Hi Rick,

Thanks for looking at my numbers - you had me worried there for a second with the weights! You're correct though (in your follow up email) - I'm using an all-up weight for the whole glider + pilot and a payload weight which is the all-up weight less the weight of the wings. I have used the number published in the builders' manual for the weight for the wings though I fully realise that the actual weight will be different... still, you have to start somewhere. I didn't bother to round any numbers which explains the 'precision'!

As I'm a trim 9.5 stone in weight I figure I'll probably have to ballast up a little anyway, so a few pounds error in the wing weight shouldn't be a big deal. Also, I've calculated the numbers for +10.5g and -7.5g even though I have no intention of doing aerobatics in this glider - it's just that our Irish Aviation Authority is so pernickety, fickle and arbitary in the way they apply their certification and licencing rules to sports aviation over here that I decided to go for a little over-kill and suffer the slight weight penalty of the extra rods.

I have a few ideas for saving weight in other areas - a much lighter skin covering (25g/sqm molded/monolithic fiberglass cloth rather than 50g/sqm dacron) and replacing the foot-launch doors with stretch lycra with a longitudinal slit down the centreline to allow your legs out. Although I have a sample, I haven't yet made up a test piece of the 25g firerglass cloth (it do seem awfully thin!) I will do so before comitting to it to make sure that it will put up with the abuse of general handling and hanger-rash. I'm not convinced it will be strong enough... but it's worth testing anyway!

I probably will taper the load transfer bars to save a little weight but will also bond it to the verticle fuselae attachment bar where they abutt. Also, although the plans specify a 1" wide verticle spruce bar either side of the web for the fuselage attachment fittings to be bolted to, I will probably reduce this to the actual width of the fitting (3/4") as the carbon fiber bar will be a good deal stronger.

I plan to use 284 Twill CF cloth throughout. It's stronger and lighter than glass cloth, like for like, and is one less material to go hunting for. Given the quantity needed I don't think the added cost will be all that significant (I hope!)

You can find a data sheet for 6082T6 (and other alloys) here: www.amari-ireland.com/technical/aluminium.html and
www.amari-ireland.com/technical/datashee...et_Al_Alloy_6082.pdf

6082 has a tensile strength of 340MPa which equals 49,312psi - you can find a conversion tool here www.chapelsteel.com/mpa-psi.html.

I initially designed the root end metal fittings using 0.1" thick 4130N stainless steel (as used by Jim Marske) but this turned out to be a bit heavier than the 3/16" thick 6082T6... so I went with that. I haven't found a data sheet for titanium (or a supplier in Ireland) yet. The aluminium supplier is just up the road from me and will probably be cheaper than titanium even if I have to but a full 5m length!

My next task is to analyse the stresses on the individual wing ribs so that I can redesign them for carbon fibre rather than 1/4" marine ply and spruce (pgs. G2 - G4 of Jim's manual.) A first quick read through these pages makes me think there's not enough detail to explain his workings. I'll report my progress as I trundle along! Have you gone through these pages/calculations yourself in detail yet?

I have got my hands on a number of samples of pultruded CF square-section tubes and rods that I think will do very nicely for the straight sections of the ribs, flaperons and the stringers along the wings - very light, stiff and massively strong! For the curved ribs themselves, I'm looking at laying up large sheets of CF - 1/4" foam - CF sandwiches and cutting the ribs out of that, possibly reinforcing the edges with 12k carbon roving. What did you use for your ribs? Any pointers or ideas would be welcome.

Ah yes - good old Nixdorf, may they rest in peace! I studied at their Centre for Advanced Technology Training for three years in the mid 80s to become a systems analyst and software 'engineer' and became horribly familiar with COBOL programming (amongst other languages)... which, thankfully, I have never had to put into practice! I still have a stack of old Nixdorf work pads! It was sad to see them go down the swanny.

Phil.

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From: This email address is being protected from spambots. You need JavaScript enabled to view it. [This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of Rick Mullins
Sent: 24 September 2011 02:06
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: Re: [Carbondragonbuildersandpilots] Re: Wing calculations




When you were calculating your bending moments you used 260.4 lbs as the payload. In the next step you calculated the wing loading and used 145.6 lbs as the glider weight (seems kind of precise for a guess at glider weight ) and max pilot weight at 190 for a total of 335.6 lbs. Isn't that the number you would have used in the bending moment calculation?


I copied the spar Jim Marske built for the Monarch and just have the load transfer rods on one side of the spar for simplicity. The one change I made was I extended the bars several inches so I could taper one end. On the first spar I built (that I later discarded) I used rectangular bars and it seemed like it would be a high stress area where the bar ended and the rods continued out to the tip. A taper would help spread the load at that transition. No calculations to back it up, it just looked like a weak area. I uploaded a picture to my photo section of the new bars.


I wasn't familiar with the 6082T6 alloy. I had considered maybe using titanium as Steve Arndt did, but I'll have to look into this as a possibility. Titanium is probably overkill.


I also got a grin out of the paper you were using for your calculations. When I graduated from college my first job was with Nixdorf computer. I worked there for 24 years doing field service. They never did very well in the US and I was laid off shortly after they were bought by Siemens

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From: Philip Lardner <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: Friday, September 23, 2011 1:03 PM
Subject: [Carbondragonbuildersandpilots] Re: Wing calculations



Hi Folks,

I've just uploaded another few pages of wing calculations based on Jim Marske's Composite Design Manual. The uploads are in my directory (Phil Lardner) in the files section of this group - filenames 'Page 15' to 'Page 19'.

Page 15 is a 1:1 scale drawing of the main wing root-end metal fittings and form the basis of the calculations on the pages that follow on.

Page 16 - 19 detail the dimensions of the CF bars that transfer the cap loads (at +10.5g) to the root end metal fittings, and the dimensions and layout of the metal fittings themselves.

As ever, I would be most grateful if someone could double check my numbers and method to make sure I haven't skipped a step of misunderstood something... or generally screwed up somewhere!

Comment welcome,

Phil.