Minimum and maximum speed for 9G in A-A configuration inF16A

Operating an F-16 on the ground or in the air - from the engine start sequence, over replacing a wing, to aerial refueling procedures
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saberrider

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Unread post22 Oct 2016, 06:01

Minimum and maximum speed for 9G in A-A configuration?
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basher54321

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Unread post22 Oct 2016, 12:52

They are variable with weight and altitude.
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saberrider

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Unread post22 Oct 2016, 13:20

basher54321 wrote:They are variable with weight and altitude.
So only at a given alt. and speed you are able to reach 9G, in a level turn. Thanks for your help.
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Unread post22 Oct 2016, 13:31

saberrider wrote: So only at a given alt. and speed you are able to reach 9G, in a level turn. Thanks for your help.

Yes - typically applies to all aircraft - that is why you see things done with charts (don't forget weight :wink: )
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saberrider

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Unread post22 Oct 2016, 13:42

basher54321 wrote:
saberrider wrote: So only at a given alt. and speed you are able to reach 9G, in a level turn. Thanks for your help.

Yes - typically applies to all aircraft - that is why you see things done with charts (don't forget weight :wink: )

Weight it will change in flight,due fuel consumption , CAT is I or III ,A to A or A to G ,but in A to A I thought 9 G is attainable no matter the weight and sometime exceeded if you are hard whit the plane.
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Unread post22 Oct 2016, 14:33

The flight manuals are available for download.
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Unread post22 Oct 2016, 17:12

In air to air without external tanks, there is no minimum speed limit for 9g, but there is an angle of attack limit, 15 degrees, The g-AoA limiter is automatic, so the pilot does not have to monitor either g or AoA in a symmetric maneuver (no roll rate). As others have said, weight, speed, and altitude determine the minimum speed at which the airplane can reach 9g without exceeding 15 deg AoA. There was also the question of maximum speed for 9g. In fact there is no upper speed limit for 9g. The airplane speed limit is 800 kcas to 2.0 mach

For air to air with external tanks, the symmetric g limit is 6.5 with any fuel in the externals, 9 with empty externals. The AoA limit for 9g is still 15 degrees. Again, there is no upper speed limit for 6.5 or 9g, but the airplane speed limit is 600 kcas to 1.6 mach. With fuel in the tanks, the g-AoA limiter will not prevent exceeding 6.5g, so the pilot has to monitor g to avoid exceeding the limit. In case you are wondering why there is no intermediate g limit for partial external fuel, the tanks are not gauged, so there is no way to know how much fuel is in the tanks, except for a full/empty indicator.

You might think a full external tank would be the most critical condition for the tank loads, but that is not always true. The tank has three compartments, forward, center, aft, and the burn sequence is center, aft, forward. The max pitch moment on the tank is with forward compartment full, center and aft empty. That's why it is important to keep the g limit at 6.5 until the tank is empty. The burn sequence is set by flutter considerations, because flutter is suppressed by forward cg in external stores. That's why external store and engine pylons are generally swept forward from wings.
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sferrin

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Unread post23 Oct 2016, 05:32

Does it have enough control authority to do a 9G turn at Mach 2? The Tomcat had to have those glove vanes for that. (Or is that the difference between a statically stable aircraft and a less stable, fly-by-wire aircraft?)
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saberrider

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Unread post23 Oct 2016, 06:10

sferrin wrote:Does it have enough control authority to do a 9G turn at Mach 2? The Tomcat had to have those glove vanes for that. (Or is that the difference between a statically stable aircraft and a less stable, fly-by-wire aircraft?)

AFAIK those glove vanes are to control pitch down momentum in supersonic in level flight .
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Unread post23 Oct 2016, 08:21

sferrin wrote:Does it have enough control authority to do a 9G turn at Mach 2? The Tomcat had to have those glove vanes for that. (Or is that the difference between a statically stable aircraft and a less stable, fly-by-wire aircraft?)


I read that the glove vanes weren't supposed to be used in high-G situations. The reason they were disabled by maintenance crews (and eventually deleted altogether) was pilots using them in high-G situations and breaking them too often. Turns out the small subset of the flight envelope they helped out with wasn't worth the hassle.
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Unread post23 Oct 2016, 10:55

sferrin wrote:Does it have enough control authority to do a 9G turn at Mach 2? The Tomcat had to have those glove vanes for that. (Or is that the difference between a statically stable aircraft and a less stable, fly-by-wire aircraft?)



F-16s can pull 9G at M2 on paper.



