Barnaby Wainfan - 7 Sins of Aircraft Design

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The 7 deadly sins of airplane design Barnaby Wainfan (Facetmobile builder, Northrop engineer)
https://www.eaatogether.org/live/forums/6174385951001
The presentation is definitely worth a watch.

I'm not sure if this is the right forum or not, but most of the examples he gives are post war failures. I think it might be illuminating to try and fit failures of projects we talk about to these sins to see how useful the list is. I've created a summary below.

Sin 1: invalid assumptions in specifications
- airplane is a tool
- ConOps defines the job and how it is to be done
- engineers design plane to meet the requirements of the conops
::: examples:
- B-58 only useful for penetration with nuke, not other missions after cold war thawing in late 60s.
- Multi-seat WW-2 fighters for anti-bomber role: Bell SFM-1 Airacuda, Boulton Paul Defiant (no forward guns),
- Failed business model: extrapolate last trend one step too far: SST: speed, Brabazon: comfort, Princess: runways built during WW2 eliminated need for seaplanes, A380: ETOPS change eliminated hub and spoke long haul system.

Sin 2: overconstrained
- too many constraints damage ability to perform mission
- Mission related: restrictive operating conditions, too many missions, unrealistic goals
::: Example: F-111
- non mission related: hangar size, configuration, specific size or other geometric constraints
::: Examples: Short Sterling: hangar size, standard RN hangar led to lack of wingspan which reduced operating altitude to below AA ceiling, US hardened shelters are 44 feet wide.

Sin 3. Dependence on new or immature tech: can give advantage, but: project can fail if tech doesn't work, overoptimism common, need to have a plan B.
::: Examples: Rockwell XFV-12,
JSF: both bet on new tech:
Boeing: low risk on propulsion (Harrier); high risk on thermoplastic wing skins to save weight
Lockheed: high risk on lift fan; low risk on structure
Both bet on new tech, the one that made the new tech work won.

Sin 4. Success of airplane depends on success of engine: engine must perform for aircraft to perform, erosion of engine performance hurts plane's performance (thrust, weight, SFC, reliability)
- If airplane is designed to limit of projected engine performance, airframe can out grow engine: weight increase, drag increase.
::: Example: Eclipse 500 very light jet, Williams EJ-22 turbofan: 500 lbs thrust/$40,000, engine did not produce thrust on time to support Eclipse production schedule, Eclipse bankrupt.

Sin 5. One airplane, many innovations (hobbyshop syndrome): all critical systems must work for vehicle to be successful, working out bugs in many new systems is much more difficult than doing one at a time, one significant failure can doom program.
::: Example: X-33, linear aerospike engine, composite crygenic LH2 tanks, metallic thermal protection system, new lifting body aerodynamic configuration; LH2 tank failed in testing, configuration changed dramatically as aero stability and control issues emerged.

Sin 6. Lack of margin and fallback options: design margins necessary to accommodate shortfalls as design becomes real, weight growth, thrust reduction, higher fuel consumption, higher drag, payload growth.
- Highly integrated design may not have the flexibility to adjust, design margin and fallback options must be designed in from the beginning.
The conventional wing-body-tail configuration works because of the ability to adapt the configuration during design.
::: Example: A-12 GD/MD; weight growth caused by poor load paths and difficulty making large composite parts, approach and launch speeds increased requiring wind over deck, no way to increase wing area of CLmax, span constrained by carrier suitability, sweep constrained by observables, tailless configuration cannot trim flaps.

Sin 7. concept driven design: concept believed to offer some vital advantage, concept becomes more important than suitability of the configuration, advantage may not be real, or may be offset by inherent disadvantages in the concept, design compromises to keep concept pure and fix problems it causes.
- Magic configurations: triplanes, aft tail pusher props, turboprop canards, BWB (maybe for very large aircraft, jury is still out).
::: Example: Beech starship: turboprop canard, all composite, pusher engines; there was no performance advantage over conventional layout to justify price.

The first thing to come to my mind was an example of Sin 4: the Allison T40 engine's reliability leading to the failure of all the aircraft built around it. The Skyshark and Tradewind especially were promising aircraft.

