Hidden Truth/Hidden Truth.iso/data/genufo/genufo/alien/main_archive/j_upto_r/pancakes.info.txt

Internet Message Format | 1997-01-02 | 35KB

From: [e-mail] (John Powell)
Newsgroups: alt.paranet.ufo
Subject: V-173 & XF5U-1, 1/7
Date: 10 Dec 93 01:48:00 GMT


Excerpt: Chance Vought V-173 and XF5U-1 Flying Pancakes, ISBN 0-942612-21-3

        V-173 & XF5U-1 Program Highlights:

 7 MARCH 1939:     V-173 blueprints submitted to the Navy.

 7 APRIL 1939:     Navy requests that NACA investigate the V-173
                   proposal.

11 JULY 1939:      Navy requests that Vought build a flying model based
                   on NACA wind tunnel tests.

15 AUGUST 1939:    Vought proposes a full scale flying model.

 2 OCTOBER 1939:   Navy approves testing at NACA of 24" free-flying
                   V-173 model.

 6 MARCH 1940:     NACA wind tunnel test results forwarded to Navy.

30 APRIL 1940:     Based on wind tunnel tests ailevators are added to
                   the V-173.

 4 MAY 1940:       Navy places contract for the V-173.

   OCTOBER 1940:   Aielron controls and adjustable stabilizers added to
                   the V-173.

14 April 1941:     VS-315 propeller drive system designs submitted to
                   the Navy.

30 JULY 1941:      Navy assigns serial number 02978 to the V-173.

15 SEPTEMBER 1941: V-173 ready for delivery to NACA for wind tunnel
                   testing.

   DECEMBER 1941:  Wind tunnel tests conducted at NACA Langley.

19 JANUARY 1942:   Navy requests Vought submit a proposal for two
                   experimental fighters based on VS-315 specifications
                   and successful V-173 wind tunnel tests.

10 FEBRUARY 1942:  Navy requests 1/3 scale model of the VS-315 (XF5U-1).

   MAY 1942:       E. J. Greenwood assigned as project engineer to work
                   with Zimmerman.

30 JUNE 1942:      VS-315 informal proposal submitted to Navy.

10 SEPTEMBER 1942: Navy requests letter or intent.

17 SEPTEMBER 1942: Letter of intent issued for VS-315 (XF5U-1).

23 NOVEMBER 1942:  First flight of V-173 made by Boone Guyton.

24 APRIL 1943:     XF5U-1 propeller drive system approved by Navy.

 3 JUNE 1943:      R. H. Burroughs makes forced landing of V-173 on
                   Lordship Beach.

 7 JUNE 1943:      XF5U-1 mock-up inspection.

 6 AUGUST 1943:    Final XF5U-1 mock-up inspection.

22 OCTOBER 1943:   V-173 modified with all-flying horizontal stabilizers
                   after forced landing.

   NOVEMBER 1943:  Flapping prop blades proposed for XF5U-1.

31 DECEMBER 1943:  CDR. Ramsey and LCDR. Booth fly the V-173.

18 FEBRUARY 1944:  Vought submitted a proposal to modify the XF5U-1
                   propeller hubs.

28 MARCH 1944:     Vought proposes to terminate V-173 contract and
                   incorporate the V-173 program into the XF5U-1
                   contract.

13 MAY 1944:       V-173 contract changed.

27 MAY 1944:       Voughts final proposal for termination of V-173
                   contract and consolidation into the XF5U-1 contract.

18 JANUARY 1945:   Vought requests permission to transport XF5U-1 to
                   Muroc Dry Lake (Edwards AFB), California, for flight
                   testing.

