If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
Cockpit Colin wrote:
Newby question here - I've always been curious as to why any aircraft in the 1 to 1 thrust to weight ratio class (F/A-18? F4? F14? etc) would have trouble being able to "simply" power out flat spins / falling leafs etc. Can anyone give me a bit on an insight? One way to think of it (not too scientific) is that adding power just adds more "juice" to the spin. The power vector rotates around, just making the plane do whatever it's doing with that much more vigor. |
#22
|
|||
|
|||
An airplane in a flat spin has very high angle of attack. Way above
any normal spin mode. Once stabilized flat you are sort of like a frisbee, rotating with all the incoming air hitting just the bottom of the plane. The break out of this spin or any for that matter, you must lower your angle of attack somehow. In upright spins this means, stick full forward. Flat spins, fwd stick doesn't help because the air flow is under not over your vertical control surface, stabilator in the F-4 case. The rotation can't be altered for the same basic reason. Power changes don't give you any significant nose up or down impulse. If you deploy your drag chute it will just ride above you and not inflate, like a streamer. You have lots of time to try lots of things on the way down but like I said, we lost a lot of F-4s trying everything but never found anything that worked. Answer was, be gentle when using rudders when vertical and nose high. The F-4 gave you plenty of warning when you did something it didn't like. Wing wobble, some buffet, very loose nose in yaw, and often some "Oh ****s" from the rear seat. My theory, and I never tried it, was if all else failed in a flat spin, have the back seater eject and maybe the reaction to the seat firing would lower the nose a hair. You just never told the RIO what your plan was. In Navy planes, he could eject me but I couldn't eject him. A serious design fault IMHO. Actually there was a way to eject the rear seat from the front but it wasn't widely advertised. |
#23
|
|||
|
|||
One way to think of it (not too scientific) is that adding power just
adds more "juice" to the spin. The power vector rotates around, just making the plane do whatever it's doing with that much more vigor. I understand what you're trying to say, but I just can't get a handle on the physics of it ... Sure, I can understand how (without power) the aircraft would want to continue rotating about it's centre of gravity (like a spinning top) - but with power applied it would seem to me to want to accelerate the aircraft in a given direction - which I would of thought would have initially increased the distance from the centre of the spin to the centre of gravity (one and the same with no power) to something bigger and bigger until control was regained. In the case of a little power I could see how the aircraft might continue to spin (perhaps to a point where the nose or some point further forward becomes the spin center) - but with a LOT of power I would have thought that eventually the aircraft would just start traveling in the direction of the thrust (with less inclination to turn). Obviously I'm wrong, but I just can't understand why adding say, 16,000 to 32,000 pounds thrust along a given line won't accelerate the aircraft away from the centre of the spin. I can only visualise it increasing the spin rate if the thrust was somehow vectored 90 deg. Where am I going wrong? Cheers, CC PS: Thanks to the 2 other posters - I hadn't thought of decreased engine power in the equasion, and I can appreciate how adding power in a conventional spin maked things worse - it's just the flat spins / falling leafs etc that have me baffled. |
#24
|
|||
|
|||
Well, okay, I rise to the challenge. I have a little over 700 hours in
the 104A (including some time in the Dash 19 version) and just over 2000 in the F4D/E/E-LES. I was fortunate in that the IP who checked me out in the F4 respected my 3000 hours fighter time and together we explored the envelope. I found the F4 to be an honest airplane (as was the 104) and once you learned what it was trying to tell you you could fly it to its real envelope, not the Dash One or NATOPS figures, but what it was really capable of. 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. As for fighting the birds, once in knife-range the old engined 104 vs F4 it was the pilots - with the Dash 19 it could run the F4 out of fuel, keeping the speed up and the G on, working the vertical a lot better, and then assassinate it. With a missile fight - if the Sparrows worked the 104 was going to be in trouble. Muscles per G? I guess I'm a bad example because at 6-2 and 225 I never had any problem getting the stick wa-a-a-y back. Landing - on a wet slippery runway at DaNang my routine was on-speed plus a slow chevron, aim for the numbers at the end of the runway and about eight feet up (eyeball guess) have the back seater pull the throttles back while I popped the chute. PS I did not like the loss of speed in the LES version for a