CFD non axisymmetric design external pods etc.....

large scale build russian buran complete with external pods 2500 punds of thrust. In need of help with off axis drag calculations with buran strapped on side. Any one had any experience with software that may help.......

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xasltd said:

large scale build russian buran.......

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A bit of understatement?

Unsymmetric designs are tricky (as you probably well know), I think all available analysis tools are based on the assumption that the design is axi-symmetric (and the thrust line runs through the middle). TRF may have a few guys who have built stuff in your size range but you may have better luck getting appropriate advice on a couple other rocketry forums (and I am NOT at all wanting you to 'take your thread and leave,' I would love to follow your analysis and build and see how this works). Looks cooool. Pls keep us posted?

unfortunately nearly all cfd software I can find is for axisymmetric design. Wind tunnel testing is out of question....too expensive. Trying to avoid the boiler plate model mock ups.......

I am impressed. I have built several large US shuttle 1/64 scale and I am working on a Burran same scale.
If you find out how to do it I would be interrested.

xasltd said:

unfortunately nearly all cfd software I can find is for axisymmetric design. Wind tunnel testing is out of question....too expensive. Trying to avoid the boiler plate model mock ups.......

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You need to look at some general purpose, unstructured CFD codes like Fluent, Star, OpenFoam, etc that can model any arbitrary geometry. These work well for automotive and industrial problems. Not sure how well they work for the Mach number regime you want.

Good luck.

Changing the subject a bit, why all the threaded rod?

Your construction is similar to what we do on large projects, except we notch the stringers, avoiding the need for L brackets where they meet the rings/bulkheads.

What are the dimensions?

-Kevin

Hello, we use the threaded 8mm bars to hold it straight before applying rivets and sheet aluminum. It also serves to pass the shock of the parachute through the structure. We had double left/right threaded, high strength plastic M22 bolts made, which thread into some machined blocks for holding the explosive bolts. I will try to get as much info and pics up as possible...thanks The main central tank with 4 x 98mm motors weights in at about 350 pounds. It is 4.3m long from nose tip to motor end.

troj said:

Changing the subject a bit, why all the threaded rod?

Your construction is similar to what we do on large projects, except we notch the stringers, avoiding the need for L brackets where they meet the rings/bulkheads.

What are the dimensions?

-Kevin

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id be interested to see how you do that, do you have any pics.....??ta

Buckeye said:

You need to look at some general purpose, unstructured CFD codes like Fluent, Star, OpenFoam, etc that can model any arbitrary geometry. These work well for automotive and industrial problems. Not sure how well they work for the Mach number regime you want.




Good luck.

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many thanks i will check them out!!

Run your recovery attachment down to the base and you won't need all that threaded rod - weight and expense. Not to mention a lot of work to install!

What size are those nylon bolts? They seem awfully large - we use quarter inch, if I remember right. Make sure the epoxy plug is thickened and the hole drilled in the bolt isn't too smooth, or the plug will pop out without shattering the boot - we learned that in ground testing.

I'll have to find some pictures that show how we do the stringers.

-Kevin

the bolts are 22mm with a 5mm hole. We then put epoxy into the small hole where the cables exit to fill the cavity, stops the epoxy from firing out.......

xasltd said:

the bolts are 22mm with a 5mm hole. We then put epoxy into the small hole where the cables exit to fill the cavity, stops the epoxy from firing out.......

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What are you holding together with them? How many are you using?

When we tested the bolts we used, they averages about 200lbs of load before they'd break, after they were drilled out. Yours, being much larger, are significantly higher than that.

I'm very intrigued by what you're building; not only are you techniques similar to ours, but a full Buran stack is just impressive!

I'll try to dig up some pictures tonight.

-Kevin

8 bolts and 16 machined ali blocks.....you do not want to know what the cost was! The bolts are made by a british aerospace company who make stuff for the military. Each bolt was about $30 or £25........

the whole stack weighs in at around 500 pounds. Each external tank at 25 pounds each. Shuttle at around 20 pounds.

xasltd said:

8 bolts and 16 machined ali blocks.....you do not want to know what the cost was! The bolts are made by a british aerospace company who make stuff for the military. Each bolt was about $30 or £25........

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Yeah, machining is expensive -- our booster hardware for the Delta III we built was $250, and one of the guys did a fair chunk of the work at home, himself, with a mini lathe he has.

What are you holding on with the bolts? Based on your weights, I suspect you could get away with smaller bolts, which may or may not reduce your expense.

What are the threaded aluminum blocks for? For us, we used nylon washers and nuts, rather than threading anything into blocks.

-Kevin

A block is mounted (in each external pod + main tank) through the 8mm studding as per pic above. We then use double end bolts (below pic) drill out both side. That way we have redundency throughout the system. If one side fails to go off, we still have the other. The ali blocks help to keep the epozy 'bung' in its place so the head shears off.....

Interesting. So you have a charge on either end, so it doesn't matter which one fires.

We held our boosters on with aluminum pins, each of which goes into a receiver block. The recovery timer in the booster detects when the booster separates, and starts its timing from that point. That way, if one doesn't come off for some reason, it doesn't fire an ejection charge.

On our second flight of the Delta III, we had two boosters get hung up (missing O-rings), so this feature saved us from a disaster.

-Kevin

Here are a couple photos that show how we install rings/bulkheads on the stringers.

One shows a couple rings on a stringer, slid into their slots. If you look closely at the stringer, you can see other slots of various sizes, as well as seeing the notches in the bulkheads.

The other photo shows an edge-on view of how the ring slips into the stringer. These slots are tight enough that it takes a mallet to pop things into place. First a dry fit of everything, then we remove stringers one at a time, apply wood glue, then reinstall them. They don't come apart.

-Kevin

PS: Bonus points to the person who can tell me why one of the bulkheads says "chessie" on it.

Okay, this time I'll include the pictures. :eyeroll:

-Kevin

what do you use to cut the timbner slots? router.....

xasltd said:

what do you use to cut the timbner slots? router.....

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Router and a spiral upcut bit.

We take all the stringers, lay them out and clamp them together. Then a guide for the router gets clamped in place across them all, and we do the same slot in all the boards in one shot. Move the guide, cut, move, cut....down the length of the stringers. Then unclamp the stringers, rotate 90 degrees, reclamp, then cut the next part of the slot on all of them, then do that one more time, so that we have slots that go around 3 sides of the stringers.

With the slots tight, the entire assembly is rigid even before we apply glue.

-Kevin