Low Altitude Performance

[KJ_Lesnick]

I know general characteristics that favor low altitude high-speed performance are the following

• Low aspect ratio
  
• Heavy wing-loading
  

Are there others?  I ask this because tt doesn't seem to be perfect as the F-4 Phantom didn't have the lightest wing-loading and flew somewhat rough at low altitude.

I'm also curious how certain aircraft flew at low altitude such as the English Electric Lightning as it's aspect ratio was fairly low (2.5), and it's wing area wasn't exactly light either

[eatthis]

the only thing known to have kept up with a lightning in low altitude acceleration tests was the f104! (im sure the tornado is seriously rapid on the deck too along with the f111)
id guess its about small frontal area and LOTS of power (the reason i reckon the tsr2 wouldve been ridiculous at low altitude, even lower frontal area than a vark and nearly twice the power!)

[sandiego89]

general characteristics that favor low altitude high-speed performance are the following

• Low aspect ratio
  
• Heavy wing-loading
  

Are there others?  I ask this because tt doesn't seem to be perfect as the F-4 Phantom didn't have the lightest wing-loading and flew somewhat rough at low altitude.

Perhaps include:

wing area- associated with wing loading, but size itself can be a factor.     
low drag.
high thrust.
airfoil characterisitics- shape, thickness, etc.
Control system
Wing flexibility (not so much a factor for fighters, but is for larger aircraft)
Thermal tolerance.  Inlets and canopy especially can be limitations. 

The Phantom had a good amount of wing area, so this tends to give a bumpy ride down low.  The wing was also designed for carrier ops so had higher lift and all sorts of features to trick the air.  The F-15 is also reported to have a bumpy ride down low.   

[Weaver]

Fatigue life is also a factor. Low-level flight produces frequent vertical accelerations that eat an airframe's fatigue life at an accelerated rate. Aircraft that are designed for low-level work have unusually robust airframes so that they can use their full performance range right down on the deck. Aircraft with lighter, weaker airframes may be faster at high level, but they're frequently fatigue-limited at low level to speeds slower than the specialised ones.

Probalby the most well know example is the MiG-25. At high altitude it could do Mach = 2.8 (with missiles), but at low altitude, it was stress-limited to just Mach = 0.8. A Tornado F.3 that couldn't catch a Foxbat at 50,000 ft could outrun it at 500 feet.

[KJ_Lesnick]

eatthis

the only thing known to have kept up with a lightning in low altitude acceleration tests was the f104!

But was the Lightning smooth down low or rough riding?


sandiego89

wing area- associated with wing loading, but size itself can be a factor.

I never heard anything to suggest that the size itself would be an issue.  If I may ask, where did you get that from?

airfoil characterisitics- shape, thickness, etc.

That makes sense

Wing flexibility (not so much a factor for fighters, but is for larger aircraft)

The flexing would cause the buffeting?

The Phantom had a good amount of wing area, so this tends to give a bumpy ride down low.  The wing was also designed for carrier ops so had higher lift and all sorts of features to trick the air.

I was always under the impression wing-loading and aspect ratio were the primary factors, the T/C of the wing was 6.6 to 3.0 from root to tip.  The shape of the wing (and cambered tops) might have played a role.  Admittedly most of the features for low speed came in the form of blown slats and flaps.

[rickshaw]

The major determinant of how fast a jet can go at low level is the inlet and cockpit canopy temperature limits.  The Buccaneer was reportedly untouchable on the deck, like the F-111, whereas the F-16 and F-15 were hopeless.  Many USAF fighter pilot discovered this to their cost during Red Flag when the strike aircraft would be carving up the landscape and they would be at medium altitude and they would dive to try and catch them.  Before they could even get close, their cockpit was red-lighting on inlet temperature while the Bucc and F-111 just continued on at high speed.  Their inlets were designed to gulp higher density air at near Mach 1 while the F-16/F-15 wasn't.   However, put the Bucc and the F-111 at medium altitude and it would be gasping for air to even break Mach 1.    It was apparently very disconcerting to the fighter pilots, the first time it happened.  It was why the Buccs and RAAF F-111s were always being invited back after the USAF retired their own F-111s.

[sandiego89]

The flexing would cause the buffeting?

[/quote]

Kendra, in strictly non-aeronautical terms, a "bendy" wing can give a smoother ride.  REDUCE the effects.  Especially important for larger airlines.

[KJ_Lesnick]

rickshaw

The major determinant of how fast a jet can go at low level is the inlet and cockpit canopy temperature limits.

But how much heat is produced when flying at Mach 1.3 @ 500 feet?  I figure Mach 2.5 @ 50,000 feet would be way worse...

The Buccaneer was reportedly untouchable on the deck

I thought it was subsonic?


sandiego89

Kendra, in strictly non-aeronautical terms, a "bendy" wing can give a smoother ride.  REDUCE the effects.

Oh

[eatthis]

rickshaw

The major determinant of how fast a jet can go at low level is the inlet and cockpit canopy temperature limits.

But how much heat is produced when flying at Mach 1.3 @ 500 feet?  I figure Mach 2.5 @ 50,000 feet would be way worse...
FAR less air pressure = far less fricition

The Buccaneer was reportedly untouchable on the deck

I thought it was subsonic?

it is subsonic but high subsonic and it can sit at that speed all day at 0 feet

sandiego89

Kendra, in strictly non-aeronautical terms, a "bendy" wing can give a smoother ride.  REDUCE the effects.

Oh

[rickshaw]

rickshaw

The major determinant of how fast a jet can go at low level is the inlet and cockpit canopy temperature limits.

But how much heat is produced when flying at Mach 1.3 @ 500 feet?  I figure Mach 2.5 @ 50,000 feet would be way worse...

Like so many things you are wrong, Kendra/Robyn.   Air density is considerably higher at sea level.  The higher the air density, the greater the friction, the greater the heat generated.

The Buccaneer was reportedly untouchable on the deck

I thought it was subsonic?

High subsonic.  It's entire raison de'entre was to be able to penetrate and attack Soviet naval air defences at low altitude, as an asymmetric response to Soviet battle cruisers.  It could sustain Mach .8-.9 all day.  Hence the claim that they were laid down in shipyards, rather than built on a production line.

[Librarian]

I can distinctly remember my Wife's brother talking about the 'hell' of flying fast and low in his F-15E. Superglue your fillings back in was one term he used.

[PR19_Kit]

  Hence the claim that they were laid down in shipyards, rather than built on a production line.

And machined from solid forgings of HUGE size as well.......... 

[Rheged]

  Hence the claim that they were laid down in shipyards, rather than built on a production line.

And machined from solid forgings of HUGE size as well.......... 

.....so there's no truth in the rumours that Buccaneers  were  quarried from solid unobtainium blocks. 

[Mossie]

The first bit isn't far from the truth at all.  The Brough site is right on the north bank of the Humber and was sited there so they could build floatplanes.  So not quite a shipyard, but things with hulls...

[KJ_Lesnick]

Rickshaw

Like so many things you are wrong, Kendra/Robyn.

Sorry...

High subsonic.

Thought so

It could sustain Mach .8-.9 all day.

Wasn't the A-6 able to do the same?