27

I've been wondering this for quite a while: Why do the missiles on the F-16 point down a little bit?

See how they point down?

I went and did a little searching and found out that the F-16 isn't the only plane that has this feature, so I'm going assume it's not the F-16s frame specifically. I also doubt it's tactical because all the weapons are pointing down, regardless of the weapons role in combat. In fact I saw a few photos where the bombs closest to the fuselage were pretty level with the ground (and bombs pretty much always go down, so...)

Does it have to do with aerodynamics, or perhaps ease of loading? Why is the load-out on the F-16 mostly pointed slightly downwards?

fooot
  • 72,860
  • 23
  • 237
  • 426
Jae Carr
  • 24,145
  • 38
  • 131
  • 228

9 Answers9

25

If you take a look at the picture again, you'll see that the missiles are in fact lined up quite nicely with the nose of the plane. The missiles are not pointed down, they are pointed forward. The wings and engine (and the entire back two-thirds of the plane) are pointed up, which provides the lift to keep the plane in the air during normal flight. You can see pretty well the alignment in reference to the horizon in this picture (found by @jay-carr):

Image of F16 showing nose and mounted missiles pointed at the horizon.

Just to cut off the potential comments about how planes generate lift, reference is here.

fooot
  • 72,860
  • 23
  • 237
  • 426
  • I think a lot of people here are actually familiar with how airplanes actually generate lift (in fact I suspected this may be the actual reason.) If you could explain it a bit here though (for anyone who isn't aware), and how it relates the mounting of the weapons here, that'd be nice :). – Jae Carr Jun 13 '15 at 04:02
  • After a little more research. I wonder if they are, at least in part, angled down to reduce induced drag from the fins of the missiles in normal flight (again, owing to the slight nose up angle of the F-16 in normal flight.) – Jae Carr Jun 13 '15 at 04:10
  • And after a little more research, success: http://arizonaexperience.org/sites/arizonaexperience.org/files/base_images/f16_100709-f-1851b-0515.jpg When the plane is flying normally (with the nose up a bit) all the missiles are level with the horizon, heading straight into the oncoming air. Feel free to use that picture to improve your answer,then I'll probably delete all these comments... – Jae Carr Jun 13 '15 at 04:11
  • @JayCarr at cruising speeds I suspect the AoA is much lower, as it in in the rhino. Your theory would only hold true for a small subset of AoA's anyway. – Rhino Driver Jun 13 '15 at 04:21
  • @RhinoDriver AoA of the wings compared to AoA of the actual forward momentum (and thus incoming airflow) of the craft should hold true for a large percentage of actual AoAs, the only difference that really shows up is when the speed drops and flaps are applied or when in combat maneuvers (at which point, who cares about induced drag from missile winglets.) In a cruise though, it could make a big difference. And even though that's a small subset of AoAs, it is the one that is being used the vast majority of the time. – Jae Carr Jun 13 '15 at 04:25
  • 8
    @JayCarr that's not true for the Rhino, 250 vice 350 makes a large difference in nose position. And anyway, as a guy that flies the Rhino, I'm telling you that the main reason our ordinance is hung in the manner it is, is to mitigate midair collisions during jettisons. I doubt the viper is dissimilar in that respect. I have no doubt that secondary considerations revolve around efficiency though, but efficiency doesn't trump safety--that's why the Rhino is such a pig. – Rhino Driver Jun 13 '15 at 04:33
  • Great picture @JayCarr! I'm hesitant write up a description of the aerodynamics since I'm tired and would be prone to mistakes, but I welcome someone who wants to edit it in. I did add the image in, which I found to be in the public domain. I linked the image from another source. –  Jun 13 '15 at 04:37
  • @SamuelScheiderich - lol, take your time, there's no rush. Plus if you wait maybe someone else will come along and write it up for you (not me, not smart enough.) – Jae Carr Jun 13 '15 at 04:46
  • 2
    @RhinoDriver - Hmmmm...... You make a very good point, and I'm not about to argue with an actual F-18 pilot... So instead I've written Lockheed and I'm going to see what they say (if they even respond). If they don't, I'll probably just watch the vote count and see what the community says. – Jae Carr Jun 13 '15 at 04:47
  • As another point, I'm now noticing all the pitot tubes in the above picture are parallel with the weapon mounts, and those have to point straight into the wind to function, yes? Thus giving a stronger indication of the direction of the airflow. – Jae Carr Jun 13 '15 at 18:55
  • And the canon, for that matter. The aerodynamic shield around it is also parallel. – Jae Carr Jun 13 '15 at 18:57
  • 4
    @JayCarr If you can get an actual answer from Lockheed I'd love to hear it. I'm pretty curious about it myself. That's the info we've been fed. If its for a different reason, I'd love to know. – Rhino Driver Jun 13 '15 at 22:46
  • 2
    This answer is very plausible but te picture actually demonstrates very little. It's very hard to tell whether the photograph is straight, since the literal horizon is mountainous and the features on the ground are too small to determine where true vertical is. (And, if the camera isn't pointing absolutely level, perspective will make the verticals in the frame lean in or out except very close to the centreline.) – David Richerby Jun 14 '15 at 11:44
16

