Model 560, Aero Design photo by Wayne Entrekin, Ron Smith Collection For his book Stars and Commanders, Dave Duntz conducted years of research, including with Ted Smith’s unpublished memoir. The memoir is presented in part here, as Chapter 12 in Duntz’s book. You can purchase Duntz’s book at www.starsandcommanders.com.
Carl Wooten began to set up a small group of dealers, and we had many prominent people visit our plant, among which was Colonel McCormick, who owned the Chicago Tribune and had a converted B-17 equipped as a luxury business aircraft. The Colonel and his pilot, Wayne Thomas, visited with us for several hours one day and Wayne Thomas, who was also the aviation writer for the Chicago Tribune, was good enough to give us good press in the Tribune as well as writing several good stories about our program for some of the trade magazines. While at Bethany, they had placed an order for one of the first Aero Commanders. Another famous visitor was Mr. Charles Kettering and his son, Gene Kettering. They, too, placed an order for an aircraft and Carl also appointed Gene as one of our first distributors.
The first production model 520 was rolled out for first flight in August 24, 1951, just eleven months after we moved into the 20,000 square-foot hangar on Tulakes Airport. An unbelievable achievement! The first production aircraft was assigned to Carl as the company demonstrator. We used the prototype for this purpose prior to this.
First completed Model 520
Our preparations for the roll-out of the first Model 520 included inviting dignitaries, city fathers, and giving company personnel the afternoon off. We built just outside the north side of the hangar, a platform for our special guests to sit. Microphone and speakers were installed, and each of our management team spoke for a few minutes. I reviewed for them the past but said today we were here to honor our visitors, our employees and, most important, the completion of the first production Aero Commander built in Bethany, Oklahoma. I spoke highly of the capability of our people and their dedication to get the job done. I might mention that unless one accepts the challenge to be different, to accomplish something with a purpose, bearing the hardships as they come along, one merely joins in that stream of people who are content and are satisfied with just being one of the masses and satisfied just to do a day’s work. But in the true sense, these people are needed and in their way are just as important to the progress of industry as are those who are the leaders.
Stanley Draper of the Chamber of Commerce was there. He was very proud of the project, as if he himself had built the airplane. In the years to follow, Stanley was good for us. He had a tremendous record of accomplishing things for Oklahoma City such as attracting industry and getting new city streets and highways built and improving their airports. He was responsible for getting the F.A.A. to establish the heart of the F.A.A. on Will Rogers Field in Oklahoma City. Stanley Draper had vision and a true sincere love to see Oklahoma grow. He had been responsible for establishing the Oklahoma City Industries Association and he interested some of the members of the Association in purchasing stock in Aero Design.
At about 3:00 P.M. the ribbon that was strung across the hangar door in front of the airplane was cut by my secretary, Mary Burton. The flight crew pulled the first airplane out onto the ramp, breathing the warm clear air of Oklahoma. Unpainted, it shone there in the bright sun as much as saying: “I am ready to try my wings.”
Model 520 taxiing for first flight with Ted Smith in right seat and Bert Bantle in left. Photo by Wayne Entriken, courtesy AAHS Archives
Since the airplane had to be made ready for first flight including the installation of flight test instrumentation, our visitors, instead of witnessing the first flight of the new airplane, were kept interested in watching the performance of the prototype flown by Bert Bantle and indeed he put on a beautiful show.
A few days later Bert and I made the first flight of the Model 520 which went well indeed and the airplane performed to specification. From then on, all flights were conducted in preparation for the F.A.A. certification flight tests. These were conducted at 5500 pounds gross weight, an increase of 700 pounds over the original prototype. The increase in gross weight was not hard to come by since the detail analysis done previously for certification of the prototype supported it. Just like the A-20 that grew from the 7B Model at 12,000 pounds to the last of the A-20 series that ended up for ferry flight close to 25,000 pounds for takeoff and a combat weight of over 22,000 pounds.
There were many other changes between the prototype L3805 and the Model 520. The model designation 520 was based on using larger Lycoming GO-435 engines of 260 H.P. each for a total of 520 H.P. The 520 was the first to use electric actuating trim tabs on rudder and elevator, and the first to use electric shutoff valves for the fuel system. For the F.A.A., however, the electric trim and electric fuel valves set them back somewhat since there were no guidelines for them to refer to and the case had to be submitted to Washington for a determination of what would be required for certification. We also had a simple single fuel tank system with five tanks emptying into a center sump from which fuel was drawn. This gave the F.A.A. another first to work with and again they had to go to Washington for a ruling.
