1923 B3 'Charlotte II' in 1:3 Scale

[ARUP]

I bought Vincenzo Pedrielli's book 'Asiago 1924, International Gliding Competition in Italy'. It is about the first gliding competition in this Asiago Plateau area and was probably one of the first gliding competitions in Italy. Germany was the leader as far as gliding was concerned so why not hold a meet and gain experience and share ideas? That was the concept and it worked very well for Italy in future. The University students of the Berlin Akaflieg built a series of flying wings, the 'Charlotte II' being one from 1923. Hermann Winter did the piloting duties at Asiago. The 'Charlotte II' didn't seem to be much of a performer but it sure is interesting! The full scale had a span of 14.65 meters so the model will be ~4.88 meters in span. The three views in the book are by Vincent Cockett. He kindly sent more information about this sailplane via e-mail. Thanks Vince! The plans are drawn but no wood has been cut. This was going to be a 'secret project' which I was going to spring open to everyone at the upcoming Horizon Hobby Aerotow of 2016.

[Melchizedek]

I have a request Michael. When you get going on this build. Can you embiggen your photos? Please

Kevin

[ARUP]

I'll try, Kevin. My ISP is terrible and I think I have the sizes at a level it can handle. I take pictures with lots of pixel density but have to 'belittle' them before posting!

[lenb]

Oh Boy!!!
START CUTTING

[Dion Dunn]

This is going to be good!!!

Hey, I thought we were going to build Peanut Scale rubber jobs for our next project! 😉

[lenb]

He's starting to thaw out

[ARUP]

W-w-w-what a-a-a-are -y-y-y-y-y-y-y-you t-t-t-t-t-t-t-talkin' a-b-b-b-bout! S-s-s-s-started c-c-c-c-cuttin' w-w-w-wood t-t-t-today. P-p-p-p-pea-n-n-n-n-nuts g-g-g-gettin' d-d-d-drawn, t-t-t-too!

[stihac]

so cool! looking forward to the build

[ARUP]

Hiya Petr! What have ya got on the building boards? Dion- I started a Peanut Fokker D-VIII 'Flying Razor'. I talked with my buddy so you are now in the unofficial MWMW club. (Mt. Washington Mole Whackers). We are going to see what it takes to become an 'official' Flying Aces squadron now that the requisite three (?) members are on the role.

The flying wing 'Charlotte' has some interesting construction hurdles to overcome. One is the 'twist' that the wing has along its length. It is approximately 8 degrees from the root end to a rib station (#15 if the root end is #1) just before the extended portion of the wing starts. The ribs are built up full scale fashion so just putting the ribs on the two spars and forcing a twist isn't possible or structurally sound. The spars will be built up so their ability to be twisted will be limited. There is just one template to make the 15 identical length ribs each panel. An 'adjustable spar slot jig' is set onto the rib template so that the slot to receive the spar can be progressively angled. Two identical ribs are built then the 'adjustable spar slot jig' is set for the next two ribs. It will all make more sense when a few more ribs have been made so the differences can be seen. I am using the scale airfoil which is the Gottingen 365.

Another construction consideration is the wire or cable TE on the full scale. It is easiest to just cut wood and scallop it to get the effect but doesn't look proper when the covering is translucent as on the 'Charlotte'. This model will be done to resemble the full scale item. A segment of aluminum tubing at the TE will allow cable to pass along the TE.

Then there are even more considerations! Covering will commence from the under surface LE to the TE then around and across the upper surface to the LE again. The constant chord portion of the wing can get done in one piece. The extended portion of the wing can get done in another piece of fabric folded across the cable TE on the bias of the weave and attached in a similar fashion. I think I have a solution to sealing the weave of the fabric without 'sticking' the upper surface to the lower surface at the TE. They will be in close proximity so this is definitely going to be difficult to tackle. The wings are going to have an 'auto-connect' elevator and aileron feature so that all RC equipment will be in the fuselage. Stay tuned!

