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F4 question

Old 19th Apr 2019, 08:18
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F4 question

Currently reading ‘war for the hell of it’ by Ed Cobleigh, it’s an interesting story about his service in Vietnam flying the F4 in the USAF


He describes the take off procedure, after releasing the brakes and applying maximum power he would immediately apply full back stick, maintaining this input during acceleration down the runway until the nose started to lift off, he would then ease off the stick input gradually until the aircraft lifted off



I’ve read a few books on the F4 and this seems to be normal procedure when operating from a land base, I find it a bit puzzling, it reminds me of a soft field take off in a light aircraft, the Phantom is about as far as you can get from that



I’ve not seen this done on other fighters. Anyone have further insight ? was this technique used in the RAF ?
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Old 19th Apr 2019, 09:03
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Yes, we were taught to use full aft control column for take-off, releasing the back pressure slightly and as required when the aircraft was about to become airborne.
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Old 19th Apr 2019, 09:10
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was this technique used in the RAF ?
Yes, this was SOP on all RAF variants i.e FG1, FGR2 and F4J. I regret that, 30 years later, I cannot recall why but I assume that it was due to aerodynamics plus ensuring best use of runway.. Someone out there will have the answer.
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Old 19th Apr 2019, 10:10
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On heavy for jet aeroplanes that tend to use an awful lot of runway the procedure was changed in the 1950's. Holding the stick back and accelerating with the elevators up would increase the drag once they get some effect but not enough to lift the nose. Lifting the nose wheel and waiting for the aircraft to lift off also slows the acceleration.

The technique arrived at was to let the controls stream until about 25 knots before the calculated unstick and then rotate the aircraft so that it unsticks at the desired speed.

far more gentlemanly; or should I say personably.
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Old 19th Apr 2019, 14:56
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Did not the Fleet Air Arm use a piece of calibrated string attached to the control column to prevent too much forward movement of the column after a catapult launch?
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Old 19th Apr 2019, 15:01
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I don't know the reason for this technique in the F-4 but I have what seems to be a plausible explanation. With a tricycle undercarriage aircraft, when initially rotating on the ground the point of rotation is the mainwheels. As the aircraft unsticks, the point of rotation in pitch becomes the centre of gravity which is forward of the mainwheels. Therefore, the horizontal stabilizer instantly has a longer moment arm resulting in an instantaneously larger nose up pitching moment for a given stabilizer angle. This could result in an unpredictable response in pitch. However, using the F-4 technique, as the nosewheel starts to lift off the runway the pilot is given a cue to smoothly move the stick forward which results in a smooth capture of the desired pitch attitude after unstick. I suspect that it is just that the pitch response characteristics of the F-4 in this flight regime make this a good technique. Also, it is simple and calculation of a rotate speed is not required.

However, there is the potential for the horizontal stabilizer to scrape the runway during rotation. On one of my very early sorties in the F-4 I was flying a totally clean F-4K which thereby had a very aft c.g position. It rotated more rapidly than I had seen on my previous sorties and although I moved the stick forward more quickly the stabilizer tips still scraped the runway. Luckily, the rubbing strips worked and there was no damage. I was not the first to do this so we refitted a ballast Sparrow on the front station!

Full aft stick take-off rolls are also flown on Hunter post-maintenance test flights to check the nosewheel lift-off speed although the pitch attitude is then checked and a normal unstick speed used.
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Old 19th Apr 2019, 15:05
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Originally Posted by beardy View Post
Did not the Fleet Air Arm use a piece of calibrated string attached to the control column to prevent too much forward movement of the column after a catapult launch?
I believe that this was to stop aft movement of the stick top due its inertia during the acceleration of the catapult launch.
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Old 19th Apr 2019, 15:33
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Originally Posted by LOMCEVAK View Post
I believe that this was to stop aft movement of the stick top due its inertia during the acceleration of the catapult launch.
I'll buy that
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Old 19th Apr 2019, 16:32
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Beardy,

It was called a stick positioning device and consisted of a small drum of cable, the end of which could be clipped to the forward side of the stick top. As Lomcevak said, its purpose was to prevent inadvertant aft movement of the stick during catapult launch. The drum had a clutch which could be overridden by pulling harder if necessary to raise the nose in an emergency. During my apprenticeship at Hawker Siddeley Aviation Brough in 1970, I worked in Structural Test and carried out the endurance test on the device which consisted of operating it several thousand times by hand and checking the breakout load of the clutch at regular intervals. Not the most exciting way of pushing forward the frontiers of aviation.

