the grass. I'd done a stall test higher up and found that she slowed down to a crawl before dropping a wing and losing height.

The prop/spinner balance is a different matter. There's a lot of noise on full throttle, so apart from the launches, I flew on half throttle all the time. There's still some noise, but not half as bad. I will have to replace the spinner before much longer.

After the (anticipated) disappointment with the Mustang's plastic spinner and the advice from the guys at RC Groups, I ordered a JP alloy spinner and 4mm adaptor from the Sussex Model Centre, price £16.95. Order to delivery was about 3 days - amazing service, thanks SMC. This morning I took the old spinner off, which was just as difficult as I had thought, since one of the screws had burred over and I had to saw/dremel the thing off!

The new one fitted straight from the packet, with a nice backplate and a collar adaptor for my motor. I tested the prop/backplate only and it seemed to spin up nicely, with none of the vibration and noise of the earlier spinner.

The actual spinner is held onto the special prop nut with a long allen-key headed bolt: not quite long enough actually, so I added a prop washer from my spares box and this time it bolted on securely. On test, there was some vibration, so I rotated the spinner 180 degrees and tried again, this time with great success, at least at the relatively restrained rpm I could live with in the house.

So I have a lovely new shiny spinner, not the right profile or colour, but this time practicality takes precedence over scale fidelity.

The Mustang, like many WWII fighters, needs an 81mm (3.25") spinner at 1/8th scale. I now feel confident that a second try at a light fighter will be worthwhile: I had in mind a twice-size West Wings Spitfire Mk 22: span 48", scale 1/9th, or a TA 152 at the same scale, enlarged from the Al Lidberg kit. I have both kits in the loft, bought against the day when I would have time to make them. Doesn't everybody do this squirreling?

Happy happy days!

Note - some of this stuff has already appeared in the BIMBO RC Groups thread - Mike

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