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Dec 14, 2013, 01:25 AM
You know nothing....
Stuart A's Avatar
http://www.google.com/translate?u=ht...ngpair=ru%7Cen

Hot wire cut wing.Even traditional rib construction is a series of points,'smoothed' out by spars and covering.
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Dec 14, 2013, 01:39 AM
REMOVE TRUMP
vespa's Avatar
Wow! What a fantastic video! Probably the best aerodynamics video I've ever watched. Right up to the point where the narrator claimed a 60% increase in aircraft efficiency. That really took the fun out of it for me. Did he mean 6%? Under what conditions? And patents? On washout?

I hate to be so negative about such a great project. The use of washout to simultaneously address both adverse yaw and structural efficiency is absolutely fascinating, inspiring, and quite possibly, novel. But the video conspicuously omitted any numerical performance figures, failed to even mention the elephant in the room (the speed range limitations of washout), and then claimed to have invented a "breakthrough in aerodynamics" with a "60% increase". Come on, you guys are smart enough to know better than to make claims like that to a scientific community without detailed supporting evidence.
Dec 14, 2013, 06:16 AM
Registered User
Quote:
Originally Posted by Alien_Tech
Thought you guys might like to see this:
Can you say more about the covering used on this model?
Dec 14, 2013, 08:45 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Quote:
Originally Posted by Alien_Tech

Edit: If you CNC'd a female mold with a negative of the intended twist, weighted the core to conform to its shape, then hot wired it, that could work.
You don't need to CNC a negative.
You could hot wire the bottom of the blank with templates front and rear to produce the required twist. Then as you say weigh/clamp it flattened out and cut the cores.

I used this method to do some upswept tips on a conventional glider , both to cut the cores and when putting on the skins.

https://www.rcgroups.com/forums/show...&postcount=459

Pat MacKenzie
Dec 14, 2013, 09:11 AM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by vespa
Wow! What a fantastic video! Probably the best aerodynamics video I've ever watched. Right up to the point where the narrator claimed a 60% increase in aircraft efficiency. That really took the fun out of it for me. Did he mean 6%? Under what conditions? And patents? On washout?

I hate to be so negative about such a great project. The use of washout to simultaneously address both adverse yaw and structural efficiency is absolutely fascinating, inspiring, and quite possibly, novel. But the video conspicuously omitted any numerical performance figures, failed to even mention the elephant in the room (the speed range limitations of washout), and then claimed to have invented a "breakthrough in aerodynamics" with a "60% increase". Come on, you guys are smart enough to know better than to make claims like that to a scientific community without detailed supporting evidence.
Hi Vespa,

The reason that there isn't more data is the video is because it hasn't been cleared for public release yet. It will be in time, and it will answer many questions I'm sure.

I agree the 60% thing is sensational, especially when it isn't quantified. That number is for an aircraft design taken to the extreme, and not referencing the efficiency of wing alone in the video. The wing shows about 11% less induced drag though.

That number could theoretically be reached if it were applied to a new design of an airliner. This new lift distribution if applied across the board ( wing, remove the tail, turbo fan blades etc) could result in an 60% cost reduction over what we see now. This is what was alluded to in the video, the airline industry is the target audience.

The other part of this that's not quite clear is that this isn't simply traditional washout. There is twist in the wing, similar to washout, but it's highly varied locally along with varying dihedral. This is what gets the vortex to shed early and get the same effects as Whitcomb's winglet.
Last edited by Alien_Tech; Dec 14, 2013 at 09:25 AM.
Dec 14, 2013, 09:13 AM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by Cable
Can you say more about the covering used on this model?
Hi Cable,

Nothing special, just carbon over a foam core.
Dec 14, 2013, 09:17 AM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by pmackenzie
You don't need to CNC a negative.
You could hot wire the bottom of the blank with templates front and rear to produce the required twist. Then as you say weigh/clamp it flattened out and cut the cores.

