F-16C, F-16E vs F-14D

[eloise]

one F-4 pilot backflip to make Mig-17 overshot. I will try to find it.

This documentary?

yes that it

[garrya]

People tend to forget one thing, the F-14 with the wings forward at 20-22 degrees is a high aspect ratio jet (the wings are nearly straight). That is why is turns pretty good at low speeds. Ironically, the A-10 has a high aspect ratio wing, and at 270-300 KIAS can out radius any of the teen series fighters. But as an A-10 pilot once told me, who wants to be turning and bleeding airspeed at 270 KIAS in a dogfight?

I found the chart for A-10

and one for F-86, Mig-15 (re-draw from Boyd chart)

[basher54321]

Personally, i haven't heard about the story of F-14 pilot who pulls 14G but it wouldn't surprise me, I heard that some pilots did it in IAI Kfir and Mig-21 or F-4 as well. However, in my opinion, limits are there for safety, it was carefully calculated by Grumman based on the airframe and how they are used, some pilots are very lucky to pull off these crazy stunts and get away with it but that isn't recommended for all pilots.
If we go for a comparison without any G limit then I think we also need the sustain G diagram for F-15, F-16 with V-max switch engaged (102% engine thrust instead of 97%). There are many restricted maneuvers that more impressive than over G the aircraft. In one documentary that was posted here, one F-4 pilot backflip to make Mig-17 overshot. I will try to find it.

Where did you get the ultimate load limit for F-14, F-15 and F-16?

The standard structural margin is around 150% apparently (ref JWill)- so e.g. the USAF wanted a 9G 8000 hour airframe so this would have been tested on the F-16 under worse conditions to around 13.5G as I understand it.

I don't have any good sources on the F-14 design other than it had a 6000 hour requirement at either 7.5G or 6.5G - however if there is something out there confirming the original F-14 requirements that would clear that up. (Wasn't the SH a 6000 hr 7.5G carrier design?)




One aspect is definitely safety - departing an aircraft has been used tactically to gain an advantage since the beginning - there are a few examples from WW2 and the way that F-4 looks to flip over looks more impressive than the AI Jet fighter in the film Stealth!

Generally these few pilots have been A. Very Good and B. Very lucky.

What would be useful is a list of F-4s that were lost or put themselves into serious danger over Vietnam due to departure because from what I have read it was more than quite a few - and the list no doubt includes experienced pilots - so the one impressive backflip in all those years of war starts to look slightly unimpressive.

As well as safety the limiters allow any pilot to max perform the jet without being Chuck Yeager and you will note pretty much every Jet since the F-16 came along has had them in one form or another.

There is still the safety issue of being prevented from pulling up and hitting the ground. Some jets allow the pilot to override the limiters for emergency situations and some do not apparently - take for example a Mirage 2000 about to hit the ground at 300kts - the pilot can over G the jet but here it is probably AoA limited and if you went through the AoA limiter it could depart and crash anyway in theory.

You wonder if modern simulators have allowed pilots to get a better sense of how much room they have at low altitudes and depend more on that! The Auto GCAS sounds a good thing don't know if the pilot can disable that must be more info on it.

[F-16ADF]

My brother's squadron operates the A-10C. It literally can turn on a dime, yet generally has terrible sustainability.
Many of those air-frames have over 10k hours (time to go to the boneyard). Quite a few have tail code FY that date from the late 1970's. The teen series were great in their day. But by 2017 they need to go. Just too old, large RCS, and maintenance intensive.

[eloise]

My brother's squadron operates the A-10C. It literally can turn on a dime, yet generally has terrible sustainability.
Many of those air-frames have over 10k hours (time to go to the boneyard). Quite a few have tail code FY that date from the late 1970's. The teen series were great in their day. But by 2017 they need to go. Just too old, large RCS, and maintenance intensive.

A cannon dogfight between A-10 and the teen series will be an interesting one, from what i have heard A-10 airframe is protected up to 23 mm rounds so the teen series pilots will need some luck.

You can see retracted and extended envelope of maneuver flaps from graph below:

At sea level, maneuver flaps are fully extended below Mach 0.51, partially retracted from Mach 0.51 till Mach 0.58 and fully retracted at higher speed
At 35K ft, maneuver flaps are fully extended until Mach 0.86, partially retracted from Mach 0.86 till Mach 0.87 and fully retracted at higher speed
Difference of approximately 0.3 Mach between sea level and 35K ft.
P/S: Come to think of this, since maneuver flaps start to be retracted at some specific wing sweep, does this mean wing fold back sooner at sea level than at 14k ft?

Good observation

[F-16ADF]

Maybe in a 1 v 1 a very skilled A-10 pilot could have some luck on the initial pass??

I think in a 2 v 2 or many v many the A-10's would get murdered. Their opponents would just use the vertical, and wait for them to bleed down. Just my opinion.