24 MARCH 1945:     Vought requests contract amendment after auditing
                   cost estimates.

13 April 1945:     Vought requests reduction in flight and static test
                   programs.

19 MAY 1945:       Vought requests Navy waive V-173 final demonstrations
                   and BIS trials.

26 MAY 1945:       R. H. Burroughs makes forced landing on Mill River
                   golf course.

20 AUGUST 1945:    XF5U-1 rolled out with F4U-4 style four blade
                   propellers.

17 MARCH 1947:     XF5U-1 contract cancelled by the Navy.


Introduction

        This book was created from manuscripts written by and provided
by Art Schoeni public affairs official for Vought from 1953 to 1978.
These writings have been published in; Aeroplane Monthly (Nov. & Dec.
1975), Air Classics (Vol. 11/8 Aug. 1975), and Historical Aviation Album
(Vol. VIII). Two other good references on the Pancakes are Aeroplanes
Vought by G. Moran and Air Enthusiast (Vol. 4/6 June 1 973). The other
major contributor to this book was Tommy Thomason who provided a modern
view of the program and the kit reviews. The V-173 drawings were
provided by Ed Clendenin of Eagle Talon models.




        Anyone having photos or other information on this or any other
naval or marine aircraft, may submit them for possible inclusion in
future issues. Any material submitted will become the property of NAVAL
FIGHTERS unless prior arrangement is made. Individuals are responsible
for security clearance of any material before submission.  ISBN
0-942612-21-3 Steve Ginter, 1754 Warfield Cir., Simi Valley, California,
93063.


        The "Flying Pancake", "Flying Flapjack", "Flying saucer", and
"Zimmer's Skimmer" were all names used to describe Charles H.
Zimmerman's unorthodox V-173 and XFSU-I aircraft. Two other
descriptions; the world's fastest and slowest-flying airplane and the
world's first vertical takeoff and landing airplane, might have been
used to describe the XF5U-1 that was built but never flown. Zimmerman's
brainchild was conceived and designed to do just that, but was never
given the chance. The protracted development program and the advent of
jet aircraft caused the cancellation of the project on 17 March 1947.

        The "Flying Pancake's" designer, Charles Zimmerman, graduated
from the University of Kansas in 1930 with a degree in electrical
engineering. Included in his course of study was a class in introductory
aeronautics which helped him secure a job with NACA (National Advisory
Committee for Aeronautics) at their Langley Field facility. Before he
got into the business of designing and building the Pancakes, Zimmerman
made a name for himself by first solving the problem of a free-spinning
wind tunnel and then developing a free-flight wind tunnel.

        In a NACA design competition for a civilian lightplane in 1933,
he designed a circular-wing aeroplane that was to fly at high speed and
yet hover like a helicopter. The plane would utilize wingtip-mounted
airscrews rotating in opposite direction to the wingtip vortices,
thereby preventing their formation and increasing the aerodynamic
efficiency. Initially two engines driving their own propellers were
planned, but later both engines drove a common drive shaft for safety.
His design won the competition with its aerodynamic excellence and sound
engineering. However, NACA rejected the idea for further development
because it was "too advanced". One of the runner-ups became the popular
Ercoupe.

        Although NACA shelved the idea, Zimmerman did not. With the help
of two co-workers, Richard Noyes and John McKeller, Zimmerman worked on
the concept in off-duty hours. During 1934-35 several test models were
built to try out flight characteristics. As originally planned, the
little airplane was to carry three passengers lying prone to promote
streamlining, changing to upright positions in flight. The idea was
incorporated in a US patent procured by Zimmerman in 1938. The idea had
been abandoned before then because of its marginal comfort.

        One of the flying models Zimmerman built was a one-man, wooden
flying machine with a seven foot wingspan and powered by two 25 h.p.
Cleone engines from France. He and his associates never could get the
two engines synchronized, and he turned to a 20 inch span rubber-band-
powered model in 1936. The model performed as predicted and after NACA
executives reviewed films of the tests, it was suggested that he try to
interest private industry or the military in the concept. Zimmerman
convinced Eugene E. Wilson, president of the United Aircraft
Corporation, that the idea had merit, and he joined the Chance Vought
Aircraft division in 1937.

        In October 1938, Zimmerman attempted to interest the Army in a
short range liaison-observation type aircraft designated V-170. The Army
declined, and in November he tried to interest the Civil Aeronautics
Authority with his V-171 design (a larger V-162). He tried the Army
again in December with a V-172 attack-bomber version, which was again
rejected.

