Lightweight fighter: how would've you done it?

krieghund said:

I agree that the Zero meets the intent of this thread.

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Only Tomo can say.


The Zero was NOT designed as a light weight fighter as in lighter than the nations "standard" fighter. The Kinsei engine was the only other viable engine for the Zero and it may not have given the range required. The Japanese did have larger 14 cylinder engines available but with their larger diameter and weight they may have been more suited to the bombers they were used in. Both the Zero and the Oscar were designed to very stringent performance specifications and a heavier plane may not have meet ALL the performance requirements.

I may be misunderstanding Tomo but I think he is proposing "light" fighters that use a second rate ( or second tier) engine.

Specifically the "emergency lightweight fighter" was the following:
Ta 183 Huckbein; ordered into production without prototype.
Blohm Voss BV-215.02 6 prototypes ordered as complimentary and backup to Ta 183 (my bet as a much better design due to use of slats)

The above 2 were the 'interim solutions'

Junkers EF.128, this was continuing development
Messerschmitt P.1112 Messerchmitt Me P.1112 Luft '46 entry this was also continuing development.

The above were the 'optimal solution' with much more fuel load, easier to protect tanks, bifurcated intakes that helped protect the engine from bomber return fire.

The P.1112 used a 200hp engine driven compressor for intake 'boundary layer suction' so that splitters were required. Succesfull tested in a half model in a wind tunnel.
The EF.128 used a similar system but used passive suction behined the conopy to draw of the air.

This system allowed a sort of coke bottle shape that conformed to an early area rule the Germans had discovered.

All had slats to hand spanwise flow issues on the swept wings except Ta 183. Ta 183 was actually a tailess aircraft with elevon control, the T-tail was for trimming only. The aicraft lacked slats it may have ended up with boundary layer fences, the Germans knew of these, having installed some in an early Me 109B.

The Me P.1112 is probably the best, but EF.128 is also good. The active instead of passive boundary layer suction of P.1112 in EF.128 would be best.

The lightweight fighters is quite different from the 'volksjaeger' that He 162 won. Personally I prefer the designs of Blohm Voss B&V P.211.01

buffnut453 said:

Don't know the specs for the CW-21B but wasn't that designed from the outset as a lightweight fighter (IIRC the term "interceptor" was used because of its rate of climb).

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It would fit the bill almost perfectly, however it had a 1,000 hp engine. It would be a great basis to begin with however.

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There were a number of fighters available that already meet these requirements, the American P-26, Japanese A5M, and a number of German/Italian/British Bi-Plane fighters.

The mininal requirement for a lightwieght fighter is that it can match speeds and altitude with any aircraft, carry a radio, radio compass, IFF, self sealing fuel tanks, pilot back armour, oxygen, maybe some pilot face armour and have the fire power required to bring down bombers and ememy aircraft so that missions and lives lost are not conducted in vain.

Soon looks like a P-47 Thunderbolt. Seversky argued that size is important to do the things that needed to be done.

One thing a lightweight fighter needs is canon armament. At least 1 x 20mm or 2 x 20mm or best of all a single 30mm. One can't afford the weight of more than two heavy machine guns, or worthless rifle calibre pop guns. The single Mk 108 30mm used on some Me 109 had no problems disassembling a thunderbolt wing in 1 hit. The gun was very light lightweight and got its power from being able to fire shells with a great deal of explosive content (cheap also due to minimal metal consumption). Downside is with a Muzzle velocity of under 600m/s max range is 250-300m tops.

Tomo was talking about 1940 so some of the requirements (IFF) barely exist and 1940 bombers were usually not quite as tough as 1943-44 bombers.

also in 1940 the MK 108 didn't exist.

Going by country in 1939-40 you have:

England, only viable engine in the 900hp class is the Bristol Mercury. On 87 octane the MK VIII gave 725hp for take-off and 840hp at 14,000ft. The MK XII could give 830hp at take off and 890hp at 6000ft.
Only gun in service is the .303 Browning with the 20mm Hispano (with drums) waiting to come on stage. Eight Brownings weigh 225lbs and 2800 rounds (350rpg) weigh 186lbs. The Hispanos weigh around 110-120lbs apiece (without drums) and 120 rounds of ammo weighs 75lbs (without drums).