How would you categorize some other projects? Or what projects do you think failed for reasons not listed in these sins?
 
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Nimrod MRA4 - Sins 1 & 7

Sin 1 Invalid Assumption in Spec, -
-Four engines was the only acceptable solution. Of course the job is being done today by a twin.

-The engineerIng resource ramp up was known to be invalid by both parties as the contract was being signed. = 2 years of delay (Original CDr 1999 slipped to 2001)

-The Russian submarine threat all but disappeared during the achieved development timescale;- hence the MR4 fleet sized dropped to unsustainable levels. = No business case

Sin 7 Concept Driven design with perceived advantage -
-Four engines (again) forced the reuse of existing airframe. Initially seen as a cost advantage but as time progressed nearly everything needed was new and costly, exceeding the ability of manufacturing to produce the vast number of small component batches = 3years of delay (First flight Dec2000 slips to Aug 2004)

<No the wings did fit = no delay despite the bull...t>

- A “make it with last century technology because FBW is known to be expensive” wish lead to cable operated ailerons which BAESYSTEMS struggled to deliver. There was nobody left who could do clean sheet design of cable flight controls = 4 years of delays from redesigns <yes 3 redesigns>, retesting, recertifications, and many associated repeat flight tests (the original planned 18 months of flight testing takes 5years)

The ongoing Liliam scam - All seven Sins I reckon
 
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no examples for Sin 4?
I'm sure there are quite a few planes that had good designs but were hampered by poor engine tech..
i'm guessing a few of the PRC designs

as for the XFV-12.. had they resolved some tech issues. could that fueselage carry much? it looks like there's few ideal places for pylons
 
Sin 5: Canadian Avro Arrow tried to develop a new air frame, new engines, new missiles and fire control system at the same time.
All systems were progressing, but at slow paces and high costs. The Arrow prototype flew with American-made engines because Orenda Iroquois engines were not ready in time,

This - late 1950s dilemma - reflects a bigger political problem with generals and admirals maintaining grandeous dreams in the face of decreasing defence budgets. Meanwhile, the Canadian Army wasted time and money developing the abortive Bobcat armoured personnel carrier and the Royal Canadian Navy wasted money on HMCS Brador hydrofoil even after they had decided to concentrate on flying helicopters from DDEs. Fierce inter-service rivalry say admirals and generals competing for shrinking budgets.
 
no examples for Sin 4?
I'm sure there are quite a few planes that had good designs but were hampered by poor engine tech..
i'm guessing a few of the PRC designs

as for the XFV-12.. had they resolved some tech issues. could that fueselage carry much? it looks like there's few ideal places for pylons

And exactly ZERO volume for fuel in the wings...
 
no examples for Sin 4?
I'm sure there are quite a few planes that had good designs but were hampered by poor engine tech..
i'm guessing a few of the PRC designs

as for the XFV-12.. had they resolved some tech issues. could that fueselage carry much? it looks like there's few ideal places for pylons
I mentioned the Allison T40 which, other than a handful of Tradewinds that saw service, killed the Skyshark, Super Savage, and everything else it touched. There are a lot of designs hampered by poor engines, most of the early 50s designs come to mind, but that's a bit different than failing because the aircraft is built around an engine that doesn't appear on time or at all.

I suppose the L1011 might fit sin 4, since by the time RR and Lockheed got bailed out and had the engine working in the L1011 the DC-10 had already captured the three engine widebody market.

I've seen drawings of the XFV-12 with a pair of sidewinders on each wingtip and a couple sparrows on the fuselage, but no bombs. I think Spangenberg said as designed it had negative range, which isn't terribly useful.

riggerrob: I'm not so sure about the Arrow, since an argument frequently put forth about it and the TSR.2 is political issues killed them. If the "customer" changes their mind and becomes hostile to the program, or changes the conops during development (Sandys white paper perhaps), I don't think I would call that a design sin.