        Zimmerman constructed an electric-powered model, the V-162,
which was operated by two pilots using remote control. Tests were run in
a hangar, with the tethered airplane flying so well that the US Navy
became interested and advanced research funds. The V-162 was hinged so
that the rear quarter of the circular fuselage,  including the two
vertical rudders, acted as an elevator.

        By 1939 drafting work, engineering design and aerodynamic studies
were underway with Navy financing.

        The prototype V-173 was constructed with standard wing fabric
covering the entire plane, in an effort to save weight and money.
Originally the V-173 had no horizontal outboard stabilizers, but model
tests indicated that this idea was unsatisfactory and the "flying tail"
(all-moveable tail) was developed. Two Continental A-80 engines, rated
at 80 h.p. each, turned 16 foot 6 inch three-bladed propellers, although
the original plan had called for two-bladed units. The stork-like fixed
landing gear gave the plane a 22 degree nose-high ground angle.

        The basic wing area and wing planform were the same for the
V-173 and the XF5U-1. The wing area was 427 square feet, with the
planform being derived from a circle 23 feet 4 inches in diameter by, in
effect, sliding the tip sections forward relative to the root chord so
that the quarterchord points were in line. The sections were
symmetrical, NACA 0015, and there was neither twist nor dihedral in the
wing.



        The major differences between the two planes were in weight and
power. The V-173 weighed about 3050 pounds for most of its flights,
giving it a power loading of 19.1 pounds per horse power. The high power
loading was the major defciency of the aircraft and the main cause of
two forced landings it had during testing. The engines later installed
in the XF5U-1 were Pratt & Whitney R-2000-7 of 1,350 h.p. each. To
achieve greater performance it was planned to install more powerful
Pratt & Whitney R-2000-2(D) engines of 1,600 h.p. each. With these
engines the 16,802 pound (loaded) aircraft would have had a power
loading factor of 5.2 pounds per horse power. It was still doubtful that
the airplane could take off vertically and fly forward at 500 m.p.h.
Thus there was talk of powering the XF5U-1 with modern turbine engines.
It was thought that it would then have been able to fly easily on one
engine and have been capable of demonstrating its inherent capability to
hover and otherwise per form as a V/STOL aircraft.

        Because of its light weight, low power notwithstanding, the
V-173 could lift off the runway in calm air after a 200 foot run. In a
25 knot wind it could be airborne in a zero run. It cruised during tests
at about 75 m.p.h., and had a top speed of 738 m.p.h. Because it was an
experimental aircraft, it carried only 20 gallons of fuel for short test
flights.

        "The V-173 was carefully designed with a unique wooden structure
which was expensive to build but light, efficient and trouble free. The
gearing, shafting and propellers indeed were highly experimental, and we
were not in a position to develop them as thoroughly as would have been
desirable prior to flight", Zimmerman said.

        The V-173 was test flown for the first time from Stratford,
Connecticut, on 23 November 1942 by Boone T. Guyton, a former Navy
fighter pilot and Vought's chief test pilot. During its test life the
V-173 was flown for a total of 131 hours by Guyton, Richard Burroughs,
Charles A. Lindbergh and a number of Navy pilots.

        The V-173 had gone through weeks of engine runs and ground taxi
tests. Guyton had conferred endlessly with Zimmerman after he had taken
the airplane five feet into the air on a taxi run. "I guess we're ready
to fly, Charlie," he told Zimmerman.

        "The initial flight of the plane was one of the most interesting
I had made in my career as a professional pilot", Guyton said later.
"Strapping on the football helmet I used as a crash helmet, I checked
out the engines and controls. As I taxied out from the line Zimmerman
waved, shook both hands and walked toward the crash truck from which he
was to watch the flight.