Usually stores are hung off an aircraft in such a manner to facilitate a safe auxiliary free-fall release. The AUX release is used if the CAD misfires and the stores cannot be physically ejected downward away from the aircraft. Although this wouldn't really apply to the wingtip loaded aim 9's, so I can't really account for those. In the super hornet the pylons are canted outwards for just this reason.

In fact, the emergency jettison doesn't even release the wingtip aim 9's because, in the case of the Rhino, the wing is more efficient with them in place. The wingtip 9's act as a winglet of sorts.

Rhino Driver
  • 8,768
  • 1
  • 32
  • 47
  • 1
    And CAD is...? (I can guess from context, but what's it stand for?) – cpast Jun 13 '15 at 01:37
  • 1
    @cpast For the life of me I can't remember what it stands for, but its a small explosive charge. It's been described to me akin to a shotgun blast. – Rhino Driver Jun 13 '15 at 01:43
  • 7
    Cartridge Actuated Device. – Todd Wilcox Jun 13 '15 at 03:02
  • Is three degrees really going to make a difference in that situation? The line of the weapons intersects the intake of the aircraft, it seems like you'd need a great angle to achieve what you're talking about. – Jae Carr Jun 13 '15 at 04:07
  • 1
    @JayCarr There are no stores inline with the intakes of any aircraft I'm aware of. You'd be right to assume that'd be very dangerous. To answer your question, yes, it probably makes a great deal of difference. Even more so, the small cant adds a tremendous amount of drag, this is especially exacerbated in the Rhino which is also canted outwards. – Rhino Driver Jun 13 '15 at 04:11
  • 1
    I can't speak to the F-18 obviously, but I assume it's similar to the -16. I'm not sure exactly if this was part of the design for the Viper. Anyway, you can't jettison any of the air-to-air stores, not just just the wingtips. Additionally, and I assume the Hornet has the same design, but the computer runs through some logic to figure out if it needs to delay dropping certain stations to prevent collisions. –  Jun 13 '15 at 17:56
  • 1
    @TUMBLEWEED Its the same in the rhino, you have to fire them off. Its been awhile since I've looked at the jettison logic, but I'm pretty sure it jettisons in a predetermined, sequenced order. The order might actually be the same each time. – Rhino Driver Jun 13 '15 at 22:43
8

A related reason is ensuring safe store separation.

A lot of testing is done to ensure your munitions and fuel tanks don't come back to greet you.

So this doesn't happen: YouTube video of 'Aircraft Store Separation Incidents'.

The B-1 bomber had a similar issue initially where weapons would not exit the bomb bays and just skip along on the laminar flow underneath the aircraft. They had to add these spoilers to the fronts of the bays to break up the airflow. The spoiler is the waffle iron looking plate in the front. It drops down when the bay is opened for weapon release. http://miramar.airshowjournal.com/2005/IMG_0327_2.jpg - philosoguido - https://www.reddit.com/user/philosoguido

The B-2 has similar waffles.

ChrisW
  • 3,094
  • 1
  • 23
  • 28
Hephaestus Aetnaean
  • 3,974
  • 2
  • 25
  • 32
6

It's not just the wingtip launchers that are canted downwards. All pylons are canted downwards a couple degrees (~2 I believe). This is to reduce the AOA to 0, thus reducing induced drag at pickle. There might be more to it in terms of aerodynamics, but I didn't engineer the jet.

