F-16 vs F/A-18

hummingbird · by **hummingbird** » 07 Feb 2018, 12:13

A typo on my part, I meant max sustainable load factor, which remains at 0.82 Mach at virtually all altitudes. Hardly a coincidence :wink:

And ITR IS connected with the min radius, hence why it's listed as such in the manuals.

The min sustainable radius is larger, being 2,000 ft for the F-14D @ 10 kft for example, and 2,700 ft @ 15 kft, as opposed to the min of 1,500 & 1,800 ft at the same altitudes.

F-16ADF · by **F-16ADF** » 07 Feb 2018, 16:01

Here is another take on the 1981 Su-22 Fitter shootdown from "F-14 Tomcat" by Mike Spick. It says 6G, but as I said, there are now 3 books. And who is right, I don't know.

As far as the negative Ps, I suggest you read JB's post about it (what he posted earlier in this thread) AND this posting, on how to read an EM diagram properly:

viewtopic.php?f=2&t=26829&p=296429#p296429

eloise · by **eloise** » 08 Feb 2018, 00:57

hummingbird wrote:A typo on my part, I meant max sustainable load factor, which remains at 0.82 Mach at virtually all altitudes. Hardly a coincidence

What are you trying to imply?

hummingbird wrote:And ITR IS connected with the min radius, hence why it's listed as such in the manuals.can give it for a lighter F-15A as well at 15,000 ft = 2000 ft.

Alright i will bite, post the whole manual page for F-15A so we can put it to rest.

hummingbird · by **hummingbird** » 08 Feb 2018, 19:38

eloise wrote:What are you trying to imply?

It's the point where the notch in the lift curve happens on every lift curve chart, i.e. the point where the LE slats & TE flaps sieze to function, altnernating between 0.82 M at low alt and 0.85 M at high alt as seen on the sweep program chart.

eloise wrote:Alright i will bite, post the whole manual page for F-15A so we can put it to rest.

Bite? You know what ITR is right? It's the absolute max rate achieveable by riding the CLmax, which you to ride to achieve the absolute min radius. Min sustainable radius is quite different, being the point where the max lift & Ps=0 curve intersect.

F-15A chart, weight approx. 39,000 lbs.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 08 Feb 2018, 20:16

hummingbird wrote:Min sustainable radius is quite different, being the point where the max lift & Ps=0 curve intersect.

F-15A chart, weight approx. 39,000 lbs.

Your posted chart says otherwise.

It is GENERALLY where max lift and Ps=0 intersect assuming they do so at a speed reasonably higher than stall speed.

hummingbird · by **hummingbird** » 09 Feb 2018, 01:19

sprstdlyscottsmn wrote:Your posted chart says otherwise.

It is GENERALLY where max lift and Ps=0 intersect assuming they do so at a speed reasonably higher than stall speed.

Yes you're right, I missed typing the word "usually" at the end, it being the case most of the time with these modern jets (F-16 in particular). At 15,000 ft the min sustained radius of the F-15A is 3,000 ft at ~0.4 M (as seen on the chart) and 2,700 ft for the F-14D and also at ~0.4 M.

gta4 · by **gta4** » 09 Feb 2018, 02:35

In fact, humminbird just proves that F15 has a Cl max of 1.6: look at the turn rate chart. A 39000lb F15 can reach 22deg/sec at 15000ft. This is enough to calculate the Cl max and It is 1.6.

gta4 · by **gta4** » 09 Feb 2018, 02:38

I have a Russian estimation on F15's performance (byTsAGI). It shows a Cl max of 1.08 and a Climb rate of only 280m/sec. Russian always tend to underestimate westerners, you know.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 09 Feb 2018, 14:52

There is a paper out there that not only confirms CLmax of 1.6 but also shows that it occurs at 40 degrees AoA.

garrya · by **garrya** » 10 Feb 2018, 02:59

Quick maths,

Speed of sound at 15000 ft = 322.2 m/s
Air density at 15000 ft = 0.774 kg/m3
Gravity = 0.9066

F-15 speed = 0.39M
F-15 Gload = 3G
Aircraft mass = 39000 lbs = 17690.1 kg
References wing area = 608 ft2 = 56.485 m2

Lift = g-load*mass*9.8066
Lift = 0.5* CL* Velocity^2*air density*reference wing area

CL=

sprstdlyscottsmn wrote:There is a paper out there that not only confirms CLmax of 1.6 but also shows that it occurs at 40 degrees AoA.

https://www.nasa.gov/centers/dryden/pdf ... H-1243.pdf

gta4 has another report from MIT too but i don't have the link

gta4 · by **gta4** » 10 Feb 2018, 06:28

This is Soviet's estimation on F-15's performance in 1980s.
The estimated Cl was only 1.08, and the estimated rate of climb was only 300m/s.

Soviet has the tendency to underestimate westerners. I have numerous examples on that.

gta4 · by **gta4** » 10 Feb 2018, 06:30

And we have an official document showing that F-22 can hit Cl_max = 1.9-2.1

eloise · by **eloise** » 11 Feb 2018, 04:45

hummingbird wrote:max sustainable load factor, which remains at 0.82 Mach at virtually all altitudes. Hardly a coincidence. It's the point where the notch in the lift curve happens on every lift curve chart, i.e. the point where the LE slats & TE flaps sieze to function, altnernating between 0.82 M at low alt and 0.85 M at high alt as seen on the sweep program chart.

Sustainable load factor is also a function of thrust, and engine thrust change with speed so you can't deduce the flaps deactivate point from that. The Ps= 0 has a gradual trend too.
Furthermore, why do you keep invent your own flap deployment regime when both interlock point and envelope are illustrated very clear in the manual?.

hummingbird wrote:F-15A chart, weight approx. 39,000 lbs.

That chart didn't come from F-15 manual either why should it be trusted more than NASA who tested on an actual F-15 with modern equipment

pmi · by **pmi** » 11 Feb 2018, 13:26

f-16adf wrote:They consolidated, because of the end of the Cold War. Resulting from the subsequent defense draw down. So technically their survival depended on a "fatter" defense budget. With the recession of 1991 (anybody remember that?) and the last few years of Bush 41 and later Bill Clinton (the guy who said "I didn't create a 4 trillion dollar national debt") everything contracted.

The 'peace dividend' accelerated the consolidation but it was a process that was well underway.

Republic, Convair, North American, Vought, the McDonnell-Douglas merger etc.

Jet aircraft had become a mature technology. How many fighter types was the USAF fielding in 1955, 1960, 1970, 1980 & 1990 (just before the fall of the Soviets)? Those numbers were dropping consistently & the length of service for front line types was consistently increasing.

The US was moving to a smaller number of individual platforms long before the end of the cold war & some of those companies were going away regardless of what happened post 1992. But you know...thanks Obama!

Oh and an appeal to authority based on a few classes you took as an undergrad? Seriously?

F-16ADF · by **F-16ADF** » 11 Feb 2018, 13:57

First, I never said "all".

Second, never blamed Obama, entirely for defense. I do blame him for telling us that the ACA would lower yearly premiums by $2,400, which turned out to be false. Same for "if you like your doctor you can keep him" another tall tale. I know it's hard to grasp, but Obama was never blessed with the charism of infallibility.

Defense per capita GDP, was going down in the 1990's:

"Defense spending stood at 6.8 percent of GDP at the height of the Reagan defense buildup. But, beginning even before the breakup of the Soviet Union it began a decline, reaching below 6 percent in 1990, below 4 percent in 1996 and bottoming out at 3.5 percent of GDP in 2001, about half the level of 1985."

Hmm, ....I never knew 4% is greater than 6.8%