totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

It was pointed out to me on another forum that I had confused the LoX and CH4 tanks, so pumping between those tanks is a non-starter. But perhaps pumping LOX between the nose header and the main would do the same thing.

[MinimumSky5]

Given that the propellants in the main tanks will be sloshing around every which way during reentry, I doubt that they'd want to add more in, it could mess up the center of mass, and result in engine starvation during that start if the landing burn. 

[sevenperforce]

1 hour ago, MinimumSky5 said:

Given that the propellants in the main tanks will be sloshing around every which way during reentry, I doubt that they'd want to add more in, it could mess up the center of mass, and result in engine starvation during that start if the landing burn. 

Tricky proposition. I admit we don't know much about the pumping mechanism or approach to begin with. They are using autogenous pressurization for the tanks -- is that how they're pumping props around already? Is there enough piping to move the CoM around that way? We just don't know.

[tater]

 

https://www.pmview.com/spaceodysseytwo/spacelvs/sld024.htm

 

[sh1pman]

SpaceX now has a serious competition.

 

[Wjolcz]

Most lifting bodies have the wing curve up by the end. Maybe that's what Elon means by static areo?

What happens at supersonic and subsonic speeds if to that we add a bend like this?:

Maybe the wings will have bends like this because having a flat sheet of metal slamming against the air at supersonic speeds and creating lower pressure behind is a horrible idea.

[Silavite]

4 hours ago, sevenperforce said:

Not a bad idea. I am unsure of whether it would have enough control authority to provide fine adjustments. More importantly it would have little or no roll authority.

I was thinking that roll could be handled purely by the RCS (and thrust vectoring when applicable). There isn't a need for rapid rolling, and I don't see where large external torques in the roll axis would arise.

[mikegarrison]

Inverted gull wing is for one and only one reason -- landing gear height. That was certainly the case for the F-4U Corsair, which needed the clearance for that monster prop on the front.

[tater]

35 minutes ago, mikegarrison said:

Inverted gull wing is for one and only one reason -- landing gear height. That was certainly the case for the F-4U Corsair, which needed the clearance for that monster prop on the front.

What's interesting is that the F6F prop dia was only a few inches smaller than the F4U (they had the same engine, too (slight carb difference). The F6F had the wing dihedral start right past the landing gear. I guess it was just pot-bellied so the wings were lower WRT the prop shaft.

[Silavite]

22 minutes ago, mikegarrison said:

Inverted gull wing is for one and only one reason -- landing gear height. That was certainly the case for the F-4U Corsair, which needed the clearance for that monster prop on the front.

The pedant in me feels obligated to point out that the inverted gull has an added bonus of reducing interference drag for a low mounted wing. That said, this was indeed likely nothing more than a bonus as opposed to the more pertinent consideration of a 13' propeller chopping through carrier decks.

[mikegarrison]

5 minutes ago, tater said:

What's interesting is that the F6F prop dia was only a few inches smaller than the F4U (they had the same engine, too (slight carb difference). The F6F had the wing dihedral start right past the landing gear. I guess it was just pot-bellied so the wings were lower WRT the prop shaft.

Landing gear design tradeoffs are among the most important and least-recognized issues in airplane configuration. Landing gear is *heavy*, and making it as short as possible is always good. The two airplanes most recognized for the "inverted gull wing" shape were the Corsair and the Stuka, and they both chose it because of landing gear clearance issues. (In the case of the Stuka it had fixed gear, so the shorter they could make it, the less drag it caused.)

As you note, the F6F also had a "bent wing", but it was a lot more subtle.

Edited April 19, 2020 by mikegarrison

[CatastrophicFailure]

 

[see addendum]

Edited April 19, 2020 by CatastrophicFailure

[CatastrophicFailure]

Addendum:

 

[mikegarrison]

Steel studs? What does that mean? Surely those bands of steel plate are not studded like a porcupine, are they?

Is it a stud somehow buried in the tile which they are then going to bolt to the rocket by drilling a hole?

[tater]

10 minutes ago, mikegarrison said:

Steel studs? What does that mean? Surely those bands of steel plate are not studded like a porcupine, are they?

Is it a stud somehow buried in the tile which they are then going to bolt to the rocket by drilling a hole?

I think the idea is that something like a nut is welded to the outside, then the tile is bolted to that. I saw a pic at some point...

[mikegarrison]

9 minutes ago, tater said:

I think the idea is that something like a nut is welded to the outside, then the tile is bolted to that. I saw a pic at some point...

https://en.wikipedia.org/wiki/Weld_nut?

We tend to use nut plates for similar things. Same idea, but the nut is captured in a plate that is riveted, instead of welded.

[tater]

3 minutes ago, mikegarrison said:

https://en.wikipedia.org/wiki/Weld_nut?

We tend to use nut plates for similar things. Same idea, but the nut is captured in a plate that is riveted, instead of welded.