Word finally came back from Washington pertaining to the electric trim. The requirement was to show the airplane could be controlled manually without excessive force by the pilot in case the trim tab mechanism malfunctioned with a fully deflected tab on either rudder or elevator or both. If necessary, power could be reduced to reduce pilot force input.
We had a little more difficulty with the electric fuel valves and sump. Although fuel tanks of the bladder type are permitted in the cabin section of an aircraft, the sump, attached to the bottom of the fuel cell just behind the rear seat and at the top of the baggage compartment, did not meet the requirement. It was possible to have fuel vapors enter the cabin if a fuel leak occurred at the sump fitting or the hose. This problem was resolved by encasing the sump in a vapor proof housing of metal construction and providing overboard drains. For explosion protection we merely installed, on one side of the vapor-proof box, a patch of nylon impregnated with Buna rubber, which was similar to the material used for fabricating the fuel tanks. The patch was about 4 inches by 6 inches and was retained with a metal frame and this too was sealed to make the entire box vapor proof. In later models of the aircraft the vapor box was eliminated, but the rear bulkhead of the cabin was sealed off from where the fuel sump was located.
The electric fuel valves, again through a determination from Washington, had to be a motor driven type. In case of an electric failure, the valve gate would remain in the position it was prior to the potential failure. We had planned on this type of valve anyway and started out using a valve built by the Whitaker Corporation in Los Angeles. One drawback, however, most of their motor driven valves had parts a minimum of 1 ½ inches in diameter and were really designed for military jet aircraft where very large fuel lines are required. We only needed a ¾ inch opening. It was necessary then to design a casting not only to support the valve, but to also reduce the port size. Several hundred aircraft were built this way before Whittaker was able to build a valve with a port size compatible with the fuel flow requirements of the Commander.
With the electric valves, the fuel system management became the simplest of any aircraft in the world.
As history will show, fuel system management, both in single engine, as well as twin engine aircraft, has caused hundreds of accidents. Most systems, other than the Aero Commander, are usually located on the floor with various positions on the handle to select different tanks on board, and some twin-engine aircraft have a cross feed system which adds further complications. No cross feed is necessary in the Aero Commander fuel system since all of the fuel can be used on one or both engines. In case of an engine shutdown on either side all that is necessary is to shut off the fuel to the inoperative engine and the balance of the fuel remaining can be used for the operating engine.
By the end of December 1951 all the new engineering data had been submitted to the F.A.A., and the production articles had been followed by the F.A.A. inspectors for conformity to the engineering drawings.
From time to time we visited with F.A.A. engineering and flight test people so that we would have a well-coordinated program. This time we had Bert Bantle for our Company pilot and he would ride with the F.A.A. on flight tests when the time came.
During our own evaluation of the 520 in preparation for the type certification flights, a couple of very hazardous things took place.
The first was when engineering had calculated ballast and its placement for C.G. (Center of Gravity) tests. Bert took off believing the aircraft to be loaded to 30% aft C.G. However, in checking the aircraft for static longitudinal stability, he found the aircraft extremely unstable with very high divergent characteristics. Bert landed soon after he found the condition. The weights and placement of ballast were recalculated, and it was found that errors were made in the calculations and the airplane was actually loaded to 43% aft C.G. It was fortunate that he was able to control the aircraft since a 43% aft C.G. location put the limit considerably aft of the neutral point of the airfoil and this accounted for the serious instability problem and the divergence. Most aircraft loaded this way would have become uncontrollable and would have ended in a crash, another plus factor for the basic design of the Aero Commander.
On another occasion Bert and I had taken off to run the airplane up to its maximum dive speed of 300 M.P.H. indicated. We had found during previous flights that the trim tabs on the elevators were marginal to meet the trim requirements at forward C.G., so as a quick fix I had added a piece of .032 material about one inch wide to the trailing edge of the two tabs installed on the elevators. No frequency studies had been done with the tab and its extension.
Anyway, we took off, climbed to 13,000 feet, let the nose down at about a 20-degree angle with power on, and at 240 M.P.H. indicated airspeed, the aircraft began to vibrate violently. The rudder pedals were moving back and forth with violent force and both Bert and I thought that we had lost the tail or at least a portion of it. I started to move toward the door to energize the quick release mechanism so that we both could bail out before it was too late. By now we were less than 5,000 feet and, although Bert had reduced the power, the airplane retained its violent shudder and the rudder pedals continued to move fore and aft with a force so violent and so rapid that it was impossible to even get a foot on one or both of the rudder pedals. Just as I was unbuckling my belt and starting to move toward the cabin door, the horrible and terrifying vibration ceased, and the rudder pedals neutralized. Checking rudder control, Bert found the rudder pedals to be free as if they were not connected. We had no control in yaw. Had we lost the rudder and part of the tail? We did not know. We did know that we still had elevator and aileron control for these controls responded normally. We gradually descended and headed for the long runway at Will Rogers Airport about eight miles south of Tulakes.
