[/QUOTE]If one needs carbon molds for carbon parts, then nobody told the companies that I work for - and those airplanes are just a "touch" more expensive than Raptor. I've seen tooling the size of a backyard swimming pool machined from stainless steel as well as tooling foam and everything in between.
Ok, I simplified rather than explain all of the ways we can "adjust" on tooling and design of graphite fiber parts. My apologies for that. There are several ways carbon fiber tools can be avoided in carbon fiber parts. The fundamental issues are:If one needs carbon molds for carbon parts, then nobody told the companies that I work for - and those airplanes are just a "touch" more expensive than Raptor. I've seen tooling the size of a backyard swimming pool machined from stainless steel as well as tooling foam and everything in between.
Regarding the use of carbon fiber in the building of molds for the Raptor program,I will explain. The use of carbon fabric and high temp tooling epoxies( surface coat,and resins) was only utilized in molds pertaining to the pressure vessel and critical structural components( Spar molds, firewall ,etc. Very few tools beyond the pressure vessel) . This was done to allow ,once in production and if necessary or desired , two future options. Those options would have been either wet layup cured at elevated temp in mold,or utilizing prepreg for its weight and superior Tg ( thermal distortion, for those unfamiliar with composite materials)properties. All other tooling was E glass and room temp resins. And there were LOTS of those.Ok, I simplified rather than explain all of the ways we can "adjust" on tooling and design of graphite fiber parts. My apologies for that. There are several ways carbon fiber tools can be avoided in carbon fiber parts. The fundamental issues are:
So how can you skip graphite molds?
- Graphite fiber has negative thermal expansion coefficient along the length of the fibers. Non-symmetric laminates and highly directional laminates will thus change shape with temperature, perhaps even to the point of part damage as the autoclave cools following cure;
- Make the mold with the same schedule as the part, and both will change shape together over the temperature range of the cure and cool-down cycle. This way you can make a mold dead-on for shape and size, oven cure the part and have it come out of the mold straight and on dimensions as the mold at room temp.
Each has its advantages and disadvantages to cost, fit, and function.
- Use parts that are either non-critical on size/shape and/or flexible enough that they may be fit to shape after cure and still function fine;
- Do not oven cure. If the part does a room temp cure and is then either not post-cured or is post-cured off the tool, then it comes out of the mold the same as the mold, and may even stay that way;
- Use omindirectional lamination schemes - you have equal fiber count around the clock - 0/45/90/135 or 0/60/120 - Shape changes will be quite small this way. Yes this also removes the advantage of directional tailoring of stiffness and strength. Black aluminum, if you will. This may need tool shapes corrected for thermal expansion differences between mold material and laminate at cure temperature if highly precise dimensions are needed;
- Take the desired shape at its assembly temperature, analyze for its thermally induced change of shape at the cure temperature, analyze for the mold shape at room temperature and how it will change shape between room temp and cure temp, then cut the mold to the shape that will give both needed cure temp shape and needed nominal temperature shape. This can be tuned by going "metal safe" on the mold, then fine tuned after parts are made.
I am accustomed to composite parts being stiff (free standing), so the adjustments after demolding are pretty much limited to edge trimming - curvature adjustments are then usually difficult to impossible. The negative thermal expansion coefficient is very useful for things like satellite hardware, supports for antenna, RF waveguides, and other things where zero length change with temperature is required or highly desirable. For items like that, symmetric laminations at specific + and - angles can make zero thermal expansion in one direction. These parts are best made with tooling that responds to temperature identically to the intended part.
So yes, molds made of other materials are possible and can produce workable parts. The acceptability of each method is dependant upon how good the de-molded shapes must be, tooling budget, and how much tuning is acceptable in the tools and subsequent assembly processes. The unconditionally good way to build oven cured graphite fiber directional parts is to build molds with the same laminate schedules and cloths as in the parts.
Did PM do this? I have no idea and am unwilling to watch his many many videos to find out. Maybe someone else noticed and remembered and is willing to tell us. If so, he may have also told us why he made tools in the way he did...
I think you're flying backwards. Shouldn't the big wing and prop be at the back?My friend took a video of my takeoff yesterday from Los Banos KLSN. 310HP Cessna P210. No flaps.
Liftoff was around~70 KIAS with time 7 seconds from rolling. Takeoff weight was 3440#. Ground roll was 860 feet.
I can't imagine the feeling of having to wait >20 seconds prior to rotation. It must be terrifying.
Where was this?I saw a Velocity takeoff in front of a crowd last Saturday. He was too aggressive with the elevator on rotation and I got to witness the stall behaviour my LEZ friend told me about. Fortunately he didn't shove a bunch of down in it like we've seen Peter do. He just held on and it damped out after maybe 3 cycles as airspeed increased.
Obviously Velocity now are taking an interest in a 'clone' of there a/c. I did suggest several posts ago that Velocity could/should consider some sort of bilateral, agreement with PM to ensure that the Raptor is airworthy??? etc, as a crash of the Raptor would tar the Velocity or similar canards with the same brush, making their well proven design unsafe in the eyes of "Joe Public". The alternative is to distance themselves completely with PM /Raptor, with some sort of statement of ' just because it looks the same, beauty is only skin deep !!!!Just checking out the comments again and saw Velocity Aircraft posted this: "If you’re interested in time in a Velocity please let me know. We will make that happen and high suggest you do this."
Good idea. Nice offer.