        "As I pulled into the wind, I noticed the police guard searching
for cameras among cars parked along the road by the runway. Kids hanging
on the fence were ushered back. Halfway down the take-off run, the same
bump in the runway I had hit hundreds of times before annoyed me. The
crash truck, overhung on either side with eager observers.  paced my
run.

        "As soon as we were airborne and away from the ground effect,
which was large on this type airplane," Guyton said, "I was quickly
distressed by the extreme heaviness and sluggishness of the controls. It
was apparent that there was a question as to whether I could obtain
enough control to bank the airplane sufficiently to complete a turn back
to the runway. I was already considering the probable effects of a water
landing straight ahead in Long Island Sound."

        Although thoughts of a crash crossed Guyton's mind, he also
thought about the ten years Zimmerman had worked to get the NACA, Chance
Vought and the Navy to accept his concept of a high speed, short
take-off and landing airplane. "My thoughts were subconsciously on
Charlie back on the runway," he said. "The man whose anxious moment was
now the culmination of his years of maximum effort on this single
project."

        Guyton had the 3,050 pound airplane's stick gripped tightly in
both hands. It took a lot of muscle to move it, but the response was
positive. He flew it up to 300 feet. The Sound was below and the nose
still pointed skyward. Banking slightly, he started a slow sweeping
turn, noticing that the rudders were effective and the engines were
running at nearly full power.

        "Slowly the airplane moved back toward the airport. I felt
elated and had a foolish impulse to yell, 'Charlie, she flies!'" He
brought the Pancake down to the end of the runway. The landing proved to
be "not at all normal." Guyton applied power to effect the flare and
decrease the vertical descent, as a helicopter pilot might do. Still
using all his muscle on the stick, he eased the nose still higher with
three-quarter's power.

        "I managed to get the stick full aft and the airplane settled so
quickly on the ground from its last few feet of descent that it was both
startling and pleasing. The V-173 rolled about 50 feet, it seemed.
Landing speed was about 50 m.p.h. I immediately noted to myself that
this airplane, designed to be a vertical take-off and landing airplane,
showed every promise of filling its design concept mission."

        Guyton climbed down through the entry hatch in the floor of the
discus-shaped aircraft, to be congratulated by Zimmerman and the ground
crew upon sucessfully completing the 13 minute first flight.

        The heavy control forces which required Guyton to use both hands
on the stick were soon reduced. By varying propeller blade angles and
improving the power characteristics of the engines slightly, performance
was improved. Trim tabs on the "flying tail", were added and proved
helpful.

        After about 40 or 50 flights the stabilizing flap, as Vought
called it, was added to the trailing wing edge. As Guyton recalls, "I
had problems getting the tail down effectively during a low or no power
landing. I called it ground effect. The trailing edge flap was to
provide automatic relief by deflecting up under the ground effect load
when perhaps ten feet above the landing surface. It proved effective,
but as I recall, not startling. The airplane always had a tendency to
pitch nose down as the flare for landing was made, and more so when
power was reduced.



        Guyton reported that the cockpit comfort left much to be
desired. Lack of power boost on the controls made stick movement
difficult, visibility was poor, and he developed backaches from having
to lean forward to see where he was going. The cockpit was almost flush
with the wing's leading edge. Plexiglass openings in the floor, to let
him see the ground on take-off and landing, were useless ---- Guyton
reported he was too busy to use them.

        During the first and subsequent test flights, of which Guyton
made 54, vibration in the cockpit was a persistent problem. This was
caused by resonant frequency between the propellers and the nacelle
structure, which Zimmerman greatly alleviated by installing vibration
dampers on the propellers. The problem was not met in the heavily
constructed XF5U-1 but it led to develpment of articulated propeller
blades in the fighter to avoid the non-symmetrical airflow at high
angles of attack. Brakes in the V-173 were marginal for taxiing and
braking purposes, although safe but cumbersome for ground maneuvering.

        Guyton summed up his feelings about the airplane after the first
few flights: "To a pilot, being able to apply full power, raise the nose
as high as it could be held, have control of the plane about all axes
without stalling, was a fascinating event." With full aft stick, full up
elevator, full power on both engines, and the airplane in a flight
attitude of 45 degrees, he was able to maintain lateral and longitudinal
control at all times.