And I'm not sure what to call overoptimistic cost estimates: we can build it for this much - no we can't *cost overruns*. I don't know if that's a sales issue by overpromising to get the contract, a management issue by deliberately underbidding, a design issue by assuming problems will be easy to overcome, or a customer issue because the customer rejects realistic estimates (N/G A-12) because they want something at an unrealistic price (GD/MD A-12) and get trapped in a money pit because of it. Whatever it is, it punishes accurate assessments and rewards optimistic ones.
 
And I'm not sure what to call over optimistic cost estimates: we can build it for this much - no we can't *cost overruns*. I don't know if that's a sales issue by overpromising to get the contract, a management issue by deliberately underbidding, a design issue by assuming problems will be easy to overcome, or a customer issue because the customer rejects realistic estimates (N/G A-12) because they want something at an unrealistic price (GD/MD A-12) and get trapped in a money pit because of it. Whatever it is, it punishes accurate assessments and rewards optimistic ones.

Very true.

Frequently now in the defence industry, the business model is based on a very profitable after sales, with the trick being not to make too big a loss to deliver the basic platform. Where this goes badly is when there’s long delivery delays;- the contractor incurs extra cost, goes into bigger debt and can’t survive until the after sales. They know a government needs the capability, so will not let them go bust and this might affect the original bid price.

This new age with significant capital projects coming once every twenty years, the pre bid to entry into service being 10-35 years (big complex projects JSF configuration studies late 80’s, F35 EIS 2015 ) making money by a simple sales transaction just doesn’t work anymore.
 
Sin4 - isn’t this happening on our eyes with B777X program. Russian Myasishchev M-4 Molot.
 
... riggerrob: I'm not so sure about the Arrow, since an argument frequently put forth about it and the TSR.2 is political issues killed them. If the "customer" changes their mind and becomes hostile to the program, or changes the conops during development (Sandys white paper perhaps), I don't think I would call that a design sin.... [/QUOTE]

Agreed!
Avro Arrow may not have been an engineering failure, but she was definitely a management failure. Engineers were too slow in developing all the complex new technology requested by overly-ambitious RCAF generals under a Liberal government.
As soon as John Deifenbaker and his Conservative Party won a federal election in 1958, they cancelled a few "Liberal" programs, most noteably the Avro Arrow (1959). When Deifenbaker waivered over purchasing Bomark missiles, the Conservative Party lost the next federal election.
 
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Sin4 - isn’t this happening on our eyes with B777X program. Russian Myasishchev M-4 Molot.
Nope, the GE9X is a certified engine. I cannot say too much more due to being part of that program, but I can say that it is a fantastic engine, and our customers will be very happy with it.
 
About the AVRO Arrow, read Requiem for a Giant by Palmiro Campagna. He answers many questions about the reasons it was cancelled and has the supporting documents to prove his case.
 
Sin #4:

Westinghouse J40. Billed as a "super-engine" that would produce double the power of existing engines, the US Navy fell for the hype and specified the J40 for several new designs before it had even run on a test stand.

Finally passing acceptance trials a full year late, it only produced 75% of the claimed target power, and even that version was highly unreliable (a higher-powered version was tested but repeatedly failed on the test stand). The afterburner development was even further behind schedule.


Aircraft designed for J40:
McDonnell F3H Demon - first production version with J40 cut short and removed from service, later redesigned production versions ended up powered by the Allison J71 which was larger and heavier, but just matched the promised power of the J40.
Never achieved the success that many felt it could have due to gaining some 2,600 lb empty weight and 9,000lb MTOW, in great part due to the changes needed to fit the J71, and the J71 having greater fuel consumption than the J40, reducing the combat radius.

Douglas F4D Skyray - Douglas chief designer Ed Heinemann was skeptical about Westinghouse's promises, and designed the F4D with a larger engine bay... which was able to accept the larger and heavier but more-powerful Pratt & Whitney J57 easily. Smart man.

Douglas A3D Skywarrior - same designer, same story, same production engine.

Grumman XF10F Jaguar - variable-sweep design that had far more problems than the engine... test pilot Corwin "Corky" Meyer, the only pilot to fly the Jaguar, described it as entertaining to fly "because there was so much wrong with it." Would have required a nearly complete redesign to enter production.

