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-   -   Could Spey Phantom reach mach 2? (https://www.pprune.org/military-aviation/639673-could-spey-phantom-reach-mach-2-a.html)

Finningley Boy 4th Apr 2021 12:23

Could Spey Phantom reach mach 2?
 
During my research for for a current project I came across a report by the RAF which claimed that in trials the spey-engined F-4 could reach, in trial conditions, a maximum speed of 1.9 mach at altitude. The F-4J, its closest J79 engined comparison didn't set the heather of fire either, about 2.04 mach. However, I'm sure at least one ppruner could throw some personal light on such blunt figures.

FB:)

garyscott 4th Apr 2021 18:03

Sounds about right.
Spey Phantom had a slightly lower max at alt, but quicker accel down low compared to J79 equipped F-4.
At height, the J79 could attain a higher Mach than the Spey.
Spey - having a wider ar5e wouldn’t have helped the aerodynamics much.

Alex Whittingham 4th Apr 2021 18:30

I did hear of an RAF F4 on airtest with no tanks or external stores which managed to get 'on the step' of ram effect and easily exceeded M2.0 and accelerating, but it is apocryphal - and I don't know which engines. Similar J79 spam tale here

wrmiles 4th Apr 2021 18:37

Does it matter, since I have the impression that you reach the max mach number and bingo fuel at about the same time.



waterbottle 4th Apr 2021 21:26

A friend that flew Phantoms, 15C and E commented that the Phantom was faster. In fact he was very complementary about it in a number of areas over the F-15. Didn’t get into much detail, and not sure of the fits that he was comparing. His experience was F-4 in Vietnam and then F-15 through the 70’s and 80’s.

MAINJAFAD 5th Apr 2021 00:44


Originally Posted by waterbottle (Post 11022368)
A friend that flew Phantoms, 15C and E commented that the Phantom was faster. In fact he was very complementary about it in a number of areas over the F-15. Didn’t get into much detail, and not sure of the fits that he was comparing. His experience was F-4 in Vietnam and then F-15 through the 70’s and 80’s.

The operations manual for the USAF F-4C/D/E is on the internet if you look for it. Maximum sustained speed for the J79 powered Phantom (clean or with 4 AIM-7) was listed as Mach 2 / (IAS over 700 knots) above 30.000 ft or Compressor Inlet Temperature of around 121 Degrees C (which ever was reached first). However these limits were allowed to be breached for 5 minutes in any one flight and the aircraft could be taken to Mach 2.4 for a very limited period. I did read somewhere that the CIT limits on the Spey were lower than the J79 and that was one of the reasons that the UK engine powered Phantoms were slower. Airspeed limits with the wing tanks fitted was Mach 1.9.

Finningley Boy 5th Apr 2021 02:20

mainjafad,

Presumably mach 2 was possible when in clean configuration?

FB


gums 5th Apr 2021 04:05

Salute!

Good grief. The speed at various altitudes was supposed to be whatever the government specified in the contract. If not, then maybe it had better performance a thousand feet higher or lower. Big deal. 0.10 M is not a big deal when supersonic. Few fights in combat to this day have involved 1.8 M or 2.x M.

The speed is to get to the fight or the intercept.
====================
I flew the non "reheat" ( have to honor the primary posters here) version Spey in the A-7D. It was called the TF-41 and licensed to Allison for U.S. production. Is.that the same motor?

Someone mentioned acceleration, but sounds more like the plane more than the motor. The TF-41 was sluggish compared to the J-79 , or most GE motors. My P&W motors could not accelerate nearly a quickly as the GE ones.

Anyway, a few knots here and there is only important making up the E-M chart, and only plane I know of that flew up at the top of that chart was the SR-71.

Gums sends...





BEagle 5th Apr 2021 08:44

Hey gums, in its day the A-5 Vigilante was certainly capable of M2+!

Over 60 years ago, Cdr Heath and Lt. Monroe accelerated to M2.1, then climbed the jet to over 90000 ft, establishing a new world record (and double flame out!).

Operating the RA-5C off carriers in the Viet Nam war must have been pretty demanding....

LOMCEVAK 5th Apr 2021 11:00

When discussing maximum speeds it needs to be made clear whether it is the maximum in level flight or in a dive. I am sure that a Spey engined F4 could not achieve 2.0M in level flight but I did manage to in a dive. The configuration was clean except for one Sparrow on a front station to keep the cg clear of the aft limit. The profile was a max reheat climb to 48,000 ft at the optimum subsonic climb Mach number (0.95M from memory) then a shallow dive (about 5 deg) to the tropopause. I managed to get 2.05M although the first time that I tried I only reached 1.95M because I started the dive from only 45,000 ft.

The really impressive speed aspect of the F4K/M was at low level. The reheat light-up time was slow but then it would reach the IAS limit of 750kts at sea level easily and with less than max reheat even in ‘C’ fit with 2 underwing tanks.

Dominator2 5th Apr 2021 11:55

I agree with LOMCEVAKS numbers but would add that if approaching the Trop too quickly it was possible to make a second climb once above M1.03 (Ramps travelled) back up to 45,000ft and then a 5 deg dive would achieve M2.0+.

