karl,

I used some basic truss calculations and some asumptions for the loads that will be placed on the frame by the empenage. There is a great book "Stress without the Tears" that will walk you through the calculations. It is a must have for your aviation library. I just made a bunch of oversimplified assumptions for the structural design and modeled the fuselage frame after your basic steel tube glider. One question that I have yet to answer is the buckeling strength of the CF tubes. You can try to do some Euler calculations, en.wikipedia.org/wiki/Buckling, or look at charts for similar materials, but without testing a few sample to destruction, you just don't know.

My plan is to make a CF tube with CF sleves such as from this website. www.acpsales.com/OnlineStore.php?cat=4957. They appear to be 5.6 OZ cloth with the fibers in a 45 degree orientations. One concern with making your own tubes is that the fibers may not be a true 45 to the axis. This will reduce the strength a little. The required strength will determing the number of sleeves per tube. I am planning on covering either a steel or PVC pipe with shrink wrap and moulding the sleeves on the outside. Very similar process to what Marske suggests. If I need to bend a tube for what ever reason, I think you can encase it between 2 pvc halves, run warm air inside to get it over its transition temperature, and then bend it as required. To increase the buckeling strength I plan to cut out foam cylinders and stuff them inside the tube at a yet to be determined spacing.

I am currently traveling and do not have most of my calculations with me. If I did I would have posted a spread sheet that I could stand by. From the basic calculations that I performed I can definatly say that it is worthy of more study. After that other email that I sent I started to redesign a basic fuselage on autodesk inventor. I wanted to make it similar to the monarch from the spar forward and a tube frame for the rear. I feel that the monarch fuselage may provide better crash/hard landing protection to the pilot. I also like the simplicity of an open cockpit design. I tried to design it on Autodesk inventor, but the designed lacked elegance, so I am back to the drawing board. I can say for certail that the CG calculation showed that there will be issues with a far forward CG. This is why i really want to know how much forward sweep I can get away with. What need now is a few pitures of naked steel tube sailplanes to get better ideas for the construction. I think a schleicher K 8 would be a god place to start. -Ed


From: KarlS <This email address is being protected from spambots. You need JavaScript enabled to view it.>
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Tuesday, March 13, 2012 11:28 PM
Subject: [Carbondragonbuildersandpilots] Re: CDII -fuselage




Hi Ed,
It was I that suggested the carbon frame covered in dacron. That could be "hyper light". I was wondering about your calculations. Could you share any info? Just curious.

I still believe it would be fairly simple for anyone to make carbon beams using graphlite rod and dow blue foam with a glass or carbon skin perhaps that converge into a carbon tube truss tail structure.

Kenny and Dan had some dialog that was very similar to what I was thinking with a keel and side beams. I had drawn up some sketches months ago but they aren't that great and I was kind of embarrassed to post a picture. But exactly what Dan and Kenny discussed.

To all,

An option also for some of the construction to make it simple for the every day man is old fashioned aluminum. Very thin though. Not for the fuselage but maybe D tubes similar to the video below. Perhaps integrate some graphlite rod in conjunction with.

That would be a lot easier than composite molds and layups etc.

This is a great video. The dialog at the end is cute.



Just tossing ideas out there.

Karl

--- In This email address is being protected from spambots. You need JavaScript enabled to view it., Edward Pickens wrote:
>
> The comment about this being an important brainstorming session was spot on. I know I have learned a lot and considered solutions that I may never have reached if I was going about this by myself. The other day it was mentioned to use carbon tube covered with dacron to make the fuselage. I did some basic calculations, and the weight savings are increadible. It also dropped the cost a very substantial amount for the fuselage. The issue now is the CG is too far forward for big guys even with a little forward sweep in the wings. I was wondering if anyone knew of a book that covers forward sweep in detail. Every text that I own only mentions a few lines about forward sweep, then moves on. I would really like to know what my limits are and how the structure needs to be changed to accomidate the new wing design. -Ed