Their appearance has sometimes led them to be compared to potato mashers or waffle irons. By contrast, grid fins are a lattice of smaller aerodynamic surfaces arranged within a box. Design characteristics Ĭonventional planar control fins are shaped like miniature wings. On July 25, 2019, China launched a modified version of Long March 2C which featured grid fins atop the first stage for controlled re-entry of the spent rocket stage away from people in nearby towns and cities. The 1st stage of the private Chinese company i-Space's Hyperbola-1 rocket appeared on Jto be equipped with steerable grid fins for attitude control. In 2014, SpaceX tested grid fins on a first-stage demonstration test vehicle of its reusable Falcon 9 rocket, and on Decemthey were used during the high-velocity atmospheric portion of the reentry to help guide a commercial Falcon 9 first stage back to land for the first successful orbital booster landing in spaceflight history. Grid fins have also been used on conventional missiles and bombs such as the Vympel R-77 air-to-air missile the 3M-54 Klub (SS-N-27 Sizzler) family of cruise missiles and the American Massive Ordnance Air Blast (MOAB) large-yield conventional bomb, and on specialized devices such as the Quick-MEDS delivery system and as part of the launch escape system for the Soyuz spacecraft. In Russia, they are thus often referred to as Belotserkovskiy grid fins. They were developed in the 1950s by a team led by Sergey Belotserkovskiy and used since the 1970s in various Soviet ballistic missile designs such as the SS-12 Scaleboard, SS-20 Saber, SS-21 Scarab, SS-23 Spider, and SS-25 Sickle, as well as the N-1 (the intended rocket for the Soviet moon program). Definitely a heads-up launch.Grid fins (or lattice fins) are a type of flight control surface used on rockets and bombs, sometimes in place of more conventional control surfaces, such as planar fins. Now I've just got to get enough nerve to lop the ears off, clean up the ends, and launch it. I chose the latter, because the former would just add weight, and I don't want any more in the aft end of this rocket. It came down to reinforcing the joint along the fillet, or removing those long tails on the fins to reduce leverage. And I know that comes from flexing on impact. It's the paint cracking along the fillet that is the problem. I can't say how fast, but watching the video, I'd guess 50 fps or faster. I can I say without reservation that without the paper, I would have lost the fins in this rocket's third flight, when the chute fouled and the rocket came in hard and fast. Avery label paper wrapped around the leading edge, then trimmed. Regarding papering the fins, I did, with a single sheet of 50 lb. At this point all I can say is the rocket doesn't fly backward. I'm having a little trouble keeping that much weight moving fast enough to get reliable results. suggested I do a swing test before cutting anything to set a benchmark for tests after cutting. OR says the stability is good, but they look awfully small to me. The fin in the third profile down is what I'd like to get to, which is basically the same fin minus the ears. And, as you can see in that first OR profile in my leading post, those ends-or ears, as I call them-are quite large. All I can do is remove fin area from the trailing ends. Thanks in advance.Ĭlick to expand.I can't move the fins anywhere. I appreciate any input I can get-advice, criticism, suggestions. ![]() I'd hate to cut these fins down, thinking the design will be stable, only to have it do somersaults right off the rail. Is that fin shape workable? OpenRocket tells me it is, but I'm reminded of OR's trouble modeling certain design aspects (unusual transitions or stubby fins up by the nose cone come to mind). The stability dropped to 1.38 (still good), with a significant reduction in pitch rate-down to about 16.5 degrees. ![]() I also trimmed the corner of the trailing edge, thinking this might help absorb ground impact by tipping the rocket onto its side quicker than it would with a flat-bottomed fin. Then I ran simulations with the fins shortened enough to allow the motor nozzle to extend below the trailing edges, thereby absorbing some of the landing impact. ![]() The stability has decreased to 1.41 calibers, with a pitch rate of ~21 degrees-a slight improvement. Next, screen shots of the modified fins with 1.25" cut off the trailing ends. Next to it are plots with pitch rates-the first deviation being ~21.5 degrees. The first is the rocket profile in OR, showing a stability of 1.47 calibers. I started by chopping off 1.25" in OpenRocket, then running simulations that would indicate any reduction in stability, focusing on plots that include pitch rates.īelow are screen shots of the rocket with the unmodified fins. I'm trying to reduce the amount of fin flex on landing (it's causing hairline cracks in the paint along the fillet) by reducing the size of the fin's trailing end.
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