Also agree that the F4K/M would easily reach 750kts at low level. I have to admit accidentally reaching 795kts chasing some USAF F111s over the North Sea before noticing the speed. Fortunately the tanks stayed on and there was no damage. Any way, as a Flying Officer my "top cover" was my Flt Cdr in the RCP.

ex82watcher 5th Apr 2021 12:10

LOMCEVAK,a question if I may,in the event you have described,you say that you carried one sparrow to keep within c of g limits.What would happen in a wartime situation,if you had fired all missiles and dropped the tanks.Would you then be flying outside those limits ? would that be possible for very long ?

LOMCEVAK 5th Apr 2021 13:25


Originally Posted by ex82watcher (Post 11022710)
LOMCEVAK,a question if I may,in the event you have described,you say that you carried one sparrow to keep within c of g limits.What would happen in a wartime situation,if you had fired all missiles and dropped the tanks.Would you then be flying outside those limits ? would that be possible for very long ?

Without the Sparrow you were still always forward of the aft cg limit but handling was degraded. What I should have said above is that we carried a Sparrow to improve the flying qualities in pitch from those at close to the full aft cg limit. Flying without the Sparrow and using the published full back stick take-off technique I did once scrape the tips of the horizontal stab on take-off.

Dominator2 5th Apr 2021 13:54

LOMCEVAK

I did once scrape the tips of the horizontal stab on take-off.
.
I believe that the recommended technique was Full Aft Stick until the nose started to rise and then move the stick forward to hold the takeoff pitch attitude 8-12deg. The aircraft "should" then fly off the ground smoothly. This would even allow a wingman to stay in position during a formation takeoff!

Even with the correct calculations there was a lot of variation due to such factors as nose oleo pressure and C of G.

Your advice about the Forward Sparrow and C of G is correct and was introduced as part of the "dulling down" process. As the ac became ever more G limited and fatigue became an issue, HQ 11Gp looked for anything to reduce over stresses. Yes, without the Fwd Sparrow the ac was even more pitchy, however, once practiced it was a joy to fly. The Ballast Sparrow just made it heavier and less responsive.

212man 5th Apr 2021 14:08


Originally Posted by LOMCEVAK (Post 11022755)
Without the Sparrow you were still always forward of the aft cg limit but handling was degraded. What I should have said above is that we carried a Sparrow to improve the flying qualities in pitch from those at close to the full aft cg limit. Flying without the Sparrow and using the published full back stick take-off technique I did once scrape the tips of the horizontal stab on take-off.

interesting that when I look at the numbers the Sparrow is about 1% of the weight of the aircraft (230 kg vs ~25,000). Was the difference just c of g or aerodynamic?

ex82watcher 5th Apr 2021 14:40

Thanks for the answer LOMCEVICK.I had one experience at flying outside of limits,and it wasn't very pleasant Decided to take my uncle for a quick flip in a Jodel.The a/c was full of fuel,and John was a big chap,and as a very low-houred PPl,I stupldly didn't think of W+B,and set off.Once airborne,despite full nose trim,I had to use a lot of forward stick just to maintain level flight.I didn't like it and went round and landed from a very flat approach.Never made that mistake again !

Dominator2 5th Apr 2021 15:05

ex82watcher, Your story reminded me of a trip I did while doing my PPL at a flying club on the South Coast near Brighton. One day I had gone to Biggin with my Instructor in a Cessna 150 for some Flying Club business. While there a chap asked if we could give him a lift to Gatwick.

I reminded my Instructor that we were in the 150 but he said that it would be OK. The Cessna 150 is a 2 seater with an allowance for a 30lb bag behind the seats!

The takeoff took nearly the whole length of Biggins runway and then our rate of climb was almost non existent.

When we arrived at Gatwick we were twice told to orbit due to airliners on approach. Each time we turned we entered light buffet with 30 deg AOB!!! It was only later having a chat with a fellow student with a beer in hand I realised how close we had been to stalling a number of times very close to the ground.

LOMCEVAK 5th Apr 2021 15:36

Dom2,

The stab scrape occurred on my fourth Phantom sortie, the other three having been in ‘C’ fit. I was trying to fly the technique that you describe but I was too slow in moving the stick forward to arrest the nose up pitch rate so overshot 12 deg pitch attitude. Lesson learnt!

212man,

I believe that it was just cg related as there was quite a long moment arm to the front station.


A4scooter 5th Apr 2021 16:38

I had a conversation with a former USAF Phantom pilot who had done an exchange with the RAF and he commented that the Spey version reached mach 2 very quickly but wouldn't go any faster while the J79 version although not having the same acceleration was the faster aircraft.

BEagle 5th Apr 2021 17:08

I'm highly envious of the speed limits some are quoting on this thread! By the time I flew the F-4 (usually in 'C' fit) in the late '70s, we were limited to around 500KIAS, but I think that in 'B' fit it was 600? We also had a g limit of around +4 and spent most of the time at 350KIAS or less due to the fuel 'moriarty'. Then once a year the tanks came off and we were allowed a bit more speed and g at Deci', but that could come as quite a shock when you've had to potter about at such pedestrian limits for most of the year.

I recall a 527th Aggressor pilot asking why I hadn't tried to defeat his tracking with a 'guns jink' - when I told him of our restrictions, he asked what the heck the RAF was playing at by limiting us in such ways.....


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