Hulls, Hydrofoils, and Float Tests in the NACA Tanks, 1915 to 1945

Hulls, Hydrofoils, and Float Tests in the NACA Tanks, 1915 to 1945

By Jay Shaw

Since the establishment of the National Advisory Committee for Aeronautics (NACA) in 1915, it had worked closely with the United States Navy. Not only had the US Navy partnered with NACA, but the creation of the latter was also a rider to the former’s funding bill.[1] This history of NACA has been overshadowed by its successor, the National Aeronautics and Space Administration (NASA), into which the former was absorbed in 1958. Thus, much of the critical work by NACA has been overlooked. Indeed, if NACA is remembered at all, it is for using wind tunnels in aeronautical research, but there was much more that it was responsible for. This article redresses this deficit by examining how NACA used water tanks in seaplanes’ aeronautical and hydronautical advancements after the First World War. It also highlights the people and agencies involved in the research and the means of conducting the research.

The United States Navy, Seaplanes, and the First World War

The US Navy, realising that aircraft would play a vital role in any future war, recognised that something had to be done to improve its readiness and improve its fleet of seaplanes The US Navy partnered with NACA to investigate and perform research on its aircraft, including seaplanes and flying boats. These planes would be critical in defence and coastal patrols. As a part of the first line of defence against German U-boats, the seaplanes would be a priority for the US Navy. The seaplane was considered a fixed-wing aircraft with a fuselage designed for floatation and containing a hull.[2] However, because it realised that aviation was still a technology in its infancy, the US Navy requested that NACA help make the naval seaplanes as efficient as possible. NACA, in supporting the tasking of the US Navy through its work on seaplanes, ensured a long and productive close bond with the Navy.

By the end of the First World War, the US Navy had several seaplanes with varying hulls, float types, and missions. These seaplanes operated from bases on shores because the US Navy did not have aircraft carriers or capital ships to launch such craft. The prevailing view then was that if the enemy were to attack, it would be by submarine, so it made sense to send patrols out from the shore to search for submarines. Several kinds of seaplanes were designed and used by the US Navy during the First World War. In 1919, Commander H.C. Richardson, the Superintending Constructor of Naval Aircraft for the US Naval Buffalo district in Buffalo, New York, who had also been Secretary to NACA’s main committee on formation in 1915, explained that:

[t]he principal work was done with two types of seaplanes, namely, the HS-2, the single-motored plane developed from the HS-1, and the H-16, a copy of an English seaplane.[3]

These two seaplanes were used because they were the most readily available. This shows how poorly the US Navy seaplane fleet was in 1919. However, according to Richardson:

The Navy Department fully appreciate[d] the desirability of experimenting to improve existing types and the development of new types of seaplanes and airplanes, directed to the solution of those problems which have arisen in the war and, more particularly, to the development of seaplanes or airplanes for operation with the fleet.[4]

Richardson was an active proponent of seaplanes for the US Navy. Therefore, because of the efforts of those such as Richardson, the US Navy was on track to update its seaplane fleet.

Unfortunately, the seaplanes of this period were unscientifically constructed. Their range was not that far, and their stability in flight left much to be desired. Actual aerodynamic testing was needed to ensure that any aircraft was worthy of combat and that the seaplanes were no exception. Richardson wrote in 1919 that:

[t]he problem confronting the Navy was largely determined at the time the United States entered the war [1917] by the fact that the operations of the German and Austrian fleets had been reduced principally to minor raids […] and the only real sea-going operations comprised the activity of submarines.[5]

This would be the primary mission of the seaplanes for many years: the patrol of waters in search of submarines. The submarines’ effect in the First and Second World Wars should not be taken lightly. The amount of cargo tonnage that could be destroyed by an undetected submarine could be immense.

Richardson’s 1919 article is crucial as he addressed the US Navy’s needs and how the seaplanes could aid it. His outline reads almost like a ‘wish list’ that NACA would eventually find itself working on. First, Richardson felt that performance, first and foremost, relied upon horsepower. He argued that:

[t]he performance in power flight is determined by the horsepower required and the horsepower available, and of course, the latter must always exceed the former or power flight is not attainable.[6]

Considering that Richardson wrote this in 1919, he seems to have firmly grasped the needs of seaplanes. However, the power plants of any aircraft currently were still in an age of infancy. As such, Richardson’s idea that seaplanes were reliant on horsepower was unfortunately ahead of the technology that would make the machines efficient.

