Design Exercise: A British F-4 Phantom-like aircraft

[iverson]

Leaving aside all the alt history stuff I am still puzzled by this exercise.
While you may be taking bits and pieces to design a late 1950s alternative to the F4 you are starting from the experience of 2021.
By putting together some engines, systems, weapons and an airframe you are simply drawing your favourite type of plane outside of any valid context.

You are right, of course. But if one does immerse oneself in the actual context, the circumstances remain the same and the UK inevitably buys the F-4 Phantom. No room for speculation there. The RAF and the RN had good reasons for choosing the Phantom when they did.

If we want to go on speculating, we need to remember that the Phantom itself is only the Phantom from the perspective of 2021. From the front end, it did not look at all likely to be a great fighter. It started as a single-seat attack plane designed by a company that did not exactly have a string of world-beaters behind it (Phantom I, Banshee, Demon). But it happened to have two superb engines (something for which the Navy did not have much of a record), an airframe capable of taking a big radar dish, and room for a second seat. If anything, it was pure accident that it turned out to be the best fighter of its generation.

So what set of accidents might have produced a viable British alternative?

 

[zen]

One of the things that I came across was being given a copy of a study. In which it becomes increasingly clear that something like the F4K wouldn't fit AW.406.
It's too heavy.
It's unable to fly more than 0.5 hours CAP with a missile load.

It only does by two major factors.
1. A series of tweaks to the design.
More power
More blow
A higher attitude at take off.
Either limiting it to the 199ft stroke catapult
Or
always having natural wind to assist....
2. Dropping the fully loaded weight limit and as a consequence making Hermes and Victorious too marginal for F4K operations. Effectively ruling them out leaving only Eagle and Ark Royal.

Now what this study also invites, is adding alternative options in and seeing if they deliver.
Which it turns out, without actually having a design, just a series of figures. Can indeed produce aircraft that do.
Raising the question of what design would actually achieve those numbers

Especially possible if you reach for engines of 30" diameter or use just one big engine.
But of course the real curiosity is can something designed in the 50's using the RB.106 or Spey do it.....

In design terms. Shorts PD.13 and the modified B.103 'Buccaneer' achieve something close. With enough scope to trade away Strike and Attack features for Fighter features (thinner wings, loosing internal weapons bays, trading CSA and related weights for reheat etc). Real designs, with hard calculations behind them. That can be tweaked until they deliver.

In the AH sense a series of components do point to something more like the F4 being desired. Just it never lined up and got into motion.
There is a study based on what it needed to defend the Fleet against Soviet bombers. Mostly concerned with stern chase Interceptors, and SAMs.
In which it points out a mach 2 jet fighter with collision course weapons is an alternative and can extend the Intercept to 200nm, with AEW assisting Tpe 984.
Easier to calculate Interception.
This in the mid 50's shows, they could have specified something like the F4.

 

[uk 75]

Something that has always irritated me is how the Buccaneer is built to operate from Hermes and manages to do so, yet noone in the Royal Navy sees that they need a fighter version which can operate the same way.
If the UK could design a Buccaneer why couldnt it design something similar to replace Sea Vixen.

 

[zen]

The problem is DH110 ought to have entered service by '54, and consequently a successor effort for '64 ought to have begun at that time.
Quite rationally assuming a 10 year service life.
Run concurrent with the Strike requirement N/A.39 the two tendering processes could even have merged.

 

[zen]

The reason the Buccaneer can launch from a 151ft stroke catapult with 14,000lb of thrust is down to the effective Lift Coefficient at Launch greater than 0.8. Due in major part to blown surfaces.
Something like 40,280lb with a 25kt WOD I suspect.

The notional F4 Phantom with early Spey had a projected figure of 0.59 (15 degrees nose high).

So either a twin Spey or Thames has to somehow get a better figure or weight has to be cut out.
Or the amount of fuel has to be reduced by virtue of greater efficiency.
Of the three to meet AW.406 limit of 40,000lb max weight. There has to be a reduction in weight.
....?

However things get easier if we use lighter and smaller engines.
Hence why Blackburn favoured the BE.33 or AS.151 over the Gyron.

