Berkut Wing construction

[RSD]

How were the Berkut's wings constructed - fibreglass over foam like a long-EZ or another method?

[Kent Ashton]

https://www.berkut13.com/berkut6.htm  carbon, apparently, but I read that the wings were very stiff and gave a rough ride in turbulence.  Other than weight saving, I don't seen any reason why fiberglass wouldn't be better--and cheaper.

[Jon Matcho]

I recall reading that the first Berkut wings were carbon skins on foam cores, and then they later replaced the foam cores with carbon ribs.  

2 hours ago, Kent Ashton said:

...I read that the wings were very stiff and gave a rough ride in turbulence.

I recall reading the same thing somewhere on the 'net, and recall discussing while flying in Marc Zeitlin's Cozy IV.  Marc pointed out the flex of the wing, and that we were not feeling it much in flight.  If it were carbon, we'd be feeling it.  

[Kent Ashton]

1 hour ago, Jon Matcho said:

I recall reading that the first Berkut wings were carbon skins on foam cores, and then they later replaced the foam cores with carbon ribs.  

I recall reading the same thing somewhere on the 'net, and recall discussing while flying in Marc Zeitlin's Cozy IV.  Marc pointed out the flex of the wing, and that we were not feeling it much in flight.  If it were carbon, we'd be feeling it.  

Ya know, we are both guilty of saying "I recall XXX" or "I remember saying someone said XXX".  This is lazy.  We should strive to document what we're saying.  Here is a comment about the ride from  http://www.airbum.com/pireps/PirepBerkut.html

Quote

The extreme stiffness of the airframe was very noticeable when cutting through turbulence. Since we were whistling along at over 200 mph and nothing in the airframe was flexing to absorb energy, even moderate chop hammered at us with sharp edges.

and about the construction of the wings from  https://en.wikipedia.org/wiki/Berkut_360

Quote

Early Berkuts used wings and canard that were structurally similar to the Long-EZ and used solid blue 2 lb/cu. ft. density Dow STYROFOAM PI cores cut to shape with a hot-wire foam cutter, but with carbon fiber reinforced polymer skins instead of fiberglass. The fuselage and winglets remained fiberglass. Later versions (kits produced after spring 1999) used fully molded carbon fiber canards and wings with high density, 5 lb/cu. ft. 1/4" thick PVC or SAN foam cores, leaving only minor fairings and tip surfaces to be carved from foam. The Berkut has always used the Roncz 1145MS canard airfoil, which is more tolerant of insect and rain contamination than the GU 25-5(11)8 airfoil originally used on the Long-EZ.

This kit was sold with "molded wings (including  flat stock for ribs and spars)" so I you seem to be correct about the wing with ribs.  https://www.canardzone.com/forums/topic/17030-berkut-project-for-sale/

I don't know if Berkuts were ever built with Long-ez spec wings but there is plenty of discussion about Berkuts found with a google search.

 

[TMann]

As someone who has actually built the Berkut wings vs. 

2 hours ago, Kent Ashton said:

"I remember saying someone said XXX".  

I love working with carbon, especially carbon uni.

I have a little bit of documentation here.

[Jon Matcho]

1 hour ago, Kent Ashton said:

Ya know, we are both guilty of saying "I recall XXX" or "I remember saying someone said XXX".  This is lazy.  We should strive to document what we're saying.

Agreed.  There's just so much time in the day and the pros/cons of foam/fiberglass vs. ribs/carbon are beyond RSD's original question:

6 hours ago, RSD said:

How were the Berkut's wings constructed - fibreglass over foam like a long-EZ or another method?

You and I both answered the question the best we could (original Berkuts had foam-core wings, and later used a rib structure).

However, your link to Wikipedia is still just text without a citation; essentially hearsay anyway.  So... there's more work to do in order to back up our claims, but at this point that's all I've got. 🙂