It's Not A Copy

From Matronics


  By Jim Goolsby

"To be or not to be." Or when is a copy a copy? Nine years ago when I 'discovered' the CJ-6A and fell in love with the airplane, I was told incorrectly that the CJ-6A was a copy of the Yak 18A. It was a popular fable of the time. Even my export shipping paperwork from China had it listed as "CJ-6A/Yak18A". But these two airplanes are very different in design and their actual histories reveal that. It may be that I'm still like Don Quixote, jousting at windmills, but I'm going to try to straighten out some of you diehards.

It seems that years ago, most westerners didn't believe (and some still don't) that the Chinese were capable of anything but copying Russian stuff aviation wise. This view may have started when the PRC (PeoplesRepublic of China) started assembling the MIG-15 used during the Korean War. Afterward, the PRC under one of its many "5 year plans" of industrial expansion, started building the Yak-18 (379 aircraft between 1954-1958) for use by their Air Force, Navy, and CAAC. They gave this aircraft the "CJ-5" designation. At the same time they were training young engineering students in their universities to establish an aviation industry. A Mr. Azhou Zhang, a British educated engineer, was responsible for the first ever-static test program in China. This program was tested on the CJ-5 (Yak-18) starting in May 1954.


CJ-5 (Yak-18) Power by the 160hp, M-11FR. The first aircraft to be produced in China 1954-1958

The first Chinese production CJ-5 flew on July 3, 1954. According to official Chinese literature, the CJ-5 was "totally" manufactured in China. However, Doug Sapp of Omak, WA. who has a Chinese CJ-5 believes that only the major airframe assemblies were actually built. Many of the instruments, wheels, and other small parts had Russian lettering on them. This was borne out in a speech by Bushi Cheng at Manitowoc, Wis., in July 2001 where he noted that at that time the instrument factories were just being built and Russian parts were used. The 5 cylinder M-11FR (160hp), that powered the aircraft, became the first production (under license) aircraft engine in China.

In the meantime, a design team, head up by Zhiqian Huang (a US educated aeronautical engineer) and Zhengda Ye (educated in Russia), was assigned the project of designing a jet trainer. Part of that design team, whose average age was 22, was a young man named Bushi Cheng. The "Chief Designer", Shunshou Xu, urged the team to "read 300 Tang dynasty poems and not stick ourselves to just one MIG theory." We might call it 'thinking outside the box' and they did just that.

The aircraft they designed was designated the JJ-1, and it first took to the air on July 26, 1958 piloted by Zhenwu Yu. Powered by the PF-1A jet engine, (thrust 3,500 lb.) designed and built at the Shenyang Aero Engine Factory. This was a .5 mach cruise trainer that, according to Bushi Cheng, had excellent handling characteristics. However, development and production were halted because of a change in the Air Forces training program. At one point, the Air Force had planned a three step-training syllabus. Trainees were to be taught the basics in the CJ-6, then moved up to the JJ-1 for introduction into jets, and than up to the UMIG-15 (2 seat MIG-15) for the final training phase. They changed to a two step phase, dropping the need for the JJ-1. The one and only JJ-1 prototype is now located in the Air Force Museum outside of Beijing. The JJ-1 was China's first indigenous designed aircraft.


The JJ-1 prototype. China's first indigenous designed aircraft.

The need for a better performing basic trainer with a tricycle gear became apparent. The "Yak-18A", derivative of the Yak-18 was available from Russia; however, its performance was disappointing to the Chinese. Importantly too, China was mass-producing aluminum, which was more readily available than the steel used in the Yak-18A's truss airframe. Plus the Chinese were sensing that this was an opportunity to develop further their own indigenous design team that had produced the JJ-1. More simply put, they felt they could design a better aircraft.

The first general layout of the design was assigned to the late Jiahua Lin and Bushi Cheng (then 27 year old). In conversations with Bushi Cheng, (now a professor emeritus at a number of universities in China, as well as an author of both text and popular science fiction books plus a concert violinist) I learned that they started their design process by first interviewing numerous flight instructors. They wanted to understand what the instructors wanted in the new airplane. Mainly, they learned that commonality of instrumentation and aircraft operating systems were thought to be the most important. So - if you look inside the CJ-5 and then the CJ-6A, you will see they are practically the same, but that is where the similarity ends.