Convair Skate - proposed hull-borne seaplane fighter, never more than a series of paper proposals, from single-seat to 2-seat, single-engined to twin-engined - and even a submarine-carried version!
https://up-ship.com/blog/wp-content/uploads/2011/05/skate1-1024x622.jpg
https://www.militaryfactory.com/aircraft/detail.php?aircraft_id=1211
http://aviadejavu.ru/Site/Crafts/Craft34938.htm
 
I just leave it here - B777X certification is now scheduled for 2025.
Perhaps Sin 3,5, and 6, but not Sin 4. GE has engines that are certified to what the customer wanted and are waiting to go on aircraft for the GE9X engine.

I make these statements not as an employee of my company, but one that loves aviation.

The delay right now is likely related to the flight control architecture as well as now there is so much sensitivity that few want to be the one that signs the cert reports on the regulator side, so it is very much cert by committee. Other industry cert efforts are seeing their programs be delayed due to changes in the FAA methods, with the latest being Gulfstream. It is not to say that this is a bad thing, but anytime there are major changes in the cert program, the first going through it always takes longer. Boeing and the FAA are now having to deal with the fallout of their previous errors.
 
IIRC, engineering the gear-box / clutch power transfer to F-35's lift-fan had to 'seriously push envelope'. As I understand it, there was a nasty tendency for early designs to 'spontaneously disassemble'. Fortunately, on test-stands rather than in aircraft...

Is there public info on how they resolved their 'implausible' power/weight issue ??

Aside from that, any aircraft or engines designed without 'wriggle room', never mind 'growth potential', seem doomed. Gone are the days when a nimble design team could metaphorically cut the wings and engine pods off a 'Manchester', double the 'inner' sections and create the 'Lancaster'...
 
Sin 3:
1) the definition of the sin encapsulates the vulnerability that lurks at the core of the entire weapons system concept, and to a certain extent may overlap with sin 6 in specific cases.
2) The US decision to develop the primary jet fighter which would end up fighting the air war over Vietnam without an internal gun, requiring field lashups and redesigns when armament limitations and rules of engagement collided. (Other nations were guilty of it too, e.g. the UK with the Sea Vixen and the F.3 version of the Lightning, but the Phantom was the one that saw the most combat and was lucky enough that it carried enough missiles to offset the issue.)

Sin 5: Republic XF-103 and BAC TSR.2.
 
IIRC, engineering the gear-box / clutch power transfer to F-35's lift-fan had to 'seriously push envelope'. As I understand it, there was a nasty tendency for early designs to 'spontaneously disassemble'. Fortunately, on test-stands rather than in aircraft...

Is there public info on how they resolved their 'implausible' power/weight issue ??

The clutch technology comes from Carbon/Carbon aircraft wheel brakes, which was a really good starting point. Very high power light weight gearboxes are tricky little blighters due to the ridiculous number of vibration modes. When this goes wrong they discombobulate (running tickety boo to sweeping bits up off the floor) very rapidly. Carbon/Carbon wheel brakes can tend to vibrate especially when cold which generally gets dampen out between the tyre and the long main landing gear leg (although sometimes it can get worse!!) . So the challenge was to join together something that was prone to vibrate with something that was sensitive to vibration. The guys made a great job of doing this but it did take quite a bit of time.
 
Thank you. Be akin to brake-squeal on cars. IIRC, seems 'simple', but is exquisitely sensitive to material formulation...

FWIW, I've met such vibration modes in our lab's old test-tube centrifuge. If you pushed your luck with the balancing, and set an unfortunate speed, it could dance like Fred Astair & 'Ginger' Rodgers. One day, it climbed its feet from their safety cups and made a dash for the exit...

Wasn't such resonant frequency stuff how Stuxnet nobbled those Iranian gas-centrifuges ??
 
You can make a test tube centrifuge whistle making a sound like its bearings are failing by putting some dry ice chunks in a test tube of water. It caused my chemestry teacher to rapidly leave his seat to check on the shrieking dynamo and shut it down. I calmly walked up and retrieved my test tube of no longer smoking water and sat down. He switched it on again and there was no whistle. I resumed my studies.
 