However the F8 Crusader cuts undercarriage weight by varying the incidence of the wing. Saving enough weight to offset the increase in weight for the wing and power services to move it.

Shorts PD.13 got by this by the virtues of doing away with the tail and vectoring the engines..and podding the main gear.
The A6 Intruder prototype actually tried the vectoring thrust. Not worth it in the 50's it seems.

In theory (and certainly used at the time in studies) having the engines in nacelles Canberra style spreads the weight more evenly and cuts structure weight. But at a price if an engine should fail.

 

[H_K]

Where there any single-Spey concepts studied or proposed by any UK companies?

I’m thinking something along the lines of the Spey Twosader: single-engine, big fuselage (high fuel fraction), big wing with lots of lift. Somewhat like a single engined B.123 or P.1152 perhaps?

(The Spey seems to have been the best available engine, and single-engine design would be cheaper, less draggy and lighter for carrier use)

 

[zen]

Single Medway concepts Yes.
Since Spey was a scaled down Medway.
A reduced range and load version of B.123 from Brough.
The P.1152 from Hawker.
Earlier Vickers Supermarine Single Engine Type 571.
And even P.1121.

Later on P.146 was a back up STOL solution in case P.1127 failed. That used a Spey or a larger version of RB.199.

 

[uk 75]

Forget single engines. The RN will not accept them.
We've got the Buccaneer and it can do the job as an attack plane.
What do we need to do to get an interceptor version with radar and 4 Red Top/Sidewinder plus 4 Sparrow/Skyflash?
Buccaneer had longer range and better payload than Tornado.

 

[zen]

I'd argue the PD.13 was worth the risk, and with Avons, replacement with Thames or Spey and the inclusion of reheat is quite achievable.
The obvious major change is from vectoring nozzles to blown wing.
Which ironically fits well with the outer wing control surface system.

 

[H_K]

Forget single engines. The RN will not accept them.
We've got the Buccaneer and it can do the job as an attack plane.
What do we need to do to get an interceptor version with radar and 4 Red Top/Sidewinder plus 4 Sparrow/Skyflash?

The idea of a single engine is to ensure carrier compatibility with the Centaurs. I don’t see a large twin-engined interceptor with 8 missiles allowing that.

If we’re talking of a British Phantom then one of the main selling points surely would have been the opportunity to buy something smaller/cheaper to replace the Lightning/Hunter and that would have export potential.

 

[uk 75]

Ok folks I'll leave you to it. Fantasy time.

 

[zen]

The failure to develop such next gen engines of appropriately 30" diameter is I think a central issue here.
And we can effectively specify what they ought to look like.

Something along the following lines.
A weight of 1,650lb.
Dry thrust maximum 8,825lb
Reheated 14,905lb

Implying a conservative fusilage weight of 3,725lb
Needing a wing of 400 square feet

This should lead to a total dry weight of appropriately 20,000lb
And with engines
s.f.c dry 0.7lb/lb/hr
s.f.c reheated 1.8lb/lb/hr

This should give us a figure of roughly 13,000lb (1,625gal) of fuel for launch, climb, 2 hours CAP with reserves for combat and recovery.

For DLI with 2 Red Top this is 32,400lb
For CAP with 4 Red Top 33,300lb.
Strike with 4,000lb of bombs is 35,650
And maximum being under 40,000lb
This meets AW.406 completely.
Meaning Take off in 25kt WOD using the 151ft stroke catapult.
And recovery using uprated mk14 arrestor gear.
Folding to 52ft length or less
Folded span of 22ft or less

However.....
This figures for the engines is a bit optimistic for the time.
Essentially a real world late 50's engine is likely to weigh much more and this imposes weight increases on fusilage, undercarriage and wing (even without increasing area).

What isn't reducible is the avionics, cockpit, pilot etc.....

Still as I churn through these numbers it's clear there is enough scope to meet AW.406. Even if the engines weigh 3,000lb per engine.
Because the thrust and s.f.c figures are entirely achievable for this period.

Of course it's not an F4 with 8 missiles.
But then the F4k span folded was i think 27ft a full 5ft wider than specified.
Weight busted the limit wide.
Needed bow catapult to incorporate mk6 catapult elements.
Needed DAX arrestor system.
An in turn effectively excluded Hermes and Victorious.

