wing spar design

hi guys i need some help with sizing wing spar its build from aluminium the spar height is 5.15" and lenght 8' the loads in half of the wing spar is 900 lbs and at attach poin 1990 lbs ,i need to know where i can find a formula to calculate what spar cups i can use my idea is use 0.032 web top and bottom spar cup 7/8x7/8x1/8 2024 t3 tapered from 1/2 span of spar and 7/8x1/8 another plate running on other side of web to half of spar top and bottom the spar is stressed to 3.8g' thank you

The reason no one has responded before is probably because you are asking us to do your analysis for you. Won't happen. Search on "books" and "analysis" and you should find other design threads that talk about design tools. Then you will have to get educated on what it takes to analyze aero structures...

Billski

The book Low Power Laminar Technology by Alex Strognic has an example calculation for a spar about the size of your design.

He uses 2024 angle bonded to plywood web. I would not use bonding, rivet instead. But the calculation is helpful.

If you don't know exactly how to analyze a spar for your project and someone does it for you, it does not end there. You will need to analyze the root fittings and the structure where it joins the fuselage, any torsional effects etc etc. The TLAR approach ("That Looks About Right") is a recipe for suicide. Having said that, it is not impossible to learn this stuff, but you do need to do do some serious reading on the subject. Nobody here discourages new designs, or is trying to be a negative influence in any way, but not doing some basic maths can get you killed in this game.

Also, the first wing needs to be load tested. More often than not, the spar will start to buckle before the calculated ultimate load is reached. Better to find the weak point before flight.

Originally Posted by BBerson

Also, the first wing needs to be load tested. More often than not, the spar will start to buckle before the calculated ultimate load is reached. Better to find the weak point before flight.

Couple of questions for those in the know.

1) What would it typically cost to get a comprehensive stress/flutter analysis done on a small conventional single seat design?

2)I hope this isn't a dumb question but as far as actual load tests go. Would a properly scaled down version of the full size wing and other components be suitable. IOW say a 1/2 scale, in all respects, wing built with the same materials and construction technique's as the projected full scale. Would an ultimate load test of the scale wing be valid/usable?

im not trying let somebody doit for me im just trying get some more info on actual problem i have all loads ,all bending moments and shear stress at each point figured but after reading alex strojnik books like with other books lot a problems they did not say what formula for example (m=pl/4 just example) you can use to determine cross section for spar my wing design is spar in one piece i asked designer who does all the analysis but for that price i can buy a new airplane,when i build the wings im goint to load it with 4 g' of actual gross weight to find out if its strong enough,i think they were lot of planes build in early 60',70' without any stress analysis and they are proven design,so no one here sad go a head and do it ,im doin it if i dont build it ill never find out if the plane i draw on piece of paper will fly it always will be just dream

another one on the books i asked several times if someone can recomend easy to read books on stress analysis ,no responce ,after reading about 20+ books i did not find any good book ,one good book i found is from 1942 which im using a lot to do all stress loads ,bending moment etc ,so if anyone know really good easy to read book please let me know

Amtech Services can revue your calculations for a small fee. He charged me about $20 per page many years ago, very reasonable.
For current rates send a stamped letter to:
Amtech Services
R.D. 8
Mansfield, Ohio 44904

Originally Posted by Lucrum

Couple of questions for those in the know.

1) What would it typically cost to get a comprehensive stress/flutter analysis done on a small conventional single seat design?

2)I hope this isn't a dumb question but as far as actual load tests go. Would a properly scaled down version of the full size wing and other components be suitable. IOW say a 1/2 scale, in all respects, wing built with the same materials and construction technique's as the projected full scale. Would an ultimate load test of the scale wing be valid/usable?

The cost of a complete design/analysis depends somewhat on the materials used and the prescribed application. Depending on who does the work and how complete it is, a ballpark figure for the comprehensive analysis of the basic wing panel might run anywhere from about $2,500 to $5,000, or more for more exotic or higher performance applications.

For the single seat design and assuming composite materials, you might figure on spending about $3,500 to $4,500 for the structural analysis. Most likely there would be an additional charge if you also wanted full fabrication and assembly drawings on top of that. But you really don't need to do a flutter analysis for this end of the airframe spectrum. An experienced designer should know how to design the structure so that it stays away from any particularly nasty tendencies.

Regarding the scale model, no, it wont do you any good since structural characteristics and capabilities are not linear nor necessarily proportional. Also, factors such as those that account for stress concentrations will not scale either.

If the designer has sufficient experience and does a complete enough job of the design and analysis tasks, there's a pretty good chance that you wont have to do any testing, unless you of course want to cover all the bases. But the trick there is finding a properly qualified person to do the work.

Very helpful, thanks orion.