IIRC, engineering the gear-box / clutch power transfer to F-35's lift-fan had to 'seriously push envelope'. As I understand it, there was a nasty tendency for early designs to 'spontaneously disassemble'. Fortunately, on test-stands rather than in aircraft...

Is there public info on how they resolved their 'implausible' power/weight issue ??

The clutch technology comes from Carbon/Carbon aircraft wheel brakes, which was a really good starting point. Very high power light weight gearboxes are tricky little blighters due to the ridiculous number of vibration modes. When this goes wrong they discombobulate (running tickety boo to sweeping bits up off the floor) very rapidly. Carbon/Carbon wheel brakes can tend to vibrate especially when cold which generally gets dampen out between the tyre and the long main landing gear leg (although sometimes it can get worse!!) . So the challenge was to join together something that was prone to vibrate with something that was sensitive to vibration. The guys made a great job of doing this but it did take quite a bit of time.
I believe they also took some tech from the Top Fuel dragster clutch packs, which are very carefully allowed to slip some at low output shaft speeds because otherwise the engine torque will destroy things. And when you're talking about absorbing some 10,000horsepower and probably 5000ftlbs torque, you get impressive "rapid unscheduled disassemblies".
 
I think Sin # 7 can be applied to unconventional aircraft (eg. canards, unusual engine configuration, weight distribution leading to adjustment of wing planform) such as tailless or flying-wing military aircraft (both proven) that gave advantage to performance in exchange of flight characteristics and introducing new concepts to alleviate these problems (that may trigger Sin # 5 whatsoever).

Moreover the last sin could impact the military requirements for the aircraft designed and its role (eg. air force wants large nukes on flying wing bomb bay, flying wing fighters)
 
Sin # 1 (assumptions in specifications) could be applied, I think, on aircraft that fell victim to numerous changes on military aircraft requirements, preferably flight performance and armament.
 
Sin 1: Breguet 690 Series, Consolidated-Vultee XP-81, Curtiss XP-46, Curtiss XP-62, Curtiss XF14C-2, Vultee XP-54, Lockheed XP-58, Kawasaki Ki.60, Fiat C.R. 42.

Sin 2: Messerschmitt Bf 110, Brewster F2A Buffalo, Boeing XF8B, Bell P-39 Airacobra, Nakajima Ki.43 Hayabusa, Nakajima Ki. 44 Shoki, Focke-Wulf Fw 200, Loire 210, Westland Welkin, Fairey Fulmar.

Sin 3: Bell XP-83, Nakajima Ki.87, Tachikawa Ki.94 Berezniak-Isaev BI-1.

Sin 4: Hawker Tornado, Curtiss XP-60, Republic P-43 Lancer, Mikoyan-Gurevich MiG-3 Bloch MB-150 series, Potez 630 Series, Heinkel He 280, Westland Whirlwind, Blackburn Firebrand, Fiat G.50.

Sin 5: Commonwealth Woomera, Kyushu J7W1 Shinden, General motors P-75 Eagle, McDonnell XP-67, Northrop XP-56, Kawasaki Ki. 64, Kawanishi N1K1-J Shiden, Mitsubishi J2M2 Raiden, De Schelde S.21, Polikarpov I-16, Messerschmitt Me 210, Amiot 350 Series.

Sin 6: Horten Go 229, Mitsubishi Ki.46 Dinah, Commonwealth CA-12 Boomerang, V.L. Myrsky, Caudron C. 714, S.A.I. 207, Focke-Wulf Fw 187.

Sin 7: Curtiss XP-55 Ascender, Bachem Ba 349 Natter, Heinkel He 177, Blohm und Voss BV 141, Kawanishi E15K1 Shiun, Aichi M6A1 Seiran, Arado Ar 231, S.A.I. S.S.4, Piaggio P.119.
Is the Northrop XP-79 can be considered under Sin 7?
 
