tag:blogger.com,1999:blog-7598615455712402973.post7521241803581446066..comments2024-03-25T11:14:45.840-04:00Comments on Polymath: Clamshell wings for hypersonic reentry of rocket stages. UPDATED, May 4, 2023.Robert Clarkhttp://www.blogger.com/profile/16114043697010364282noreply@blogger.comBlogger1125tag:blogger.com,1999:blog-7598615455712402973.post-51553631571831932592023-05-16T18:53:56.057-04:002023-05-16T18:53:56.057-04:00There are two things about this clamshell wing not...There are two things about this clamshell wing notion that strike me as extremely serious problems to resolve, especially if done as a payload shroud opened up as two clamshell wing-doors. (1) weight and balance is way-to-hell-and-gone off, and (2) there are numerous extreme heat protection pitfalls. <br /><br />Clamshell halves of a payload shroud are near the nose end of the vehicle, and are likely to have a larger crossflow drag than the round body of the aft portion of the vehicle. That puts the center of the combined crossflow force (the lift) way far forward of the likely vehicle center of gravity. “Starship”-like aft fins folded out to the side will help with this, but would necessarily have to be just about as big as the clamshell doors. And that will be heavy.<br /><br />There are two separate heat protection issues to worry about: <br /><br />(1) The concavity trapping pressure underneath is likely going to experience very nearly stagnation levels of heating, over pretty much all of the exposed surfaces, which is nothing like anything ever flown before. Even at only LEO entry speeds, this will require ablatives, not low-density re-radiating ceramics, just like on the Shuttle. This issue also applies to any other cavities exposed to the stream when you open the doors. Tufroc tiles might work, and then they might not. They did fly as leading edges on the X-37B, but those stagnation surfaces are smallish, with lots of cooler adjacent structures into which heat can move. It’s very, very likely that nothing else but ablatives will work. That’s Avcoat and PICA. They’re the best we have. <br /><br />(2) The oddly-shaped junctions between all these parts will be subject to extremely-severe shock interference and shock impingement heating effects. On the X-15A-2 flight, that quantified as (at “only” Mach 6.7) a factor-7 increase in heating rates in the shock interference zones, and a factor-9 increase in heating rates in the shock impingement zones, and all the ablative coating was stripped away from the affected surfaces underneath the tail. Tufroc simply cannot handle heating abuse like that, and the ablatives are going to erode away very, very fast in those zones. <br /><br />Just food for thought.<br /><br />Yes, the lower weight/area will reduce peak heating some during entry, but not by all that much. <br /><br />By the way, that Chinese hypersonic concept ABSOLUTELY cannot survive in hypersonic flight. The surfaces and structures that are parallel to each other, will each shed shock waves that impinge upon the other. The resulting shock impingement heating will cut the vehicle to pieces, in a matter of several seconds, anywhere beyond about Mach 6. I don’t care what it’s made of! There is no “manurium” or “unobtainium” from which to make the thing, which can stand that abuse. (Same goes for that “Skylon” design in the UK. The nacelle spike shocks will cut the wings off.)<br /><br />I’m also pretty sure that talking about mass ratios of 30 is utter BS, no matter how you construct anything. Getting to 10 is pretty far out there. <br /><br />GW<br />Gary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.com