But if this conceptual design meets AW.406 fully. It's operable from Hermes, Victorious, and even a modernised Centaur.

Anyway the next generation engines being turbofans were lighter. RB.153 was about 1,450lb for example. Making an early 60’s design even more achievable.

 

[H_K]

Where can I find more info on AW.406?

Also why was twin engine such a critical RN requirement when the USN was operating deck loads of mostly single engined aircraft?

 

[zen]

So quick answers.
AW.406
a)TO from BS.4/151ft catapult ISA 25 degrees with 25kt WOD.
b)Climb to cruise out, loiter 100nm from CV
c) loiter for at least 2.5 hours
d) accelerate to combat speed and Intercept target of Mach 2.5 at 65,000ft. 5 minutes full power.

e) return to CV at 20,000ft with sufficient fuel for recovery, overshoot and subsequent landing. Using uprated mk14 arrestor gear with a maximum of 25kts WOD.
Other requirements
a) ISD by 1970
b) Two crew
c) AI detection of Canberra sized target at 60nm
d) Max folded dimensions 52ft long, 22dt wide
e) Intercept with 4 AAM initially Red Top
f) Secondary Strike with 4,000lb sortie of 200nm at Mach 0.92 at 500ft
g) Max speed at 36,000ft Mach 2+ in normal Interceptor configuration.
h) Ferry range 2,500nm
j) All up weight of clean aircraft with full internal fuel of 40,000lb or less.

Then engines....
Experience of single engine types, despite being fairly reliable centrifugal powered Attacker and Sea Hawk, led RN to prefer twin engines.
This also was a covert means to resist the imposition of NMBR.3 'winner' P.1154.
Which is mostly down to the realisation they wouldn't be getting P.1154 for light Attack and day Fighter duties to compliment their desired OR.346 system.
But were in fact only going to get P.1154 and this was going to have to fulfil FAW duties as well.

In the process they excluded ALL single engined aircraft. Even though previously they'd been looking at things like the F8U-III, Spey Twosader, etc...

 

[zen]

If....if we assume the RB.106 Thames is roughly the same size as the Spey.
But produces 15,000lb dry and 21,000lb reheated....
And even assuming a weight of 4,250lb for each complete engine.

Then in comparison to the notional Phantom with Speys of the time.
The Thames powered aircraft can launch without reheat and only a reduction of 2,845lb in fuel.
While in reheat it can launch with over 1,000lb of extra weight, equivalent to 2 more Red Top (making a total of 6).

Yet if we assume a s.f.c figure in loiter of 0.7, this is actually superior to the then military Spey's 0.77.

 

[H_K]

Thanks Zen. Wouldn’t a vanilla F-8E or F5D Skylancer, each with 2 drop tanks, come decently close to meeting these AW406 requirements, including the CAP endurance part?

Even more so if fitted with a 20,000lb thrust Spey engine in place of the heavier, less fuel efficient & less powerful J57?

Trying to picture what incremental evolution from existing technology could have achieved… assuming some design changes or scale up would be required of course to fit the 2nd seat and extra avionics.

 

[zen]

So Shorts did offer a 'anglicised' F8 Twosader with Spey, and other UK systems.
Quite attractive really.
However.....

It wouldn't meet AW.406 in part due to the lack of the F8U-III style inlet, restricting it to below Mach 1.8.
Nor I suspect would it meet CAP endurance requirements.

By contrast P1154 could make over Mach 2 with the right inlets, and could meet CAP endurance minimum.
But it's loiter ceiling stood against it.

The ideal was something like a F4K with VG wings, though it bust the weight limits and recovery limits.
So a scaled Spey solution such as RB.153 however did meet all requirements.
Hence why Type 583 was proposed twice to the RN

 

[H_K]

Yes I was thinking of the Spey Twosader.

I’m pretty confident it could easily meet the 2.5hr CAP requirement. The F-8 with drop tanks could fly a ~2hr CAP at 150nm with much more conservative assumptions (20min combat time ie. 5min AB/15min MIL thrust, 5% reserves plus fuel for 20min at sea level)… so probably already meets the RN requirement. Add the Spey and things only get better.