Germany has two/three engines. The old Jumo 210, does anybody think the 109C was a viable fighter in the Spring/summer of 1940? Assuming it was still in production and would not affect Jumo 211 deliveries. Next choice/s are the BMW 132 and Bramo 323 9 cylinder radials. These engines weigh almost 1200lbs and have about 16 sq ft of frontal area. Almost the size of a Cyclone but with 100-200 less horsepower.
Guns are either the MG 17 at 12kg each or the MG FF at 28-29KG.

France has a mixed bag of engines. The Hispano 12Y series might fit under 900hp but every under 900hp 12Y delivered is one over 900hp 12Y engine NOT delivered. Same with the Gnome Rhine 14K/N series. France does have the Hispano 12X series of engines and the Gnome-Rhone 14M engine but these are 700hp engines. Both engines were used in several French "light" fighter prototypes in 1939-40.
Guns are the typical rifle caliber machine gun and the 20mm Hispano with drums.

Italy has a real problem, they are already using under 900hp engines in their first line fighters and arming them with a pair of 29kg (?) guns. The only engine available (without dropping closer to 600hp) is the Isotta-Fraschini Delta air cooled V-12 with a power of between 700-800hp depending on model and date. It was used in the Later Italian light fighters and one French Prototype.
Guns are the typical RCMG and the already mentioned 29kg 12.7mm machine gun.

Soviets have limited engine options. The Klimov series is already spoken for, no sense trying to make a lower powered version. The M-88 sereis is too big and already spoken for. Leaves just the M-61/62 series (licensed/modified Cyclones) except the are already at 1000 or more HP. The I-16 may fit into this "light fighter" category.
Guns are the Russian bright point. There RCMG has a high rate of fire, their 12.7 is powerful and light as is their 20mm cannon.

ANY other European nation not mentioned is using license built engines and usually not fully up to date ones. This generally means that their power to weight ratios are not as good as as the home countries latest developments. For instance the 870hp engine used in the Romanian IAR 80 was a Licensed Gnome-Rhone 14K while the French were building the 14N with improved cooling (and higher power) and had the 14R (with center bearing) in development. All used the same dimension cylinders.

That leaves the US and Japan.

The only 750-900hp engines in the US were the P&W Hornet and Twin Wasp Junior and older models of the R-1820 Cyclone. Building low powered Cyclones instead of high power ones makes no sense and P&W was moving beyond both of those engines anyway. Twin Wasp Junior was used by Finland in Fokker XXI's.

Us guns are the typical RCMG and the Browning .50.

buffnut453 said:

Hmm...wouldn't have included the Jag in that list. It started out life as an advanced trainer but, courtesy of requirements creep, ended up as an under-powered ground attack aircraft.

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You would be hard pressed to find a better GA aircraft for the time.

The best contender that I can think of is the Brisol F5/34. At an empty weight of 4,200lb its very close to your requirement. Its performance was good and it had 8 x LMG which was more than adaquate in 1939/40. It tests it held its own in many ways against the heavier fighters and all in all was a good package.

I have tried to see how weight could be saved and apart from switching from 8 x LMG to 2 x HMG have failed to do so. It engine was light yet delivered respectable power, so all in all its the aircraft I would go for.

i put my choice so a "high performance" biplane (generic also for sesquiplane) in 1940 were usefull and were light they are true light and cheap.

i think all european "new" (SE) monoplane fighter were light fighter, all the temptatives to build a very light fighter were not sucessfull (for a reason or an other)

I'll say the Fokker D.XXI

Engine: 830hp Bristol Mercury VIII
Empty Weight: 3,180lbs
Armament: 4 x 7.9mm Brownings but perhaps replace 2 with a 20mm cannon

I would however build the version with retractable landing gear. It was designed but I'm not sure it was ever built.

Mentioned earlier, I think the CW-21 meet all these requirements for a 1940 requirement. Although the aircraft did not fare well in combat (I believe mainly due to tactics and fighting against superior numbers) on paper it should have been comparable to the zero. It did not have self sealing tanks or armor protection. From Wiki;

Length: 27 ft 2½ in (8.29 m)
Wingspan: 35 ft 0 in (10.66 m)
Height: 8 ft 2 in (2.48 m)
Wing area: 174.3 ft² (16.19 m²)
Empty weight: 3,382 lb (1,534 kg)
Loaded weight: 4,500 lb (2,041 kg)
Powerplant: 1 × Wright Cyclone R-1820-G5 nine-cylinder air-cooled radial engine, 850 hp (634 kW)

Performance
Maximum speed: 314 mph (273 knots, 505 km/h) at 12,200 ft (3,700 m)
Cruise speed: 282 mph (245 knots, 454 km/h)
Range: 630 mi (548 nmi, 1,014 km)
Service ceiling: 34,300 ft (10,500 m)
Rate of climb: 4,500 ft/min (22.9 m/s)

Armament

Guns:
2 × 0.3 in (7.62 mm) M1919 Browning machine guns
2 × 0.5 in (12.7 mm) M2 Browning machine guns

I always thought the CW-21 was a good looking aircraft if anything else!