[Dion Dunn]

You always pick the easiest planes to model.....

[ARUP]

Yessir, Dion! Lots of screening criteria are in place choosing a subject to build. 'Looks', rarity, features, novelty and historical aspects are just some. I don't expect much in the way of performance but maybe the 'Charlotte' will surprise just like the 'Vampyr'!

Properly sized sticks were ripped from 1/4" x 4" x 36" Basswood boards in preparation to build the ribs. To make bending sticks to suit the upper Go365 scale foil the sticks were soaked in hot water then a covering iron at max temperature was used to 'steam iron' them over a jig. Do not use ammonia for this unless you want the wood to become brittle. My first jig was a cookie tin but has since been modified to what is shown. The Go365 foil on my plan was traced onto another sheet of paper. The spar slots are represented with centerlines. There are 15 ribs that gradually change in angle of attack from 8 to 0 degrees inboard to outboard. The spar slot centerlines all intersect at the bottom of the spar slot. This intersection is the 'pivot point' for a spar slot jig. The first and last spar slot centerlines were drawn to a convenient length. A nice convenient length was measured up and above the rib pattern from the intersection point so that a distance between the two centerlines was easily divisible by 14. Mine was 14mm so that each spar slot centerline is 1mm apart at this length. Next, a centerline was drawn from the 'pivot point' to the 1mm spaced markings. I labeled them 'A' to 'O'. It takes much longer to type this than do it! You can see the spar slot jig in action on the plan! It has relief cuts on the under surface to clear rib structure.

[ARUP]

The first rib and all the jigging blocks were laid down. Micarta patterns (brown items in picture) were cut so that the nose TE filler pieces could be duplicated. The nose piece was made a little deeper than needed so that when all the ribs are on the spar they can get sanded 'flat' for the LE to be added. A jig will be made to get the nose end of the ribs sanded to approximately the proper angle for the LE. Construction starts by fitting the lower stick which is the bottom of the foil so as to cut the taper at the TE for the upper stick. The upper stick and the filler pieces are then glued, followed by the other sticks inside. The spar slot jig has the same width as the spar material to be used. It is pinned in place and has an indicator on its upper end to align with the spar slot centerlines on the plan. It takes about an hour to build each rib. Once the glue has dried the rib is taken off the plan, ends trimmed to proper length then both side are sanded. Gussets are cut and added to both sides of the ribs at the junctions of the sticks. Each rib is ~19" (~480mm) long. So far ribs 'A to 'E' are done. I've got quite a few more to go but thought you'd like to see some of 'em!







The pic showing the micarta patterns to cut the balsa nose piece and TE triangle piece was corrupted so isn't shown. I'll try to get another photo showing how I'm making these parts.

[Melchizedek]

Michael, is the entirety of each rib (minus the gussets) made from basswood ? Cross members of the truss ?

I will consider using a truss rib on my next build. Not only is it elegant, but looks far stronger an lighter than any other way.

Kevin

[ARUP]

Kevin, all frame members are basswood. The gussets are 1/64" ply. Balsa was used at the LE and TE sections to tie the upper and lower foil curved sections together. The ribs are very strong. They are probably a little heavier than 1/8" thick sheet balsa items which was considered. I built one test rib and compared it to balsa. The strength difference was significant as it relates to the rib ends where the TE cable gets mounted. That was the deciding factor for truss ribs here. The ribs really don't need much strength otherwise for they only create the foil shape. For real strength I'll use compression struts with drag and anti-drag bracing cables to trammel the wings per full scale practice just like what was done for the Franklin 'Eaglet' which has its own thread, here, too! I really enjoy building these structures. It is almost a shame to cover them up because I think they are very pretty! Thanks for your interest! P.S.- I haven't tried uploading pics as you graciously explained via PM. I still have problems logging onto the site (and others) from time to time because my local ISP is crummy.

[stihac]

Awesome work Michael! I love the look of build up ribs. I need to get back to the shop. I've not done much all winter.

Petr