        "Throughout the entire flight test program we never were able to
make the airplane stall completely or even approach a spinning
condition. A notable flight characteristic was the rapid decrease in
speed as the airplane was pulled into a tight turn. I found this
deceleration to be almost a fascination that would make the plane a
formidable opponent in a dogfight.

        "On the initial flight, because of the engines' low power, the
airplane could not be flown at sufficient speed to gain a level-flight
attitude. This, coupled with the high stick forces, made me apprehensive
about being able to turn and land at the field. The Zimmer Skimmer as
the plane affectionately was callied, was interesting and fun --- but
not comfortable --- to fly.

        "The nose-high attitude, at all low speed flight ranges except
in maneuvers and dives, gave mushy, high stick forces and slow response
to the controls. With restricted vision from the cockpit sideways and
down or aft and down, I always felt like I had a reasonable workout
after flying. The aircraft also had a nose-down tendency during landing.

        "It was a truly different airplane to fly. It felt normal even
on the first landing after that hairy, long slow turn. You actually
applied power in flaring for a landing. Being a former naval carrier
pilot, I was keen for the idea of vertically landing a 500 m.p.h.
fighter to a hook installation on a cruiser or battleship."

        After Guyton made the first thirteen flights, he was seriously
injured in an F4U Corsair crash, and Richard Burroughs took over flying
the V-173 for a time. Charles A. Lindbergh made flight number 34, and
several Navy pilots made flights, including CDR Ramsey, CDR Booth and LT
Najeeb E. Halaby, later head of the FAA in the US. Other company pilots
who flew it were William B. Boothby, C. L. Sharp and W. H. B. Millar.

        During its flying career, the Pancake was involved in several
mishaps which were not too serious because of its light weight and slow
speed. On one occasion it landed on Mill River golf course at Stratford.
Being a secret project, the plane was placed under guard and towed back
to the factory at night.

        An engine vapor lock forced it to make an emergency landing on 3
June 1943, on Lordship Beach on Long Island Sound. Pilot Burroughs
flipped it over on its back in soft sand trying to avoid running over a
sunbather, whose towel was found underneath the upturned Pancake when it
was righted.

        The aircraft broke two propeller blades in the mishap. Lindbergh
and Zimmerman were watching when it disappeared from sight and rushed to
the beach. Up to then Lindbergh had declined to fly the aircraft. "He
was worried that if the aircraft turned over on its back the cockpit
would be crushed and he would be trapped," Zimmerman recalled. "The
aircraft did overturn, the canopy was not crushed. Burroughs exited
through it after shoving some sand aside." Lindy then remarked to
Zimmerman, "Now I'm ready to fly it." The airpiane was towed back to the
nearby plant and repaired.

        A third near-serious event came during the thirtieth anniversary
airshow of Chance Vought Aircraft in 1947. With Guyton at the controls,
the plane had difficulty getting up flying speed and lift in the hot
air. It nearly ran into high tension wires and a cliff near the end of
the runway.

        After the airshow the V-173 flew back the Vought factory in
Stratford, Connecticut. It was to be the swan song for spectacular-
looking airplane that had paved the way for the XF5U-1 Navy fighter. The
full-scale but lightly-built V-173 was put in storage at the Norfolk,
Virginia, Naval Station. Today, its vertical fins and "flying tail"
removed, it is in storage at the Smithsonian Institution's Air Museum
warehouse in Silver Hill, Maryland.

        Shortly thereafter the XF5U-1 contract was suddenly cancelled on
17 March 1947, after it had made a number of success taxiing trials but
before it had a chance to fly. The day of the jet engine had arrived and
XF5U-1's chance to prove itself was ended and the XF5U-1 was ordered to
be demolished.

        In September 1941 the Navy asked Vought to build two military
versions of the V-173 designated VS-315, which later became the XF5U-1.
One would be a flight test aircraft and the other was to be used for
static testing in the laboratories.