[outlaw162]

One aspect is definitely safety - departing an aircraft has been used tactically to gain an advantage since the beginning - there are a few examples from WW2 and the way that F-4 looks to flip over looks more impressive than the AI Jet fighter in the film Stealth!

basher,

Our reserve unit flew F-4s for 8 years, and during that time we only lost 2 Phantoms......both loss of control during 2v2 DACT against, of all airplanes, the lowly A-7. Both guys tried the drag chute before ejecting. Fortunately both crews were able to 'take the bus home' although one WSO sustained a broken arm. (1 kill for the Tulsa Guard, 1 kill for the ABQ Guard ) I flew remedial rides with both guys so they could demonstrate how much more conservative they had become. One of the pilots told the accident board, 'there were only two reasons for this accident' and then held up his left and right hands.

I 'spect the CGI rendering of that 'flip' is optimistic and that it was possibly a rapid loaded rudder reversal that reached a fairly high pitch attitude and was continued all the way underneath, maybe by momentum and not by choice. From the cockpit, violent departures can of course be disorienting, and a cockpit's eye description may not coincide exactly with the description offered from another aircraft.

In 1978, the ANG started conducting formal A-7 departure training (both high and low energy departures) based on the program the USN passed on to us. USAF did not have 'formal' departure training in their syllabus at the time. We only had single-seat A-7Ds at the time (no Ks) and all training was conducted with the instructor in the chase position. We did this for folks from every A-7D Guard unit including the PRANG at San Juan. Often the description the student would give of what the aircraft did when it departed did not always match what you saw from outside.

The A-7 recovery was 'hands off' and the recovery rate was 100% and totally predictable. A-7 always recovered......

.....which points to why the F-4 training units did not run formal departure training.

[basher54321]

Thanks outlaw - I have seen another comment along the lines of them using a bit of artistic impression in that recreation

Good job those guys got out although I hope the court had a sense of humour!

[madrat]

Protection from 23MM proximity fused rounds is very different from 20MM AP and incendiary rounds. And the engine can't really digest any of them.

[outlaw162]

Good job those guys got out although I hope the court had a sense of humour!

basher,

at that time, there was either some justice in mil aviation or the regulars didn't really care what you did with the old junk.....the guy that spilled his guts was back in the front seat very shortly, while the other, less forthcoming, guy spent some time in the back seat before getting back in front.

in any case they both eventually ended up in F-16s.....where theoretically they couldn't hurt themselves....at least not in this way.

edit: (BTW, you could go over the top in an F-4 unloaded at very slow speed and have it fall on its back, but it took a bit more vertical room than depicted in the CGI.)

[sprstdlyscottsmn]

And the protection is only against single round destruction of the aircraft. There was only one location found where a single 23mm would down the plane (Canopy? Tail where H-Stab spar is?). Hit it with a few dozen and all bets are off.

[hummingbird]

The widest point is around 0.1 Mach, I think it makes a noticeable difference for sustain turn rate.

Yet it doesn't. Look at the charts for pete's sake, the lift curve doesn't experience a notch until at 0.85 mach, even at below 14 kft. You can check the doghouse plot if in doubt.

Also note that while the wing sweep starts earlier at lower alt, the point where the LE slats stop operating is STILL at 0.85 mach irrespective of alt.

Wingsweep.png

@ 0.7 Mach @ altitude > 20k ft, the wing sweep is at 21° auxiliary flaps are extended, below 14k ft, the wing sweep is at 31-33°auxiliary flaps are retracted
@ 0.85 Mach @ altitude > 20k ft, the wing sweep is at 47.5°main flaps are extended, below 14k ft, the wing sweep is at 53-55° main flaps are retracted.

nvm the auxilliary flaps, they're used mainly for landing, the main flaps still work until 50.5 deg sweep, furthermore it's the LE slats that really make a difference and they work up until mach 0.85 and 55 deg sweep.

btw I probably should remind you that I'm the one who've provided all these fine charts, garrya got them from me.

The chart provided by Garry shows the L/D ratio reduced as wings sweep back.

Ofcourse, that's a given at certain speeds as the AR goes down, but check out the points of intersection, do you understand these? If so, what's your point?

The calculation provided by sprstdlyscottsmn shows CLmax reduced as well

Not sure what you want someone's seperate calculation for when you have actual flight test data right infront of your nose?

Want to know the F-14's min radius, max rate or Clmax, simply look at the charts. Simple as that.

I also think F-15 can excess F-14 instantaneous turn rate.
Lift = 1/2 * air density *Reference Wing Area * Lift Coefficient * airspeed ^2 and Lift = aircraft weight * amount of G aircraft pulls;

It can't, as so thuroughly proven by the charts.