Yeah, there's a pic on NSF someplace after the hopper test where they pulled the tiles, and you could see the nuts welded to the surface.

https://forum.nasaspaceflight.com/index.php?topic=49622.msg2030732#msg2030732

 

[mikegarrison]

15 minutes ago, tater said:

Yeah, there's a pic on NSF someplace after the hopper test where they pulled the tiles, and you could see the nuts welded to the surface.

https://forum.nasaspaceflight.com/index.php?topic=49622.msg2030732#msg2030732

I don't imagine that could possibly be the final design, because it looks like the fasteners are a way for the heat to get right past the tiles and into the skin. Maybe they will have some kind of cap over them or something?

LOL, by the way, Google is now showing me ads with pictures of nut plates. You make one little search.....

[tater]

Yeah, they would have to fill in the top. Seems bizarre, though in reality the air compresses in front of the surface and the peak heating is offset from the actual hull. So bow shock heat, gap, tile, gap, hull. The tile---> transmission via the bolt is clearly a thing, though I suppose discrete hotspots far enough away to dissipate?

[Ultimate Steve]

21 minutes ago, mikegarrison said:

LOL, by the way, Google is now showing me ads with pictures of nut plates. You make one little search.....

Seriously. Kinda off topic, but once I had to get a source for a paper I was writing (proposal essay about putting air conditioning in our high school and why we should do it) about air conditioning and the easiest to phrase source I found came from a site which sells accordion room dividers, of all places.

A large chunk of the ads I see on Instagram are now for room dividers.

[mikegarrison]

1 hour ago, Ultimate Steve said:

Seriously. Kinda off topic, but once I had to get a source for a paper I was writing (proposal essay about putting air conditioning in our high school and why we should do it) about air conditioning and the easiest to phrase source I found came from a site which sells accordion room dividers, of all places.

A large chunk of the ads I see on Instagram are now for room dividers.

I don't mind. If you click on a few ads for places that sell dresses, Google serves you up pictures of pretty women wearing dresses for months.

1 hour ago, tater said:

Yeah, they would have to fill in the top. Seems bizarre, though in reality the air compresses in front of the surface and the peak heating is offset from the actual hull. So bow shock heat, gap, tile, gap, hull. The tile---> transmission via the bolt is clearly a thing, though I suppose discrete hotspots far enough away to dissipate?

I expect much of the heat comes via radiation rather than direct contact with hot gas. As the tile surface heats up, the heat flow slows down because radiation heat transfer is to the fourth power of T_h - T_c. You don't have to have the whole tile hot to stop the radiative heat -- only the outer surface needs to be hot. So as long as the tile itself does not conduct heat well, it works.

But this is why you don't want the fastener itself to see the hot luminescent plasma, because if it can see the plasma, the plasma can see it. That means it's a radiative heating leak path.

Edited April 19, 2020 by mikegarrison

[CatastrophicFailure]

Relevant, interesting vid...

 

[magnemoe]

4 hours ago, mikegarrison said:

I don't mind. If you click on a few ads for places that sell dresses, Google serves you up pictures of pretty women wearing dresses for months.

That was an good advice, then you get adds who are nice to look at

The adds can be a bit weird to, remember buying an sofa at Ikea, I ended up getting adds for sofas for weeks, same with car parts. Well I already bought the sofa and the parts so the adds are a bit pointless. 

[tater]

7 hours ago, mikegarrison said:

I expect much of the heat comes via radiation rather than direct contact with hot gas.

Yeah, this is true for bow shocks.

 

 

7 hours ago, mikegarrison said:

I don't mind. If you click on a few ads for places that sell dresses, Google serves you up pictures of pretty women wearing dresses for months.

My wife and daughter were apparently using this machine to look at bathing suits. Win!

[sevenperforce]

Fascinating -- it looks like they plan to test vibration impact for two different mounting approaches:

At left you have the familiar three-stud attachment. You can tell this is being used because of the adjacent stud-holes. At right you have some sort of metal frame that they fit into.

Or they may use both -- framed in the high-heat regions, bolted in the medium-heat regions.

 

 

10 hours ago, CatastrophicFailure said:

Addendum:

 

Not sure why Tim is confused, but Elon already answered this before. They are lightweight, ruggedized siilica tiles that do not ablate. Their purpose is to hold the highest-heat interface away from the steel so the steel survives uninjured. They are a what the Shuttle tiles were supposed to be, but couldn't.

The Shuttle tiles were quite lightweight -- basically glass foam -- but had to be very thick because they were protecting an aluminum skin. They were also bespoke. Virtually every tile was a different shape due to the shape of the STS Orbiter. They were glued on to save weight, which was a time-consuming and faulty process.

Because Starship is a near-perfect cylinder, all the tiles are the same shape, and they can be bolted on easily. Failsafe redundancy because they have three bolts. They are also vastly thinner (lighter, less bulky) because the steel substrate can take much more heat on the back end than aluminum.

15 hours ago, Wjolcz said:

Maybe the wings will have bends like this because having a flat sheet of metal slamming against the air at supersonic speeds and creating lower pressure behind is a horrible idea.

That's the whole idea. These flaps are permanently stalled; that's what gives them their control function. More like airbrakes than traditional flaps or elevators or other control surfaces. The only lift is compressive body lift.