        The V-173 was finished in glossy bright (chrome) yellow upper
surfaces which wrapped several feet under the forward leading edge. The
lower surface, vertical stabilizers and landinq gear were painted with a
silver dope. On the upper surface the two engine access doors were
outlined in black and there was a black line extending almost completely
aft from the back of the canopy.


        A wooden mock-up of the fighter was completed on 7 June 1943. By
November it was decided that the interim propellers on the XF5U-1 would
not do, and that propellers with articulated or "flapping blades" would
be required.

        Flight tests in the V-173 were progressing satisfactorily and
the contract for the program was consolidated with the XF5U-1. Such a
contract was issued on 15 July 1944. Because of the nature of the
Pancake development program, Vought requested the Navy for permission to
transport the XF5U-1 flight test vehicle to Muroc Dry Lake in
California, where unlimited emergency landing space and few observers
would make testing easier. This move was never made. Plans had called
for the aircraft to go to Muroc via the Panama Canal that December for
its first flight.

        Gear box problems in the big right-angle drive shafts to each
propeller had negated the chance to fly the XF5U-1 safely from any
airfield other than Muroc. The quarter-million dollar price tag on the
test program also was a factor, and the Navy preferred to spend the
money on jet aircraft. The complicated shafting and gear boxes presented
problems that might have hampered the project anyway as other turboprop
projects of that era also were having gear box trouble.

        The original propellers installed on the XF5U-1 fighter were
conventional Hamilton Standard Hydromatics, similar to those on the
F4U-4 Corsair. It was unlikely that these props were used for any other
purpose than for appearance or for engine and gear shaft testing. It has
been speculated that the F4U-4 props were used for taxi tests, but that
capability is questionable since the XF5U-1 drive system was intended to
operate counter-rotating propellers and the F4U-4 props were of the same
hand, although the left hand blades appear to be reversed with the
Hamilton Standard Insignia being on the back side. This would have
allowed some shakedown of the aircraft systems with the engines running
at low power.

        When it was discovered that flapping blades would be required to
avoid vibration by unsymmetrical airflow and to resist heavy loads when
flying at high angles of attack, Zimmerman had a problem. "For a time it
appeared the project would have to be abandoned," Zimmerman said, "but
after a desperate weekend of work I came up with a design using two
pairs of teetering blades, similar to the Bell helicopter rotor, one
pair mounted ahead of the other to form a fourbladed propeller."

        The XF5U-1 was powered by a pair of Pratt & Whitney R-2000-7
engines developing 1,350 h.p. each. The predicted speed range of the big
fighter was amazing. Whereas other designers could not better a
one-to-four ratio in landing speed to top speed, the Vought machine was
expected to achieve a range from 40 to 415 m.p.h with the original
engines, 20 to 460 with water injection and 0 to 550 with gas turbine
powerplants. Carrying 261 gallons in the prototype V-173 the XF5U-1 had
an expected range of 1,000 miles.  Compared to the V-173's take off in
200 feet in calm air, the XF5U-1, which weighed 14,550 pounds (empty),
would have required 721 feet to take off with the original engines. The
XF5U-1 also had a slightly lower ground angle of 18 degrees which was
nearly 5 degrees less than the V-173.

        Armament for the XF5U-1 was to be six .50 cal machine guns or
four 20mm cannons and two 1,000 pound bombs or drop tanks. The guns were
to be stacked vertically between the engines and the cockpit. The guns
were never installed in the XF5U-1.

        When the end came the Navy ordered the flight test fighter to be
destroyed. The static test example had already been broken up during
laboratory strength tests, as had been intended. The sad task of
destroying the aircraft fell to Lee C. Stetson, acting chief of the
experimental department, which had built the two machines.

