hi phil

good thinking with the weight saving on the foot launch door..i wonder if it cross braces the fuse.
the dragon is not practical for foot launch.plan for roll or bungy launch from a hill or better still tow launch in front and at the bottom of your hills will save you driving up the hill and you can land back at your tralor and it will be easier to set up on the flat out of the wind.

im surprized mask used stainless steel for fittings...crane cables are not stainless steel,they are steel.sail boats have stainless steel fittings and hang gliders.
ss superior in term of corosion but not fatigue.
aluminium needs to be over engineered ,to protect it from fatigue.
in cycling cromolly bikes never seem to brake.
in off road cars iv seen them come back from high carbon steel frames to lower carbon/softer frames becaus of craking,also they are painting them with a clear paint so they can spot craking.
russ.




On Sun, Sep 25, 2011 at 12:42 AM, Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:



buckling isn't an arbitrary number or factor, but is based on geometry (boundary conditions, unsupported length and stiffness (young's modulus). The geometry with regard for buckling can be improved by packing the rods into the corner (as opposed to packing them along the upper spar cap). You want to make them as stable as possible. remember GOOD aluminum has a stiffness of around 10.3 E6psi and an allowable compression of just 65,000 psi (compression usually is cut-off at Fcy); however, the stability even then is a failure mode, so the actually allowable can dip below that. The carbon rod, even if you cut the compression to 100,000 psi is really almost double what you'd get out of aluminum and the density is .101 for Al and .056 for the graphite. what that says is the amount of material needed will still be pretty darned weight efficient. Is 100,000 psi conservative in compression? maybe a bit, but how much weight does that actually mean? -- not so much. The wood is only good for around 9ksi BTW!


One other thing I know is that my buddy's wing passed the physical hardware test (second wing! -- the first one had a spar web failure in a mode that we didn't expect). Frankly it doesn't matter if you plan on testing (maybe), but if you don't, I would certainly err on the conservative side if it doesn't translate into too much weight. Also, I would seriously consider at least a limit test on the wing (ultimate/1.5) which should not yield or have any snap, crackling , or popping and since you are analyzing to 11 g, a limit test at 7.3 Gs (or even 6 Gs) would mean you've made a really safe wingbox


--- On Sat, 9/24/11, Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


From: Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.>

Subject: RE: [Carbondragonbuildersandpilots] Re: Wing calculations
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Date: Saturday, September 24, 2011, 8:27 AM





Interesting points - and thanks Kenny, I'd appreciate any useful data or equations you can dig up that might help.

I wonder why Jim Marske is recommending a figure of 200,000psi in compression? In one email to me he says:

---

"Oh, for max cap stress use 200,000 psi due to compressive buckling."

---

...while in a later email he says:

---

"Yeah, I admit that the max allowable strength for the rod is confusing. Even in wood, aircraft spruce is rated at 9,400 psi for max rupture strength, then in compression it asks for only 5,000 psi. The official answer was, ‘you must allow for compressive buckling’. Truth is, the compressive strength of most materials would be higher if you can keep the material from buckling when in compression.




I use 280,000 psi as that is what the factory engineer recommended. I have had a structural engineer who did a lot of carbon rod testing in a major aircraft company tell me that the only way you can get honest compressive data is to build a spar and test it. Even a half size spar will work.




Now, why do I sometimes use 150,000 psi? Suppose you have a carbon rod spar but have covered the wing with plywood sheets. Now you load the wing to where the rods are loaded to 150,000 psi. At this load the plywood skin will rupture because it cannot stretch anymore, it has reached its elastic limit. The skin has reached 9,400 psi. (Here I’m assuming that the grain is spanwise) However, the carbon rod spar has reached about half its maximum load."

---

It really is difficult to know what numbers to believe... and I'd rather not find out the hard way in the air!

If you can point me towards a link or data sheet for Titanium I'll recompute for that and keep looking for a supplier, but I'm reasonably happy with the 6082T6 fittings as they are. As you say, sharp corners and tight radii are to be avoided as micro-fractures from manufacturing can propogate under extreme loads.

Hope you're feeling better soon.

Phil.

---

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 Kenny
Sent: 24 September 2011 13:52
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: [Carbondragonbuildersandpilots] Re: Wing calculations



I'm starting to look at the spreadsheet now, I'm sorry it's taken so long. I've been under a bit of pressure at work and then this week had a completely rotten case of bronchitis

Two thing stood out though. We used 200,000 psi for tension and 100,000 psi for compression for the carbon rods. Also for the spar web shear strength you have the strength of the fabric, but you also have a buckling-type (stability) failure that also need to be checked. I can get you the equation Monday (from my stress book at work) if someone doesn't have it already.

One other thing about aluminum though is you have to be careful of fatigue. The static margin might seem large, but these days that rarely sizes anything the has repeated loading. Ti, on the other hand is much better in fatigue. To reduce the fatigue peak stresses make sure that there are no sharp radii etc. that can cause high peak local stresses. Having said that, if you have designed the fittings for 11 gs then it's probably OK for static since acrobatics likely won't be at the top of your to-do list.

--- In This email address is being protected from spambots. You need JavaScript enabled to view it., "Philip Lardner" wrote:
>
> 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...Datasheet_Al_Alloy_6
> 082.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.
>
> _____
>
> 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
>
> _____
>
> From: Philip Lardner <philiplardner@...>
> 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.