Since the airplane had very high directional stability, it seemed to be holding a heading rather nicely. We both felt that most of the vertical fin must be intact or nearly so.
What little directional control we needed was obtained with asymmetric power and aileron. Bert made a perfect landing, braked to a slow taxi speed, turned off the runway to the ramp and we got out of the airplane and walked around to the aft end to inspect. All of the tail was intact including the rudder, but the rudder was floating free. Upon closer inspection, we found the bolts had sheared where the rudder torque tube was attached to the bottom closing rib of the rudder.
We had experienced a severe case of flutter caused by the tab with its one-inch sheet metal extension. The extension on the tab had lowered the tab frequency to a point where flutter was initiated by the tab. The flutter in the tab affected the whole rudder system to the extent of transferring the flutter mode in rotation to the rudder up to a time when the attach bolts failed. Once free the flutter of both tab and surface stopped immediately. Once again, the Old Man Upstairs had his hand on our shoulder and kept us and the airplane out of the newspaper headlines.
This was the second time since the beginning of the Aero Commander that Bert and I shared an experience never to be forgotten. But this type of thing is one of many that can happen in engineering flight test work.
The next day we went to work on redesigning the elevator tab—eliminating the one-inch flat extension. Design requirements set by flutter criteria indicated that the natural frequency of the tab had to be above 2,400 cycles per second to avoid flutter at an excess of 300 M.P.H. indicated air speed. The redesigned tab provided the same area as the one that gave us trouble but was stiffened internally to a point where it had a vibration frequency of over 2,400 cycles per second. Within two days we had two new tabs built and installed on the airplane. Prior to the installation, however, we ran a vibration test on one of them to determine its natural frequency. Our vibration tests showed the new tab to be well above this range and we were confident that the maximum speed dive could be completed successfully.
Bert and I took the airplane up once again easing the speed up to 300 M.P.H. indicated—in fact as I recall we went through 300 and hit almost 320 I.A.S. before gradually pulling out of the dive. Everything was normal and we were now ready for the start of official F.A.A. flight test.
An F.A.A. project pilot was assigned to the flight test phase. The entire program was completed within a week’s time and the type certificate for the Model 520 was issued to us on January 31, 1952, just 16 months after the move into the empty facility at Tulakes Airport.
One note of interest regarding the all metal propellers: A requirement existed that necessitated an in-flight vibration survey on the propellers prior to complete approval for its use on a twin-engine airplane. Mr. Crichlow of the F.A.A. Power Plant Section in Washington had given us approval on the metal propellers for use on the prototype and we had gone through a second short certification program on the prototype to use the metal propellers, but Crichlow had given us a restriction of 200 hours at which time the propellers had to be replaced. The 200-hour life was a concession granted by Crichlow to help us obtain certification on the prototype with the metal propellers. This, although the operating life was short, was a great help to us in getting the original prototype program going. A little later, propeller vibration surveys were conducted in flight and all of the data indicated the stresses on the blades and hub were within the limits specified by the propeller manufacturer, Hartzell. The data was presented to the F.A.A. in Fort Worth and the 200-hour restriction was lifted for the production Model 520.
Model 520 factory production line. Photo by Wayne Entrekin
After certification, we had several customers standing by to take delivery of their aircraft. However, although the line was full, none of the aircraft as yet were either painted or upholstered. For the painting we set up a position on the assembly line, curtained it off, and painted the airplanes on a second shift. Number one production aircraft was assigned as a company demonstrator and was painted predominantly a dark green and white. For upholstery we had made arrangements with a company in Detroit who had a large fixed base operation including a good upholstery shop and they were honored by upholstering the first few production Aero Commanders. We flew the first production airplane to Detroit one evening and a week or so later returned it to Tulakes Airport. The company in Detroit continued to do our upholstery and we continued to paint the airplanes on a second shift basis, cleaning and priming one night—painting and trimming during the next two nights although the second and third airplanes were delivered with just the prime coat—the second one going to the Chicago Tribune and the third to Shirley Murphy of Indianapolis. Murph, as we called him, spent days and nights at the factory watching his airplane being assembled. I have never seen such a persistent and interested person. He literally loved that airplane. He had flown the prototype for checkout and as time went on, he kept trading up the new models of the Aero Commander as the program progressed over the years. Murph flew his airplane constantly—day and night—and took great enjoyment in conversing back and forth with airline captains all over the country. He was a flying buddy to them all and all to him. He was one of our staunchest supporters and as a result of his enthusiasm for the Commander, he undoubtedly was responsible for many sales.
