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Composite spar design & composite wing design?

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karoliina.t.salminen

Well-Known Member
Joined
Oct 7, 2008
Messages
407
Location
Finland
Hello,

I am thinking of a concept which is targeting at both high AR and very good empty to gross weight ratio at the same time. The weight of the resulting wing will pretty much dictate the feasibility of the concept. I want to calculate the weight based on actual materials that are going to be used, instead of using the rule of thumb estimation equations from Daniel Raymer's book I have. If I know how much fabric I am going to use, I can estimate how much resin is going to be used and resin + fabric + foam equals the weight of the wing without the control mechanisms (and weight estimation of these will be next step after this basic wing estimation).

I think there are several people designing their own planes, some have already designed and built even many of them, and they have already calculated their spars and wing skins. So looks like there are some of the best people in the world to know this topic on this forum. So could you please help me to get started with this? I had some stress analysis long time ago at university but there was absolutely nothing about sizing of composite structures where the stress direction is to be known and the fiber direction will be aligned with the stressed direction. I have attended several composite courses but these have been targetting for composite aircraft repair, not actually designing one from scratch. I know there is a lot to study, but everybody has to start someday. I would like to avoid "metal thinking" as much as possible and be able to use the benefits of the fiber direction as much as possible.

The application is: molded composite (carbon) wing (fabricated on female mold) of large span and relatively
large AR and I need to know how much the spar and skin might weight to be able to conclude the feasibility of the concept as the wing will determine if the plane will be too heavy or good enough.

1. Which books should I get, which publications should I read, are there any excel sheets made for it by someone - to learn the sizing of composite spars (carbon spar).
I found some spar calculator xls for other materials from this forum, but have not found for carbon spar anything except
for the basic program from Martin Hollman's book. I have not yet had the efforts to porting it to C++ unlike some other programs from his book that I have already a C++ version done, so I can't use it for preliminary sizing of the spar (yet) and I would like to know if someone else has excel sheet for that already so I wouldn't need to port the program. To understand what the program does would be helpful too: The book does not explain how the sizing method works, it only tells about basics of calculating matrices and then it shows the Basic code and then it expects that you get it what was the methodology used. There is a information gap in between.

2. Same question for the wing skin and other structure. The basic structure will be sailplane-like, so there is skin on both outside and inside of the wing panel and there is foam or honeycomb between these and then minimum amount of ribs inside the wing (so that the skin is the main load bearing component on twist and the spar takes the bending loads). Some kind of preliminary sizing would be needed for that too to end up with the wing weight estimate. Basically I need to know answer for the question: how many layers of the fabric I need per square meter of wing skin for each wing station.

I know that for optimized results FEM analysis is needed but I think it can not be made if the starting point is not known, so I would need to end up with this starting point.

Any advice on this would be great. If you have a good excel sheet for the purpose, if you could share it with me, I would be very happy as well. Thanks in advance.

Best Regards,
Karoliina
 
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