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Catapult Build for Ducted Fan Models

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Gordon Whitehead 112/11/2019 21:04:35
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333 forum posts
153 photos

Re the H-K bungee setup, there's a video here which shows how to set it up and avoid some possible pitfalls. The ends of the ramp are designed to not snag the wing undersides, so I stand corrected there. Whether the distance between the ramp rails is compatible with the distance between the nacelles on a 52in span Canberra is something to consider, and could be cured by changing the lengths of the cross-tubes. The safety pin mod is worthy of note, as are the comments regarding tailplane clearance, and ensuring the bungee pin is well pushed down. Personally I'd use a screw picket/dog stake for that job.

Hope this helps

Gordon

Stephen Jones12/11/2019 23:02:37
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2737 forum posts
1597 photos

Hi Gordon,

Thank`s for the nice comments.

When the load is on the peg it locks that pedal up and needs a good press down to release it.

Just watched the HK video Funny thing that cord arrangement is setup the same way as mine.

Also worth noting is that wind direction can change pushing the model on take off to one side if the wind is not head on.

So my solution was to stake out two ends of the bungee and the Centre to have the cord attached and pulled back to the model that way you are guaranteed the model will launch in the desired direction.

Steve.

Gordon Whitehead 115/11/2019 14:36:55
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333 forum posts
153 photos

Hi Steve

If I understand correctly, you stake the bungee elastic down at both ends at right angles to the line of flight, and then fasten the cord linking it to the plane at the centre of the elastic. This then has the effect of preventing the bungee elastic being deviated by the wind. During launch, which doesn't take long of course, the model on the end of the linking cord will be pushed a bit sideways by a side wind, but far less than if the cord was in line with the whole length of the stretched elastic.

We fly on a narrow field bounded by trees, often with cross-winds, and if that idea works well it's worth bearing in mind for future reference. The only possible downside seems to be that there are two bungee stakes to try to miss on landing winkwink

BTW, I think I also saw another thread about the Miles Student in your avatar. I can't remember if it was ducted fan or pusher, or which forum it was in, but I do enjoy reading design and build threads. After partaking in this thread I'm beginning to feel like having another go at a li'l EDF, having had much joy from the little ones several years ago. Must finish my current bipe project first, though.

Gordon

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