The Mach 2.0 requirement doesn’t really make sense in hindsight, but I guess back then everyone thought it was the holy grail… relaxing that requirement might have allowed for designs similar to the F5D Skylancer which had excellent low speed / high lift characteristics even if at the cost of slightly slower top speed.

Also curious how much fuel did the P.1154 carry to meet the CAP requirement?

 

[zen]

Correction to make, P1154 didn't quite make 2.5 hours. But did at 2.3 hours.
By contrast F4 with then Spey (11,269lb dry, 18,650lb reheated), made 0.5 hours dry thrust TO and 1.85 hours with reheat.
VG concepts made in excess of the 2.5 hours figure with dry thrust, and both in reheat exceeded 3.5 hours.

All had been modified to 13,000lb of internal fuel except the scaled down Spey Type with 12,800lb. This to permit a more direct comparison.

Intriguingly we can see some suspicious numbers emerge from the paper, in that the s.f.c figures for the BS.100 was given as effectively 0.95!

Mach 2 makes sense when you're dealing with a Mach 2.5 target at 65,000ft. Especially as the variable shock inlet is yielding results from much lower down the Mach range compared to a fixed type.
Especially true when you're missile is Red Top which is sort of a complex sidewinder on steroids with one hell of a warhead.

Another Intriguing thought....had a reheated BS.75 type engine (itself a scaled down straight through Pegasus) scaled to J79 to Spey diameter become available. At a weight of roughly 1,650lb and s.f.c of 0.65......
Then the national F4 starts to drift into meeting requirements.
Since engine weight drops, so can fusilage and wing and less fuel required.

Say a drop from 28,250lb to 22,600?
And fuel down from 13,000lb to 11,000lb?
Fighter 35,250lb
Strike 37,600lb
assuming thrust is similar to Spey
Max TO dry 38,000lb
Max TO Reheat 42,600lb

Though altitude performance might suffer more.
This said BS.75 was 7,750lb so reheat ought to be something like say 12,750lb
Then TO dry is 36,392lb
And reheated 39,826lb
Enough to give margins for such a machine.

 

[H_K]

@zen lots of interesting numbers though I admit I’m a little left behind in the dust and not sure I understand them all! Could you summarize maybe the basic figures of merit for your ideas? (T/W, Fuel fraction etc)

For example, a Spey Twosader would weigh:
~18,000lbs empty
~28,000lbs clean w/9,200lb fuel, 2 pilots & 250rds 20mm
~29,000lbs deck launched intercept w/1,000lb missile load (2 Red Top + pylons)
~34,000lb CAP same as above w/ 2 300gal drop tanks w/4,000lb fuel

Fuel fraction would be:
0.32 on internal fuel (Deck launched jntercept)
0.39 with max fuel of 13,200lbs (9,200lb internal + 4,000lb external).

Thrust/weight with 20,500lb Spey would be:
0.7 DLI T-O weight / 0.84 mid-mission w/50% fuel
0.6 CAP T-O weight / 0.76 mid-mission

That should give a decent baseline to then scale up to more powerful engines or different aerodynamic configurations (e.g. a delta wing like the F5D Skylancer would be similar to the above but ~1,000lbs lighter).

 

[zen]

I'll get to the numbers later, but I will remark that it's both odd and a shame Vought didn't produce a twin engined version of the F8...

 

[zen]

So this early Spey powered notional F4 has a wingloading at TO of 85.2lb per sqft. Curiously this is in reheat.
Dry thrust wingloading is 76lb per sqft.
Thrust to weight ratio 1.142lb weight to 1lb thrust in reheat.
But 1.7171260732lb per 1lb thrust in dry.

Limit was 0.45 thrust to weight ratio.

 

[uk 75]

Buccaneer S2 operated happily from Hermes.
Take that design give it a different wing to allow a faster speed and space for underwing missiles and tanks.

 

[zen]

Buccaneer S2 operated happily from Hermes.
Take that design give it a different wing to allow a faster speed and space for underwing missiles and tanks.

Well....
Right back at the original B.103 to NA.39, with the BE.33 engines it was also proposed as a fighter.
Though the wing would let it down at altitude.
Several more optimised Buccaneer variants were offered, making a good CAP fighter.
Though adding say, Avons would require a change in the main spar 'o' rings to fit them....it is quite do-able.