Sin 1: Breguet 690 Series, Consolidated-Vultee XP-81, Curtiss XP-46, Curtiss XP-62, Curtiss XF14C-2, Vultee XP-54, Lockheed XP-58, Kawasaki Ki.60, Fiat C.R. 42.

Sin 2: Messerschmitt Bf 110, Brewster F2A Buffalo, Boeing XF8B, Bell P-39 Airacobra, Nakajima Ki.43 Hayabusa, Nakajima Ki. 44 Shoki, Focke-Wulf Fw 200, Loire 210, Westland Welkin, Fairey Fulmar.

Sin 3: Bell XP-83, Nakajima Ki.87, Tachikawa Ki.94 Berezniak-Isaev BI-1.

Sin 4: Hawker Tornado, Curtiss XP-60, Republic P-43 Lancer, Mikoyan-Gurevich MiG-3 Bloch MB-150 series, Potez 630 Series, Heinkel He 280, Westland Whirlwind, Blackburn Firebrand, Fiat G.50.

Sin 5: Commonwealth Woomera, Kyushu J7W1 Shinden, General motors P-75 Eagle, McDonnell XP-67, Northrop XP-56, Kawasaki Ki. 64, Kawanishi N1K1-J Shiden, Mitsubishi J2M2 Raiden, De Schelde S.21, Polikarpov I-16, Messerschmitt Me 210, Amiot 350 Series.

Sin 6: Horten Go 229, Mitsubishi Ki.46 Dinah, Commonwealth CA-12 Boomerang, V.L. Myrsky, Caudron C. 714, S.A.I. 207, Focke-Wulf Fw 187.

Sin 7: Curtiss XP-55 Ascender, Bachem Ba 349 Natter, Heinkel He 177, Blohm und Voss BV 141, Kawanishi E15K1 Shiun, Aichi M6A1 Seiran, Arado Ar 231, S.A.I. S.S.4, Piaggio P.119.
Is the Northrop XP-79 can be considered under Sin 7?
In September 1942 John Northrop proposed to the USAAF the construction of the MX-322 (XP-79), a rocket-powered point-defense interceptor with flying wing configuration and prone-pilot with glass bubble nose. The airplane should be powered by an Aerojet XCAL R-2000 A-1 bi-propellant rocket engine, with 906 kgp (2,000 lbf) peak thrust, and was theoretically capable of reaching an altitude of 12,000 m (39,360 ft) and a maximum speed of 865 km/h (538 mph).

The prone position would permit greater maneuvering g-forces than a conventionally seated pilot and save the drag generated by a conventionally windshield/canopy ensemble. The proposed armament was four wing-mounted 0.50 cal Browning M-2 heavy machine guns, with 250 rounds per gun. The airframe was to be built of welded magnesium alloy and include 45-degrees angled, 20 mm thick plates to provide armor protection for the propellant tanks.

In many published reports the armored leading edge was misinterpreted as a collision tactics ramming device and the XP-79 was wrongly denominated Flying Ram.

In the original blueprints the mock-up initially had a central fixed skid or a modified landing gear with two retractable skids, but it was replaced by four retractable legs with wheels in a later design (MX-365) in July 1943.

The XP-79 should use two GALCIT Jet Assisted Take Off solid fuel rockets, with 453 kgp (1,000 lbf) peak thrust each. The Aerojet engine employed two primary combustion chambers, with 339 kgp (748 lbf) peak thrust each, and two auxiliary chambers with 113 kgp (250 lbf) each.

The whole ensemble, Rotojet, revolved to generate propellant pumping action through centrifugal force. The excessive complexity of the mechanism caused considerable delays in the availability of the engine and the XP-79 was canceled in September, 1944.

XP-79 technical data

Wingspan: 10.90 m (35.7 ft), length: 3.65 m (12 ft), height: 1.05 m (3.44 ft), wing area: 25.82 sq. m (287 sq. ft), max weight: 3,115 kg (6,876 lb.), estimated max speed: 865 km/h (538 miles), ceiling: 12,200 m (40.000 ft).



