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Newbie Joined: Jul 06, 2008 Posts: 9 Status: Offline

A recent airshow was my first time seeing the Raptor in person, and I took a lot of photos. As a designer, (CAD and RC models, not actual aircraft) it is a thing of beauty.

It caught me by surprise to find the rather large gap at the base of each vertical fin, where the rear section meets the fuselage. Does anyone know why that is? (Seems like it would create a lot of drag.)

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Can you give me a link to a photo? I've got alot of pics of the Raptor but I'm not quite sure what you mean.

Is this the gap you speak of? (kind of hard to see but it's got a red circle around it)

Newbie Joined: Jul 06, 2008 Posts: 9 Status: Offline

That's it. (base of both vertical fins)

I'm sure that's not an "manufacturing error", since all the Raptor photos I've seen have it, but I don't recall seeing that kind of thing on any modern aircraft.

Elite Joined: Oct 30, 2006 Posts: 627 Status: Offline

I’m not an aerodynamicist, but since modern day fighters are starting to to look like F-1 cars with the bulges and gaps. I would have to say the gap is a means of providing laminar airflow to help cool that complex engine nozzle system.

Elite Joined: Jul 22, 2005 Posts: 964 Status: Offline

All it is really is a fairing and isn't load bearing (other than from aero forces) so there's no need for it to be attached at the bottom which simplifies manufacturing.

Evidently it doesn't affect RCS. That's incredible, considering that I read somewhere that a loose nut was the difference between an invisible F-117 and one that had dangerous RCS flareups.

Elite Joined: Oct 30, 2006 Posts: 627 Status: Offline

Look at the streaks on the airframe coming from the gap (leaky something) streaks go straight from the gap to the nozzle showing the airflow.

Alpha Romero did this with the DTM upswept pipes you see on kids Hondas nowadays.

The hot air from the exhaust flowed up behind the rear wing causing more cold air to fall on the wing creating more down force.

Bernoulli’s Principal I believe.

Elite Joined: Jul 22, 2005 Posts: 964 Status: Offline

Tinito_16 wrote:

Evidently it doesn't affect RCS. That's incredible, considering that I read somewhere that a loose nut was the difference between an invisible F-117 and one that had dangerous RCS flareups.

It's all RAM/RAS there. The piece you're thinking of was a metal screw on Have Blue.

Another thing I notice is right angles... Isn't that unstealthy?

Elite Joined: Jul 22, 2005 Posts: 964 Status: Offline

Tinito_16 wrote:

Another thing I notice is right angles... Isn't that unstealthy?

If it were a reflector. It's not.

sferrin wrote:

Tinito_16 wrote:

Another thing I notice is right angles... Isn't that unstealthy?

If it were a reflector. It's not.

Well but doesn't the aircraft itself reflect some radar waves? Or did they figure out how to make an object steathy regardless of it's shape?

This is in no way a doubt about the Raptor's stealth, I just found it interesting that there seem to be right angles in some of the panels on the back end of the plane.

Elite Joined: Dec 14, 2005 Posts: 687 Status: Offline

Just like tanks where the armor is thinnest on the rear; in stealth aircraft the rear has typically been the most visible on radar. (Especially since the F119s have augmentors, similar to the F101 and RCS of the Bone.) Trunking or masking inside the inlets works up front, but you can't do that in an afterburner!

I'd venture to guess that the augmentor ducts/flame-holders reflect more radar than those little 90* panel lines between the airframe and engine nozzle.

My Two Cents

TEG

Could be a bleed air section for the engine bay to prevent fuel vapor build up. F-16's have them on both sides inboard of the speed brakes. Seems logical at least and would explain the build-up of fluids in that area. Even though there is a gap, there does seem to be some good shaping there. Also, just look above to the rudders. The gap is very similar. Smile

Veteran Joined: May 26, 2008 Posts: 286 Status: Offline

Tinito_16 wrote:

Another thing I notice is right angles... Isn't that unstealthy?

Dude, you should write LM a letter. They need to know about your discovery just as soon as possible! They must have forgotten to keep their rear end shapely!

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Gap at bottom of vertical fin rear