Arguably again though if it NA.39 was to be providing the basis of a fighter as well. Then the Shorts bid was more worth the risk.

 

[zen]

So....Crusader with Spey
What we need is Coefficient of lift at launch....and this has to factor in the angle of attitude....at least for the wing.
Without that though we can apply other figures.
12,515lb thrust TO = 27,811lb weight
20500lb thrust TO = 45,555lb max weight

Wing A = 375sqft
Ergo TO = 31,950lb weight in reheat
Or 28,500lb weight dry

Conflicting figures, but it ought to be good for the higher figures.
Intriguingly the J57-P-23 is 5,175lb in weight.
39" diameter, length 244"
Mass flow 165
s.f.c 2.1
Thrust 11,700lb dry, 17,200lb in reheat.

Avon 300R
Weight 2,890lb
35.7" diameter (I think it's overall diameter is 37"), length 126"
Mass flow 150
s.f.c 1.853 reheat, dry 0.932
Thrust 12,690lb dry, 17,600lb in reheat

While the Spey 202
Weight 4,093lb
43" diameter, length 204"
Mass flow 204
s.f.c 1.95 reheat, 0.63 dry
Thrust 12,140lb dry, 20,515lb in reheat.

While RB.106
Weight possibly around 4,250lb
37" (35" Compressor face?)
diameter, length 126"?
Mass flow 290?
s.f.c something between 0.85 to 0.7 dry, and roughly 1.8 in reheat.
Thrust 15,000lb dry, 21,000lb in reheat.

So on this basis, compared to J57-P-23.....
Avon powered F8 is 2,210lb lighter. While having 400lb more thrust.
Spey powered F8 is 1,010lb lighter.
While having 914lb more Thrust.
Thames powered F8 is 850lb lighter.
While having 3,800lb more thrust.

 

[zen]

More thinking on the scaled Spey.

In theory....
If fusilage is lighter according to a ratio set by the Spey housing fusilage. Then the scaled Spey housing fusilage ought to be much lighter.
By similar logic the wing out to be much lighter to carry the fusilage and all it contains by a ratio compared to the Spey aircraft.
And in turn the undercarriage ought to also be lighter to carry this lot.

So if a Spey fusilage is 5,700lb, then the scaled Spey ought to around 3,850lb.
And following this logic an aircraft using scaled Speys ought to be around 21,450lb empty.
My only query is then about how much I can reduce tail weight. The figure I quote is based on the P.1154 tail, which is much lighter. But perhaps is too light?

Assuming the same fuel fraction the amount of fuel would be less.
From 13,000lb to 9,870lb
Interceptor (4 red Top) 31,320lb
Strike (4,000lb load) 33,670lb
CAP (4 AAM+350gal DT) 34,170lb

Following this it occurs that if the wingloading is a hard limit when scaling the aerodynamic form. Then the wingloading does remain a constant.
So the wing would have to reduce in area, justifying the reduction in wing weight. From 500sqft to 380sqft.

TO Weight would thus be set by the same Coefficient of Lift, and scaled to available thrust. Of 25,350lb from two scaled Spey Engines.
Resulting in TO weight dry thrust 25kts WOD as 36,392.5
And in reheat 39,781lb

Meaning TO max could include a theoretical extra 350gal DT (making 2) or addional 6,000lb for a maximum of 10,000lb of Strike ordinance.

This Theoretical Aircraft could meet all of AW.406.

 

[H_K]

Avon 300R
Weight 2,890lb
Thrust 12,690lb dry, 17,600lb in reheat

I think I’ve mentioned this in the past, but that Avon weight doesn’t include the burner section. That explains why it seems so much lighter on paper than the J57… no idea what it weighs with reheat.

 

[zen]

Avon 300R
Weight 2,890lb
Thrust 12,690lb dry, 17,600lb in reheat

I think I’ve mentioned this in the past, but that Avon weight doesn’t include the burner section. That explains why it seems so much lighter on paper than the J57… no idea what it weighs with reheat.

I'll one-day be able to check my poor photocopy of a table of RR engines, but I don't think that's right...

 

[H_K]

I'll one-day be able to check my poor photocopy of a table of RR engines, but I don't think that's right...

