My question concerns the X-33 space 2

[djaytch99]

My question concerns the X-33 spaceplane and the use of honeycomb cores in composites.

My understanding of the situation is that the program was cancelled due mainly to the failure of the composite fuel tanks, which, after core delamination was detected, it was decided to use a different material thus increasing the weight, resulting in reassessment and eventual cancellation of the program. I'm sure that is an over-simplification of the circumstances, but what puzzles me is that for many years now state-of-the-art in honeycomb technology has always revolved around the industry standard: ie strips of metal or similar, glued together to form hexagonal open-ended tubes of varying diameter and length.

My interest in this subject stems from the fact that due to my own discovery of a new method of producing honeycomb, I have been searching the patent databases to see what the competition has to offer. Imagine my surprise to find that there are literally hundreds of ways to form honeycomb, many of which would certainly do a better job than current designs. It doesn't seem to matter whether it's aerospace, powerboats, automobiles or whatever, good ole' state-of-the-art honeycomb is where it's at, and always has been! So, what is the problem?

David

 

[bobhexa]

Hi David,
The problem encountered by the X33 was due mainly to cryo-pumping which could really only occur in a honeycomb, closed cell, core material...which of course is the current state of the art. I sense a touch of cynicism?
I personally feel that if engineers worth their salt could realise that the continued unabashed use of standard honeycomb in aerospace, powerboats, automobiles or high speed trains is an archaic pavlovian response ...... "Well, we've always used ribbons in our honeycomb".
Good engineering now demands us to re-evaluate and realise the major disadvantages of honeycomb which have been adopted and accepted all in the name of saving weight.
Catastrophic failure without regular maintenance checks is guaranteed.
Incidentally all these applications generally invove people and fast moving objects. Someone was asking earlier on, in the aeronautical forum, as to whether aircraft are really glued together. Well in the main that is true.honeycomb is probably 25% glue. That is the nub of the problem.If only the glue would stay stuck there really wouldn't be a crisis.
The closed cell honeycomb composite panels in craft which undergo ambient pressure changes combined with the minimal surface bonding area of laminates to core is tempting fate.
So if the glue had a larger bonding area then all would be fine and delamination would not be the focus.
If somebody could invent a structural panel that was ventable,formable, as light or lighter than present art and that had a mere 500 percent increase in bonding area we will get to mars and back and the Americas cup yacht race will be won by a craft with a forsail almost up front without causing the boat to snap in half.
The present honeycomb model was discovered by an undergraduate doodling with strips of cardboard and he started the ball rolling.........it is now time for engineers to start thinking more laterally and move beyond an archaic solution,
Best regards
Bob ]

 

[vonlueke]

How about aluminum foam core? Would that work? Thanks.

 

[bobhexa]

Aluminum foam core is an extremely good solution in that it has the rough texture plus a far larger surface area which promotes a good bonding of the face sheets.
In terms of lightness of material it wins hands down, in so far that it has no glue required to add to the weight.
Ventable is a moot point depending on which process is used.
In one method a foaming agent is mixed with powdered aluminum and produces ,when heated, gases which form bubbles within the molten aluminum. It solidifies into a block of aeriated aluminum which does not vent. A bit like Aero Chocolate!

Another method involves filling a mould with something like rock salt (engineers worth their salt?)or clay balls (no comment) compressing it all so the fill will snuggle up tightly to its neighbour and then injecting molten aluminum into the mold and ,when cool, one then washes out the salt/clay and .... "bingo" ........ a lightweight aluminum sponge which vents.
One can imagine the number of steps required to make this a very expensive method of manufacture...... never the less it could be done .
Let us now focus on formability...by all accounts metal foam core using the 2nd method. which allows venting, would need to be milled from a solid block to produce a panel with surface curvature as it does not naturally flex.
So the results are in:
Ventable.......................... Yes
Formable.......... ............... No
Lightweight....................... Yes
500%increase in bonding area...... Yes


Best regards
Bob

 

[WKTaylor]

The X-33/-34 suffered from several major problems that finally came together, causing melt-down.

The Cryonic tank for liquid [slush?] hydrogen was mandatory for weight savings [bigger volume requirement - relative to the LOX tank].

The thermal and pressure stresses destroyed joints between major assemblies. Unfortunately, these joints would have been uninspectable [within reason] "in service".

Many areas of the program had major cost over-runs, but the "problems were getting solved". HOWEVER, the LH2 tank problem wasn't getting solved... and would require massive redesign to correct the defficencies [engrs painted the design into a very tight corner].

Simply put: The design stumbled over too many design obstacles and costs got out-of-hand... and no one stood-up to the political pressure and everyone "avoided" the hard questions... until the obvious tank-design failure sealed it's fate.

I believe the MCDonnell-Douglass design had great merit... but wasn't "sexy"... or "hi-tech" [old concept]. OH WELL...

WKT

 

[bobhexa]

Eureka!!
I have been pondering on the disadvantages of honeycomb in the aerospace industry.......closed cells....minimum bonding areas etc.
The main disadvantage of honeycomb type cores is that of delamination. This is caused primarily by the failure of the epoxy adhesives to maintain a bond between the skins and the core because of the very small bonding area that honeycomb cores offer. This is further exacerbated by the fact that honeycomb type cores create pockets of trapped air within the closed cells of the core when the skins are attached. The air pressure experienced at high altitudes is much lower than the trapped air within the cells with the result that the skin is pushed away from the inner core by the air pressure. Ingress of water into already partially delaminated cells at high altitude freeze into ice particles which expand and force the skin to separate from the core. Eventually after many cyclic operations the skin will delaminate. Lightning strikes can cause entrapped moisture to immediately turn to steam with catastrophic results to the integral strength of the panels.
I do believe I have the solution to it all.
If NASA or the FAA would like to contact me I would be pleased to enlighten them.