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Negative G

Unread postPosted: 04 Dec 2017, 21:14
by saberrider
I know that most fighter jets are enable to get only +9 ,-3 . My question is the speed for negative G is higher that positive one?

Re: Negative G

Unread postPosted: 05 Dec 2017, 01:16
by vilters
Negative "G" limitations and times are fuel and oil related.

An airframe does not care that much about the actual speed.

But engines need fuel to run and oil for the bearings, and hydr systems need a constant oil supply too.

Re: Negative G

Unread postPosted: 05 Dec 2017, 04:53
by saberrider
Time is @30seconds ,but max. speed is the same as for 9G maneuvers ? Because it is hard to get +9G's and easier to hit -3G's?

Re: Negative G

Unread postPosted: 05 Dec 2017, 12:12
by vilters
Max time for -1G level inverted flight was 10 seconds in military power.

Also note that the LEF movement is not programmed for a lot of negative "G".
They only go 2° UP at max deflection for supersonic flight.

Re: Negative G

Unread postPosted: 05 Dec 2017, 12:50
by bouliult
vilters wrote:Max time for -1G level inverted flight was 10 seconds in military power.

Also note that the LEF movement is not programmed for a lot of negative "G".
They only go 2° UP at max deflection for supersonic flight.


The max time (at least for the F-16AM/BM) negative G is 30 seconds in military power en 10 seconds in burner. Be aware that inverted and negative G are two separate things. You can fly inverted and still have positive G's, and upright and have negative G's. The pilot is also a factor in this situation, negative G's are a lot harder to handle than positive. So it might be the pilot who is the time limiting factor.

Re: Negative G

Unread postPosted: 07 Dec 2017, 16:12
by Gums
Salute!

Good point Bouli.

Two quickies:

1) Early FLCS laws did not allow more than 1 neg gee below 140 knots. So a gear down dirty roll was a challenge, but not much as the gear limit speed was lots higher than that, and roll rates came into play.

It's easier to get to the neg 3 gee limiter than the plus 9 gee limiter due to the speed required.

2) The T-bird pass with one inverted is lways a joy to see. So #5 as lead rolls inverted just before rwy ( where I watch) and #6 camps out rel close for the pass. All in mil power.

Gums recalls...

Re: Negative G

Unread postPosted: 07 Dec 2017, 20:39
by saberrider
Thanks , Gums for telling us about minimum speed rolls with To/ LG configuration .I guess it is still present today due to the max. travel up /down of the stabilators.

Re: Negative G

Unread postPosted: 07 Dec 2017, 20:45
by saberrider
It was hard to keep a leveled position to the a/c with landing gear down ?

Re: Negative G

Unread postPosted: 07 Dec 2017, 21:06
by saberrider
If just keep (at safe alt. but in To/L. and slow speed due to gear limitations) pushing the stick when upsidedown what's happens?In my Sim just roll out and noses down.It is. realistic enough ?

Re: Negative G

Unread postPosted: 07 Dec 2017, 22:56
by Gums
Salute!

Good grief, Saber!!

Just use the control laws and the aero data your model or sim jet is experiencing.

You know, AoA versus gee versus IAS ( CAS for purists). Oh yeah, once with Cat III laws we had rate limits and AoA limits not there for Block 1, 5 and early 10.

Your problem is lack of rate and gee sensors around the plane that all feed into the FLCS confusers. Maybe you should re-work your model.

Gums opines....