Walbut
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Old 19th Apr 2019, 19:12
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On 228 we taught using full aft stick till 10 deg nu and then holding till lift off. This ensured formation take-offs were together. One of the instructors queried this technique, but full aft stick produced an earlier lift off than rotating at lift off speed. No special skill was required for this technique as all members of a formation did the same thing!
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Old 19th Apr 2019, 22:45
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On the F-4, all versions, the nose gear was heavy loaded. (Just look at any landing, even with a light aircraft, once the mains touch? The nose drops like a rock even when the chute is pulled early)

To reduce wear and tear on the nose wheel and strut it was advised to lighten the nose ASAP during a full fuel take off and even more so with stores.
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Old 19th Apr 2019, 23:52
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Originally Posted by Vilters View Post
On the F-4, all versions, the nose gear was heavy loaded. (Just look at any landing, even with a light aircraft, once the mains touch? The nose drops like a rock even when the chute is pulled early)

To reduce wear and tear on the nose wheel and strut it was advised to lighten the nose ASAP during a full fuel take off and even more so with stores.
Interesting to hear all this analysis . Back in the day , you didn't think too much about things , you just did as you were told , and it generally worked ok . What's that old saying about too much knowledge being a dangerous thing ? Favourite Chick Childerhose quote re guage markings--" green means go ; that's all any fighter pilot should be expected to remember " .

Mind you , in the F4 , it was always a good idea to pay close attention when the instructor told you " when it buffets , use your boots"....
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Old 20th Apr 2019, 04:01
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Thanks for the replies


As a Civilian Pilot my question would be what about single engine safety speed ?


The aforementioned technique seems to provide a lift off at the lowest possible speed
but would you have adequate rudder for aircraft control if you were to lose an engine at that moment before reaching what we would call V2 ?
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Old 20th Apr 2019, 06:09
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From a USAF F-4E manual stilton.

NORMAL TAKEOFF - The slats out-flaps down position is recommended for all takeoffs. After taking the runway and completing necessary pre—takeoff checks, engines can be run to 85% with brakes held and nose gear steering engaged to ensure nose gear alignment. With both engines operating in excess of 85% and the brakes locked. there is a possibility of rotating the tires on the wheel rims or skidding the tires. Check for normal rpm response and approximate readings of 450‘C EGT, 4000 pph fuel flow, one quarter nozzles, and 30-40 psi oil pressure. After releasing brakes, advance both throttles rapidly to full military power and check rpm, exhaust temperatures and nozzle position. WSO check the ramps fully retracted. If an afterburner takeoff is desired, shift the throttles into the afterbumer detent and advance full forward for max thrust. Maintain directional control with nose gear steering or rudder as required. The rudder becomes effective for steering at approximately 70 knots. Wheel braking should not be used for directional control during takeoff roll. Nose gear steering should he disengaged when rudder steering becomes effective. If it becomes necessary to re-engage nose gear steering at the higher speeds, rudder pedals should be returned to neutral prior to engagement since rudder displacement necessary for rudder steering will generally be excessive for nose gear steering. Sufficient aft stick should be applied prior to nose wheel lift off speed to attain the desired pitch attitude. As the nose rises, pitch attitude must be controlled to maintqain a 10° to 12° (first pitch mark) nose high attitude for aircraft fly-off. Caution must be exercised to preclude over-rotation due to excessive aft stick or an extended take off due to late lift off. The basic take off attitude should be held during acceleration and transition to a clean configuration. Trim change and control action during this period are normal. The AUX AIR DOORS. WHEELS, and MlASTER CAUTION lights may illuminate momentarily as the landing gear and flaps are retracted.

CAUTION - Rapid full aft movement of the stick between takeoff airspeed and 30 knots below takeoff airspeed may result in the stabilator hitting the runway with the possibility of stabilator actuator damage.

NO-FLAP TAKEOFF - No-flap takeoffs are not recommended. However. if it is determined that no-flap takeoffs must be performed to satisfy mission requirements. aircrews should be aware that takeoff roll and airspeed will be increased and the takeofl attitude will be slightly steeper. Stabilator effectivetress is considerably increased and extreme caution must be exercised to prevent overrotation which could result in the stabilator striking the runway.