On January 12, 1943 the Northrop-Maywood aircraft factory was authorized to build three prototypes, but in March the USAAF decided to modify the third airframe (43-52437) as XP-79B powered by two Westinghouse 19 B turbojets.The wingspan of the new model was shortened 61 cm (24 in) and the overall length increased 23 cm (9 in). The wing trailing edge contained elevators, flaperons and split decelerons, the foot pedals were connected to air valves, located in ducts on the wing tips that opening the split surfaces to provide braking effect, caused the airplane to turn.

After the accident suffered by the demonstrator N-9M-1 on May 19, 1943, the USAAF ordered the installation of a pair of large vertical stabilizers to prevent flat spin. The XP-79B was destroyed during its first flying test on September 12, 1945. The project was cancelled in January 1946.

XP-79B technical data

Wingspan: 11.58 m (38 ft), length: 4.26 m (14 ft), height: 2.13 m (7 ft), wing area: 25.83 sq. m (287 sq. ft), max weight: 3,933 kg (8,682 lb.), estimated max speed: 880 km/h (547 mph), ceiling: 12,000 m (39,360 ft), range: 480 km (298 miles).

Engines: two Westinghouse 19 B (XJ 30) turbojets with 618 kgp (1,364 lbf) thrust each.

In January 1943, the U.S. Air Material Command ordered the construction of three gliders to prove the concept XP-79. The MX-334/I was used in the aerodynamic tests in the NACA-Langley wind tunnel.

The MX-334/II had skids and flew for the first time on September 4, 1943, towed by a Cadillac. The take-off was quite bumpy, and it was decided to install a detachable trolley. The next flight took place on October 2, towed by one P-38 Lightning.

An Aerojet XCAL R-200 rocket engine, with 90 kgp peak thrust, was installed in June 1944. On July 5, the MX-334/II was towed to 2,500 m (8,200 ft) and successfully made its first powered flight, becoming first rocket plane in America.

The MX-334/III was destroyed at take-off on November 10, 1943. After the accident of the N-9M-1, the other two prototypes received stabilizing vertical surfaces, with support wires.

The MX-334/II changed its designation to MX-324 and got a new (fixed) tricycle landing gear, the main wheels having trousers and the asymmetric nose wheel a spat. The installed engine weighted 194 kg (428 lbs.), including a tank of Monoethylaniline fuel, a tank of nitric acid oxidant, four pressurized gas bottles, the combustion chamber, and the electric control system.



MX-324 technical data

Wingspan: 10.90 m (35.7 ft), length: 4.34 m (14.2 ft), height: 2.13 m (7 ft), wing area: 23.41 sq. m (260 sq. ft), max weight: 1,656 kg (3,656 lb.), estimated max speed: 480 km/h (298 mph), ceiling: 5,200 m (17,056 ft), range: 480 km (298 miles).

Airframe: wood/plywood/steel tubing.
Ah, I am asking is the aircraft would fall under the seven sins of aircraft design, not for the overview.
 
As to Sin No 1 being root cause of XP-46, XP-62 I would say 'more due to lack of talent' than specification over control.

The two features distinct from P-40 design were 1.) imbedded radiator aft cockpit, and 2.) New airfoil section NACA 23016.5 which hopefuly would drive performance to stated AAF-MD requirements.

Neither the new wing, nor the attempt at a meridith effect cooling sysem, reduced drag to a level that was achievable with the Allison V-1710-39 to push the XP-46 at mandated condition of self sealing tanks, full combat fuel load an armament.

The elapsed time between contract (9/39) and first flight (2/41) was beaten by at least 8 months by North American's X-73 independent of Alison's inexcusablly late delivery of commited V-1710-39 for X-73. And, the XP-46 was 1000 pound lighter than production NA-73/Mustang I which was 30mph faster than Xp46 - both fully loaded.

The XP-46 when suitably burdened by armor plate, minimum armament, and combat fuel load out - dropped 50mph in top speed. That implies Induced drag increase due to Dekta GW, but more likely due to CD vs alpha increase of the wing body at the 'new angle of attack' for high speed operation.

Don Berlin spearheaded XP-46 and XP-60, then left to run XP-75 design. Is there a thread here?
 
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