Hello Viking
Finns installed retractable landing gear into two D.XXIs, they were FR-117 and FR-167, the first flew first time with retractable landing gear in Jan 41, the latter in March 1942.

Fokker D.XXI as light fighter, no, especially those with Twin Wasp Junior were rather poor fighters. I-153 was clearly better as a fighter, it was at least very manouvrable. And I-16 Type 29 is maybe the best candidate, empty: 1545kg/3406lb, gross: 1966kg/4334lb, max speed 461km/h, turned very well, armament one 12,7mm and 2 7,62mm mgs, the Berezina gave the ability to pierce enemy's back armour.

Juha

For a lightweight fighter to be of any use it has to have the same approximate performance of the fighters it may meet, otherwise why build it.
To get to that point with less HP means something has to be left out of the usual requirements.
Pilot weight is pretty much fixed, so something else has to be changed to get the weight down. Reducing pilot protection was the way a lot went, less or no armor, no self sealing tanks.
Lighter weight armament. The Russians had some light MGs and cannons, fast fire rates also, but i'm sure their service life per weapon wasn't long either.

About the only lightweight fighter of any success was the Fokker 21's with the Finns, but they took several aircraft commonly called substandard by other users and got good service out of them.

Maybe a Fokker 21, with retractable gear , more time spent on it's aerodynamics, and Russian Beresin B-20's

FLYBOYJ said:

Mentioned earlier, I think the CW-21 meet all these requirements for a 1940 requirement. Although the aircraft did not fare well in combat (I believe mainly due to tactics and fighting against superior numbers) on paper it should have been comparable to the zero. It did not have self sealig tanks or armor protection.

I always thought the CW-21 was a good looking aircraft if anything else!

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I agree that the CW-21 never had an opportunity to live up to it's potential.

How ever it does help point out the performance "problem" with the light fighter as outlined by Tomo. It's engine may not qualify as a 750-900hp engine depending how how someone views the ratings.

It's engine was actually good for 1000hp for take-off for one minute. The 850hp rating was in low blower and was a maximum continuous rating.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/9d8387f8163ad7d98525670e0065ae06/$FILE/ATTZCGXO/TC154.pdf

From a practical stand point why fit the fighter with the 1000hp take off G5 Cyclone at 1234lbs when you could fit it with the 1100 hp for take-off (for 5 min) G105A model at 1274lbs lbs?

Why deliberately make low powered models of the engines?

I wonder if the CW-21's structure would stand up to combat. It looks like one heavy caliber bullet strike just forward of the tail would break it.
I know you shouldn't judge by appearance, but the aircraft does look frail.

Shortround6 said:

I agree that the CW-21 never had an opportunity to live up to it's potential.

How ever it does help point out the performance "problem" with the light fighter as outlined by Tomo. It's engine may not qualify as a 750-900hp engine depending how how someone views the ratings.

It's engine was actually good for 1000hp for take-off for one minute. The 850hp rating was in low blower and was a maximum continuous rating.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/9d8387f8163ad7d98525670e0065ae06/$FILE/ATTZCGXO/TC154.pdf

From a practical stand point why fit the fighter with the 1000hp take off G5 Cyclone at 1234lbs when you could fit it with the 1100 hp for take-off (for 5 min) G105A model at 1274lbs lbs?

Why deliberately make low powered models of the engines?

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Sometimes you have to de-rate an engine because of airframe stress

tyrodtom said:

I wonder if the CW-21's structure would stand up to combat. It looks like one heavy caliber bullet strike just forward of the tail would break it.
I know you shouldn't judge by appearance, but the aircraft does look frail.