  • 2
    Usually the AOA is not equal to zero. Also for commercial airlines the fuselage is not at 0 degrees. Since it is also possible to generate lift using these bodies (rockets or fuselages) you want to have them at the angle that maximizes lift/drag. – ROIMaison Jun 15 '15 at 15:03
  • @ROIMaison do you have some source? In the F-16, the AOA is roughly ~2 degrees at 350-450 knots. With the pylons canted downwards ~2 degrees, the AOA should (according to my math) be 0 degrees AOA. You're comparing the fuselage of an airliner to that of a missile... They aren't the same. –  Jun 15 '15 at 22:39
  • I don't really have a source, I just applied the same logic used on the fuselage to the positioning of rockets. You're right that the two aren't the same, and maybe the size of the rockets is too small to generate any significant lift. – ROIMaison Jun 16 '15 at 06:55
  • I don't know why but I didn't see your answer when this question was more active. It looks like you're confirming what Samuel Scheiderich suspected though, and I figure you would probably know... His question is voted a bit higher though, hence I accepted his as the answer. Yet another situation where I wish I could mark multiples as correct... – Jae Carr Aug 14 '15 at 17:42
  • @ROIMaison: They did that on the N-250. It was optimized by some academics at TU Munich and the fuselage AoA was found to be aerodynamically optimal at 2° nose up. When the aircraft entered service, the flight attendant complained bitterly that they now have to push their carts uphill and must constantly prevent them from rolling back. – Peter Kämpf Feb 18 '16 at 07:25
  • 1
    @PeterKämpf The Wikipedia article doesn't indicate that it has entered service yet. Some academics messed that up? –  Dec 10 '17 at 10:23
3

I believe it's a bit of washout in the wing. Washout is a slight twist to the wing, reducing the angle of incidence at the tip and reducing the probability of tip stall.

Fred Larson
  • 2,468
  • 20
  • 22
  • 1
    Downvoter: If this answer is not correct, please fix the linked Wikipedia article, including the photo caption. – Fred Larson Jun 15 '15 at 15:15
  • 1
    It's incorrect because it has nothing to do with washout. The weapon is mounted such as to be horizontal when the aircraft is flying straight and level, which means it's flying with a slight nose-up attitude which translates into a slight angle of the wing as well. – jwenting May 01 '19 at 05:24
3

Not sure about the AIM-9, but the AIM-120 is mounted 6 degrees down from F-16 bore axis. That means that from the pilots point of view its seeker view is centered in the middle of the HUD (below the bore-sight cross which is in upper part of the HUD). That might also be part of the reason for that alignment; to make it more convenient for the pilot to aim when shooting in BORE mode.

Invariant
  • 1,731
  • 2
  • 15
  • 25
0

I think the reason here is mainly (but not exclusively) the same as why the underwing nacelle of a jetliner is also bent downward a couple of degrees in respect to the fuselage axis: to be aligned to the local flow ahead of the wing and minimise therefore the drag.

Normally the same type of external weapon is used on different aircrafts and its shape cannot be obviously optimised for all of them. For this reason it is mounted on each aircraft in such as way to minimise the aerodynamic interference with that particular aircraft. So if it mainly hangs in front of the wing, it should also generally point a bit downward. As highlighted by some comments/answers, interference here is also important for a safe jettisoning.

sophit
  • 11,796
  • 1
  • 28
  • 61
-2

That's wing washout. It's built into the wing to help the aircraft maintain stability in a stall. For instance, the F/A-18 has a wing washout of approximately 4 degrees. This means that if the root of the wing is flying at 10 degrees AOA, the tip is flying at 6. This is used to help maintain aileron effectiveness in a stall.

https://www.boldmethod.com/learn-to-fly/aircraft-systems/how-wing-washout-makes-your-airplane-and-wings-more-stable-in-flight/

MD88Fan
  • 2,484
  • 13
  • 34
  • 1
    this information was already given by 5-years old answers – Federico Oct 22 '20 at 12:43
  • 1
    Maybe so, but I was just trying to give a more detailed answer. – MD88Fan Oct 22 '20 at 12:49
  • 3
    I also don't think this answers the question. Just because a wing has washout doesn't mean that all the mounts need to follow that washout. You could always canter the pylons to point the missiles in any direction you would like, so I doubt washout has anything to do with it honestly. – Jae Carr Oct 22 '20 at 16:03
  • @JayCarr I don't know, it seems like the STRONGEST way to mount it is in line with the wing, plus the missile will be basically level at a typical flying AOA. – MD88Fan Oct 22 '20 at 20:08
  • 1
    @MD88Fan if you have some evidence to back up your logic I’d be happy to see it in the answer. – Jae Carr Oct 22 '20 at 21:31
  • 1
    @JayCarr The wingtip pylon currently runs along the wingtip- if you twisted it so that the missile was level when the aircraft was on the ground, the pylon would not be taking full advantage of the wingtip to provide a surface to mount on. – MD88Fan Oct 23 '20 at 13:12
-4

Its so that the thing goes down (and away) from the aircraft when it is released.

For example, imagine the missile was canted up instead of down. Due to aerodynamics it might fly into the wing it was released. The armament is canted downward to prevent this.

Tyler Durden
  • 13,282
  • 4
  • 43
  • 67