Benny was right... basic flex experiment 1-A

General Discussion
1

After building a noserider with a scooped out tail deck I was surprised at how much flex it had. Ben Sparks (Benny1) confirmed my finding and has stated that the shape of the deck is more important than any of the various material tweaks. For any doubters interested in checking this out…

Get some scrap fiberglass, carbon, whatever. Laminate the different scraps to some inflated balloons using whatever resins you want - epoxy (RR 2000, 2020, 2040), polyester, urethane? It doesn’t take much… a sample the size of your hand would be just about perfect. For compsand guys, just vacuum a test sample against any domed molding surface you can find.

When resin is fully cured, pop the balloons or remove the samples from the mold and flex the test panels “with” and “against” the domed curvature.

In my tests I found that Benny was right. All of the samples resisted flexing against the dome curvature. They all (including “stiff” carbon fiber) flexed quite easily in the same direction of the domed curvature.

IMO this, along with the Morey “spoon in faucet” test, should be a basic standard performed by all of you techno-weenies out there.

2

Yeah but if you scoop the deck aren’t the rails going to be more abruptly domed? Making the rail line really stiff?

3

Check.

I think that’s why Bert Burger and others have gone so thin. Bert also does the concave deck as shown on his vacuuming thread…

I just presented it as more of a general flex concept experiment than a total design.

4

well when i get back from my dumb surface modeling class give me a chance to work up a slice in ms paint to see what you guys think of this design throughout the full board.

from my understanding the more of a spoon shape the more its going to flex, with thin hard rails that hold the more pressure there is to bend the board. the more the board bends the more it holds the wave and when you turn the more energy is transfered into the board so when you come out of the turn you have more speed and what not.

adding concave to the bottom would add to the speed.

so in theory you could get a thin board which planes well and holds its energy. and make it from strong carbonfiber or what have you

so either i make sense or i am completely off the wall and should go to a mental hospital.

let me know.

5

This is news? Anyone who’s been around a while knows that back when boards had domed decks they didn’t snap nearly as easily as they do these days. Granted, there’s other factors. But a domed deck will resist snapping better than a flat one, that’s certain.

Conversely, it’s the idea of a scooped deck as implemented by Yater that proved the benefits of flex. Then, Greenough took it even further.

6

well here is what i drew up in inventor during class today.

7
Quote:

well here is what i drew up in inventor during class today.

Really? Where is it?

8

“This is news?”

Yeah, they just covered it on CNN.

9

here!

i just suck at uploading

10

Hi John,

Remember my 9’8" green board? I know it’s a noob attempt but you can most definitely feel the difference. Even with the T-band stringer. Next time I’ll thin it out a little more.

Marc

11

dome stiffens a board

sandwich panel theory will tell you that the thickness of the core is the most influencial

then, density/ stiffness of core materials

then shape i guess

roy was posting some stuff on compsand about concaves making a plank more flexible

made sense

but i think there was a thought that it can also stiffen a structure when applied to sandwhich panels

in the case of the deck it creates two domes at the rail lines

i wouldnt know myself just guessing

i cant see why bert would be trying to make that board more flexible

ive used schedual like that and he would overpower that board easily

it would flex like a noodle (due to thiness .one pound core and d cell)

maybe he does it to increase overall flex

and used a springer to compensate

12

I’ve seen several very short boards from the early-mid 70’s that had tail channels and the deck followed the same profile to maintain a consistent thickness, which was thin. Any shape (hat, dome, etc) will be stiffer than just flat. I must agree with Paul that the internal core structure will have the most effect if you want to change flex or stiffness.