Besides using primarily aluminum-alloy material and a fundamentally different structure, the new design was to use an entirely new power package also. It was an eight-cylinder horizontal opposed air-cooled engine and a new propeller that were in development in Czechoslovakia, known as the "Doris-B". With this engine installed, the CJ-6 prototype's nose sections looked very much like a T-34's. A full-scale wooden mockup was built at the Shenyang Aircraft Factory; however, in May 1958 the development work was moved to the Nanchang Aircraft Factory. Some 5,100 pages of engineering drawings were released to the factory. Interesting note: all of the first airframe's major sub-assemblies were riveted together in 14 days. The final assembly was completed in 7 days by 3 work shifts. A full-scale airframe was used for static tests to destruction and drop tests of the landing gear performed.

The prototype with the "Doris-B" engine and prop first flew on August 27, 1958. The test pilots were Yinxi He and Maofan Lu. However, the engine and prop didn't match each other and some "severe technical problems" required a major change. The Czech engine never made it out of development and in July, 1960, the power section was changed to the readily available 9 cylinder radial Soviet A-14P and F530D35 propeller.


The #1 CJ-6 prototype. Note the Czech (Doris-B)
horizontal opposed engine. Bushi Cheng is at far left.

Flight test on the prototype resumed with the engine change out. This included spin tests performed by Zhaolian Huang a western-trained (USA, England, etc.) pilot. The results of the spin tests showed that no modifications of the basic design were required. Problems found in the prototype's design were: (1) Unbalanced fuel consumption between wing tanks. (2) low engine cylinder temperatures. (3) excessive right yaw and (4) poor oil cooling. Though manageable now, these are the most notable operational characteristics that need to be monitored while flying the CJ-6A even today.

The production prototype made its first flight on Oct. 15, 1961. The flight-test program lasted 612 flight hours and included over 1,800 takeoffs and landings. In January 1962, the government approved full-scale production at the Nanchang factory. Then in 1963 the Chinese started producing their own version of the AI-14R nine cylinder radial engine called the HS6 (260 hp). This was the standard engine for the "CJ-6" until 1965 when some production aircraft started getting the HS6A (285-hp) engine. The aircraft designation became the "CJ-6A" with the 285hp engine, which are most of the imports to the US.


A standard CJ-6A. Engine is a 285-hp HS6A.. Terry Calloway, owner and pilot.

Between the years 1964 and 1966 an armed variant of the CJ was produced. However, the records only show that 10 CJ-6As were "retrofitted" at Nanchang factory with hard points for armament and were designated the CJ-6B. It was speculated that the HS6D (300hp) engine was fitted also, however, this engine did not become available until 1975. It is not known if these ten aircraft went into the Chinese military inventory or were for a foreign customer as has been written elsewhere. China's Nanchang factory built 15 aircraft for Albania, 35 for Bangladesh, 50+ for North Korea, 12 to Zambia, with unknown numbers to Tanzania and Cambodia. In mid year (2002) Sri Lanka purchased 10 aircraft for their air force.

The CJ-6 is still in limited production, one of the longest in the world. The aircraft also has a new designation, the "CJ-6G". It is available with a variety of modifications, including increased power, increased fuel tank capacity, western avionics, some airframe strengthening, higher maximum gross weight, and even hydraulic brakes. She is still China's first indigenous designed and produced aircraft.


The Yak-18A

A very short history of the Yak-18A

The Yak-18A is not a direct follow-on of the Yak-18, as the designation may seem. Her direct lineage comes from the Yak-18U.

The "U" was a straight Yak-18 with the main gear turned around so as to fold forward, then mounted on the rear spar and a nose gear was then placed on the front (very much like its present day prodigy, the Yak-52). It still had the 160-hp M-11-FR-1 engine and performance was considered poor. The 18A was the next design variation. Basically, her nose was lengthened 18 to 21 inches (depending on whom you talk to), wing span increased 12 inches and the 260 hp AI-14R engine installed. She was in direct competition with the CJ-6, who, at that point, shared the same power plant.


The Yak-18U

Well that's the basic history of the CJ-6A and the Yak-18A. So why is it not a copy of the Yak-18A? "Hey man, they look the same to me!" Below I tried to compare apples to apples. Let's see what happens.

