D-Cell Progress

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Postby fltofancy » Mon Oct 22, 2007 7:39 pm

FYI for those keeping up with the Seagull (Skylark) project.
Sheetmetal formed nose ribs attached to the spar. Leading edge skins and fuel tanks are next.
Gene
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Postby xgary » Mon Oct 22, 2007 8:05 pm

Gene , what will the completed weight be ?

why the riveted Spar ? you can bend like a lazair ?

Nose ribs ? I still think the lazair way with foam is stronger.

Dale Kramer still hanging around here ?
Care to comment ?
Shorty .............
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Postby fltofancy » Wed Oct 01, 2008 2:07 pm

Hi Shorty,
Sorry it has taken so long to get back to you.

I expect these D-Cells will be slightly heavier than original, but I can only guess as to how much, shouldnt be more than a couple pounds each.

My spar design is for a 350 lb person stressed to +4, -3 g's. The original spar design has too many joints for me, and I can make one with less joints using the following design.

The spar has one joint, where the taper begins. So the spar web is one continous piece of .050" sheetmetal from the inboard rib all the way out to the joint at the taper (12 ft) and another piece of .050" sheetmetal from the joint to the outboard tip rib (6 ft tapered section) for a total span of 18 ft without the tip winglets. In the picture you can just see part of the joint doubler plate on the left hand side. The spar capstrips (not visible in picture) are 1" x 1" x .125" L-angle and are continous from inboard tip to outboard tip (18ft) upper and lower. So with these "massive" parts I decided to use MS20426ADX-XX and MS20470ADX-XX rivets for the assembly, these are standard solid aircraft rivets. The leading edge skins will be riveted to the upper and lower spar capstrips with the protruding head rivets. I have a fantastic adhesive specially formulated for aluminum bonding to attach the noseribs to the leading edge skins for a nice clean leading edge just like original. This is surely overkill, but I can always choose thinner materials as the design proves itself out. I know Dale's original design uses much lighter materials, but this design is for heavy pilots and larger engines (Hirth F-36 and RCS Radials up to 25hp).

So, yes foam ribs may be "easier" (to make and install), as I have put quite an effort into making these hydroformed sheetmetal ribs, but I am also locating my fuel tank in the lightening holes of the first 5 inboard ribs (foam ribs would likely take the loads of the fuel tank, but would certainly dissolve if any fuel were to come into contact, a very likely possibility) and therefore chose to go to the extra effort to make sheetmetal ribs. Also they are lighter than the foam ribs, not enough to make up for the additional weight of the other components, and certainly stronger than the foam ribs. I really like the simplicity of the foam, but there have been many problems with them laying over and breaking away at the glue line. I have the ability to make the sheetmetal ribs and so I say why not.

The latest progress on the project:
Fuel tank
I have made a test tank to sit inside the lightening holes of the noseribs from 4"dia thin wall PVC pipe with internal baffles to control sloshing. The hydrodynamic tests have gone perfect with the baffles holding up to the vigorous water hammering of the test. The flow test indicates fuel flow through the baffles of approximately 3 gal/min, plenty to feed the larger engines. The gasoline test shows no degradation after 1 month of continous exposure.

Installing the fuel tanks with plumbing and leading edge skins is next and should start in Oct '08.
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