Belly Fins?

Does anyone know what purpose the belly fins on some planes have?

[edit on 12/6/04 by Hyperen]

STABILITY AND IF FORWARD ON THE FUSE, VECTORING THE AIRCRAFT ON THE AXIS

and depending on what you are talking about (pics would help), it very easily could be antennas.

Try to google 'canards'. It might be what you are talking about. Something to do with creating vortex lift and horizontal pitch stabalization.

I know what canards are I think. They are the things at the front on planes like Eurofighter. I will get some pics.

By "belly fins," you mean the compartment at the bottom?


external image

What compartment on the EF?

Those are the air intakes aren't they?

[edit on 12/6/04 by Hyperen]

Here are some pictures of what I mean







These Belly fins are on the F16

Originally posted by Hyperen
What compartment on the EF?

Those are the air intakes aren't they?

[edit on 12/6/04 by Hyperen]

Yep

Also on the SEPECAT Jaguar

Those are there for increased stability, and to, much as the vertical stablizer, keep the aircraft flying straight at high speeds.

Looks similar to the place where the wheels come in and out.
Or it could just help the plane glide smoothly in a straight direction.

Originally posted by Milk
Those are there for increased stability, and to, much as the vertical stablizer, keep the aircraft flying straight at high speeds.

If they are there for that, why use them on just a few planes?

Are the planes they are used on less stable in some way?

Originally posted by Hyperen

Originally posted by Milk
Those are there for increased stability, and to, much as the vertical stablizer, keep the aircraft flying straight at high speeds.

If they are there for that, why use them on just a few planes?

Are the planes they are used on less stable in some way?

Most fighters are designed to be stable in certain directions, and unstable in others. This allows for greater maneuverablilty/better response (less control movement = more movement of the aircraft). Most commercial aircraft are very stable on the other hand. Each aircraft has 3 planes of rotation. Vertical, Lateral, Longitudinal. Depending on the needs of the aircraft and the stability on each of the planes of rotation, it may need more help in one plane of rotation so that it matches the stability of the other planes of rotation, or offsets it so that the aircraft performs the way it is needed to.

Aircraft are also designed for specific purposes. The aircraft you showed may be designed more for straight, level flight (patroling as opposed to actual air fighting), and so it would make more sense for it to be more stable while going straight. Most subsonic aircraft dont need that kind of help, and the tail/vertical stabalizer is plenty big enough to keep it going straight. Remember, the tail on most fighters is pretty small, for various reasons. That fin appears to just be an "extention" of the tail that goes below the aircraft. Of course, unless you contact the manufacturer, who may be under a non disclosure agreement of sorts, it is merely speculation, although, I am quite confident in my assumption.

Hope this helps. If you want more information, U2U me, and I will get you some resources that I believe are free (I had to buy them for my schooling, Im an aircraft mechanic) from the FAA. You may be able to find them on the net somewhere. They are basically just text books, but put out by the FAA/DOT/NTSB.

OK. I'm happy with that explanation so no need for those textbooks. They'd probably be over my head anyway.

Originally posted by Hyperen
They'd probably be over my head anyway.

Doubtful, they are written pretty well. I wasnt implying that my answer is the only answer, and telling you to do reasearch, just thought you might be interested in some follow up reading.

Maybe I will. Do you have the names of those books or any good links?

Here are some that are easier reading, yet informative:

Jeppesen General Textbook

Jeppesen Airframe Textbook

This one is easy reading, but is put out by the FAA (published by Jeppesen).

AC 43.13-1B with change 2A

Then we have the more confusing (slightly) FAA publications which explain in a lot more detail.

AC 65-12A

AC 65-15A

AC 65-9A


On a second look, I dont think they are made available for free from the FAA, but like I said, you may be able to find them in PDF format or something. Any college that has an aviation maintenance program would have them for roughly the same price or cheaper (I paid less for mine). The ACs (Advisory Circulars) have the most accurate information, and it is the information that the FAA uses to develop tests and stuff. Anyhow, I hope this helps at least a little.

Thanks for those. I will look at them in the morning as it is late here and I am tired.

They were added to the Jaguar in order to improve lateral stability as after the prototype had flown it was discovered that the fin was too small to cope on its own. Adding the ventral fins was easier and cheaper than a whole new enlarged vertical fin. Although my 1974 OBA shows the F-16 prototype with them already fitted before the first flight they are much smaller than they are today. On most aircraft with them it is a truism that if they are absent from earlier versions or prototypes of that same aircraft then they have been added as a way of getting some cheap stability. Note, the Tornado, RAF NICKNAME : The Fin, doesnot have or need them. If anything it is 'overfinned' for low level ops in the first place.