Sales activities continued to accelerate. Carl Wooten, now with the demonstrator, was making tours around the country setting up distributorships and, with briefcase in hand, was also selling airplanes—showing the airplane at special events and to companies around the U.S.A.
By late December of 1952 the production line was full. Carl Wooten took quite a few deposits on 520 deliveries in the late winter of 1951-1952. The price of the aircraft had been established at $45,000 equipped with a full flight and engine group of instruments, the Hartzell all metal propeller and Lear VHF and ADF radios.
After using the number one aircraft for about a year, the Asahi newspaper in Japan bought the airplane, ferried it to Japan and used it daily to distribute the Asahi newspaper throughout Japan. In a few years they bought a later model Aero Commander and took old number one and placed it on a pedestal on the roof of their facility in Kyoto, Japan.
We became very close to Lycoming and their staff: Floyd Bird, who was Vice-President and General Manager, Clarence Wiegman their Chief Engineer, Ray Vandergrift, Ray Cowden their Sales Manager, Rube Fox their Installation Engineer and others. All of us became friends of the sincerest kind and all had a great personal respect for each other. This brings to mind a story that must be told about an experience we had together on the early models of the 520.
I remember after we started to deliver the Model 520s, that we began to experience cylinder overheat problems in the field. We had checked engine cooling for certification and everything was within limits, but when hearing about the field service overheat problem during full power climb outs, we instrumented a production airplane using thermocouples and a Lewis potentiometer. We found that in fact the heads were overheating. In checking back, we learned by accident that the boys who had made up the thermocouples for the F.A.A. certification flights for No. 1 Model 520, had connected two 10-foot 8 ohm leads together. This put the leads completely out of calibration and showed the engines to be running cool. When starting the new tests with the proper length calibrated lead and 8-ohm calibration for the full length of the lead, it showed the engines were in fact running hot.
The program to cool the engines was probably the most frustrating experience we ever had in the entire series of the Aero Commander. We literally tried everything in the book to get the engines within limits. Clarence Wiegman and Rube Fox came down from Williamsport and together we literally tried everything to no avail. All of this happened prior to the time that any of us, including Lycoming, had any idea that fuel flow and fuel distribution played a very important role in engine cooling. In running fuel distribution checks we found cold cylinders and cylinders that were running way overboard in temperature. We found carbureted engines, when installed in a cowling, tended to lean the engine and depending upon the design of the air box, also could drastically affect distribution.
In the final analysis, we tricked the carburetor and air box—again a very simple fix. We designed a collar with two small baffles of .032 aluminum alloy material welded in place. We inserted this collar with its baffles just below the carburetor and what it did was trick the carburetor into increasing the fuel flow to the engine. It also straightened out the distribution so that all cylinders were running within 200 degrees of each other in temperature and the whole engine was running within limits in max-power climbs. Almost thirty days had gone by before the final fix came about. Again, the simplest type of change in the box to overcome a very obstinate problem.
Aero Commander 560 Brochure from the Ron Smith Collection
The most popular years for the Aero Commander were from its first production certification through 1960. During this period many different versions were built. The 520 was replaced by the 560. It was the same as the 520 except for an increase in power to 280 H.P. and a change in the vertical tail to one having a 15 degree sweep back. Together with the sweep angle change we changed the nose shape of the rudder to one of a diamond. Upon full deflection of the rudder, aerodynamic balance was reduced so that the nose section never unported into the airstream. The first in the industry to sweep the vertical fin and rudder, but not just for appearance. The swept tail did add some additional aesthetics to an already beautiful airplane, but the main reason for the change was to add tail power and to further reduce any possibility of the rudder locking tendency that had appeared in the prototype L-3805. The 560 also contained an improved augmenter exhaust system and interior refinements.
By 1955 the airplane stood No. 1 in the industry and the aircraft gained an enviable reputation as being the finest twin engine business aircraft being produced anyplace in the world. The Model 560 was the last of the refinements to the series made at Bethany. All future developments, which were many, were accomplished at the R&D Division at Norman, Oklahoma.