Richardson also understood that lift was an essential component of flight. He explained that:

[t]he lift of an airplane surface and its resistance to advance are determined by the lift and drift factors, which vary with the type of section used and also with the angle of attack at which the surface is presented to the relative stream of air.[7]

The US Navy realised, however, as much as Richardson showed advanced thought on the subject, that the research involved was outside the Service’s scope. NACA, set up as an agency that was available to help government and civil agencies in aeronautics research, would be the agency to help the US Navy address the fundamental science of seaplane aeronautical research.

A Curtiss H-16 at the Langley Aeronautical Laboratory at Hampton, Virginia, c. 1929. (Source: Wikimedia)

The Importance of NACA’s Research

While often overshadowed by NASA, the work of NACA deserves examination because of the enormity of its contribution to aeronautics. As NASA historian James Schultz explained:

[t]hroughout its history, with research and applied engineering, the Center [Langley] has been responsible for some of the 20th century’s fundamental aeronautical and aerospace breakthroughs. The Nation’s first streamlined aircraft engine cowling was developed at Langley Laboratory […] the tricycle landing gear; techniques involving low drag-producing flush riveting; [and the] development of the sweptback wing.[8]

Similarly, historian Michael Gorn asserted:

[t]he proliferation of wind tunnels [about thirty had been built at Langley up to the 1950s] reflected the NACA’s true institutional identity: it concentrated on aeronautics.[9]

While Gorn is correct, NACA could not have focused solely on aerodynamics and prospered. Aerodynamics was just one piece of what NACA did. It was established to investigate all flight modes, and hydrodynamics was a crucial part of NACA’s work. While not as aerodynamically sophisticated as land planes, seaplanes and flying boats needed hydrodynamical studies to meet the needs of the US Navy. It is a mistake to overlook this field that so many within NACA worked on.

Once NACA started its research on hydrodynamics, it did so without any presumptions and began its research by looking at the fundamentals of the aircraft. George W. Gray, in his early history of NACA, explained this adeptly. He stated that:

[a] large part of the effort of the hydrodynamic staff at Langley has been expended upon the twin problems: trying to effect a seaplane body that will combine low water resistance with low air drag.[10]

Even before this, however, the question was whether seaplanes could even take flight. Then, again, the problem was that of power plants. As Gray pointed out, the studies:

[h]ad yielded some disappointing surprises: new designs that would not take off at the speeds planned or that would not lift the desired loads at any attainable take-off speed.[11]

With the water tanks of NACA, however, the guesswork was taken out of the equation. However, none of this would have been possible, at least in a reasonable amount of time, without some organisation to make it happen.

Langley and the Water Tanks

Langley, located at Hampton Virginia, was NACA’s research centre, established in 1917. It focused primarily on aeronautical research but would eventually be used to test space equipment such as the Apollo lunar module. However, the first ten years at Langley comprised only the testing of aeroplanes. There was no work at all done on seaplanes. To do this work, NACA had to have something other than a wind tunnel to test the seaplanes.[12]

The drag tank also called a tow tank, drag tunnel, or even the drag basin, was the solution to the research needed. Gray stated that:

[m]any of the studies in wind tunnels were applicable to seaplanes, and they in common with landplanes benefited from improvements in wings, propellers, engine cowlings, and other developments of the 1920s.[13]

The study variables were applicable, but these were still seaplanes, and there was a need to test them in water. Gray elaborated that NACA knew that it needed a better way to test the seaplanes:

[i]t was recognised that the airplane on the water has problems that are not shared by the airplane in the air or on the landing strip, and in 1929 the Committee in Washington decided to enlarge the organisation and equipment at Langley to provide for research in hydrodynamics.[14]

It was then that hydrodynamic research began at Langley.

Langley constructed two tanks: tank number one and tank number two. Tank number one became operational on 27 May 1931 for $649,000.[15] Its purpose was ‘to study the hydrodynamic resistance and other performance features of water-based aircraft.’[16] A vital design team member was Starr Truscott, who published numerous studies based on research from tank one. A few additions were made to the tank, including a new higher-speed (80-MPH) carriage (a rail that the aircraft being tested sits on) installed in 1936-1937 and a tank extension of 900 feet to 2,960 feet in 1936.[17] Eventually, the need for another tank would arise, leading to the construction of tank two.

