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F4 question

Old 21st Apr 2019, 06:18
  #21 (permalink)  
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Originally Posted by Audax View Post
The full aft stick technique catered for the many configurations, weights, loads and/or the variable c of g positions these configurations created, the aircraft got airborne when it was ready. As for yaw on a single engined reheat overshoot, there was a tiny amount but as the engines were so close together it was of no great consequence, Iíve done hundreds as a Phantom instructor!

Thanks for that Audax, itís been fascinating to receive such enlightened information, the minimal yaw in a single engine scenario was unexpected despite their being mounted so close together, I expected the significant thrust asymmetry would produce more than what you describe


Interesting that it was possible to scrape the ends of the stab if you overrotated, Iíd not conceived of that as a possibility but it makes sense with the significant anhedral in the F4 tailplane



So another question, I understand the F4 was designed from day one as a Naval fighter and bringing it aboard the carrier involved flying a steady angle of attack to a no flare touchdown



Was this technique also used on land based Phantoms ?



Ive seen a number of videos where that appears to be the case
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Old 21st Apr 2019, 10:38
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AoA was used for the approach and landing. A rough ‘on’ speed was worked out depending on aircraft weight, this was checked against the AoA on finals to hopefully mitigate against the AoA system giving erroneous readings, touchdown was unflared, holding 19.2 units.

Interestingly, we were always told that as the beast was designed for carrier ops, the brakes weren’t all that great. When we did the short landing trials, driven by the Falklands, we proved that wrong. By hitting the ground at 21/22 units with the brake chute deployed at 200ft on finals and standing on the brakes, on an average day we could stop in less than 3000ft.
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Old 21st Apr 2019, 11:15
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With the low set anhedral stabilator, if you held a constant stick position all the way to touchdown the aircraft would pitch slightly nose down due to the stab entering ground effect before the wings. Apparently, this did not occur when landing on a carrier deck because you didn't get the same ground effect. Personally, unless on a runway length limited landing, I would apply slight aft stick just before touchdown in order to maintain a constant pitch attitude and AOA.

Different F4 marks/models had different brakes so the braking issues did vary. The F-4M/FGR2 certainly had the 'good' brakes.

One other interesting aspect of the F4 was that in a crosswind you did not kick off drift because the aileron-rudder interconnect would generate excessive roll if you did; you touched down with the 'crab' applied.
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Old 21st Apr 2019, 13:56
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Thanks for the replies, Iím still curious about the practice of using AOA instead of an indicated airspeed for land based operations


It makes sense landing on a carrier where you want the lowest possible touchdown speed but why carry that practice over to landings on a conventional runway ?


Furthermore it looks like no flare was used, in terms of wear and tear on the airframe there must have been a good reason to not
arrest the descent at least slightly before touchdown ?


Is this related to the issue with stabilizer tip clearance?
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Old 21st Apr 2019, 14:24
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There was a USMC exchange pilot at LU around 1985 who flew the circuit like it was a carrier and flew the F4 into the ground. I swear to god a few times it looked like the wing tips would touch the ground, let alone the stabilizer.
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Old 21st Apr 2019, 15:14
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F4 Takeoff technique was standard on most models. The aircraft sat on the ground with the wing at a low incidence. 3/4 to full aft stick was used to rotate the wing to the optimum angle. As the speed increased through 100kts it was required to ease the stick forward to capture about 12deg pitch angle. The aircraft would fly off between 145 and 205 kts dependant on configuration, temperature and altitude. It was possible to "pull" the aircraft airborne early, however, not recommended.

Three main components affected the takeoff speed and distance; technique, C of G and nose strut extension. Any one of those out could extend the takeoff by 20%!! A USAF article written in the Phantom Digest in about 1970 called "Late Rotators" explain it very well.

As for approach and landing the F4 was a beast apart from other aircraft. Due to it's unique handling characteristics the aircraft had to be flown using AOA as the main reference. Apart from the AOA gauge the pilot was provided with Head Up Indexers and on some models Audio AOA. Once mastered to was possible to fly a stable approach very accurately to a precision touchdown. All naval variants (B,J,K,M,N,S) had strengthened landing gear, smaller wheels and were designed to land with No Flare. The USAF originated models (C,D,E,F,G) had different landing gear and wheels and required a flare to reduce the descent rate prior to touchdown. The UFAF IPs did not appreciate my naval landing technique.

As LOMCEVAK stated, Kicking off drift was a NO-NO.