Airframe construction
Tricycle gear, low wing monoplane, tandem seat (2) Tricycle gear, low wing monoplane, tandem seat (2)
All aluminum, flush rivet, semi-monocoque. Welded steel truss, with aluminum stringers
covered with aluminum panels and fabric.
Wing construction and Airfoils
Aluminum cantilever with flush riveted, stressed skin. Aluminum construction, fabric covered
Center section --------NACA 23016 Center section --------Clark-YH
Inter section of outer panel-------NACA 23015.2 Inter section of outer panel-- Clark-YH
Tip ----------------------NACA 4412 Tip ----------------------Clark-YH
Dihedral --------------------------- 7 degs. Dihedral ---------------------- 7.2 degrees
Twist ------------------------------ 3 degs. Twist -------------------------- unk
Angle of sweep ------------------ none Angle of sweep ------------------ 2 degrees
Aspect ratio ---------------------- 6 Aspect ratio ---------------------- 6.61
Tail surfaces.
Cantilever aluminum stabilizers, Metal construction, fabric covered, with external wire bracing
Rudder & Elevator: Fabric covered Rudder & Elevator: Fabric covered.
Airfoils --------------NACA 0009M Airfoil ---------------- ?
Landing gear
Landing gear Pneumatic operated with trailing link shock absorber. Fold inward flush with center section with fairing gear doors. Main gear leg shock absorber. Folds forward and remains outside of wing. No doors nor fairing
(CJ-6) HS6 260-hp License copy AI-14R
(CJ-6A) HS6A 285 hp (Chinese version M-14R)
Russian built ----- AI-14R 260 hp
MTOGW --------------------------- 3,080lbs

Avg. EW --------------------------- 2,410lbs

MTOGW ------------------- 2,895lbs
Avg. EW ------------------- 2,255lbs
Speeds & Altitudes
Vne ---------------------------217mph Vne ----------------------------211 mph
Max level flight speed (sl) --------178mph Max level flight speed (sl)-------159mph
1000m (3,281') -----------------176mph 1000m (3,281') ------------------148mph
2000m (6,562') ------------------173mph 2000m (6,562') ----------------138mph
3000m (9,842') ------------------167mph 3000m (9,842') -------------- 126mph
Max altitude -------------------17,061 ft. Max altitude -------------------16,405 ft.

Of particular interest to me is the difference in airfoil sections that make the CJ-6 a distinctly different design from the Yak. The Clark-YH airfoil on the Yak was pre-1933 and was used in a slightly modified form in the real hero of the Battle of Britain, the Hawker Hurricane. The NACA 23000 series airfoils, however, were wartime developments and did not see common use until after the war. The post war Beechcraft Bonanza uses the NACA 23015 airfoil. Note, also, that on the Yak the Clark airfoil is through the whole span while on the CJ-6 the wing sections taper to a NACA 4412, an airfoil suited for the dynamics there. In all, it is a more sophisticated and efficient design.

The overall cleaner aerodynamics of the CJ-6, with it's flush riveted wing, has a speed advantage flat out at altitudes. The stowing of the main gear has much to do with this and the Chinese did not sacrifice any strength but actually the design improved ruggedness by using the trailing beam shock absorber. The gear design took into account the many hard landings expected from ham fisted students on rough fields.

The one feature that both aircraft share is the cowling for the radial engine they both used. A case now of mistaken identity leading to some believing the CJ-6 was a copy of a Yak. If the Czechoslovakian Doris engine had came to fruition this would not have been the case.

So why do aviation folks who should know better, still call the CJ-6 "Yaks"? Part of it is laziness. It's easier to say "Yak" than "CJ-6". Controllers who work all day long with spam cans of Cessnas and Pipers get thrown into confusion by different call signs. It's easier for them to hear and say, 'Yak', and they will know only that when they "see" it, it will look different.


Believe it or not, some CJ owners still think the CJ is a copy of a Yak. They like to point out the engine, the pneumatic system, the instruments etc. etc. They think that the systems make the airplane; but they don't because 'systems' are common to all aircraft. A wheel is a wheel, be it on a Piper or Cessna. The same manufacturer of a tire, tube, rim, and brakes may be used on several makes and designs of aircraft. It's the same for engines, instruments, and avionics packages.

