Moldless vs molded weight

[zolotiyeruki]

I've been watching the RevelAero posts on Facebook, and have been wondering: Could you make a Long-EZ/Cozy/whatever even lighter if you used molded parts for the wings and canard?

I understand the biggest benefit of moldless construction when RAF was selling plans--it makes composite construction accessible to the average Joe, without the need for expensive tooling, or selling complete assemblies, etc.  But if you had molds for the wings/winglets/canard, could there be some weight savings to be found, compared to moldless foam core construction?

This is just spitballing--I recognize that you'd need to do some proper engineering to determine rib spacing, wing spar design, layup schedule for the skins, etc.  But roughly speaking, would you expect to see much of a weight difference?  I imagine you'd have less filling and paint on the outside, and less weight on the inside due to the absence of foam, but more weight due to the ribs. And I'm ignoring for now any difference in the time required to use one or the other technique. 

[Kent Ashton]

Yeah, I imagine you'd have a lighter airplane, but also a lighter wallet and a 5% chance of flying compared to a person that builds from plans.  You propose to save time on filling and painting  but the time expended in mold-making to get such parts is enormous.  If money is no object, try Aerocanard   https://aerocad.com/16-aerocanard-fg    or just build a Velocity.   Ronenberg's molded Berkut did not sell enough to stay in business.  Here is another molded dream:  "A-solution"    https://www.canardzone.com/forums/topic/21972-sales-ive-seen/?do=findComment&comment=63573     Bob spent months--maybe years--making  beautiful molds that never produced an airplane as far as I know.   RevelAero, with their beautiful computer-cut, anodized and carbon fiber parts, looks very expensive to me, especially for a one-seater.   They may sell a few but I doubt the market will support them.

 

 

Edited January 26, 2022 by Kent Ashton

[zolotiyeruki]

Yeah, I acknowledge the realities you bring up, in terms of cost, time to build, likelihood of finishing, etc.  I'm not seriously proposing tackling such a project, I'm simply trying to get a feel for what the weight impact would be.

[Marc Zeitlin]

1 hour ago, zolotiyeruki said:

Yeah, I acknowledge the realities you bring up, in terms of cost, time to build, likelihood of finishing, etc.  I'm not seriously proposing tackling such a project, I'm simply trying to get a feel for what the weight impact would be.

In a perfect world, if you could magically build exactly the same aircraft but mold/VB it, I've estimated that you'd save maybe 70 lb, max. The reason is that out of the 1150 - 1200 lb that a COZY MKIV weighs empty, or the 850 - 1050 lb. that a Long-EZ weighs empty, first you have to remove EVERYTHING that isn't composites, and see what you have left, and THEN see what you've  got left that's moldable, since all assembly layups are not (and the plane wasn't designed to be assembled in molds or with features that use molds or VB'ing. Then you've got to remove the composite landing gear bows and nose strut.

And once you do that, you realize that maybe you've got 300 lb. of composites, all told, that's modifiable without a redesign of the aircraft (which even this would need, to some extent). You're not going to reduce the weight of any of the fiberglass, so what you've got less is fill (but at 12 lb. / gallon for epoxy, MAYBE you can save 10 - 20 lb. of fill) and layup epoxy. If you assume that you can cut the glass/epoxy ratio from 45/65 (decent contact layups) to 55/45 (decent VB'ing), you can get a 100 lb. layup down to 82 lb. So for 300 lb. of composites, you'd save 3 x 18 = 54 lb. Add the 10 - 20 lb. of fill, and you're in the 60  - 70 lb. range.

As Kent says, clearly not worth the time and effort unless you're in business manufacturing them.

And don't expect hollow wings to weigh substantially less than solid core wings, even with bagging - they won't. Bill Simpson on the Homebuiltairplanes.com forum has posted regarding the comparative weights, and until you get to very large wings, solid core is at least as good from a weight standpoint.

[zolotiyeruki]

Thanks for taking the time for such a thorough reply, Marc.  60-70 lb on a 900-1200lb aircraft is nothing to sniff at, but not a game changer, either.  I lurk on the HBA forums as well, but hadn't seen this particular discussion.  I'll go do some more searching to see if I can dig it up.

[zolotiyeruki]

On 1/27/2022 at 12:26 PM, zolotiyeruki said:

Thanks for taking the time for such a thorough reply, Marc.  60-70 lb on a 900-1200lb aircraft is nothing to sniff at, but not a game changer, either.  I lurk on the HBA forums as well, but hadn't seen this particular discussion.  I'll go do some more searching to see if I can dig it up.

For the benefit of anyone coming along later with a similar question, a relevant post by the aforementioned Billski is here: https://www.homebuiltairplanes.com/forums/threads/wing-design-for-lightest-possible-wing.31780/page-2#post-477756