Landed using the wrong techniques it was possible to use over 10,000 ft of runway to stop. As Audax stated, on 64(R) Sqn we perfected the short landing technique prior the the Falklands deployment and managed to stop in 2500 ft without using a cable. The brakes,however, would be very hot. Chute deployment should occur so that full deployment occurred at touchdown and not before. A 200ft deployment would be a little early in my opinion.
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Old 21st Apr 2019, 15:23
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F I belts and braces

FI

belts and braces
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Old 21st Apr 2019, 15:30
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Anyone recall the two A1 QFIs flying a 21AOA approach at Akronelli and landing in the undershoot? Tsk, tsk.....
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Old 21st Apr 2019, 15:34
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FI ‘83



Photo credit, Jeff Bell.
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Old 21st Apr 2019, 15:34
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Dom2, have to take issue with you that 64(R) did the short landing trials, at least in the early days. Boscombe sent a Hunter with AoA gauge to us on 29(F) Sqn as we were the ones going down there. I flew in the Hunter and then flew the Boscombe guy in the back of the Phantom. We ascertained that 21/22 AoA was fine, plus pulling the chute at 200 to 250ft to ensure it was fully deployed on landing.
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Old 21st Apr 2019, 15:37
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A further trial was completed by 29(F) Sqn at Waddo in ‘84. A 3000’ x 50’ strip was marked out on the runway and we practiced day and night short landings.
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Old 21st Apr 2019, 16:15
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Salute!

Some really great stuff on the last few posts
.
I flew three birds with an AoA gauge or indexer or bracket in the HUD.

The VooDoo did not emphasize use of the AoA gauge for landing or best cruise/holding. It was mainly an indication of how close you were to the pitch-up.

The A-7D and F-16A had an AoA bracket in the HUD for approaches and it was very useful as Lom has explained. The A-7D, being a USN derivative, but with vastly more advanced avionics, retained the USN "indexer" chevrons on each side of the HUD to show best approach AoA. Because stall and best approach speed changed a lot due to external ordnance and configuration, AoA was the best indication versus rules of thumb that related all the factors to a best approach speed. So if the guess was within 5 or 10 knots when the AoA indexers showed where to fly, then it was easy to transition and fly the AoA. The A-7D and F-16 had the AoA bracket in the HUD, so pulling or pushing that thing wrt the flight path marker made approaches a piece of cake.

I adopted the USN practice of flying the A-7D down to the runway with little or no flare. The F-16 required a bit of flare if you were hot or you would bounce. And as LOM has stated, no cross control for crosswinds!! Land the thing in a skid with the aileron interconnect feature would bite you in the butt when weight on wheels happened and the feature kicked out. F-16 was really touchy about that, but gear was close together and it was no biggie right after touch when landing wings level in a crab.

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Old 21st Apr 2019, 17:17
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Another part of landing the F4 that made it different was Boundary Layer Control (BLC), In either 7th or 12th stage BLC lift was being enhanced by air bled from the engines. If the throttles were retarded to idle too early the aircraft dropped like a stone. Better to fly the aircraft onto the ground.

Since the USAF operated off very long runways the BLC was inhibited. Then the jets E/S onwards got slats and that changed the aircraft's handling in the landing phase. Far more difficult to land in a very strong Xwind. I was happy to land a FGR2 with 35kts across whereas an E model with 25kts across was a handful!!
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Old 21st Apr 2019, 18:20
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Isn’t that why we bought the F-4J when we needed to top the numbers? IIRC the other option was the F-4S, but that had the leading edge slats and they were worried about the handling difference.
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Old 21st Apr 2019, 19:28
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Originally Posted by stilton View Post
Thanks for the replies, Iím still curious about the practice of using AOA instead of an indicated airspeed for land based operations

It makes sense landing on a carrier where you want the lowest possible touchdown speed but why carry that practice over to landings on a conventional runway
In any type you actually want to approach at a given AOA but most aircraft do not have AOA gauges so you fly an airspeed to achieve it. Flying AOA keeps it simple; the number is always the same whereas you have to adjust the airspeed for weight. In addition, a swept wing aircraft such as the F4 typically approaches below minimum drag speed, on the backside of the drag curve. The technique required to fly an accurate approach is to control AOA with the stick and rate of descent/approach path with power. Hence, you need an AOA gauge and you fly an AOA value and achieve an accurate approach.

Apart from the AOA gauge the pilot was provided with Head Up Indexers and on some models Audio AOA.
The F-4K/FG1 had audio AOA but the F-4M/FGR2 did not. The tones used were identical to those on the Buccaneer. BUT, they worked in the opposite sense! When at the correct datum AOA for the approach in both types, you had a 'steady note'. But, when the AOA was less than this you had 'beeps' in the Buccaneer and 'burps' in the F-4 and vice versa when greater than the datum AOA. Not many pilots were current on both at the same time but I was for a while. I had a Buccaneer background so when flying the FG1 I used the gauge until 'on speed' then maintained the AOA using the on-speed tone.

