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Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 22 Jun 2020, 22:05
by quicksilver
This for comparison —

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 23 Jun 2020, 00:29
by sprstdlyscottsmn
It already reduced subsonic drag. I can only think of three reasons to change it to that shape. Weight, CLmax, Wave Drag. It sure won't be cost.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 23 Jun 2020, 00:45
by quicksilver
Trades, trades, trades.

Am wondering what the (apparent) reduction in fuel capacity vs reduction in DI buys them...

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 23 Jun 2020, 00:46
by marauder2048
sprstdlyscottsmn wrote:It already reduced subsonic drag. I can only think of three reasons to change it to that shape. Weight, CLmax, Wave Drag. It sure won't be cost.


2nd crew-member egress?

It's often non-obvious, non-aero things: for the F-16, the redesign from the prototype tanks was motivated by the
damage to the tank from the cannon fire blast wave.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 23 Jun 2020, 02:46
by quicksilver
marauder2048 wrote:
sprstdlyscottsmn wrote:It already reduced subsonic drag. I can only think of three reasons to change it to that shape. Weight, CLmax, Wave Drag. It sure won't be cost.


2nd crew-member egress?

It's often non-obvious, non-aero things: for the F-16, the redesign from the prototype tanks was motivated by the
damage to the tank from the cannon fire blast wave.


The primary problem was a significant issue with loads/structures unrelated to the gun.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 23 Jun 2020, 18:55
by marauder2048
quicksilver wrote:
marauder2048 wrote:
sprstdlyscottsmn wrote:It already reduced subsonic drag. I can only think of three reasons to change it to that shape. Weight, CLmax, Wave Drag. It sure won't be cost.


2nd crew-member egress?

It's often non-obvious, non-aero things: for the F-16, the redesign from the prototype tanks was motivated by the
damage to the tank from the cannon fire blast wave.


The primary problem was a significant issue with loads/structures unrelated to the gun.


Could be my misreading; I read the gun blast issue as causal in the redesign.

cft-f16-blast-1.png

cft-gun-blast-2.png

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 24 Jun 2020, 01:19
by quicksilver
Read carefully the first sentence of the first paragraph and the first two sentences of the second paragraph.

That doc does not address it but there were unanticipated loads issues with the first design, and thus the design necessarily evolved as a consequence. As it evolved, gun issues emerged — as outlined in your reference.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 24 Jun 2020, 02:40
by marauder2048
quicksilver wrote:Read carefully the first sentence of the first paragraph and the first two sentences of the second paragraph.

That doc does not address it but there were unanticipated loads issues with the first design, and thus the design necessarily evolved as a consequence. As it evolved, gun issues emerged — as outlined in your reference.


Interesting. Just re-read the related AIAA paper:

"Optimizing The F-16 Conformal Fuel Tank Using Design And Experiments"

and there is a rather buried reference to a loads assessment methodology
which drove CTF design and which is "(not discussed in this paper)"

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 27 Jun 2020, 17:35
by mixelflick
Interesting how the CFT's on the F-16 and 18 don't hurt its performance much, whereas the F-15's it does. Actually, I think I read they're not so bad subsonic, but added a lot more drag in the supersonic part of the envelope.

Of course, the F-16's and 18's CFT's came many years (decades) later..

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 27 Jun 2020, 19:00
by wrightwing
mixelflick wrote:Interesting how the CFT's on the F-16 and 18 don't hurt its performance much, whereas the F-15's it does. Actually, I think I read they're not so bad subsonic, but added a lot more drag in the supersonic part of the envelope.

Of course, the F-16's and 18's CFT's came many years (decades) later..

The F-16/18s CFTs are clean. The F-15Es CFTs have weapon station attachments. The F-15C CFTs aren't nearly as draggy.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 29 Jun 2020, 19:04
by marauder2048
mixelflick wrote:Interesting how the CFT's on the F-16 and 18 don't hurt its performance much, whereas the F-15's it does. Actually, I think I read they're not so bad subsonic, but added a lot more drag in the supersonic part of the envelope.

Of course, the F-16's and 18's CFT's came many years (decades) later..


The Indian trials told a different story for the F-16s wearing conformals.
But I tend to think the increase in weapons carriage outweighs perf losses.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 01 Jul 2020, 15:47
by mixelflick
Oh?

How/where did you hear about those results in Indian trials?? Curious..

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 01 Jul 2020, 18:50
by marauder2048
mixelflick wrote:Oh?

How/where did you hear about those results in Indian trials?? Curious..


mixelflick wrote:Oh?

How/where did you hear about those results in Indian trials?? Curious..


Some of the performance evaluations were leaked to one of those Indian newspapers in a manner
similar to the leaked Swiss Gripen trials but less formal.

I can try to dig it up.

It's not so surprising; the CFTs are a pretty delicate balance between AoA, transonic performance
and fuel capacity. If they were really performance-tradeoff free, the original OML would have incorporated
them directly.

I think it was Hillaker who said (in terms) once you start seeing thing added above the wings the design is dead.

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 02 Jul 2020, 00:07
by geforcerfx
marauder2048 wrote:I think it was Hillaker who said (in terms) once you start seeing thing added above the wings the design is dead.

Could be Worse
Image

Re: Commander Naval Air Forces wants more F/A-18s

Unread postPosted: 02 Jul 2020, 01:07
by marauder2048
*shudder*