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#1
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The one aerodynamic thing I didn't like
was the G-dig decelerating through M 1.0 while loaded up - it came on really sudden and if you happened to be looking outside (as is usual while chasing someone) you were looking at a probable over-G. Can someone tell me more about "G-dig" (using low-time piston guy type language!) Thanks! Cheers, CC |
#2
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IIRC the F-4 experienced an increase of the actual G-loading when
manouevering through the Mach 1. If you were pulling close to the structural limit you could have an overstress problem. Aerodinamics thing, displacement of the center of pressure, that kind of thing. Maybe a Phantom driver could explain it better. "Cockpit Colin" escribió en el mensaje ... The one aerodynamic thing I didn't like was the G-dig decelerating through M 1.0 while loaded up - it came on really sudden and if you happened to be looking outside (as is usual while chasing someone) you were looking at a probable over-G. Can someone tell me more about "G-dig" (using low-time piston guy type language!) Thanks! Cheers, CC |
#3
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Dang, Walt! I love the stuff you post here. Have you ever thought
about writing a book? You and a few others here (Ed R. comes immediately to mind) have the gift to write in detail and help those of us who were not there get sense of what it was like. Thanks for the post. Blue skies to you all. |
#4
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![]() "J.A.M." wrote in message ... IIRC the F-4 experienced an increase of the actual G-loading when manouevering through the Mach 1. If you were pulling close to the structural limit you could have an overstress problem. Aerodinamics thing, displacement of the center of pressure, that kind of thing. Maybe a Phantom driver could explain it better. The aerodynamic center shifted forward abruptly as you were decelerating through about .95 IMN. As the aero center shifts forward, the stabs downward trim force becomes greater and a pitch up occurs. (This is rather typical transonic behavior, although it varies from jet to jet.) In the F-4's case, if you were pulling 6 G or so, you'd suddenly find yourself around 9 G during this transient. At medium/high altitudes, the airframe would give a hint that this was about to happen with a subtle buffet cue. You could reduce your back stick just as the aircraft dug in and maintain your G without exceeding it. If you were low (say 5,000', higher IAS for .95) the buffet cue wasn't there and it could sneak up on you. I experienced the low altitude manifestation once and use the incident as an illustration of the effects (big time overstress) of transonic pitch up for my aero lecture. R / John |
#5
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On Tue, 29 Mar 2005 06:17:42 -0600, "John Carrier"
wrote: of the center of pressure, that kind of thing. Maybe a Phantom driver could explain it better. The aerodynamic center shifted forward abruptly as you were decelerating through about .95 IMN. As the aero center shifts forward, the stabs downward trim force becomes greater and a pitch up occurs. (This is rather typical transonic behavior, although it varies from jet to jet.) In the F-4's case, if you were pulling 6 G or so, you'd suddenly find yourself around 9 G during this transient. At medium/high altitudes, the airframe would give a hint that this was about to happen with a subtle buffet cue. You could reduce your back stick just as the aircraft dug in and maintain your G without exceeding it. If you were low (say 5,000', higher IAS for .95) the buffet cue wasn't there and it could sneak up on you. I experienced the low altitude manifestation once and use the incident as an illustration of the effects (big time overstress) of transonic pitch up for my aero lecture. R / John Walt used the term "G-dig", but I always heard it called "Mach tuck"--(coincidentally we had a guy in the squadron with last name Tuck, so his call sign became Mach -- rather than the more conventional "Friar".) Most jets of the period really couldn't command a lot of G when supersonic--the slab simply didn't have enough authority. So, if a fight was engaged in the supersonic speed range, guys trying to get as much turn rate as possible would have a yard of stick pulled into their gut. When the airplane decelerated through the Mach, that slab prepositioning when it went sub-sonic would then command a whole lot more AOA and G. Overshoot of the allowable G limit was damn near inevitable. One solution was to ask the back-seater to keep on eye on the mach for you and call when it looked like you were going to transition. Good situational awareness also helped--you knew your altitude, your entry airspeed, your attitude and your tactical position relative to the adversary. Predicting when you were going to go sub-sonic was then a function of art rather than science for the experienced guys. Ed Rasimus Fighter Pilot (USAF-Ret) "When Thunder Rolled" www.thunderchief.org www.thundertales.blogspot.com |
#6
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#7
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![]() "Doug "Woody" and Erin Beal" wrote in message ... On 3/29/05 6:17 AM, in article , "John Carrier" wrote: I experienced the low altitude manifestation once and use the incident as an illustration of the effects (big time overstress) of transonic pitch up for my aero lecture. R / John John, Even the Hornet does it. I've got a few "811's" (maintenance overstress code) due to transonic pitch up. .95 to the merge and load on the G's, and the FCS can't keep up (i.e. reduce the pitch rate fast enough) to keep the g-meter from exceeding 7.5. Worst I've ever seen was 8.4--still category 1 overstress only (low limit--visual inspection only). Most A/C do it to some degree (even the lowly T-45 ... 1.04 on a good day, downhill). Some are worse than others. The F-8 wasn't much of a problem. At low altitude, the F-4 didn't give a hint and could be. Never ran into it in the Turkey, but there were so many moving parts .... R / John |
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