Wing loading = Aircraft Weight / Reference wing area ; or we can say: aircraft weight = wing loading * wing area;
For a level flight condition; if we are to put this into lift formula it becomes;
Wing loading * aircraft G load = 1/2 * air density * Lift coefficient * airspeed^2
In other words, Lower wing loading=> smaller Cl needed.

F-15 wing loading: 41,000/608 = 67.4 lb/ft²
F-14 wing loading: 55,620/565 = 98.4 lb/ft²
F-14 has 46% higher wing loading so for an equivalent instantaneous G, F-14's CLmax need to be bigger than F-15's CLmax by 46%

Problem is you're using reference wing area and not effective lifting area, thus you're arriving at an inaccurate conclusion. The F-14's actual effective lifting area is way higher than the reference wing area:



In short the F-14 doesn't need as high a CLmax as you'd think to equal the F-15 in G's.

NASA test shows F-15's CLmax = 1.6 at AoA 40° so F-14 needs CLmax = 2.33 for equal G, higher than what we calculated for F-14 from the lift chart.

cft.jpg

F15 Cl Cy.jpg

[/quote]

See above.

PS: there's a reason the F-14's features a lower stalling speed than the F-15, so what does that tell you about the CLmax & wing loading ?

PS PS: I'm piss drunk, but couldn't refrain from answering anyway, so please excuse any misspellings

[eloise]

Yet it doesn't. Look at the charts for pete's sake, the lift curve doesn't experience a notch until at 0.85 mach, even at below 14 kft. You can check the doghouse plot if in doubt.
Also note that while the wing sweep starts earlier at lower alt, the point where the LE slats stop operating is STILL at 0.85 mach irrespective of alt.nvm the auxilliary flaps, they're used mainly for landing, the main flaps still work until 50.5 deg sweep, furthermore it's the LE slats that really make a difference and they work up until mach 0.85 and 55 deg sweep.

The lift curve @35k ft experience a big notch @ 0.85M, this is the point where wing sweep back and manuever flaps are locked according to diagrams



But if you look at the maneuver devices charts, when you reduce the altitude, clearly the wing sweep back sooner, maneuver flaps are also retracted at slower velocity, up to 0.3M different between sea level and 35k ft



Garry brought up good point when he said flaps are retracted at certain wing sweep angle, but they retracted sooner at sea level than at 14k ft, there is a big possibility that wing sweep backward even sooner at sea level.

Slats are the only things seem to be retracted at the same speed irrespective of alt, but maneuver flaps and wing sweep are also vital to generate lift. In short, you cannot say the lift curve is the same between 35kft and lower altitude.

Not sure what you want someone's seperate calculation for when you have actual flight test data right infront of your nose?
Want to know the F-14's min radius, max rate or Clmax, simply look at the charts. Simple as that.

The flight test data doesn't give me lines above 6.5G curve, so to extrapolate over G values like you wanted i need to find CLmax.

It can't, as so thuroughly proven by the charts.

What charts are you talking about? There isn't any instantaneous turn charts for F-15C. If you are referring to the sustain turn rate charts then it comes at no surprise that F-14 can sustain higher G values @ slow speed because its high AR wing has steeper lift curve than F-15's wing.

[eloise]

Problem is you're using reference wing area and not effective lifting area, thus you're arriving at an inaccurate conclusion. The F-14's actual effective lifting area is way higher than the reference wing area:

In short the F-14 doesn't need as high a CLmax as you'd think to equal the F-15 in G's.

When you use lift equation to calculate lift, you need to use reference wing area. The differences in lift generated due to body lift, flaps, slats, aspect ratio... are included in CL value. That how you know which airframe is more efficient.
If you use effective lifting area instead and substitute it in the lift chart, you will end up with a very small CLmax for F-14. Don't believe me? Run the Math yourself.

there's a reason the F-14's features a lower stalling speed than the F-15, so what does that tell you about the CLmax & wing loading ?

F-15 @ 42,000 lbs (about 1000 lbs heavier) @35k ft @ speed = Mach 0.35, has enough lift for 1G with CLmax (can't maintain it due to high AoA)


F-14 @55,620 lbs @35k ft also needs 0.35M for 1G


Anyway, landing speed of F-15 is much higher than F-14 because the landing approach AoA is 20-22° instead of 40° AoA where F-15 reaches CLmax according to NASA flight tests data.

[garrya]

btw I probably should remind you that I'm the one who've provided all these fine charts, garrya got them from me

You gave me 10K ft turn chart, 35K ft lift chart and slat chart. Whereas wing sweep charts, flap chart and L/D are from the manual i downloaded.

Problem is you're using reference wing area and not effective lifting area, thus you're arriving at an inaccurate conclusion

He isn't wrong. Reference wing area serves as a reference point, body lift is represented by CL
http://www.aerospaceweb.org/question/ae ... 0078.shtml