I used this method to do some upswept tips on a conventional glider , both to cut the cores and when putting on the skins.

https://www.rcgroups.com/forums/show...&postcount=459

Pat MacKenzie

Interesting idea Pat, could you elaborate on it a little bit? I'm having a hard time visualizing exactly how this works. The challenge as I see it is somewhat akin to hot wiring a ball.
Dec 14, 2013, 09:23 AM
Registered User
Quote:
Originally Posted by Alien_Tech
Interesting idea Pat, could you elaborate on it a little bit? I'm having a hard time visualizing exactly how this works. The challenge as I see it is somewhat akin to hot wiring a ball.
If I remember correctly, Hobie cut flat cores and then heat pressed laminate to get the up-swept wings on the Hawk. Seems something similar could be done to get the twist. Would be a lot of work for one-off, but production might make it worth-while.
Dec 14, 2013, 09:24 AM
Pile-it
Alien_Tech's Avatar
Quote:
Originally Posted by Cable
If I remember correctly, Hobie cut flat cores and then heat pressed laminate to get the up-swept wings on the Hawk. Seems something similar could be done to get the twist. Would be a lot of work for one-off, but production might make it worth-while.
They were heat pressed into a mold I would think.
Dec 14, 2013, 09:39 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Quote:
Originally Posted by Alien_Tech
Interesting idea Pat, could you elaborate on it a little bit? I'm having a hard time visualizing exactly how this works. The challenge as I see it is somewhat akin to hot wiring a ball.
When I made my upswept tips I first cut a curved sheet of foam with the required up sweep. Both top and bottom were cut.
I made it fairly thin so it would bend flat reasonably easily for hot wiring the core from it. Once done this gives the core in the shape you want.

Then when putting on the skins I put the beds back onto the pieces that were cut from top and bottom to create what were in effect upswept moulds.

Its possible you could skip the step of doing the twisted core, particularly since your changes are smaller than what I was doing with my tips.
Just make a twisted base to lay the conventional flat cores+beds in while putting on the skins.
As long as the twisted base is hot wire cut the airfoil section won't be affected, just the twist/"dihedral" to match how the base was cut.
Take your mean lines and project them to the front and back of the block to develop the required hot wire profiles.

Hope that makes sense

Send me your drawing files and I could work out the details for you

Pat MacKenzie
Dec 14, 2013, 09:47 AM
Registered User
Quote:
Originally Posted by Alien_Tech
They were heat pressed into a mold I would think.
They were. You can get an idea of the process from this page.
Dec 14, 2013, 09:53 AM
less is more
Knoll53's Avatar
Quote:
Originally Posted by Alien_Tech
Interesting idea Pat, could you elaborate on it a little bit? I'm having a hard time visualizing exactly how this works. The challenge as I see it is somewhat akin to hot wiring a ball.
Not to answer for Pat, but if I'm understanding Pat's method, he pre-bends the foam blank BEFORE the hot wire cut, then cuts through that deformed blank. After cutting, the foam returns to it's un-deformed state and in this case a non-linear twist could be created.

It appears that with just a series of simple wedges, spaced and aligned as ribs, any twist could be created. This would also probably provide a rather smoothly faired twist.

Has anyone tried this method to create wing twist in a foam wing???


edit: looks like Pat and I double posted
Kent
Dec 14, 2013, 10:05 AM
I don't want to "Switch Now"
pmackenzie's Avatar
That's the general idea. except instead of a series of wood wedges the base would be hot wire cut with the desired twist and "varying dihedral".
(Not sure what the correct term is for the latter?)
Dec 14, 2013, 10:08 AM
less is more
Knoll53's Avatar
Quote:
Originally Posted by Cable
They were. You can get an idea of the process from this page.
Wow !.....I had no idea the high level of "tech" that went into a Hobie Hawk. So that wing was just a stressed skin system with blue foam for shear. Amazing.

Thanks for posting Cable.

The photo is an example of Stuart's comment.

Kent
Dec 14, 2013, 10:19 AM
less is more
Knoll53's Avatar
Quote:
Originally Posted by pmackenzie
That's the general idea. except instead of a series of wood wedges the base would be hot wire cut with the desired twist and "varying dihedral".
(Not sure what the correct term is for the latter?)
Varing dihedral, or upswept wing tips, is generally not the goal with BSLD. Or at least it hasn't been so far. We're happy just to get the non-linear twist.

I think that I understand your system Pat. It's somewhat complex. I'd probably have to see a 1/2 hour video to fully understand how it works. I'd sure like to see more examples of this method.

It appears that just the simple wedges could provide the non-linear twist and a straight hinge line.....if done right.

Kent


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