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TOPIC: Sizing your Javelin - some random thoughts

Sizing your Javelin - some random thoughts 1 year 6 months ago #795

  • ahmetcalfe
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Although I have posted on test gliding a foam profile Javelin model under the Flying section I am posting now in the Building section as I am still deciding on how big to make the next one and will try and post my thoughts.

Getting the size right is important, while an L1 Rapier might power a particular model up to a height of say 25 feet, an L2 might fly the same model up twice as high to 50 feet and I like them flying at 50 feet plus. It is all down to the weight, drag and wing area of the model, get the right combination and you can even get an L1 powered model to fly at 100 feet, as does my lightweight foam Hawk (see bottom pic below).

The Depron foam model Javelin spans 6.5” whereas as you can see in the first pic I have now made a larger balsa version at 9.75” span which weighs only 6g so far. I’m expecting the finished all up flying weight to be around 10g if I finish the balsa model with acrylic silver brushed on as per the 508 (see bottom pic). But the question is, is it large enough? I’m sure this will be fine to test out with a catapult and is probably perfect for the earlier wimpy L1 Rapiers of around 60mN, however, as I feel this is a little small for the recent more powerful L1’s I’m probably going to make a bigger version still for an L2LT. For a larger version I have already been drawing up a camo scheme and it will be done in iron on T shirt material as per the Hunter (see bottom pic).

As to how much bigger still needs deciding and to help me sort it out I have assembled a few other like models in the next photo. This pic shows the balsa Javelin amongst a group of some of my Rapier powered profile models, the two right hand models are both for L1 Rapiers, the foam Hawk spans 10.25” and weighs 10g and the balsa Hunter spans 8.4” and weighs 17g. The Hunter sounds heavy for an L1 but the small wing, read low drag, probably helps it to fly so well. The left hand models are bigger overall and were designed for the Rapier L2 LT, the Supermarine 508 spans 12.5” and weighs 14.5g whereas the Boulton Paul P111A spans 13.5” and weighs 17.5g. Except for the balsa Javelin of course which has only been test glided across the bedroom all the other models have been flown many times and even if I do say so myself, they fly very well.

The Rapier L2 LT (low thrust) is a particular favourite of mine as it runs longer than other Rapier motors for 20 – 22 seconds and if the model is not too big and heavy you can get some splendidly long flights. So it looks like I’m going for a 13” version for L2 LT and now I must get on and finish the camo scheme drawing that is, if I can get it onto A4 T shirt transfer paper without using too many sheets. Watch this space.
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