Airborne Awesomosity

On a Float!


In the late 1940s, one of many US Air Force research projects was being conducted by the EDO company, attempting to modify an aircraft such that it could be operated from ice and snow as well as from water. The testbed was a Grumman OA-9 Goose, modified with a hydro-ski configuration consisting of 4 parts, a main ski, tail ski, and two wing float skis. The concept worked, but was only beachable with the use of a bulky cradle. The flight tests also demonstrated that the primary hydro-ski was the only component required for a successful aquatic takeoff, and this fact attracted US Navy interest in further research and development, to explore the hydro-ski as a means to improve the rough water handling of seaplanes.

Hydrofoil Grumman 1

A single hydro-ski was adapter to a Navy Grumman JRF-5 Goose, and it was successfully flight tested. This aircraft was also modified with an extended landing gear assembly to allow it to be beached without the use of a cradle assembly. Since one ski seemed to work well, another modification with twin hydro-ski’s was tried, one on each side of the hull, also allowing for beaching without modification. The tests of this design were not as successful, as the side mounted skis threw spray up into the engines, and more pilot input was required when the skis would unport from the water, as one ski would typically lift before the other.


Since the single main ski had proved a viable option in the previous testing, a larger seaplane was given this modification for further testing. A Martin PBM-5 Mariner was selected and modified with a single ski mounted on a retractable strut. The tests showed that the hydro-ski did provide for a significant improvement in operation in higher sea states, but there was concern about the added weight. Additional research occurring at this time using a towed tank model indicated that similar results could be attained using a smaller, penetrating hydro-ski. Based on the model testing, a ski with one-third the area of the original was installed on the Mariner, which underwent successful operational testing, validating the test tank results.


The next step? Moving in the 1960s from the hydro-ski to the high speed hydrofoil designs being developed at that time. Tune in tomorrow to see how the research took these new developments on board, and meanwhile, enjoy this video of one of the Gooses (Geese?) during the testing!


The video, which inspired me to research this particular topic combining two things I think are awesome, found at, and pictures and info from  [Spoiler alert! If you follow this link, you might read ahead on some of the information that you will see tomorrow. So don’t say I didn’t warn you!].

  • skitter

    That. Is. Awesome.

    Too bad the dual skis were worse in the water, because then putting wheels in each would make land-landing much more straightforward. Now I'm trying to think of a simple wheel configuration for the single ski/foil.