All naval variants (B,J,K,M,N,S) ...
The F-4M was not a naval version. However, the YF-4M (XT852) that was still flying through to at least 1990 did have the drooped ailerons and slatted stabilator as per the F-4K/FG1.
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Old 21st Apr 2019, 21:06
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Sometime in the 1980's I attended a meeting at Boscombe Down to discuss heavy weight and single engined landing limitations for the UK Phantoms. Don Headley represented the BAE test pilots and I guess there were Flight test and Aerodynamics reps from BAe as well, but I can't remember who they were. My only reason for being chosen to attend was because, at the time, I understood the flight systems and the workings of the flap and BLC system and the associated 7th/12th stage bleed. It was intended to try and test various combinations of settings to allow approaches to be flown, potentially I think, even in reheat. I remember expressing some concern about some of the tests being proposed and Don Headley put me firmly back in my Flight Systems box. He pointed out that my concerns were based on the behaviour of the Buccaneer which could really bite if you reduced blowing pressures too far and in practice, the Phantom was much more benign. The main reason for the difference was that Phantom primarily 'blew' the leading edge of the wing and if blowing pressures were reduced, and the slits became unchoked, the aircraft would pitch nose down. Buccaneer on the other hand primarily blew the trailing edge of the wing and if BLC pressures fell too low, the aircraft pitched nose up which was the last thing you needed when low and slow and close to the ground. At the time the prospects of hot weather trials for UK Phantoms were pretty slim and Don probably did not want me to prejudice the chances of going on an interesting, if high risk, flight trial in an exotic location. I cant remember if or where the trials ever took place but in the back of my mind, I think it might have been Akrotiri

One minor deviation from this thread was that it fascinated me what you could hear on a Phantom engine run. I can remember the Rolls Royce rep pointing out to me when the engine changed from 7th to 12th stage bleed and vice versa you could hear it quite clearly among all the other racket from the engines when stood alongside wearing ear defenders.

Walbut
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Old 21st Apr 2019, 21:28
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Originally Posted by Dominator2 View Post
All naval variants (B,J,K,M,N,S) had strengthened landing gear, smaller wheels...
Not quite, only the F-4B, F-4N and all but the last 12 RF-4Bs had the narrow wheel/tyres, the F-4J, F-4K, F-4S and last 12 RF-4Bs had the wider wheels/tyres first seen on the USAF's F-4C...

-RP
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Old 22nd Apr 2019, 10:35
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Originally Posted by walbut View Post
Sometime in the 1980's I attended a meeting at Boscombe Down to discuss heavy weight and single engined landing limitations for the UK Phantoms. Don Headley represented the BAE test pilots and I guess there were Flight test and Aerodynamics reps from BAe as well, but I can't remember who they were. My only reason for being chosen to attend was because, at the time, I understood the flight systems and the workings of the flap and BLC system and the associated 7th/12th stage bleed. It was intended to try and test various combinations of settings to allow approaches to be flown, potentially I think, even in reheat. I remember expressing some concern about some of the tests being proposed and Don Headley put me firmly back in my Flight Systems box. He pointed out that my concerns were based on the behaviour of the Buccaneer which could really bite if you reduced blowing pressures too far and in practice, the Phantom was much more benign. The main reason for the difference was that Phantom primarily 'blew' the leading edge of the wing and if blowing pressures were reduced, and the slits became unchoked, the aircraft would pitch nose down. Buccaneer on the other hand primarily blew the trailing edge of the wing and if BLC pressures fell too low, the aircraft pitched nose up which was the last thing you needed when low and slow and close to the ground.
Walbut
I agree with Don that the Phantom was less affected by low blow pressures than the Buccaneer, but the Bucc had much more extensive BLC. The slits were all along the top of the leading edge of the wings, along the front edge of the mainplane flaps and under the leading edge of the tailplane. Even at minimum blow pressure and at datum speed the stabilised rate of descent was very high. Unblown approaches (45-10-10) were 19 KIAS faster than blown approaches with 45-25-25.

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Old 22nd Apr 2019, 15:07
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The F-4M was not a naval version
.
All that I meant was that the K and M were both based on the J. Most of the RAF interaction with the aircraft, radar and weapons (AIM7 and AIM9) was with the USN.

As for Indexers and Audio AOA, there were various variations and combinations throughout the Family of F4s in different nations and forces.
Even such things such as Slotted Stabilator (F4F) were adopted in later variants.
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Old 23rd Apr 2019, 04:52
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Thanks for the great replies gents
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