WARNING - Due to increased stabilator authority with the flaps up, aircraft rotation can be initiated at lower than normal airspeed: and overrotation is a definite possibility. If it appesrs that overrotation is occurring, positive oontrol rnovernent (stick forward) rnust be taken to prevent the stabilator from contacting the runway and/or loss of control.

MINIMUM RUN/IHEAVY GROSS WEIGHT TAKEOFF - A minimum run/heavy gross weight takeoff (aircraft over 55,500 pounds) is accomplished in the same manner as a normal takeoff with the following exceptions. It is
recomended that all minimum run/heavy gross weight takeoffs he rnade with aterburner. During the talreoff run. full aft stick must he applied prior tn reaching 80 knots. As theaircratt starts to rotate.thestick should be adjusted to maintain 10° to 12° pitch attitude for aircraft fly-off. The possibility of a main landing gear tire failure increases with an extended takeoff‘ ground run under heavy gross weight conditions. Nose wheel liftoff speed and takeoff speed is increased during heavy gross weight conditions. In the event of an aborted takeoif, it must be remembered that stopping distance is greatly increased as abort speed increases.

CAUTION - With a combination of light gross weight and aft CG, the minimum run takeoff technique (i.e., full aft stick prior to reaching 80 knots) produces rapid pitch rates during nose rotation. This combination can exist when the radar package and nose gun (or equivalent ballast) are not installed.
but would you have adequate rudder for aircraft control if you were to lose an engine at that moment before reaching what we would call V2 ?
The manual uses a decision speed, same as civil V1. Failure prior to, abort, after continue. If the take off is on military power checklist says to go to full afterburner on the good engine, so rudder authority wouldn't seem to be an issue.
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Old 20th Apr 2019, 18:23
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but would you have adequate rudder for aircraft control if you were to lose an engine at that moment before reaching what we would call V2 ?
The engines are only about 3 ft from the a/c centre line, so I don’t think asymmetric thrust is a big deal. Actually, surely it’s Vmca you refer to?
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Old 20th Apr 2019, 19:56
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212man - not sure about the F4 but in the FA-18E you needed full rudder deflection to stay straight with one donk out and the other in blower...with a similar engine configuration.
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Old 20th Apr 2019, 20:12
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Salute!

Don't think many of the RAF folks who contribute so much here, but maybe some RCAF F-5E drivers could help.

Seems to me that the F-5E gear configuration and cee gee was such that they needed to crank up the nose for takeoff. Apparently the elevatror didn't have enough control authority to change pitch at a reasonable speed racing down the runway. I lurched one day behind our "agressor" folks and they had some gizmo that actually extended the nose gear to raise the nose.

I only flew the F-18 sim once at St Louis, but apparently the rudders were canted in for takeoff to help get a nose up pitch moment.

Gums wonders....
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Old 20th Apr 2019, 22:20
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Originally Posted by LOMCEVAK View Post
I don't know the reason for this technique in the F-4 but I have what seems to be a plausible explanation. With a tricycle undercarriage aircraft, when initially rotating on the ground the point of rotation is the mainwheels. As the aircraft unsticks, the point of rotation in pitch becomes the centre of gravity which is forward of the mainwheels. Therefore, the horizontal stabilizer instantly has a longer moment arm resulting in an instantaneously larger nose up pitching moment for a given stabilizer angle. This could result in an unpredictable response in pitch. However, using the F-4 technique, as the nosewheel starts to lift off the runway the pilot is given a cue to smoothly move the stick forward which results in a smooth capture of the desired pitch attitude after unstick. I suspect that it is just that the pitch response characteristics of the F-4 in this flight regime make this a good technique. Also, it is simple and calculation of a rotate speed is not required.

However, there is the potential for the horizontal stabilizer to scrape the runway during rotation. On one of my very early sorties in the F-4 I was flying a totally clean F-4K which thereby had a very aft c.g position. It rotated more rapidly than I had seen on my previous sorties and although I moved the stick forward more quickly the stabilizer tips still scraped the runway. Luckily, the rubbing strips worked and there was no damage. I was not the first to do this so we refitted a ballast Sparrow on the front station!

Full aft stick take-off rolls are also flown on Hunter post-maintenance test flights to check the nosewheel lift-off speed although the pitch attitude is then checked and a normal unstick speed used.
Many many years ago my father was an AWI on exchange with the USN when, on a particular take off run, a Student failed to follow the above routine, with the result being a stall as inferred followed by a very low level ejection, depositing TN Senior on the Runway.