Tank number two, operational on 18 December 1942, again had Truscott, along with John B. Parkinson and John R. Dawson, on the design team.[18] The basin was 1,800 feet long by 18 feet wide and 6 feet deep. It also had a 60-MPH carriage.[19] The express purpose of tank number two was ‘to test models of floats for seaplanes and hulls for flying boats by dragging them through seawater.’[20] According to Gray, the significance of tank two was that:

[r]esearchers experimented with radical departures from accepted hull design, trying to find the specifications for a seaplane body that would combine freedom from porpoising and skipping, low water resistance, and superior performance in the air. Out of these experiments came a novel design known as the hull with a planing tail.[21]

Every step in the building of the tanks, from the basin to the tires on the towing carriage, had to be carefully thought out to ensure the best product for research use. Truscott, one of the designers of both tanks, realised that using NACA tanks required certain necessary features solely for use with the seaplanes.[22]

Truscott related that the tank located at Langley was:

[o]f the Froude type; that is, the model which is being tested is towed through still water at successive constant speeds from a carriage spanning the tank. At each constant speed, the towing pull is measured, the trim and the rise, or change of draft, are recorded and, if the model is being towed at a fixed trim, the moment required to hold it there is measured and recorded.[23]

The tank itself was covered by an enclosure meant to protect it from the water itself (so that turbulent water after a test could settle more quickly), wind, and the weather, rather than to provide any comfort to the engineers.[24]

Pneumatic tires were installed and were ‘each driven by an independent electric motor through a single-reduction herringbone pinion and gear. The […] tires are high-speed bus or truck tires, with smooth treads.’[25] The carriage had to have the means to propel itself, which was achieved using ‘our electric motors propelling the car […] nominally of 75 horsepower, but for short periods they may be safely called upon to deliver 220 horsepower each.’[26] ‘Finally, the device used electrical braking to break the current for regenerative braking.’[27]

Given the construction of the tanks, much work had to come together to test seaplanes. Of course, the whole purpose was to test the seaplanes for fundamental problems that could inhibit the aircraft’s performance. Resistance, porpoising, skipping, and performance were why the tanks existed. Solutions to these problems were needed for a more efficient aircraft. NACA engineers sought to reduce resistance; the force encountered when a plane is in the air moving forward or a seaplane in water, to help with take-off and landing.

Porpoising, a dangerous event that often occurs in the water, is something that NACA was tasked to find a solution to. According to Kenneth Davidson and F. W. S. Locke, Jr., writing for the Stevens Institute of Technology in 1943:

[p]orpoising is a self-sustaining oscillatory motion in the vertical longitudinal plane [… ] and can originate in an instability of the uniform longitudinal motion in smooth water […] in the words of one test pilot, it is always unpleasant and it may be catastrophic.[28]

Essentially a seaplane will move up and down in the water out of control of the pilot. So it is easy to understand why the US Navy was interested in the dynamics of porpoising and what needed to be done to eliminate it. If left unchecked, not only could the seaplane not fly, but it could also be damaged, or worse yet, the pilot injured or killed.

Performance was made up of several things. Engine performance, aerodynamics, and propellers were factors in all aircraft, but with the seaplane, there was a demanding service life on the water. In addition, s were composed of thousands of rivets, so corrosion was a considerable fear. It could be disastrous if the corrosion worked through a rivet at the wrong time. The hull of the seaplane was another vital factor. The construction, what it was made of, the aerodynamics, and how to prevent porpoising and skipping of the aircraft were things that NACA still needed to work out.

With the tow tanks available, miniature models could be constructed of the hulls or floats of the seaplanes, put upon the carriage, and pulled at the desired speed. If the results did not achieve the desired results, costly mistakes could be prevented. This opened new doors for aeronautical research that paid huge dividends in the coming years. While NACA was still beginning its seaplane research, progress would come more rapidly with the tow tanks at hand.

