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Looking at an image of the orbiter on the ground, it's obvious the nose landing gear is positioned higher than the other landing gear in the wings, making the nose of the orbiter droop down. As far as I know, the orbiter was the only aerial vehicle that has its nose down; most other airplanes have their landing gear level, or if not, they have tail wheel landing gear with the nose up. What's the reason for this?

enter image description here

Fred
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DrKlutz
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    Not an answer, but I think it's notable that most aircraft need level or upward-pointed wings on the ground to take off from a runway. But the shuttle never left the ground that way. It only needed to worry about landing. – Seth R Jun 24 '21 at 14:02
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    It's not the only aerial vehicle to be nose-down on the ground. Some smaller regional jets (for example, the CRJ-900) also sit in a slightly nose-low attitude. – Skyler Jun 24 '21 at 14:03
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    So it will land of the main gear, and only drop the nose much later, with less violence? Kinda like all airliners do? It's just more pronounced in the SHuttle, because the shuttle will never be trying to aerodynamically take off, thus can afford a strong negative angle on the wings once all wheels are on the ground. And of course smaller wheel = less mass. – CuteKItty_pleaseStopBArking Jun 25 '21 at 10:38
  • I also wonder how important the drogue chute (which deploys while the front gear is still in the air) was in this regard. As it was attached above the engines, it must have caused a quite substantial upward pitch, which would brake the front smackdown. – leftaroundabout Jun 26 '21 at 14:07

1 Answers1

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There are really two questions here: why is the main gear long, and why is the nose gear short?

The main gear for most aircraft are designed to carry most of the aircraft's weight and therefore they're positioned near (slightly aft of) the center of gravity. The space shuttle lands at a high angle of attack (a very nose-up attitude) because of its delta wings. In order to provide adequate clearance to avoid a tail strike, the main gear needs to be long.

Tail scrape attitude
Shuttle Crew Operations Manual - Section 4.9-1

Concorde also had delta wings and landed at a high angle of attack. It similarly had very long main gear.

Concorde landing
Source: Wikipedia

In order to keep the aisle level for passengers boarding and exiting, Concorde also needed a long nose gear.

So why didn't the shuttle have a long nose gear strut? To save weight. Every pound/kg of mass you add to the nose gear strut results in that much less payload you can take to space. The shuttle didn't have passengers walking up and down the aisle, so there wasn't much of a requirement to keep it level.

An interesting consequence of the negative (nose-down) angle of attack after touchdown was that it applied extra load on the main gear. At that angle, the wing wants to "lift" the shuttle downward into the runway. So, after the nose gear touched down, the elevons were positioned 10° down, which changed the angle of attack of the wing and helped reduce the weight being applied to the main gear. This was called "elevon load relief". See Shuttle Crew Operations Manual - Section 7.4-19

Bret Copeland
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    An interesting aside, "nose gear slapdown" was often the driving load case for a shuttle mission. – Erik Jun 23 '21 at 21:02
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    I would add that other delta-wing aircraft need to keep the nose up to maintain the angle of attack needed for taking off from a runway. The shuttle, of course, had no such requirement. – Nimloth Jun 23 '21 at 22:09
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    Beep trim derotation! Great answer. – Organic Marble Jun 23 '21 at 23:04
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    @Nimloth Well, technically, the space shuttle has the absolute highest AoA requirement (straight up) during takeoff, but that has nothing to do with its landing gears. – Nelson Jun 24 '21 at 04:48
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    @Nelson if you really want to be technical, straight-up attitude doesn't mean a high AoA. If you assume zero wind, then your AoA is simply the angle between where your nose is pointed and the direction of travel. If you're pointed straight up and you're traveling straight up, then your AoA is zero. – Bret Copeland Jun 24 '21 at 06:33
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    @Nimloth The shuttle's wings were also much smaller relative to the vehicle, such that it couldn't even really fly so much as just glide down to a landing. It's not like NASA was ever going to make it circle the tower for a while before clearing a runway. It basically had one approach attempt after reentry (and maybe an emergency backup slightly further along in roughly the same direction? Don't think that was ever needed though.) – Darrel Hoffman Jun 24 '21 at 13:44
  • @BretCopeland: If you want to be even more technical, wings don't have to align perfectly with the nose, so AoA is actually the angle between your wings and the direction of travel. (e.g. airliners angle the wings up a couple degrees relative to the body, so they can maintain cruise AoA with the nose even closer to level. This reduces drag, because the body isn't as efficient a wing as the actual wings, so you want it closer to nose-on.) I assume the shuffle aligns the wings with the nose so they can minimize drag on all parts simultaneously for re-entry heating, so true there. – Peter Cordes Jun 24 '21 at 14:01
  • @DarrelHoffman: I've seen it done in simulation where a 360 was done as a response to coming in way too high. In the early days there may have even been fuel left in the OMS engines that could be used to fine-tune but in the later days there wasn't. – Joshua Jun 24 '21 at 14:02
  • @DarrelHoffman: Yeah, I was thinking the same thing. Shuttle and Concord both have smaller wings than typical subsonic aircraft. Delta-wing enables high AoA without stalling (I think), but the fact that they need it at landing speed to achieve a reasonable sink rate might be due to having smaller wings than you'd want for a subsonic cruise design. Is that accurate, @Bret? I guess other delta-wing aircraft to look at might be Mirage / Rafale fighters, since despite being designed for supersonic operation, fighters have large wings for their size (for turn rate). – Peter Cordes Jun 24 '21 at 14:06
  • @PeterCordes Delta wings both enable and require high AoA in low-speed flight, while simultaneously working well in transonic and supersonic conditions. – TooTea Jun 24 '21 at 14:34
  • I suspect that the Concorde's long nose gear has more to do with the droop nose than with keeping the floor level of passengers. Just eyeballing the image, it doesn't look as though you could shorten it much without scraping the nose on the runway. – jamesqf Jun 24 '21 at 17:27
  • I'll add to the saving weight comment. It wouldn't just be to save the weight directly associated with the physical gear, but also the corresponding ballast needed to shift the center of gravity back. At least toward the end of the program, the orbiter was flown with maximum ballast since it was naturally so front heavy (especially in contingency return scenarios). – Agbullet Jun 24 '21 at 18:23
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    Interesting point about "load relief". On normal aircraft, you want to load the main gear as much as possible during the landing run to enable better wheel braking - hence spoilers etc. (The design load for the landing gear comes from the landing impact anyway). I always assumed that negative lift at such attitude was the main benefit of such arrangement for the Shuttle. – Zeus Jun 25 '21 at 02:01
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    Another interesting thing worth mentioning could be that the Soviets built a test version of Buran that could take off on its own power horizontally. And it had, necessarily, a tall nose gear with a positive (nose up) attitude on the ground. – Zeus Jun 25 '21 at 02:07
  • @nelson AoA is relative to air motion, not to the ground! – CuteKItty_pleaseStopBArking Jun 25 '21 at 10:40