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[Jeremy McCreary]

Well, my avatar here really is under a big top -- 288 mm in diameter! Weighs only 88 g, though, as the thin fabric "fairings" cover a fairly sparse 6-spoke frame.




Not that the fairings do a lot of good aerodynamically. Spin time is only ~15 s with either multiple twirls or the planetary starter shown. As you might imagine, the top moves a lot of air just by virtue of its size. The barely tolerable wobble is probably part fairing flutter and part frame flexure.

The orange fabric parts are LEGO parachute canopies. For a 4 g minifig, we're talking express parachute, mind you. But for the 1.8 g top below, the descent rate's not bad.



Guess that makes the top a real paratouper.

I'll let myself out.

[ortwin]

Oh it is LEGO. At first I thought I am seeing those little umbrellas that come on your ice cream sometimes or in your cocktail.

[Jeremy McCreary]

Was really hoping that this top would stay up longer. But it needs a lot more AMI, and I need to reduce the gap between canopies somehow.

In the meantime, have a Mai Tai with a little umbrella and pretend you're on the beach in Tahiti.

[ortwin]

Tahiti,.... that is where those coconut tops grow?

[Jeremy McCreary]

Tahiti,.... that is where those coconut tops grow?

Exactly.

[ta0]

LEGO has parachutes . . . What's next? 

Just joking! Nice to see that you have that flexibility withing the LEGO world.
Another rather unusual top.

[the Earl of Whirl]

Very interesting!!!

[Jeremy McCreary]

Paratoupie
The top's now performing well enough to get a name — the Paratoupie.

Since the prototype above, I managed to eliminate most of the wobble and triple the spin time — now 45 s with either multiple twirls or a 1:4 planetary starter. From the outside, the changes are subtle...




And the fabric "skin" still flutters at speed, though not as much since I flattened and tightened it...




The big changes are all under the skins...




Main changes
1. Added lots of AMI — mainly with the blue/black wheels
2. Lowered CM substantially
3. Added more chord struts to stiffen the "airframe"
4. Flattened the fabric's outer surface profile from tent-like to more pancake-like
5. Further reduced internal airflow by bringing the skins' outer edges closer together
6. Reduced fabric flutter by increasing skin tension

Further aerodynamic gains seem unlikely, but the airframe still has room for more AMI


Tops and airplanes
Why am I talking about skins and airframes? Well, it finally hit me today: A modern airplane hides most of its core functional components — airframe, engines, landing gear, hydraulics, cockpit, cabin, cargo hold, etc. — under a lightweight streamlined skin. And more of my LEGO tops should be hiding their guts and bones under a thin skin as well. That way I can to some extent decouple the mass distribution and structural design from that of the outer surface exposed to the air.

Of course, we've been discussing the value of fairings a lot lately. Just never put it together quite that way.

[ta0]

Tops and airplanes
Why am I talking about skins and airframes? Well, it finally hit me today: A modern airplane hides most of its core functional components — airframe, engines, landing gear, hydraulics, cockpit, cabin, cargo hold, etc. — under a lightweight streamlined skin. And more of my LEGO tops should be hiding their guts and bones under a thin skin as well. That way I can to some extent decouple the mass distribution and structural design from that of the outer surface exposed to the air.

Of course, we've been discussing the value of fairings a lot lately. Just never put it together quite that way.

It seems that this may be the start of a new realm of LEGO tops. 

The top's now performing well enough to get a name — the Paratoupie.

I don't know if you did it on purpose, but this is very close to parapluie, umbrella in French. So now you should make one that closes as an umbrella for storage  Better still if it automatically opens when you spin it and closes when you stop 

[Jeremy McCreary]

@ta0: No, didn't think of parapluie for the paratoupie. But I'm totally using it for the umbrella top now in R&D at your suggestion. Thanks for the idea!

When I borrowed the paratoupie's upper skin for the coming parapluie, the former's spin time dropped 50%. So at least the upper skin's a net benefit when it comes to spin time.

But as they say, every paratoupie has an azure lining...



In my book, that trippy visual's well worth the price. And it's even better in person and video. The colors, man!



Predicting how a patterned top will look at speed can be a crap shoot. This one turned out to be a very pleasant surprise.

[Jeremy McCreary]

Parapluie progress report

Getting the orange canopy to fold up is the easy part.



Keeping it from unfolding too much at speed is trickier.



Without some limiting mechanism, ground clearance would all but disappear, as I have to keep the CM as low as possible to have any spin time to speak of.

The temporary chains will be replaced with suitable elastics so that degree of opening grows both visibly and tangibly with speed.

[ta0]

Wow! The parapluie came fast! Nice work!

Of course, you could spin the umbrella upside down to keep the clearance.

[Jeremy McCreary]

Wow! The parapluie came fast! Nice work!
Of course, you could spin the umbrella upside down to keep the clearance.

Thanks! Happened to design a similar 6-stay folding frame for a made-up amusement park ride a while back. That saved a lot of time.

CM gets way too high if the canopy points upward. I'll be lucky to get 10 s of spin out of this thing.

Never mind. Works both ways, though neither spins long. Testing will tell which can be made to spin longer

[Joah]

Paratoupie
The top's now performing well enough to get a name — the Paratoupie.

Since the prototype above, I managed to eliminate most of the wobble and triple the spin time — now 45 s with either multiple twirls or a 1:4 planetary starter. From the outside, the changes are subtle...

And the fabric "skin" still flutters at speed, though not as much since I flattened and tightened it...

The big changes are all under the skins...

Main changes
1. Added lots of AMI — mainly with the blue/black wheels
2. Lowered CM substantially
3. Added more chord struts to stiffen the "airframe"
4. Flattened the fabric's outer surface profile from tent-like to more pancake-like
5. Further reduced internal airflow by bringing the skins' outer edges closer together
6. Reduced fabric flutter by increasing skin tension

Further aerodynamic gains seem unlikely, but the airframe still has room for more AMI


Tops and airplanes
Why am I talking about skins and airframes? Well, it finally hit me today: A modern airplane hides most of its core functional components — airframe, engines, landing gear, hydraulics, cockpit, cabin, cargo hold, etc. — under a lightweight streamlined skin. And more of my LEGO tops should be hiding their guts and bones under a thin skin as well. That way I can to some extent decouple the mass distribution and structural design from that of the outer surface exposed to the air.

Of course, we've been discussing the value of fairings a lot lately. Just never put it together quite that way.

Very interesting correlation... never thought of approaching top making the same way as making an airframe...creative gears a turning...great project each of your iterations has such intricate internal framework.

[Jeremy McCreary]

@Joah: Thanks! Handy having such a verstile construction system around.

As a topmaker, often find myself wishing for stiffer structures and better aerodynamics. But the system's pretty good as it is. Just need a versatile fairing system to go with it, LEGO or otherwise.