As it happens, I was clearing out my loft recently and came across the old man’s helmet from those days and the very ejection handle/face screen used on the fateful day.

TN (Jnr).
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Old 21st Apr 2019, 03:28
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Originally Posted by megan View Post
From a USAF F-4E manual stilton.

NORMAL TAKEOFF - The slats out-flaps down position is recommended for all takeoffs. After taking the runway and completing necessary pre—takeoff checks, engines can be run to 85% with brakes held and nose gear steering engaged to ensure nose gear alignment. With both engines operating in excess of 85% and the brakes locked. there is a possibility of rotating the tires on the wheel rims or skidding the tires. Check for normal rpm response and approximate readings of 450‘C EGT, 4000 pph fuel flow, one quarter nozzles, and 30-40 psi oil pressure. After releasing brakes, advance both throttles rapidly to full military power and check rpm, exhaust temperatures and nozzle position. WSO check the ramps fully retracted. If an afterburner takeoff is desired, shift the throttles into the afterbumer detent and advance full forward for max thrust. Maintain directional control with nose gear steering or rudder as required. The rudder becomes effective for steering at approximately 70 knots. Wheel braking should not be used for directional control during takeoff roll. Nose gear steering should he disengaged when rudder steering becomes effective. If it becomes necessary to re-engage nose gear steering at the higher speeds, rudder pedals should be returned to neutral prior to engagement since rudder displacement necessary for rudder steering will generally be excessive for nose gear steering. Sufficient aft stick should be applied prior to nose wheel lift off speed to attain the desired pitch attitude. As the nose rises, pitch attitude must be controlled to maintqain a 10° to 12° (first pitch mark) nose high attitude for aircraft fly-off. Caution must be exercised to preclude over-rotation due to excessive aft stick or an extended take off due to late lift off. The basic take off attitude should be held during acceleration and transition to a clean configuration. Trim change and control action during this period are normal. The AUX AIR DOORS. WHEELS, and MlASTER CAUTION lights may illuminate momentarily as the landing gear and flaps are retracted.

CAUTION - Rapid full aft movement of the stick between takeoff airspeed and 30 knots below takeoff airspeed may result in the stabilator hitting the runway with the possibility of stabilator actuator damage.

NO-FLAP TAKEOFF - No-flap takeoffs are not recommended. However. if it is determined that no-flap takeoffs must be performed to satisfy mission requirements. aircrews should be aware that takeoff roll and airspeed will be increased and the takeofl attitude will be slightly steeper. Stabilator effectivetress is considerably increased and extreme caution must be exercised to prevent overrotation which could result in the stabilator striking the runway.

WARNING - Due to increased stabilator authority with the flaps up, aircraft rotation can be initiated at lower than normal airspeed: and overrotation is a definite possibility. If it appesrs that overrotation is occurring, positive oontrol rnovernent (stick forward) rnust be taken to prevent the stabilator from contacting the runway and/or loss of control.

MINIMUM RUN/IHEAVY GROSS WEIGHT TAKEOFF - A minimum run/heavy gross weight takeoff (aircraft over 55,500 pounds) is accomplished in the same manner as a normal takeoff with the following exceptions. It is
recomended that all minimum run/heavy gross weight takeoffs he rnade with aterburner. During the talreoff run. full aft stick must he applied prior tn reaching 80 knots. As theaircratt starts to rotate.thestick should be adjusted to maintain 10° to 12° pitch attitude for aircraft fly-off. The possibility of a main landing gear tire failure increases with an extended takeoff‘ ground run under heavy gross weight conditions. Nose wheel liftoff speed and takeoff speed is increased during heavy gross weight conditions. In the event of an aborted takeoif, it must be remembered that stopping distance is greatly increased as abort speed increases.

CAUTION - With a combination of light gross weight and aft CG, the minimum run takeoff technique (i.e., full aft stick prior to reaching 80 knots) produces rapid pitch rates during nose rotation. This combination can exist when the radar package and nose gun (or equivalent ballast) are not installed.The manual uses a decision speed, same as civil V1. Failure prior to, abort, after continue. If the take off is on military power checklist says to go to full afterburner on the good engine, so rudder authority wouldn't seem to be an issue.

Thanks for that comprehensive reply, it sounds like the full aft stick from the beginning of the take off roll technique was
primarily used on heavy weight take offs to save wear and tear on the tires and that looks like the best answer so far
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Old 21st Apr 2019, 05:03
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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, I’ve done hundreds as a Phantom instructor!
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