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That was its known weakness, just like the Zero it fell apart rather quickly when damaged

FLYBOYJ said:

Sometimes you have to de-rate an engine because of airframe stress

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I understand that, the low rated Cyclones were kept in small scale production for various aircraft that were never certified for higher power versions, either new builds or replacement engines for older airframes. In the context of this thread however, why build low powered engines for a second rate fighter when, for nearly the same man hours and material you could build the higher powered version of the engine?
If the plan is to build this "light" or "alternative" fighter in quantity ( and if not why bother) stressing the "fighter" airframe for a higher powered engine for a better performing combination shouldn't be that big a deal. It is one thing to overpower a general aviation aircraft or even a transport but if a fighter comes apart because of an extra 10-30% in power something probably wasn't right to begin with.

Agree....

Really well outlined, excellent points Shortround6, you put knowledgeable words to how I was abstractly feeling about the thread, where I normally enjoy being creative.

A light fighter by definition are the interceptors that sacrificed range for climb rate or other performance benefit, using a finite available supply of engine variations. They don't really fall into weight classes like the way modern Jet design has, which is an inferrence that modern fighters are more heavily avionics orientated and weight can almost certainly be related to combat role capabilities. There's no comparison between the F-16 and F-15 for example, although within their respective classes both are superb aircraft.

What it comes down to in warbirds is not really weight classification, but role classification. To correctly apply combat conditions you should compare the A-10 Boston with an Me-110E/F or a Ju-88A/C for example, they're pretty analoguous for deployment roles and field use and already we can see why exactly the Luftwaffe often gained local air superiority unless being numerically overwhelmed.
By the same margin, you should call the Fw-190A a "fast bomber" (schnellkampf: schlacht u- jabo, analoguous to a high speed attack-fighter or fighter-bomber rather than an air superiority fighter or an interceptor, for which it is generally unsuitable), a good comparison to the Fw-190A is the Thunderbolt or Typhoon/Tempest, I'm sure we'd all agree at least on that.

The Luftwaffe had some unique specification in the schnellkampf and later kampf-jabo units which pulled twin engine qualified bomber pilots and put them in single engine fighters for army close support operations in contended airspace, often unescorted and relying upon high speed and surprise for effect. Behind the scenes it represented an effort to build a body of jet fighter pilots within the Luftwaffe as they had to be twin-engine qualified due to low powered engine technology. Jets were initially given to transferred zerstörer pilots and individual celebrities in practise of course, Nazism was nothing if not nepotistic and Göring had a stubborn streak.


Essentially this means by mid-43 a specification was created for purpose built single engine fighter-bombers or fast-bombers (ie. not just bomb trucks, but real hi-po bomb trucks in true F/A-18 style), and the high alt Ta-152/3 höhenjäger was given this secondary role (creating the escort fighter specification under the zerstörer class).
This represents a design requirement departure from Allied fighters, I can't think of any purpose designed for the role, but the Ta-152C is and its contemporaries are the twin-engine medium gunships it was replacing, rather than hi-po regular fighters or even adapted fighter-bombers.

So that's a "light fighter" specification of the zerstörer concept (C-1 zerstörer and tactical recon variant, C-3 schlacht/jabo/SK variant), general fighter was to remain the Dora series until transition to jets was completed over, predictably some years.

But sure in Jets exists the "light fighter specification" which really means more lightly, inexpensively equipped series for general service and export. The kind of engineering specifications for this kind of fighter proposal are high turnaround, low maintenance, good field performance and good ferry range, not so much speed and equipment fit.
Doing this sort of thing in WW2 craft gets you the gnome engined auxiliary combat units, only the Hs129 and Fw189 in that class really, or things like army spotters with bren guns.

tomo pauk said:

Let's say the air force wants a lightweight fighter, with 1st examples in service in 1940. The design is limited to a powerplant of weight under 1700 lbs complete (engine + prop + lubricating + cooling), under 900HP, to carry 200 - 300 lbs of armament, 200 - 300 lbs of ammo, fuel quantity between 80-100 US gals (or whatever it's SI or Imp equivalent, for all the measuring units) in protected tanks, at least some protection for pilot. Use just the bits pieces from one country per one design.
edit: the empty weight is to be under 4000 lbs.
What would be you proposal?

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NAA first proposal P-509. Study completed Dec 1939, presented to AFPC March 11, 1940.

Gross Weight 6455 pounds w/180 sf wing, 1000 Hp Allison, Span 34 ft, Fus.Lngth 26ft. 120gal unprotected fuel, NACA 2516 airfoil. Armament up to 4x20mm, no cowl guns. Projected top speed 400mph at 19K. Never built other than mock up. Full AAF design standard - structures.

NA-73 spawned by P-509.