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Pumpkin drop event

Wingtip extensions

Jeffagain

Junior Member
#1
Hi, completely new to this, and must say its a mass of information, a really helpful & useful community here.
Plus exactly what we realise we were looking for now we found it.

Actually don't want a show on wingtip extensions, least not yet.
Its a research essay my son has done for qualification as part of his college applications and wanted for him to be able to model the effects to add to the book study. RTF looks inflexible & out of budget so the rapid prototype build that foamboard offers is really promising, & the low cost will help with the expected flight failures too!
Had a search on here and there didn't seem much directly though suggestions that experimenting is doable at scale.

We had been thinking we might need monster size to get noticeable differences but would be really pleased if someone can suggest a starting size at which adding wingtips might give us something measurable. Really hoping 3' wing will be enough. Also weren't sure what kind of speeds we might need, be great if we can get away with using the nearby steep hills and save trashing electronics or nitros during the anticipated crashes too.
As for the measuring, - had been thinking of fixing trailing threads on the wings and see how much they tangled as a measure of vortex, & maybe average distance as a measure of flight efficiency, but likely there is a smarter way someone can suggest. Not looking for him to do a nailed down scientific chart just demonstrating noticeable changes.

Was thinking of doing a really basic build, like a triangle section stick like fuselage with stubby fixed wings hoping to max the vortex, have some goes using the information on here about basic build techniques, CG and such then report back once we had something worth discussing.

Of course someone might well have been here, done that and be able to post all the details - in which case please just point us the best path as the experimenting and documenting is the whole point for him.

Foamboard, knife and glue gun, poised and ready.
 

Mudpie

Junior Member
#2
Vortex Generators

Actually,

it may be easier and cheaper to just add vortex generators just behind the leading edge. This will increase lift and reduce stall speed.
 

RAM

Posted a thousand or more times
#3
He's probably seen this video already but I'll post it just in case. https://www.youtube.com/watch?feature=player_detailpage&v=VN3C7K7c9nw#t=2592
It should start at the 43min mark where he talks about winglets.

Based on this video I think he might be able to show something by making some flying wings and playing with different configurations of wing tip. I guess he could use changes in trim settings (numbers should be visible on the transmitter) for different tip configurations as proof of their effect.

Check out this thread from davereap as well. http://forum.flitetest.com/showthread.php?9016-A-simple-flying-wing-method
 
Last edited:

Jeffagain

Junior Member
#4
"numbers should be visible on the transmitter"
Knew there would a smarter way, last time I saw an r/c close up it was still analogue.:eek:
Digital sounds definitely my sons style, and way more likely to work than tangling cotton.

Interesting thread too - I was wondering myself just how much all the detail theory worked when you scale right down,
its another top reason for going the way of rapid build, just so easy to chuck a wing and try again.

Think we'll start at 3' wingspan and see what we can get happening.
Once we get one off the ground.....

Cheers
 

earthsciteach

Moderator
Moderator
#5
Your thought of using stubby, fixed wings is good if you are talking winglets. High aspect ratio wings have far less induced drag from wingtip vortices than stubby, short ones.

What parameters are you and your son thinking of measuring for comparison?
 
#6
How about building a foam board wind tunnel complete with smoke to show wing tip vortices? A little foam board, some clear plastic, a fan and rheostat, a way to hook up a gram scale to measure different amounts of drag with different winglets, and video or pictures of the different vortices produced.

You may just pull off some repeatable quantifiable results and have fun with your kid doing it.

YMMV
 

Jeffagain

Junior Member
#7
Thanks again guys bcos you know what - it works! :applause: Over to the Flitetest crew :D

Ended up taking just an afternoon for my son to build his own wing , design wingtips to match from his research, and prove them effective, photograped and documented. Its all going in his college application and he has the self built bits to show too. It feels like he has already done his first college practical on aerodynamics, so all being well he will being taking Flitetest with him to carry on.

The way we tested was from a suggestion made by a London rc club forum, to try with a wheel, like a windmill on its side.
What i did was make an axle from a 1" dowel through a box with a block on one end to attach the wing, on the other end I finally had a headless nail with a drill on that to drive it round at reliable speed. That build was the hard part, though didnt take that long. & so to the kitchen table.

We took A1 foamboard, 33" long and decide to try 6" depth base layer, 4.5" mid layer and 3" top layer to make the sandwich style wing shown on here. As the wing was going to rotate we cut the middle & top layers in two and made the leading edge face opposite ways, with a gap in the center to screw through a wood strengthener to the axle. We left out the spanwise rod suggested as we werent going to fly, and added having open slots at the end in the middle layer to take extensions.

To try to 'measure' the vortex we attached cotton thread in colors at 1/2" intevals from the wingtip and alternating 4" long theads from the trailing edge and 6" long threads from the middle layer.
Spinning it up by hand, then with the drill we got absolutely no tangles until I tried with the drill on low torque and slowed it with my hand to about 2,3 revs per second; then we got reliable tangle in the correct direction from wingtip to 4" in.
Im making that about 20mph at the tip but my math could easily be out.

First up was wingtip fence, airbus style and the upright big tip.
One on either end. They both reliably showed mild tangle at the tip with no tangle further in at the 2,3 rps speed. Proven.
He also tried a blended tip, and hoerner style tip, these were kind of in between, but that may have been sizing or positioning made them less effective. We ended there as that was enough for his project but the practicality is proven and could, we think, be worthwhile on checking out on any stub wing to see the effects.

Now it is proven at this scale tht gives us confidence and time to get in the air and try with actual flying models, checking trim changes, or other suggested techniques. Be interesting to know if it could be pushed as far as getting 20% extra flight time from the same charge.

Also I think this could be an ideal intro project to involve any high school age in, as it can done indoors, cheaply and they can try their own ideas out really fast and witness the results simply and easily.
 
#8
The basic sandwich wing mounted on the rig
basics.jpg
Vortex shown by tangles when spun at 2 revs ps
tangles.jpg
A wingtip fence added
fence.jpg
Reduced vortex tangle
fencelesstangle.jpg
larger fence, reduces vortex tangle more
largetip.jpg