# Is aerodynamic lift ever useful in rocket flight?

When a rocket is traveling through an atmosphere, the component of the aerodynamic force in the direction of motion is called drag, and the component perpendicular to that is called lift. Usually a rocket is pointed in nearly the same direction as motion, but not necessarily exactly. See the NASA illustration below.

For simulation, and for flight guidance and control, consideration of lift is essential. Lift is therefore important.

My question though: is lift ever useful when rockets are traveling in an atmosphere?

And here, I mean "rocket-shaped" rockets; not car-shaped, or plane-shaped rockets, but the long, approximately cylindrically symmetric ones that tend to fly from low altitudes up into space. (yes, and more frequently these days, back down again).

• I assume you are ground ruling out Pegasus as a "plane-shaped rocket"? Commented Jul 9, 2016 at 17:40
• @OrganicMarble for here, for now, yep. A search did lead me to this interesting video: https://www.youtube.com/watch?v=oY3GclS5VUQ, and then to this question.
– uhoh
Commented Jul 10, 2016 at 2:01
• If there are fins, and they deflect the airflow to cause a force perpendicular to the direction of flight (say, for steering), that would be lift. It happens to also cause drag. Commented Jul 10, 2016 at 10:16
• This is related to the CG and CP mentioned in the down-voted answer (which I up-voted). This could also happen, in the passive sense, to a cylindrical rocket without fins. Commented Jul 10, 2016 at 10:21
• It is lift, even if it's a momentary steering force. It only acts in one direction. Commented Jul 10, 2016 at 10:23

Angling to get lift is going to increase the atmospheric cross-section of the rocket and so increase drag. For any reasonable angle of attack, the drag force is going to be much larger than the lift force, so I believe that for powered ascent it makes the most sense to minimize drag, which means zero AoA and zero lift. This also, as Mark Adler notes, minimizes lateral stresses on the vehicle, allowing structural weight to be minimized.

Note that the total drag losses on a large rocket in ascent to LEO are small -- for Saturn V, about 0.5% of the total ∆v expenditure. Since low-AoA lift is a small fraction of drag, any gain from body lift would be extremely small.

Of course, there have to be minor excursions from zero AoA during a powered ascent (though hopefully only small ones); these should be positive AoA in order to take advantage of what little lift there is.

That said, lift is useful for steering during unpowered flight; the Falcon 9 first stage uses body lift to control its downrange flight to an ASDS. It's also very important for control of reentry vehicles, but those aren't "rocket-shaped rockets" so they're outside of the scope of your question.

• An argument for the use of lift might go as follows. Drag vs angle is almost flat (quadratic or at least symmetric) near zero angle, while lift is roughly linear. Therefore sufficiently small angles will give some "almost free" lift relative to the change in drag. The counter argument given by @MarkAdler as you mention is that carrying the increased mass of the airframe necessary to accommodate the additional side loading will end up costing more than any lift could offset.
– uhoh
Commented Jul 10, 2016 at 1:07
• The smallness ∆v impact of drag on the Saturn V is good to know! I'm interested in the other end of scale, small(est) launch vehicles where drag will become much more significant. I found this question and answer on the smallest examples. I remember seeing a question about smallest possible launch to orbit vehicle, but I can't find it now.
– uhoh
Commented Jul 10, 2016 at 1:13
• Also - kudos for noticing that the answer to "is lift ever useful when rockets are traveling in an atmosphere?" is actually yes, an example being assistance in re-entry control of rocket bodies - the most notable being Falcon 9's 1st stage return to earth and controlled landing on a bulls-eye for re-use. :-)
– uhoh
Commented Jul 10, 2016 at 1:20
• Once I master orbital insertion guidance in my sim, maybe I'll tackle simulation of lift (currently it pretends AoA is always zero) and see if there's advantage to maintaining a small positive angle. Commented Jul 11, 2016 at 15:38
• Just fyi I happened to hear Declan Murphy of flightclub.io mention the use of lift in F9 return trajectory in the TMRO episode The beautiful data of rocket launches after 32:10. youtube direct link: youtu.be/WpcbFdSB_Ik?t=1930
– uhoh
Commented Feb 6, 2017 at 7:14

As far as I know, no. In order to make a cylindrical rocket as light as possible, they are flown to minimize the side loads to the structure -- as close to a zero angle of attack as possible. If they wanted to use lift, it would increase the mass of the structure to be able to take substantial drag forces from the side. There would not be sufficient benefit from the lift of a cylindrical structure to offset that mass increase.

Wings or other lifting surfaces on the other hand (which you are ruling out), could potentially provide some benefit in the early parts of ascent. That was the case for Pegasus.

You said it yourself, Lift is important for guidance and control. As a matter of fact a rocket is designed in such a way, that the center of pressure is aft of the center of gravity. The distance between CG and CP is also called the caliber stability margin measured in rocket caliber.

You can use the fins of a rocket to control the direction and magnitude of the lift force and therefore change the positon of the center of pressure and therefore the stability of your rocket in the atmosphere.

Hence, yes, lift is useful.

Yes lift is useful and helpful to rockets even those going to space. The angle of attack thru the air causes lift that can help reduce gravity losses. The control systems automatically adjust the angle of attack to follow the chosen flight path thereby accounting for lift and drag.

Aircraft rely almost completely on lift to overcome gravity - rockets attempt to get to orbit fast to reduce drag and gravity losses but a little help from the atmosphere is welcome - they have to overcome drag so they may as well try to generate some lift to compensate. The rocket shape matters here as some shapes have a better lift to drag ratio - something like the Saturn 5 is not as good as a smoothly curved design with a ballistic shape. I expect the aerodynamic lift that is attainable is quite low and cost of drag is high so space rockets are optimised to reduce drag and gravity losses instead of optimising for aerodynamic lift/drag ratio as an aircraft would. The Northrop Grumman Pegasus first stage has a small wing like an aircraft to provide some extra lift on the first stage. A vehicle like starship which has drag flaps will get some extra drag and lift from these features during the short period that the rocket remains in the atmosphere as it performs it's gravity turn.

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– Community Bot
Commented Aug 14, 2022 at 18:29
• Can you site any reference showing that a non "plane shaped rocket" benefits from lift? As Mark Adler points out, real rockets fly at near zero alpha. As written, this post is "some internet person saying something". Commented Aug 14, 2022 at 18:41
• This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review Commented Aug 14, 2022 at 18:45