Fundamental Research

In 1935, NACA found itself in a position to make future research easier. Engineer Antonio Eula performed tank tests on seventeen different hulls and floats.[29] Eula purposely picked a random number of floats that had been tested in the laboratory over the last few years. He did this because:

[i]t affords an opportunity to draw some general conclusions regarding seaplane floats of given weight, given wing structure, any given position of the center of gravity.[30]

Another reason is that not much data existed to make work easier for future engineers. His most important conclusion drawn from the tests was that ‘the best models have a maximum relative resistance not exceeding 20 percent of the total weight.’[31] Just that information itself was enough to help any future engineers working with the drag tanks to give them a starting point from which to work.

Along with porpoising, skipping continued to be a problem with seaplanes. During the Second World War, the problem of skipping was considered a significant enough problem that needed further research. In 1943, John B. Parkinson at NACA addressed the problem. He began by defining just what skipping was. He reported that ‘skipping is a form of instability encountered in water take-offs and landings, so-called because of the resemblance of the motions of the seaplane to those of a skipping stone.’[32] Rising out of the water before the seaplane achieved flight was hazardous. A plane entirely out of the pilot’s control can lead to injuries, if not death.

One of the critical problems with the testing up to this point was that scientific testing had not occurred. Parkinson explains that ‘investigations of skipping have been mainly qualitative and the data have been based on the impressions of pilots or observers.’[33] Using models and even full-size aircraft for testing, Parkinson established that instability caused most problems. Using measurements taken from the fore and aft of the step-in hull helped determine where the problem for each type of seaplane was located. Once that was established, the engineers could make the corrections. Of course, it could never eliminate all problems because any seaplane on the water is prone to unpredictable water. However, it did go far in helping establish methods to solve the skipping problems.

It was realised that the research had to be compiled to make it easier for future engineers to find the information they were looking for. So, in September 1945, engineers James M. Benson and Jerold M. Bidwell released a bibliography containing information about seaplanes.[34] In this bibliography, many details covering everything from conventional hulls and floats to floating and handling were written about in a way that compiled the common information in past reports. Not only would this make it easier for future researchers, but the bibliography also pointed out areas in which more work needed to be done. Examples such as this are one of the reasons that NACA was able to achieve the success that it had.

A US Navy Consolidated PB2Y-3R Coronado transport aircraft loads cargo at the Pan American Airways dock, Treasure Island, California in January 1943. (Source: Wikimedia)

NACA Water Tank Research and its Impact on Second World War Seaplanes

The Consolidated PB2Y Coronado is an example of how this research aided in Seaplane use during the war. In its original design, when fuelled for a long-range mission, this seaplane had a gross weight of 46,000 pounds of which 3,000 pounds was the payload. The US Navy wished to increase the payload.[35] Using models of the Coronado in Tank No. 1, the NACA changed the line of the step of the hull and installed ducts for ventilating the bottom area aft of the step. This increased the gross weight to 68,000 pounds, of which 12,000 pounds was payload. It’s stability was so assured that the plane, during its war service in the Pacific Islands was repeatedly used to make landings on dark nights when the seeing is poor, and the craft must descend on a steady glide path until water is touched, a more hazardous procedure than daylight landing.[36] 


The success of NACA was based on hard work and dedication to research. Working alongside government agencies such as the US Navy and even civilian aircraft manufacturers, NACA helped the United States evolve from a country far behind Europe in aeronautical research to the world’s leader in aeronautical research. The research conducted on seaplanes, long overlooked, helped refine the seaplanes, and even today, seaplanes are still in use.

Jay C. Shaw graduated with a bachelor’s in history from Columbia College in Columbia, Missouri, in 2016. He began work on his PhD in History with the University of Missouri – Columbia in 2022. He retired in 2016 from the US Air Force as an Aerospace Ground Equipment Craftsman in support of both the C-130 Hercules and the B-1B Lancer airframes. He volunteered at the Army Engineer School History Office at Fort Leonard Wood for over a year, where he worked more than 350 hours proofing sources for a book on the history of the Army Engineer School.

Header image: Digging the channel for Tank No. 1. In the late 1920s, the NACA decided to investigate the aero/hydro dynamics of floats for seaplanes. A Hydrodynamics Branch was established in 1929 and a special towing basin was authorized in March of that same year. (Source: Wikimedia)

[1] University of North Texas (UNT), UNT Digital Library, Annual Report of the National Advisory Committee for Aeronautics, Administrative Report Including Technical Reports Nos. 1 to 7, 1915.