F-14 glove vanes - sorry didn't note the source

Notice the emphasis of destabilizing to reduce the tail download - I don't have the A manual but for the B/D the Centre of Gravity shifts at 4 different stages of flight and over M1.5 it is describes as being neutral not stable - I don't know if that applied to the A and you got the extra effect of the Glove Vales on top of that.

Tomcat glove vane.jpg
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johnwill

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Unread post23 Oct 2016, 16:34

sferrin wrote:Does it have enough control authority to do a 9G turn at Mach 2? The Tomcat had to have those glove vanes for that. (Or is that the difference between a statically stable aircraft and a less stable, fly-by-wire aircraft?)


During the 1977 original flight test, the highest mach number for a high g test was 1.60 at 30,000 ft. The test condition was 7.2g as part of the 80% load survey. When extrapolated to 9g, the data showed 9g would have been available. There was no reason to try 7.2g at 2.0/40k since the airplane would be at a very low weight, the structural loads would have been low.

You are correct to question the control authority at high mach numbers, as required tail deflections (not structural load) will approach max capability. So, at 2.0/40k, the g limit is 9, but it might not be attainable due to tail deflection limits. I seriously doubt if anyone has ever tried it. Another problem is maintaining 2.0 mach as the g increases from 1 to 9. The best way to try is to start from max mach at 50k and split-S down to 40k hoping to get 9g, 2.0, and 40k at the same time.
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Unread post23 Oct 2016, 18:27

I have tried it on FCF, not at Mach 2 but up close to it. First, the idea of doing 9G at Mach 2 is unobtainable because as soon as you start to apply some back pressure to turn you are no longer at Mach 2. It takes a long time, lots of airspace, and gas to get to Mach 2. I only tried to get there once on an FCF and from then on I only usually went out to about 1.95 or so. Usually you do the 9G limiter test later in the flight at lower altitude but I once tried to do it at 40K at the end of the Mach run so it was close to Mach 2. As I posted earlier the jet is very sluggish at that speed and the G-onset was quite unimpressive compared to a limiter pull at 20K and 450+ KCAS where that test point is usually performed. The jet did not get to 9G until it went subsonic, which happened fairly quickly as I recall. I do not recall what G it peaked at while supersonic but it wasn't 9. It is also important to note the FCF is done completely clean. That is not an A-A configuration. Once you add Aim-120s and AIM-9s plus the rails/pylons on 2/8 and ECM pod and tanks to have any range/endurance forget about Mach 2. But we learned a long time ago that those Mach speeds were not that important otherwise we would still be flying F-104 type jets. Going Mach 2 is only important if you are trying to run away, something most of us were loathe to do.

As to min speed for 9G you can look through the forum to find an EM diagram to see what it is for a given altitude and load. Rule of thumb was 440 KCAS +- 20 at medium altitude. Below that the AOA limiter starts to decrease G available. I would always make sure I was above 450 to do the 9G check. I was OK with 8.8-9.2 G although I do not recall if there was a specific range in the TO. Again, max G and Max speed are not as important as overall performance across the 200 KIAS to low supersonic. That is where all the fighting occurs.
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Unread post24 Oct 2016, 19:01

johnwill wrote: With fuel in the tanks, the g-AoA limiter will not prevent exceeding 6.5g, so the pilot has to monitor g to avoid exceeding the limit. In case you are wondering why there is no intermediate g limit for partial external fuel, the tanks are not gauged, so there is no way to know how much fuel is in the tanks, except for a full/empty indicator.


I flew Block 1 through Block 42, and I'm pretty sure that we could check the actual fuel quantity in the external tanks. My old F-16A-1 shows the rotary fuel tank quantity selector having TEST-NORM-RSVR-INT WING-EXT WING-EXT CTR positions.
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guy@rdaf.dk

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Unread post24 Oct 2016, 19:13

Meteor wrote:
johnwill wrote: With fuel in the tanks, the g-AoA limiter will not prevent exceeding 6.5g, so the pilot has to monitor g to avoid exceeding the limit. In case you are wondering why there is no intermediate g limit for partial external fuel, the tanks are not gauged, so there is no way to know how much fuel is in the tanks, except for a full/empty indicator.


I flew Block 1 through Block 42, and I'm pretty sure that we could check the actual fuel quantity in the external tanks. My old F-16A-1 shows the rotary fuel tank quantity selector having TEST-NORM-RSVR-INT WING-EXT WING-EXT CTR positions.


That is still the case today. Selecting the switch to WING or CTR EXT will show the remaining fuel in the externals. The totalizer also uses this input to show total fuel on board.
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