Flight characteristics of the F-4 Phantom

[Skuzzy]

Every book I can put my hands on defines "delta" wing as a shape with no mention of flight characteristics.  I am talking about the definition.

[Vraciu]

Every book I can put my hands on defines "delta" wing as a shape with no mention of flight characteristics.  I am talking about the definition.

I see.  Yes that would be accurate.

[PR3D4TOR]

Not true.  Pure delta wings are notorious for high drag particularly at lower speeds.   This is why they're not used.

What is a "pure delta" and when did anyone but you use that definition in this thread? And what do you mean "they're not used?"

[Shuffler]

I make pure delta wing paper planes. They have blue lines... is that still a delta?

[Puma44]

The conformal tanks increased pitch authority so we could get a couple more degrees AOA if we wanted it.  High drag up at that high AOA made it of limited usefulness except maybe when forced into in a knife fight with a superior performing fighter, in which case the extra pitch authority could be used to try to get a first-shot advantage.  That could force the other plane to defend instead of pressing its offensive advantage.  That could permit a first shot and a separation attempt in some circumstances.  However, if the shot missed or the other pilot didn't flinch, it would leave the F-15E very slow and vulnerable.

The flight control stability rules also had to be modified slightly from the F-15C/D since the CFTs and nav/targeting pods made the F-15E slightly more prone to spins.  The modifications made the plane a touch less agile in some areas, but you could still fool the stability system to get it to flip-flop around. Again, this was of limited utility due to lower thrust/weight and extra drag compared to other fighters but could sometimes be useful in a last-ditch scenario or if flying against clearly inferior opponent.

Also, the CFTs and other added airframe weight increased pitch momentum and inertia.  So while pitch authority was greater, pitch rate and response was slightly slower sometimes.  Again, there were ways to exploit this and make the plane do some unexpected things, but the tactical usefulness of this is limited.

Thanks!  Always wondered what the effect was re the conformals.

[Puma44]

For what it's worth, in the 106 community, it was commonly referred to as the "Six" or "Iron Triangle".  I guess "Iron Delta" just didn't have the same ring to it.  Did it make a difference calling it a delta or a triangle?  Not a bit.  It still burner climbed to 45,000 feet and sped along like a scalded ape!

Don't recall anyone ever going at it over the popular vs actual description of the wing shape. 

[PR3D4TOR]

The 106 was such a beautiful plane. I wish there was more info on how it stacked up against its contemporaries. Unfortunately it being mostly limited to the continental US and serving in a strict interceptor role makes that difficult.

[Puma44]

Yes it was.  The Lamborghini of the fighter world.  The F-4, more like the Hummer.

[Puma44]

The "Iron Triangle"

[eagl]

Oh, and all the aviation articles I can find about the F15 suggests it is a modified cropped delta shape with a leading-edge sweepback angle of 45°.  Does that sound about right eagl?

Yes.  And the flight characteristics do indeed support the broad general characterization of the wing planform shape as a modified cropped delta.

[eagl]

Not true.  Pure delta wings are notorious for high drag particularly at lower speeds.   This is why they're not used. 

"not used" = false.  Eurofighter, Rafale, Gripen all use a delta wing plus canard.

[Vraciu]

"not used" = false.  Eurofighter, Rafale, Gripen all use a delta wing plus canard.

I have repeatedly stated "with the exception of the eurocanards".

And these are still not true deltas, but they're as close as we will see because of the inherent disadvantages of deltas overall.

[Vraciu]

Yes.  And the flight characteristics do indeed support the broad general characterization of the wing planform shape as a modified cropped delta.

Incorrect.   It is a cropped swept wing--by your logic a 757 is a modified cropped delta.


In any case, it is not a delta.   Period.   Read your own words.
 

[eagl]

Every book I can put my hands on defines "delta" wing as a shape with no mention of flight characteristics.  I am talking about the definition.

My aero engineering class at the USAF academy, and later on courses during fighter pilot training, all contained specific behavioral characteristics that were generally common or similar among pretty much all delta wing designs.  The term "delta" wing was applied to any wing ROUGHLY triangular in shape, although a great number of variations such as cranked arrow, ogive delta, clipped delta, etc. were accepted and considered as "delta wings" in general because their performance characteristics were so similar.

Specifically noteworthy were descriptions of how in all of the delta shape variations, the lift generation would SMOOTHLY transition from traditional "airfoil" lift/drag profiles to a profile driven by strong vortices generated from the wing root as AOA increased.  While this significantly increased drag, it also dramatically flattened the lift curve, nearly eliminating traditional stalling behavior.  While the drag increase could be partially mitigated by features such as a drooped leading edge, combining a delta wing with a traditional horizontal stabilator or canards (lifting, fixed, or free-floating) provides a huge increase in performance and maneuverability.  Still, even with a tail or canard, all "delta" style wings (modified, cranked, clipped, whatever) will feature a flat lift curve due to the vortices generated at the wing root.

This is a direct contrast to "swept" wings, which have completely different characteristics at high AOA such as a tendency to tip stall and a much more abrupt "stall" drop-off in lift as AOA is increased.

As for the utterly ignorant statement that a delta wing isn't useful because it has too much drag, take a good look at the B-58 hustler...  That's one FAST airplane created with low drag in mind, very well designed for its purpose, and proof positive that a delta wing is sometimes the best (or only) way to achieve performance requirements.  That's just as true today as it was 50 years ago.

[Vraciu]

They have low drag in cruise.   They have high drag in maneuver and when slow. 

Yello?  Yello?   Is this thing on?   *tap* *tap* *tap* 

The Concorde and Hustler were designed for missions that delta wings are good for--high speed level flight.   They're not dogfighters and they chew up runway like there is no tomorrow.   

Deltas give you one good hard turn and that's it because they are draggy as hell.    They're not optimal for sustained maneuvering compared to other designs.