Here you go. Here’s the specs for the Avon 200 series from Aeronautics magazine (1960)… multiple sources on Google Books with the same specs. (I’ve also seen the same specs quoted from original source material in my book on the Etendard IV for the Etendard IVB with Avon 200, so no reason to doubt the magazine specs)

Thrust / SFC / Weight / Length / Diameter
Metric units on top, imperial units below

Avon RA-24 and RA-28 dry weight is 2,860 - 2,890 lbs for 9,500 - 10,000lb thrust respectively. Lengths quoted confirm this is for the engine only, without reheat.

Fewer specs available for the Avon 300 series, but no way a more powerful engine with added modules is any lighter, especially with reheat added. Most likely someone is quoting the 200 series dry weight by mistake and assuming it’s the same for the 300R.

 

[zen]

Certainly I dimly reccal the Spey was something over 2,000lb or so, and 4,090lb is with the reheat Chambre.
Edited addional.
Found something

Military Turbojet/Turbofan Specifications

Subsonic Spey 2,471lb used in Buccaneer.
2740lb in Nimrod.

Additional thought...

https://www.secretprojects.co.uk/threads/roll-royce-spey-205-25-000lbs-thrust-mystery.1682/

Spey 205 with potential for 25,000lb of reheated thrust......

 

[BlackBat242]

So....Crusader with Spey

Avon 300R
Weight 2,890lb
35.7" diameter (I think it's overall diameter is 37"), length 126"
Mass flow 150
s.f.c 1.853 reheat, dry 0.932
Thrust 12,690lb dry, 17,600lb in reheat

While the Spey 202
Weight 4,093lb
43" diameter, length 204"
Mass flow 204
s.f.c 1.95 reheat, 0.63 dry
Thrust 12,140lb dry, 20,515lb in reheat.

I have found one citation for the Avon 200's weight: https://airandspace.si.edu/collecti...on-mk-28-49-turbojet-engine/nasm_A19670027000 Weight: 1,709 kg (3,768 lb) (Approximate)
Note that the accompanying photo does NOT show an afterburner, nor does the description say it had one - but the number may have been for one with afterburner.
Jane's Aircraft engine section listed a length of 138" for the 300 series with afterburner.

The Spey seems to have had a "basic engine body" diameter of 37.5" - the 43"-44" diameter is for the afterburner module.

 

[Apophenia]

FWIW, Wikipedia also lists Avon 301R dry weight at 2,890 lb (1,310 kg). Alas, Wiki claims to have sourced this data from "Lightning F.6 Avon 301R Specs" (lightning.org.uk).

However, the only engine data provided by the WayBackMachine grab of that referenced page are the outputs Wiki quotes under "Maximum thrust". Where Wiki found the rest of their data is anyone's guess ...

-- https://en.wikipedia.org/wiki/Rolls-Royce_Avon
-- https://web.archive.org/web/20080410235516/http://www.lightning.org.uk/techdata.html

 

[H_K]

The Spey seems to have had a "basic engine body" diameter of 37.5" - the 43"-44" diameter is for the afterburner module

I get approx 36-37” (92-94cm) for the Spey’s front end and 42.5” (108cm) for the afterburner, using this source:

The Spey-Powered Phantom Changes

18 November 2016: For a note on F-4K XT-595 first flight markings, see http://tailhooktopics.blogspot.com/2016/11/f-4k-first-flight-marking...

tailhooktopics.blogspot.com

Also played around with a Spey vs. Atar 9B comparison (eg. Mirage IVK)… not much difference in width except for the Spey’s fat afterburner.

Finally a comparison of Avon vs Atar dry installation in the Etendard IVB/IVM:

My takeaway… J79 vs Spey vs Avon vs Atar were all equivalent sizes as dry engines for a low altitude fighter bomber, however with some differences in the burner length/width that would impact installation and center of gravity on a Mach 2 fighter (plus higher mass flow requiring larger intakes for the Spey).

 

[orlovsky]

From RR well into the Spey AB development:

 

[Archibald]

BAC P.141 or P.146, loved both designs in Tony Butler books.
P.141 with two RB.172s or RB.199s.
P.146 with one big powerful RB.168 Spey.