        Both R-2000 engines were removed, along with instruments and
other salvageable items, and the aircraft was then placed under a crane,
from which hung a huge steel ball. The first few drops failed to dent
the strong framework, so measurements were made and the ball dropped
between main beams and spars. The wrecking ball went through the
metal-and-balsa sandwich skin, called Metalite, and hit the pavement
below. After a few more drops the shiny new aeroplane was a pile of
twisted aluminium. Blowtorch wielding employees completed the
destruction by cutting the framework into small pieces. These scraps,
together with jigs and materials from other projects were piled together
for bidding by the local scrap dealers.

        During this procedure the Navy requested Vought to return some
$6,000 worth of pure silver used in making bearing plates in the
propeller gear boxes. Both guards and engineers attempted to find the
silver in the snow covered pile of metal, but in the end the company
paid the Navy for the silver and sold the scrap to a dealer. When the
dealer found the silver he tried to sell it to a downtown jeweler who
called the police and the F.B.I. At which point, Vought officials had to
vouch for the scrap dealer's right to have the silver.

        With the completion of the Flying Pancake program, the Navy
approved the transfer of the V-173 to the Smithsonian. Although a light
aircraft, the V-173's width of more than 30 feet almost filled a city
street. A tractor towed it through Stratford and Bridgeport during the
daytime and put it aboard a tugboat for transport to Norfolk. It took
the tugboat two days and nights to make the short voyage in a snowstorm.
Transfer to the Smithsonian storage yard came at a later date.

        So the fifteen year dreams of inventor Charles H. Zimmerman with
the financial and engineering support of Chance Vought Aircraft went out
the door on the eve of apparent success. Later projects like the XC-142A
and XV-15 would be destined to pick up the testing legacy of the Flying
Pancakes.

        A 1990s View of the F5U

        Tommy Thomason, an exective with Bell Helicopter Textron, had
this to say about the program: "It is probably just as well that the F5U
program was terminated when it was. The concept will live on as an
unfulfilled dream rather than as the disappointment it would have
probably become. The performance projections were undoubtedly optimistic
and the actual and prospective shortcomings of the concept and design
were being overlooked or minimized.

        "By necessity, the design embodied transmissions, gearboxes, and
shafting. These are inherently troublesome in development and a burden
operationally. The layout required that the drive train turn 90 degrees
twice between the engine and the propeller and each 90 degree turn
reduces efficiency and reliability and increases weight and maintenance
requirements.  These shotcomings are accepted in a helicopter because
they permit true hovering flight but the F5U was not able to hover so
they would have been less acceptable.

        "It should be noted that there was only one prototype and there
was a distinct possibility of a gearbox failure if extensive bench
testing had not been accomplished under flight loading.  Since this is a
difficult environment to duplicate even if the flight loads had been
accurately predicted, which is doubtful, it is probable that the
gearboxes were underdeveloped and an inflight failure was not unlikely.
Most failures would have resulted in the loss of the only prototype and
a possibly tragic end to the test program.

        "To achieve maximum propulsive efficiency at both low and high
speeds and use the full horsepower available, the transmissions would
have to have had two speed gearing. This results from the fact that the
propeller should turn faster in very low speed flight than in high speed
flight while the maximum torque capability of a piston engine occurs
over a relatively small range of RPM. A two speed transmission would
further increase the drive system complexity and the pilot workload.

        "The low aspect ratio of the F5U penalizes long range cruise
performance.  Vought claimed that the propeller slipstream minimized the
impact but this would not be the first time that a manufacturer was
overly optimistic about an unusual and basically unproven aerodynamic
feature based on small scale or even full scale wind tunnel tests. The
V-173 was too underpowered to verify cruise performance predictions even
if its landing gear had been retractable.

        "The low aspect ratio also produced another characteristic that
may not have been viewed as entirely beneficial, that of rapid drag rise
during a pull up or level flight turn. This characteristic is shared by
delta wing fighters and provides the ability to make one, but only one,
really big move. It has some value as a defensive tactic but the time
required to reaccelerate limits the capability to reengage.

        "The size of the propellers severely limited the aircraft's
ability to employ conventionally launched rockets or missiles.

