Saturday, February 21, 2009


Ok so i have been slack. I still dont even have a mould for the new hull or even a block or foam. absolutely no progress there. the 3d file is router-ready but thats about it. Had a few projects that took over and now that theyre done im back at uni and so progress i fear will be slow. 

anyway ive been still tinkering with the blue boat - broke the gantry and it was off the water for a while and now its fixed back up again, a truly crap repair job later. one of the things i did was redistribute some area between the foils, just for the sake of an experiment. so i cut 100mm off the rudder span and added that to the centreboard, in the form of these wingtips. 

 Everyone i talk to says "wingtips are tricky, you need to do 3d analysis and work out the nature of the vortex at the design speeds etc." Anyway i pretty much ignored the advice of everone who knew what they were talking about and just designed some in rhino that looked good, cut them out, took a mould etc. I think they came up pretty good, the foil sections are pretty accurate at least. and they seem to work too, subject to a bit more testing, two things have happened; the boat launches much better and at lower speeds, and the hum that i used to have is gone. also there is no noticeable loss in stability from a smaller rudder (550 span i think) and it all feels smoother, and the boat want to go straighter. i could be kidding myself about that last bit. foiling manoeuvres were easier. also i have a new wand which i reckon is my best one so far, with a paddle about 200mm from a very flexy tip. If i do anything else i may want to extend the flap onto the wingtip, i dont seem to have quite as much response.

anyway heres a pic of my wingtip, if anyone wants one for their old and shit square foil let me know and ill make you a pair of blanks, im keen for another opinion. chord is like 115mm or so.


MARKLA said...

Everyone i talk to says "wingtips are tricky, you need to do 3d analysis and work out the nature of the vortex at the design speeds etc."

wot a croc - wing tips do one important thing, increase the apparent aspect ratio of the wings, creating more lift at lower induced drag.

I think you did the right thing in having a go - it is always going to help you takeoff speeds.

A more important topic that design of wingtips is whether you want to optimize your foils for a low take off speed or a high top speed. I do not believe you can achieve both.

nick flutter said...

yeh i think your right
the best thing was that i increased the actual span by like 100mm. the upturned tips are small i figure even if they totally dont work they wont be that much extra drag.

juryk said...

good job! how did you cut the moulds and was it a square planform foil you applied them to? what about the rudder?

nick flutter said...

right so i didnt touch the rudder because half the time its lifting and half the time its sucking down, so that makes the tips more complicated, and because the lift per span is less, its probably not creating a huge amount of induced drag. i guess.

The mainfoil planform is square, except i modified the flap so that it tapers a bit, to reduce induced drag with the flap fully down. earlier i cut a triangle 100mm x 15mm from the flap aft corner and reshaped the end of the foil slightly.

To make the tip mould i made a plug out 2.5mm balsa sheets - i sliced the 3D model in 2.5mm sections, running laterally, and printed a set of templates onto paper, which i glued to the balsa and cut it all out with a scalpel. Stuck all that together and gave it a quick coat of bog and a sand, then took the mould off that under vacuum.
worked pretty well i got a fairly accurate result.

Karl said...

Home brew STL! Ve have ze technologie!

Dave Buzzard said...

Hi Nick

i've got a set of mk1 prowler square foils. Your section on the wingtips is interresting, can i ask a few questions
several months down the line what are your thoughts on the wing tips?
how did you join the tips to the foils? drilled/dowels?
i'd like to try and make some tips as well would you mind me using your design?


Dave Buzzard