[2] While modern definitions of seaplanes, flying boats and float plane are more clearly defined. At the time NACA was formed, the language used was less clearly defined. As evidence by Richardson’s article cited beloew, it is clear that the types of aeroplanes discussed would, by modern defintion be considered flying boats. However, he refers to them as seaplanes.

[3] H. C. Richardson, ‘Airplane and Seaplane Engineering,’ SAE Transactions 14 (1919), p. 334.

[4] Richardson, ‘Airplane and Seaplane Engineering,’ p. 365.

[5] Richardson, ‘Airplane and Seaplane Engineering,’ pp. 333-4.

[6] Richardson, ‘Airplane and Seaplane Engineering,’ p. 338.

[7] Richardson, ‘Airplane and Seaplane Engineering,’ p. 338.

[8] James Schultz, Crafting Flight: Aircraft Pioneers and the Contributions of the Men and Women of NASA Langley Research Center (Washington, D.C.: National Aeronautics and Space Administration, 2003), p. 25.

[9] Michael H. Gorn, ‘The N.A.C.A. and its Military Patrons during the Golden Age of Aviation, 1915-1939,’ Air Power History 58, no. 2 (2011), p. 25.

[10] George W. Gray. Frontiers of Flight (New York: Knopf, 1948), p. 67.

[11] Gray, Frontiers of Flight, p. 67.

[12] UNT, UNT Digital Library, Starr Truscott, The N.A.C.A. Tank: A High-Speed Towing Basin for Testing Models of Seaplane Floats, Technical Report, June 9, 1933, p. 4.

[13] Gray, Frontiers of Flight, p. 65.

[14] Gray, Frontiers of Flight, 65.

[15] James, R. Hansen, Engineer in Charge: A History of the Langley Aeronautical Laboratory, 1917-1958 (Washington, D.C.: National Aeronautics and Space Administration, 1987), p. 450.

[16] Hansen, Engineer in Charge, p. 450.

[17] Hansen, Engineer in Charge, p. 450.

[18] Hansen, Engineer in Charge, p. 466.

[19] Hansen, Engineer in Charge, p. 466.

[20] Hansen, Engineer in Charge. P. 466.

[21] Gray, Frontiers of Flight, p. 80.

[22] UNT, UNT Digital Library, Truscott, The N.A.C.A. Tank, p. 5.

[23] UNT, UNT Digital Library, Truscott, The N.A.C.A. Tank, p. 5.

[24] UNT, UNT Digital Library, Truscott, The N.A.C.A. Tank, p. 5.

[25] UNT, UNT Digital Library, Truscott, The N.A.C.A. Tank, p. 5.

[26] UNT, UNT Digital Library, Truscott, The N.A.C.A. Tank, p. 5.

[27] UNT, UNT Digital Library, Truscott, The N.A.C.A. Tank, p. 5.

[28] Kenneth S.M. Davidson and F.W.S. Locke, ‘Some Systematic Model Experiments on the Porpoising Characteristics of Flying-Boat Hulls,’ NASA, June 1943.

[29] UNT, UNT Digital Library, Antonio Eula, Hydrodynamic Tests of Models of Seaplane Floats, Technical Memorandum, May 1935, p. 1.

[30] UNT, UNT Digital Library, Eula, Hydrodynamic Tests of Models of Seaplane Floats, p. 1.

[31] UNT, UNT Digital Library, Eula, Hydrodynamic Tests of Models of Seaplane Floats, p. 1.

[32] UNT, UNT Digital Library, John B. Parkinson, Notes on the Skipping of Seaplanes, Wartime Report, September 1943, p. 1.

[33] UNT, UNT Digital Library, Parkinson, Notes on the Skipping of Seaplanes, p. 2.

[34] UNT, UNT Digital Library, James M. Benson and Jerold M. Bidwell, Bibliography and Review of Information Relating to the Hydrodynamics of Seaplanes, Wartime Report, September 1945, p. 1.

[35] Gray, Frontiers of Flight, p. 74.

[36] Gray, p. 74.