        "Finally, the stability and control in high speed flight of an
aircraft with very large flapping propellers was not well understood in
the late forties and it is very doubtful that Vought got it right by
happenstance. The vibration and loads due to flapping would have also
required extensive development work and may not have been resolvable."

        V-173 Specifications

        Wingspan . . . . . . . . . . . . 23 FT 4 IN.
        Length . . . . . . . . . . . . . 26 FT 8 IN.
        Height . . . . . . . . . . . .  12 FT 11 IN.
        Gross Weight . . . . . . . . . . . 2,258 LB
        Prop Diameter  . . . . . . . . . 16 FT 6 IN.
        Ground Angle . . . . . . . . . 22 DEG 15 MIN
        Engines   . . . . . . . . 2 Continental A-80
                                          80 hp each

        Takeoff (Calm) . . . . . . . . . . .  200 FT
                              25-knot wind in 0 feet
        Climb to 5,000 feet  . . . . . . . . . 7 MIN
        Full Speed . . . . . . . . Sea Level 138 MPH
        No Armament


        Chance Vought XF5U-1 Specification

        Power Plant: (proposed) Two Pratt & Whitney R-2000-2(D) Twin
Wasp turbo-supercharged 14-cylinder two-row radial air-cooled engines
each rated at 1.600 hp for take-off and war emergency and driving 16-ft
(4.88-m) four-bladed articulated airscrews. Internal fuel capacity, 280
US gal (1 060 1) and provision for two 150 US gal (568 1) drop tanks.

        Armament: (proposed) Six 0.5-in (12.7-mm) Browning MG 53-2
machine guns with 400 rpg and provision for two 1,000-lb (453.6-kg)
bombs on ventral racks.

        Performance:(Estimated at 16,802 lb/7 620 kg) Max speed at
military rated power, 363 mph (584 km/h) at sea level, 401 mph (645
km/h) at 10,000 ft (3,048 m). 418 mph (673 km/h) at 15,000 ft (4,572 m),
435 mph (700 km/h) at 20,000 ft (6,096 m), 456 mph (734 km/h) at 25,000
ft (7,620 m), 482 mph (775 km/h) at 30,700 ft (9,357 m), at war
emergency power. 394 mph (634 km/h) at sea level, 431 mph (694 km/h) at
10,000 ft (3,048 m), 451mph (726 km/h) at 15,000 ft (4,572 m). 472 mph
(759 km/h) at 20,000 ft (6,096 m), 492 mph (792 km/h) at 25,000 ft
(7,620 m), 504 mph (811 km/h) at 29,900 ft (8, 808 m); Initial climb
rate at normal rated power, 2,200 ft/min (11,18 m/sec), at military
rated power. 3,070 ft/min (15,60 m/sec), at war emergency power, 3,950
ft/min (20,06 m/sec) ; time (normal rated power) to 10,000 ft (3,048 m),
4.9 min, to 20,000 ft (6,096 m), 11.1 min; service ceiling, 32,000 ft
(9,754 m); endurance at 1,000 ft (305 m), 1.04 hr at max speed, 1.81 hr
at 90% max speed, 3.44 hr at 75% max speed, 4.26 hr at 60% max speed;
max range at 1,000 ft (305 m), 910 mls (1,465 km) at average speed of
236 mph (380 km/h); take-off distance (calm), 930 ft (283 m), into
15-knot (28 km/hr) wind, 680 ft (207 m), into 25-knot (46 km hr) wind,
520 ft (158 m): stalling speed (full load without power), 105 mph (169
km/h), (full load with military rated power). 46 mph (74 km/h).

        Weights: Normal loaded, 16,802 lb (7,620 kg); max overload.
18,917 lb (8,581 kg): landing weight, 15,542 lb (7,050 kg).

        Dimensions: Overall width (across tailplane), 32 ft 6 in
(9,90m); overall width across airscrews (diagonal), 31 ft 9 in (9,68 m),
(square). 36 ft 5 in (11,10 m); length, 28 ft 7.5  in (8,72 m); height,
14 ft 9 in (4,50 m).



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