dubious gain in turn rate for a measly 180 degrees. I'd been through that in the F102 - turn like hell and then dive for airspeed after having lost 250 knots in 180 degrees. Never got out of control when I was flying it but had a stud try to pick up a wing with aileron down around first nose-rise in an approach to a stall. This guy had been previously current in F4s and had tons of Hun time so I was complacent. (Bad Walter! Bad boy! No donut!) Anyway my lightning reactions responded and my white knuckles now firmly gripping the rear stick hit the radar scope and the bird unloaded to zero alpha in a microsecond and we were back flying again. (Said reactions honed by 104's propensity to pitch up when working it slow and hard) Used to spiral up in the F4 turning toward the sun just out of a being-tracked position and at the appropriate time and 200 KIAs or slower go zero alpha, full rudder, inboard engine idle and outboard full AB and sort of do a lateral pivot on a dime and blast past the other guy going straight down accelerating in both ABs while he was still going up and getting even slower. This also worked in the Dash 19 104 with the advantage of much faster accel due to 1+:1 T/W. Damn. I miss that kind of flying! Walt BJ |
#25
|
|||
|
|||
Before I read that post I was confused about getting out of flat spins using
power - but now I'm envious, and confused about getting out of flat spins using power! wrote in message oups.com... Well, okay, I rise to the challenge. I have a little over 700 hours in the 104A (including some time in the Dash 19 version) and just over 2000 in the F4D/E/E-LES. I was fortunate in that the IP who checked me out in the F4 respected my 3000 hours fighter time and together we explored the envelope. I found the F4 to be an honest airplane (as was the 104) and once you learned what it was trying to tell you you could fly it to its real envelope, not the Dash One or NATOPS figures, but what it was really capable of. 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. As for fighting the birds, once in knife-range the old engined 104 vs F4 it was the pilots - with the Dash 19 it could run the F4 out of fuel, keeping the speed up and the G on, working the vertical a lot better, and then assassinate it. With a missile fight - if the Sparrows worked the 104 was going to be in trouble. Muscles per G? I guess I'm a bad example because at 6-2 and 225 I never had any problem getting the stick wa-a-a-y back. Landing - on a wet slippery runway at DaNang my routine was on-speed plus a slow chevron, aim for the numbers at the end of the runway and about eight feet up (eyeball guess) have the back seater pull the throttles back while I popped the chute. PS I did not like the loss of speed in the LES version for a dubious gain in turn rate for a measly 180 degrees. I'd been through that in the F102 - turn like hell and then dive for airspeed after having lost 250 knots in 180 degrees. Never got out of control when I was flying it but had a stud try to pick up a wing with aileron down around first nose-rise in an approach to a stall. This guy had been previously current in F4s and had tons of Hun time so I was complacent. (Bad Walter! Bad boy! No donut!) Anyway my lightning reactions responded and my white knuckles now firmly gripping the rear stick hit the radar scope and the bird unloaded to zero alpha in a microsecond and we were back flying again. (Said reactions honed by 104's propensity to pitch up when working it slow and hard) Used to spiral up in the F4 turning toward the sun just out of a being-tracked position and at the appropriate time and 200 KIAs or slower go zero alpha, full rudder, inboard engine idle and outboard full AB and sort of do a lateral pivot on a dime and blast past the other guy going straight down accelerating in both ABs while he was still going up and getting even slower. This also worked in the Dash 19 104 with the advantage of much faster accel due to 1+:1 T/W. Damn. I miss that kind of flying! Walt BJ |
#26
|
|||
|
|||
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 |
#27
|
|||
|
|||
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 |
#28
|
|||
|
|||
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. |
#29
|
|||
|
|||
"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 |
#30
|
|||
|
|||
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 |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
CFI without commercial? | Jay Honeck | Piloting | 75 | December 8th 10 04:17 PM |
RAF Blind/Beam Approach Training flights | Geoffrey Sinclair | Military Aviation | 3 | September 4th 09 06:31 PM |
AOPA Stall/Spin Study -- Stowell's Review (8,000 words) | Rich Stowell | Aerobatics | 28 | January 2nd 09 02:26 PM |
us air force us air force academy us air force bases air force museum us us air force rank us air force reserve adfunk | Jehad Internet | Military Aviation | 0 | February 7th 04 04:24 AM |
12 Dec 2003 - Today’s Military, Veteran, War and National Security News | Otis Willie | Naval Aviation | 0 | December 12th 03 11:01 PM |