I'd like to use the example of one model of the Lockheed Constellation and Douglas DC-7c. They used the same Wright (3350) engines. They used hydraulics for gear, flaps, and brakes. Their electric systems, I'm told were very much alike, including the make of CBs. There was not much difference in speeds or weight (same class). Their construction was state of the art at the time and therefore similar. However there is not one person who can say they were copies of each other. To many in the airline industry at the time, the "Connie" was the most beautiful and elegant airliner to take to the air.

In my conversations with Bushi Cheng, now 73, I could hear the pride he felt in being involved so deeply with the design of the CJ-6. He was a teenager on the streets of Guilin during WWII and remembers being impressed by the pilots of the AVG (Flying Tigers) who flew from there. This led to drawing airplane pictures in his school notebook and finally to the Qinghua University, where he designed his first 'real' airplane as a graduate student. It was a cabin, high wing monoplane, with strut braced fabric covered wings. The fuselage was aluminum monocoque with conventional gear. It had a M-11FR (160hp) engine with a Yak-18 cowling on the nose. It was called the "Diligence" and was a design project for the Shengyang Institute students to build.


Bushi Cheng Designer of the CJ-6 Author's note: The Chinese people sign their names by last name first, first name last. It was several years before I realized this and often called him "Mr. Bushi."

In July 2001 our Yak Pilots Association raised money to have Bushi and his wife Yxie, come to our Manitowoc formation clinic and AirVenture 2001. In all these years of being involved in China aviation industry, Bushi Cheng had never gotten a chance to fly in the airplane he designed. I asked why. He looked off into the distance as if looking back then smiled and shrugged his shoulders. "Too busy. No time." Well we made sure that he got to do just that at Manitowoc.

There are now some 200 CJ-6As located in the United States. Because of its low acquisition costs, simple systems, rugged reliability, and excellent flying characteristics, it has become a very popular Warbird in the sport aviation community. Most of the aircraft are certified under Experimental Exhibition category that has some minor flight restrictions but is free of expensive STC approved parts requirements. This category also leads to a number of innovative modifications by the individual owners that do not require FAA approval.

One of the most popular modifications is the exchange of powerplants from the HS6A (285hp) to the Romania built, Russian designed, M-14P, with 360 hp available. This engine will almost double the rate of climb as well improve altitude performance. The mod is easy to do since the engines have the same physical dimensions plus the cost of a new M-14P is quite reasonable. This change also requires a different propeller and often a new composite 3 bladed prop built by Whirlwind or MT and will add considerable performance.


CJ-6 Designer Bushi Cheng poses on the aircraft in which he got his first-ever CJ-6 ride -- N21710 owned and flown by the author.

Another modification often done is to increase the fuel load above the 42 gallons normally available. Adding either internal or external tanks does this. There are several different schemes on internal tank placement. The most popular is putting the tanks behind the main gear wells in the center section. Though not the easiest nor least expensive, but from the standpoint of aerodynamics together with weight and balance considerations, is the best solution.

Removal of the out-dated Chinese radios, some 180 lb. of them, is the modification almost mandatory for CJs coming into the US. Installing lightweight western avionics not only allows usability but also allows an increase in payload. Because the original Chinese radios are all located behind the rear seat, their elimination provides an excellent spot for a baggage compartment.

A modification of the exhaust system is a change often done for both a safety and a practical reason. The original exhaust pipes, though designed for easy maintenance, are made of a very poor steel material. It rusts out very quickly and could cause a fire hazard. There are a number of vendors who make stainless steel replacement exhaust pipes for the HS6A engine. Since these parts do not require an STC blessing, they are quite reasonable in price. The change out takes less than an hour and a half. As of this writing the factory is now turning out stainless steel pipes for the American market.


The Yak-2001 Red Star Fly-in, Castle AFB, California ½ the CJ-6As that attended!

With such ease of maintenance, it's excellent handling qualities and the affordable initial cost, its no wonder that the CJ-6A has become very popular, along with its running mate from the communist world, the Yak-52. These 'cold war booty' have allowed an insight into what was the mysterious and dark speculation behind the 'Iron and Bamboo curtains' of their aviation world. With airplanes like the CJ-6A, it is now possible to see the insights on how other people perceived what was needed in a flying machine and how their life experiences and values affected their designs. They produced great airplanes that may not go down in our history as such but are very significant in theirs. The CJ-6 was a product of great changes taking place in China and, like its culture, it was definitely not a copy.

Checklist: Helmet strapped down. Visor closed. Boots in stirrups. Monster in sight. Lower lance. Charge!